Max-prop pitch settings - SailNet Community
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post #1 of 12 Old 02-23-2010 Thread Starter
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Max-prop pitch settings

I have a 34 with a max-prop. The boat is out of the water with the shaft out and prop off. I have always had a problem with over heating with this boat and the max rpm I can push my 3HM35F to under load is 3100 rpm. I was going to reduce the pitch one setting when we reassembled it, but there is now some confusion as to what it was originally set at. does anyone have any knowledge that that may help us make the right setting decision?

Thanks
John

Last edited by johnharch; 02-23-2010 at 08:09 PM.
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post #2 of 12 Old 02-23-2010
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If you did not write down or take a picture of the settings then call PYI, tell them the engine, trans model, rotation and reduction, prop size etc. They will give you a recommendation. Odds are it will be correct. If you are really concerned that is where you were go one setting down and see what it gives you. If that's not correct you can always increase the pitch at the next haul, pay a diver to change it or if you are going cruising full time do a short haul and re-pitch.

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post #3 of 12 Old 02-23-2010
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Max Prop Pitch

John,
We had a similar problem on our PSC 34 with a 17" 3 blade Max Prop. Last spring we took it apart and found it had been set at 18 degrees equivalent to a pitch of 10" (based on my notes). From memory we reduced the setting by two steps (from 18 to 14 degrees) equivalent to an 8" pitch.
The result was we eliminated the overheating and the rpms for any given boat speed increased 25 - 30%.
The PYI web site has much good info and the video really helped.
Good Luck
Steve
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post #4 of 12 Old 02-23-2010 Thread Starter
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Thanks for your quick replies. Pegusus, that is very helpful.

I should explain more where we are. When we pulled the shaft, I told the mechanic that I wanted the prop backed off one step to see if that helped the rpm and overheating problem. He wrote down the settings, but when he reassembled it, it was very flat. Possibly he wrote the numbers wrong. He called Max-prop and they told him what they recommend and that was very different from what he had. I have since dug through my documentation and found notes from a PO on what he had it set at (maybe). So tomorrow morning, I will get together with the mechanic and decide what to put it at.

I don;t have a diver who is willing to do it underwater and I would like to avoid the expense of another haul out to reset it if possible. It's been an expensive winter for boat repairs already.
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post #5 of 12 Old 02-24-2010
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John, We have the same boat and engine. We changed our 17" 3 blade Max Prop from an original factory recomendation of 18 degrees to 14 degrees to achieve the best results with RPM and load. It breaks down to 10.4 pitch. A right hand rotation prop will have the following settings. X=T and Y=B
Hope that helps.

John Schwab
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post #6 of 12 Old 02-24-2010
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Quote:
Originally Posted by johnharch View Post
I don;t have a diver who is willing to do it underwater and I would like to avoid the expense of another haul out to reset it if possible.
PYI maintains a list of divers that can do Max Prop work. They may be able to recommend one in your area.
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post #7 of 12 Old 02-24-2010
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When I bought my PSC 34 with a Yanmar 3JH2E, the surveyor noticed the engine wouldn't reach its specified max RPM of 3600. The prop was being sent back to PYI anyway for a general overhaul, and PYI recommended that while they were at it, they should reduce the prop diameter from 17" down to 16" (changing the pitch alone was not enough in my case). PYI assured me they were very familiar with this situation with PSCs and were highly confident in their recommendation. I agreed to let them do this, and it did solve the low max RPM issue. I was told that that PSC was intentionally going with an oversized prop to add some bite, but of course this puts additional strain on the engine and is said to reduce its life.
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post #8 of 12 Old 03-05-2010 Thread Starter
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The boat went back in the water today and I don;t seem to be making much headway with my RMP and maxprop setting issues. It turns out that my prop was set at 12 deg. I talked to PYI and they were very little help and suggested it should be at 18 deg. We set it to 14 deg and I now hit just under 3100 rpm at full throttle. The overheating issue may be better now, but I'll have to spend more time on the water to be sure. The mechanics seem to be just as baffled as I am and are suggesting that it is a fuel restriction issue. This of course wouldn't explain the overheating and I get a different opinion from everyone I talk to.

I can't read the id plate on my transmission and wonder if anyone knows for sure what the reduction ration is?

John
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post #9 of 12 Old 03-06-2010
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My Yanmar Diesel Engine Operation Manual lists two forward reduction ratios for the 3HM35 engine/KBW10E gear -- 2.14 and 2.83. Checking mine with a mirror, it is 2.14.

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post #10 of 12 Old 03-06-2010
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Most likely you have the KBM10 transmission with a ratio of 2.14.

One other caution . . . don't assume the tach gauge for the engine is accurate, have the actual RPMs measured with a photo tachometer. The surveyor found my tach gauge was off by 200 RPM.

It's interesting to hear that PYI just told you it should be set at 18 degrees and that they weren't very helpful. Almost every comment about PYI service I've read here (and there are a lot) indicates they were extremely helpful, and they were for me as well.

In my case (PSC34, Yanmar 3JH2E, KBM10 transmission, 17" Maxprop) the PYI technician was very clear that pitch change alone was not enough to get the engine to run at 3600 RPM and that's why they recommended reducing its diameter by one inch while it was in with them for refurbishing. The tech said PYI was very familiar with "this situation" with PSCs. Although you won't be able to reduce your prop diameter without sending it to PYI, nevertheless, PYI does have the in-house knowledge (at least some of their tech's do) to give you the optimal settings for your boat. I'd call them back and challenge them further.
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