I am replacing the mast base, and I want to make sure the mast is watertight. Someone suggested I use silicone - what kind is best? One person said aquarium sealant would be good....

Jonathan

if you're going to use sealant, get a marine grade sealant like 3M 5200.

Make sure clean the surfaces really well before you apply too.

This may not be necessary since the base of the mast won't be in the water during a capsize. And if it is you have more serious problems than water in the mast. If some water gets in the mast from the top of the pole during a capsize an unsealed base would drain water after righted. by the way: why are you replacing it? last thursday when I was 'sick' I went sailing instead of work(the conditions happened to be perfect). I was lowering the mast and one of the holes that the pin goes thru broke off. I am stilled pissed about that. It was a relative new $69 part. Do you h17 guys rotate the mast 90 degrees or 180 degrees when lowering the mast?

90 degrees.

and I have an extra mast base laying around here somewhere that I'd sell for half of what hobie wants for a new one.

if your boat goes turtle, you will quickly appreciate the fact that the bottom of your mast is sealed.