[MHml] Cat Rudders Toed In?

[thomas deane]

and toe in on your cars front wheels. thomas deane
----- Original Message ----- 
From: "thomas deane" <tdeanesr at hotmail.com>
To: "Informed discussion of multihull issues" <multihulls at steamradio.com>
Sent: Friday, September 01, 2006 12:52 PM
Subject: Re: [MHml] Cat Rudders Toed In?


> and this is why the early polynesions put toe in on their canoe and ama.
> thomas deane
> ----- Original Message ----- 
> From: "Glenn Brown" <gbrown at alumni.caltech.edu>
> To: "Informed discussion of multihull issues" <multihulls at steamradio.com>
> Sent: Friday, September 01, 2006 11:40 AM
> Subject: Re: [MHml] Cat Rudders Toed In?
>
>
>>>     Our new to us 35' Cat (designer unknown) appears to have
>> > both rudders toed in about half a degree from parallel.
>> >  Is this a normal thing with cats or a builder's mistake?
>>
>> That amount of toe-in is not at all unusual for small performance cats,
>> where toe-in in the 0 to 1 degree range is considered acceptable.  I
>> think 0.5 degrees is what the Olympic Tornado sailors found optimal for
>> that boat by experiment, though the theory behind it is not 100% clear.
>>  In general, toe in reduces the angle of attack of the windward foil,
>> reducing its lift and increasing the AoA and load on the leeward foil.
>> Running less lift on the windward rudder with toe-in reduces helm
>> perturbations as that foil enters and leaves chop, and reduces the
>> tendency to round up when the hull lifts.
>>
>> For laminar foils, toe-in can also reduce total rudder drag if parallel
>> rudders both run outside the low-drag "bucket" (at an AoA of more than
>> about 3 degrees), and if toe in allows the windward rudder to enter the
>> low-drag bucket.  In this case, toe-in can cause the drag on the
>> less-loaded windward foil to drop more than the drag on the more-loaded
>> leeward foil increases.  However, loading the rudders to such a high
>> angle of attack only pays if you have relatively inefficient forward
>> foils, such as most low aspect ratio centerboards and keels.
>>
>> --Glenn
>>
>> P.S.: Your NACA 0012 foils are not laminar flow foils.
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