I fixed mine several times and
this is what I did to ELEMINATE the problem. The basic issue is a lack of voltage getting to the solinoid. This comes from connections that are either loose (say battery terminals) or corroded (say starter key switch terminals). If you can get rid of the "post terminals" and put on "auto type" on your battery banks. If you don't want to do this then get out the sand paper and clean ALL the terminals and cables then smear a generous mittenfull of grease to keep them from corroding again. Remove the engine instriments pannel from the boat and examine the termnals on the key switch. You will find they are brass and have been out in the weather for a while. Did you notice the lack of a gasket on the engine instriment panel? After cleaning the threads and the nuts and the wire terminals, with special attention to the nut that stayes attached to the switch, put it all back together and then paint the terminals with a good enamal paint. Go get yourself some cork or other gasket material and make a gasket for the engine panel and Go out sailing.OBTW I had this problem for two years on and off and after i painted the key switch terminals the problem has never returned, even after a whole winter in the bay.