How to find the right prop...

[polarsusd81]

I have a Mariner 15 and one of the prop blades is missing . It is one of the Japanese built Mariners and I have the serial number from the motor, and found some markings on the prop itself. On the prop I found 9 1/4x12-3 which I know is the diameter x pitch - blades. I also found another marking that said 639 and then had a 9 under the 3. I have talked to a few places in town and everyone gives me a different story and I would like to get the right prop. It looks like I will have to order it online, but I want assurance it will fit if I place the order. Is there anyone out there that really knows the Japanese Mariners and can explain them to me?

Also, along with the prop question is another. For pitch, does a lower or higher number give you more top end speed? I would like to go somewhere in the middle. I have seen them in a range from 7 to 12 for 15hp motors.

Thanks much,

Tom

[Ralph Wiggum]

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Also, along with the prop question is another. For pitch, does a lower or higher number give you more top end speed? I would like to go somewhere in the middle. I have seen them in a range from 7 to 12 for 15hp motors.

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Higher pitch = more top end speed, but less hole shot

[Whoaru99]

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Also, along with the prop question is another. For pitch, does a lower or higher number give you more top end speed? I would like to go somewhere in the middle. I have seen them in a range from 7 to 12 for 15hp motors.

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Higher pitch = more top end speed, but less hole shot

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Yes, but the prop pitch goes in conjunction with the size/weight of the boat.

Generally, it's done by monitoring engine RPM then changing prop pitch up or down until the engine runs within the full throttle RPM range recommended by the engine manufacturer. 1" pitch change translates to about 200 RPM change in the engine at WOT.

There is enough history behind this that a dealer should be able to tell you fairly accurately what pitch to select based on the size of the boat and "normal" loading.

[polarsusd81]

After doing a little bit more research, I think I am going to try to get a 9 1/4x9 prop. The 12 I have right now just doesn't allow the boat to get up on plane right now with me and my buddy plus the gear. With only me, it can do it but it is still struggling. I just think the old engine isn't what she once was.

Thanks for the help,

Tom