Could I take it even farther and put the big sailing rudders on the amas themselves ala catamaran, and get good steerage without mounting a rudder on a kayak which definitely doesn't need one for itself?
You can buy beach catamaran and carry folding/inflatable/small rigid kayak for fun.
I tried to go your route some 20 years ago, modifying a kayak into fully blown trimaran. It never worked for me. Chief from Watertribe has tried to go this route without much success. Every year somebody trying to bring some kayak based paddling/sailing, supposedly fast trimaran into Everglades Challenge, I have never seen one succeeded, exept Balogh system and Hobie AI.
There are too many design limitations. To make weatherly trimaran you have to build very strong and stiff platform. It becomes too heavy very fast for one person to handle, to paddle, to cartopů
Did you look at Raptor outrigger?
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