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 Post subject: Boat,Transmission,Engine size equals Prop Size ?
PostPosted: 28 Jan 2018 09:59 
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Skipper

Joined: 09 Jul 2008 12:51
Posts: 212
Overheating, max speed, max rpm and prop sizes has been talked about a lot on this forum... I have a W50 engine with the short profile tran (Hurth 10). I really suspect I am over propped since the engine should easily attain 3000-3200 RPMs without overheating. I don't get near that. My hull speed is good 6-7 knots depending on sea conditions.

I was speaking to a expert prop guy the other day and he said this is something he encounters all the time.. boats that are over propped. He said it's a recipe for wearing out your engine sooner that later. He explained it this way... you wouldn't run your car engine in 5th gear ALL the time would you ? up a hill, down a hill, on level ground ? It then made sense to me.

I remember a few of the folks on this forum that reduced pitch and then were able to attain greater RPMs... especially those of you that have a W50 engine and the Hurth 10 transmission. Which prop size and pitch seem to work best.

Can I hear from those of you that have already covered this ground ?
Thanks,,,


 
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 Post subject: Re: Boat,Transmission,Engine size equals Prop Size ?
PostPosted: 28 Jan 2018 15:02 
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Midshipman

Joined: 01 Nov 2014 12:50
Posts: 68
Location: Toledo
You didn't mention your prop dimensions and type.
Verify your tach is correct. Borrow or buy a handheld optical tach. (Our W40 tach reads slow).
Also make sure you use clean hull, prop, etc. As baseline for your tests.


 
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 Post subject: Re: Boat,Transmission,Engine size equals Prop Size ?
PostPosted: 28 Jan 2018 19:55 
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Skipper

Joined: 09 Jul 2008 12:51
Posts: 212
Tach is fine,,,, hull is clean... I've covered ALL that ground. I'm looking for someone that has covered the prop resizing ground


 
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 Post subject: Re: Boat,Transmission,Engine size equals Prop Size ?
PostPosted: 28 Jan 2018 20:21 
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Skipper

Joined: 21 Oct 2006 15:36
Posts: 247
I have a W50 with a 2:1 ratio transmission
and a 2 blade 16 in prop. Originally, it had a14" pitch. The prop was way over pitched. I could barely get the engine over 2400 rpm without it overheating. I had the pitch reduced to 11.5 in. I can now reach 2700- 2800 rpm, and can easily cruise at 2500 2600 rpm. To achieve full rated rpm (3200), 9 to 10 in pitch would probably be optimal.

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Jim Voelxen
Odyssey #191
Home Port: Osterville, MA


 
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 Post subject: Re: Boat,Transmission,Engine size equals Prop Size ?
PostPosted: 29 Jan 2018 12:15 
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Skipper

Joined: 09 Jul 2008 12:51
Posts: 212
Jim, thanks. I knew someone had to have covered this ground before. Can you tell me who you bought the reduced pitched prop from ? thanks


 
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 Post subject: Re: Boat,Transmission,Engine size equals Prop Size ?
PostPosted: 29 Jan 2018 16:51 
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Skipper

Joined: 21 Oct 2006 15:36
Posts: 247
I brought it to a prop shop. They can reduce the pitch.

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Jim Voelxen
Odyssey #191
Home Port: Osterville, MA


 
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 Post subject: Re: Boat,Transmission,Engine size equals Prop Size ?
PostPosted: 03 Feb 2018 20:34 
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Skipper

Joined: 29 Dec 2006 09:38
Posts: 461
I think the stock T37 prop (I still have one) is grossly over pitched. I think it is a ticket to engine destruction. As a delivery skipper, I found that there was a penchant for production boat builders to over pitch their propellers—I am guessing it made everything quieter and made sure you went fast. Problem is, as your mechanic described, an express ticket to shortening the life of your diesel. I strongly suggest you invest, if at all possible, in an adjustable pitch prop—-feathering if possible. It adds more speed than anything you could do with sails and saves your engine. Having a prop repitched is an expensive proposition and a crap shoot. If you have an externally adjustable pitched prop you can adjust it cheaply until you get it right. I had to adjust mine several times to get it just right.
Ray Durkee
T37 #373


 
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 Post subject: Re: Boat,Transmission,Engine size equals Prop Size ?
PostPosted: 04 Feb 2018 12:47 
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Tactictian

Joined: 16 May 2009 08:06
Posts: 101
Okay....here comes the post the will jinx my engine and make this the last season. When I bought this boat around 20 years ago, I switched from the stock prop (over pitched as Ray stated) to a Gori 16” which is also way over pitched. I bought the prop at a tag sale for $250 and figured if I liked it, I would make the jump to a new folding prop that was the correct size and pitch. I never got around to that. I cruise the boat at 6-6.5kts at around 1500 rpm. If I try to take it up to 2000, the noise and vibration is not worth the extra half knot. If I need the extra power though, it is there. The engine has a bit under 6,000 hours, starts easily and does not smoke (except for a few seconds on cold startup). Regular maintenance includes oil change (Castrol diesel straight 30 weight) and filter changes either once a season or every 50 hrs (or so) whichever comes first. It leaks a lot of oil but as far as I can see, doesn’t burn it. I live with the leaks and probably pull a quart or two out of the engine sump every season. As I say, now that I have confessed, the engine will probably pack in this year! I hope not.

Chip Seltzer
Esprit
T37 #324


 
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 Post subject: Re: Boat,Transmission,Engine size equals Prop Size ?
PostPosted: 15 Feb 2018 21:51 
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Skipper

Joined: 29 Dec 2006 09:38
Posts: 461
Well, that is a great story. I am wondering if you have actually checked the tach accuracy. They are notoriously off, but it seems you would notice that.
Interesting....

Ray Durkee
T37 #373


 
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