Engines alignment issues

[Gordon J]

Ok, story thus far. Needed bottom paint and decided to renew the bellows on my pss shaft seals, and since going this far also decided to change cutlass bearings. This is a powercat located in Croatia. The yard had a deuce of a time getting the shaft flange off. After two days of pounding and heating they where able to remove the first shaft flange.

Fast forward to check ride, the boat had a terrible vibration starting at 1400 rpm and continuing to about 1900 fades and then starts again at about 2400.

Yard re-hauled the boat and found, not surprisingly that the flanges were not true. Machine shop took care of that. Three alignments later still have a terrible vibration.

Mechanics at the yard now tell me I have bad engine mounts on this 2016 boat with 1100 hours. This on a boat that ran smooth prior to being touched by this yard. I told the yard owner to point out the bad mounts and I would gladly change them. I inspected each one and they look good to me. There is some rust on a couple but all appear sound and the rubber supple. All are adjustable.

The boat had been in and out of the water four times now. A machine shop said shafts are true, and propellers are literally out of the box.

Suggestions, ideas on where to look would be helpful. I reached out to Steve d'Antonio hoping to buy some time for a consult, but couldn't get anyone to answer the phone.

Ideas theories welcome.

Gordon

 

[boomerang]

If you watched them align the couplings to within ~.004 of an inch and then, after a seatrial ,the alignment is out, then yes, maybe you have a bad mount. I'd be more concerned about the "days" of banging to get the coupling off. Have you checked to see if the shaft is true when you were hauled? It's easy enough to do with a pointy stick held stationary on the shaft while turning, for a rough idea of the condition.

 

[Gordon J]

Machine shop verified that shafts are true. Boat was not any further out of alignment after sea trial, but the mechanics went through the motions again to recheck. Also, eight mounts or even one on each engine would not typically fail simultaneously.

 

[Larry M]

I’d check the strut and or the cutlass bearing. Did they use a slide hammer trying to separate the coupler from the shaft? And how was the old cutlass bearing removed and the new one installed? There isn’t much left that you haven’t covered.

 

[rgano]

I had my 500-hour prop pulled and checked after I bought the boat because I was getting some vibration around 1800 RPM on the way to my 3000 RPM cruising speed. It looked fine with no evidence of ever having hit anything. Prop shop said one of the five blades was over and inch out of true with the others and said he had seen them out by that much straight from the factory.

 

[Comodave]

I had my 500-hour prop pulled and checked after I bought the boat because I was getting some vibration around 1800 RPM on the way to my 3000 RPM cruising speed. It looked fine with no evidence of ever having hit anything. Prop shop said one of the five blades was over and inch out of true with the others and said he had seen them out by that much straight from the factory.

Yup. Entirely possible.

 

[Keysdisease]

A natural rubber engine mount has a performance within specifications lifespan of approx 10 years. After that they will still perform, just not as well when it comes to isolation.
This is from Rubber Designs Literature:

The life expectancy of the rubber elements will be approx. 20 years in ideal circumstances. Unfortunately ideal circumstances are not feasible, therefore the (working) life expectancy will be approx. 10 years. The life expectancy of the rubber elements is dependent on the environmental circumstances (weather influences, contaminants, etc).

Where mounts fail prematurely is often the mount under the injection pump. Fuel will kill a rubber mount. Yards and engine guys love to point to mounts as the cause of vibration. It far from being the culprit most of the time. As mentioned, I would check everything else first, because 8 year old mounts should not be "bad"

A vibration analysis should be able to pinpoint where the source is. Using accelerometers vibration can be graphed and knowing the rpm and gear reduction and blades on a prop a vibration can be identified as prop rate, shaft rate, firing rate, gear mesh, etc.

$00.02

 

[Keysdisease]

and propellers are literally out of the box./QUOTE]

This does not ensure a well balanced prop. Before I retired my neighbor was a prop shop. They found plenty of new props that were not true or balanced

 

[Gordon J]

Thanks, good thought

I had my 500-hour prop pulled and checked after I bought the boat because I was getting some vibration around 1800 RPM on the way to my 3000 RPM cruising speed. It looked fine with no evidence of ever having hit anything. Prop shop said one of the five blades was over and inch out of true with the others and said he had seen them out by that much straight from the factory.

We took the new props to a prop shop. They were dead on.

 

[psneeld]

How about the engine/transmission?

Have you uncoupled the shaft and run the engine up in and out of gear?

 

[boomerang]

How about the engine/transmission?

Have you uncoupled the shaft and run the engine up in and out of gear?

Good point.

 

[psneeld]

Good point.

Too easy to only think inside the TF box...

 

[Gordon J]

Good thought, but

How about the engine/transmission?

Have you uncoupled the shaft and run the engine up in and out of gear?

No, I have not done this, but one of the few things I like about the Volvo engines is that they are super smooth. I doubt that would be very informative.

