Keel Shudder - advice?
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?
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
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.
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.
P.S Have just spotted Babylon's query regarding his rudder doing a similar vibration though I doubt you play a song!!
Last edited by ianat182; 08-05-12 at 09:26.
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.
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'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 !
Last edited by Seajet; 08-05-12 at 17:15.
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