Davy wrote: I think you are right Andy that the moving weight idea would be needed (linked to a level controller??) to get stability.
I don't think fitting the weight to a leveller would work out so well. Perhaps if the software was modified to include some hysteresis to dampen the response a little?
I think the Resurgam would just have to be a model that dribbles around the lake in a sedate fashion. I can't imagine the 1:1 version was any kind of hotrod of the high seas either.
With a decent metacentric height, and a low speed, static forces should keep the boat stable underwater.
The other option is to cheat, and make a tilting prop.