Mounting an outboard on a boat

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    Posted: 16 Jan 2022 at 11:18pm
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So........on the final stretch of what seems a very long road in my Condor Craft refurbishment. 

Due to mount a 50hp 2 stroke Johnson onto my raised transom - is it beneficial to sandwich a Polypropylene transom pad between the two? Logic says it will reduce possible vibration but has anyone had/used this method and what was the results?


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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 17 Jan 2022 at 8:16am
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Pads are sandwiched for alloy boats... corrosion etc.
Back in the day, older boats including 'glass often had a pad, usually wood. I believe was to spread the load, any stress on the transoms.
Also they where often wedges , back in the day on fixed and manual  tilt motors. Set the trim angle at low cruise speeds. Hurt the hole shot, getting over the bow wave, espec if under powered. Keep in mind back then (pre mid 80s sometime) the engine hp rating was taken at the crank, not as now at the prop.
If I had the pad, I would put it in. not going to do any harm and if anything maybe help absorb vibration etc.

From memory , the johnson spec for top transom hole is/ was 3/4 or 1" from top of transom.  And ball park for caviation plate will be a shade above the line of the hull. 0 to 1/4"

When measure, measure the vertical, not the length on the transom as it is 12.5 deg off vertical from memory.
 Hope some of the above helps.
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Post Options Post Options   Likes (0) Likes(0)   Quote funandfunction Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jan 2022 at 12:06pm
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Vibra-Stop Engine Mounting Systems | Dixon Manufacturing Ltd.

There's a bit more involved  if the aim is to isolate vibration.
This system uses urethane bushes through the transom.
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If there is a vibration issue, I would be looking at fixing what causes the vibration... things like prop balance, gearbox bearing, engine tuning etc.

Urethane bushes / pads these day tend to be for corrosion issues between metals.

 There are 3 types 'vibration'
That caused by things out of balance and eventual trash bearings and seals etc.
resonation.. resonation doesnt get 'fixed ' by insulating , but rather by absorbing panels stuck to the main panels..
As per vehicles that have a thick (usually tar) section glued to the center of a door or trunk side panel. It doesnt need to cover the whole panel.
 Noise insulation , which is reduced by sound insulation as thru floor and and firewalls of cars.

 Personally if I clip say a prop, and have, I would far prefer to feel such vibration than have it hidden.. Hidden I will end up with a bill runing into several may + $1000.
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Post Options Post Options   Likes (1) Likes(1)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 21 Jan 2022 at 9:20am
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Vibration pads will never hide an out of balance prop. Every outboard motor will generate a high frequency vibration. That vibration will be transmitted through the hull and will cause some resonance. It's those motor vibrations that the vibra stop type controls are designed to eliminate, much like the engine mounts on a car. Those who have ridden a motorcycle which has the motor bolted directly to the frame will know what I mean.
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Completely up to you and probably doesn’t need to be the full vibration stop setup. I do see a lot of plastic outbourd mounting plates used on new boats but I couldn’t see just a plastic outbourd mounting plate absorbing much vibration. Tidies up the motor installation and does help to guard against from any clamp damage you may get around the outbourd later on after a bit of use.

Don’t see any negative is using a nice tidy mounting plate.
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 22 Jan 2022 at 8:47am
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Vibration pads will never hide an out of balance prop.

Disagree from actual experience.
 Prop balance is critical, just like a car tyre a little out of balance..
Slightly out of balance will be absorbed, has have experienced in the past while re propping
A prop well out of balance will not be absorbed.
 A prop slightly out of balance will still screw bearings seals etc..
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Post Options Post Options   Likes (0) Likes(0)   Quote Pcj Quote  Post ReplyReply Direct Link To This Post Posted: 22 Jan 2022 at 11:49am
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Have a mounting plastic plateii believe it is more for angle motor.yoy will still get vibration through vessel as bolts through motor through plate and tightened against Hill vibration transfered through bolts.i would look at mounts for wear on motor it self prop blade damage.
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Post Options Post Options   Likes (0) Likes(0)   Quote Pcj Quote  Post ReplyReply Direct Link To This Post Posted: 23 Jan 2022 at 4:48am
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Originally posted by Steps Steps wrote:

Vibration pads will never hide an out of balance prop.

Disagree from actual experience.
 Prop balance is critical, just like a car tyre a little out of balance..
Slightly out of balance will be absorbed, has have experienced in the past while re propping
A prop well out of balance will not be absorbed.
 A prop slightly out of balance will still screw bearings seals etc..
slightly out of balanced tyre ,you wont notice if on rear but you will slightly on front,but the wearing is the issue,even after 100km .
So a out balanced prop or damaged shaft,wont take long before more damage done
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Post Options Post Options   Likes (0) Likes(0)   Quote smudge Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan 2022 at 7:29am
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Originally posted by Steps Steps wrote:

Vibration pads will never hide an out of balance prop.

Disagree from actual experience.
 Prop balance is critical, just like a car tyre a little out of balance..
Slightly out of balance will be absorbed, has have experienced in the past while re propping
A prop well out of balance will not be absorbed.
 A prop slightly out of balance will still screw bearings seals etc..

Yes I guess there is a point where you won't notice it.
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Post Options Post Options   Likes (0) Likes(0)   Quote OneWayTraffic Quote  Post ReplyReply Direct Link To This Post Posted: 24 Jan 2022 at 11:44am
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Just like Cancer. Just because you can't notice it doesn't mean that it isn't killing the motor. 
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