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Old 01-23-2012, 10:27 AM   #1
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Motor Mounts

Does anyone have this sort of set up as far as motor mounts go?

There doesn't seem to be any vibration damper. the mounts hang over the stringers and seem to be hard mounted with just bolts.

I was thinking of changing the mounts to provide for quiet and less vibration.

I'm thinking if I changed anything I would have to reconfigure the entire mounting system.

The 4 th pic shows the actual mount as far as where the bottom of the engine is mounted to the stringers.

SD



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-- Edited by skipperdude on Monday 23rd of January 2012 11:35:06 AM
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Old 01-23-2012, 11:35 AM   #2
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RE: Motor Mounts

I'm no expert, but that does not look like a system I would want to rely on.* It looks like the set bolts make contact with glassed over wood, and are chewing into it.* At a minimum, I would put steel pads on either side of the mount so the stringer is compressed by something other than the set bolt, but even then, relying on compression rather than a positive mechanical attachment seems sketchy.
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Old 01-23-2012, 11:45 AM   #3
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RE: Motor Mounts

Quote:
Delfin wrote:
I'm no expert, but that does not look like a system I would want to rely on.* It looks like the set bolts make contact with glassed over wood, and are chewing into it.* At a minimum, I would put steel pads on either side of the mount so the stringer is compressed by something other than the set bolt, but even then, relying on compression rather than a positive mechanical attachment seems sketchy.
*Agreed. Bear in mind this system has been on the boat for 38 years.

It does seem an odd way to mount a motor.

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Old 01-23-2012, 11:49 AM   #4
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RE: Motor Mounts

Not the best photo showing the Coot's motor mounts (picture taken to document small oil leak, since fixed), but it does show either half of the front and back starboard mounts.

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Old 01-23-2012, 11:52 AM   #5
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RE: Motor Mounts

The engines in most of the lobster boats around here are hard mounted to the stringers, although I can't recall if the setups resemble yours.
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Old 01-23-2012, 11:55 AM   #6
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RE: Motor Mounts

Found this backside view.

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Old 01-23-2012, 11:59 AM   #7
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RE: Motor Mounts

While I have very limited experience and exposure to marine engine mounts, I agree with Carl. That does not look like a very good setup. The motor mounts on our boat and on the few other boats where I have paid attention to them, consist of a lower half that is mounted to the engine stringer and an upper half with a hard rubber doughnut, if you will, between them. The mounts on the engine block sit on adjustment nuts on a heavy, threaded rod in such a way that the weight sits on the upper half of the mount that's fastened to the stringer. These mounts are not soft because an engine mount that allows the engine to move around a bit--- like a car's engine mounts--- will not keep the engine in alignment with the propshaft. See photo.

The fiberglass engine stringers in our boat are capped with heavy aluminum extrusions that are solidly secured to the fiberglass stringers underneath and the mounts sit on the heavy extrusions, not the fiberglass itself. I have no idea if this is typical of other makes of boat as well.

An alternative if one want's to really reduce the vibration transmitted to the boat is to use--- like a car--- a flexible connection to the prop shaft, usually in the form of a U-joint and a sliding section of shaft. Now the engine can be mounted on much softer mounts because it no longer has to be held in rigid alignment with the shaft. The flexible system I am most familiar with by name is AquaDrive http://www.aquadrive.net/
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Old 01-23-2012, 12:24 PM   #8
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RE: Motor Mounts

The mounts that you folks are showing are the one's i was hoping to install but it really seems like a mojor refit to accomplish something like this.

After 38 years, I guess I will have to go with what I have.

I just found it strange to have the motor hard mounted and for what purpose?

SD
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Old 01-23-2012, 12:35 PM   #9
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RE: Motor Mounts

Quote:
skipperdude wrote:

I just found it strange to have the motor hard mounted and for what purpose?

SD
*Well, if the hard mount is done right and the vibration is not detrimental to the boat, you never have to change the engine mounts.* Mounts like the ones in the photo I posted wear out over time.* The rubber doughnut gradually collapses and eventually it will collapse far enough to allow metal-to-metal contact beween the upper and lower halves.* At that point the mounts have to be changed.

While it's not rocket science to do this, you do have to disconnect the prop shaft(s), figure out how to jack up the engine(s), and then after the new mounts are installed you have to re-align the prop shaft(s).*

After 25 years the mounts in our boat were getting really tired in 1998.* We knew this when we decided to buy the boat, but they went another five or six years before a surveyor said, okay, that's it.

