You may want to look at a Windlass of some sort. You could mount it to a gimble mount to be able to remove it. There are quite a few different models on the market...I'm sure there's one out there that will fit your need/budget.
If you are just looking for a pulley, Scotty make a system that they call a Trap-Ease. It's essentially a pulley on a boom that you install into a Scotty rod holder mount.
Here's a link:
http://www.scotty.com/marine/product.../trapease.html
I use the Scotty mounts for my rod holders and they are very solid, however I have never used or even seen the trap-ease in use so I cannot verify its sturdiness.
I hope this helps and good luck with those lobsters.