Proper prop pitch for PDQ 36 with YGM20s

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chrispeck
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Proper prop pitch for PDQ 36 with YGM20s

by chrispeck » Tue Jul 17, 2012 11:11 pm

When leaving the boatyard in Cleveland and heading north on the Great Lakes this spring the mechanics said the pitch was wrong on my Yanmar YGM20 diesels. A sea trial on the boat just before she left suggested the engines couldn't get to full RPM, which the yard attributed to wrong prop pitch. So, should that issue now be addressed as the boat lies in Northern Michigan prior to a long motor cruise south on the Illinois, Mississippi, Ohio and Tennessee rivers this fall?
And where to find info on proper prop pitch for these engines and this boat?

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SecondWind
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Re: Proper prop pitch for PDQ 36 with YGM20s

by SecondWind » Wed Jul 18, 2012 9:35 am

The original props on the SD20 saildrive are 15x11 VOLVO.
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Re: Proper prop pitch for PDQ 36 with YGM20s

by fredandkathy » Wed Jul 18, 2012 1:07 pm

We have the same Yanmars on our 32LRC and when we purchased the boat the PO said the Michigan Props, original from PDQ, were not ideal and full crusing RPM would put too much strain on engines. I asked my mechanic and he advised that it is a complicated process to determine the proper prop size & pitch and to consult with Michigan prop, which I tried to do several times without success. I keep the revs below 2,800 and all seems fine.

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Re: Proper prop pitch for PDQ 36 with YGM20s

by maxicrom » Wed Jul 18, 2012 4:15 pm

We have a 1991 PDQ36 with a single Yanmar in the port hull and the prop we have is an Autoprop 3 blade feathering and it works great for us. We've had the boat for over 6 years now. I don't think the previous owner did much in the way of maintenance - two years ago while we in the yard for maintenance and mounting the Torqeedo on the starboard hull I ordered new bearings for the AutoProp and it was fairly easy to rebuild.

If you do regular (annual) maintenance and adjust the prop as recommended I'm sure it will provide good service. As the website says, we do have very good forward and reverse performance and it seems feather pretty well under sail. All moving parts are in the prop blades and it fits a standard shaft.

http://www.autoprop.com/

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Re: Proper prop pitch for PDQ 36 with YGM20s

by chrispeck » Fri Jul 27, 2012 12:29 am

Thanks for advice on pitching the props on our Yanmars aboard our PDQ36 LRC. . When we're back on Lake Huron in a few days we're planning the wide open throttle exercise to determine max RPMs on the engines under no stress and then see what we can achieve with engines engaged. Mechanic says this will help determine how far out of pitch the props are. If we can get to 3000 RPMs with engines engaged his advice was not to worry about pitch and simply run engines at 80% of top RPMs, or about 2700.

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Re: Proper prop pitch for PDQ 36 with YGM20s

by Bob » Wed Aug 08, 2012 8:01 am

I had 15x9 on mine but changed them to 16x11 and it made a big difference in performance. Someone else on the group also had 16x11which caused me to think about the change. I regularly cruise at 2800 rpm and can push it further if need be. My hypothesis is that some LRC had skegs and some did not. Those with skegs got the 15s those without got the 16. I had to scallop the skeg to get the 16 to open. My first LRC did not have skegs but I didn't have it long enough to determine the size of the props. I have had the oil tested by Blackstone Labs twice and the engines show no sign of wear with ~3500 hrs on the engines. I may send out the gearbox oil in the future to check for wear.
Bob Johnson
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Re: Proper prop pitch for PDQ 36 with YGM20s

by Bob » Wed Aug 08, 2012 4:35 pm

I was hurried this morning and did not give more detail. The props I have on now, 16x11, push the boat at 7 -7.5 at 2800 RPM. I have never tried to max out the RPM's as anything over 2800 shows little speed improvement but increases fuel consumption. If you do a forum search you will find past discussions about props but I will recap my findings here. Yanmar saildrives had 2 different output shaft lengths which led to 2 different hub lengths. Took me a long time to finally get this answer. I originally had mixed hubs when I bought the boat. One hub had no provision for the 3 pc. zinc set while the other did. On my maiden voyage up the ICW from New Smyrna Beach to Maine I threw a blade due to stress cracks from electrolysis. A set of blades ,next day air and a diver I was on my way again. When I finally pulled the boat I put the hubs that the PO bought but said were too loose on the shaft. These both had provisions for the three piece zincs. When installing these hubs with the up sized blades I discovered why they seemed loose. The new hubs were for the longer output shaft and of course I had the shorter one. When the hub is tightened down it binds on the large zinc so I think whoever put them on for her just backed off a turn to allow rotation. The upshot is that before I install new saildrive zincs I have to take a belt grinder with 30 grit and grind about 1/8" off to properly seat the hub. I was going to try to get the right hubs so I could go to the newer style split zinc but as I understand it these props are no longer made and Yanmar has a replacement design. This was 2 yrs ago and I have not laid eyes on one so I can't comment on that. Finally if you are reading this post then you have a LRC and know the stern is low and could definitely use Dave's hull extensions. See the thread about hull extensions I responded to. Lets get some folks together and get it done while we have the chance!
Bob Johnson

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