Sounds like your resistor is open or there's a bad connection to the resistor.
Corrosion is a problem with boats is it not?

Bypass the resistor which will apply a full 12 volts to the coil and see if the engine fires.

Don't run it very long.
The resistor is there to cut the voltage down to about 7 volts or so which keeps the points from burning up.

Most cars have an ignition switch that applies a full 12 volts to the coil during startup and when the starter drops out, the ignition voltage reverts to approx. 7 volts for constant duty running.