Knocking sound at 2000 rpm’s

[Prozac]

After a couple of months repairs and maintenance of new to me 1987 Hunter 28.5 I took it out for a shakedown cruise. As I motored out I noticed a knocking sound at 2000 rpm’s. Checked the bilge and quite a bit of water filling about six times per minute. When taking the engine out of gear the least slowed. I am guessing a bent prop shaft or struts? Any advice would be appreciated. Currently no way to get it on the dry for repair. Thanks all!

 

[jssailem]

I am guessing a bent prop shaft or struts?

WOW.
Yours is as good a guess as any. It is the type of issue that could be a lot of things.
You said: "quite a bit of water filling about six times per minute."
What does that mean?

• The bilge was filled six times a minute?
• You had 6 drips a minute
• 6 gallons a minute

Sounds like a lot of water. Where was it coming from? The shaft log? The transmission? the engine block?

And the "Sound". Where was that coming from? Beneath the boat? Banging the hull? Can you dive the boat? Could there be something like a fender or a length of line whipping about on the prop causing the noise?

 

[Prozac]

WOW.
Yours is as good a guess as any. It is the type of issue that could be a lot of things.
You said: "quite a bit of water filling about six times per minute."
What does that mean?

• The bilge was filled six times a minute?
• You had 6 drips a minute
• 6 gallons a minute

Sounds like a lot of water. Where was it coming from? The shaft log? The transmission? the engine block?

And the "Sound". Where was that coming from? Beneath the boat? Banging the hull? Can you dive the boat? Could there be something like a fender or a length of line whipping about on the prop causing the noise?

Bilge pumping about six times per minute. Looks like leak coming from behind stuffing box area and flowing into void(shaft log) where stuffing box is located. I have not been under the boat but do not think it is anything wrapped. Will do that on next trip out. The noise was not engine noise but more from shaft area beneath the boat. Thank you!

 

[shemandr]

I am not the one to answer this question but I would look at the alignment of the engine/drive train. Sometimes what is aligned on the hard isn't in the water. Or maybe the prop shaft was bent in the launch process. Were you there? Maybe the strap was on the prop shaft?
Bad outcome, 'though.

 

[Prozac]

I am not the one to answer this question but I would look at the alignment of the engine/drive train. Sometimes what is aligned on the hard isn't in the water. Or maybe the prop shaft was bent in the launch process. Were you there? Maybe the strap was on the prop shaft?
Bad outcome, 'though.

Thank you. It’s been in the water since before 2015. The boat is in the water at Lake Ouachita State Park. Really hard to get service on sailboats in this area.

 

[jssailem]

That helps.
I think look under the boat to check what might have happened.
A lot might have changed since 2015.
You get any ice up there in the winter?
Good luck

 

[Prozac]

That helps.
I think look under the boat to check what might have happened.
A lot might have changed since 2015.
You get any ice up there in the winter?
Good luck

No ice in Arkansas.

 

[jdrutten]

That completely sucks!

... When taking the engine out of gear the least slowed. I am guessing a bent prop shaft or struts?

When you say it "slowed" when taking the engine out of gear, does that mean that water was still coming in even when out of gear? If it's been in the water for 9 years, then there's at least one shaft angle that doesn't leak. Have you noticed any water in the bilge prior to taking it out? Or have you heard the bilge pump running at the dock? Does it leak if you have it in gear at the dock? Does water come in If you turn the shaft by hand, or is the leak definitely linked to the rotation of the engine/transmission at 2000 rpm? Try to get a very specific location of the leak. I certainly don't have any qualified answers, but in addition to the bent shaft and engine alignment possibilities, I'm wondering about your engine mounts, stuffing box hose, and cutless bearing as well. At a minimum, it's easy enough to tighten up your stuffing box hose clamps if you can.

