This is probably a really stupid question to ask but how would you know if your coil is bad on your boat ?

Power up the positive (+) side of the coil with 12VDC and use a jumper wire to connect to the negative (-) side and tap it to a known good ground with a spark plug on a coil wire with the plug body grounded with no other wires attached to the coil, it should spark when you hit the ground...

If no, it's coil time, if yes, look elsewhere..BTW, no such thing as a stupid question unless you already know the answer....

Good luck

GT