Like I said, the process to change them is not rocket science but I don't have the time, experience, or tools to do the job easily, particularly in the confines of an engine room.* So we hired the job out to our local diesel shop.* They said it would take two days of work for two people to do both our engines, and that's exactly what it took.* And they did it right the first time, so for us it was well worth the money.

Someone with more time, more experience, the right tools for lifting the engine(s), aligning the shaft(s) and so on, could easily do it themselves if they had a mind to.

But witha hard-mounted engine, which Dave says a lot of lobserboats use, it's not an expense or down-time that will ever be incurred.
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Old 01-23-2012, 01:03 PM   #10
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RE: Motor Mounts

Quote:
Marin wrote:skipperdude wrote:

I just found it strange to have the motor hard mounted and for what purpose?

SD
*Well, if the hard mount is done right and the vibration is not detrimental to the boat, you never have to change the engine mounts.*

But witha hard-mounted engine, which Dave says a lot of lobserboats use, it's not an expense or down-time that will ever be incurred.

*I guess it is one of the lessons learned when refitting a commercial boat built for work and not pleasure.

It sounds like the boat is just set up that way I think I will just let it go.

*Great insight as to methods of mounting an engine.

"I did Not Know That."* Thanks

SD
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Old 01-23-2012, 01:07 PM   #11
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RE: Motor Mounts

In my previous post I worded it badly. After replacing worn engine mounts you don't "re-align the prop shaft(s)" you re-align the engine(s) with the propshaft(s).
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Old 01-23-2012, 01:08 PM   #12
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RE: Motor Mounts

The engine in Pioneer is hard mounted with heavy fabricated steel plates sitting on top of, and through-bolted to the engine beds. I don't have a pic but they are a bit more substantial than what you have shown. Of course, the engine is 14.6 litres (Cat 3406) and* heavy so they need to be large.

The engine has been in the boat for 32 years and, apart from a bit of surface rust, they seem fine. If everything is fine after 38 years, I wouldn't want to change things too much. Shaft alignment, once correct, never needs to be adjusted.
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Old 01-23-2012, 04:26 PM   #13
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RE: Motor Mounts

My new to me aluminum boat has a hard mounted Perkins. Yes there is quite a bit of noise, no vibration. A noise reduction would be nice, but it is not as simple as swapping out the mounts, and then there is the maintainence issue.

Earplugs for those in the pilothouse?
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Old 01-23-2012, 06:12 PM   #14
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RE: Motor Mounts

Quote:
charles wrote:
If it aint broke dont fix it. There will always be plenty of "things" to fix.
Actually the system that is on your boat is way more substantial than two screws into the stringer on the so called soft mounts---what is on CCRIDER and has been there since 1981 with no problem
Just my anecdotal evidence.
*Some things if they look suspect are ALWAYS better fixed in port....hopefully the port of your choice and better*than out at sea.
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Old 01-23-2012, 06:19 PM   #15
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RE: Motor Mounts

Quote:
skipperdude wrote:
It sounds like the boat is just set up that way I think I will just let it go.
Don't know your boat's work history or how hard it was worked but if those mounts did the job all those years*with no problems and they aren't causing you any problems now I cannot think of a reason to change the setup.

If the level of vibration is unacceptable--- and you haven't said that it is--- then there might be a reason to go to something else.* But whatever you did it would be expensive since it would involve modifying the stringers and most likely the block part of the mounts too.* But if vibration, noise, and alignment are not issues, as Charles said, if it ain't broke, don't fix it.
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Old 01-23-2012, 06:32 PM   #16
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RE: Motor Mounts

What kind of engine and HP?* 90 percent of the boats out there just have some steel angle through bolted to the stringers with any one of dozens of isolation mounts readily available to support the engine.* Relatively cheap and simple to do with a little knowledge of what's needed.

MUCH preferable to relying on a system that may be on it's last legs orf questionable design and difficult to maintain.

In less than a day for not much more than the cost of the isolation mounts...you could have a much more conventional setup.
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Old 01-23-2012, 07:07 PM   #17
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RE: Motor Mounts

Quote:
psneeld wrote:
In less than a day for not much more than the cost of the isolation mounts...you could have a much more conventional setup.
*You think so?* From the photos of the current setup it would appear that to use "conventional" mounts like the ones most (?) boats like ours have he would need to have new block brackets designed and fabricated.* If he just sticks a conventional mount under the existing mount he'll have to cut down the stringers because the engine will sit too high for the prop shaft.

