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Weight equalisation

Printed From: Yachts and Yachting Online
Category: Dinghy classes
Forum Name: Dinghy development
Forum Discription: The latest moves in the dinghy market
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=13883
Printed Date: 05 Jul 22 at 3:59am
Software Version: Web Wiz Forums 9.665y - http://www.webwizforums.com


Topic: Weight equalisation
Posted By: 2547
Subject: Weight equalisation
Date Posted: 28 Dec 21 at 11:17am
Question. 

What classes still use weight equalisation?



Replies:
Posted By: Sam.Spoons
Date Posted: 28 Dec 21 at 11:53am
The only active (though not very) classes I can think of are ISO, Laser 4000 and RS 600. 

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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: MartinG
Date Posted: 28 Dec 21 at 2:04pm
RS800

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49er 865
K6 159
RS800 1133 (sold)


Posted By: Neptune
Date Posted: 29 Dec 21 at 2:46am
Rs700

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RS200 and returning to a Musto, ex 300


Posted By: 2547
Date Posted: 29 Dec 21 at 10:56am
All UK classes, any international classes use it?

49er did but dropped it years ago. 


Posted By: Jamie600
Date Posted: 30 Dec 21 at 7:28pm
My personal theory is weight equalisation was initially a marketing ploy which spread in the UK due to the unique market where we had RS, Topper and Laser all banging out t*t for tat models, some successfully and some not so

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RS600 1001


Posted By: iGRF
Date Posted: 30 Dec 21 at 7:46pm
What's needed more is height equalisation.

I can see the benefit of racks extending further out, had them on the EPS and the Blaze and if I recall the MPS also had variable racks, or maybe not and my guy wanted them the class didn't so he left the class. Interesting the RS 700 does, or does it and doesn't everyone cheat anyway?

I'm thinking platform soles for the Contender and also wonder wether a high or low hook is a better option and when.

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Posted By: JimC
Date Posted: 31 Dec 21 at 4:16am
Well that existed as well, but it all got complicated. Say a 5'6 sailor v a 6'6 one. Just run it on height and the little guy has to cross 2 feet more boat every tack than the big one. Now add an adjustment for extra leverage and it's even further.
To my mind what largely killed the concept was the realisation that at club level variances from sailor size are minute compared to those from sailor ability, and at Olympic level the crews trained to a perceived ideal weight anyway. So in both cases the hassle of managing it didn't deliver any great benefit.


Posted By: Fatboi
Date Posted: 31 Dec 21 at 10:18am
Mozzy would be the expert, but the 800s do weight and righting moment equalization pretty successfully if you are between 139 and 151kgs. 

https://www.rs800.org/documents/p1b64dd5ob9t0jpm1eeoov3su3.pdf


Posted By: Brass
Date Posted: 31 Dec 21 at 10:15pm
Surprised no one has mentioned the Tasar


Posted By: Grumpycat
Date Posted: 31 Dec 21 at 11:03pm
Itís a lovely boat BUT.

1) itís a rare beast in the uk .
2) Itís under canvassed for uk sailing conditions 


Posted By: iGRF
Date Posted: 31 Dec 21 at 11:09pm
Originally posted by Brass

Surprised no one has mentioned the Tasar


How is the Tasar weight equalised? We've now got five or six racing at our place, other than them being quite light to launch and recover off the beach I don't see any equalisation method.

There's also a bunch sailing over in Whitstable, where having that extra inbred sixth finger helps with that boom spanner thing I guess.

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Posted By: Brass
Date Posted: 31 Dec 21 at 11:55pm
https://www.tasar.org/media/101985/TAS2019_CR_190408.pdf

C.6 Crew Weight
C.6.1 The TASAR, while racing in all sanctioned events, shall carry a minimum total crew weight of 130 kgs.    The crew shall be dressed in shirts and shorts, swim-wear or the equivalent, without shoes, all dry, at weigh-in.
C.6.2 In the event that the weight of the crew, thus weighed, shall be less than 130 kg, such crew may race the TASAR, provided that, throughout the event, ballast equal in weight to at least the difference between the crew weight and 130 kgs is carried secured in the cockpit.    The ballast carried need not exceed 12 kg.


Posted By: iGRF
Date Posted: 01 Jan 22 at 12:14am
Originally posted by Brass

https://www.tasar.org/media/101985/TAS2019_CR_190408.pdf

C.6 Crew Weight
C.6.1 The TASAR, while racing in all sanctioned events, shall carry a minimum total crew weight of 130 kgs.    The crew shall be dressed in shirts and shorts, swim-wear or the equivalent, without shoes, all dry, at weigh-in.
C.6.2 In the event that the weight of the crew, thus weighed, shall be less than 130 kg, such crew may race the TASAR, provided that, throughout the event, ballast equal in weight to at least the difference between the crew weight and 130 kgs is carried secured in the cockpit.    The ballast carried need not exceed 12 kg.


OH Joy! They kept quiet about that, bet half fo them didn't know.. One of them does I bet he's been a previous class champion, am I going to give them the protest headache from hell.
Happy New Year everyone, except Tasarati!

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Posted By: Brass
Date Posted: 01 Jan 22 at 1:55am
OH Joy! They kept quiet about that, bet half fo them didn't know.. One of them does I bet he's been a previous class champion, am I going to give them the protest headache from hell.
Happy New Year everyone, except Tasarati!


You might like to look at the rest of CR C6 at the link I posted.


Posted By: Mozzy
Date Posted: 01 Jan 22 at 9:31pm
The 800 system works really well. It equalises for leverage and weight within a range. As someone who likes these things I've done all the calculations and mathematically it checks out, but also in practice it works very well.

The result is that the majority of the fleet are sailing in a very narrow bracket and even those outside the bracket are brought closer together. 

The major pro to this, is as a twin trapeze skiff that need a good size water to sail on, it's already a pretty narrow niche, so broadening out the competitive weight range help maintain good sized fleets. This is less of an issue for an olympic boat, but very welcome on the amateur scene. 

Downsides
1) is the boat is effectively 'slowed' down to equalise, if you consider maximum racks and no leads as the boats true potential (personally I find the boat plenty quick enough in equalised mode and making it any faster would likely lead to more breakages, a harder boat to sail, and smaller fleets)
2) it's admin weighing in at each event
3) lead is surprisingly expensive
4) inevitably where people aren't weighed in there are people on the wrong settings (although there is a pretty simple calculation you can do which will get you 90% there)

For me 1 isn't a negative and the rest are worth it to open up the competitive weight range. 





Posted By: Mozzy
Date Posted: 01 Jan 22 at 9:42pm
Some further points (if professional sailors got involved)
1) Is the ideal weight for the boat above, within or below the equalised weight/ If it was found to be (and that might vary on forecast and venue) then everyone would end up off one end of the scale.
2) If you are have a BMI < 21 it is possible to be off the low end of the weight equalisation (i.e. you have the maximum 5 lead) but you are still on the leverage scale. This results in you sailing at the same leverage as the boats equalised, but lighter (always preferable)
3) If you are very tall and again have low BMI it is possible to be off the leverage equalisation but still on the weight equalisation. This means you are sailing at the same weight as the other, but with more leverage (okay if windy)
4) If you dip weight before weigh, then rehydrate, in you sail the boat heavier than everyone, but with more leverage (okay if windy and within the range of how much you can dehydrate)
5) if you bulk before weigh in (then pee / poo) you sail the boat lighter than everyone but with less leverage (okay if light and within the range of a poo / wee)

Most of those 'gains' are within a pretty narrow range and some have a downside. 

