I am reasonably expert in righting a catamaran. I am more expert at that than I am at sailing them!!!
In order to be able to right a Hobie Cat
type of catamaran, most people reckon you need a crew weight of at least 1/3 of the all up weight of the cat.
For a cat which has not turned turtle (i.e. with a small float at the top of the mast
, or a completely sealed mast), in anything over a F4 you first need to ensure that all sheets are released. Then you need to swim the bows around to point at about 45 degrees to the wind
, with the wind
on the trapoline tending to right the boat. You use a line attached to the base of the mast
throw over the upper hull with a few convenient knots in it, and then the crew stand on the upper side of the bottom hull as far away from the tip of the mast as possible and lean out as far as possible using the rope
with the knots to get as much leverage as possible. If you don't have enough leverage, you will need to point at a greater angle to the wind - at the risk of the boat flipping over immediately after coming upright.
If the crew weight is less than 1/3 of the all up weight, then in calm conditions you cannot right the catamaran without outside help. In windy conditions, you might be able to do so, however, you will be very prone to the cat flipping over again once it comes up.
Once the mast and sail is out of the water, then the boat will typically come upright fairly quickly. In lively conditions the trick is to quickly get your wait onto upwind side of the cross member
between the hulls which supports the mast. Hanging on there will also tend to ensure the boat heads up into the wind, and will stop it flipping over again. This is typically where I board as well - although it is a bit of an effort to be able to climb out of the water onto the trampoline.
It is difficult to see how you could possibly get enough weight far enough out board to right a cruising cat. However one could imagine some kind of spar attached under neath the cat, attached to the middle of the boat directly under the mast. This would be have an attachment point 1/3 of the way along which would be attached to a line going over the upper hull and attached to the mast. This would point up at an angle of 60 degrees or some from the water and have a large bag at the end into which you could pump enough tonnes of water to flip you upright. A small float or hydrostatically inflatable
bag at the top of the mast should prevent the cat turning completely turtle.