Propeller Slips

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Have a 17 year old Mariner 45, 4 cylinder, 45 hp outboard motor. Had been running fine until 2 years ago when boat speed suddenly began reducing after running engine for about 45 minutes. Acts as though propeller is slipping or prop is losing torque. Reducing engine speed & reversing engine has no affect on problem? Appears to be a heat related problem but have no clue what it might be. Thought it was the rubber hub so I replaced the entire prop. No help? Also replaced the water pump. Again. NO HELP?? All comments welcomed.

 

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Re: Propeller Slips

Welcome to iboats.<br />Paint a line from the prop nut out to the other side of the hub. If it moves, the hub is spinning out.<br />You say it acts as tho it is a heat related problem. It could be cavitation, but the heat-related thing kind of brings us back to the hub.<br />But do check the hull for any dents, bumps, barnicles or anything else that might introduce bubbles to the water before the prop.<br />Iether one will make it act like a slipping clutch on a car, or black ice and traction in a car.