My marine battery fell off my tailgate and is leaking acid I think its be beyond fixing. I have another battery in my garage that's smaller I use for my gator tracktor. Its a 12 volt. Will it work for a small blowup boat and trolling motor?

Probably not.  First off, it's probably a cranking battery, which running it down constantly with the TM will kill it.  Second, it's probably not going to have enough Ah capacity to run for more than a very short time.  You can always try it and see, if it will run long enough, it will last a little while before it goes totally belly up.

Its not ideal, but it will work in a pinch.  It will, however, shorten the lifespan of a cranking battery much faster than normal use.  Cranking batteries are designed to to provide high current for short periods of time.  If they are discharged or kept at a low charge state for extended periods, it can lead to sulfation of the plates.  If you do use your cranking battery to run a trolling motor, I would recommend not running it down below 50%, and charging it back up immediately after use.