Hull Stability

[Larry DeMers]

Brad

For a quick check, take a look at the freeboard when you're heeled over by the gust. If the mean waterline is not yet at the deck edge, the boat can still absorb more heeling moment. If the deck edge is awash, it's approaching the peak of its righting arm curve. That's where "the risk [of a knockdown] significantly increases," if the wind stays at the gust level or gets stronger.

Bruce Barber

...I don't know if I am reading this right or not, so allow me to tell you about my experience one day a couple years ago, and refered to by jon Larson on an earlier post. We were motor sailing, all sails up, in 0-5 kts wind. We rounded a corner of an island, and I saw a white wall of water ahead, with white caps kicking up and flying in all directions underneath it. The sky was pure blue..no clouds. I had time for one thought.."Oh Sh..t, we have all sails up and here comes a microburst". By the time I reacted and headed for the main sheet, the boat was heeled past our inclinometer (50 deg.) and continuing over with the boom in the water. The rudder still had control most of the time (I could feel it hit air pockets -no backpressure). During this time, I managed to kill the engine and give her full right rudder, but my wife was having a heck of a time getting the main uncleated at the angle we were at. The mast was parallel to the water with the spreaders in the water perhaps half way. We finally got the main uncleated and the boat rounded up and then the wild flying of a loose boom and the flogging of our staysail and genoa got our attention. The wind had our knotmeter pegged, but the CG reported a 70 kt gust, with 50-55 kts behind that. We were in 7 ft. waves within 20 minutes.

Point is that the boat had plenty of reserve righting at 90 deg., and so it should. All properly designed cruising boats have at least 90 deg. righting moment I believe, and some go as far as 120 deg. righting moment before they go turtle. The design of the turn of the bilge, as well as the aspect ratio of the lwl/beam and amount/location of the ballast regulates this mostly.

We sail rail down every weekend..heck that's only 30 deg. over. I hope that you are not trying to say that this is the point where one should start thinking about a non-scheduled adventure, as my experience says that is way off.

Larry DeMers
s/v DeLaMer
Cape Dory 30 #283 ~~~~~~~~Sailing Lake Superior~~~~~~~~~~

I'm looking for some information on the hull stability for my CD32 sloop. Info on the 31, 33 or 330 would be good enough. Reasonable opinions are also welcome.

Here is the issue. We sail the Chesapeake Bay near Baltimore. During the summer I fly a 150 genoa most of the time, not bothering to reef unless the wind picks up and stays up over 18-20 kts. The heel of the boat is about 20-25 degrees. When a gust comes along (+20kts) and the boat heels over 30+ degrees, my crew becomes very anxious, concerned about the possibility of a knock down. My response is to relax and enjoy the r

demers@cray.com