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Rudder rake effects?

Printed From: Yachts and Yachting Online
Category: Dinghy classes
Forum Name: Dinghy development
Forum Discription: The latest moves in the dinghy market
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=13882
Printed Date: 25 Jun 22 at 8:30pm
Software Version: Web Wiz Forums 9.665y - http://www.webwizforums.com


Topic: Rudder rake effects?
Posted By: Oatsandbeans
Subject: Rudder rake effects?
Date 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?



Replies:
Posted By: iGRF
Date 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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https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals      https://www.corekite.co.uk" rel="nofollow - New Core Kite website


Posted By: 423zero
Date 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.

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Robert


Posted By: Oatsandbeans
Date Posted: 27 Dec 21 at 12:13pm
Yes thatís 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.)


Posted By: PeterG
Date 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.

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Peter
Ex Cont 707
Ex Laser 189635
DY 59


Posted By: Noah
Date Posted: 27 Dec 21 at 2:02pm
On any boat with pretentious to any sort of performance, Iíve found that 2:1 down haul purchase is needed, and a decent (i.e. not worn out) break-out cleat that is properly adjusted.

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Nick
D-Zero 316



Posted By: Sam.Spoons
Date 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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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: ColPrice2002
Date 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!


Posted By: Riv
Date 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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Mistral Div II prototype board, Original Windsurfer, Hornet built'74.


Posted By: JimC
Date 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.


Posted By: PeterG
Date Posted: 29 Dec 21 at 10:20am
And even on not modern, lower performance boats, you don't really want a perfectly balanced rudder. You want some feedback through the tiller - just not too much.

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Peter
Ex Cont 707
Ex Laser 189635
DY 59



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