good luck with your boat idea! Some Germans built similar things, but I don´t know if they made it through... They wrote a book about it:
They were travelling on 2 XT 500s, they also have a website, something with abgefahren...
If you can not do it, I recommend a German Sailboat "Stahlratte"(steelrat)
they have a website and explain how to contact them and where the start, I know for sure they thake bikes!
Friend of mine did it a couple of months ago, check out their website, great pictures!
See you one day at the HU Germany Meeting!!!
Jens - El Aleman
right now at Cusco!