Besides several fixed keel designs, Blank Yacht Design provides the design and engineering for different keel systems with variable draft.
The possibility to reduce the draft is appreciated by owners, who sail in areas with tides, like parts of the North Sea, but also by owners, who want to sail and
anchor in shallow waters and bays, where the swell is usually much less than further out. Many harbours and marinas require a retractable keel, this is often of
keen interest if a sailor also makes demands for sailing performance.
Every solution has advantages and disadvantages. We are happy to give you any advice to find the optimum solution for your yacht.
Lifting keels provide a relatively simple and strong solution with the whole ballast content in the bulb.
In our swing keels (Centre Board) systems, the whole ballast content is positioned in the keel foil. Only this solution provides good righting moments and as a result
good sailing performance. Internal ballast in form lead pigs, massive steel plates or something similar is not very effective.
In combination with properly designed rudders, all of our variable draft keel systems offer excellent sailing characteristics. These compared
to the traditionally used fixed keel and one rudder systems are often better, in terms of performance as with twin rudders one of the rudders is almost always fully
immersed and can therefore effectively steer.
Swing keels . . .
The demand for swing keels systems has steadily increased in the past years. One of the reasons is, that the keel
system can be easily and almost invisible integrated under the raised salon arrangement of deck house yachts. Since in our swing keel systems, the whole ballast is in the
foil, these systems offer the opportunity for excellent sailing performance.
Material for bearings POM (Polyacetal), bronze or wounded fibres can be used for bearings. Our keels swing about 70 to 75 degrees and in combination with an adequate
hydraulic system all of our systems have been working for several years without any problems.
We have developed three different systems, several of each of which have been built.
The swing keel system of Life 75 is mainly used for smaller boats. This yacht can reduce the draft from about 2,00 m to 0,69 m.
The largest yacht currently built has a length of 68 ft and has a swing keel system with a lead foil of about 13 t, this yacht can reduce its draft from about 3,82 m to only 1,58 m. The effect of both systems on the interior arrangement is little.
A big advantage of swing keels is, that the keel foil is locked down in the "sailing" position and stays down, even if the yacht should capsize in a storm. The hydraulic systems we use make this feature possible.
The swing keel system of Life 75 allows easy trailering and larger yachts can be sailed into shallow bays where one can find less swell and have access to most harbour's or marinas.
Major advantages of our swing keel systems compared to many other systems:
- full ballast in elliptical keel foil, no internal ballast needed
- keel foil and bearing can be installed from underneath and can be removed if needed (as with a fixed keel)
- gap behind keel is closed by hatch to achieve a smooth surface and to avoid drag
- closing hatch works as geometric function of keel movement and closes and opens the space behind the keel foil automatically
- hydraulic cylinder is positioned over the CWL and is not permanently in the water
- hydraulic cylinder can be serviced or replaced any time without dismounting the keel system
- in case of grounding, keel foil raises and stays up until lowered by helmsman, avoiding next rock
- transfer of keel loads by steel surfaces, avoiding peak loads to GRP, similar principal as with a fixed keel top plate
- excellent sailing and steering performance with swing keel in combination with dual rudders of adequate size and shape
- keel system is in general maintenance free
- keel foil is locked down by hydraulic system, even if yacht capsizes
- simple push button control
Lifting Keels . . .
In many of our different yachts, lifting keels have been included. The designs range from yachts with a length of
about 26 ft up to 60 ft. This includes a former BOC racer that can reduce draft from about 3,5 m to 1,55 m.
Lifting keels can be included in many interior arrangements. Concepts with a keel box reaching from hull bottom to the deck usually offer a stroke of about 1,2 m 2,0 m.
Besides the conventional lifting keel systems, we have designed in the past years for several of our yachts lifting keel systems with a reduced stroke and without any structural parts, avoiding rods, keel boxes or similar, which can often interfere with the interior design..
These designs offer a stroke of about 750 mm and with a well designed keel bulb these or any other lifting keel design offer a very good righting moment and therefore a robust sail plan and therefore performance.
Telescopic Keel . . .
These keels are a good choice to add to existing designs. The stroke range is about 500 to 800 mm. With this design two or three parts of the foil slide in each other with an overlap.
With many existing designs, the internal structural parts like floors and longitudinals can remain as they are.
Since all parts are completely under water, the system requires the use of high quality stainless steel.
In some of our GRP yachts, we included lifting keel systems made from aluminium. All these systems still work well, even after many years of use.
Major advantage of our lifting keels:
- sleek and fast foil with full ballast in bulb
- best righting moment
- load for hydraulic cylinder is just keel weight and friction
- CG stays in same longitudinal position if keel is raised