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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a forum dedicated to diesel engines and their applicable accessories.


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  #11  
Old 02-04-2013
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Re: Repower confusion (horsepower)

Must include a conspiracy theory to any good story. Just because the smaller motor costs less, doesn't mean they make less profit on it. Not saying that's true. Just saying, if underpowering doesn't make sense, it doesn't make sense.
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Old 02-04-2013
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Re: Repower confusion (horsepower)

Quote:
Originally Posted by chef2sail View Post
I guess the reason I asked though is that I prefer the Yanmars slightly. For many of the same reasons you enumerated plus the Yanmar was not a converted engine and was built originally as a marine engine

I thought the 53 Hp Yanmar 4JH54 was a normally aspirated one and that it was the 73 HP 4JHTE was turbo charged.
I'm also a Yanmar fan and my 75hp turbo on my 18,000 lb. 331 is/was ('99) available without at around that 53hp. Nauticat always liked to over power their motor-sailers going back to the original 33 with a Ford-Lehman and I'm glad they did. I know I wouldn't consider re-powering yours (if it were mine) with anything under 50hp - but that's just me
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Old 02-04-2013
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Re: Repower confusion (horsepower)

While I have not had to power boats, Figuring out how much HP to have in a dumptruck for various and sundry reasons have come into play for what I do. Realty is, some boats, just like auto/trucks will be easier to move at X knots than another. Weight is not always the key. It may be in auto terms, aerodynamics that can add or subtract 30% off a base HP needed to move something.

In out boats cases, I would swag, type of prop, even the actual weight of the prop could vary the HP needed. It takes MORE hp to move say a 5lb prop than a 3 lb prop. That extra 2 lbs of prop, could be equal to 1000 lbs of actual sedentary wt on the boat, because the prop is turning, vs sitting there!

The HP amount, could also vary based on the torque the motor is producing at the time, along with trans reduction.......so many varables that ones head could spin.

At the end, which motor you choose, its up to you. For around here with our currents, more HP might be better per say.

Marty
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Old 02-04-2013
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Re: Repower confusion (horsepower)

I'll have to take another look at the Yanmars, I thought the 55 +- hp versions were all turbo. I have owned a Yanmar and it was/is a great engine. I am going to contact Beta again and see if they can email me the specs they showed me at the show so I can post them here, it seemed strange that 38 hp came up as the recommended hp.

Chuck- we have an MS4 trans, and I think the gear ratio is about 2.5:1, but I'm not sure. It runs through a Walter V-drive, but that is a 1:1 so doesn't affect overall ratio.

I hate to just go with a gut reaction for hp, but there doesn't seem to be much benefit to installing an engine with 17hp that won't be used or needed either (if I went with the 43 hp model vs 60). Our current engine will easily exceed WOT in all conditions, even towing a 10' inflatable, but I thought it was because the prop was under pitched (which it might be, I don't know now).
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Old 02-04-2013
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Re: Repower confusion (horsepower)

