Tilt keel
The term tilting keel refers to a keel that can be swiveled to windward about a longitudinal axis lying deep in the ship in order to increase the righting moment of the keel bomb . The English name is Canting-Keel . The terms tilting keel and pendulum keel are also common . If the pivot axis is transverse to the boat's longitudinal axis, it is a pivot keel .
The weight savings on the keel bomb and the fact that the ship can be driven with less heeling (more upright) results in a higher ship speed. In contrast to the use of water ballast on the windward side of the hull, the tilt keel technique can reduce the heel of the yacht without increasing its weight.
technology
Traditional fin keels have the disadvantage that their righting moment only comes into play when the ship is heeling . The purpose of the tilting keel is to develop a high righting moment even with a low heel.
The keel is swiveled around a longitudinal axis in the ship's hull by means of hydraulics (in rare cases also by cable). Constructions with one or two hydraulic presses are used, whereby weight saving stands against reliability.
The point where the keel passes through the hull is problematic . The hull opening must be relatively large due to the axis of rotation lying within the hull. In most constructions, the ship's hull is sealed using rubber. While this seal is waterproof, it would not withstand the water pressure at high speeds. The passage through the fuselage is (additionally) secured by means of so-called bomb doors , which in addition to the seal also benefits hydrodynamic aspects.
To reduce the drift of the ship, one or more additional swords must be used with tilt keelers .
Problems
The main problem is the price of this complex keel construction. So far it has been used almost exclusively on a few regatta ships (Schock 40, Cookson, Volvo Open 70 , Open 60 , Mini 650 ). This technology has therefore not found its way into normal cruising yachts . In addition to the high costs, this is also due to the space required.
The Volvo Ocean Race 2005-2006 was one of the first long-distance offshore regattas to use this technology. Several ships had problems with this technique; this ultimately even led to the loss of a ship. The fault was due to the underestimated dynamic forces that the keel construction is subject to at high speeds and in rough seas. Mostly problems arose with the hydraulic rams of the keel adjustment and the sealing of the keel passage point on the hull.
history
In 1991, the Frenchman Michel Desjoyeaux was the first sailor to use the tilt keel technique in an ocean race. He won the second stage of the Mini Transat from Madeira to the Caribbean with his Mini 6.50.