To iterate, all summer long and coming into the yard everything was smooth. It was only after the mechanics got hold of things that problems started. This is not an engine or transmission issue.

 

[Xlantic]

Have they checked the shaft is properly aligned with the strut(s) and shaft log, as well as the engine

Maybe a strut became misaligned.

Speaking of Steve D'Antonio, here is a Passagemaker article available in his website:
https://stevedmarineconsulting.com/wp-content/uploads/2019/01/Prop-Getting_The_Shaft.pdf

The article is appropriately named "Getting The SHAFT" ...

 

[psneeld]

No, I have not done this, but one of the few things I like about the Volvo engines is that they are super smooth. I doubt that would be very informative.

To iterate, all summer long and coming into the yard everything was smooth. It was only after the mechanics got hold of things that problems started. This is not an engine or transmission issue.

Banging on the flange is one of the biggest damagers of transmissions.

So is prop removal depending on the method.

 

[Xlantic]

When they aligned the engine, did they compensate the overhanging weight of the shaft and the coupling which can lead for the unsupported end of the shaft to "droop"?

In yet another D'Antonio article he mentions this can be an issue for long spans and heavy shafts/couplings.
https://www.proboat.com/2010/11/running-gear-alignment/

Last year I aligned the replacement engines in my boat. Remembering the article, I calculated the weight to compensate as 20 kilograms: half the weight of the overhanging shaft plus the weight of the coupling.

To compensate, I used a 20 litre container filled with water, a couple of pulleys attached to a 2x4 across the engine hatch opening and a line attached to the end of the shaft, pulling up with a 20 kg force. (See schematic below.)

 

[Gordon J]

Likely not the problem

Have they checked the shaft is properly aligned with the strut(s) and shaft log, as well as the engine

Maybe a strut became misaligned.

Speaking of Steve D'Antonio, here is a Passagemaker article available in his website:
https://stevedmarineconsulting.com/wp-content/uploads/2019/01/Prop-Getting_The_Shaft.pdf

The article is appropriately named "Getting The SHAFT" ...

I had the same thought. I wrote to Steve who said a misalignment was not likely to cause vibration.

New engine mounts were installed and, while somewhat less, still have a vibration beginning at 1400rpm. It was aligned on the hard. Today a mechanic s will recheck the alignment while it is on the water.

BTW. The old mounts appeared good.

Gordon

 

[Gordon J]

Not required

When they aligned the engine, did they compensate the overhanging weight of the shaft and the coupling which can lead for the unsupported end of the shaft to "droop"?

In yet another D'Antonio article he mentions this can be an issue for long spans and heavy shafts/couplings.
https://www.proboat.com/2010/11/running-gear-alignment/

Last year I aligned the replacement engines in my boat. Remembering the article, I calculated the weight to compensate as 20 kilograms: half the weight of the overhanging shaft plus the weight of the coupling.

To compensate, I used a 20 litre container filled with water, a couple of pulleys attached to a 2x4 across the engine hatch opening and a line attached to the end of the shaft, pulling up with a 20 kg force. (See schematic below.)

Literally only 18 inches or so between shaft log and transmission. Three mechanics use a cutlass bearing to center in Stern tube.

Gordon

 

[Gordon J]

No banging on transmission

Banging on the flange is one of the biggest damagers of transmissions.

So is prop removal depending on the method.

The shafts were disconnected from the transmissions before all the violence.

Gordon

 

[RickyD]

Have they checked the shaft is properly aligned with the strut(s) and shaft log, as well as the engine

Maybe a strut became misaligned.

Speaking of Steve D'Antonio, here is a Passagemaker article available in his website:
https://stevedmarineconsulting.com/wp-content/uploads/2019/01/Prop-Getting_The_Shaft.pdf

The article is appropriately named "Getting The SHAFT" ...

I was going to mention this as well since my friends boat could not go over 1400 without serious vibration. It was found that one strut was 1/2” out of line. Hard to understand how since there are two struts on each shaft and this one was short and stout closest to the engines. It’s as if it was assembled this way from the start. Yes, he bought it used and moving the strut fixed the vibration completely.

 

[cardude01]

If you do all the above recommendations to get rid of most of the problem and still have some vibration, you could install these to get rid of any remaining vibrations. I have one on my boat and it works well.

https://bruntonspropellers.com/sigmadrive/

 

[kapnd]

A propeller that is perfect out of the box may no longer be perfect after installation!
Make sure that the installer blocks the propeller from the base rather than the tips while torquing down the nuts.
Also, a piecemeal inspection of the components of the drivetrain does not insure that they are in harmony.

 

[Rearmount]

Also something to check. Make sure that the transmission flange or prop flange is not warped from removal. Both can be taken to a machine shop to get refaced and keep port and stbd parts together from the shop.