A Question for you auto sparkies.

Hook up an amp meter and see how many amps it's whacking into the battery.

Steve.
I had a 70hp. Evinrude on the last boat. Reckoned on doing something similar to your idea, but sadly the alternator/diodes setup only catered for about 4 amps to the battery.
I think this is because the starting of the motor actually takes so little from the battery that a voltage unregulated 4a. recharge is consideres more than adequate. (which it is)
Would love to find a small enough alternator to fit in the space available though... from a motorbike possibly?
furph

I would not risk it.

Rather take a 2nd battery just for the fridge. The specs on the motor say 11 amps but that would be max at max revs and a willing battery.

Specifications:Propshaft Rated Horsepower 40hp (29.8kw)
Max RPM at Full Throttle: 4500-5500
Cylinders/Configurations: 3
Displacement: 42.5 cu in (697cc)
Bore & Stroke: 2.68" x 2.52" (68 mm x 64 mm)
Cooling System: Water-cooled, with thermostat & pressure-controlled
Ignition System: Modular CDI
Starting: Manual or Electric
Gear Ratio: 2.00:1
Gear Shift: F-N-R
Steering: Remote or Tiller
Alternator System: 11 amp (130 watt)
Trim Positions: 3
Exhaust System: Through prop
Lubrication System: Single point variable ratio
Fuel Induction System: Loop-charged (1 carb)
Operator Warning System: Overheat, low oil level
Shaft Length: Short 15" (381mm) Long 20" (508 mm)
Weight: 152lb (69kg)
Counter Rotation: N/A
Fuel Tank: Separate 6.6 US gal (25 litres)
Propeller Option: See dealer
Prop Selection (Pitch): 8"-19"
Propeller Drive: Splined rubber hub
Oil Injection: Std on electric N/A on manual
Carb Star Rating: N/A
SmartCraft Capabilities: N/A

Thanks for the info, I thought as much.

Cheers Steve.

One HP can provide about 500 watts of charging.

A 12 volt 150 amp alternator puts out 1800 watts (using about 4 HP)

So this motor would have adequate power to drive a Car Alternator - provdid you had the right gearing.

no there is only going to be 1/2 amp to charge battery