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prop size

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stumac145

New member
G,day,
Thank you admin for the join
i have a prop question
i have a mercury 1150 1971 115hp.I originally had a 13x19p alloy prop fitted to the motor but after having to remove with heat the rubber is now spinning under load.
i have since brought a second hand quicksilver laser 2 14x20p and modified thrush washer off old prop as i never got one with the prop and also had to file away a part of the trim tab for clearance it all fits good.i have seen that the later 115hp mercury big foots have a 14 inch prop so I'm hoping there should not be any other issues?
ps after reading mercury prop guide going from alloy to stainless i should go up 1 pitch size for flexing of the alloy prop i,m just worried about the diameter change
thanks Stu
i had to reseal prop main shaft and put some new bearings in the gear leg as it has been in the water for years also worked on the motor head.
 
Last edited:
Check the WOT rpms you may be a little over propped with the 20p. The main reason you go with more pitch on a stainless prop is because of weight the heavier prop has alot more torque value. If the 14X20 reaches proper wide open throttle rpms just run with it.
 
Weight of prop does nothing to do with torque.....
DIAMETER
"Diameter is determined primarily by the rpm at which the propeller will be turning and the amount of power that will be delivered to the propeller," (Mercury Marine's manual) Diameter "usually increases for propellers used on slower boats and decreases for faster boats.
PITCH..
Blades should be as thin as possible, since it takes more power to turn a thick blade(ALUMINUM). Stainless propellers are five times stronger than aluminum, which is why they can be thinner and still retain adequate strength and flex less Hence, stainless-steel props are more efficient. That why 95% of SS props are even pitched and aluminum are odd pitched.
 
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