CS 20 Stability

[Noklin]

I was reviewing Graham

[JeffM]

Back in the fall when I was a few months into building my CS20, I looked at a few other designs and began to become concerned about the CS20's hull strength. (See the "hull strength" thread in the design forum if you like.) I was concerned because I wanted to be able to go out in the ocean a bit. In a phone conversation with Graham, he told me the hull was plenty strong, and my chief concern should be whether I could right the boat if it capsized off shore while I was alone. His opinion: a 20 foot boat was at the borderline of single-handed capsize recovery. I intend a capsize recover test to be among my first few "shake-down cruises." I have a little way to go in construction, but hope I'll be able to accomplish that this season. I'll let the forum know how it goes.

Jeff

[brian watkins]

I don't think I've ever heard a mention in the forum of a Core Sound actually capsizing. Has it ever happened? Seems fairly unlikely, with the hull shape, low (-ish) rig, and the flexible masts, but maybe in a race? Anyone?

[Brent]

I frequently sail solo on my CS20. The boat and I have been out in conditions where the wind blows the beards off the whitecaps, yet I have never gone over. We have gotten the rails wet a few times. I weigh 150 lbs, so heavier guys should have fewer concerns. Heavy weather sailing is a hoot, lots of spray and speeds in the double digits.

I find the boat less tender than most centerboarders, which I attribute to the hull design and low center of effort. The boat certainly handles conditions that keep the other centerboarders on the shore. I consider a good reefing system essential equipment for the kind of sailing I do.

There are a few salty tweaks to keep in mind in heavy weather sailing, but maybe that is another discussion.

[Designer]

The CS20 is a good stable boat but with the right combination of too much sail for the conditions and bad boat handling, any unballasted boat can capsize.

There are two issues we need to address after a capsize. First we need to stop the boat from inverting. Once she inverts we will need assistance, unless we are clever enough to unrig the boat while it is upside down. Sealing the masts at the top is the most important step to discourage inverting (this alone won't stop an inversion but it will slow it down and makes a big difference in the force needed to right the boat). Furthermore, I am considering some experimenting with some floatation at the masthead.

The second issue is the righting moment. I have not tried to right a CS20 but I think that it would be hard to do alone without some modifications. I can't even imagine what a 3/4" steel centerboard would do to her upwind performance, but it would be bad. A better option would be to shape the standard board in wood and then cut off the lower third. This is then used to make plaster of paris mould in to which you could pour in lead. This could be scrounged wheel weights, fishing sinkers etc... It would put the weight where it would do the most good, would not rust and would be cheaper. Yes you would have to modify the uphaul.

In all of the years that I have sailed CS20's and CS17's in the Great Race we have never reefed but feathered through the gusts and have never felt like we were under threat of a capsize. Having said that I have heard of two CS20 capsizes, both were with raw beginners and both needed outside assistance. I think that a competent crew of two can right the standard boat unaided.

[Bruce Leonard]

I've capsized Lightnings and Thistles a few times. It happened once while sailing my Thistle solo in Narragansett Bay. The Thistle is a 17 ft. planning centerboard dinghy that has too much sail area (175 sq. ft. and is completely open. Even the bow is without decking. It weighs about 450 pounds.

When I flipped it, I was able to get on the centerboard pretty quickly. This is the best way, I think, to keep the boat from turning turtle. I then got the boat pointed into the wind and up she came, only to capsize again in the opposite direction because of the tremendous volume of water already in the boat.

By the time I got the boat up again and bailed (the Thistle has no decking), I was exhausted.

It's important to keep your cool, use your enegy wisely and get on that cnterboard !

I have a CS 20 in RI not far from my friend to the North who wants to conduct the test. Maybe we can collaborate on this.

[Noklin]

I appreciate all of the replies. It sounds like the way to go is to build the CS20 with the wood centerboard per the plans, test capsize it to see if I can right it alone and then if necessary follow Graham