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From: 735769 <735769_at_ican.net>
subject: Re: [Paddlewise] Rocker: too many sea kayaks
Date: Wed, 6 Oct 1999 08:28:48 -0400
Shawn wrote;



>Does a drop skeg (below the waterline, obviously) have as much drag as a
>rudder (which is at the waterline and behind the boat's wave) due to the
>added wetted surface?

First, rudders need not have more surface area that skegs. Many do but that
does not mean they have to.

In general surface piercing foils cause more drag than equivalent area
rudders suspended below the boat. Rudders suspended below the boat can
experience increased drag due to the flow between the rudder and the hull so
in sprint boats and rowing shells they try to get as tight a fit as possible
between hull and rudder. Of course, builders have tried just about every
configuration imaginable and you can't get them to agree on much.  :-)

Large open trunks cause greater drag with skegs but you can get around this
in several ways. 1. You can use a skeg that keeps the slot full at all
times.
2. You can use some form of seal like they use on sailboats (not a great
idea on sea kayaks to my mind)
3.You can mount the skeg at the stern with the trunk exiting through the
radius at the stern.  The latter works because the flow at the stern has
gone turbulent and even travels in the same direction as the boat so no
increase in drag occurs. At one yacht company where I worked some felt the
open trailing edge could reduce drag by reducing the suction at the stern.
Well, Maybe.

Someone may know of more ways. ETC.

Cheers,
John Winters
Redwing Designs
Web site address, http://home.ican.net/~735769

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