My gut feeling is that the ideal weight is within the equalised range. So unless you are confident in a forecast you'd be taking a big risk to do 1, 4 or 5. 

Guy and I fell in to line 2 for the 2020 nationals (rack 9/10 and 5 leads). If we were professional I would make sure we hit that weight every year. But, it's only a 1.5 kilo advantage.  We could have dropped about 1.5 kilo and gone to rack 10 and taken a 3 kilo advantage. But with a system weight of ~300 kilo this is very small gains.
And we've also won two nationals on rack 6 and 7 and three and four leads. And we've also won plenty on rack 5 and three leads at other events. 


Posted By: PeterG
Date Posted: 02 Jan 22 at 10:20am
I'm thinking platform soles for the Contender and also wonder wether a high or low hook is a better option and when.

Interesting idea. Given what fun tacking a Contender is at the best of times for those not accomplished limbo dancers, I think they might cause problem! However, what about adjustable hydraulic ones? Shrink down to thin soles for tacking, extend them once your on the wire when it's blowing?

Low hook is the better option if there's a lot of power, and you can manage it, given whatever the sea is doing. You get a bit of extra righting moment, but also, if you heel from a nearly horizontal position the change in righting moment is small. If you're already well up you get a much larger loss of righting - what you don't want in a gust.


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Peter
Ex Cont 707
Ex Laser 189635
DY 59


Posted By: iGRF
Date Posted: 02 Jan 22 at 1:38pm
Originally posted by PeterG

<span style="font-family: "Helvetica Neue", "Lucida Grande", "Segoe UI", Arial, Helvetica, Verdana, sans-serif; : rgb251, 251, 253;">I'm thinking platform soles for the Contender and also wonder wether a high or low hook is a better option and when.</span>
<span style="font-family: "Helvetica Neue", "Lucida Grande", "Segoe UI", Arial, Helvetica, Verdana, sans-serif; : rgb251, 251, 253;"></span>
<font face="Helvetica Neue, Lucida Grande, Segoe UI, Arial, Helvetica, Verdana, sans-serif"><span style=": rgb251, 251, 253;">Interesting idea. Given what fun tacking a Contender is at the best of times for those not accomplished limbo dancers, I think they might cause problem! However, what about adjustable hydraulic ones? Shrink down to thin soles for tacking, extend them once your on the wire when it's blowing?</span>
<font face="Helvetica Neue, Lucida Grande, Segoe UI, Arial, Helvetica, Verdana, sans-serif"><span style=": rgb251, 251, 253;"></span>
<font face="Helvetica Neue, Lucida Grande, Segoe UI, Arial, Helvetica, Verdana, sans-serif"><span style=": rgb251, 251, 253;">Low hook is the better option if there's a lot of power, and you can manage it, given whatever the sea is doing. You get a bit of extra righting moment, but also, if you heel from a nearly horizontal position the change in righting moment is small. If you're already well up you get a much larger loss of righting - what you don't want in a gust.</span>


Inflatable shoe soles would do that..

But more seriously is it not logical to have the hook as high on ones person as possible in a breeze (and low when its light), given the better angle and leverage having the weight anchor point further away from the boat? Not that I see the range of hook height adjustability on trapeze style harnessses. Windsurfers used to have access to a range of hook heights, from chest harnesses down to low slalom seat style with wave waist style in the middle.

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Posted By: Do Different
Date Posted: 02 Jan 22 at 4:14pm
Confused Not getting your point iGRF. Given adequate core strength I cannot see how hook position on your body makes any difference; low riding jeans high or nipple warming high waisters. Yes the moment will change but as the moment increases the tension will decrease.


Posted By: iGRF
Date Posted: 02 Jan 22 at 5:42pm
Originally posted by Do Different

Confused†Not getting your point iGRF. Given adequate core strength I cannot see how hook position on your body makes any difference; low riding jeans high or nipple warming high waisters. Yes the moment will change but as the moment increases the tension will decrease.


Surely the angle of the wire? A low hook gives a narrow angle, a high hook would give a bigger angle, need to do a drawing.



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Posted By: ohFFsake
Date Posted: 02 Jan 22 at 6:52pm
Originally posted by iGRF

...need to do a drawing.

Your drawing is a thing of beauty, and in itself perhaps justifies the existence of this entire thread.

But it also demonstrates that in terms of mechanics it makes no difference where the hook attaches to the sailor, except in terms of their comfort.


Posted By: tink
Date Posted: 02 Jan 22 at 7:16pm
Hook height (on the body i.e. crew always horizontal) makes no difference what so ever on a dinghy, the CoG of the crew will be the same.  It is different on a windsurfer as the mast is canting to windward. 

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Tink
https://tinkboats.com

http://proasail.blogspot.com


Posted By: A2Z
Date Posted: 02 Jan 22 at 8:46pm
What did you use to draw that? 
LOL


Posted By: iGRF
Date Posted: 02 Jan 22 at 9:27pm
Originally posted by A2Z

What did you use to draw that?†
LOL

I spent a lot of time drawing it on a special computer programme you should keep a copy it'll prabably be worth lots of money when I'm gone.

As to the physics of it, last time I tried to pull a lever, it certainly helped by standing further away from it than right under it. I'm not proposing this, I'm simply asking the question.

If not, why not.

If that were a static boat in the boat park and you wanted to pull it over, surely you would use the wire and walk further away, would it not be easier?

Surely it's why tall sailors have more righting moment than short sailors because they extend the base of the triangle.

Therefore it must make sense to extend the hook as far up the body as possible if you're short of that body length?

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Posted By: Paramedic
Date Posted: 02 Jan 22 at 9:34pm
It has to make a difference.


Posted By: Rupert
Date Posted: 02 Jan 22 at 9:53pm
Maybe just tie it round the neck?

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Firefly 2324, Lightning 130, Puffin 229, Minisail 3446 Mirror 70686


Posted By: Do Different
Date Posted: 02 Jan 22 at 10:53pm
Gawd bless you Tink for even trying. 



Posted By: 423zero
Date Posted: 02 Jan 22 at 11:41pm
Imagine lying on a plank with no wire, you would still have same effect.

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Robert


Posted By: Grumpycat
Date Posted: 02 Jan 22 at 11:42pm
Originally posted by Rupert

Maybe just tie it round the neck?

Love your logic,Rupert LOL


Posted By: iGRF
Date Posted: 02 Jan 22 at 11:52pm
Originally posted by 423zero

Imagine lying on a plank with no wire, you would still have same effect.


I don't think so, a plank surely is applying the moment through the hull.

A wire is using the additional leverage of the mast height.

Having a higher hook wouldn't that be like sitting further out on the plank?

The plank acts like a lever, but is shorter and lower down, say what 2-3 mtrs?

Doesn't The trapeze wire transfer the weight application to the mast, which in turn levers the boat, or at least counters the sail pressure, the mast is what 5 mtrs?

Someone clever needs to do the maths and prove it to me.

Because all my instincts tell me to use a higher hook.

