Crank position sensor is most likely not your issue. It's basically an on/off switch that senses a reluctor wheel on the crank, hall effect style. CPS is basically works or doesn't, no intermittent issue. It's not a bad idea to check it for wear, it can "loosen" on engines with higher hours and contact the reluctor wheel. It's rare on a boat engine but can happen, shims are available to achieve the .030" gap.
My guess is you're experiencing an intermittent ground issue somewhere. Start at the batteries and work your way to the engine