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| Dacron |
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A synthetic polyester material.
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| Daggerboard |
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Similar to a centerboard, except that it is raised vertically. Like a keel, daggerboards are used to prevent a sailboat being pushed sideways by the wind.
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| Danforth Anchor |
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A brand of lightweight anchor. It has pivoting flukes that dig into the ground as tension is placed on the anchor. It does not have a stock.
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| Davit |
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A device that projects beyond the side of the boat to raise objects from the water. Typically a single davit is used on the bow of a vessel to raise an anchor, and a pair are used on the side or stern of the vessel to raise a dinghy.
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| Daybeacon, Daymark |
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A navigational aid visible during the day. In the United States and Canada, square red daybeacons should be kept on the right and triangular green daybeacons should be kept on the left when returning from a larger to smaller body of water. Also see can and nun buoys.
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| Daysailer |
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A small boat intended to be used only for short sails or racing.
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| Dayshape |
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Black diamond, ball, and cone shapes hoisted on vessels during the day to indicate restricted movement ability or type. For example three balls means aground.
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| Dead Ahead |
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A position directly in front of the vessel.
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| Dead Before |
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Running with the wind directly behind the boat.
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| Dead Reckoning |
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A method of determining position by making an educated guess based on last known position, speed and currents.
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| Deadlight |
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Fixed ports that do not open, placed in the deck or cabin to admit light.
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| Deadrise |
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The measurement of the angle between the bottom of a boat and its widest beam. A vessel with a 0º deadrise has a flat bottom, high numbers indicate deep V shaped hulls.
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| Deck |
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The surface on the top of the boat that people can stand on.
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| Deck Stepped |
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A mast that is stepped (placed) on the deck of a boat rather than through the boat and keel stepped. The mast of a deck stepped boat is usually easier to raise and lower and are usually intended for lighter conditions than keel stepped boats.
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| Deckhead |
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The underside of the deck, viewed from below (the ceiling.)
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| Depth Sounder |
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An instrument that uses sound waves to measure the distance to the bottom.
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| Deviation |
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See magnetic deviation or compass error.
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| Dinghy, Dink |
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A small boat used to travel from a boat to shore, carrying people or supplies. Also known as a dink or tender.
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| Dismast |
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The loss of a mast on a boat. Generally this also means the loss of some or all of the ability of the boat to sail.
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| Displacement |
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The weight of a boat measured as a the weight of the amount of water it displaces. A boat displaces an amount of water equal to the weight of the boat, so the boat's displacement and weight are identical.
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| Displacement Hull |
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A type of hull that only floats, even when in motion, as opposed to a type of hull that allows a boat to skim across the surface of the water. See planing hull.
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| Displacement Speed |
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Also hull speed. The theoretical speed that a boat can travel without planing, based on the shape of its hull. This speed is 1.34 times the length of a boat at its waterline. Since most monohull sailboats cannot exceed their hull speed, longer boats are faster.
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| Distance Made Good |
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The distance traveled after correction for current, leeway and other errors that may not have been included in the original distance measurement.
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| Distress Signals |
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Any signal that is used to indicate that a vessel is in distress. Flares, smoke, audible alarms, electronic beacons and others are all types of distress signals.
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| Dive Flag |
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(1) A red flag with a white stripe. (2) The alpha flag is the legal requirement for boats with divers in the water. Boats should probably display both flags when they have divers in the water.
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| Dividers |
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A navigational tool used to measure distances on a chart.
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| Dock |
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(1) An platform where vessels can make fast. The act of securing a boat in such a place. Docks are often subdivided into smaller areas for docking known as slips. (2) The act of entering a dock.
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| Documentation |
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Licenses or registration papers for a vessel. Types of documentation vary depending on the country, vessel size and purposes.
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| Dodger |
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A cover attached to the top of the cabin at the front of the cockpit. Dodgers help shelter the cockpit from wind and water.
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| Dolphin |
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A playful sea mammal. Also a type of fish. Also a group of piles used for mooring or as a channel marker.
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| Dorade Vent |
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A type of vent designed to let air into a cabin and keep water out by the use of baffles.
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| Double-Braid |
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A line consisting of a braided inner core and a braided outer sheath.
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| Double-Ender |
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A boat with a pointed stern. Known as a double-ender because the stern may look very similar to the bow.
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| Douse |
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(1) To drop a sail quickly. (2) To extinguish a candle, lamp, or fire.
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| Down Helm |
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To steer a sailboat toward the wind.
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| Downhaul |
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A line used to pull down on a spar or sail.
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| Downwind |
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In the direction the wind is blowing.
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| Draft |
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(1) The depth of a boat, measured from the deepest point to the waterline. The water must be at least this depth or the boat will run aground. (2) A term describing the amount of curvature designed into a sail.
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| Drag |
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The resistance to movement.
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| Dragging |
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Description of an anchor that is not securely fastened to the bottom and moves.
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| Draw |
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Draft. The depth of water that a boat requires to stay off the bottom. A vessel "draws" a certain amount of water.
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| Drawbridge |
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A bridge that can be raised vertically to allow boats to pass underneath.
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| Drift |
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The velocity of a current.
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