It is a relatively straightforward task to create a mast raising/lowering crane for use on the water, but you have to have a few things...side stabilizers only work if there are pivot points at mast base height on both amas. Once you have those you can use a slug on your mainhalyard and two equal length lines and hoist the slug to tighten so mast stays amidships (of course, if your mast must remain sideways, one will be shorter than the other). You'll need your jib halyard (spin halyard is even better) attached to the bow chainplate by way of the mainsheet and A frame. Now you need leverage-simplest is to build an A frame that pivots at those same pivot points at mast base height. Here's a link to how a monohull did the same thing, same principles...
http://www.watkinsowners.com/howto/mastcrane.pdf