thresher off a yak? big deal. thresher in a tube!
so as not to completely threadjack... v tube or u boat for the ocean, both are great for flyfishing and can handle some chop. Any full waders work fine, or wear a wetsuit and a good pair of booties. with a ripping current you'll need to plan out your entry and exit spots, since kicking against a good current gets tiring real quick. You should be able to kick against a light or moderate current without a lot of trouble. I've never tried it but I hear you just aren't able to get enough speed out of a round tube to deal with much current, so the v or u shapes are the way to go. I think of it more like planning a dive than a fishing trip. plan your dive and dive your plan...or fishing trip in this case.