Keel Shudder - advice?

[Tim Good]

I have recently bought a swing keel Beneteau 26 from 1986. On our first passage from Salcombe to Dartmouth yesterday there would be shudder / vibration from the keel as we went over 6.5 - 7 Kts. It is a fairly disconcerting and it makes the whole hull vibrate.

Does anyone have any experience with this and or any recommendations?

 

[William_H]

keel vibration

Like rudder hum or vibration you need to fair off the keel or change the shape a little ensuring that both sides are symetrical. If there is any way to tighten the pivot bolt that might help also. good luck olewill

 

[Seajet]

A bit of 'hum' from a lift keel is not unusual, but the amount of vibration you're describing sounds a lot; has the keel pin been inspected, hopefully this was done before you bought her ?

I'm sure it's a matter of fairing in as OleWill says - a thick coat of paint on the keel can stop moderate hum too !

I'd want to check the keel pin and hole / bush in the keel though, a priority if this hasn't been surveyed - if it was and you trust the presumably good report, try fairing in.

 

[Tim Good]

A bit of 'hum' from a lift keel is not unusual, but the amount of vibration you're describing sounds a lot; has the keel pin been inspected, hopefully this was done before you bought her ?

I'm sure it's a matter of fairing in as OleWill says - a thick coat of paint on the keel can stop moderate hum too !

I'd want to check the keel pin and hole / bush in the keel though, a priority if this hasn't been surveyed - if it was and you trust the presumably good report, try fairing in.

Thanks. Yes it had a survey and the guy couldn't get to the pin easily but said there wasn't anything to worry about in terms of play when the keel was down so I just assumed that was that. I suppose that is the ignorance of a first time buyer maybe

Possibly need to have it checked but I ideally need to know how urgent it is since it is on the south coast of England at the moment and I need to bring it back around to Bristol.

 

[ianat182]

Had this been a sailing dinghy the vibrations would be generated from both rudder and centreboard; usually the cure is to plane a square edge, about 3mm across the trailing edge of each blade, perhaps 6mm on a larger boat.
Your boat is approaching hull speed anyway, and getting close to a plane; in a dinghy we would have raised the centreboard to a least 2/3rds depth, and this altered the angle of flow often stopping the vibration, so perhaps you could try this and mark the position for future reference.
Squaring off the trailing edge of the foils helps the water flowing across the blades to break off cleanly from the trailing edge which is often a vertical one, so altering the profile when raising the board to a longer airfoil section probably eliminates the cause. This latter is just a guess however.
Apart from the humming /vibration no damage is being done anywhere, though as mentioned above, the pivot bolt will need a check at some time for any wear.


ianat182


P.S Have just spotted Babylon's query regarding his rudder doing a similar vibration though I doubt you play a song!!

ian

 

[Seajet]

NorthCave,

well I can understand the surveyor saying that, as on most boats the pin is very difficult to check; the snag is it's the most important bit to check on a lift keel boat !

To be honest it's very difficult to know what to suggest from here; I do think Ianat182's suggestion of raising the keel slightly is a good one, one slightly mind as we're talking of ballast here as well of course.

My head says 'you'll be fine', and I'm sure you will, but my heart and instincts say 'check it'.

Is there a class association ? Fellow owners would be a real boon to chat with right now; may be well worth putting up another thread titled '*** swing keel owners' or similar, should get results here.

I have a lift keeler and run the owners association for the type, when it comes to keels or rigs, I always say my acid test is

imagine you're beating off a rocky shore in a dark night in a F6 with your family aboard; this is not the time to start worrying things might fall off or fall over !

I think speaking to fellow owners and lifting the keel slightly are your first best options.

 

[Tim Good]

NorthCave,

well I can understand the surveyor saying that, as on most boats the pin is very difficult to check; the snag is it's the most important bit to check on a lift keel boat !

To be honest it's very difficult to know what to suggest from here; I do think Ianat182's suggestion of raising the keel slightly is a good one, one slightly mind as we're talking of ballast here as well of course.

