Graupner B24 setup and balance

[Andy W]

I've had this boat for some time. It went well enough on an Aveox 1406/2Y and a 40mm plastic prop, 8 zapped 2000RC cells. I wanted more power, however, and felt it was not coming out of the water enough to really get on step. The hull is double-stepped, by the way - I'm a complete novice, but I would assume the idea is to get the whole of the boat out of the water except for the rearmost step? Anyway, I installed a different power system (Mega 22/30/3 and 12 cells) and in the process, relocated the battery to the rear of the hull (it was forward before) and now the model balances 'about' on that last step. It sits LOW in the water when idle, but on low power, the nose comes up about 20-30 degrees. A burts of power, however, and it shoots up out of the water, and flies - about the speed I'd like it to run - but it's very unstable, and has flipped upside down twice in one run. Second time, water got in the servo and killed it - everything else is good. Now, in it's previous configuration (battery forward) it had spun around many times, but never flipped in about 20 runs. The weight is actually lower now, but it's gone inverted twice on one charge.

Again, I'm a complete novice here - where should the model balance? Why is it unstable when the weight is in the back?

Appreciate any info.
..a
(Andy W - RCGroups.com moderator)