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 Post subject: Re: Engine running hot?
PostPosted: 28 Aug 2012 06:23 
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Joined: 29 Dec 2006 09:38
Posts: 656
If you are at hull speed at 2400 RPM, you should examine the pitch on your prop. On my factory prop with the W50 I had the same situation. Your engine should be able to reach max RPM (W50 is 3000, but be sure your tach is still working right---they can be off by using different alternators and pulleys--using a strobe might be in order here) at hull speed. If you cannot reach max RPM at hull speed, you are overpitched and lugging your engine and shortening its life. You also will not be able to get full power to the prop in an emergency situation. Diesel engines do not like lugging. Overheating is only one symptom of the destruction going on (although heating issues could be from other soures as well). I had this situation and I believe it shortened the life of my W50. I think the T37 was shipped with an overpitched prop. I am not sure why they did this, whether it was that they did not know, or it helped keep the engine quieter and give the appearance of speed at lower RPM. In delivering other production boats, I found this overpitching a common problem.

Source for this would be David Gerr's excellent book, "The Propeller Handbook".


 
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 Post subject: Re: Engine running hot?
PostPosted: 28 Aug 2012 08:32 
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Skipper

Joined: 13 Feb 2011 21:19
Posts: 337
Location: Canyon Lake, TX
Mine's rock steady at 179 degrees on the gauge.

Unless someone forgets to put the transmission in gear. Embarassed Then it runs a lot cooler. We were motorsailing down the ICW and started the engine and throttled up because our speed had dropped. Evidently, when we throttled up was exactly when the wind came back up and neither one of us noticed the shifter in neutral until after I noticed the temperature was only about 165. Engage the transmission and Viola! 180.

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Wayne
Master and Commander of the Sailing Vessel Impetuous
I'm not a complete idiot, some parts are missing.
Subservient to no man except SWMBO
Any day without dock lines is a GOOD day!


 
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 Post subject: Re: Engine running hot?
PostPosted: 28 Aug 2012 09:09 
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Joined: 21 Oct 2006 15:36
Posts: 268
I agree with Velera's comment, and will modify my previous response to provide more detail.

My boat has a 16"D x 14P" double bladed prop. I believe that was the prop that was provided standard on the W50. I'm not exactly sure what the reduction ratio is on my transmission. I've found two ratios quoted in the boat's documenation: 1:1.8 and 1:2.0. I've never bothered to actually determine mine, but these different ratios, if they do exist between boats will make a big difference on the pitch needed. Perhaps, when I get a chance I'll determine mine so I can be helpful to others. UPDATE: I measured the reduction ratio of my transmission. It is 2:1.

When I first got my boat, I had some overheating issues. I fixed all of the typical sources: new raw water pump, broken impellor vanes in the raw water pump elbow, possibly fouled HXs, radiator cap, thermostat, fouled intake screen, etc., etc. All these fixes caused some improvement, but I couldn't run the engine above ~2300 to 2400 rpm, without having the temperature to start slowly rising above 180F. At this RPM, the boat was clearly at hull speed, and I would create a wake like a power boat. My guess was that the engine was actually running close to rated HP, at this RPM, but the cooling flow was running at about 3/4 flow at max RPM (~2400/3200 = 0.75), hence the overheating. Remarkably, the engine exhaust was normal, and not black, which would have been a clear indication of overpropping.

About 3 years ago, I had my prop re-pitched to 12" (i.e., a 2" reduction). After I did this, I gained about 300-400 rpm, which means I now get the same symptoms at 2700 -2800 rpm. But, importantly, I can now cruise indefinitely at 2400 to 2500 rpm, which is 75% to 80% of max RPM - my minimum goal. By extrapolationg my data, I would guess that 9" to 10" pitch would be ideal for a two bladed 16"D prop. Perhaps I'll change sometime in the future.

BTW, I checked the calibration of my tach. It's right on (+/- 50 rpm).


Jim #191

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Jim Voelxen
Odyssey #191
Home Port: Osterville, MA


Last edited by jvoelxen on 26 Nov 2012 19:16, edited 1 time in total

 
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 Post subject: Re: Engine running hot?
PostPosted: 28 Aug 2012 17:05 
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Skipper

Joined: 27 Oct 2006 10:32
Posts: 827
For what it's worth, I recently installed a new prop: a Varifold 16 X 11 two blade, replacing a 16 X 12 Martec folding. The Varifold people calculated the 11 inch pitch and is probably correct for my W-40 with a 2:1 Hurth tranny.
My experience with both props is similar making about 6 to 6.2 knots at 2200 rpms and getting close to hull speed at 3000 rpms. The big difference with the Varifold is the greater ability to stop the boat and reverse with more control......amazing difference.
My engine temps have always stayed at 180 with either prop traveling at 2200-2300 rpms, even after all day of motoring........something that can be common here on the Chesapeake Crying or Very sad


 
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 Post subject: Re: Engine running hot?
PostPosted: 29 Sep 2012 09:56 
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Skipper

Joined: 09 Jul 2008 12:51
Posts: 251
I have a W50....

With a two blade fixed prop I achieve hull speed (about 6.5Kts) at around 2300 RPMs. My engine stays around 180 degrees. When I increase RPMs to 2400, the temp goes to around 190. At 2500 RPM and higher it goes to 200 and pretty much stays there. I really achieve no more speed over 2300 RPM so I'm thinking that's the sweet spot for speed and engine temp.

Just my opinion....


 
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 Post subject: Re: Engine running hot?
PostPosted: 30 Sep 2012 11:48 
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Skipper

Joined: 29 Dec 2006 09:38
Posts: 656
Not trying to start an argument but some clarification. Sounds lile your pitch is set approximately right. At 28.5 feet water length, your hull speed is probably more like 7 knots unless you are exceptionally heavily loaded or have a very dirty bottom. That you are reaching 6.5 at 2400 rpm would be just about right for 80%. This all assumes your tach is right and that you have some way of accurately measuring speed through the water (absent wind and current) which is difficult. So you are getting about 80% speed at 80% power setting if all that is right. Someone correct me if my calculations are wrong.

Ray


 
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