Originally Posted by trapper7
I have a German made engine...(HB .40 PDP) For plans I found the ones on this site and am copying them: http://www.rcuniverse.com/forum/rc-airboats-246/8234813-40-46-build-plans.html
I am VERY open to any advice.
Ah yes.. An old HB. Good engines - I have a .61 non-PDP myself. I have a piston/liner/rod for the .40 PDP Blitz too. Keeping my eyes open for a good donor engine in need of said parts.
With internal combustion as a power source, you should be okay with the plans as they're written. I friend had problems with that boat using electric power. I suspect the batteries and such threw the CG off pretty far. I highly recommend building the engine mount such that you can shift the engine fore/aft to adjust the CG. The CG should be roughly 1/3 hull length from the transom as a starting point. Keep your prop diameter and pitch reasonable. Don't try a big diameter or high pitch props - especially with an older cross flow engine like the HB. Look to a 10x4-10x6 or 11x4. I don't think a 9" diameter is going to give enough thrust. Also, build your hull as light as possible. Think balsa or lite ply for the stringers and such. Your main hull runners (that will attach to the engine stand) should be birch plywood and use thin birch ply for the sheeting. I use 3/16" or 1/4" for my main/high stress areas such as engine mounts and such and thin 1/32" or 1/16" ply for the sheeting. Best advise for adhesive is 15min or 30min epoxy for bonding the hull together and use a thinned 30 or 60min epoxy or a slightly thinned epoxy finishing resin. Thin fiberglass cloth inside the hull is a good idea - I typically use 1/4oz cloth for inside the hull and on the bottom sheeting for added strength.
Hopefully that isn't info overload. I have built 9 or 10 boats with several running 50mph plus. So far I've been lucky and none of them have blown apart.