http://www.rcgroups.com/forums/showthread.php?t=1006894

In addition to that; in a small hull, the position of the floodchamber wall can be critical in order to keep room for all the goodies that should fit inside.
Once you've determened the weight, nececary to make the hull flip back, take that weight in water.
Put the hull on it's side,support it so it stands stable, and pour the water in the hull.
With a marker you can mark the 'waterline' inside the hull and have the optimal position for the floodchamber wall.

Proceed as describes in the link by making a template.

Another way is to make a template out Depron, position it in the hull and laminate it in position with glasscloth and epoxy resin.
Let it cure thouroughly, preferably in a warm environment.
Cut the hole in the transom and scratch out the Depron.
Use a slosh of Acetone to (quickly) wash out the remaining Depron (that's the reason the epoxy has to be cured 100%, or the Acetone will deform it).

Regards, Jan.<br type="_moz"/>