1/4-20 is a machine thread size, not a screw.If that is meant to attach through the hull, there must be either a threaded backing plate or nuts and washers on the inside of the hull. If the machine screw is not holding yet still threads in and tightens, you could try some Loctite to keep it from working loose.
If it is possible to access the inside of the hull, find a helper, use a a new machine screw, nut, and washer to be sure its tight. Seal the holes to prevent water intrusion into the hull core.
Just my idea, others may have a better method and experience.