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iGRF View Drop Down
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    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.

Edited by iGRF - 02 Jan 22 at 11:55pm
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423zero View Drop Down
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Posts: 3420 		Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post 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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Posts: 219 		Post Options Post Options   Quote ohFFsake Quote  Post ReplyReply Direct Link To This Post 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. 
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mongrel View Drop Down
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Posts: 304 		Post Options Post Options   Quote mongrel Quote  Post ReplyReply Direct Link To This Post Posted: 03 Jan 22 at 7:03am
If you move the hook position higher up your body, I think you’d risk damaging your back.  
Also, with a high hook on the harness, in a lull where you’d 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?)
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Oatsandbeans View Drop Down
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Posts: 382 		Post Options Post Options   Quote Oatsandbeans Quote  Post ReplyReply Direct Link To This Post 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 don’t have to think about anything else it will just confuse your thinking (a bit like the lee bow effect conundrum!)
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Paramedic View Drop Down
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Posts: 929 		Post Options Post Options   Quote Paramedic Quote  Post ReplyReply Direct Link To This Post 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.


Edited by Paramedic - 03 Jan 22 at 8:07am
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Paramedic View Drop Down
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Posts: 929 		Post Options Post Options   Quote Paramedic Quote  Post ReplyReply Direct Link To This Post 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 don’t 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.
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Oatsandbeans View Drop Down
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Posts: 382 		Post Options Post Options   Quote Oatsandbeans Quote  Post ReplyReply Direct Link To This Post 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.
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tink View Drop Down
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Posts: 789 		Post Options Post Options   Quote tink Quote  Post ReplyReply Direct Link To This Post 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 




Edited by tink - 03 Jan 22 at 8:26am
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Oatsandbeans View Drop Down
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Posts: 382 		Post Options Post Options   Quote Oatsandbeans Quote  Post ReplyReply Direct Link To This Post Posted: 03 Jan 22 at 8:49am
The shrouds don’t really come into this. The loads are balanced when the rig tension is applied and yes the windward one’s tension will change whilst sailing it doesn’t 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.
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