New Posts New Posts RSS Feed: Weight equalisation
  FAQ FAQ  Forum Search   Register Register  Login Login

Weight equalisation

 Post Reply Post Reply Page  <12345 13>
Author
Sam.Spoons View Drop Down
Really should get out more
Really should get out more


Joined: 07 Mar 12
Location: Manchester UK
Online Status: Offline
Posts: 3325
Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 22 at 11:25am
Originally posted by iGRF


I already know, that one minute you can be standing on the gunwhale leaning back even and the boat just trucks along fast displacement, but if you can just by virtue of a big enough power increase to counter your weight, get right out, the weight comes off your feet is pretty much all transferred through the rig and the boat quite literally leaps forward (I'm talking little Farr 3.7 which I always found a tad underpowered)

This is the key, the power increases and you push out a bit further to balance it and you go faster.

I'm now beginning to wonder here wether it was my harness hook in the wrong position and wether had I positioned it higher I could achieve that breakout point earlier. You even lengthen the trap lines to drop lower to increase that angle, the flatter you are the more unweighted the boat becomes and the faster you go, is all I know. At that point it's just like a windsurfer raceboard, but what I don't know 100% is why and I want to, those Contenders are heavy ass MFs.

The boat is not 'unweighted', it still weighs the same, but it has passed 'the hump' and started planing. The flatter you are the further from the CoB your CoG is so the greater the leverage and the more power you can balance so you go faster.
Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"
Back to Top
ohFFsake View Drop Down
Far too distracted from work
Far too distracted from work


Joined: 04 Sep 08
Location: United Kingdom
Online Status: Offline
Posts: 219
Post Options Post Options   Quote ohFFsake Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 22 at 10:34am
In terms of the physics, what this all boils down to is a single mass (comprised of boat, rig and sailor) which are all fixed in relation to one another, once the sailor is on the wire.
This mass has a centre of buoyancy, typically somewhere between the centre line and the leeward chine, and a centre of gravity which is typically somewhere to windward of the hull for a trapeze boat.
The righting moment is the difference between those two. How the sailor is attached to the boat has no effect whatsoever on this equation, whether they are hanging on a wire or sitting on a rack or a sliding seat. All this affects is how the forces are resolved within the boat, the righting moment is dictated simply by the how far away from the centre line their weight is.

Looking at the trapeze system in more detail, if the wire is hooked on to the sailor higher up their body this will increase the tension in the wire as it is now supporting the same mass but with a greater horizontal component. This is balanced by an increased force acting inwards via the sailor's feet pressing on the gunwhale, but again this is purely all about resolving the static forces within the boat and has no effect on the overall righting moment.

So yes it will feel different, and indeed it is quite intuitive to grasp that the more vertical the wire the more you are hanging from it, whereas when the wire becomes more horizontal there is more force trying to pull you back into the boat. But once all these forces are resolved the righting moment is the same
Back to Top
423zero View Drop Down
Really should get out more
Really should get out more


Joined: 08 Jan 15
Location: United Kingdom
Online Status: Offline
Posts: 3214
Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 22 at 10:30am
How was your back? You must have good core strength.
Robert
Back to Top
iGRF View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 07 Mar 11
Location: Hythe
Online Status: Offline
Posts: 6490
Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 22 at 10:26am
Here check this one, the rig is even canted slightly to weather yet I know for a fact that the lee shroud aint helping that much because it had come adrift at the start of that particular race and I was playing catch up at the time.
All my weight is coming down through the wire and at that point the boat was trucking well, one of my better days. The harness hook is already quite high, I also know this because the bloody thing had come adrift and was riding up, those useless new QR zhik models do that from time to time.

So had the hook been lower and the angle of that wire narrower (acute?) would the rig have been working as efficiently? I know things slow down as you come in but that is usually because you head up at the same time.



Edited by iGRF - 04 Jan 22 at 10:28am
Back to Top
iGRF View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 07 Mar 11
Location: Hythe
Online Status: Offline
Posts: 6490
Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 22 at 10:04am
Originally posted by Rupert

GRF, bung a spring balance in the trapeze system, go sailing, take photos and prove everyone wrong. Simple.


Not sure that would prove anything other than the loads passing through the wire.

I already know, that one minute you can be standing on the gunwhale leaning back even and the boat just trucks along fast displacement, but if you can just by virtue of a big enough power increase to counter your weight, get right out, the weight comes off your feet is pretty much all transferred through the rig and the boat quite literally leaps forward (I'm talking little Farr 3.7 which I always found a tad underpowered) I'm now beginning to wonder here wether it was my harness hook in the wrong position and wether had I positioned it higher I could achieve that breakout point earlier. You even lengthen the trap lines to drop lower to increase that angle, the flatter you are the more unweighted the boat becomes and the faster you go, is all I know. At that point it's just like a windsurfer raceboard, but what I don't know 100% is why and I want to, those Contenders are heavy ass MFs.

Edited by iGRF - 04 Jan 22 at 10:07am
Back to Top
Rupert View Drop Down
Really should get out more
Really should get out more


Joined: 11 Aug 04
Location: Whitefriars sc
Online Status: Offline
Posts: 8939
Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 22 at 9:13am
GRF, bung a spring balance in the trapeze system, go sailing, take photos and prove everyone wrong. Simple.
Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686
Back to Top
JimC View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 17 May 04
Location: United Kingdom
Online Status: Offline
Posts: 6582
Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 03 Jan 22 at 9:37pm
The position of the hook/trapeze wire makes no difference to righting moment, but it makes all the difference in the world to the loads on the gear, the ability of the sailor to move in tune with the boat and the effect on the mast bend. So the intuition that its crucial is correct, but the reasoning as to why is wrong.

This is all rather allied to the lee bow effect discussion, where what IGrf called a lee bow effect was generally a real thing, but it was most definitely not the fallacious lee bow effect that used to be touted in some books.

Its an internet lesson really, before two people are to have any chance of agreeing on an answer they both need to have exactly the same understanding of the question. Something that has been proved in the last year or so by the US physics professor who made a complete fool of himself by claiming the "Downwind faster than the true wind" phenomenon cannot work.
Back to Top
Sam.Spoons View Drop Down
Really should get out more
Really should get out more


Joined: 07 Mar 12
Location: Manchester UK
Online Status: Offline
Posts: 3325
Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post 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.


Edited by Sam.Spoons - 03 Jan 22 at 9:33pm
Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"
Back to Top
423zero View Drop Down
Really should get out more
Really should get out more


Joined: 08 Jan 15
Location: United Kingdom
Online Status: Offline
Posts: 3214
Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post 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.

Robert
Back to Top
iGRF View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 07 Mar 11
Location: Hythe
Online Status: Offline
Posts: 6490
Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post 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.

Edited by iGRF - 03 Jan 22 at 8:05pm
Back to Top
 Post Reply Post Reply Page  <12345 13>

Forum Jump Forum Permissions View Drop Down

Bulletin Board Software by Web Wiz Forums® version 9.665y
Copyright ©2001-2010 Web Wiz
Change your personal settings, or read our privacy policy