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Weight equalisation

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iGRF View Drop Down
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 22 at 11:56am
Originally posted by ChrisI

Love the discussion and Happy New Year to all.
Nice picture GRF and glad to see you've been out over Christmas/New Year.
Here's a suggestion on your original question (from another engineer ) if you have a spare moment in a coffee break.
Make up a model but make it with one mast and a trapeze (with weight etc) EACH side so it is exactly balanced.
Then without changing the position of the weights change the attachment point on one of them and see if the thing unbalances.


Yes, exactly what I was planning to do, have even got a set of warehouse scales to set it all up on.
Just need to set it up with a model helm that won't shut up moaning all the time.
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2547 View Drop Down
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Post Options Post Options   Quote 2547 Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 22 at 12:00pm
Well I have missed a lot since starting this topic ... I wasn't really expecting to see some people trying to rewrite the laws of physics but I should have expected that.

Anyway ... seems the answer to my original question is that weight equalisation in dinghy sailing is a concept that is almost forgotten bar a few classes in the UK.

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Post Options Post Options   Quote ChrisI Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 22 at 12:09pm
PS Very interesting data analysis on the RS800 from Mozzy... many thanks.
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 22 at 2:46pm
Originally posted by iGRF

I know I've read somewhere the wider area the weight is displaced over, the earlier to plane, it was the physics behind formula boards, it's why wide goes earlier than narrow, and I'm sure the fact that c of g of that out fit moves from the centre line further to weather and the bigger the weight component of the crew of the whole package the earlier it all goes.
Now I'm not disputing all your schoolboy physics bollox, but I swear to God there's more going on with this weight transference, now wether it's the wire angle, the helm angle, but nothing has changed with all your calculations except at some point everything knotches up, and we breakout.

I'm guessing it's 'cos it's never a steady state, windsurfing we'd pump a couple of times in a gust to get over the hump, the act of extending to windward to counterbalance a slight increase in wind strength will have a similar effect if you are on the point of planing anyway. Once you are planing there is less boat in the water thus less drag so you don't need as much power to keep planing as you did to get planing.

I agree WRT the wide/FW idea, I think boats are not so different to windsurfers when it comes to the effects of rocker and planing areas and the basic concepts, that wide flat planing areas get going sooner than narrow/curvy ones is easy to see as is the trade off that wide flat boats are slower in displacement mode.
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 22 at 4:54pm
Which still gets back to the original question, what's best to achieve that high or low hook?
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Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 22 at 5:59pm
Griff, what do you make of the 'dead downwind speed' thing? Thought you would be all over that.
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Post Options Post Options   Quote fab100 Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 22 at 6:13pm
Originally posted by iGRF

Which still gets back to the original question, what's best to achieve that high or low hook?


Mozzy’s et al have told you, pay attention - hook should be just above your CoG.

If you want more righting moment you need to trapeze low, perpendicular to the mast with the boat absolutely flat as that moves your CoG out marginally further. And be out in your tippy-toes, and in platform boots in your case. Which all works as long as you are not crashing into waves, obvs.

As usual, the moral is that if you’d learn to apply accepted best practice, you’d gain far more on the water than by trying to invent new tricks that aren’t there.

Interesting thread tho; it’s wakened the place up.
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Post Options Post Options   Quote Mozzy Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 22 at 6:26pm
oFF, does tension in the wire increase when it's higher up the body? I would have thought it decreased as it will be supporting less of the weight of the sailor.

If the hook was exactly on the CoG and the sailor flat wiring then all the weight would be on the wire. But as that goes higher up the body more weight is supported by the feet.

If the hook is below the CoG then tension increases as the feet would have to push up on the gunwale to stop the sailors feet flipping above thier head. It would feel like hiking.

You could get almost an infinite amount of tension in the wire by attaching it closer and closer to your feet... if your body didn't give way first.

So going back to the tree analogy, you can either get more tension in the wire attaching it lower, but at a less effective angle or less tension at a more effective angle with a higher hook. Thus preserving the same resultant righting moment produced by the sailor no matter where they attach to the wire (we summed in addition to the force on the gunwal / rack).
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 22 at 6:52pm
Originally posted by 423zero

Griff, what do you make of the 'dead downwind speed' thing? Thought you would be all over that.


If like me you joined the AYRS which I ran into during my eccentric speed week and revolutionary sail design period, in which I had to develop a sail to allow light weight me to take on heavyweight speed meat heads. You meet all those kind of guys, how to sail dead upwind, perpetual motion devices, although I must admit that device is genius in that it works. I love eccentrics that want to defy the alleged laws of physics, one day someone may find the means to travel faster than light, which I once proved to my physics master at school in theory at least only to be treated with as much derision as I receive here.

Honestly I don't fully understand a lot of what the informed guys have clearly postulated, nobody has adequately explained in a manner that convinces me for instance that a rack and wire achieve the same thing and that need to be disproved.

So this theory v mechanics thing aint over for me, there's something missing that I haven't completely grasped, even if you assume the weight transfer goes up the wire, then down the other side via the lee shroud, the leverage is still greater than that same weight being applied to a static rack which might scientifically explain at least why a trapeze is faster.

Edited by iGRF - 04 Jan 22 at 7:12pm
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 04 Jan 22 at 6:56pm
.double post.

Edited by iGRF - 04 Jan 22 at 7:10pm
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