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Posted By: 423zero
Date Posted: 03 Jan 22 at 12:00am
You are thinking about pulling the boat over if you were standing on the ground, the higher the rope the more leverage you have. When trapezing and you are horizontal, height of cable makes no difference, you are ten stone on a plank and ten stone when using wire and core strength to stay out flat.

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Robert


Posted By: ohFFsake
Date Posted: 03 Jan 22 at 1:35am
Originally posted by iGRF

Originally posted by 423zero

Imagine lying on a plank with no wire, you would still have same effect.


I don't think so, a plank surely is applying the moment through the hull.

A wire is using the additional leverage of the mast height.

Having a higher hook wouldn't that be like sitting further out on the plank?

The plank acts like a lever, but is shorter and lower down, say what 2-3 mtrs?

Doesn't The trapeze wire transfer the weight application to the mast, which in turn levers the boat, or at least counters the sail pressure, the mast is what 5 mtrs?

Someone clever needs to do the maths and prove it to me.

Because all my instincts tell me to use a higher hook.
Sorry, but your instincts is all wrong!

In terms of applying righting moment the use of the mast is entirely incidental. It's there to hang the sails on which happens to make it a convenient place to hook a trapeze to but that's as far as it goes. Once you are hooked on you are just part of a static system in equilibrium, and as someone else pointed out you would have the exact same righting moment if you were lying on a plank.

The only thing that affects your righting moment is how far away from the centreline your body mass is, and altering the position of your hook doesn't change that. 




Posted By: mongrel
Date Posted: 03 Jan 22 at 7:03am
If you move the hook position higher up your body, I think youíd risk damaging your back.  
Also, with a high hook on the harness, in a lull where youíd sit up in the harness (and/or bend your knees) your ass would end up in the water, especially on a Contender with low freeboard.

(iGRF - Have you got any pictures of your Contender to post on here yet?)


Posted By: Oatsandbeans
Date Posted: 03 Jan 22 at 8:01am
Exactly right-the only thing that matters for the righting moment is the distance from the centre line to the centre of mass of the sailor. You donít have to think about anything else it will just confuse your thinking (a bit like the lee bow effect conundrum!)


Posted By: Paramedic
Date Posted: 03 Jan 22 at 8:06am
So:

If the height of the wire on the mast makes no difference why bother with a trapeze at all?

If the angle of the wire to the body (Position of the wire on the body effectively) doesn't make a difference why not just trapeze off the centreboard case all of the time and reduce your windage?

A higher hook on the body must make a difference but isn't practical and probably doesn't make enough difference to make the impracticalities worth dealing with.


Posted By: Paramedic
Date Posted: 03 Jan 22 at 8:13am
Originally posted by Oatsandbeans

Exactly right-the only thing that matters for the righting moment is the distance from the centre line to the centre of mass of the sailor. You donít have to think about anything else it will just confuse your thinking (a bit like the lee bow effect conundrum!)

So if you aren't pulling on the mast why does the windward shroud go slack in marginal trapezing conditions?

The effect may be negligible but there simply must be one beyond positioning the body further out.


Posted By: Oatsandbeans
Date Posted: 03 Jan 22 at 8:19am
If you sit on the side then put your weight on the wire, yes the tension in the shroud will reduce as the mast is now supported by two wires. Not quite sure how this helps.


Posted By: tink
Date Posted: 03 Jan 22 at 8:25am
How sail boats work (simplified)
Imagine all the sail forces act from a point F1 a distant D1 above the centre of buoyancy of the hull (red dot)
The sailors weight acts about F2 a distance D2 horizontal from the centre of buoyancy 

To stop swimming F1 x D1 must equal F2 x D2 

The wire is completely irrelevant 




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Tink
https://tinkboats.com

http://proasail.blogspot.com


Posted By: Oatsandbeans
Date Posted: 03 Jan 22 at 8:49am
The shrouds donít really come into this. The loads are balanced when the rig tension is applied and yes the windward oneís tension will change whilst sailing it doesnít contribute to the heeling effects. The simplest way to get your head around this ( probably been said earlier) is to see the problem as two balanced moments (turning forces) one from the rig and the centreboard and the other from the crew weight and the hull buoyancy.


Posted By: iGRF
Date Posted: 03 Jan 22 at 9:38am
Lot of cack handed thinking here. Itís the mast and sail attached to it thatís trying to tip the boat over. So just as fatter head sails have more adverse heeling moment so does having a wire attached to the mast high up to counter the heel What then happens the combine weight downforce is spread to weather . The bigger the wire angle the further to weather. Taller helms therefor being faster and able to sail the boat flat,
I agree with the issues having a too high hook would cause in lulls a consequence of my thinking marred by years of having a boom to hang on if necessary, but I think I might have a work around. The point still wrankles though as to why so many think itís wrong

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Posted By: 423zero
Date Posted: 03 Jan 22 at 9:50am
Think about the angle the wire is from your body to the mast, it's not much off vertical, if you stood at the side of your boat and tried to tip boat on its side using the exact same angle, you wouldn't tip it over.

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Robert


Posted By: iGRF
Date Posted: 03 Jan 22 at 9:56am
Originally posted by Oatsandbeans

Exactly right-the only thing that matters for the righting moment is the distance from the centre line to the centre of mass of the sailor. You donít have to think about anything else it will just confuse your thinking (a bit like the lee bow effect conundrum!)
Ah but Iíve proved myself correct time and again with my tidal lee bow theoryís by winning race after race, just as my hook height theorys proved correct in windsurfing as I pioneered lower and lower hook height in the early days. However Iím not claiming to know this one, which is why Iím asking the question and so far nothing written here so far has convinced me not to try. I think like lots of things yíall have been doing it wrong all these years 😉

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Posted By: tink
Date Posted: 03 Jan 22 at 9:57am
Originally posted by iGRF

Lot of cack handed thinking here. Itís the mast and sail attached to it thatís trying to tip the boat over. So just as fatter head sails have more adverse heeling moment so does having a wire attached to the mast high up to counter the heel What then happens the combine weight downforce is spread to weather . The bigger the wire angle the further to weather. Taller helms therefor being faster and able to sail the boat flat,
I agree with the issues having a too high hook would cause in lulls a consequence of my thinking marred by years of having a boom to hang on if necessary, but I think I might have a work around. The point still wrankles though as to why so many think itís wrong

I believe professionally you where something in marketing I am an Engineer. The wire and where it is attached to the mast or the person has no effect of the righting moment. The only factors are total sail force, effective height of sail force, how far outboard the crew weight is and the crew weight 

Think about a TOY unstayed mast and sliding seat no wires, wind increases more force in sail sailor moves outboard more on the seat itís that simple. 

The trapeze wire and the shrouds are irrelevant 


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Tink
https://tinkboats.com

http://proasail.blogspot.com


Posted By: iGRF
Date Posted: 03 Jan 22 at 10:01am
Originally posted by 423zero

Think about the angle the wire is from your body to the mast, it's not much off vertical, if you stood at the side of your boat and tried to tip boat on its side using the exact same angle, you wouldn't tip it over.
Youve just made the case for me. Exactly why moving the wire further away helps pull the boat over.

