I think it's called something like a shear leg crane or somesuch.
The trailer can only hold 1200lbs, so it doesn't have to be too heavy duty. The crane frame components would be part of the side boards when not in use. The wood would be used compressively, which is how they are strong. The boat winch is the item that would take all the strain, so I need to check into how strong that is.
The boat winch is something I have already on the trailer at that location.
I'd just need to get the chain lift part. Maybe a cable come-along?
The crane end should only go to about even with the trailer tires. I will probably have a couple of ropes to enforce that. If it goes past it's center line, bad things would happen.
Anybody build something like this before? Anything I should know about my idea.