Shaft vibration

E

erice

Member
Member
Joined
Jan 4, 2012
RO Number
32840
Messages
84
I've got a vibration rb2@gr5t about 1700 rpm's. last week I scraped a bunch of barnacles from shafts, props ok. I checked the shafts while under way and found the port shaft log visibly moving. Also noted I feel more vibration on turns and at faster speeds. Can I continue to use the boat until haul out, or does this need repair now.
 
Based on what you've said, I'd say repair now. You will only do more damage by continuing to run it like that IMO.
 
"Can I continue to use the boat until haul out, or does this need repair now."

Yes.

---

At all levels, vibration accelerates wear to bearing and support structures. And you always have vibration, but under "normal operating conditions" it takes a very long time to wear out those surfaces. The more vibration you have, the more rapid the wear will occur.

SO, if the vibration is visible to the eye, I would guess that you have an above average ( well above average ) wear rate. So, yes you can operate, but it depends on how much damage you can tolerate. My tolerance is low, so I would not operate till the source is found and corrected ( and the resultant damage is repaired ).
 
That depends. If you run slow and the oscillation is not bad, you can continue home for example. We cannot judge the severity of the damage so it's tough to make a recommendation.
But if the shaft is wobbling like a drunk, forget it. Pull the boat and get it fixed. A couple of thousands at the egress will be visible at slow speeds depending on how many struts there are etc..
 
The shaft log is visibly moving? Is it loose at the coupling or has the cutlas bearing failed? Either way I would not run it prior to repair, but that's me.
 
If in doubt at least have a pro look at it. I'm thinking it depends on your situation as described by Boatbum above.
Bill
 
It's just possible it's not the prop or shaft if you can't see anything obvious U/W with a mask. Check tightness of strut fasteners and engine/transmission mounts, and make sure shaft anode has not slipped and alignment at the transmission /prop shaft coupler is within .003" all around . Check to see if you can move the shaft any side direction at the cutlass bearing.

But with noticeable visible movement there , the more you use the worse it gets and could cause leakage or broken shaft with loss of prop and other damage.
 
If the vibration is THAT noticeable, haul the boat and have it checked out. You could check the runout at the egress before hand. If you did not clean the props evenly perhaps there is something going on there. Put a stick on the rudder with a bungy cord. Pull all the blades around past it. They should all touch it similarly or just miss it similarly. Do this at a few different radii on both sides.
 
The vibration could be caused by a shaft alignment problem in addition to what is already mentioned above.
Bill
 
If the port shaft log is really moving, you have a major issue that could sink th boat at the dock. Just so we are on the same page, the shaft log is the fiberglass tube sticking inside the hull on which the stuffing box is attached.

If you meant that the stuffing box is moving as the shaft rotates then it sounds like a bent shaft, or mis aligned.

I would not run the boat at speeds where the vibration can be felt, but it it feels smooth at hull speed (1000/12000rpm) then you ll be fine for a while.

What kind of boat, engines, etc
 
Pascal, it is the stuffing box, my mistake. It's a 1989 sabre "fast" trawler, twin dd 8.2turbos with twin disc 502 transmissions, 1 3/4" aquamet shafts.
 
Boat bum: I did as you suggested, with the first blade not quite touching, the second just touched and the third snagged the edge enough to make it snap back slightly when it went by. Sound like a bent shaft?
 
quote:
Originally posted by erice

Boat bum: I did as you suggested, with the first blade not quite touching, the second just touched and the third snagged the edge enough to make it snap back slightly when it went by. Sound like a bent shaft?

Click to expand...


It sounds to me like both your shaft and prop are going to the shop. You might even have to send in the strut. What did you hit or did you ground?
 
Stephen: to my knowledge I have not hit anything or grounded. Last fall I had my prop scanned again by ocean props in Portsmouth ri; he told me then that both props were still rated class 1 condition. Could I have hit something or grounded? I think I would have noticed. In 2011' I watched something and got a bunch of pot warp wrapped around the wheel, port side. I tried going in reverse to clear it, but ended up diving on it. Luckily, it came off as a bunch.
 
Is it possible your marina experienced a very low tide and your boat bounced on something?
 
Are your motor mounts good? Are the stringers solid where the mounts are secured?
Al
 
Lobsta1: I don't know about the mounts, I'll have them checked ASAP. Stringers seem fine, but I'm not an expert so they will be checked also.
 
I'm going to pull the props and have them scanned first. Then I'll have the mounts checked. By the way, if I have to adjust or replace the mounts, what kind of money am I looking at?
 
quote:
Originally posted by erice

Boat bum: I did as you suggested, with the first blade not quite touching, the second just touched and the third snagged the edge enough to make it snap back slightly when it went by. Sound like a bent shaft?

Click to expand...


Once more with feeling: "Based on what you've said, I'd say repair now. You will only do more damage by continuing to run it like that IMO."

:-)
 
Hauled boat last week, checked port shaft with dial indicator, found it out by .005". Sent dhaft to H/H propellor in Salem ma., they found it was out by .014". It'll be straightened and hope to be back in the water very soon. Thanks for all the responses.
 
You must log in or register to reply here.
Back
Top