shake, rattle and roll

[jimbim]

ok, my engine, according to some charts, is a bit big for my boat -- 33hp Kubota in a 27-footer -- but this in not a size problem I don't think. Lots of sailboats have very big engines and they seem to purr happily along even if there is no room to change a filter.... Besides, I can't afford to re-engine.

I have engine vibration problems... and frankly I do not trust or respect a certain mechanic that I had look at the problem a while back, nor can I understand his English, but that's my problem, not his.

Anyway, is there a way to determine what causes vibration -- propellor, engine pads or something else?

It doesn't vibrate in neutral, nor in reverse. When going forward, there seems to be several vibration zones she goes through as I accelerate, in which the vibration worsens, but generally she still vibrates anytime I'm in forward -- heaven forbid I leave a kettle on top of the stove.

I am on the hard now. Was planning to pull the engine and have the gearbox reconditioned. Is there anything I should check while I'm doing this that might be related to vibration? What should I look at on the engine pads to make sure they are all right?

Any suggestions appreciated.

[BC Mike]

There are a few things I can think of. The engine mounts, the shaft bearing, the prop, the bed or stringers that the engine sits on, the alignment, and harmonics.
The harmonics or frequency of the engine and hull will play a different tune as the revs change. The shaft should be aligned to the engine when the boat is in the water. The strut bearing is replaced when the boat is out of the water and you can have the prop checked at the same time.
Make sure the engine mounts are in good condition and have not come apart. You did not say what kind of prop or drive you have so I am assuming a fixed prop on a strut. If you are using a fixed prop the Campbell is reported to be smooth.
Diesels in general thunder more than some folks think they should and it is a surprise to the new owner. If this is the case have someone else listen to it.
That is a lot of hp for a small boat unless your boat is exceptionally heavy. You did not say. If your boat is of light to moderate displacement, then that motor could well be rattling its cage, so to speak. Yanmar has a help site that discusses this.
Michael

[jimbim]

Thanks Mike, and sorry I didn't say. It's a Vancouver 27 (disp 8,700 ++). Yes, fixed prop.

There was a bit of a vibration problem when I bought her, but it has gotten worse, which suggests to me it's not the prop, but I honestly don't know.

I'll visit the Yanmar site.

[JGI417]

I think I would first check shaft to engine alignment, and as prev. post check condition of the engine mounts, I had a freind who had about the same problem and the alignmet cured the problem,
John

[jimbim]

This is from yanmarhelp.com:

----------------

The common causes of vibration are listed below:

* The engine idle rpm needs setting correctly.
* Engine / propeller shaft misalignment.
* Faulty engine mount. The elastomer deteriorates due to spilled diesel, excessive weight and/or old age.
* Improperly secured engine mounts.
* Incorrectly selected engine mounts. The elastomer has a 'hardness factor' and stiffer mounts must be fitted to compensate for heavier weights, e.g., if a fridge compressor has been added. ( Use the genuine Yanmar mounts, they work well. )
* Mechanical trouble, e.g. an injector not set at the proper pressure, poor compression on one or more cylinders, valve clearances incorrect, incorrect fuel pump timing or a sliping gearbox/transmission clutch cone (slipping cone normally @ low rpm).
* Modified engine mount brackets. Don't change the engine, always change the engine beds!
* Propeller cavitation. The propeller is too small or the appendages in front of it are causing cavitation.
* Damaged propeller
* Damaged/bent propshaft
* Problem with shaft strut or p-bracket i.e.lose out of alignment with other stern gear
* Worn or damaged cutlass bearing
* Incorrectly sized propeller shaft tube. The old fixed type 'Admiralty' gland on the prop shaft tube meant the shaft to tube clearance could be about 1/16th inch and the two parts would never touch as the shaft was held in the central position by the gland. With the advent of the modern 'dripless' glands the shaft can move about with the flexibly mounted engine. This can occasionally cause the shaft to bounce on the tube, especially if heeled over while motor sailing. A larger diameter propeller shaft tube (about 2.5mm or 1/8th inch clearance) is one way of resolving this problem. Alternatively, install a thrust bearing or an 'Aquadrive' CV joint which will hold the shaft in the central position.
* Other things in the boat, like the pots and pans in the galley thrashing about.
* Engine imbalance from the manufacturer has happened twice that I know of and both of them were over 10 years old when they were complained about!
--------------

