The Vendée Globe Race, 3 out of 20 boats (15%) lost their keels, that’s amazing, these are IMOCA 60 class boats with canting keels.
The boats are getting lighter and faster and the shocks experienced in 30,000 mile circumnavigation on the boat and its appendages is violent in big seas, fatiguing their steel canting keels.
If a boat goes up and down a wave at zero heel with a standard keel you are only going to produce more or less tension in the keel. With a canting keel the same motion produces a bending or whipping moment :watching3 under certain conditions the bending moment could be reversed :scared: take a look at the first 45 seconds at the canting keel in this tank test … no wonder they break !
Hi Alan
I take a look… but the problem of bending of the canting keel in the video, it seems me much more an optical effect of refraction rather than a mechanical problem of flexion/torsion.
If you watch the video to the second 20, the hull seems not to pitch or move but the bulb seems going up and down visibly when the small wave passes.
Normally tank models for tests are very strong and stiff in order to not induce parasitic effects /errors during the test so I do not believe that a tank model can bend that way during a test in quasi-static conditions as during the second 20.
The kanting keel problem is more than anything else related to the concentration of loads on the structure of the hull which has an opening in the pivot point and concentrated loads of hydraulic ram, however, should be connected to valves that prevent overloads as well explained Pete Goss’s book where he talks about his 50-foot Aquaquorun.
Goss believes that the presence of Kanting keel and the hydraulic control with safety valves against overloads in certain conditions allows to safeguard the structure better than with a fixed keel.
Clearly the search for maximum performance also leads to lower margins in the design phase and the races are also the test.
A few years ago they had problems in many of hydrodynamic pressure on the doors of the compartment closed canting keel, then have them resolved and so on: each generation of boats researches any ways to go more often and are also discovered new problems
In short, I think certainly the Kanting keel are highly stressed because even allow higher performance by increasing the total righting moment of the hull and the power of the sail plan, but I’m not so sure that what you see in the video is so “significant”.
Bye
You are right, cannot detect keel visual flexing on the model, I was only using the visualisation of the video to illustrate the pitching of the hull and whipping effect it has on a canting keel sailing through heavy seas (waves) You don’t need much imagination to see the fatiguing would be taking place… the shocks must be enormous !!!
I don’t agree with Pete Goss’s opinion after 3 boats in the Vendée losing their canting keels, there can be no question this is a serious issue right now.