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Originally Posted by jrd22 View Post
Chef- I had it down to a short list of the Beta 60 and the Cummins 3.3 from Transatlantic Diesel (65hp). I also looked into the Yanmar and Volvo but rejected both because they use a turbo and I wanted naturally aspirated (I have nothing against turbos on larger diesels but feel they are an unnecessary complication for small sailboats). I did not look at Westerbeke mainly because of the comments about high parts prices I have read here (I have Volvos, been there, done that), but I'm sure they are good engines and maybe I didn't give them a fair shot. The Cummins is a great engine but Transatlantic is the only place that marinizes them and there aren't too many around. I also talked to a Cummins rep and he questioned whether Cummins would honor the warranty(I think they would) in a marine application (they're an industrial engine) which gave me some doubts. I rejected it because I want to go with something more mainstream.
In my former business I had several pieces of equipment that used Kubota engines and they were reliable and almost impossible to destroy, even though we ran them in the absolute worst conditions imaginable. Beta has a good reputation and people with them seem universally happy with them based on the threads here on SN. I like the fact that they aren't trying to squeeze every last HP out of the engine by using a turbo and intercooler, and that it's a slow rpm engine with a fairly flat torque curve so it should be able to maintain speed into rough weather. I also want to reduce the noise of the engine in the pilothouse and the lower rpm should help a lot with that (the Cummins puts out almost 55 hp at 1800 rpm, which was a big plus in my book). After actually seeing a couple of the Betas at the show I was pretty impressed with how they've done things, it looks simple and I didn't see anything that I didn't like. Beta also offers custom mounts which will make the installation a lot easier (current engine has much wider mounts than most and at two different elevations). I also liked that even though I was set on the 60 HP model the Beta rep spent quite a bit of time convincing me that I didn't need it and could save money by dropping down to the 38 or 43 hp model (big savings for me, much smaller sale for them).
Bottom line, I think almost all of the various engines offered are probably good, you just need to find one that you're comfortable with and doesn't pose too many difficulties changing over from what you currently have.
JR, your attitudes (on engines ) mirror mine. Turbos on a sailboat engine just seem WRONG on a visceral level. As to the slow turning - don't forget that diesels need to work - they don't like running at RPM's way down the power curve. They need to be sized so they run at optimum revs, not loafing along.
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Re: Repower confusion (horsepower)

I used a lot of Perky's back in the day and the prop we almost always used was an 18 by 12 two blade and a 15 by 10 three blade. I always figured the Perkins 4-108 to be an honest 35 hp no matter what I read. Powered many a Valiant 4 quite well.
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Re: Repower confusion (horsepower)

It's not 'extra' HP.
Your boat is a LOT like my Irwin 38, a little longer, a little heavier.
(32 lwl, 20k pounds, 5 inches narrower).

Generally a larger diameter is good because it means you can make less RPM and develop the same power via torque, and your transmission being a 2.5:1 helps with that.
Of course you need to ensure you have clearance for that 18 inches, to prevent vibrations through the hull.
It also helps because you get more blade area (with more diameter) to absorb the pressure of the thrust.

You've got a 35 foot LWL which = 8 knot hull speed (13.5 feet per second)
IMHO you should be working a pitch that gets you there at 80% of RPM.

The math is straight forward using Dave Gerr's formula
(Pitch x shaft rpm) * Slippage (.48 for our type of boat, on average) / 12 for feet per minute, divide by 60 for feet per second.

I'd go with a 14 pitch when you get the presumably adjustable maxprop, as to horsepower - as much as you can afford, given the price/efficiency break point on fuel consumption and such.
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Re: Repower confusion (horsepower)

Quote:
Originally Posted by bobperry View Post
I used a lot of Perky's back in the day and the prop we almost always used was an 18 by 12 two blade and a 15 by 10 three blade. I always figured the Perkins 4-108 to be an honest 35 hp no matter what I read. Powered many a Valiant 4 quite well.
There's your answer JR - For the purpose of this discussion your boat and a Valiant can be considered virtually the same. The 38 HP recommended by the dealer was spot on, the 43 HP you prefer would be generous and at a lower RPM with a beefier transmission and 60+ HP would be absurd overkill - probably not even as durable over the long haul since it would always be loafing instead of working hard.

As an aside, I've never heard anyone with a 4-107 or 4-108 in a boat around that size - 10 - 14 tons - complain about being underpowered.
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Re: Repower confusion (horsepower)

There have been a number of comments about the Yannies being marine designs from the get-go vs. others being marinized industrial engines.

Assuming such conversion pieces as the cooling/heat exchangers, cam timing and so forth are properly optimized in a converted engine, what benefit is there to a "marine design" engine? What would be done differently from a design standpoint?

If they were designed to run at very low RPM like old Gardners I could see it but the Yannies are "high" rpm engines like the conversions.
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Re: Repower confusion (horsepower)

What I'd like is a marine engine with more consideration paid to noise and vibration. How about a small straight-six diesel instead of 3 and 4 cylinders? (a straight six has perfect primary and secondary balance) Or a 3 or 4 cylinder with balance shafts?
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