*** Help - prop question ***

[bkvette3]

Hello - would anyone be able to tell me what the part # would be for an original OEM aluminum prop that would have been installed on a 1990 Mercury 115 HP 2 stroke outboard from the factory??? I am thinking it was 48-18118-17P but am not sure.

Thanks in advance.

 

[steelespike]

I don't think there is a "factory" pitch.The pitch would be selected based on the boat and typical use.
Assuming a boat type/size typical for a 115 a 17" or 19" pitch is a reasonable starting point.
If you have a prop get us the pitch and the lightly loaded wot rpm and gps speed.
We can help tell if your setup is working. The rpm rating is 4750 to 5250.

 

[bilge rat jim]

Propellers aren't installed at the factory. The outboards arrive without a prop, are then rigged to the hull, and then the rigger (and the customer) select the best prop for that particular installation.

 

[bkvette3]

Thanks guys for the info - much appreciated. I learned something today.

Boat and outboard in question is a 1990 16ft Vanguard Phantom (980 lbs - as per sales brochure) with a 1990 Mercury 115HP. Never had the original prop - just curious what prop would have been on it originally - but looks like there would be a lot of variables as mentioned above.. What I have now is a High Five 20" pitch prop (WOT 5400 RPM @ 49-50MPH). Also have a Laser II 22" pitch prop (5400 RPM @ 47.1 MPH). Over revving - should I be increasing the pitch of both of these props by one inch to bring the RPMs' down to 5200 RPM. Will I gain any speed (if any)??? Or any other suggestions. Thanks in advance.

 

[steelespike]

I have a feeling either your speedometer is off high or your tach is off low. If the speed is not by gps then it may be off.
Using your numbers 5400 @ 49 indicates less than 1% slip. The high 5 should have low slip numbers possibly under 10%.
your 22" prop is right at 13%, fairly typical.
A one inch pitch reduction "Should"lower the rpm about 200 on each prop.