Yanmar 4JH3E Prop- RPM at full load

[Silverman]

Hello, I just returned from a boat survey for a Moody 42 CC, Bill Dixon design.
Survey was in MD USA
It was Force 6 winds so we did not go out for a test sail.
The surveyor chose to test the engine at the dock, with double sets of lines.
Engine was Yanmar 4JH3E, with a shaft driven 3 blade prop. Dimensions unknown.
Engine sounded great and went up to 3800 rpm with no load.
When the transmission was engaged (not a sail drive), the max rpm at full throttle was 2500 RPM.
NO sense of how long this prop has been on the boat.
We assumed the pitch and diameter are too large, not sure why that was done.

So the question is : Did running at 65% OF MAX rpm for all those years seriously impact on engine life? Should I be concerned. As stated above it sounded great, started right up after being on the hard all winter, and had no off color smoke.
Thank you in advance.

 

[Don S/V ILLusion]

Probably not (with emphasis on the first word) but rather than guess, if I was contemplating buying it, I would have an engine inspection to determine condition. A good diesel marine diesel mechanic can provide some clarity and certainly more than anyone on the internet.

nice boat!

 

[Silverman]

Thanks for the response, will try it again on the actual sea trial. Current owner not providing/doesnt have any maintenance records.

 

[senang]

The boat being stationary at the dock this will impede on the max rpm. How much? that’s the question.

 

[Silverman]

Thank you for your comment, I have found some articles that indicate the cause is "too much pitch or too much load". Tying the boat to the dock could support "too much load" as you suggest.
I am new to this and relying on surveyor and the broker for guidance.
Will try to stay calm until we can run it on the sea trial.

 

[fstbttms]

Having earned a significant portion of my living over the last 27+ years installing propellers, I have always understood that testing at the dock does NOT provide accurate RPM numbers. Your surveyor should know this. Of course, it's takes just about as much training and experience to call yourself a surveyor as it does to be a hull cleaner.

 

[Ralph Johnstone]

The cleanliness of the prop is another consideration. This allowed me a max. of 2000 RPM BUT with much attending black smoke.

If your 2500 RPM was due to excessive load, regardless of what caused it, you'd expect black smoke. Possible the PO limited the governor control (AKA throttle) to a max. of 2500 RPM.

Definitely needs repair before proceeding any further with the inspection.

 

[Davidasailor26]

Possible the PO limited the governor control (AKA throttle) to a max. of 2500 RPM.

Except that it went up to 3800 in neutral.

There was a thread not long ago of another member who was only able to reach 2200 RPMs at the dock but 3000 underway. Similar to your situation with no smoke or other issues. I’d attribute the problems to that, but an engine inspection or at least running it under normal load in better conditions wouldn’t hurt.

 

[Ralph Johnstone]

Except that it went up to 3800 in neutral.

Scratch that idea .