OK, this is the classic case of what went wrong where? All of us are guessing until someone traces the circuit with a voltmeter.
If you blew the power before/at the ignition switch, that's in the boat circuit, and you'll have to find the power line to the switch and trace it back. If you blew the power after the ignition switch, then you can worry what blew to/in the motor.
The best/only way is to get a voltmeter, start measuring the voltages at various points along the way and find the point where you get/lose power, depending which way you're going. Then you've found the failed wire and you can see if it's a blown fuse, fried connection or what.
Voltmeters are $2 at Harbour Freight, and a voltmeter is the only way to troubleshoot electric circuits. Any voltmeter will do, just learn how to use it.
Boris