Vibration problem canting keel

[nico]

What do u think about the vibration problems on the new Sill? Could it be due to a too thick fin section with a lack of off-axis fibers?

http://www.scuttlebutteurope.com/ 27th

[SailDesign]

Sounds bad. We had no problem on the Black Sea 40's, but their bulbs were slightly off-axis longitudinally to ensure some torque on the foil at all times. The trailing edges were cut at a 45 degree angle to minimise humming.

Steve

On the "Daily Sail" it was mentioned that they may add carbon to one of the two boats even though the fin might be too thick then. The idea was to make the transat at all costs.
Sure will be interesting to hear what the solution is...

[ClarkT]

Sounds like they are using the keel bulb to twist the strut. A passive sort of trim tab rather than the active trim tab Doug suggested CBTF will be coming out with. I read one article that mentioned they had moved the keel bulb aft on one boat as a way of solving the problem, as Steve suggests. It's definitely a slippery slope if you try to use your ballast foil to create 'downlift' and additional righting moment, but whenever they get it dialed in, it should be awfully fast.

Didn't reaize I had suggested CBTF might be working on a keel flap for added power(neg lift) but I know I am for use on a canting keel boat equipped with a forward retractable hydrofoil and an aft T-foil. The potential speeds for this kind of monohull are mind boggling not to mention having that good old trusty hunk of lead there to pull you out of a jam....

[tspeer]

The article reports two completely different phenomena, cavitation and flutter. I suppose cavitation induced separation could promote flutter, but the mention of cavitation sounds like a misnomer to me.

I suspect they have the center of gravity of the keel bulb too far aft on a strut that does not have enough torsional stiffness. Both fixes - recasting the bulb and adding carbon - point to this as the problem. Also the retirement of Bonduelle, since cavitation would hardly be cause for quitting but fear of losing the keel in an "explosive" flutter event would be.