Schwert ( German: Schwert "sword") - a retractable fin that prevents the demolition of the vessel under the wind. A yacht equipped with a dagger, but not having a ballast keel , is called a dinghy .
A vessel, especially a sailing one , blows under the wind at any heading relative to the wind , especially in sharp heading, when moving to the tack , it zigzags against the wind. When moving in the same direction as the wind, the dagger is usually raised. Also, raising the dagger allows the ship to go in shallow water or moor to an unequipped shore.
Raising or lowering the daggerboard, you can to some extent control the centering of the vessel.
Content
Construction of a daggerboard
The daggerboard is usually installed in a special waterproof well that rises above the level of the waterline in the diametrical plane of the vessel.
By design, daggers are dagger or rotary. A dagger-type daggerboard is inserted into the dagger-hole, like a sword in a sheath (origin of the name). The rotary dagger is fixed on the horizontal axis so that when meeting with an obstacle it leans back and up, which reduces the risk of damage.
Usually, a daggerboard is lowered by its own weight, and a special tackle called a daggerboard hoist is used to lift it.
Swing and ballast keel
Yachts having a small ballast keel, from which the dagger itself is pulled out, are called compromises . This design allows to some extent combine the high stability of the keel yacht and the small draft of the dinghy.
Svertsi
Shverts - this is a variant of the shverta, in which the turning or lowering planes are attached to the sides of the hull. Schwerz is easier to implement, since it does not require a waterproof well (therefore, early Dutch coastal vessels were equipped with shverts). In motion under the sail, the windward shverts are raised.
Features
- A pair of dowels is more effective than a dagger installed in the diametrical plane, since the pair design allows you to give the daggers an asymmetric profile, giving greater lift in the direction of the opposite side. Since the windward dagger is always raised, only one of them works, creating an effort in the direction of the windward side. However, this does not apply to schwerts that cross the interface of the media (water-air), in the area of which a significant part of the lifting force is lost due to vertical deviations of the incoming flow (air suction on the convex side of the profile and an increase in the water level on the inside), which leads to an increase in inductive resistance (an integral part of the total resistance arising from an increase in the angle of attack caused by a decrease in lift at the ends of the wing). Thus, shverts, which are usually used instead of asymmetric daggers on inflatable sailing ships for technological reasons, despite the asymmetric profile, do not exceed the symmetrical dagger installed in the hull efficiency and are significantly inferior to asymmetric daggers.
- Unlike the ballast keel , the daggerboard does not increase, but reduces the stability of the yacht.
- The most high-speed modern yachts , for example, yachts of the VOR60, VOR70 classes, are equipped with dowels, but are not dinghies, as in addition to them they have a ballast false wing.