Thanks for your positive comments!
Julian - your buoyancy bag may explain why Matt thought that my adding a bit of equipment very far forward in my BC20 might not be a bad thing! When I was trying to use an electric outboard and had two 110Ah batteries on board I wondered about putting a bag in the ballast tank to offset their weight (which was just forward of the aft tank). I didn't use one because I was worried it might move around in the tank. I assume yours is jammed in when inflated.
Matthew - my BC20 has a forward facing bailer to fill the ballast tanks and that worked well for the aft tank (even though it appears to still have it's flap!). However on the BC20 the pipe connecting the two tanks is the limiting factor in how fast they can be filled/emptied. The electric Whale Gulper pump fitted by SB took well over 30 minutes in emptying and I now have a Johnson Reversible Ballast pump (supplied by Matt) which I use to both empty and fill the tanks electrically. Notes on the timings, electric power needed, and plumbing installed are on my blog (access them via:
http://www.seatern.org.uk/SeaternDiaries/firstyear01.php )
Re. the homework... what was the temperature difference between the anvil and the water in the swimming pool?!
Michael - having spent most of my sailing life in dinghies I've had quite a few capsizes! When masts were wooden turning turtle happened less often than when they became alloy. I think it is generally accepted (David Hudson may have views on this) that having a lot of buoyancy in the side tanks makes a dinghy much more likely to turtle. If the capsized dinghy floats at an angle such that the top of the mast and sail dip under water then, if the hull is blown downwind, the water pressure on the sail forces the boat to turtle even if the mast is buoyant. John Claridge Boats have redesigned the side tanks on a new version of the Seafly dinghy specifically to minimise that happening. The idea is to allow the hull to partially sink so the hull (when on it's side) is vertical and the mast and sail lie parallel to the water. This also makes it easier to get onto the centreboard from the water. The alternative solution is, as you suggest, is some form of mast top buoyancy. Given that Matt favours fat headed mainsails, maybe new sails could have a buoyant top panel incorporated. Even a little buoyancy that far up would help.
One further comment on turtling - if you have continuous jib sheets (do some SBs?) it might be worth fitting righting lines. Normally tucked away under the gunwale, they could make getting the boat back upright much easier.
Peter