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Rudder rake effects?
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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 Topic: Rudder rake effects?
    Posted: 27 Dec 21 at 9:49am
I have never understood why racing dinghies are so sensitive to rudder rake. In most boats I have sailed ( forget the laser for a minute) if the rudder is not fully vertical the boat feels like a dog. Anyone got any explanation?
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iGRF View Drop Down
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Posts: 6499 		Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 27 Dec 21 at 12:05pm
I always assumed it was caused by the extra pressure from the water flow leveraged more by the swept back angle, I hate when it happens, which it seems to a lot, with slippy cleats on two of my rudder setups and running aground down the lake knocking the rudder back and jamming the rope further into the cleat making rectifying it a ballache.
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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: 27 Dec 21 at 12:12pm
Blade is shaped for maximum efficiency in the vertical position, some are just flat though. Could also be increased cavitation.
Robert
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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: 27 Dec 21 at 12:13pm
Yes that’s what I thought, but the centre of lift of the rudder is back from the pivot anyway so having the rudder not right down would only move it back a bit more but that bit seems to make a big difference to how the boat feels.( I struggled with the RS system of a rope in a cleat , always seemed to move.)
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PeterG View Drop Down
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Posts: 822 		Post Options Post Options   Quote PeterG Quote  Post ReplyReply Direct Link To This Post Posted: 27 Dec 21 at 12:14pm
Generaly (Lasers excluded!) they are designed to be nearly balanced, around the gudgeon/pintle axis when right down. If raked back they are unbalanced and the tiller load increases very quickly.
Peter
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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: 27 Dec 21 at 2:02pm
On any boat with pretentious to any sort of performance, I’ve found that 2:1 down haul purchase is needed, and a decent (i.e. not worn out) break-out cleat that is properly adjusted.
Nick
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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: 27 Dec 21 at 3:02pm
Whenever a boat heels to leeward weather helm is generated, we pull the tiller to compensate. As Peter G says loads increase dramatically with a raked rudder as it has it's CoE much further behind the pivot than a vertical rudder.
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ColPrice2002 View Drop Down
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Posts: 222 		Post Options Post Options   Quote ColPrice2002 Quote  Post ReplyReply Direct Link To This Post Posted: 27 Dec 21 at 9:19pm
Sailing with a raked rudder increases the force needed to steer. Simple leverage...

If the boat is absolutely flat, then there should be no force on the rudder...
Any heel and you'll feel it on the tiller.
Practice by rudderless sailing!
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Riv View Drop Down
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Posts: 353 		Post Options Post Options   Quote Riv Quote  Post ReplyReply Direct Link To This Post Posted: 27 Dec 21 at 10:44pm
I remember the first rudder I ever built, it was for an IC, had too much area forward of the shaft, went out turned around, just! Got back in and got the saw out.
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Posts: 6661 		Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 28 Dec 21 at 10:01pm
Originally posted by ColPrice2002

If the boat is absolutely flat, then there should be no force on the rudder...

Most modern high performance boats are tuned so that there is side load on the rudder. You are dragging the foil through the water anyway so it may as well contribute.
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