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Posted By: tink
Date Posted: 03 Jan 22 at 10:02am
Originally posted by iGRF

Originally posted by Oatsandbeans

Exactly right-the only thing that matters for the righting moment is the distance from the centre line to the centre of mass of the sailor. You donít have to think about anything else it will just confuse your thinking (a bit like the lee bow effect conundrum!)
Ah but Iíve proved myself correct time and again with my tidal lee bow theoryís by winning race after race, just as my hook height theorys proved correct in windsurfing as I pioneered lower and lower hook height in the early days. However Iím not claiming to know this one, which is why Iím asking the question and so far nothing written here so far has convinced me not to try. I think like lots of things yíall have been doing it wrong all these years 😉

As I said yesterday windsurfers are different because the mast mast is able to tilt relative to the position of the centre of buoyancy. I would draw another picture but it wonít have any impact on your thinking and Iím going sailing instead. 


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Tink
https://tinkboats.com

http://proasail.blogspot.com


Posted By: 423zero
Date Posted: 03 Jan 22 at 10:08am
The wire is purely to support your weight, positioned correctly it offers support for your back.

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Robert


Posted By: Do Different
Date Posted: 03 Jan 22 at 10:17am
I have a friend who is an engineer. He once told me that he spent half a night in a pub with a bloke who was convinced putting a wind turbine on his car to generate electricity as he drove along could feed an auxiliary motor to save petrol.   
Nuff said.


Posted By: iGRF
Date Posted: 03 Jan 22 at 10:22am
So whatís now being suggested the Contender doesnít need a wire and trapeze at all because youíre an Engineer and Iím in marketing?

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Posted By: rb_stretch
Date Posted: 03 Jan 22 at 10:22am
Originally posted by Paramedic

So:

If the height of the wire on the mast makes no difference why bother with a trapeze at all?

If the angle of the wire to the body (Position of the wire on the body effectively) doesn't make a difference why not just trapeze off the centreboard case all of the time and reduce your windage?

A higher hook on the body must make a difference but isn't practical and probably doesn't make enough difference to make the impracticalities worth dealing with.


If the mast and the body were perfectly stiff, then you would have the wire at the tip of the mast and the top of the head, as that creates the least tensile force in the wire. The closer the wire moves to the foot of the mast and to your feet, the higher the tension in the wire. Actual positions are really determined by the highest, relatively stiff point in the mast (usually where supported by shrouds) and where our bodies are most comfortable with the force.


Posted By: 423zero
Date Posted: 03 Jan 22 at 10:28am
Griff, if you didn't have a trapeze you couldn't have your feet on side of boat and lie out horizontally, you would have to put your feet under hiking straps, but because you are nearer centre line of boat you have less righting.

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Robert


Posted By: mongrel
Date Posted: 03 Jan 22 at 12:15pm
Originally posted by iGRF

Originally posted by 423zero

Think about the angle the wire is from your body to the mast, it's not much off vertical, if you stood at the side of your boat and tried to tip boat on its side using the exact same angle, you wouldn't tip it over.
Youve just made the case for me. Exactly why moving the wire further away helps pull the boat over.

& why in a lull you bend your knees to reduce your righting moment.


Posted By: iGRF
Date Posted: 03 Jan 22 at 12:58pm
Originally posted by mongrel


Originally posted by iGRF

Originally posted by 423zero

Think about the angle the wire is from your body to the mast, it's not much off vertical, if you stood at the side of your boat and tried to tip boat on its side using the exact same angle, you wouldn't tip it over.
Youve just made the case for me. Exactly why moving the wire further away helps pull the boat over.

& why in a lull you bend your knees to reduce your righting moment.


And why you'd have to bend your knees further and earlier with a higher hook?

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Posted By: Sam.Spoons
Date Posted: 03 Jan 22 at 1:21pm
Originally posted by Do Different

I have a friend who is an engineer. He once told me that he spent half a night in a pub with a bloke who was convinced putting a wind turbine on his car to generate electricity as he drove along could feed an auxiliary motor to save petrol.   
Nuff said.

I'm guessing this is something to do with the 'apparent wind' effect we know and love.
 

https://www.youtube.com/watch?v=jyQwgBAaBag" rel="nofollow - https://www.youtube.com/watch?v=jyQwgBAaBag


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Posted By: Sam.Spoons
Date Posted: 03 Jan 22 at 1:30pm
Tall people have more righting moment not because the trap hook is further from the boat but because their CoG is further from the boat. Moving the hook doesn't change that.

How high up the mast the wire attaches (almost always at the hounds IME) is also irrelevant WRT righting moment but the lower it is the more load on your legs to stay standing horizontally off the side of the boat

You have to have the trap hook at or slightly (but only slightly)* above your CoG to be able to move around the boat, if it's too far above and you feet slip off the gunnel your legs will fall in the water, if to low your head/body will fall into the water.

* In practice slightly above your CoG has proven to be most efficient.


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Blaze 671 "supersonic soap dish"


Posted By: tink
Date Posted: 03 Jan 22 at 1:56pm
Originally posted by iGRF

So whatís now being suggested the Contender doesnít need a wire and trapeze at all because youíre an Engineer and Iím in marketing?


You could fit wings on a contender and the crew could create the same righting moment as a trapezing crew, the key thing is where the crew c of g is. As a engineer this stuff is my bread and butter so my understanding of this stuff is rather relevant.

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https://tinkboats.com

http://proasail.blogspot.com


Posted By: iGRF
Date Posted: 03 Jan 22 at 2:27pm
Originally posted by tink

Originally posted by iGRF

So whatís now being suggested the Contender doesnít need a wire and trapeze at all because youíre an Engineer and Iím in marketing?


You could fit wings on a contender and the crew could create the same righting moment as a trapezing crew, the key thing is where the crew c of g is. As a engineer this stuff is my bread and butter so my understanding of this stuff is rather relevant.


Well I would beg to differ, then what do I know, I've only spent thirty odd years marketing harnesses and harness hooks in wind and more recently kitesurfing where the idiosyncrasies are very different. So you'll excuse me for choosing to find out for myself, when I can find a suitable harness with the option to vary hook height.

As for fitting racks on a contender, or using your Toy example, they may very well apply sufficient righting force but they will be slower. If you are truly an expert engineer, then I shouldn't have to explain why, but if you wish, I'll try and find a better drawing programme to illustrate why.

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Posted By: Sam.Spoons
Date Posted: 03 Jan 22 at 2:28pm
Originally posted by tink

Originally posted by iGRF

So whatís now being suggested the Contender doesnít need a wire and trapeze at all because youíre an Engineer and Iím in marketing?


You could fit wings on a contender and the crew could create the same righting moment as a trapezing crew, the key thing is where the crew c of g is. As a engineer this stuff is my bread and butter so my understanding of this stuff is rather relevant.

The B14 is a good example, huge racks and a 3.05m beam give the same righting moment as a trapeze would, note where the crew's feet are.





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Blaze 671 "supersonic soap dish"


Posted By: Do Different
Date Posted: 03 Jan 22 at 2:39pm
Give it up people, there's nothing to be gained here.    iGRF has an undoubted history of being a demon windsurfer and marketeer but time and time again he has demonstrated that he entirely missed out on secondary school physics lessons. I have respect for skills and wish him well with his Contender experience.


Posted By: Sam.Spoons
Date Posted: 03 Jan 22 at 2:40pm
Originally posted by iGRF

As for fitting racks on a contender, or using your Toy example, they may very well apply sufficient righting force but they will be slower. If you are truly an expert engineer, then I shouldn't have to explain why, but if you wish, I'll try and find a better drawing programme to illustrate why.

