First thing to do is check the voltage going into your coil , it should'nt be over about 9.5 volts . Next, if you have already put in a Ballast resistor , where did you put it ? It should be in front of the coil on the hot lead going to the coil . Next... make sure that the "Coil" that is on your boat "requires" a ballast resistor then find the specs for the resistance of the coil and "Ohm" test the coil.

If you have the proper voltage , under 12 volts , at the coil... and if the coil needs the ballast resistor you installed , there should be no way that you are getting more voltage than your system requires at the points... All the Points do in your distributor is to tell the coil when to fire by collapsing the field to make the spark go from the coil to the cap and out the spark plug wires.

Hope this Helps. Good luck !         Joe