Hey Thomh....
Take the plugs out, then remove the grey shield on back of motor, that will expose the pto, turn that counterclockwise, should spin freely, if so, then mount the plug boots on grounding post (top of mag cover), still w/ plugs out, then crank, nuth'n, try hook'n cables to starter (underneath exhaust), if she kick, like try'n to fire, then solenoid bad, BTW, dont hook w/ running car.
Check battery for good readings, if so, you can jump the solenoid, w/ scredriver/thick gage wire, then see.
Starter can be accesed with'n the boat....