Engine noise and vibration questions

[Jedediah]

So I've been trying to decide the next major project to jump into (really should be electrical but...) and have been toying with the idea of making the engine a bit quieter--read into that a lot quieter. Its a small inboard Universal 12HP 2cyl. diesel that has old mounts, needs a rebuild, etc. But what I'm really wondering about is this, has anyone tried an Aqua-Drive system? I haven't even found out what the price is yet but it seems to make sense from a purely vibrational standpoint. Does it work, does anyone have one, and would anyone recomend it?

http://www.aquadrive.net/

[jollyboat]

I do not have any experience with the Aqua-Drive so from the point of noise reduction from ones use I can only talk out of my hat. While powereing your boat with a Universal diesel 2 I would bet you would be better off investing your efforts in conventional methods of noise reduction before moving forward with a system like the Aqua - Drive. To start you are working with an engine that is not the smoothest of the bunch as all naturally asperated 2 cylinder diesels (some make more than others) make their fair share of vibration and operational noise. Ensuring that your mounts are not torn and that the studs are properly anchored in the rubber bases is a good place to start. Engine alinement is next and can provide some challange to the unexperienced but with a small engine like yours it would be worth your while to give it shot. In the event that you are not able or comfortable with alining your engine a trained marine mechanic can make this a short job. Anual service to the engine is also critical to the life of the engine and it's proper operation ( which is nice) and will also help to reduce noise levels. At this point you might take a close look at the construction of the engine box. Any loose or poor fitting cabinet work will contribute significantly to engine noise as this provides ample room for the noise to escape. At this point, with your engine box as snug fitting as possible, investing in a high quality lead lined sound down will further reduce noise levels. Higher quality sound down is expensive but with a pint sized engine compartment sized to house a 12 hp 2 cyl. diesel I do not think it will break the bank. Remember that your engine needs to breath so take that into consideration when you are sealing the compartment. Also take into acount anything that might chaffe on the sound down do to its decreasing the overall volume in the engine compartment. Hope my 2 cents is helpful in some way. I am only a bottom sanding grunt on the forum so please take my suggestions as such. Good Sailing.

[Jedediah]

Brian,
You bring up a load of great ideas. The mounts are not torn and the engine compartment isn't sealed or insulated--it does however have my finally working webasto heater in it. I haven't checked the alignment yet but will soon, nor looked at the prop to see if it is even close to balanced. But what does worry me is the amount of vibration I can still feel thoughout the boat, say at the pulpit. And since I'm simply looking at upcoming projects I thought I'd get a feeling about the Aqua-Drive in the sailing community, perhaps not the best since sailboat engines always seem to be the loudest. Thanks for the ideas though

Jed Smith
Cal 29

[jollyboat]

Jed,

Engine vibration from diesel engines is just part of the charm but with a little engineering keeping this to a minimum can be done. All twin engines, gas included, produce a fair amount of shake, rattle and roll and with the compression levels of diesel engines being that much greater than that of gasoline fired engines, theirs can be a denture rattling event.
A lot of the vibration that we feel is moved through the air via sound waves so your 'sound control project' will help a lot from the start. Installing the sound down under the cockpit sole ( if possible ) is another way to dampen the vibrations and sound. Further measures could be taken by mounting your wheel binnical on a heavy rubber pad (such as that of the baseball diamonds 'white home plate' available at sport stores)
cut to fit in an appealing mannor. The backing plate system could be installed with a rubber pad as well. This would help - mucho. Again, these are only the humble opinions of a 'bottom sanding grunt' and hopefully taken as such for what they are worth. Cheers and Good Sailing.

[Tim]

I don't know what the price of the Aqua-Drive is, but that device is really intended for much larger craft, with larger engines and a true need for the smoothness that the device would help create. I honestly don't think that it would make enough of a difference in a small boat with a shaky 2-cylinder diesel, and many sailboat installations don't allow enough physical space for such a device anyway.

Brian is right in that your small Universal diesel is never going to be smooth or quiet. Ensuring that your engine alignment is correct should be your first task, along with double-checking to make sure your prop and shaft are in good condition with no bends or dings. These small things can make a huge difference when transmitted through the whole boat.

Note also that flexible engine mounts lose their initial composure over time, and eventually require replacement--they are a maintenance item, not a one-time installation. So if your mounts are old, as you say, it's quite possible that they have lost their ability to properly distribute the engine vibration, which would transmit more sound and movement to the boat as a result. Just the fact that they look OK might not be enough. From the sound of your description, it seems like your mounts may not be up to snuff, and this would be the most likely reason for the sort of all-over boat vibration that you are feeling.

Not all flexible engine mounts are created equal, either. Some are rather firm, and would transmit more movement to the boat; others are very soft (like those supplied with the small Yanmar diesels), which are effective at dampening the natural engine vibration.

Small diesels tend to be the most shaky when running at low RPM; most smooth out appreciably when at higher speeds, especially cruising speed. If you experience vibration at cruising speed, it may well be the result of your shafting, alignment, or propeller--or some combination thereof.

My opinion is that any boat with flexible mounts ought to have a Drivesaver or other similar flexible coupling between the shaft and transmission couplings, to help allow for the movement that will occur with the engine when on the flex mounts. Of course this also goes along with my philosophy of galvanic isolation of metallic components, rather than bonding, but one can still bond the shaft through a flexible coupling by jumping a grounding wire over the flex coupling, if one is of the bonding frame of mind.

Good luck! Take one step at a time, and it's likely that you'll see a noticeable difference in your engine performance.

[Jedediah]

According what I got back today from the DLNW it would be ~$800 (CV05) for the parts. This is of course omitting the cost of putting a bulkhead in place that the thrust bearing could rest against.

I tend to like the idea of a drivesaver better, thanks for heads up Tim. It'd be easier to find an inch to move the engine forward than 10 for the aqua-drive.

And thank y'all too for the wonderful suggestions. Are there any suggestions on great engine mounts since I have a not so smooth engine to start with? I'll undertake the suggestions when I rebuild the engine here shortly.

How about an 8KW turbine? Anyone tried on a sailboat yet? I bet it'd be smoother... :)