Many thanks Dave, very much appreciated. Some important stuff there. I like the idea of the drop-in mast and leeboard pairing, though my gut feeling is perhaps this would put the leeboard too far forward for the larger sail (and thus longer boom) I would want to run with amas. I was imagining a second aka behind the front occupant with a good long leeboard to allow it to be angled back and fore, though perhaps a longer leeboard from the forward (or single) aka would work. A jury-rigged experiment on a boating lake would likely be a good plan!

I note your suggestion to use a single aka - I found this interesting and will think on it. This would certainly allow for a single mount for mast and amas and easy rigging, though as noted above I would be concerned that perhaps I would still need a second mount for the leeboard further back to avoid a weather helm with a larger sail. If this is so, then a second aka might make sense.

I emailed Klaus Metz regarding the Trika 540 and he came back to me today. He stated that to his knowledge nobody had built the 540 as a SoF design and no such plans are available. He did have one customer who asked him about it but he advised him against it. He was very complementary about the Chuckanut 15 design. Klaus said;

"In my view the question is whether you want a very light kayak which can also be sailed or a fast sail boat which can also be paddled. If you lean towards the first one you will be happy with a skin-on-frame. If you lean towards the second a small kayak trimaran as the Trika is the way to go. As you know, you can't have it all!"

I think he's hit the nail on the head there. The Trika as a 17 foot 'kayak' with a plumb bow and transom stern would, I imagine, be rather less than manoeuvrable when paddled. On the other hand the 15 foot traditional-kayak hulled Chuckanut would be considerably easier paddled but less able under sail. I think given that two out of the three jobs I want it to do will not involve sail, I must conclude that the Chuckanut would be the better bet. If I love sailing it and want to build something faster and with more load for camping gear under sail, I could always build a Trika a couple years later. :)