Interested to hear your explanation?


-------------
Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: tink
Date Posted: 03 Jan 22 at 2:42pm
Originally posted by iGRF

Originally posted by tink

Originally posted by iGRF

So whatís now being suggested the Contender doesnít need a wire and trapeze at all because youíre an Engineer and Iím in marketing?


You could fit wings on a contender and the crew could create the same righting moment as a trapezing crew, the key thing is where the crew c of g is. As a engineer this stuff is my bread and butter so my understanding of this stuff is rather relevant.


Well I would beg to differ, then what do I know, I've only spent thirty odd years marketing harnesses and harness hooks in wind and more recently kitesurfing where the idiosyncrasies are very different. So you'll excuse me for choosing to find out for myself, when I can find a suitable harness with the option to vary hook height.

As for fitting racks on a contender, or using your Toy example, they may very well apply sufficient righting force but they will be slower. If you are truly an expert engineer, then I shouldn't have to explain why, but if you wish, I'll try and find a better drawing programme to illustrate why.


I give up if you are not prepared to accept basic laws of physics I not going to try and change that

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Tink
https://tinkboats.com

http://proasail.blogspot.com


Posted By: iGRF
Date Posted: 03 Jan 22 at 3:09pm
Originally posted by Sam.Spoons


Originally posted by iGRF

As for fitting racks on a contender, or using your Toy example, they may very well apply sufficient righting force but they will be slower. If you are truly an expert engineer, then I shouldn't have to explain why, but if you wish, I'll try and find a better drawing programme to illustrate why.

Interested to hear your explanation?


The same reason a B14 would be faster with the crew twin trapezing, and why a windsurfer planes up wind earlier than a dinghy and a Cat is faster than a mono.


Because the centre of gravity of the boat with a crew flat wiring is moved to an extent that the boat displaces less at the point of contact with the water so creates less drag and therefore goes faster, the more the crew weight is part of the actual hull which occurs in hiking boats, then the displacement is entirely foccussed inboard.

Move that weight outboard and away you go..


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Posted By: iGRF
Date Posted: 03 Jan 22 at 3:12pm
Originally posted by tink



I give up if you are not prepared to accept basic laws of physics I not going to try and change that


Humans wrote the basic laws of physics and they have frequently been proved wrong.

That's the trouble with engineers, they only do as they're told and never question anything.

Rules are and have always been, made to be broken.

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Posted By: iGRF
Date Posted: 03 Jan 22 at 3:28pm
Originally posted by Do Different


Give it up people, there's nothing to be gained here. † †iGRF has an undoubted history of being a demon windsurfer and marketeer but time and time again he has demonstrated that he entirely missed out on secondary school physics lessons. I have respect for skills and wish him well with his Contender experience.


I entered the Grammar School in the A stream, passed Physics at O level, questioned the physics master on his definition of light at the time 1964-5 and was proved right many years later. Have an IQ according to some of 166. (stupid logic puzzles) Question everything always, sometimes I'm right, sometimes I'm wrong, have probably been wrong more often than right, but that's not reason to stop questioning.

I do come here for a laugh, I don't take anything too seriously, but I hesitate to accept suggestions of not being as well educated or as bright as the rest of you. I just never ever accept the status quo and none of you have provided a convincing argument supporting the fact that a trapeze wire set further away from the boat does not provide better righting moment.

Do we have to re run the lee bow argument that proved my point?



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Posted By: tink
Date Posted: 03 Jan 22 at 3:31pm
Originally posted by iGRF

 


Because the centre of gravity of the boat with a crew flat wiring is moved to an extent that the boat displaces less at the point of contact with the water so creates less drag and therefore goes faster,

Please explain where the weight has gone that has caused the boat to displace less, it simply is against the laws of physics which you appear to have no regard for. 


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Tink
https://tinkboats.com

http://proasail.blogspot.com


Posted By: Do Different
Date Posted: 03 Jan 22 at 3:42pm
iGRF. I did not say that you are not a bright bloke, which you obviously are and an innovator.
However. Sometimes you are simply plain wrong on the most basic theory.



Posted By: iGRF
Date Posted: 03 Jan 22 at 3:43pm
Let's start in say 5 knots, with a 90 kilo crew sat in our Contender which weighs say 110 kgs all up, so 200 kgs point loaded.

Move the wind speed up to say 15 knots our crew has clipped in but is still pretty in board knees bent but part of his weight is going down directly through the mast via the trap wire, with maybe 10% less because he can lean out board.

Now move the wind speed up to say twenty five knots and our crew is flat wiring, his weight now directly supported via the wire, supported not entirely by the mast directed down through the hull, but in part supported by the wind side force. So where has the weight gone? It has spread over a wider area, like the twin cat hulls and in part supported by the mast and the calculation for this is something my maths can't extend to, but I'm sure is out there somewhere, don't make me look for it. But I can assure you is faster than if the weight were still supported directly by racks attached to the hull.



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Posted By: iGRF
Date Posted: 03 Jan 22 at 3:54pm
Originally posted by Do Different

iGRF. I did not say that you are not a bright bloke, which you obviously are and an innovator.
However. Sometimes you are simply plain wrong on the most basic theory.


This time I'm not wrong, I may not be correct in the harness hook positioning on my person, but the ([s]argument[/s]) discussion has gone beyond that, 'they' are now questioning the efficiency of a trapeze and how it functions and are wrong. Racks do not work the same as a Trapeze and unless you understand that, in my mind the argument against my higher hook theory also fails, though I suspect is probably right for altogether different reasons to do with the percentage of weight loss the further up the body you go, yet the bending knees fact still supports the attachment point being as far out as you can get. Why I'm still hanging on for a definitive answer.

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Posted By: A2Z
Date Posted: 03 Jan 22 at 4:27pm
Interesting isnít it?  Lots of people have told you that you are wrong about moving the trapeze attachment outboard increasing righting moment but no one has really explained why.  


Posted By: sargesail
Date Posted: 03 Jan 22 at 4:29pm
Originally posted by iGRF

Originally posted by Do Different


Give it up people, there's nothing to be gained here. † †iGRF has an undoubted history of being a demon windsurfer and marketeer but time and time again he has demonstrated that he entirely missed out on secondary school physics lessons. I have respect for skills and wish him well with his Contender experience.


I entered the Grammar School in the A stream, passed Physics at O level, questioned the physics master on his definition of light at the time 1964-5 and was proved right many years later. Have an IQ according to some of 166. (stupid logic puzzles) Question everything always, sometimes I'm right, sometimes I'm wrong, have probably been wrong more often than right, but that's not reason to stop questioning.

I do come here for a laugh, I don't take anything too seriously, but I hesitate to accept suggestions of not being as well educated or as bright as the rest of you. I just never ever accept the status quo and none of you have provided a convincing argument supporting the fact that a trapeze wire set further away from the boat does not provide better righting moment.

Do we have to re run the lee bow argument that proved my point?



Bubbles tell us about the bubbles pleaseÖ

And then weíll move on to laughing at your Lee bow vanity!


Posted By: tink
Date Posted: 03 Jan 22 at 4:34pm
Originally posted by iGRF

Originally posted by tink



I give up if you are not prepared to accept basic laws of physics I not going to try and change that


Humans wrote the basic laws of physics and they have frequently been proved wrong.

