have a poor history while yachts over 50 ft are rarely capsized and damaged. History shows that the probability of a yacht being capsized and damaged by a large breaking wave is strongly influenced by the displacement of the vessel. Although yachts have been lost in such storms I have been able to find no record of comparable structural damage. There are numerous reports of large sailing yachts surviving hurricanes of the same general magnitude. How could this possibly happen? The severity or the storm was extreme but by no means unprecedented. Although there are records of many storm casualties, I am aware of no documented instance of a well found yacht of the size and reputation of the Churchill and crewed by an ample group of expert sailors, suffering such catastrophic structural damage that it sank in a matter of minutes. The boat filled rapidly and sank in a matter of minutes. He observed that 8 ft of the heavy timber bulwark and planking had been torn off near the leeward shrouds, and the ribs were exposed. A crewman below reports that a sudden motion of the ship picked him up and threw him 7 ft. It was like hitting a brick wall when we hit the bottom". It picked the boat up and rolled it down its face - 25 tons of boat- into the trough at a 45 degree angle. "A sea came out of nowhere", said Stanley, " I could feel it from where I was in the aft coach house. Of the experienced crew of 9, two perished in the accident.įrom "Fatal Storm' by Mundle. The Churchill was a classic wooden sloop of 25 tons displacement and 55 ft. I have chosen the case of the Winston Churchill in the 1998 Sydney Hobart (SH) race as an example of a worst case breaking wave. The falling water makes a roaring sound, and from ancient times such waves were known as "growlers". Sailors have described the face of a breaking wave as a waterfall. When a wave breaks, water cascades down the forward face of the wave. The water cannot get over the crest, just as a yacht cannot get over. Similarly we know that a pendulum will cease to function if it swings up too high.Ī wave breaks because its crest is too high for the forward speed of the wave. They determined that the waves would break when the wave height exceeded 1/7 of the wave length. When scientists increased the height of the waves in the flow channel by moving the paddle more violently they observed that the waves became very steep and collapsed forming a breaking wave. However, regular waves do not threaten a well found yacht unless the yacht is permitted to surf down the forward face and reach a high speed. Of course this is why pendulums were used for clocks.įrom these studies we can obtain an effective engineering understanding of regular waves. Thus waves formed of liquid lead would have the same speed as water wavesĪ pendulum would have the same period if the weight were lead or brass. Where A and B are constants and L is the wave length and pendulum arm length. Period of a wave = A L seconds Period of a pendulum = B L seconds. In fact the formula for the period of a simple pendulum is remarkably similar to that of a wave. Note that the weight of the water or the weight at the bottom of the pendulum has no effect on the period of either a wave or a pendulum. The mass of waters moving up and down is the weight and the wave length is similar to the length of the arm of the pendulum. These simple relationships help us understand that waves are packets of energy floating on the water surface. (23 knots) and a period between wave crests of 7.7 seconds.įor regular waves the wave height does not affect the wave speed. Thus a wave with a wave length of 300 ft.
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