Might be a little more helpful if you describe
the lenght of the boat, approx weight, and
if the trailer is bunks or rollers.

But, basically, the general idea is:

Get some Jack stands.

Put them under key points of the boat.

Pull the trailer forward.

You probably will have to keep moving stands
around the crossmembers of the trailer so
you can pull forward more. Etc.

Stands can be expensive. If you can borrow some
that's helpful.


PS: There were a few threads on this subject not that long
ago. Go to Google. Hit Groups. Hit Search. Limit
by Data to, say, the past year or 1.5 years. Do a
few searches on different words.

Good luck.