Starter or battery issues?
 

Just got a new (used) boat and did all the typica stuff to it to ensure it was up to date on services. New batteries, oil changes, topped everything off, etc..

Boat ran great but I'm having trouble with the port motor starting. The motor wouldn't turn over so I put a new battery in. It helped a little but it still won't turn over unless you try it 4-5 times. Its not clicking like a dead battery, its like it doesn't have enough power to turn over. If you turn the key off and try again and again, it will eventually fire off. It gets about a half rotation in before it comes to a halt. If you can get it to turn one full rotation, it fires up and runs great. Alternator is showing 13.3v on plane..

Do I have a bad starter?

Edit: And I charged the new battery overnight thinking the battery may have been low from sitting on the shelf or something.

I would guess its your starter solenoid. Go to where you have that little red reset button on your engine and there is a solenoid should be black with 3-4 wires going to it and is cylinder shaped with a metal bracket. They can be found on ebay for 10 bucks. If you had a bad starter and your battery is new it should at least click

If not I would get a voltmeter and have someone turn the ignition on and test the leads on the alternator, starter solenoid and starter. But first start at the battery.

My guess is the solenoid swap that out, its about a 10min job and cheap. Those little things go bad all the time so replacing it isnt going to be wate.

First check for loose wires, connectors, and connector corrosion.
Then jump the terminals on the solenoid and see if the starter spins properly, if still spins slowly, then this sounds more like a starter problem.

Sounds like bad connection

true start at battery and check every single connection and while your at it, lightly sand every single one and diaelectric grease, then tighten. If not this its that solenoid, my was the same thing.

commonly overlooked connection. the big ground wire on the block. but it sounds like your bad connection in this case is the brushes on the commutator. this is a very simple starter motor. take it apart and clean-free everything up. like most things in boats, they don't get a lot of wear. they get wet and either stick or break.in this case it is most likely the spring-loaded levers that push the brushes onto the comm.

Hydro-locking? Just a thought.....

Just went through these EXACT symptoms end of last season on a friends 2x 454/bravo Mach 1 290. Check the big center ground connection between the motors but I will bet $$$ she needs a new starter/solenoid

Well I swapped the solenoid on it since I could get it at our local NAPA and still having the same issue. Checked every wire I could and didn't get anywhere.. I did, however, bang on the starter with a hammer and it seems it freed up whatever was going on inside. It is still considerably slower starting than the stbd motor so I'm going to go ahead with a starter swap.

I figured that would be the case. Relay is just a switch and shouldn't slow down the starter. Of course a bad ground or poor connection will. Take the starter into a rebuild shop, it just may need new brushes, who knows. By the way I am a service engineer at GM for Starters and Generators.