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 Post subject: Prop Pitch and Engin Speed
PostPosted: 29 Dec 2006 11:15 
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Skipper

Joined: 29 Dec 2006 09:38
Posts: 579
Something I wish someone had told me when I got the boat.....

According to my mechanic, diesels of this vintage (the W-50) want to cruise at a steady 70 to 80% of power (I do not want to start of big controversy here--there are differing opinions but most mechanics agree most folks run diesels too slowly, they disagree on how much over 70% they should be run). For the W-50 I believe that would be above 2100 RPM. When I got the boat it had what I think was the original Michigan Sailor two blade propeller on it and taking it above 2000 RPM produced a lot of black smoke. My conclusion is that this prop was grossly over pitched and when I put on my three bladed feathering prop we were able to adjust this. I am wondering if a lot of people still have a Michigan two blade and if that was over pitched. I used to do deliveries and noted that most production yachts come with over pitched two bladed props. I am not sure that mine was a stock prop for Tartan.

That is sort of like putting your car in 4th gear and driving real slow. Not good for a gas engine and terrible for a diesel.

David Gerr suggests that you should be at 100% RPM at top speed. I am set a bit behind that.

FWIW.

Ray Durkee
S/V Velera
Bocas del Toro Panama


 
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 Post subject: Re: Prop Pitch and Engin Speed
PostPosted: 29 Dec 2006 11:27 
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Skipper

Joined: 20 Oct 2006 16:10
Posts: 682
Location: Out of Waukegan, IL
We still have the stock two-blade and have always capped the Westerbeke at 2000 RPM. Only in "Oh-Crap" moments does it get beyond that. By your theory we're doing it a disservice. But I guess the only yardstick is performance. We've never had to do anything but change the oil but we don't put a lot of engine hours on each year. 22 seasons all <100 engine hours. Perhaps we're not the best example.

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SMMO/First Mate aboard High Flight #299
1981 - Full Keel - Furling Main (A boat for the lazy crew...)


 
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 Post subject: Re: Prop Pitch and Engin Speed
PostPosted: 31 Dec 2006 15:46 
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Midshipman

Joined: 22 Oct 2006 19:25
Posts: 61
I have a 2001 Westerbeke 44A rather than the W50. The 44A provides 40 hp at 3600 rpm in contrast to the W50 which provides 41 hp at 3200 rpm. The both have a 2.47:1 transmission. I have a fixed 3 blade propeller: 16 diameter, righthand, 11 pitch, which works well on the 44A. Jay.


 
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 Post subject: Re: Prop Pitch and Engin Speed
PostPosted: 31 Dec 2006 20:26 
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Skipper

Joined: 27 Oct 2006 10:32
Posts: 826
I have a W-40 which I run at 2200 rpm's and she seems to do fine.....temp and pressure stays steady, 2/3 gallon/hour.


 
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 Post subject: Re: Prop Pitch and Engin Speed
PostPosted: 02 Jan 2007 14:40 
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Skipper

Joined: 10 Nov 2006 22:56
Posts: 171
Location: Portland, Oregon
Ditto on the W40 RPM. We run Rainbow at 2100 RPM, steady oil pressure and temp, for a boat speed of 6.5 knots.

Jay

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Jay and Muki Kerr
Tartan 37 Betty Lou (formerly Rainbow)
Hull # 118, fin keel
St. Helens, OR
Betty Lou's Blog


 
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 Post subject: Re: Prop Pitch and Engin Speed
PostPosted: 16 Feb 2007 12:17 
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Midshipman

Joined: 30 Oct 2006 15:40
Posts: 63
I agree with the statements. WOT (wide open throttle) is 3500 rpm. Never use this except in an emergency. Originally, we could only get 2300, but accidently found the cable misrigged.

We cruise at 1800 to 2500 rpm depending on the distance, sea state, etc. But typically, we set a boat speed to match others in our group, and then find a throttle setting that doesn't have everything rattling.

Never have a black smoke issue except when gunning the engine.

We have used a Martec geared, folding prop for 6 years without incident. This prop wore beyond repair limits (1200 hours of motoring) and now we have a Seahawk geared, folding prop. The dealer (Martec) claimed he was customizing the pitch for our boat to cruise optimally at 2200 rpm and with max thrust at about 2800 rpm. Just launched last week, but so far it appears we will be cruising at 200-500 less rpms. So just maybe this prop is worth the extra $$$.

I would certainly look for some other cause of black smoke than being over-propped with this engine.

Jammin'
#226


 
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 Post subject: Re: Prop Pitch and Engin Speed
PostPosted: 14 Apr 2007 09:10 
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Rail Meat

Joined: 14 Apr 2007 08:25
Posts: 7
We will need to replace the 3-bladed prop in the near future. It is currently a 17 inch RH with an 6 pitch (reduced from 8 pitch). The transmission was replaced with a Twin Disc model MG340 forward and reverse reduction marine gear. The reverse is lousy with this prop. So perhaps a smaller diameter prop with an increased pitch might remedy this. The engine is a Universal 40hp. Any ideas? Roger Rippy


 
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 Post subject: Re: Prop Pitch and Engin Speed
PostPosted: 17 Apr 2007 09:47 
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Skipper

Joined: 20 Oct 2006 16:10
Posts: 682
Location: Out of Waukegan, IL
Our dock neighbors (Kyoga) had a T37 with a W40 and their 3 blade prop was just too much for the engine. If you engaged in idle (forward or reverse) the engine would stall. Caught me very much by suprise a couple times when shuttling their boat.

Just a word of warning when specing out a prop.

_________________
SMMO/First Mate aboard High Flight #299
1981 - Full Keel - Furling Main (A boat for the lazy crew...)


 
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 Post subject: Re: Prop Pitch and Engin Speed
PostPosted: 18 Apr 2007 07:11 
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Rail Meat

Joined: 14 Apr 2007 08:25
Posts: 7
Well I went to the Michigan Wheel web site and took advantage of their free online prop analysis. We are still going back and forth, but they seem to think that my fixed prop 17 RH 6 is way out of pitch for the Universal 40. The unknown at this point is the gear ration of the transmission and I will have to check it out this weekend. The original Hurth transmission had a 2.0:1 reduction gear. That transmission had been replaced with an MG340 which comes with three different forward gear ratios, to include the 2.0:1. At this point I am inclined to replace this prop with another three-bladed fix prop; less moving parts usually translates into less maintenance. We had a folding three-blades prop on our Bristol and it worked well, but it eventually wore out and repair would have entailed shipping it off to Germany. So back to the original 2-bladed prop for that boat. I was always of the opinion that the general rule that the prop diameter should be 15 times the shaft diameter was a good starting point. In that case, I should have a 15 or 16 inch right-hand prop with a pitch probably around 12 inches. We'll wait and see what Michigan Wheel comes up with. Roger


 
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