OK guys i have a small bass boat exactly like this one

http://www.1stdirectproducts.com/minbasfisboa.html

The problem is it is starting to leak.  I installed two plugs to drain the water so i could load into back of truck by myself.  In a couple of hrs fishing it will take on at least 4 gallons or so of water if not more.  I need to use some kind of sealent around the plugs and to seal up a small crack around 4in long on the back and also want to seal around the seams.  The seams look like they are not sealed anymore.  Does anybody know of a really good sealent to use in this application.  Everything I have tried doesnt seem to be doing the job.  Any help would be greatly appreciated.

3M 5200 Marine Sealant/Adhesive. Patching plastic boats is tough. I know of nothing that will stick permanently. Maybe the tube of glue that comes with a swimming pool repair kit.

If the leak is a crack, rough up the surface around it, clean thoroughly with acetone. Put a bead of the 5200 or adhesive on the crack/hole and work it in with a putty knife. Then, put another small bead over the crack/hole, put a piece of wax paper over the bead, and using a bondo spreader or even a silicone spatula, spread the bead to to 3/4" or so beyond the the crack/hole, and leave it for a few days.  The wax paper can be peeled off after the adhesive sets. 

The 5200 can take a few days to completely set up. They do make a fast set version, but I have no experience with that.

You want to have a smooth feather edge transition away from the leak. If you leave a ridge, it can get hung and pull the patch off.

It has worked on my plastic canoe, but I've also had to repeat when the patch has dragged across anything other than grass or moss.

You might be able to use a soldering iron, and melt the plastic back together, but the stuff is so thin, that would be tricky.

What have you used? Is the crack below the waterline?

I would suggest a fiberglass repair kit.  I repaired cracks in an aluminum boat this way,  and used it for ten years with no problems.

Ken

I would try a product called Plumber's Goop. Made for fixing plumbing, so it is waterproof. goes on like silicone, but dries very hard, like an epoxy. I used it to mount a plastic cup in my kayak to be filled with water and mounted my transducer in it. Has been working for over 5 years. Comes in a tube kind of like tooth paste size, and is resealable for future repairs. Strong stuff, follow the instructions.

J.B. Weld for the win Alex.

That stuff is amazing.