http://secure.seawardkayaks.com/ecbuilder/item177.htm

that one or the double. You might consider glueing on a block on the stern to make the stern installation possible. I'm coming from the standpoint of a sea kayak that might be in ocean waves and not flat water paddling.

In 2002 when the Sport Tandem was being made Brandon/Heather of "Team CLC" had a Feathercraft II rudder on their BIG double. They experinced the Feathercraft aluminum rudder bending numerous times from wave/leg action alone until they replaced the rudder blade with a stronger one, ss I think.

http://www.clcboats.com/notesfromourshop/spring2002.php

The following review was done by a former CLC employee who took the ST on it's first exposure to actual sea kayak conditions with wind/waves. I asked Josh how it handled as I was concerned whether the FeathercraftII rudder was deep enough as I had paddled it on flat water without a rudder before installing one on the first prototype/demo ST.
The impression I got from him was that directional control did change every time the stern came out of the water. This would be in 2-3' waves. If you anticipate use in waves I would strongly recommend fixed footbraces with pivoting rudder controls as you really don't need to be applying more pressure on footbraces than needed to move a blade. And in a relatively tippy double in waves you shouldn't compromise bracing with push/pull controls.

When he came back from the trip he was a little pissed at me because the screw attaching the rudder wire to the yakima braces ripped out in some rough water. Not sure who's fault that was,,I did attach it,,but he said paddling the ST without the rudder in waves was not fun.

I'm guessing Brandons experience with the FeathercraftII rudder bending was a consequence of his substantial leg strength pushing the blade against some strong forces and the blade is at it's limit is long boats in waves.

http://www.paddling.net/Reviews/showReviews.html?prod=1100