Yamaha 75HP 2-Stroke Prop Selection

[AquaZu]

I understand that this is a difficult question to answer with limited information, but I am hoping to get a baseline here.

I bought a beater boat last week for dirt-cheap. Don't laugh, it's a 17' Bonito Tri-Hull with a 1999 C75 Yamaha 2-Stroke on it. For the price, it was worth it for the trailer and motor alone, which popped 120-125 PSI on all cylinders.

Problem is, it needs a new prop. There is a stainless three blade on there now that is so bent up I do not even want to run it once. Plus, it's also not marked and the boat doesn't have a tachometer installed to check anything with.

Can anyone give me a baseline idea for diameter and pitch so that I can go buy an aluminum 4-blade to put on it? I was going to go with the 4-blade because I think the boat is going to need a little bit of help with the weight....

I will eventually get a tach to verify, but I need a place to start and get the boat on the water.

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[Sea Rider]

Welcome to Iboats,

Need to install a tach in first place prior testing any prop. Check with Yam which prop comes usually factory delivered with, can go say with a alum 3 blade prop with 2 less in pitch as a starter. Factory delivered props are usually medium pitched.

Happy Boating

 

[AquaZu]

I called Yamaha Tech support and he said that the motors were shipped without props and that is was up to the rigger to fit the prop to boat. That makes sense, but he couldn't even give me a ballpark to start with, which is what I am looking for.

 

[Sea Rider]

If current beaten prop is repairable at a prop shop have it repaired, that will be your starter prop. Go for a wot spin as usually loaded and check if inside at least middle to max wot rpm range factory stated. Can go from there maximizing a less pitch 4 blade prop.. Impossible to check wot rpm without a tach.

Other alternative, check if Yam has a prop selector, and start from there.

Happy Boating