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jjm
10-29-2007, 05:22 PM
"I have a late 1980’s Beneteau First 26 which had a Yanmar 1GM10 inboard diesel. As this engine required an extensive and expensive overhaul, I decided to replace it a few months ago with a new 14 HP Yanmar 2YM15. The new engine was fitted by the local Yanmar Agent. The sterngear – coupling, shaft, and propeller were unchanged.

When trying the new engine just after installation (with a clean hull) it was noted that the engine was vibrating/shaking quite a lot at certain revolutions. The Agent there and then opted to replace the standard rear engine mountings (75) with harder ones (100 – part number Y128377-08350). There was a noticeable improvement.

I took the boat out of the water in July-August for hull cleaning and anti-fouling, and while it was ashore I noted that there was no play at all in the cutless bearing. The stern gear seemed all OK – I am, however, no technical person.

The engine now has 100 hours on the clock, and I had the 50-hour first service done two months ago, including alignment check.

Although I am very happy with the engine, there are a couple of issues which I would like to clear, and I would therefore kindly ask for your comments/advice.

1. At 2000 and 3000 revs, the engine invariably vibrates/shakes, though not as much as originally, and even transmitting the vibration to the rigging. Otherwise, the engine runs smoothly. I have been told that all engines do this – they all have their, sort of, sensitive point/s where they vibrate more than normal. Is this the case? Could it be that still stiffer engine mountings are needed? The Yanmar Agent did not exclude this, but said that this also depended on whether the shaft/propeller were well balanced. This can now only be checked on the next haul-out, which could be next summer.

I also note that at these revs - which I try to avoid as much as possible – a little water sometimes leaks from the three or four year old deep sea seal into the bilge. Is this normal and, more important, is my concern that this vibration could damage or break the seal justified? (I must admit that I am very sensitive about shaft and sea-cock holes in the hull).

2. The engine and its 2.62:1 gearbox are driving a 1” shaft with what seems to be a 13” x 9” three-bladed bronze propeller (I could not see any marks on it which indicate the size) which is delivering 4000 rpm at full throttle. This is beyond the 3600-3800 indicated by the engine brochure/manual, and would thus indicate under-propping. What propeller size would you think would be more appropriate for the 26-foot long, 9’ 2”-wide, just over 2-ton boat? There is currently a three-inch clearance between the tip of the propeller blade and the hull. The distance between the tip of one of the propeller blades and the centre of the propeller is 7”, and 6.5” from the tip to the propeller blade to the shaft-hole circumference. Is the latter which determines the propeller size?

Thanks a lot."

ron_cairns
10-29-2007, 06:22 PM
Alignment is 4 thou. clearance on the coupling. This engine top rpm is 3800 and should be run at around 3000 rpm. This gives you the best fuel to load ratio. Check with some of the prop people advising engine top hp at rated rpm. Length of vessel at the water line and weight of the boat. Tell them the size of the prop you are running now and the gear ratio. They will get back to you with a recommended size and you can compair. Each engine has a vibration at a low rpm and a high rpm. A change of 100 rpm either way will make that go away.Sounds as if your Yanmar dealer has covered all bases. Then again I am not on the boat experiencing the vibration. Yes you can check shaft for true and check the prop for balance also when you get the chance.
Let us know. Regards Ron

jjm
10-30-2007, 12:01 PM
"Thanks a lot for your prompt reply, Mr Cairns. Best regards.
Joseph"

broggerp
10-31-2007, 11:21 AM
"Wouldn't running the engine at the same RPM, first in neutral and then in forward (and maybe also reverse) help discriminate whether the vibration is related to the trans/shaft/prop?

I understand running free vs. under load will be somewhat different for the engine, but it might help separate your vibration into a couple of significant components, which then might be pursued independently.

(This from a rank amateur -- take with a dose of salt water!)"

Roberto Szabo
11-01-2007, 11:10 AM
"Hello,
I have two 2YM15 with sail-drives in my 34" Catamaran and there is no vibrations/shakes, only diferents "sounds" at diferents RPM. Maximum RPM is about 3200 and I use Gori folding Propellers.

Regards,
Roberto Szabó
From Brazil"