The keel is the most important longitudinal structure of a ship or boat that is attached to the ground amidships . The keel is thus the " backbone " of the ship. The transversely stabilizing frames , the "ribs", are attached to it. At its ends, the keel merges with the stern . In addition to stabilizing the hull, it also serves to increase course stability and - especially in sailing vessels - to reduce lateral drift.
In contrast to a retractable sword , a keel is usually permanently mounted and has a considerable weight. Depending on the type of ship, there are very different keel shapes, some of which cannot be clearly separated from the sword.
Development history of the keel
In terms of development, the keel emerged from the dugout canoe. The first further development of the dugout canoes consisted of the insertion of frames and heightening of the side walls by means of attached planks . After this technique was perfected, the dugout was gradually reduced more and more until in the end it was only the load-bearing element, the keel, of the boat's hull.
The keel in sailing vessels
In sailing boats, the keel also has two additional functions:
- It is used to enlarge the lateral plan , which reduces the lateral drift of the vehicle and creates lift towards windward. This allows sailing vessels up to the wind to sail (diagonally opposite the wind move forward).
- It ensures weight stability , which protects the vehicle from capsizing (overturning) in the event of a sharp heel (lean angle).
For maximum effectiveness and good sailing properties, the keel weight should be as low and as heavy as possible. Especially in shallow inland waters, however, this leads to considerable restrictions in the choice of possible berths, which is why one increasingly relies on lifting keels or other compromises have to be made. Sailing ships with a fixed keel have a significantly larger draft than comparable motor ships.
The hydrodynamic buoyancy of the underwater hull acts towards windward and thus keeps the ship on course (see the physics of sailing ). Findings from fluid mechanics make it possible to determine efficient keel shapes on the computer. As a first approximation, the effectiveness of the keel as a buoyancy fin depends only on the square of the draft, but not on the area of the underwater hull. This is why the shapes of the keels have changed significantly over the past 50 years. Long keels were still common at the beginning of modern yacht construction, but today they are very narrow and deep.
Long keel and short keel on sailing yachts
Long keels run over a large area of the underwater hull of a sailing yacht. They are rarely built these days because short keels offer more advantages.
The short keel extends only over a small area of the length of the underwater hull, but extends further into the depth than the long keel. Short keel yachts are lighter, faster and more agile and therefore easier to maneuver. Disadvantages are a lower directional stability and a greater depth. In addition, the construction of narrow keel variants is more demanding for the manufacturer, because the enormous shear forces of the keel have to be transferred into the hull over a very small area. Fortunately, a loss of the keel is rare - 73 were counted between 1983 and 2015 - but it is one of the worst things that can happen at sea. If the keel is lost, the boat capsizes almost immediately and leaves the crew hardly time to board the life raft , which is why the accident often ends fatally, most recently in the accident of Cheeki Rafiki in the middle of the Atlantic in summer 2014.
Ballast keel, fin keel, ballast sword
A fin keel is a heavy keel fin that is generally bolted to the “actual” keel in sailing boats ( keel boats or sailing yachts ). A distinction is made between short and long keelers in these boats . Older yachts are often long keelers, modern yachts are almost without exception short keelers.
With some dinghy cruisers heavy swords are used, which realize their great mass with laminated lead ballast or by being completely and homogeneously made of metal. Such ballast swords do not form a transition to the lifting keels because, in contrast to these, they are rotatably suspended.
A keel sword is the combination of a fin keel with a retractable sword . The fin keel part is shorter towards the bottom (stubby keel) than the normal fin keel. It largely ensures the weight stability of the trunk. The sword can be extended through a slot in the keel, thus enlarging the lateral plan. This construction has the advantage that you can sail in shallow water with the sword raised.
Kimmed keel, double keel, triple keel
A keel keel consists of two short fin keel that attach to both sides of the fuselage (in the area of the notch ). They allow in waters with pronounced tides , the drying up because the yacht can be easily on the bilge keel.
Occasionally, the double keel is the variant of the keel keel, in which the ballast is mainly located in the two fin keel.
A keel keel with an additional central keel is called a triple keel.
This designation describes the arrangement of a keel in the middle of the ship - in contrast to the keel keel. It can also be the middle keel of a triple keel.
The wing keel, which was kept secret until 1983, was used for the first time at the 1983 America's Cup on the Yacht Australia II , which also won the regatta. It was developed under the direction of Ben Lexcen in Australia. The wing itself is a special form of the keel bomb and may bring hydrodynamic advantages. These benefits are most common at higher boat speeds. At slow boat speeds (little wind) the wing keel acts more as a brake due to the larger wetted surface compared to the conventional keel bomb, which causes greater water resistance. Due to the shallow draft, yachts with wing keel can also be driven in shallow waters.
Swing keels are movable keel fins that can be swiveled in the longitudinal direction of the ship and folded into the hull.
Tilting keel (pendulum keel)
Tilting keels (also known as pendulum keels or canting keels) are movable, long and narrow keel fins that carry keel bombs and are mainly used in regatta sailing yachts. They can be swiveled sideways (towards starboard or towards port ) in order to actively influence the heel of the yacht. Tilting keels make it possible to reduce the total weight in relation to similar yachts with a rigid keel fin.
Lifting keels are keel fins that can be pulled into the ship's interior using suitable lifting devices such as cable winches or hydraulic drives. Lifting keels are mainly used where keel boats often have to be transported, e.g. B. for regatta boats, or to enable ships with great drafts to call at shallow harbors.
Lifting keels, the hoisting device of which can only be operated for transport purposes, are also referred to as single keels .
Swing keels are an alternative to lifting keels.
The folding keel can be folded in to reduce the ship's draft. It is mainly used in sailing yachts. Here it enables larger ships to enter shallow harbors without needing space inside the ship.
Beam keel and shallow keel
Sailing ships, small fishing vessels and tugs have a beam keel which protects the outer skin from touching the ground and increases course stability. It consists of a long, thick-walled flat steel. A keel sloping towards the stern (keel drop) reduces drift.
Most steel ships have a shallow keel inserted into the outer skin, the material thickness of which exceeds that of the adjacent floor slabs.
Roll keels are bulges or rails attached to both sides of the ship or boat that serve to reduce rolling and rolling movements. They can usually be found on freighters or motor boats.
- Yacht , 5/2016, page 3
- so Claviez, Wolfram: Seemännisches Dictionary. Bielefeld: Delius Klasing, (3rd edition) 1994, p. 74 and p. 190; Schult, Joachim: Segler-Lexikon. Bielefeld: Delius Klasing, (9th edition) 1994, p. 88, p. 221 and p. 223, treats the terms synonymously
- Schult, Joachim: Segler-Lexikon. Bielefeld: Delius Klasing, (9th edition) 1994, p. 96