My head says 'you'll be fine', and I'm sure you will, but my heart and instincts say 'check it'.

Is there a class association ? Fellow owners would be a real boon to chat with right now; may be well worth putting up another thread titled '*** swing keel owners' or similar, should get results here.

I have a lift keeler and run the owners association for the type, when it comes to keels or rigs, I always say my acid test is

imagine you're beating off a rocky shore in a dark night in a F6 with your family aboard; this is not the time to start worrying things might fall off or fall over !

I think speaking to fellow owners and lifting the keel slightly are your first best options.

Perfect thanks for the advice. From what I can gather and advice from a Beneteau reseller it isn't a major problem and could be common on older boats. I think next winter I'll have it out and inspect the bolt to be sure.

I'll try and lift it up 1/3 next time and see what effect that makes

 

[Seajet]

Northcave,

I still think it wouldn't do any harm to start a thread on 'Beneatau 26 swing keel', it would put you in touch with other owners, and if there isn't an owners association to discuss such things, maybe you or someone could start one !

 

[Tim Good]

Northcave,

I still think it wouldn't do any harm to start a thread on 'Beneatau 26 swing keel', it would put you in touch with other owners, and if there isn't an owners association to discuss such things, maybe you or someone could start one !

I posted on the Beneteau section of sailboatowners.com and someone got me this diagram which would be useful down the line:

Do you know what the first step of checking if you need the keel fairing is?

 

[Seajet]

Err...

I'm interested that shows 'old fit' and 'new fit', wonder why it was changed, and which is yours ?

Could be a big clue here.

Otherwise all I can suggest is look for elongated hole in the keel itself + the L shaped side parts, and any wear or slop in the bushes & pin.

That's probably a horrendous job unless you're really lucky, I can see why the surveyor just checked for play; thing is there must be play somewhere to create the vibration described.

To check fairing in - or fairness - it's basically seeing if the keel surface is flat both sides so a steel rule would probably do, and - harder to check - symetrical, if it's a shaped rather than flat plate keel; to check that my first idea would be to make an accurate template of one keel side in say...thin perspex, ply ? - and run it over the keel sides.

I'd also make sure to check the keel itself is straight, not bent to one side; sounds drastic, but funny things happen to boats.

All this means boat out of the water unless you're very lucky and there's a good way of inspecting the keel assembly, so I'd redouble efforts to chat with other owners !

 

[davidwf]

If you are sailing with the lifting screw loose try putting one or two turns on it this with move the keel slightly and may stop the vibration.

I used to lift my 25.7 keel by 5 or so turns in heavy weather to reduce the weather helm as well.

David

 

[Plevier]

Err...

I'm interested that shows 'old fit' and 'new fit', wonder why it was changed, and which is yours ?

Difference is the lifting screw. Old male top female bottom. New female top male bottom. Can lubricate by pouring oil in to top of tube.

Absolutely no idea what part nos 13 and 14 are on that drawing. I had a First 29 and they were on the drawing for that too but didn't exist as far as I could see and I had the keel out!

 

[irl2605]

If you are sailing with the lifting screw loose try putting one or two turns on it this with move the keel slightly and may stop the vibration.

I used to lift my 25.7 keel by 5 or so turns in heavy weather to reduce the weather helm as well.

David

Be careful David .. By doing this you are hanging the full weight of your keel from the brass/bronze lifting nut .. These have been known to strip their treads and not allow you to lift until repaired .. its better to over wind and force the lifting mechanism up against the stainless steel saddle in the cockpit..
With regards to the hum I think I would be looking at no.s 6 & 8 in the Diagram .. These are home position locating pads that fit snugly against the housing when lowered.
The new and old mountings are simply that . The new one houses the worm inside the tube and uses the infamous bronze nut while the old one simply uses a s/s nut and long threaded bar. .. BTW there were also about 3 versions of the bronze nut.
To get to the swivel pin you need to drop the two mounting brackets and keel attached as the bin is up inside the keel box