Propeller

[Cdnguy1980]

Greetings again folks, so after closer inspection and taking the prop off, I found a serial number on it according to some research it's an OEM merc prop 10 x 9. I want to pick up a second one as it's always a good idea, but they don't make them anymore at least from Mercury, are there alternatives out there, and what would happen if I found one that is a 10 1/2" x 9? What are the key elements to prop replacement? Once again it's an 1980 20 HP

Thanks again all

 

[Silvertip]

Replacement props do not need to come from the engine manufacturer and probably didn't when the engne was new. There are aftermarket manufacturers and almost certainly have what you need. Like right here on IBOATS. The number you found is not a serial number -- it is the manufacturers part number which identifies the prop. There are three key factors regarding prop replacement. 1) the prop must be made for your specific engine. Just because it fits the shaft does not mean it's made for your engine. 2) Diameter. The 10 in the 10x9 number means the prop is 10 inches in diameter. Props may be available that physically fit on your engine but if they strike things, its not the right prop. The 9 means that prop moves the boat forward 9 inches (theoretically) with each revolution. 3) The type of boat, engine and horsepower determines how much pitch is needed to make the engine rev in its wide open throttle range with an average load. Too little pitch the engine will over rev. Too much pitch and it will lug and potentially destroy itself.

 

[Cdnguy1980]

Replacement props do not need to come from the engine manufacturer and probably didn't when the engne was new. There are aftermarket manufacturers and almost certainly have what you need. Like right here on IBOATS. The number you found is not a serial number -- it is the manufacturers part number which identifies the prop. There are three key factors regarding prop replacement. 1) the prop must be made for your specific engine. Just because it fits the shaft does not mean it's made for your engine. 2) Diameter. The 10 in the 10x9 number means the prop is 10 inches in diameter. Props may be available that physically fit on your engine but if they strike things, its not the right prop. The 9 means that prop moves the boat forward 9 inches (theoretically) with each revolution. 3) The type of boat, engine and horsepower determines how much pitch is needed to make the engine rev in its wide open throttle range with an average load. Too little pitch the engine will over rev. Too much pitch and it will lug and potentially destroy itself.

Is there a specific calculator for that? We have a 16 ft v hull boat, mostly going to used as our own taxi to interior campsites on lakes, and some water fun and fishing too.

 

[Silvertip]

There are lots of prop calculators on-line but those are a "get in the ball park" tools. Unless you have a tachometer you will never know if any given prop is right. The right prop is one that allows the engine to rev at it recommended wide open throttle rpm with an average load. Average load being what normally carry most of the time. If the engine cannot reach that rpm you need a prop with less pitch and vice-versa. But as I said - without a tach you will never know. If the engine seems to perform fine with what you have and you need a spare then stick with that. With that low horsepower messing with props will not likely gain much in performance.

 

[racerone]

Step #1 is to make sure that motor is in good condition and producing it's rated power.----A compression test is the first thing to do.