I know very little about the art of motor mounts, so I'm saying all this based just on the what seems to be the logic of what I see in the photos.

The engine mounts on our boat are one size too small.* This was done at the factory on all twin engine GB36s of this vintage because the*next size up*mount would put the header tank on each engine in contact with the underside of the cabin sole.* When we had to have our mounts changed, we looked into using the mounts of the same design but rated for the weight of the engine (and then some). Same mounting hole pattern but the mounts were*a little bit taller to accomodate the thicker rubber.* The only way we could have done this was to either have new block brackets designed and fabricated, or the engine stringers would have had to be cut down.* Either choice was an expensive proposition.

In the end, after consulting with our diesel shop as well as the head of engineering at Northern Lights/Lugger who had a lot of experience re-engining boats, designing mounts, etc. we decided to use the same slightly undersized (for the weight) mounts.* The reasoning of our advisors was that since the original mounts had held up for some thirty years before the rubber had become too tired, we'd get another thirty years out of new mounts that were exactly the same.* So there was not much value in spending a big bunch of money to do something that didn't make much practical sense to do.

Which is why I wonder if the situation on SD's boat is similar?

SD--- Are your current mounts looking suspicious to you in terms of integrity*or are you just wondering why they are the way they are?
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Old 01-23-2012, 10:10 PM   #18
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RE: Motor Mounts

Quote:
skipperdude wrote:
I just found it strange to have the motor hard mounted and for what purpose?

SD
Your mounting setup was the way all wooden fish boats were done for many years.* There really wasn't a need for soft mounts because the wood construction naturally absorbed a lot of vibration.

With the advent of "harder" hull substances (particularly metal), the need for soft mounts grew.

Quick story on my old 40' Ed Monk, Sr. bridgedeck sedan, after repower with a diesel mounted direct to wood stringers, ended up with a vibration near cruise rpm.* Raised the engine, fabricated new mount supports, and installed rubber doughnut mounts.* Result was that the vibration simply moved about 150 rpm, fortunately a little further from desired cruise rpm.* Was probably just lucky because you can spend a lot of time/money and just end up chasing the same vibration to a different place.
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Old 01-24-2012, 03:25 AM   #19
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RE: Motor Mounts

Exactly, SD, I am definitely in the "if it aint broke, don't fix it" camp, also.
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Old 01-24-2012, 05:26 AM   #20
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RE: Motor Mounts

Quote:
Marin wrote:psneeld wrote:
In less than a day for not much more than the cost of the isolation mounts...you could have a much more conventional setup.
*You think so?* From the photos of the current setup it would appear that to use "conventional" mounts like the ones most (?) boats like ours have he would need to have new block brackets designed and fabricated.* If he just sticks a conventional mount under the existing mount he'll have to cut down the stringers because the engine will sit too high for the prop shaft.

I know very little about the art of motor mounts, so I'm saying all this based just on the what seems to be the logic of what I see in the photos.

The engine mounts on our boat are one size too small.* This was done at the factory on all twin engine GB36s of this vintage because the*next size up*mount would put the header tank on each engine in contact with the underside of the cabin sole.* When we had to have our mounts changed, we looked into using the mounts of the same design but rated for the weight of the engine (and then some). Same mounting hole pattern but the mounts were*a little bit taller to accomodate the thicker rubber.* The only way we could have done this was to either have new block brackets designed and fabricated, or the engine stringers would have had to be cut down.* Either choice was an expensive proposition.

In the end, after consulting with our diesel shop as well as the head of engineering at Northern Lights/Lugger who had a lot of experience re-engining boats, designing mounts, etc. we decided to use the same slightly undersized (for the weight) mounts.* The reasoning of our advisors was that since the original mounts had held up for some thirty years before the rubber had become too tired, we'd get another thirty years out of new mounts that were exactly the same.* So there was not much value in spending a big bunch of money to do something that didn't make much practical sense to do.

Which is why I wonder if the situation on SD's boat is similar?

SD--- Are your current mounts looking suspicious to you in terms of integrity*or are you just wondering why they are the way they are?

*Yep...I'm sure.
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