That's a lot to consider, but surely I can eliminate "Other things in the boat, like the pots and pans in the galley thrashing about." Pots and pans are definitely not the cause of my problem

[delmarrey]

From the symyoms, I would vote for better quality engine mounts.

It sounds like the engine is twisting in the forward gear. If that's the case your shaft coupler may be worn internally and/or the prop. shaft maybe bent as well.

33 hp does seem a little overkill for a 9000 lb boat.

Ref. http://cruisersforum.com/showthread....ght=motor+size

[Alan Wheeler]

OK, lets be a little more like Sherlock here and see what we can deduce. so what we know.
So firstly, this is not a new installation, and the past would suggest that vibration was acceptable, but has progressively become worse.
Secondly, this is an install that has a motor in excess of what is required. That in itself is not a problem, however, my first question would be, were the engine mounts designed for this engine and it's power. Secondly, as Yanmar have suggested, are the mounts clean and free of oil, and intact, as the engine power may have damaged them, IF, the engine is bigger than the mounts are designed to handle. Check for looses mounts and the attachments to the engine beds and engine itself.
Next.
Drive Chain. The next point to check is the flexible coupling (if their is one). Was that also designed for this engine HP. Maybe it is being damaged if designed for a smaller engine. I doubt that the shaft or propellor would be damaged due to excessive HP, unless it is very light weight, but 33HP is not huge to what is required as a minimum for shaft size.
Next.
Shaft and propellor. The shaft bearing maybe worn. As it wears, more vibration resulting in more wear. Especially if in the past, the underwater parts have struck something and cuased damage. The next along the shaft is the propellor itself. This could have growth on it or it maybe damaged or even have and electrolyses problem, resulting in the blades becomes weak and tips bending or broken. As it cavitates, it wears more and more resulting in balance problems and more cavitiation.
BUT.
You mentioned the vibration stoped when in reverse. So have you been able to get a "feel" for where the vibration is being produced. Does it seem to be from the Engine itself or down the back of the boat. If the vibration stops when in reverse, then it is possible that a load is being placed on the engine mounts in a different way and the motor doesn't move as much. So that leads us back to engine or mounts. Does the engine seem to sound harsh or knocking or idle ruffer than it used to? Is it smoking excessively?
To do away with one Yanmar help suggestion, it won't be idle setting, if the vibration is felt throughout it's rev range.
Yanmar has given you some great suggestions to check and I would work through that list, but my initial suspicions would be in an area of engine mount or propellor damage.

[BC Mike]

Was wondering if Sherlock had considered the fact that there might not be as many revs used when in reverse as opposed to forward gear. Also the fact that the keel or something large is likely in front of the prop when the boat is moving in forward.
This boat might not have a strut but a hole in a skeg. I have not looked at a Vancouver 27 lately.
Michael

[Jentine]

The easiest way to narrow down a problem is to isolate various systems. I would disconnect the shaft at the coupling. Run the engine (I understand that you are on the hard, but you only need to run a water line to the raw water intake). If the vibration is gone, you will have narrowed the problem to the drive train. If not, you have narrowed the problem to the engine and transmission. Careful inspection of the mounts will quickly ascertain their condition. Broken mounts rarely stay where they belong. Running an engine with a broken mount will be very apparent. If the mounts are good, look to the engine itself for one cylinder that is not working either because of a fuel or mechanical problem. Considering the size of the engine in relation to the size of the boat, you may never notice a loss of power and performance from a non functioning or partial functioning cylinder.
You can isolate the cylinders by loosening the fuel line to each fuel nozzle in succession. The non firing cylinder will not change the sound of the engine.
Try these and report back. It will be easier for us to help you once you have eliminated the major systems as a problem area.

