removehtml]If you use a 3 blade vs 2 blade prop, will this decrease your RPM considerably? I have a Universal 26hp and the website says 3000 rpm under load. I am only getting 2500 in neutral and 2000 under load. Error: Error: expected [/URL], but found [/removehtml] instead[/removehtml]
Prop effect
- Thread starter butchrobbins
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It's not the prop
the difference in rpms most likely has to do with the calibration, or lack of, of your tachometer. You can do either of two things: 1. adjust it, by going to the Teleflex website and learning how to do it 2. live with it: go WOT at the dock in neutral and read your tach. It seems to say 2500 instead of 3000. Just proportion all of the rest of your readings based on that ratio The 3 vs 2 blade prop will not change your engine's rpms
the difference in rpms most likely has to do with the calibration, or lack of, of your tachometer. You can do either of two things: 1. adjust it, by going to the Teleflex website and learning how to do it 2. live with it: go WOT at the dock in neutral and read your tach. It seems to say 2500 instead of 3000. Just proportion all of the rest of your readings based on that ratio The 3 vs 2 blade prop will not change your engine's rpms
RPMs idle vs in gear
He's got two issues. The first is he can't reach max RPMs in nuetral. I agree it's either a tach calibration or a engine performance issue. The second problem is he's a full 1000 RPM (or 500 based on the tach) off his max while under way. If he's got the correct prop he should be able to max it out while under way. Of course that's assuming he doesn't have a foul prop or dirty bottom. Bottom line is he's got a couple of things to address. I'd start with the nuetral RPM issue and work from there.
He's got two issues. The first is he can't reach max RPMs in nuetral. I agree it's either a tach calibration or a engine performance issue. The second problem is he's a full 1000 RPM (or 500 based on the tach) off his max while under way. If he's got the correct prop he should be able to max it out while under way. Of course that's assuming he doesn't have a foul prop or dirty bottom. Bottom line is he's got a couple of things to address. I'd start with the nuetral RPM issue and work from there.
Different pitch or diameter needed.
Butch: A rule of thumb is 1 deg less pitch for a 3 bladed prop vs a 2 bladed. You can also reduce the diameter and maintain the pitch. Regardless, you should always consult a prop shop that will stand behind their work if you are changing props. This can be a costly proposition if you need to pull the boat again if it not sized "prop"erly!
Butch: A rule of thumb is 1 deg less pitch for a 3 bladed prop vs a 2 bladed. You can also reduce the diameter and maintain the pitch. Regardless, you should always consult a prop shop that will stand behind their work if you are changing props. This can be a costly proposition if you need to pull the boat again if it not sized "prop"erly!
Could you ever?
Butch, could you ever hit the RPM numbers you're referring to? If so the problem is most likely caused by something other than the prop. Before you have your prop repitched consider this. Issues such as engine performance, a prop foul with barnacles, a dirty hull or overgrowth on the bottom of the keel can all cause problems. Note that the engine performance is the only one that will cause problems while in nuetral. When is the last time you've changed filters? Is the fuel clean? Any exhaust restrictions, such as the exhaust elbow? There are many more problems but these are just some of the basics to check if she once performed but now does not. Start with the basics and move on from there. Mike
Butch, could you ever hit the RPM numbers you're referring to? If so the problem is most likely caused by something other than the prop. Before you have your prop repitched consider this. Issues such as engine performance, a prop foul with barnacles, a dirty hull or overgrowth on the bottom of the keel can all cause problems. Note that the engine performance is the only one that will cause problems while in nuetral. When is the last time you've changed filters? Is the fuel clean? Any exhaust restrictions, such as the exhaust elbow? There are many more problems but these are just some of the basics to check if she once performed but now does not. Start with the basics and move on from there. Mike
Same issue for us
I posted a virtually identical question about six months ago. We have the Universal 25 on our Catalina 36. We changed to a fixed 3 blade to the engine spec and the results were similar: nearly 3000 rpm in neutral andper spec was reduced to a little over 2500 at WOT. And we accumulated soot on the transom. The engine is tuned and all factors seem to indicate too much pitch even though the spec was followed. However, I think we are close to reaching hull speed so my only concern was whether the extra pitch stressed the engine and I got responses in all directions (from nothing to worry about to you'll ruin your engine). We will have our diver pull the prop and have our shop calibrate it again and perhaps drop the pitch. In the meantime, we have used it and I just avoid higher rpms where the engine seems to load up. I really like the solid bite of the three blade in the bay here with the strong currents and heavy ship traffic etc. Let us know what you come up with and I'll do the same.
I posted a virtually identical question about six months ago. We have the Universal 25 on our Catalina 36. We changed to a fixed 3 blade to the engine spec and the results were similar: nearly 3000 rpm in neutral andper spec was reduced to a little over 2500 at WOT. And we accumulated soot on the transom. The engine is tuned and all factors seem to indicate too much pitch even though the spec was followed. However, I think we are close to reaching hull speed so my only concern was whether the extra pitch stressed the engine and I got responses in all directions (from nothing to worry about to you'll ruin your engine). We will have our diver pull the prop and have our shop calibrate it again and perhaps drop the pitch. In the meantime, we have used it and I just avoid higher rpms where the engine seems to load up. I really like the solid bite of the three blade in the bay here with the strong currents and heavy ship traffic etc. Let us know what you come up with and I'll do the same.
Jim P.
The original size of a Michigan three blade "sailor" bronze prop for your C36 with an M-25 is 15x10x1 RH, standard bore. You can go with 15x9 or 15x11, but the 15x10 would be best and is the three blade these boats shipped from the factory with. If you have other than this size or type of prop that may be your problem. Over the years I have found "prop shops" usually don't get pitch right when it comes to displacement hulls such as sailboats. Catalina spent plenty of time making sure the 15X10X1 was the right 3 blade size for your boat...
The original size of a Michigan three blade "sailor" bronze prop for your C36 with an M-25 is 15x10x1 RH, standard bore. You can go with 15x9 or 15x11, but the 15x10 would be best and is the three blade these boats shipped from the factory with. If you have other than this size or type of prop that may be your problem. Over the years I have found "prop shops" usually don't get pitch right when it comes to displacement hulls such as sailboats. Catalina spent plenty of time making sure the 15X10X1 was the right 3 blade size for your boat...
thanks Maine
Our shop and literature spec'd the 15x11x1. It sounds like repitching will serve us well.
Our shop and literature spec'd the 15x11x1. It sounds like repitching will serve us well.
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