Hello @johncat
My suggestion that you might try using a screw extractor kit. You can take the screw to a hardware store to match the size and type; or contact the manufacturer for specifics.
Here are a few tips you can check
The boats manual should list the screw types and sizes used.
Ensure you have the correct screwdriver bit to avoid stripping screws.
A bit of lubricant can help make screw removal easier.
.
