To start with your 55hp motor is only making about 35hp without the turbo.
I'm betting the boat came out of a rental fleet and the renters were not instructed to let the engine idle for awhile to cool the turbo down and prevent coking of the oil in the turbo.
Most turbos can be rebuilt for under 500 dollars.
I hope that the bypass was done in such a way that the parts are still there to reverse the procedure.
Let me know if you need the name of my rebuilder.