2006-07-20 / Editorial

Get your boat ready for a hurricane

By Roger Marshall

If you own a boat moored in the waters around Jamestown, your best preparation for a hurricane is to make sure that the yard or facility that launched your boat is available to lift it out of the water. Be certain they have instructions to get the boat out even if they cannot contact you. An MIT study after Hurricane Gloria, which roared through Padnaram, Mass., found that of the boats that were hauled out and chocked above the storm surge, 98 percent survived unscathed. In contrast, many of the boats that stayed in the water were damaged or sunk.

When your boat is pulled out of the water in preparation for a storm, make sure that it is tied down securely. Hurricane-force winds have been known to blow smaller boats and their trailers over. You should also take the rig out of the boat. Having the rig in the boat in high winds, puts a lot of strain on the hull and chainplates because the boat cannot move. In the water, the yacht can move sideways or heel over when a gust hits, but on shore, the force of the gust must be absorbed by the hull. As a result, yachts with their rigs in place sometimes get blown over, and the tall masts can cause a chain reaction that damages other boats.

If you have to leave your boat in the water during a hurricane, putting it on a mooring is a better option than keeping it in a marina. If you do so, check to see how strong the wind is and what the storm surge will be. A severe hurricane can have a storm surge of up to 20 feet above the normal high tide level. Check, too, to see what is holding your boat to the seabed. Whether it is an anchor, a block of granite, railroad wheels, or whatever, it should be silted in extremely well, or the boat could lift the anchor right off the seabed. For example, it takes about 1,500 pounds for a 40-foot hull to sink down in the water 1 inch. A two-ton block of granite weighs around 600 pounds in water. With a simple calculation, 600/1500 = 0.4 of an inch, your boat would have to sink down into the water less than half an inch to lift that block right off the seabed! With a 20-foot storm surge, your boat could easily drag the anchoring block ashore. To my knowledge, the only anchor that will not lift out of the seabed is the Helix anchor. This anchor screws into the seabed and is reputed to have held seven boats on one anchor during a Caribbean hurricane. That this anchor is capable of immense holding power was demonstrated in some tests made with a tugboat. The tug pulled every other anchor out of the seabed using force measured in the hundreds of pounds, but the Helix anchor stopped the test when the strain gauge was about to break at over two thousand pounds. (The actual loads are shown in my newest book, "Rough Weather Seamanship.")

When leaving your boat on a mooring during a storm, do not try to stay aboard. The U.S. Coast Guard suggests that you go ashore and watch the storm, and perhaps your boat as well, through a window. But before you go ashore, remove as much windage from the boat as possible. Take off the roller furling headsail, the bimini top, and the inflatable dinghy on the foredeck. Stow them in your garage, out of harm's way. The pressure of the wind increases by the squared power of the wind speed. In other words, if the wind speed is 10 knots, the pressure is 100 units, but if the wind speed is 80 knots the pressure is 6,400 units. Quite an increase! Remember, too, that as the storm passes by, the wind direction will change, often up to 180 degrees from its original direction.

If you have expensive electronics aboard, remove them, too. They will be safer and dryer in your garage. In fact, remove as much as you can from your boat to prevent anything from happening to it. To protect the boat itself, put fenders horizontally down either side, so that should another boat break loose, it will (hopefully) bounce off the fenders rather than spear your vessel.

What should be done with the water and fuel tanks during a storm is debatable. Some say they should be topped off to give the boat more stability. However, if your boat goes ashore with full tanks of fuel there could be a real mess to clean up. Always try to think about what could happen if your boat were to go ashore and make your decisions accordingly.

The last thing to do before leaving your boat on a mooring to ride out a storm is to check the mooring pennant and run a secondary line to the chain under the mooring-buoy shackle. In many cases, the shackle is what fails, and the boat goes ashore along with the mooring buoy. In another study, MIT experts found that plastic hose pipe covering nylon mooring pennants helps the line to break. What happens is that the line stays dry under the hose, but the nylon stretches - sometimes up to 25 percent of its length. As the nylon shrinks and stretches, it heats up. Eventually the heat gets high enough so that the nylon core melts. This melting weakens the line, and it snaps. To avoid this problem, use plaited or braided Dacron line and canvas chafe protection such as that sold by Perimeter Industries or Davis Instruments.

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