That's the trouble with engineers, they only do as they're told and never question anything.

Rules are and have always been, made to be broken.

?? The whole focus of Engineering is to question everything, that is what we do. Iím dyslexic and look at problems with very fresh eyes. PS  not sure my IQ but it is in the 99.99 percentile from full educational physiologist evaluation. Iím not questioning your intelligence either, hope I havenít come across that I am. The physics we are talking is the same as a see-saw uses itís not going to disproved 


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Tink
https://tinkboats.com

http://proasail.blogspot.com


Posted By: iGRF
Date Posted: 03 Jan 22 at 4:34pm
Had to revert back to schoolboy maths and moments, now this is not a statement, it's still a question.

So lets say racks, and our helm is 90 kgs and the racks are 2.5 metres out from the pivot point which we'll call the mast base. So Distance from pivot times mass to get moment is 2.5 x 90kg equals 225Nm yes?

So now with a trapeze do we not have to accept that the pivot distance changes from the foot of the mast to the end of the rack, to the foot of the mast to the point at which the weight is acting on the mast which is the new lever at say 4 mtrs to the hounds? So our 90 kilo mass now supported flat wiring from the mast must be 4 x 90 kgs and 360 Nm?

This doesn't asnwer my question but it does give some maths to start with.

Or, do we totally discount the mast lever suggestion because it's neutralised by the sail sideforce and the calculation remains directly from the pivot point to the point at which the harness is attached or the height of the sailor?

If it's the harness hook attachment point then my suggestion holds water, if it's the height of the sailor then it doesn't.

Those holding the racks trapeze makes no difference answer will hold with the view that wether racks or trap the c.o.g of the sailor distance prevails, i.e. 250 so 225 Nm righting moment either way.

I maintain that there is an element of mast leverage and probable weight reduction as a result, but it's an interesting thing to continue to work on and I hate maths, but there has to be a formula there somewhere to support what I'm sure I've read somewhere along the path.

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Posted By: Old bloke
Date Posted: 03 Jan 22 at 4:38pm
I know its only because its Christmas and you're bored.
However, 2 simple proofs
1, picture the telltale on your main. They flow horizontally and the stronger the wind, the more horizontally they flow. So with an upright mast and horizontal flow there can't be a vertical force for the trapeze hand to counteract
2, go out to the garage, loosely screw 2 pieces of wood to form a L. Then keeping the angle the same use a piece of line as your trapeze wire, attach it to various places on the "mast" and the "trapezing sailor" and see if you can feel a difference.
It nay or may not convince you, but it will get you out from under the long suffering Mrs iGRF's feet


Posted By: tink
Date Posted: 03 Jan 22 at 4:42pm
Originally posted by A2Z

Interesting isnít it?  Lots of people have told you that you are wrong about moving the trapeze attachment outboard increasing righting moment but no one has really explained why.  

I have explained 3 times, and giving up now 


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Tink
https://tinkboats.com

http://proasail.blogspot.com


Posted By: iGRF
Date Posted: 03 Jan 22 at 4:50pm
So why does the windward shroud go loose when I'm hanging on the wire?

I'm not suggesting a vertical force, is it not a sideways force?

And if the wind suddenly dropped without me getting back in the boat the weight of the wire will pull the boat over.

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Posted By: Oatsandbeans
Date Posted: 03 Jan 22 at 4:59pm
The mast has nothing to do with it. As I said it is two moments which are balanced and composed of two forces and it the magnitude of these force and their separation that is important.
The heeling moment is composed of the heeling force (sideways) from the rig and the lift (sideways) from the foils. This is balanced by the righting moment, which is composed of the crew weight and the buoyancy of the hull.


Posted By: iGRF
Date Posted: 03 Jan 22 at 5:11pm
I've worked it out but you'll have to wait.

Mrs iGRF is not happy, I've tried to explain to her but she won't listen.




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Posted By: Oatsandbeans
Date Posted: 03 Jan 22 at 5:18pm
Grf -I tell the youngsters that I work with that if they canít explain something to their mum they donít understand it ( in your case it would be your wife!)


Posted By: tink
Date Posted: 03 Jan 22 at 5:19pm
Originally posted by iGRF

So why does the windward shroud go loose when I'm hanging on the wire?

I'm not suggesting a vertical force, is it not a sideways force?

And if the wind suddenly dropped without me getting back in the boat the weight of the wire will pull the boat over.
It goes slack because the trapeze wire is acting as a stay and taking the load off the shroud. The centre of gravity of the whole boat has not changed, the thing that is counter acting the sail force is the righting moment: that is the horizontal distance between the centre of gravity and the centre of buoyancy multiplied by the whole weight of the boat and crew.

Ignore dinghies think of a deep keel boat. When the mast is vertical the keel is actually doing nothing. Now imagine a heavy person steps on the gunwale. He will force the boat to tip towards him, as he does the the underwater shape changes and the center of buoyancy moves towards him, as this happens the keel and the centre of gravity moves in the opposite direction - at some point the movement of the keel will counter act the tipping momentum of the man on the gunwale. 
If the man on the gunwale pulled with all his might on the halyard nothing, absolutely nothing would change. His weight is still in exactly the same position and he weighs the same amount. 
If you took your Farr 3.7 on its trailer to a public weigh bridge and stood roughly where you trapeze from then actually trapezed or just sat in the boat there would be no change in the weight of the boat. 

It is very different for windsurfers as I have said because the mast pivots. 



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Tink
https://tinkboats.com

http://proasail.blogspot.com


Posted By: tink
Date Posted: 03 Jan 22 at 5:23pm
Originally posted by iGRF

I've worked it out but you'll have to wait.

Mrs iGRF is not happy, I've tried to explain to her but she won't 



Please tell me Mrs iGRF is a professor of pure physics 


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Tink
https://tinkboats.com

http://proasail.blogspot.com


Posted By: tink
Date Posted: 03 Jan 22 at 5:33pm
page 181 of Frank Bethwaites "High Performance Sailing"




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Tink
https://tinkboats.com

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Posted By: KazRob
Date Posted: 03 Jan 22 at 6:12pm
Any basic mechanics book will explain it all. If there is a fundamental problem with these principles I'm sure they would have been noticed by now. As Tink said - all that matters is the overall moment and balance of forces. If you do a free body diagram and include the angles of the wires etc you'll see it makes sense.




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OK 2148 & 2249


Posted By: Sam.Spoons
Date Posted: 03 Jan 22 at 6:19pm
Originally posted by A2Z

Interesting isnít it?  Lots of people have told you that you are wrong about moving the trapeze attachment outboard increasing righting moment but no one has really explained why.  

I can't think of a simpler way to explain it...

Originally posted by Sam.Spoons

Tall people have more righting moment not because the trap hook is further from the boat but because their CoG is further from the boat. Moving the hook doesn't change that.

How high up the mast the wire attaches (almost always at the hounds IME) is also irrelevant WRT righting moment but the lower it is the more load on your legs to stay standing horizontally off the side of the boat

You have to have the trap hook at or slightly (but only slightly)* above your CoG to be able to move around the boat, if it's too far above and you feet slip off the gunnel your legs will fall in the water, if to low your head/body will fall into the water.

* In practice slightly above your CoG has proven to be most efficient.


