Boot Key Harbor
"Marathon- the Heart of the Florida Keys"

An On-Line Cruising Guide for the Florida Keys & Cuba
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Dangerous Seas

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Another small fishing boat recently capsized here in the Florida Keys, sending its occupants into the sea to helplessly drift until found and rescued some time later. A common cause of capsizing in small fishing boats is anchoring by the stern of the boat rather than the bow. Once a wave of about any size breaks or finds its way over the transom it lowers the stern of the boat, allowing subsequent waves to more easily board the boat while the stern is held helplessly down by the anchor. Of course the higher the waves the more probable the capsizing. Broaching in beam seas and being rolled by the waves is another nightmare. This is of course affected by the stability of the boat and seamanship of the helmsman. My wife is an early warning system for broaching. It seems that when we start rolling heavily in beam seas she lets me know pretty quickly that she’s not happy – way before we’re in actual danger of broaching. How do you judge “safe” seas in terms of wave heights? Once the wave height is more than the beam of your boat you’re at risk of broaching. The boat rolls 90 degrees on its side, but the wave is still larger and continues to roll the boat over past 90 degrees. Been there – done that. That doesn’t mean you can’t safely pilot your boat in such seas however. At some point you just can’t take the waves on your beam. You have to go bow into the waves (just slightly off the bow) to avoid a broach. Even a power boat at times will have to tack back and forth to get to their destination, in order to avoid beam seas. Ultimately a breaking wave that is higher than the length of your boat defines the limit of a safe sea. You can’t even bow into these waves without a high probability of being flipped over backwards. This is what probably happened to the fishing boat in “The Perfect Storm” with 100 foot waves. (We’re ignoring for now the difference in the “steepness” of rolling waves in deep vs. shallow water). To read more about fetch, wave heights, and what a forecast of 4-6’ seas really means in terms of actual wave heights, go to www.BootKeyHarbor.com, choose “Boat Tips” from the top menu, then open the two articles on Fully Developed Sea Heights, and Marine Wx Definitions and Significant Wave Heights.

P/C Gregory Absten