Bird of Passage 57/17

Liveaboard Full Power Auxiliary Voyaging Yacht
Johan and Tove Kjellander
Designed by
Tom MacNaughton


You requested a design for a sailing vessel for offshore use and living aboard that would still be able to cruise the canals of Europe. It needs to be a full time home for two adults, two children and up to two guests. The styling is to be form follows function.

Although you intend to design the interior yourself we were to keep in mind your additional requirements. These include a sauna, which can double as a children's cabin when there are guests aboard. There should be a workbench in the engine compartment. The master stateroom should be large enough to have two office areas with computers and plenty of bookshelves. There should be a wheelhouse or a deck saloon with large windows and a comfortable place to navigate the boat from inside. In addition we assume there will need to be one small head for children and guests forward as well as the larger head for the parents aft.

The design should be as light a displacement as can fill the requirements and still sail and point well. Your last boat was 14.5 meters by 3.3 meters and proved too small. It had a swing keel. You were hoping for something about 15 to 16 meters long by 4.3 to 4.6 meters wide. Displacement should be well under 20 tons. You are looking for headroom of between 1.9 and 2.0 meters.

The major challenge is that you wanted shallow draft with a hoped for maximum of 1.5 meters. This presents the two major problems that we had to solve. First, we needed to get the center of gravity lower than the fixed draft would allow in order to be sure we had a low enough center of gravity to bring the vessel back from a roll over due to wave action in a storm. It was soon evident that the only way to do this was with a hydraulically retracted and extended keel. Second, we were faced with the fact that in this size boat the proposed maximum fixed draft was too shoal to allow a rudder with sufficient control to prevent broaching downwind. There were only two reasonable solutions to this. One would have been to use a retracting outboard rudder. However this represented engineering problems that appeared excessive. The second solution, and part of the strategy we eventually adopted, was to use a small aft "trimming" board just forward of the rudder. This can be used to vary the center of lateral plane sufficiently to reduce the required load on the rudder to whatever degree seems appropriate. In addition we have designed the rudder with end plates at both top and bottom to increase the effective pressure differential and help avoid ventilation from the surface. This will cause a slight increase in drag but is worth it because of the increased safety at sea.

You expressed the hope that we can work in full foam flotation. In light of this we laid out a carefully proportioned bulkhead arrangement that would allow the type of interior you wanted and still leave room for some flotation in the ends. Combined with the installation of additional foam in normally inaccessible areas we should be able to develop sufficient flotation to make the boat unsinkable.