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From: (no name) (no email)
Date: Thu Jul 27 2006 - 08:51:26 EDT
In a message dated 7/27/06 12:00:59 AM, John writes:
> My goal is to reduce vibration from the genset being transferred to the
> hull of my boat, which is causing sound and vibration in the cabins.
>
> I have a Westerbeke 6.0BTDA which is the 240V version of the 8.0BDTA. It
> is mounted within the standard Westerbeke sound shield. The Genset itself is
> mounted onto four basic looking rubber mounts thru which bolts pass securing
> it to two rails. This can be seen on the top right-hand corner of
>
> http://www.westerbeke.com/products/generator_detail.cfm?gen=5
>
> The genset weighs circa 450lbs and although my genset is a Westerbeke I
> assume the question could apply to any genset.
>
> These rails are mounted on top on the sound shield base, which is in turn
> mounted on top of a 1 inch fiberglass pad, which is the same size as the
> sound shield base. Bolts pass thru the rails, sound shield base and
fiberglass
> pad to secure the genset and sound shield. The fiberglass pad in glassed
into
> the hull of my boat.
>
> I see my options as a. replace the standard Westerbeke rubber mounts
> between the genset and rails with something more effective (tall mounts may
not be
> possible though because the sound shield looks like a tight fit, b. install
> something between the base of the sound shield and the fiberglass pad it is
> mounted on to reduce the transfer of vibration and c. both a & b.
>
> For b. My preferred option, I have been advised a sheet of one inch marine
> ply would work well or better yet some soft engine mounts such as -----
>
>
John,
This is a standard vibration control problem and there are a number of
manufacturers that will be happy to supply engine mounts to quiet your
generator. In
fact, because a generator operates at a constant speed and has flexible
connections, vibration control is comparatively easy. For a Westerbeke three
cylinder generator, running at 1800 rpm, your generator should have mounts
which
will deflect at least .25" with the engine at rest. To get this deflection in
a
minimum space, you need rubber mounts in shear rather than rubber in
compression. This will provide a bit more than 90% isolation. The exact mounts
to use
depend upon the engine's weight and operating rpm. For this purpose, bigger is
not better. I would probably use channel mounts with the rubber in shear and
retaining bolts to keep the engine in place in case of capsize. If that
happens, of course, you will have bigger problems than generator vibration
control.
You do not need marine engine mounts for this application. Marine mounts are
designed to handle thrust loads while providing minimum engine motion. Typical
marine mounts deflect only about .1". Any more than that and you need a
flexible coupling between the engine and the driveshaft. Besides marine mounts
are
up to 10 times more expensive than standard industrial vibration control
mounts.
The engine should be mounted on a solid and heavy base. Fiberglass or plywood
are certainly strong enough but what really counts is mass. A reinforced
concrete slab, weighing a couple of hundred pounds would be the best.
I'm sending you a short memo on engine vibration control off list. While
primarily intended for propulsion engines, the prescriptions work equally well
for
generators. If anyone else wants a copy, just drop me an e-mail.
Larry Z
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