My brother and I lifted a
Volvo MD1 out of my boat with a 2 by 6 on our shoulders, chained to the engine, and set it in the cockpit(on plywood) and then moved it to the
dock. I could not have done it this way from the
deck to the ground. I think the
Volvo was much heavier than your Yanmar. Maybe you could back a pickup truck with a
lumber rack , up to your boat and use the
lumber rack to take some of the load. Good Luck. _____Grant.