I'm betting srm is in the ballpark and that if you follow daniel t's advice then multiply by a safety factor of two you'll get about the same result. It's not really a static problem since you need to consider gusts, waves, and people falling in the wrong spot and/or getting hung up in lines (thus the safety factor). Before I built anything from scratch based on theory and assumptions, I'd do a little empirical research. Take it out in calm conditions/shallow water and practice capsize with a few gallon jugs tied to the mast to get an idea. Work up from there (more jugs) and practice capsize in more the conditions you want to simulate. As a reference the Hobie Bob and Mama bob (for the Getaway) are about 60 lbs. (7.2 gal. or almost one cu. ft. of water) of flotation. The Baby Bob is about half that.

Do consider that the required flotation amount is net (after subtracting the weight of the device and hardware). Also consider that the weight of the float on the end of a 34 foot moment arm will actually add to the weight required to right the boat.