 

[Davidasailor26]

Bilge pumping about six times per minute. Looks like leak coming from behind stuffing box area and flowing into void(shaft log) where stuffing box is located. I have not been under the boat but do not think it is anything wrapped. Will do that on next trip out. The noise was not engine noise but more from shaft area beneath the boat. Thank you!

Sounds like the water may be coming from the strut. Could be that the strut bolts have just come loose or broken allowing it to move around as the prop spins. Could be that the shaft is bent forcing the strut to move.

 

[jssailem]

What ever it is to identify the issue someone needs to lift up the boats skirt and look at the boat’s bottom

 

[marcham]

It will have to come out of the water for investigation and repair.

 

[kloudie1]

Another WAG is shaft hitting the shaft log .. The Yanmar mounts are very springy and if the shaft is not centered in the log when aligned, it can knock at certain RPMs..

 

[Stu Jackson]

Is the leak coming from the stuffing box? Have you properly adjusted the packing gland? Could the leak and noise be from separate issues?

 

[jssailem]

If this were a crime, the detectives would go to the streets and round up the "Usual Suspects".

 

[Ralph Johnstone]

I am guessing a bent prop shaft or struts? Any advice would be appreciated.

As in life, so it is with diesels ............... DO NOT go for the most complex and expensive solutions first. Leave them to last. Not being able to haul out simply makes finding the problem even more difficult.

With a problem such as what you describe, after you eliminate the obvious, the first thing you want to look at is the prop shaft alignment. The biggest item you will be looking at is the angular alignment.

I think it safe to say you don't yet have a copy of the Yanmar maintenance manual as suggested to you in your post "my remote fill is in the lazzertte under the seat in the cockpit. I'm also pretty sure you haven't a clue as to what I'm talking about when I mention angular alignment. Read and learn with the attached item on alignment.

You are now the proud owner of a 37 year old boat. It may or may not have had proper maintenance done over the years. You're going to have to accept that either you learn a whole lot about boats in a very short period

OR

You hand it over to a certified mechanic who will cost you big bucks from the get go. If he's an uncertified mechanic, he's going to cost you more than the boat is worth.

RECOMMENDATIONS :

1. Check that your prop shaft alignment is reasonable. No cost.

2. Seeing as how your boat cannot come out on to the hard, look through the archives to see how to pack a stuffing box in the water. Also see Marine How To - DIY for Boaters - Marine How To to see what a stuffing box is. Under $10.00 if you have a reasonable selection of tools.

 

[Prozac]

As in life, so it is with diesels ............... DO NOT go for the most complex and expensive solutions first. Leave them to last. Not being able to haul out simply makes finding the problem even more difficult.

With a problem such as what you describe, after you eliminate the obvious, the first thing you want to look at is the prop shaft alignment. The biggest item you will be looking at is the angular alignment.

I think it safe to say you don't yet have a copy of the Yanmar maintenance manual as suggested to you in your post "my remote fill is in the lazzertte under the seat in the cockpit. I'm also pretty sure you haven't a clue as to what I'm talking about when I mention angular alignment. Read and learn with the attached item on alignment.

You are now the proud owner of a 37 year old boat. It may or may not have had proper maintenance done over the years. You're going to have to accept that either you learn a whole lot about boats in a very short period

OR

You hand it over to a certified mechanic who will cost you big bucks from the get go. If he's an uncertified mechanic, he's going to cost you more than the boat is worth.

RECOMMENDATIONS :

1. Check that your prop shaft alignment is reasonable. No cost.

2. Seeing as how your boat cannot come out on to the hard, look through the archives to see how to pack a stuffing box in the water. Also see Marine How To - DIY for Boaters - Marine How To to see what a stuffing box is. Under $10.00 if you have a reasonable selection of tools.

Thanks all. It’s obvious I do t know as much as most but I do know some and have looked at manual you described, understand stuffing box and probably more than you might expect. Just wanted to use the forum to help with my critical thinking skill eliminating the obvious. Thanks all for you helpful advice and lecture.