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Technical protest
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fudheid View Drop Down
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Posts: 241 		Post Options Post Options   Quote fudheid Quote  Post ReplyReply Direct Link To This Post Topic: Technical protest
    Posted: 19 Nov 19 at 4:48pm
So this fence isn't producing lift? It isn't shaped to change the flow of water around the foil? Canting / lifting the rudder doesn't increase our decrease the angle the fence makes?
Having a fence doesn't enhance the performance of the foil in certain conditions, i.e. it stops ventilation, stopping the stalling of the higher aspect foil?
If I make this fence larger when does it become a non allowable wing?
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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: 19 Nov 19 at 5:06pm
Can't see it clearly on phone, but it looks like it also as a reduced chord ?
If the manufacturer designed blade purely to reduce suction and you attempt to make it into a foil ! Speaks for itself.
Robert
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fudheid View Drop Down
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Posts: 241 		Post Options Post Options   Quote fudheid Quote  Post ReplyReply Direct Link To This Post Posted: 19 Nov 19 at 5:11pm
Originally posted by 423zero

Can't see it clearly on phone, but it looks like it also as a reduced chord ?
If the manufacturer designed blade purely to reduce suction and you attempt to make it into a foil ! Speaks for itself.


Not attempting to make it a foil.
If it reduces suction is that no creating lift?
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fudheid View Drop Down
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Posts: 241 		Post Options Post Options   Quote fudheid Quote  Post ReplyReply Direct Link To This Post Posted: 19 Nov 19 at 5:15pm
That's too say, if this fence is creating any lift around it then it is a wing it contrivance under the definitions of the ERS/rule?
IF NOT.
then how much wider/ bigger can it get before the lift it generates is a wing or contrivance?
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Noah View Drop Down
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Posts: 611 		Post Options Post Options   Quote Noah Quote  Post ReplyReply Direct Link To This Post Posted: 19 Nov 19 at 5:32pm
Originally posted by 423zero

Fence is not a performance enhancer, it is a fit and forget item, purely for maintaining steerage, much the same as a release cleat on rudder or a centre board that knocks back, plus a myriad of other boat damage limiting useful inventions.

Sorry, 432Zero, I disagree. If the purpose of the fence is reduce cavitation it is, by definition a performance enhancement by virtue of the fact that the boat is easier to steer / more stable at high speed.
Nick
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JimC View Drop Down
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Posts: 6661 		Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 19 Nov 19 at 5:52pm
Originally posted by JimC

I'm not and have never been an official measurer for any class, but I have been involved in contributing to class rules for Cherubs and ICs. So take that for what its worth.

If I were looking at a Merlin I would say that a fence becomes a foil when it has any lifting capability, and most especially if there is any control capability of changing the angle of incidence. So if its a small structure not extending beyond the likely boundary area of the flow round the blade, with a symmetrical section oriented as close as possible to the likely local water flow its a fence.

[snip]

[later]
I've just looked at the rudder designs posted on the Merlin forum. I note
- structure which doesn't appear to extend beyond the boundary layer
- very low aspect ratio so very high drag if generating lift
- small total area
So unless there is some gear on the boat for changing the angle of incidence then I'd be quite happy with those - again for what little my opinion is worth.

In practical terms there will be a gap between a fence that is bigger than it needs be to do the job, and a foil that's too small and too low aspect ratio to do anything significant. The difference will be obvious. But in any case any control to accurately change the angle of incidence of the foil on the water would be a dead giveaway.
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Sam.Spoons View Drop Down
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Posts: 3400 		Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 19 Nov 19 at 6:14pm
Originally posted by Noah

If the purpose of the fence is reduce cavitation it is, by definition a performance enhancement by virtue of the fact that the boat is easier to steer / more stable at high speed.

Pedant alert (sorry)  Embarrassed 

Ventilation, not cavitation, cavitation doesn't happen at dinghy speeds (not even, I think, foiling Moth speeds).
Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"
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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: 19 Nov 19 at 6:43pm
Fence is a performance enhancing device like, 
Self bailers, they enable you to empty boat quicker than someone without.
Mast head float, stops you turtling, quicker recovery.
Duck under, stops you throttling yourself with mainsheet.
Hiking straps, allows you to lean further without falling in. etc etc etc
where do you draw the line ?
Robert
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gbrspratt View Drop Down
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Posts: 170 		Post Options Post Options   Quote gbrspratt Quote  Post ReplyReply Direct Link To This Post Posted: 19 Nov 19 at 6:48pm
Why do you need to draw a line? As you say they all improve performance? I don't really get your point. The point about the fence is how it fits in the rules?
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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: 19 Nov 19 at 7:54pm
Lost train of thoughts now  LOL Think it was in relation to adjustable wing and fence in relation to Merlin ruling.
Robert
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