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Old 27-06-2016, 16:28   #1
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Genset engine mount help, do they have to be marine?

The boat I have bought has an 8kva genset onboard with a 17hp 3 cyl kubota attached
The engine mounts are well and truly shot and need replacing.
Is there any reason why they must be marine ones?
I am being quoted around $70 to $100/corner for isoflex mounts whereas new toyota hilux ones would cost around $10/corner.
The Engine wont know its in a boat.
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Old 27-06-2016, 16:53   #2
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Re: Genset engine mount help, do they have to be marine?

Your engine mounts dont need to be marine. They do however need to be sized to not bottom out and be oriented to ensure the 6 degrees of freedom of your genset are controlled and dont ground out

I can achieve this with just about any mount, some simple measurements and a little vector math.

You want to counteract starting torque and the imbalance while running. Most 1 to 4 cyl generators are inherently unbalanced which makes it relatively easy to view the max deflections.

Orient the mounts to counteract these motions. Measure max and min deflections. Ensure they are within the design range of the mount. Ensure the mounts aren't inadvertently ground out by incorrect alignment.

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Old 27-06-2016, 17:33   #3
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Re: Genset engine mount help, do they have to be marine?

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Originally Posted by leftbrainstuff View Post
Your engine mounts dont need to be marine. They do however need to be sized to not bottom out and be oriented to ensure the 6 degrees of freedom of your genset are controlled and dont ground out
Thanks for the reply.
6 degrees of freedom?
Is this a measurable thing or are you just saying it needs room to move?

Below is a picture of the current buggered mounts, polyflex I believe and the toyota on the right
Probably have to cut off the small post on the toyota ones.
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Old 27-06-2016, 17:46   #4
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Re: Genset engine mount help, do they have to be marine?

Are you sure your mounts are shot? They can often be very soft which is good as they don't transfer vibration. Just wondering. The ones I bought for my 2 cyl Kubota were like $9 each on line... 10 years ago. They come in different load ratings etc.
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Old 27-06-2016, 17:57   #5
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Re: Genset engine mount help, do they have to be marine?

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Are you sure your mounts are shot? .
I'm guessing you never clicked on the picture to expand it out.

They should look like this

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Old 27-06-2016, 17:59   #6
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Re: Genset engine mount help, do they have to be marine?

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Originally Posted by Simi 60 View Post
I'm guessing you never clicked on the picture to expand it out.

They should look like this
It wont expand for me! I was just checking on line and they have made this a real racket haven't they? These are halfway reasonable, but not US. WaterMota Small Engine Mount - Sheridan Marine
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Old 27-06-2016, 18:21   #7
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Re: Genset engine mount help, do they have to be marine?

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It wont expand for me!
Hope that works
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Old 27-06-2016, 18:51   #8
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Re: Genset engine mount help, do they have to be marine?

That's ugly!
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Old 28-06-2016, 11:29   #9
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Re: Genset engine mount help, do they have to be marine?

My 10kva genset has a full sound prof enclosure and the whole thing is mounted on 4 air suspension pads. Similar to overload air suspension used in camper truck set ups. The previous owner did this. Bless his soul. This really dampens noise and vibration of the 3 cyl. Kabuta engine. The mounts don't attempt to restrict the natural vibration of a 3 cyl. diesel. Saves on engine mounts.
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Old 28-06-2016, 11:56   #10
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Re: Genset engine mount help, do they have to be marine?

Engine mounts are "tuned" in that they need to be of the right durometer if I got that right, that is not too soft, or too hard, Goldilocks soft.
If you get that right, and they fit, that is all there is to it.
My Yanmar has two different mounts, the harder ones go on the starter side of the engine for example.

When I installed my gen, I bought four extra mounts from Nexgen and double isolated the genset, it does help as a lot of noise is actually vibrations transmitted into the hull.
If I dive the boat, the area immediately under the generator is so loud, its horrible, you can't stand it.
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Old 28-06-2016, 12:31   #11
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Re: Genset engine mount help, do they have to be marine?

Your engine mounts do not need a marine rating, but need to be the correct version for your engine.

The PO of our vessel took it to a new level, and it works very well: The enclosed Panda 10kw generator [3 cyl Kubota diesel] is mounted [via its factory engine mounts] to a 1/2 inch [painted] steel plate [of slightly larger footprint] which is mounted to the rails built into the hull with engine mounts.

The result is the generator is attached [using anti-vibration mounts] to a ~200lb mass of steel, which is attached to the hull using anti-vibration mounts.

The net effect is very little vibration is conducted into the vessel [above and below water] Likewise for sound [the gen is in the enclosed, soundproofed engine compartment and has a split exhaust.]

I suspect this sandwiched, isolated mass approach also reduces the load on the anti-vibration mounts- perhaps increasing their longevity. [None show any signs of needing replacement in over 2300 hours of operation. [The boat came from the tropics and has air conditioning...]

And since a split exhaust is used [one each above and below the waterline] you cannot detect the gen is running when on deck [via vibration or sound] unless you cock your ear over the side where the exhaust ports are and listen for the bubbles it is blowing... When kayaking up to our boat with the gen running, you cannot detect it until within 10-15 ft or so of the side with the exhaust ports... any further away and there is no discernible sound.

If we ever frequent waters where there are other boats at anchor, we are prepared to be the type of neighbors we would prefer...

In case this is of interest since you are replacing your mounts.

Cheers!

Bill
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Old 28-06-2016, 14:06   #12
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Re: Genset engine mount help, do they have to be marine?

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If we ever frequent waters where there are other boats at anchor, we are prepared to be the type of neighbors we would prefer...

In case this is of interest since you are replacing your mounts.

Cheers!

Bill
This also should be pretty quiet when running
Mounted to metal frame in a heavy ply box which is double insulated and inside a heavy trawlers engine room.

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Old 28-06-2016, 15:06   #13
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Re: Genset engine mount help, do they have to be marine?

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Originally Posted by Simi 60 View Post
I'm guessing you never clicked on the picture to expand it out.

They should look like this

I have these engine mounts on my main engine and the polymer elastomer (blue part) has disintegrated and I to am searching for an auto engine mount alternative. Whatever the polymer in the above mount is it is not a good elastomer as the engine transmits a lot of vibration into the hull when it is idling.
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Old 28-06-2016, 15:59   #14
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Re: Genset engine mount help, do they have to be marine?

be careful you blokes / marine mounts will hold the weight of the genset during a major knockdown or roll without the genset braking loose and going through the hull or into the cockpit / if you are using non marine rated mounts suggest a safety strap or chain to keep the unit in place while dodging ships in the gulf stream. ha ha
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Old 28-06-2016, 18:55   #15
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Re: Genset engine mount help, do they have to be marine?

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be careful you blokes / marine mounts will hold the weight of the genset during a major knockdown or roll without the genset braking loose and going through the hull or into the cockpit / if you are using non marine rated mounts suggest a safety strap or chain to keep the unit in place while dodging ships in the gulf stream. ha ha
As the Gulf Stream is 12,000 NM away I am guessing i'll be ok, but I take your point.
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