Beneteou 323 Mast and boom shaking at low rpm and idle

[Sail-la-vie]

Hello. I am new to this forum and new to sailing. I recently purchased a Beneteou 323
I noticed recently at idle motor speed and low rpm The mast shake and boom shakes.
At higher rpm over 1000 rpm the shaking goes away and at no engine power. The shaking goes away.
Any idea?
Thanks in advance
Jason

 

[stuartwineberg]

Probably just resonance. We have a rattle in the companion way steps at one particular speed. As long as it stops above tick over speeds you should be ok.

 

[MontyMariner]

Might be prop shaft bearing.

 

[Sail-la-vie]

Thanks for the response
The shaking is the same at idle motor and low rpm
Thank you

 

[Refueler]

I delivered a Bavaria Match 35 and we had similar - in fact it was so bad we started to wonder if there was an engine mount failed .... but it was a keel stepped mast.

Sometimes adjustment of stays can alter the resonant frequency ... as can adjusting the halyards / kicking strap ... keeping of course to specs tension.
Many things can alter the resonance .. how tight boom mainsheets are when motoring ... is there slack in the boom attachment to mast ... are engine mounts worn out ... shaft and bearings ... incorrect fuel mix on engine causing poor firing ... so many little things can add up .. that it can become a real 'adventure' to get to a solution.

My first area to look is at the base and boom attachments. Check tension of stays ... Adjust a little and test run. Work through mast matters and then if no joy - progress to engine related ...
Watch very closely engine when starting and idling ... see if the engine is moving more than just the normal flex of mounts ... if you can see the shaft - see what it does when in gear and altering throttle ...

It will usually take time and a combo of little things to reduce the resonance ...

 

[Oily Rag]

I recently saw a similar case that was solved by shortening the topping lift and raising the boom by only a few inches. Good luck!

 

[Stemar]

If fiddling with the adjustment of the rig doesn't do it, maybe increase the idle speed a little. It shouldn't take much to stop the resonance.

 

[Sail-la-vie]

Thank you folks. I have tried to depress the standing riggings for stay and back stay. Nothing works. The vibrations only totally stop at forward or reverse rom over around 1000 rpm. At idle is the worst. I’ll try to check the engine. Thanks. I’ll update my finding
Thanks so much

 

[greeny]

Hello. I am new to this forum and new to sailing. I recently purchased a Beneteou 323
I noticed recently at idle motor speed and low rpm The mast shake and boom shakes.
At higher rpm over 1000 rpm the shaking goes away and at no engine power. The shaking goes away.
Any idea?
Thanks in advance
Jason

Is this happening when in neutral or when in gear?

 

[Alex_Blackwood]

Hello. I am new to this forum and new to sailing. I recently purchased a Beneteou 323
I noticed recently at idle motor speed and low rpm The mast shake and boom shakes.
At higher rpm over 1000 rpm the shaking goes away and at no engine power. The shaking goes away.
Any idea?
Thanks in advance
Jason

All engines have a resonant frequency. This occurs at different revs in differing installations. The same engine in a different boat may be resonant at different revs. Just don't run at that speed. There are also Harmonic frequencies ( some may say they are the same thing ) to be considered. These can cause undue vibration. I know of a case where incorrect installation of the engine mounts resulted in harmonic vibrations causing the springs in the engine injector pumps to fracture. Just saying things to consider, may be worth checking the engine installation.
Edit. Just to say that on large ships with reciprocating motor engines this is known as "Critical Revs" and is outside of the normal operating range of the engine.

 

[greeny]

Is this happening when in neutral or when in gear?

There is good reason I ask this, I owned a 323 for 10 years and experienced similar and mine was entirely due to prop issues. Every thing vibrated, boom, locker lids, crockery, false teeth.

 

[Neeves]

I don't quite understand the opening post.

Low revs, out of gear, when the prop should be stationary - is the prop still slowly turning. Maybe the issues are with the engine control/Morse cables.

Is there some fouling on, damage to, the prop.

This is apparently a recent purchase - what did the surveyor say?

Jonathan