Capsize Screen
During the Fastnet race from England to Ireland and back years ago, an unexpected storm struck the racing fleet. A number of boats were capsized, some were lost, and a number of lives were lost.A very thorough investigation was held, including tank model testing. The conclusions were:- Any boat design will probably capsize if struck broadside by a breaking wave higher than the beam of the boat.- Seaworthy boats will bob back upright when a following wave rocks them out of their stable inverted position.- Boats that are wide and light have a lot of "form" stability. They are also usually quite fast, since they can carry more sail in the same wind, and often plane. Unfortunately, these hull forms are also quite stable when inverted. So once turned over, they tend to stay that way. Think of a catamaran. Their broad beam (across two hulls) makes them the fastest hull shape. Bu once they are over, they are there to stay. Big cats have a hatch in the bottom to allow crew escape when they are inverted.- The investigators came up with the capsize screen to roughly measure which boats are too wide and light to expect a rapid recovery from a rollover. The formula imagines the displacement volume of the boat is a cube, then compares the side of that cube with the beam of the boat. If the beam is more than twice as long as the side of the displacement cube, then the boat is likely to stay inverted when rolled.- The angle of vanishing stability is a more exact measure of this characteristic. It defines the angle from verticle at which a boat no longer has a righting force to bring it back to verticle. A decent angle of vanishing stability for an ocean going yacht is 140 degrees. That says until the boat has its mast pointed 50 degrees (140-90) beyond horizontal, it is still trying to roll back on its feet. More importantly, a following wave only has to roll an inverted boat 40 degrees (180-140) to get it started to recovery. Unfortunately, many popular boat manufacturers do not publish this statistic, so we have to use the capsize screen.- But all of this has been well known for over 20 years. So when Hunter deliberately designs the 44 DS with a capsize screen over 2.00, they are saying recovering from a rollover at sea was simply not very high on their priorities for that hull.If you are really going to cross the Pacific, I'd look for a design with capsize screen below 2.00. If you want a modern, fast, design, the Hunter 42 is a candidate. Henk Meuzelaar has cruised his in the Pacific for years. But if you really intend coastal cruising, and visits to the Caribbean, the 44 DS is a great choice. If you took her across the Pacific, you would use weather history to avoid expected storms that would put you in any danger. Mostl likely you would have a great cruise. But your boat would not be good protection if it was rolled over in an unexpected storm.David Lady Lillie