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Blaze 671 "supersonic soap dish"


Posted By: A2Z
Date Posted: 03 Jan 22 at 6:40pm
Sorry, but there hasnít been an explanation as to why the trapeze wire coming out at a more horizontal angle if attached higher up the body doesnít increase the righting moment. The only explanation given is that righting moment = body weight x distance from centre of buoyancy, which is correct but doesnít explain why the trapeze angle method is wrong. After all, if you were trying to pull a tree over you would find it easier if pulling more horizontally and less down (from the same attachment point) so why isnít the same true for dinghy stability?  


Posted By: Sam.Spoons
Date Posted: 03 Jan 22 at 6:45pm
Because to pull more horizontally/less down you would have to stand further from the tree (for the same attachment point on the tree). If you stood further from the boat (either on stilts or WHY) you would have a higher downward force not because of the angle of the trap wire but because you were further from the boat. But it's not a valid analogy because to pull the tree down you would be pulling sideways and the sideways component of your effort would be what pulls the tree over not the vertical component.



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Blaze 671 "supersonic soap dish"


Posted By: A2Z
Date Posted: 03 Jan 22 at 6:47pm
No, the trapeze line (or tree rope) is more horizontal if the line is attached at the chest rather than the knees.  The man is no taller and has no more inherent leverage. 
I know the answer to this, but no one has yet explained it despite deriding GRF for asking the question.  


Posted By: Grumpycat
Date Posted: 03 Jan 22 at 6:48pm
Originally posted by tink

Originally posted by iGRF

I've worked it out but you'll have to wait.

Mrs iGRF is not happy, I've tried to explain to her but she won't 



Please tell me Mrs iGRF is a professor of pure physics 

No she is a a saint in human form Wink


Posted By: Sam.Spoons
Date Posted: 03 Jan 22 at 6:53pm
Originally posted by iGRF

Had to revert back to schoolboy maths and moments, now this is not a statement, it's still a question.

So lets say racks, and our helm is 90 kgs and the racks are 2.5 metres out from the pivot point which we'll call the mast base. So Distance from pivot times mass to get moment is 2.5 x 90kg equals 225Nm yes?

Yes

So now with a trapeze do we not have to accept that the pivot distance changes from the foot of the mast to the end of the rack, to the foot of the mast to the point at which the weight is acting on the mast which is the new lever at say 4 mtrs to the hounds? So our 90 kilo mass now supported flat wiring from the mast must be 4 x 90 kgs and 360 Nm?

No, the crew's CoG is still only 2.5m from the mast foot

This doesn't asnwer my question but it does give some maths to start with.

Or, do we totally discount the mast lever suggestion because it's neutralised by the sail sideforce and the calculation remains directly from the pivot point to the point at which the harness is attached or the height of the sailor?

Yes, it's purely the hight of the sailor (or more correctly how far, horizontally, from the mast foot his CoG is

If it's the harness hook attachment point then my suggestion holds water, if it's the height of the sailor then it doesn't.

See above 

Those holding the racks trapeze makes no difference answer will hold with the view that wether racks or trap the c.o.g of the sailor distance prevails, i.e. 250 so 225 Nm righting moment either way.

Yes

I maintain that there is an element of mast leverage and probable weight reduction as a result, but it's an interesting thing to continue to work on and I hate maths, but there has to be a formula there somewhere to support what I'm sure I've read somewhere along the path.

No, different forces, the CoG of the 90kg crew is roughly at his navel, say 1m from his feet. Now lets assume he can use toe straps just outboard of the gunnel and flat hike with his feet touching the gunnel, his CoG will be 1m out from the gunnel regardless of how wide the racks are (as long as they are wide enough for him to hike off). Now remove the racks and put him on a trap wire so he can stand horizontally off the gunnel with his CoG in exactly the same place relative to the boat and he will generate exactly the same righting moment and will be able to balance exactly the same amount of power from the rig. I'm almost tempted to make a mock up to prove it but have other stuff I have to do first.


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Posted By: Mozzy
Date Posted: 03 Jan 22 at 6:58pm
Wacko

changing the heights of the hook or termination on the mast obviously won't effect the moments. But it does change the forces which is of some importance to both the mast (and it's shape and structure) and the human body. 

Hook height... the further you place the hook up the body the more weight is on the feet. If you move the hook very low, you fall out backwards (or have to start tucking you feet under the gunwale). Generally I prefer a lower hook as it gives a bit more freedom to move the upper body around. 

If the hook height is very high it gets in the way, but also means more strain holding you bum up with the glutes. The same could be said for a low hook height and holding you shoulders up with your abbs (but you have shoulder straps and back support for that). 

Hook height on the mast is usually just set to the hounds as from a structural point of view its the best supported point of the mast and usually is still about full section before the mast tapers. So there is less you have to do to the mast to modify it to carry one or more sailors. 

What is also noticeable on the 800 with the equalisation it that as the racks go out the wires pull you inwards more. So you generally have more load on your feet. The negative is it's noticeably harder pointing your toes. But on the positive side when the boat comes on top you can have more heel before you start to swing away from the hull. 

Most 800 set their rigs up the same (or attempt to). Initially this makes a lots of sense as there isn't much variance in righting moment or all up weight so the theoretical fastest set up for all would be the same. But that lien of thinking doesn't account for how the varying body sizes load the rig and from which angle.  First of all the heavier sailors will put more compression in to the rig (duhh they're heavier) which means their windward shroud starts to flap around sooner. Lighter sailors will produce less compression, but also their wires pull more sideways. 

This creates a bit of a catch 22, where 800 sailors who are very light might be able to run less tension as they are unlikely to get the windward shroud flapping, and they will get little extra compression due to body weight on the wires which can leave the rig over straight and have them feeling over powered, despite the equalisation system giving them the same RM.  Whereas the bigger sailors might end up with flappy shrouds, which means they are getting more mast compression and more mast bend making their rig feel less powerful. Those problems are eventuated the further outside the weight range. The answer would be adjustable spreaders to get the correct mast curve with varying tension, but the spreaders are fixed. 

Interesting stuff, I think. But I don't want to derail the enthralling discussion about whether hook height changes the righting moment. 


Posted By: KazRob
Date Posted: 03 Jan 22 at 7:05pm
Perhaps another way to look at it is a hybrid between a sliding seat and a trapeze. Imagine a model yacht with a plank pivoted at the gunwhale, and held up by a wire connected somewhere up the mast (or for that matter a structure on the boat). Moveable ballast (i.e. the sailor) is simply a weight which can be fitted to the plank at a single point equivalent to the full size sailors CoG. The total righting moment provided by this is only a function of the weight and where it is along the plank and not where the supporting wire is attached. The closer to the pivot point the wire attaches, the higher the vertical reaction load at that point. The further out the wire, the less the vertical reaction load has to be to remain in balance.

i.e. 2m long weightless plank fitted 100mm out from boat CL with a 1kg weight at it's midpoint. For static equilibrium we need the sum of the moments around the boat CL to be zero. Assume the wind load balances the heeling load perfectly and the boat heels around it's CL to simplify things. 
Moment from weight around hull CL =1000+100 * 1kg * 9.81N/kg = 10791Nmm
To balance this we need a vertical reaction to this 
  1. Wire at +100mm from pivot requires Sum of moments must equal zero so vertical load = 10791Nmm/(100mm+100mm) = 53N = 5.5kg
  2. Wire at +1000mm from pivot (ie at CoG) requires Sum of moments must equal zero so vertical load = 10791Nmm/(100mm+1000mm) = 9.81N = 1kg
  3. Wire at +2000mm from pivot requires Sum of moments must equal zero so vertical load = 10791Nmm/(100mm+2000mm) = 5.14N = 0.52kg
If the sideways force from teh sail acting around the hull buoyancy is not in balance the boat will heel one way or the other. 

