2006 Beneteau 343 full power RPM

[zimboy]

I realize that this is a very old thread, I’ve looked everywhere else on the net and this is the only reference to this topic I can find (for a bene 343). I’m in the process of buying a bene343 and did the survey today. On thé engine full power test it only got to 2600 rpm. At full power there was no vibration, smoke or any other indication there was any problem, the boat got to 7.5 kts in still water. I measured the prop on haul out and it is 17 inches. According to the surveyor that is probably the original. The original yanmar tacho / engine start / stop panel with key has been replaced by the more modern version without key. My hunch is the tacho is mis calibrated, but given the feedback on this thread would appreciate thoughts on whether this could be a problem and what to look for.
Thanks for any help.

 

[kappykaplan]

the boat got to 7.5 kts in still water.

Did you/surveyor use a hand-held tach? Your reported speed in still water suggests that the tach is out of calibration.

 

[Alan Gomes]

I realize that this is a very old thread, I’ve looked everywhere else on the net and this is the only reference to this topic I can find (for a bene 343). I’m in the process of buying a bene343 and did the survey today. On thé engine full power test it only got to 2600 rpm. At full power there was no vibration, smoke or any other indication there was any problem, the boat got to 7.5 kts in still water. I measured the prop on haul out and it is 17 inches. According to the surveyor that is probably the original. The original yanmar tacho / engine start / stop panel with key has been replaced by the more modern version without key. My hunch is the tacho is mis calibrated, but given the feedback on this thread would appreciate thoughts on whether this could be a problem and what to look for.
Thanks for any help.

The fact that the surveyor thinks the prop "is probably the original" means nothing. You need to contact a prop shop with the relevant information they will need to tell you if your have the appropriate prop for your engine. They will need to know the diameter, number of blades, and pitch. For the engine, they will need to know the engine HP and transmission gear ratio. They will let you know whatever other info might be needed, but I think that's it. Armed with that info, they can tell you what the prop *should be* and can compare that to what it is.

If the boat is overpropped, that will need to be dealt with. A prop can often be re-pitched. If the prop is correct, then it points to an engine issue. Either way, since you are in the process of buying the boat, this should be a negotiating point with the seller.

And yes, it could be that everything with the prop and engine are fine other than the tach being off.

 

[Ron20324]

Which engine? I don't suppose you have the owners manual, do you?

 

[zimboy]

I realize that this is a very old thread, I’ve looked everywhere else on the net and this is the only reference to this topic I can find (for a bene 343). I’m in the process of buying a bene343 and did the survey today. On thé engine full power test it only got to 2600 rpm. At full power there was no vibration, smoke or any other indication there was aproblem, the boat got to 7.5 kts in still water. I measured the prop on haul out and it is 17 inches. According to the surveyor that is probably the original. The original yanmar tacho / engine start / stop panel with key has been replaced by the more modern version without key. My hunch is the tacho is mis calibrated, but given the feedback on this thread would appreciate thoughts on whether this could be a problem and what to look for.
Thanks for any help.

 

[zimboy]

@kappykaplan. No the surveyor did not use a hand held tacho. If you had a handheld tacho how would you measure the engine speed? Should the crankshaft pulley that drives the fan belt (I guess on a marine diesel there is no fan, so whatever makes the belt rotate) give the same number as the tacho (or some multiple of it)?

@Alan Gomes. Thanks, My feeling is the boat is a bit like a car with 80k miles on it; It's been well looked after, it's basically in good shape, but a number of things are getting towards the end of their life and will need replacing in the not too distant future. The engine is a pretty important component, so I'd like to get an idea of the remaining life of its parts and understand what's going on with the full power rpm discrepancy. Hopefully it is just a miscalibration of the tacho, but it will be good to get a more detailed assessment of the overall condition of the engine

@Ron20324 it's a Yanmar 3YM30. I found this link https://j109.org/docs/yanmar_3ym-2ym-service-manual.pdf. It's from the web so don't believe everything you see

Thanks everyone for the quick response.

 

[Davidasailor26]

Since there was no smoke and you were able to hit 7.5 knots I think it’s safe to say the engine is performing adequately. To check the RPM’s with a hand held tach yes you would measure the crankshaft pulley. That spins at engine RPM’s. If the hand held tach does match the panel tach then the prop is the next best possibility. Our 3YM30 on a heavier boat had a 17” 3 blade fixed prop and hit 3600 RPMs easily, so the diameter itself should not be a problem. Ours was a 12” pitch. If yours is much more than that then maybe it’s an issue.

 

[kappykaplan]

To check the RPM’s with a hand held tach yes you would measure the crankshaft pulley.

 

[Ron20324]

I realize that this is a very old thread, I’ve looked everywhere else on the net and this is the only reference to this topic I can find (for a bene 343). I’m in the process of buying a bene343 and did the survey today. On thé engine full power test it only got to 2600 rpm. At full power there was no vibration, smoke or any other indication there was aproblem, the boat got to 7.5 kts in still water. I measured the prop on haul out and it is 17 inches. According to the surveyor that is probably the original. The original yanmar tacho / engine start / stop panel with key has been replaced by the more modern version without key. My hunch is the tacho is mis calibrated, but given the feedback on this thread would appreciate thoughts on whether this could be a problem and what to look for.
Thanks for any help.

There is probably a prop dia/pitch stamped on the rim of the hub. If it was repitched, they should have shown that, also. My B323 I changed the 2-blde fixed to a Gori 2-blade folding. When I ordered the Gori, they asked a number of questions to make sure I got the proper specs. Although I had a 3YM20, I saw somewhere it was 22 hp, and that is what I told Gori. The prop I got was not performing like the OEM. Someone on this forum bought that one after I ordered again based on 20 hp. I was getting about 2400(?) rspm instead of 3600 with the OEM. I ordered a new one, and though I could have just bought the proper blades, I got a whole new prop so I could sell the old one on SBO. All has been well since then.

 

[zimboy]

I got the surveyors report today. There is some wear and tear on a few items that will need some work on the first haul out, but nothing catastrophic, I'm confident the boat is structurally sound. The last item is the full power test. I'm going to get the engine inspected to figure out what's causing the discrepancy, I will post the findings here once I get them. Thanks to everyone for the input and advice.

 

[JohnShannon]

The diesel tach is optical, you put a bit of reflective tape on the rotating thing you want to measure ( crankshaft ) and then it shines a light on it and measures the reflectance change as the tape comes around.

 

[zimboy]

The engine was checked out by a mechanic, including a check on the RPM using an optical tacho, and the Yanmar tacho is mis calibrated; it's reading 700 RPM too low at max throttle. Apparently there's a way to calibrate it, so that's now on my to do list. Thanks to everyone for the advice and support.

 

[kappykaplan]

Thanks to everyone for the advice and support.