Yanmar 3GM30F HP one-hour rating (??) - SailNet Community
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post #1 of 25 Old 01-21-2013 Thread Starter
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Yanmar 3GM30F HP one-hour rating (??)

I am about to buy a 38-foot sailboat with a Yanmar engine (3GM30F). The manual indicates continuous rating of 24 HP/3400 RPM, while the one-hour max output is 27 HP/3600 RPM. Two 2 boat mechanics and 1 vessel surveyor have been unable to tell me what the max output means and this is after I show them the manual. One thought that the max output referred to another model. The boat was also listed by the broker as a "27 HP" but everyone who has looked at it says it is a 24 HP engine. Please help me understand this...
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post #2 of 25 Old 01-21-2013
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Re: Yanmar 3GM30F HP one-hour rating (??)

What you seem to be wrestling with is the engine's power curve.

As revolutions increase, so does shaft output (rated in horsepower.) The ratio is not constant; at the upper end of the curve you will see that increasing revs will yield very little increased output.

Also in play is the manufacturer's recommended operating envelope. What they seem to be saying is that you can run the engine all day long at up to 3400rpm (up to 24 hp output); they also recommend that it not be run at 3600 rpm (generating 27 hp) for longer than one hour.

Hope that helps.
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post #3 of 25 Old 01-22-2013
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Re: Yanmar 3GM30F HP one-hour rating (??)

The Yanmar 3G30F is in my boat, and was used in many of the Catalina 320's. It is regarded and advertised as a 27 hp engine.
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post #4 of 25 Old 01-25-2013
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Re: Yanmar 3GM30F HP one-hour rating (??)

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Originally Posted by gamayun View Post
I am about to buy a 38-foot sailboat with a Yanmar engine (3GM30F). The manual indicates continuous rating of 24 HP/3400 RPM, while the one-hour max output is 27 HP/3600 RPM. Two 2 boat mechanics and 1 vessel surveyor have been unable to tell me what the max output means and this is after I show them the manual. One thought that the max output referred to another model. The boat was also listed by the broker as a "27 HP" but everyone who has looked at it says it is a 24 HP engine. Please help me understand this...
Interesting..but I have to ask what vessel is this Yanmar in? A 3GM30F in a 38 footer maybe slightly beyond its rated capability..
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post #5 of 25 Old 01-25-2013
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Re: Yanmar 3GM30F HP one-hour rating (??)

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Originally Posted by aa3jy View Post
Interesting..but I have to ask what vessel is this Yanmar in? A 3GM30F in a 38 footer maybe slightly beyond its rated capability..
3GM30F is in our 35 C&C MKIII. It does fine and we get 7.5 knots at 3200 rpm. Depends on Hull as well as displacement.24 HP at 3400 rpm/ 27hp at 3600 rpm

see manual specs- open up the pdf file

Technical specifications of previous models - Yanmar Marine


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post #6 of 25 Old 01-26-2013
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Re: Yanmar 3GM30F HP one-hour rating (??)

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3GM30F is in our 35 C&C MKIII. It does fine and we get 7.5 knots at 3200 rpm. Depends on Hull as well as displacement.24 HP at 3400 rpm/ 27hp at 3600 rpm

see manual specs- open up the pdf file

Technical specifications of previous models - Yanmar Marine
Exactly..depends on "hull" and why I asked the question for the need for more data... Our 34 probably displaces more then your 35..believe it not..and our 3GM30F is on the ragged edge of usefulness...

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post #7 of 25 Old 01-26-2013
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Re: Yanmar 3GM30F HP one-hour rating (??)

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Originally Posted by aa3jy View Post
Exactly..depends on "hull" and why I asked the question for the need for more data... Our 34 probably displaces more then your 35..believe it not..and our 3GM30F is on the ragged edge of usefulness...

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No I beleive it. You displace another 3000 lbs and your hull shape is not the same at all. Its funny we have power in reserve and usually cruise at 2700 rpm ( seems to be our engines sweet spot). You have to meet the moinimum requirements for diesils so you dont choke up your elbow with carboin


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post #8 of 25 Old 01-26-2013
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Re: Yanmar 3GM30F HP one-hour rating (??)

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You have to meet the moinimum requirements for diesils so you dont choke up your elbow with carboin
Your 'preaching to the choir'...
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post #9 of 25 Old 01-26-2013
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Re: Yanmar 3GM30F HP one-hour rating (??)

I believe PorFin is correct re: HP/rpm.

We too have a 3GM30F that runs "all day" with low fuel consumption. I have great confidence in this Yanmar. If you have the service manual you will see a chart showing the power curves. The owner's manual specifications specifically states the one hour vs. prolonged rpm max and related HP.

Previous owner recommended we cruise at 2400 rpm- We tend to run at 2500 - 2600 rpm. Comments by aa3jy and chef2sail cause me to wonder if I am running too low. I have had no apparent problems.

Nigel Calder recently (in Sail Mag?) wrote an article about rpm vs. fuel consumption noting that there is limited cost/benefit from pushing the boat beyond a certain point, with reduced benefit for additional fuel consumption.

In any event, perhaps your sea trial will tell you if the vessel seems to have enough power for your needs. Ideally you will have the opportunity to run it against a stiff wind or through a tidal current to see how she performs. GOOD LUCK!

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post #10 of 25 Old 01-26-2013
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Re: Yanmar 3GM30F HP one-hour rating (??)

May I suggest to whom that are following this thread and owns a Yanmar..take the owners course that is offered by Mack Boring(East Coast distributor for Yanmar). It will probably answer 99% of the questions that most typical owners will have. The training provides hands-on of the actual engine that owner has in his vessel.

Mack Boring & Parts Company - Reliable Power. Everywhere.

Highly recommended!
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