Jim

[ssullivan]

Jentine once whispered in the wind:
The easiest way to narrow down a problem is to isolate various systems. I would disconnect the shaft at the coupling. Run the engine (I understand that you are on the hard, but you only need to run a water line to the raw water intake).

Jim

Be careful creating a lot of vibration if you are on jack stands right now... boats can rattle out of position on them when a smooth-running engine is fired up on the hard.

[jimbim]

Thanks for the suggestions. Lots to think about.... There were some questions about keel and skeg. Pix and drawings here might help:

http://www.boats.com/content/default...th=6&year=2001

delmarrey, I know 33hp is overkill, but that was the previous owner (who maybe is a lot like me). If 20hp is good, 33 is better. If 5/16 BBB chain is good, 3/8 is better. And so on.

Alan, good points. As far as "feel" goes, I would say that it feels like it's coming from the engine, though the engine, shaft and prop all seem to be directly beneath you when you are sitting in the cockpit. Can't say the engine sounds any worse, and it is not smoking more that I have noticed.

[JGI417]

One other note, on my boat the prop shaft to engine alignment is only checked when the boat is in the water. I read that yours is on the hard, something to consider

[jimbim]

I know I said I wasn't re-engining but there has been a development that might change that. I have learned about a rebuilt Yanmar YSM12 (12hp) that could come available for a good price (which has yet to be "officially" determined).

Living with a 33hp monster maybe I don't have the right perspective, but do you think 12hp is enough power? If it's borderline, what problems do you foresee? Any thoughts on the engine.

[Boracay]

My 32' Harley ferro had a secondhand hand start Yanmar 7hp with one cylinder and it pushed the boat along quite nicely in all the conditions that we encountered on Sydney Harbour and a few miles up the coast.
The throttle was mounted on the engine, as was the gear change, so jumping from the cockpit down to the engine for control was interesting at times.
The engine bed was a couple of bits of angle iron bolted to the cement beds, with the engine bolted straight to that.
The VDO could read over 6 kts when everthing was clean.
It had a fuel tank on top of the engine which only took 4 litres, but that was all we ever needed, and the fuel was always clean.
I'd be more worried about making sure the propellor was right for the engine, and that the engine controls were easily to hand.
In retrospect the big advantage of the smaller engine(other than the hand start and the cost) was that the small propellor meant sailing performance was good.
You may be able to get a good price for your old engine as good quality marine engines are becomming expensive.
I have very fond memories of chugging back from a days outing with a few friends.
The engine gave off just enough warmth to warm the cabin on cool winter afternoons.

[Alan Wheeler]

Jim, for a more accurate answer, we need to know the weight of the boat. However, I think 12hp would be OK.
Advantages would be, size and weight saving. Fuel saving. Vibration and noise would be reduced as the yanmar is a little sweeter running than the more "agricultural" Kubota. Reliability maybe increased seeing as it is a rebuilt engine. Check to see What exactly is meant by "Rebuilt". You can come across the odd mechanic that thinks a steam clean, and minot tickle up is a rebuild and another mechanic that consideres a rebuild as a compleate strip and repair/replacement of all wearing parts.
So the disadvantages would be,
You have a known engine. You will have to reprop. You will need to engineer new mounts to take the engine and align it to the prop coupling. You may need new engine mounts as the originals will be made for the heavier engine and will be too hard. You may need a new shaft coupling. Cooling pipes may or may not need re-plumbing. You may have a smaller Alternator, thus reducing charge to battery banks. You may have an engine instrument panel and loom to run.
Think that covers most of the nasties. There are a few more minors, but I can't think of anything of consequence.