Deadening that dreaded donkey

The dreaded Iron Top Sail we sometimes have to rely on.....

Deadening that dreaded donkey

Postby Simon Head » Tue Mar 31, 2009 8:13 pm

Has anyone managed to develop a system to quieten down the donkey?

I have a 5hp mariner 4 stroke which is noisey in the cabin when being used- has anyone devised a way to sound proof this?

I am thinking of resolving this once and for all by using vibration mounts under the motor mounting bracket and rubber beneath the outboard clamps - has anyone already done it?
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Postby Dennis » Wed Apr 01, 2009 10:19 pm

Hello Simon

I like the idea of the anti vibration mountings. I have done a quick search on Google and found that RS Components sell a comprehensive range of cylindrical rubber mounts with a choice of threaded studs at each end. This I think would be a neat solution, although I do not know how effective it would be, until someone tries it.

I remember that someone has used rubber for this purpose because it got mentioned during posts (on Yahoo) last October (I think) when I was having on line discussions re the best outboard for a CC19. I think there was even photos of the arrangement.

Hope this helps

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Postby Dennis » Wed Apr 01, 2009 10:30 pm

Hello again Simon

I have checked on Yahoo, it was Bram Marck
CC59 "Kerina" who has used rubber to reduce vibration.

I see Bram is now a member of this group so he may be able to give some advice.

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Re: Inboard / Outboard Engine Toughts.

Postby Timbre 19 » Tue Feb 15, 2022 10:12 am

Hi, Jorgen here.
About engine vibrations, old subject in the forum but found this as inspiration: Volvo Penta MB2A 50S.
A Honda 2-cyl. 4-stroke 7.5 hp outboard + a VP drive with separate exhaust. Was installed inside the boat, weight only 29 Kg.
CC19 outboard is outside in a well, simpler. And exhaust is already solved but cooling water sensor are needed.
But if one want to sacrifice an 4-6 hp outboard, add 4 rubber cushions on a plate placed under the Bottom Covling.
Should probably be placed more submerged, and unfortunately the rig must be shorten (not long or short, instead super short).
And maybe a soundproof narrow hood at the height of the benches would be nice and becomes a separate table?
Weight? Adding weight, yes, but also removes weight from the engine + the original bracket. The same maybe.
There are problems to solve, and maybe there are serious things I missed, but the thougt attracts me.
And if someone came across a similar solution with an outboard, please let me know.

Link to a VP pdf:
https://www.fram.nl/yachts/pionier/MB2A_50S_1978_en.pdf
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Re: Deadening that dreaded donkey

Postby chrisr » Tue Feb 15, 2022 1:35 pm

Beware, it's not as simple as rubber feet on your motor... although they will probably help?

I'm no expert, but...
Because what we are complaining about is energy, it may be structure-born (vibration) and/or air-borne ("noise").
Airborne noise may then in turn excite remote structure....

There's a whole science in isolating or detuning vibration, and also in "deadening" structure.
In this case likely to be the grp outboard well, coamings, transom etc?

I use ear plugs, or industrial ear defenders if I'm really being bothered :)

Apparently, even the whine of early electric outboards (particularly those driven by extended gear drives) when amplified by structure is enough to madden some, particularly those who were lead to expect a "silent drive".
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Re: Inboard / Outboard Thoughts.

Postby Timbre 19 » Fri Feb 18, 2022 8:05 am

Hi, Jorgen here.

Thanks for reply. No, rubber cushions do not solve all problems, but it is still proven as part of the solution of sound and vibration problems?
Uses earplugs occasionally, but finds it a negative and strange solution on board a sailboat. No engine at all, experience anyone?

If the outboard engine was placed as is meant, outside the cockpit, the above problems would have been less. But do not want to
move out the engine. Because even though you are forced to dine with it, the mounting on the inside has great advantages. More beautiful boat,
service-friendly, deeper position on the propeller at seagoing and shorter boat when transporting to name a few.

Therefore, the idea attracts to keep the engine in the cockpit but get it placed lower and arrange a narrow soundproof cover. Gas via cable, then you also avoid
the Tiller that takes place and disturb. Did test 3 summers with that solution, worked great (felt like a bigger boat, not a dinghy!), but reassembled at planned sale of the engine.

Also attach a picture showing a very simple anti vbration equipment with rubber beneath the clamps, see picture. Made a short start in
the garage (winter now), could not feel any vibrations in the bracket, but longing after a test at sea with higher stress and rpm.

Addition: 2022-02-24 : And also the idea (nothing else so far) about a shorten 4 - 6 hp Outboard engine + a soundproof hood/table and rubber cushions. Yes, problems are to be solved.
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Re: Deadening that dreaded donkey

Postby zimp » Sat Mar 05, 2022 5:35 pm

Talking about the Volvo Penta MB2A 50S...
We've had a Honda 2cyl 8HP in our CC19. This is an very quit and low vibration engine. We replaced it with an engine with less weight and less drag, a Yamaha 1cyl 6HP. But the Yamaha is much more noisier compared to the Honda.
Bert, CC19, #004, s/y Zimp
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Re: Outboard thoughts become reality

Postby Timbre 19 » Thu Apr 14, 2022 10:05 am

Hi, Jorgen here, thanks for reply. And I am still inspired of the old Volvo Penta MB2A 50s with the silent Honda engine.
Has shorten this text 15 april 2022.

Has now followed my idea to reducing the dominance of the outboard according to previous posts.
Began to shorten the rig. And the new bracket of stainless steel is made so that the outboard itself is lowered.
So the top of the engine has fallen 150 mm and is now under the benches, which was the goal.

The weight of the shortened outboard + the new bracket is a total of 23.7 kg (no fuel). Before modification it was 24.5 + 5 kg = 29.5 kg.
Nice difference, but a soundproof hood/table is not done or included yet, weighs probably max. 3 kg.

Anti vibration rubber between bracket and boat + between bracket and outboard is mounted.

Costs so far are modest, about 45 Euro.
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Re: Shortened outboard now mounted in cockpit.

Postby Timbre 19 » Fri Apr 22, 2022 7:22 am

Hi, Jorgen here again.

Shortened, lowered and sound + weight-reduced outboard engine now mounted in cockpit.
Should be tested if the outboard works well before the soundproof hood is manufactured, if it is needed.
One tiller, and hand / foot gas, can be useful in narrow situations if one want to stand up, have tested before.


Added text and photo after table making - 2022-04-29:

The project "the shortened outboard" is finished, has tested a bit, seems to work. Satisfied so far, weight loss is nice.
Now have a small boat with a small table! Dimensions 45x30 cm, weight 0.7 kg. Varnished board with teak frames.
10 seconds to mount / remove, but can also be left while sailing or motoring.
One wonders if it is possible now to make a 007 martini at idle?

Sound level decreased with lowered motor + double rubber insulation so larger hood has been excluded, would take up more space and weighed more.
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