PT41 Vibration and Noise Abatement

Ski in NC said:

You can use soft mounts without going to aquadrive shaft line or whatever. The motion of the engine on the soft mounts will not be enough to cause issues with alignment. Most all modern installs use soft mounts and rigid shaft lines. No issues.

The poster who required the aquadrive did so by replacing a tranny with different dimensions, not because of going to soft mounts. (at least that is how I understood his post)

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I'm a little confused now (a lot actually), I was told by a number of people including Brian Smith at American Diesel that the mounts have to be hard or the misalignment caused under torque load will wear your cutlass bearing, stuffing box and output bearing on the end of the gear reduction unit.

If modern designs are using soft mounts how do they differ from the older designs such that alignment is no longer a problem.

psneeld said:

Just went back to the original post....

Rduval, is this the first big boat you have owned and have spent some time operating from inside a cabin?

Not to be insulting and the boat could certainly be an issue...but you are sounding like you know more and trust more from magazines (got plenty of boating friends that sound the same) than from many of us with thousands of actual cruising miles.

many of our boats are loud and may feel less than perfect at higher Lehman RPMs (say 1900 and above)...many cruise at 1600-1800 or so and say the noise and motion are pleasant but certainly far from gone.

If you are deadest on an aqua drive...go for it...not nearly as many out there for a reason...they do what they say they do but for most just not worth the complication and expense because a properly tuned, properly aligned engine and drive train, and reasonably well done sound proofed engine room is not bad at all....

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No insult taken.

I have had many vessels both sail and power, big and small. But this is our first diesel trawler, and our first of any kind where the lower helm and salon are, literally, right on top of the engines.

If the vibration was only at idle and possibly one or two specific rpm, we could easily live with that. Problem is, there are only one or two rpm's that it isn't intolerable.

Sound proofing can only do so much in our case for 2 reasons;

1) the salon floor is 3" thick and already insulated and the coolant tank already sits in a hole with 1" clearance and I'm quite sure removing the rocker covers to adjust the valves or service the injectors will require uncoupling the shafts and dropping the engines off the front mounts. (That or removing the Galley!)

2) Perhaps worst of all is that most of the noise comes from sympathetic vibration of the bulkheads, the fridge, the stove, cabin doors, etc.

So it's not so much about sound reduction from the engines as isolating the vessel from the engines to prevent the sympathetic vibration.

That's why I'm leaning towards soft mounts and, form what I've gathered so far, soft mounts seem to require a flex joint of some sort.

So that's where I sit. Clearly unclear and undecided about the best course of action.

funangler said:

I'm installing a aqua drive myself on a 42ft steel boat with a single perkins 6.354. The drive was over $3000. I should been done by the end of the week I will post if it worth it.

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I look forward to hearing that....

I think because so many have boats without aquadrive type setups....you have to make a big decision...one I also went through.

When you are in the fork in the road between multiple fixes. One is chasing down one or multiple fixes that may or may not ever solve your problem. Frustrating when it's the last thing or it never comes. But very satisfying when the first or second tweak fixes things good enough and you haven't spent much at all. This fork is best when you are doing the work yourself (most of it's easy if you are handy).

The other fork is where you run out and buy an aquadrive and start the process of redoing everything in a simple and orderly way. Chances are everything will be good at the end ....but like many of us said...not necessarily better with an aquadrive than plain old normal setup.

The only real difference is money and a gamble. No one can give advice good enough to really set your course because it's gambling your money and time.

I'm sure you have made plenty of similar decisions in your life...use your method for deducting the best answer for you.

Good luck!!!!

Rduval,
You may want to evaluate your boat more closely.

First go for a ride in a similar boat and compare vibration.

Secondly take a good look at your boat to see if there's something different about your boat. Especially something like an unusual modification. Anything that is not original may cause vibration especially if it is resonate to the same frequencies as the engine vibration. Engines vibrate. That's a given but the annoying vibration can come from something that is being excited by the engine shaking. Imagine a bulkhead is attached to the engine stringers/beds. The bulkhead may not vibrate (or drum) much at all until the engine gets to a certain frequency (rpm) that the bulkhead is resonate to. Like a tuning fork. And then the bulkhead shakes the boat so the shaking and noise is much greater than what the engine could create by itself.

If you bolted a Lehman to an extremely large concrete slab w no enclosure you would be saying "what vibration?". In that case the engine can't transmit much vibration to you because it can't shake mega tons of concrete so you don't feel any vibration. You don't hear much either because there's no enclosure to contain and resonate the vibration of the air near the engine.

