Vibration felt on floor of boat.

[Fire1386]

I recently upgraded to a 25hp Evinrude for a little more power on some of the bigger water here. One thing I have noticed since is if I am running 3/4 to WOT I can feel a vibration on the floor. Not terribly annoying, but google searches suggest a problem with propeller (bent, chipped, cracked or loose) and the other suggestion was to check the rubber isolation mounts on the motor itself to see if these are worn out. The propeller was tight and didn't appear to be bent and couldn't see any cracks on it. Have not check to see if this has any type of rubber mounts yet. The motor is clamped onto transom and bolted also. Should I have put possibly a rubber spacer between the motor and transom to help with the vibration? I would think that vibration over the long haul would not be very good, so I was looking to see if I could eliminate most of it somehow. Thanks...

 

[Johnny]

if it were my boat, it would be the "chatter" from skimming
across the 2 inch ripples on the water @ WOT ...... a very nice sound !!!

do you get a different vibration when going with or against the wind ?
how about the water surface condition.





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[DaleH]

Some rigs will produce harmonics at certain speeds, even on fiberglass boats, so there likely could be absolutely nothing wrong with the motor. Speed up or down ...

 

[Fire1386]

Good points fellows thank you. The water surface at the time was pretty calm with just a mild breeze chop on the surface such as your 2 inch ripples Johnny. I will have to recheck the next time out to see if same vibration with or against the wind, I can't say for sure at the moment. This motor is on a 1992 Bass Tracker Pro 17 aluminum boat. It would be great if that is all the vibration is from, just trying to head off any possible problems down the road. Hopefully this is just from the increase in HP that I am not use to yet. Since a lot of the lakes around here have been HP restricted since I was a young pup, I am not familiar with bigger motors and conditions they produce on the water yet. I will report back after next run on one of the lakes here that now allow it. Kind of crappy weather here today, so maybe this weekend.....

 

[Johnny]

in an aluminum boat, the hull is like a drum head . . . .
the faster you go, the more pronounced the ripples will be.
to some of us, that is a very good sound !!!

have fun - be safe - enjoy the ride

HOPEFULLY, this is the case . . . .
IF it does turn out to be something in the motor or prop,
that could be a very serious issue.......
good luck

 

[DaleH]

Rotating parts will build up harmonics. Engine manufacturers take great pains to ensure the harmonic range is in the low range of RPMs where the motor is not typically operated. For motors, like when I was on a gas turbine jet engine turboprop line, we designed-in that harmonic range to be above the idle speed range, at a value that we simply passed through it when accelerating for take off RPMs. And it was well below any conceivable cruise, operating or descent RPM.

I didn't sleep at Holiday Inn last night, but I was on the Quality Team and participated in an engine test of the harmonic range and when it hit it ... that 2,000 shaft horsepower gas turbine (just over 4' long & 2' in diameter) literally exploded and fractured herself into tiny little pieces. So harmonics can be damaging.

But rather - for you and your tinboat - I would say you are experiencing more or less what I would term 'resonance', in that you've reached a RPM range or such of the motor that may be adding or inducing unwanted vibrations into your hull. I'd opine they are more disconcerting than damaging, but yeah ... I don't particularly like it either!

But you could check your motor for the integrity of the bushings or isolation mounts, etc ... even add a rubber pad where the motor clamps mount to the hull.

 

[Pappy]

One that has not been mentioned is a bent prop shaft. By all means check the prop and the shaft first. As far as engine mounts go you would notice undue movement of the engine if the mounts are sheared. That engine has been known to have sheared mounts. Not by design but for the simple fact it is the kind of engine that is taken places that have many "opportunities" to hit and shear mounts.

 

[Fire1386]

Thanks pappy, I have not noticed any excessive movement of the engine. Are you talking about the shaft the propeller is on? Do I need to use a dial indicator on the shaft or eyeball it when I spin it? I will check that on Saturday when I get off duty....

 

[Pappy]

Although a dial indicator is best you can eyeball it while spinning the propeller. There is a dimple at the end of the propshaft you can watch. If still unsure you can clamp or tape something very close to the propshaft with the prop removed and turn the shaft and watch the air gap.

 

[JMichael]

Although a dial indicator is best you can eyeball it while spinning the propeller. There is a dimple at the end of the propshaft you can watch. If still unsure you can clamp or tape something very close to the propshaft with the prop removed and turn the shaft and watch the air gap.

As I was reading down through this thread, I was wondering if anyone was going to mention the prop shaft. Then I came to your first post. LoL I recently had an 8 hp merc with a bent prop shaft. It was very easy to detect just by eyeballing it like pappy described above. It also created the same type vibration that the OP is describing.

 

[lovedr79]

mine vibrated pretty bad when i bent the prop shaft. it would also vibrate at WOT on plane on glass water.

 

[Fire1386]

Today I was able to look at the shaft, looked good and dial indicator showed about .005 to .006 run out. Close look at propeller didn't reveal any bends, cracks or gouges on it. Tomorrow I get the chance to go back to the lake and I will see if any difference between with the wind or into the wind.

 

[Wyatt]

Wait a minute!!! You UPGRADED to a 25hp motor on a pro 17?? Now im very curious as to what was on the boat before the upgrade!! Ive never seen a BT with anything smaller than a 25 on it!

 

[Fire1386]

This one was originally purchased with a 9.9 hp on it from the factory. A lot of the lakes he lived near were hp restricted lakes. He only fished those lakes until he moved near to me and then he purchased a boat more for Lake Erie. The boat is in excellent condition for a 92.

 

[Fire1386]

Spent a lot of time on lake today. Early this morning the lake was like glass, took a run down to the dam and there was no vibration at all...... I believe what I am feeling is boat going over chop at higher speeds. Later in the morning light chop still didn't feel the vibration, in fact rest of day, no vibration really at all. I think it is just me needing to get use to faster speeds and what that feels like, I hope...

 

[Johnny]

good to hear !!

yeah, going from your smaller motor to the bigger one is sort of like
going from a Yamaha 125cc street bike to a Harley 1200 Sportster !!

happy boating !!

 

[kofkorn]

This one was originally purchased with a 9.9 hp on it from the factory.

Holy Cow! My '89 came with the 40hp on it and I thought it was slow. I've got a 60 on it now and I'm far happier. Did it plane off with a 9.9?

 

[Pappy]

Gotta' love a happy ending!

 

[Fire1386]

No it would not plane with the 9.9, that's one of the reasons I have been looking for another outboard.....