Lots of information is missing here. 1.) Is the seawall like a bulkhead with the ground level with the top of the wall? 2.)If not how high will you need to pick up the boat? 3.) If so how wide is the seawall? 4.) Can you attach a lifting device to the wall? 5.) Do you have electricity nearby? or do you need a manual lifting system?
6.) How far is the water down from the top of the seawall?

A simple lifting/swiveling gin pole setup would work. I can also be done manually. Your base support would be critical obviously, but the H16 is pretty light.

A few answers to the above questions could get you a solution.

Clayton