Daggerboards

Daggerboards slide vertically within the daggerboard-trunk. On a catamaran, the trunks are located on the outside edge of each hull, more or less at the midships position, and form the keels of the boat. The keel helps to produce the force vector required to move the boat forwards – see the definition of keel, for more.

On a dinghy, the single board is located midships and should not be confused with a centerboard which looks the same, but which rotates around a pin when raised or lowered, thus requiring a slot in the boat, allowing the board to pivot.

Depending on the boat, the boards vary in length. Fully raised they stick up into the air above the deck, fully lowered they stick into the sea about the same distance. On a modern catamaran the boards are sometimes made from fibreglass, but are often made of carbonfibre or Kevlar. Glass boards, left down at seven feet, can snap from the pressure of the water when the boat exceeds twelve knots. The boards on Bit-by-Bit are about fifteen feet long (the seven feet they stick up or down, plus the eight feet of hull they slide through in their trunks), about three feet wide and six-inches thick at their centers. They are foil-shaped with knife-edges, to allow them to slice through the water. The board’s length allows the rest of it, the eight-feet that’s in the trunk, to take the strain of the blade cutting the water at speeds approaching thirty knots. The daggerboard-trunks are made of Kevlar, built seven times stronger than the board, to ensure that the board snaps when it runs aground, instead of the trunk.

The advantages of using daggerboards over a fixed keel are: They can be raised into the hull to allow it to be sailed into water less than 2 feet deep and then be beached comfortably and then re-floated; they can be raised when the boat is sailing downwind and no form of keel is required, thus reducing friction; and they can be lowered to their maximum depth to assist sailing upwind, when a deeper keel affords a smaller angle of point-of-sail.

The photograph shows the daggerboard on the port side, sticking up into the air around midships, just behind the shroud.
Kissing the water Port side

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