What size engine?
What type of boat?
By "move" you mean to a pull-out ramp?
Raw water cooled?
Have you checked the oil for water?
Put a voltmeter on the battery terminals directly on the battery connections NOT on the cable terminals and then have someone hit the starter just long enough to get a good reading 2-3 seconds max.
What reading do you get?
Next place the voltmeter leads directly on the starter. Put one on a solid bare spot like the big field screws on the side. Place the other meter tip directly on the starter's actual power input bolt. Usually the one that the start solenoid outputs to the actual starter motor (talking GM style) (or on a Ford style, on the one big terminal). Again have someone turn the key until you get a good read. 2-3sec max.
If these two readings vary by more than 1V you probably have connection problems.
You can hunt the connection problem by setting your voltmeter down to a 2 volt setting (or there abouts) and then placing the probes across each and every wire connection.
Example: Place one probe on the battery terminal and one on the cable connector bolted to the that same battery terminal. You will come to some connection or the PERKO switch or something that will probably show most (90%) of the voltage difference between the original two readings. This would be the problem.
Possibilities: (not limited to)
Battery to terminals connections
Perko switch contacts (measured across switch terminals)
Cable swages (connector to cable)
Starter terminal to cable connections
Undersized cable/s (or secretly corroded to undersized)
Bad contacts inside starter solenoid
Bad engine ground cable/circuit
Let us know.
Good luck!
Keith Cress
Flamin Systems, Inc.-