A monohull’s resistance to heeling is created by its centers of gravity and buoyancy. Obviously, different boats will be more susceptible to rolling than others based on length, beam, displacement, roll inertia, and center of gravity. In order to be rolled, a boat’s righting moment has to be overcome. Andrew Claughton (who co-authored the University of Southampton, Department of Ship Science’s report) writes in Adlard Coles’ Heavy Weather Sailing by Peter Bruce, “During the model tests that were carried out to investigate the problem, when the breaking wave was 30 percent of the hull length high, from trough to crest, it could capsize some yachts, while waves to a height of 60 percent of the hull length comfortably overwhelm all of the boats we tested.” So, the starting point for a wave to be dangerous to rolling a boat is one that is only 30 percent high as the boat is long. Most sailors would be surprised at the minimal wave height needed to roll a boat. Therefore, the wave has to be of a certain height in order to have enough energy to roll a boat of a certain length and displacement. Along with the speed of the wave, the larger the wave is, the more energy it will contain. But without the wave breaking on the boat, the boat itself should not be knocked down.Īn ocean wave is energy. That is not to say that it will be comfortable or possibly cause the boat to go out of control. Unless the wave is breaking, the boat should ride up and over the wave regardless of the wave height in comparison to the boat length and the boat’s orientation to the wave. Yes, a boat can be pitch-poled (tossed end-over-end), but the size of the wave needed to do this greatly exceeds the size of the smaller wave needed to knock a boat down when broadside to a wave.ģ. If the boat is bow or stern onto the wave, the chances of being rolled are greatly reduced. The more a boat moves from being perpendicular to a wave, the greater the chance of a knock down. The boat is broadside or oblique to the wave. At this point the wave becomes dangerous and contains enough energy to overcome a boat’s righting moment.Ģ.
Wave height must exceed a certain percentage of the boat’s length.
When is your boat in danger of being knocked down or rolled by a wave? A study conducted by the University of Southampton’s Department of Ship Science and a similar study by the Society of Naval Architects and Marine Engineers (SNAME) along with the United States Yacht Racing Union (now US Sailing) have shown that three conditions usually have to exist:ġ.
This is not about heavy weather sailing techniques, but knowing which waves caused by heavy weather may be dangerous. But some storms do and a prudent sailor has to ask: Do I know what wave heights are dangerous to my boat? Do I know when breaking waves can occur? Do I know when these conditions might occur where I am sailing? One of the greatest concerns a sailor may have is that he or she will be caught in a situation where his boat may be knocked down or rolled by a wave.ĭespite being frightened by stories about exceptionally dangerous storms, such as those that wreaked havoc on the 1979 Fastnet or 1998 Sydney to Hobart races, not all storms create dangerous breaking waves. And you are sailing a long way from land. The waves, when you can see them, look large. At what size do waves get big enough to cause real trouble for your boat?
0 kommentar(er)