Your engine itself isn't causing your vib problem. It's what's attached to the engine that's causing the problem. If you have vibration on your boat that was not present when the boat was new and the level of vibration then was nice and low something has changed. The boat probably was fairly smooth when new so if you can discover that change or alteration your problem could be solved. And solved w/o the trouble and expense of an Aqua Drive.

Sometimes a good marine mechanic can spot unusual things that would cause excessive vibration almost immediately. They would be more likely to uncover a problem than most of us so a few bucks spent thus may be well spent. Try and find a guy that's spent 40 or so years in boat bilges as he knows what's normal and what's not.

Anyone that can EASILY afford an AD should consider installing one but most of us would find it expensive.

Rduval said:

I'm a little confused now (a lot actually), I was told by a number of people including Brian Smith at American Diesel that the mounts have to be hard or the misalignment caused under torque load will wear your cutlass bearing, stuffing box and output bearing on the end of the gear reduction unit.

If modern designs are using soft mounts how do they differ from the older designs such that alignment is no longer a problem.

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Hard mounts are not necessary to keep the shaft line happy. They do have a point that if motor moves around, alignment will change. But it just does not change enough. A flex mount might displace 1/8", and engine lifts one side, lowers the other, so shaft does not move that much.

Order a brand new Cummins engine, it comes with soft mounts. Buy a brand new boat, they come with soft mounts.

At idle, the vibes transmitted into the boat are very harsh with hard mounts. That will be fixed with soft mounts. Above idle and at cruise, the mounts make little difference. At higher revs the engine produces very little vibration. At idle, it produces a lot.

So if you have idle shake, fix that with soft mounts. More analysis needed to figure out the other noise/vibe issue.

And slap that idiot that built a galley over your rocker cover. Hate seeing stupid things like that.

Ski in NC said:

And slap that idiot that built a galley over your rocker
cover. Hate seeing stupid things like that.

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Boggles the mind really. It looks like the design was for a single and somebody wanted twins so they just put twins in there and didn't change anything else.

Thanks for the other advise too.

This post has nothing to do with vibration, but everything to do with noise.

Access to my engine room is via 3 panels along the centerline of the saloon plus two long panels, one ether side. Originally lift-out, I decided to fit the centerline pannels with hinges as in the pic below. The panels (like the rest of the engineroom overhead) were faced with that familiar "fiber-board with holes". It had become greasy and generally ragged, so I decided to remove it. Underneath was a 3" thick layer of styrofoam! OK for heat insualtion, but next to useless for sound deadening. Further investigation revealed that the long removable pannels were also insulated with styrofoam and the fixed part of the engineroom "ceiling" had nothing save fiberboard and an air-space. I replaced the whole lot with a sound-deadening material sold by our local chandlery. With both engines and the generator running, the reduction in noise level is remarkable. Other forum members with mid-80's Taiwanese boats might find it worth while exploring what their "4-inch thick saloon floors" are really made of.

Rick
If your Pt is the same as ours there is a third lift-out hatch in the galley that is underneath the counter and part of the seat but you have to unbolt the counter and seat (easy to do) and move it out of the way.

Shoalwaters said:

This post has nothing to do with vibration, but everything to do with noise...The panels (like the rest of the engineroom overhead) were faced with that familiar "fiber-board with holes". It had become greasy and generally ragged, so I decided to remove it. Underneath was a 3" thick layer of styrofoam! .... Other forum members with mid-80's Taiwanese boats might find it worth while exploring what their "4-inch thick saloon floors" are really made of.

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Mike: Good post. You described Hobo's engine room. How long did the project take and were there any Oh shits along the way?

rochepoint said:

Rick
If your Pt is the same as ours there is a third lift-out hatch in the galley that is underneath the counter and part of the seat but you have to unbolt the counter and seat (easy to do) and move it out of the way.

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Good to know that it unbolts easily. I have the same hatch but it still wouldn't give me access to take the rocker cover off.... Grrrr

Shoalwaters said:

It had become greasy and generally ragged, so I decided to remove it.

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How were the tiles and styrofoam held in place? Did you just pry them out? Did they come out cleanly?

Larry M said:

Mike: Good post. You described Hobo's engine room. How long did the project take and were there any Oh shits along the way?