The actual load in the supporting wire will depend on the angle it attaches to the plank. As wire can only take tension loads, the tension will vary inversely with the cosine of the angle between vertical and the wire. Wire vertically above connection point (0deg, cos =1, load = vertical reaction force); wire at 45deg to vertical (cos = 0.707, load = 1.41x vertical reaction force); wire at 60deg to vertical (cos = 0.5, vertical load = 2x vertical reaction load).

On teh question of why does the windward shroud go slack when trapezeing, the answer is in two parts. The load on the trapeze wire takes some load of the shroud and may be enought o take all the load off it. There is also a substantial downward load that may increase bend in the mast through column buckling, reducing it's length and taking tension off the shroud




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OK 2148 & 2249


Posted By: Sam.Spoons
Date Posted: 03 Jan 22 at 7:06pm
Originally posted by A2Z

No, the trapeze line (or tree rope) is more horizontal if the line is attached at the chest rather than the knees.  The man is no taller and has no more inherent leverage. 
I know the answer to this, but no one has yet explained it despite deriding GRF for asking the question.  

Agreed... Enlighten us then?


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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: Mozzy
Date Posted: 03 Jan 22 at 7:14pm
the tension (1000N) on the two examples above aren't the same. 

Increasing the height of the hook puts more weight on feet and less on the wire. 


Posted By: Sam.Spoons
Date Posted: 03 Jan 22 at 7:17pm
But still exactly the same hanging off the boat?

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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: KazRob
Date Posted: 03 Jan 22 at 7:17pm
In the diagram above, there is no net horizontal or vertical force and no net moment around the mast base in either case. In a boat the moment is balanced by the sail force / hull couple. In the diagram the moment is resisted by the mast base itself. The difference in tensions in the wires is irrelevant and can be calculated just basic trig and remembering that net forces and moments at any point must be zero if there is no net acceleration at that point.

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OK 2148 & 2249


Posted By: Sam.Spoons
Date Posted: 03 Jan 22 at 7:36pm
Originally posted by KazRob

In the diagram above, there is no net horizontal or vertical force and no net moment around the mast base in either case. In a boat the moment is balanced by the sail force / hull couple. In the diagram the moment is resisted by the mast base itself. The difference in tensions in the wires is irrelevant and can be calculated just basic trig and remembering that net forces and moments at any point must be zero if there is no net acceleration.

Surely the forces are there but as the are perfectly balanced they create no movement, the tree roots are easily capable of balancing the mass of the 'sailor' so the force on them does not generate movement on the trunk. In a boat the force doing the 'pulling over is the power of the rig and the force doing the 'holding up' is the weight of the sailor, the analogy is not perfect as, because the boat can heel, they need to be in perfect balance. The position of the harness hook is still irrelevant though (excepting the physical effects on the crew Mozzy mentions)


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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: 423zero
Date Posted: 03 Jan 22 at 7:44pm
The answer to the question of where to attach wire on the mast, is where it will do minimum distortion to the mast, thereby diminishing detrimental sail shape changes.

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Robert


Posted By: KazRob
Date Posted: 03 Jan 22 at 7:50pm
The basics remain the same. In simple mechanics with no significant member deflections, for no accelerations (linear or rotational), the net forces and moments at any point must be zero. In the tree analogy the tree reacts against the over turning moment by spreading the loads out through it's root system.
If you want to make it more accurate by considering member deflections, teh system becomes much more complicated to calculate but fundamentally the overall system remains in static equilibrium.


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OK 2148 & 2249


Posted By: iGRF
Date Posted: 03 Jan 22 at 7:57pm
Lots of interesting stuff thanks all for contributing.
Now where I was before SWMBO dragged me screaming from the keyboard, was the following conclusion which is:
If my current hook position, is below my CoG, then a clear advantage should be gained by moving it above.
If not then it's obviously back to the platform shoes to push us all further out.

I do still dispute the magic replacement of a rack to the exact same position on a wire simply because I still believe in the weight transferance to mast via the wire is relevant, but at this stage I'm unable to prove why.

One question to Mozzy, re "Increasing the height of the hook puts more weight on feet and less on the wire. " do you think this might be because you guys in 800s are already a way out there on the racks? I'm contemplating flatwiring in the not to distant future and probably earlier than most so need to maximise what little weight and height I have available.
It is however true though, one of the issues we used to have in the early days of kitesurfing in controlling our descent from big jumps if our hooks were too low which they used to have to be in the days before depower in order to maximise pressure on the rails to control the kite, it is wny these days so many waist harnesses with high hooks now feature. Higher hook gives better control in the air if the support comes from above the CoG.with more weight below landings are easier to control.

As to my theory of out board weight from a wire rather than through a rack and the hull I shall have to research harder or build that bloody model to find out for certain.

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Posted By: 423zero
Date Posted: 03 Jan 22 at 8:52pm
Regardless of where you put hook on your body or attachment on the mast, you will not be able to equalise your height and weight to someone 6' 6" and fifteen stone, well not sailing a standard Contender.



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Robert


Posted By: Sam.Spoons
Date Posted: 03 Jan 22 at 9:32pm
Originally posted by iGRF

Lots of interesting stuff thanks all for contributing.
Now where I was before SWMBO dragged me screaming from the keyboard, was the following conclusion which is:
If my current hook position, is below my CoG, then a clear advantage should be gained by moving it above.
If not then it's obviously back to the platform shoes to push us all further out.

I do still dispute the magic replacement of a rack to the exact same position on a wire simply because I still believe in the weight transferance to mast via the wire is relevant, but at this stage I'm unable to prove why.

One question to Mozzy, re "Increasing the height of the hook puts more weight on feet and less on the wire. " do you think this might be because you guys in 800s are already a way out there on the racks? I'm contemplating flatwiring in the not to distant future and probably earlier than most so need to maximise what little weight and height I have available.
It is however true though, one of the issues we used to have in the early days of kitesurfing in controlling our descent from big jumps if our hooks were too low which they used to have to be in the days before depower in order to maximise pressure on the rails to control the kite, it is wny these days so many waist harnesses with high hooks now feature. Higher hook gives better control in the air if the support comes from above the CoG.with more weight below landings are easier to control.

As to my theory of out board weight from a wire rather than through a rack and the hull I shall have to research harder or build that bloody model to find out for certain.

I wish I'd thought of the kite analogy*, the point is that the hook must be above your CoG or you'll land (on the board or in the boat) headfirst but it makes no difference to the power you can hold. Try moving it up (use a windsurfing waist harness maybe just to prove/disprove the concept?Windsurfing is different as you'll always be holding the boom and have your feet on the board so it doesn't relate to the trapeze dinghy dynamic. 

505's have always favoured big crews, tall and heavy, because they get the max weight as far from the boat as possible, so you would rarely find a big helm and a small crew doing well.

* Dinghy sailor since the mid '60s and windsurfer since '82 but I've never kite surfed.


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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"



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