Did you cut all of the wires or did you find it that way? It looks to me like an older style starter relay.
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That's the starter solenoid. It would have been a little help to know what motor is on this boat. Some older engines had the solenoid inside the boat rather than under the ending cowl.
Why in the world did you cut the wires instead of just disconnecting them? Or are you rewiring the entire boat aas well?