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Larry,
if I had an engineroom overhead that looked as pretty as yours, I would have thought twice about disturbing it. The easy bits were the removable pannels because I could take them back to my workshop, turn them upsidedown and work on them in comfort. The permanent bits were a real PITA because of the limited space between top of engines/generator/other stuff and the underside of the "ceiling". I filled up the cavity with layers of a heavy fire-resistant foam and spray-on contact adhesive. Use small pieces - I couldn't support a big sheet and get it to stick in the right location. The last layer was an equivalent to Soundown. I didn't like the "pins and washers" approach and I couldn't stick big sheets in place for the the reason stated. I decided to hold them with pannels of 3/16" plywood screwed in place and painted light grey. It may reflect some of the sound back down again, but it's a big improvement and anyway I have a wipe-clean engineroom ceiling! I would guess the whole thing took the best part of a week to do.

Rduval said:

How were the tiles and styrofoam held in place? Did you just pry them out? Did they come out cleanly?

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RDuval,
The fiber tiles were originally fixed in place with little mild-steel (rusty) finishing nails and in places glued to the styrofoam above. The PO has used fender washers and wood screws to hold up some of the sagging edges. The styrofoam was glued to the overhead with the Taiwanese equivalent of Evo-Stik; the fiber tiles were glued to the styrofoam with the same stuff. Being a tad anal it felt really good to get all that garbage out of there. Edit: No, it didn't come out cleanly. This is messier than demolishing old drywall.

If you are thinking of doing this:
Cover engines and everything else with drop-cloths.
Have a good shop-vac, clean up as you go.
Have good ventillation and lighting.
Face/dust mask and eye protection
Set a target of a small area for the day's work - don't try to do it all at once.
This job is a breeze if you are a double jointed dwarf with eyes in the back of your head!

Mike: Thanks for answering my question. I think I'll wait based on your comments. I can remove 5 panels but the ceiling that remains has limited clearance and to do it right, would mean moving the generator.

It's soft mounts for me and VETUS shaft rubber couplers.
Bill

Billylll said:

It's soft mounts for me and VETUS shaft rubber couplers.
Bill

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That would be an easy fix if I didn't have to lower the front of the engines....

Billylll said:

It's soft mounts for me and VETUS shaft rubber couplers.
Bill

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Well that's pretty much what I've ended up doing except I'm using Federal Flex Couplings at $308 each vs the Vetus at over $1000.

I put in the Aquadrive engine mounts first to see how much improvement they would make in vibration and noise before thinking about tackling the HUGE (and expensive) job (on my boat) of moving the engines forward on new mount plates, changing the stuffing box, etc..

WHAT A DIFFERENCE! Wow!. The boat is quiet and smooth.

Now I'm just waiting for the pair of Federal Flex Couplings to arrive to compensate for the mis-alignment caused under loading.

I'm actually using the boat at the moment with the solid couplings and don't have any shaft vibration issues or changing in the drip rate of the stuffing boxes under load but I'll feel better know there is something to take up the misalignment and prevent bearing wear.

I would have preferred to use the complete Aquadrive system but If the Federal Couplings do the trick I'll be smooth and quiet for about $6k less (counting parts and labour).

They should come any day and I'll let you know how they go.

I did the same thing to my old boat with the same parts. A 42' GB motoryacht. And it made it the smoothest most vibration free Lehman powered GB I'd ever run. No more stove rattling vibration at dead idle on start up anymore.

Capt.Bill11 said:

I did the same thing to my old boat with the same parts. A 42' GB motoryacht. And it made it the smoothest most vibration free Lehman powered GB I'd ever run. No more stove rattling vibration at dead idle on start up anymore.

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LOL Too funny... The stove rattling was the worst part for me too....

Rduval said:

LOL Too funny... The stove rattling was the worst part for me too....

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Yeah, you could always tell when some one had lost or forgotten to reinstall the anti-rattle clips for the stove burner grates.

As a follow up on this thread, I have now: Changed to Aquadrive motor mounts (Huge difference), added the GGB Inline mufflers (very significant reduction in sound level and "droning") and finally carpeting the salon with 1/2" foam under pad and, most importantly, a soundproofing underpad from Acoustiguard called BARYMAT BM-1C which also made a very significant difference.

Normal living room conversation levels are now possible underway at 8 knots cruise at 1550 RPM.

Still a few things I think I can do. There is quite a bit of noise transmitted through the bilge and up the hollow helm station which I will address from below with some sort of baffle. I also think there is a significant amount of engine intake noise which I am going to try to address with a scrap yard Cummins Diesel (non-turbo) intake silencer.

Not quite a sailboat yet but getting closer... And the Admiral isn't angry at the noise level when in the closed salon underway anymore.

Glad the Admiral is happy....
Very important to keep it that way.