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Old 01-11-2017, 04:18 AM   #1
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Cushyfloat Engine Mounts

Trying to find the correctly sized Cushyfloat Mounts for a Ford Sabre 120 (same as Lehman) with a PRM750C gear box.

Gearbox to shaft has a R&D MARINE Flexible coupling installed.

I believe that the ratings of the front and rear mountings should be different to compensate for the weight of the PRM750C bolted to the back of the engine.

Any part numbers and advice from those that have used them please?
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Old 01-11-2017, 04:40 AM   #2
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You can start here

Cushyfloat Product Range - Trelleborg IAVS

If someone does have your engine/gear setup and are pleased with the performance you will need to know the shore of the mounts they have if you want to duplicate. They will have to look here for the number

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Old 01-11-2017, 12:23 PM   #3
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Most engines without a gear installed have the center of mass slightly behind the center of the engine block. Mostly due to the flywheel. Then add the gear and cg of the package moves even further aft.

Often I have to estimate where the center of mass is using a little math and a little visual estimation. Then measure where the mounts are located, then using total mass calculate the force on each mount.

Most times the force per mount is not equal, but close enough that you can spec the same durometer mounts for each.

Metalastic has loading charts available on their site.
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Old 01-11-2017, 12:37 PM   #4
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Nicely said Ski, right on the money.

What this means: "where the mounts are located"

It makes a difference if the aft mounts are located on the engine block location or the gear location as to how they mounts are loaded.

The link in my post is to the Cushyfloat loading chart mentioned




Quote:
Originally Posted by Ski in NC View Post
Most engines without a gear installed have the center of mass slightly behind the center of the engine block. Mostly due to the flywheel. Then add the gear and cg of the package moves even further aft.

Often I have to estimate where the center of mass is using a little math and a little visual estimation. Then measure where the mounts are located, then using total mass calculate the force on each mount.

Most times the force per mount is not equal, but close enough that you can spec the same durometer mounts for each.

Metalastic has loading charts available on their site.
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Old 01-12-2017, 05:39 AM   #5
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Thank you for the replies.

Engine mounts are in the standard location for the Ford engine and there are no mounts on the gearbox.

From what I have read online, weight of the Ford Sabre 120 is 1092lbs and the PRM is 250lbs (approx 100lbs heavier than the traditional Velvet Drive) so this should be quite close to setups on many boats on TF.

Hoping that someone with a similar setup that has tried and tested the mounts will chime in.
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Old 01-12-2017, 07:30 AM   #6
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Converting your total weight of 1,350lb, converting it to Kg = 613Kg. Divide that by 4 mounts and round up a little and you get 160Kg per mount.

Just going on static weight and using the column for thrust taking applications (*M-Max) the 17-1609-65 has a max capacity of 210 Kg.

The envelope for these mounts is pretty wide, so it would probably be "safe" to use this size for all 4 mounts. (There is a reserve capacity of 100Kg for the 2 aft mounts) If the after mounts are loaded a little more due to the gear weight they will just deflect a little less, but we're talking fractions of a mm. At this loading these mounts will deflect under a static load a little over 3mm.

The next capacity size up shore 75 has a max capacity of 315Kg and will deflect a full mm less at 160Kg loading.

Without center of gravity and exact mount locations in relation to C/G I doubt you're not going to get any closer. Hopefully there's a TF member with the same setup that will chime in.

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Old 01-12-2017, 01:50 PM   #7
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I have installed these on a lobster boat. I worked with Evolution Marine to engineer the right mounts. I highly recommend them, they can engineer and provide what you need. The customer will need to provide detailed vessel and drive system information.
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Old 01-13-2017, 06:54 AM   #8
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Thank you for the replies.

This is the feedback I received from the European supplier:

"Based on the given information we would recommend 2 x 17-1609-55 on the front side and 2 x 17-1609-65 on the gearbox side, in case of a height adjuster please use the 18-1609-HAD."

Makes sense to me since the front mounts are not supporting as much weight as the rear mounts.
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Old 01-13-2017, 08:16 AM   #9
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Yea, if rear mounts are on engine flywheel housing with gear hanging off the back, the loading on those goes up. Most installs stateside put the rear mounts on the gears, that evens up the loading front to back somewhat.
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Old 01-13-2017, 08:20 AM   #10
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Sounds right to me, I was pretty close. The 17-1609-55 has a max capacity of 140Kg for thrust taking applications. If they figured the weight loadings accounting for the shift in CG for the gear correctly that should be safely within capacity

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Old 01-13-2017, 08:31 AM   #11
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Installation Instructions:

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File Type: pdf Cushyfloat installation inst.pdf (117.8 KB, 12 views)
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Old 01-13-2017, 11:24 AM   #12
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Just a thought but w real soft mounts not far enough appart due to engine torque one side could "bottom out" with heavy loads applied.

I had a small Yanmar in my previous boat w extremely soft mounts. I suspect they acted like pogo sticks and bounced back and forth on eachother. I had a harmonic vibration that I never did solve ... kind-of a rum rum rum low frequency drumming. Hated it.
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Old 01-13-2017, 11:49 AM   #13
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Does anybody else giggle every time they read "Cushyfloat"?
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