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 Post subject: Rudder camber/cant ?
PostPosted: Mon Sep 01, 2014 1:12 pm 
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Joined: Wed May 05, 2010 8:28 am
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Location: Clinton Lake, KS
One of those days where I can't work on 'time on the water' and I was letting my mind drift a minute.. Watching Volvo 70 boats... you know just one of those things.


So when measuring the toe in the other day I happened to notice that they measure about an inch or so wider at tip of the rudder than they do at the head of the rudder. on the trailing edge.

I imagine withing just the manufacturing tolerances of the various parts their could be a small range of 'adjustment'.

Is there any advantage to running a little 'negative' camber, or is the goal to have them as parallel as possible?

I can't recall ever hearing anyone discuss this. probably because within the range of adjustment there ain't much to be had.. but still?


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 Post subject: Re: Rudder camber/cant ?
PostPosted: Tue Sep 02, 2014 8:58 am 
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Joined: Tue May 27, 2003 12:44 pm
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Location: Oceanside, California
You have to measure with rudders down. Once down... leading edges should be about 1/4" closer together than the trailing edges at the same height (toe-in). The 1/4" allows some rudder slop before they drift to a more toe-out position.

Rudders, toe-out, tend to ventilate and cause steering issues / drag.

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 Post subject: Re: Rudder camber/cant ?
PostPosted: Tue Sep 02, 2014 10:03 am 
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I am not talking about toe in or out. I screwed up and had that all screwed up a couple weeks ago. I spent this weekend racing playing around with toe. I left the beach with just a little bit of toe in and kept dialing it in on the water until the leeward wake of the windward rudder was just right. Smooth sailing on that front now, and I have a better feel for what it feels like to have that adjustment both right and wrong.


When measuring toe in and out all the way up and down the rudder I noticed is that my rudders are not perpendicular to the rear crossbar. The tips of the rudders are about an inch further apart than the head of the rudder as measured from the trailing edge.


I was curious if anyone had ever played around trying to get the rudders perfectly parallel, or if there might be some advantage in either boat feel or speed to having the rudder tilted slightly to have it closer to vertical as the boat heels.



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 Post subject: Re: Rudder camber/cant ?
PostPosted: Tue Sep 02, 2014 12:03 pm 
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Hobie 16? The transoms tilt outwards at the bottoms. I think further out of alignment on that plane is better since you depend on the rudder as lateral resistance. More parallel would mean that the lee rudder would be heeling more off-vertical than the way they are designed.

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 Post subject: Re: Rudder camber/cant ?
PostPosted: Tue Sep 02, 2014 12:47 pm 
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Location: Clinton Lake, KS
mmiller wrote:
Hobie 16? The transoms tilt outwards at the bottoms. I think further out of alignment on that plane is better since you depend on the rudder as lateral resistance. More parallel would mean that the lee rudder would be heeling more off-vertical than the way they are designed.



That is what I was thinking, but I had never really given it much thought before, and was curious if it had ever been discussed. Granted there isn't a ton of room for adjustment within the factory tolerances.. But still..

I have just read a few things here and there discussing canted center/daggerboards on boats, but haven't really seen anything good discussing the same theories with rudders, and certainly nothing about such things on a H16.

I imagine this is mostly because most people are not silly enough to waste time thinking about such things.. but still... I am just curious if indeed you might be able to create less drag/chance of cavitation on the rudder by canting them inboard giving up some of the lateral resistance. Or if maximizing the outboard (at the tip of the rudder) angle will indeed give more lateral resistance without causing extra drag or dulling the feel of the helm.

Just curious as it would seem foiling boats are canting/curving foils inboard to increase stability/decrease cavitation, yet on things like the AC72 it looks like the rudders are canted outboard just a tiny bit. The Volvo 70 Monohulls are the only boats I have seen with rudders canted wildly outboard, but they also run higher heeling angles due to the monohull... A class boats, Marstorm 20's, H20, f18's f16's... You name it.. If any of them run any boards or rudders canted outboard it is by not very much.


I guess I am more interested in discussion of the theory, reasons, and science for why more cats don't try to match heeling angles a little closer, and maybe less interested in screwing around with it on my H16


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