Designer (Rolf Eliasson) says:    Back to start

Some commentary about Sofia

Little boat, small worries. Yes it may be true for the owner, but definitely not for the designer. A lot of things was given from the start, as that Sven (Yrvind) had done the rough work: concept, i.e. a lightly driven hull as to take care of herself with finite sails, a tandem construction of keel and rudder, shallow going and with possibility to sail up on the beach and park.

Let us begin with what is said to be an easily driven hull. Nobody would contradict that a plank is more easily pulled lengthwise through the water than sideways. In all, a slender hull is preferable. Seeing that it is a cosy cruising boat we strive for, not a high achieving planing boat, which would take a hull shape simililar to a mini-transat-boat. Smart but difficult. No, let us stick to an older, reliable hull concept: tapering along (naturally) and even tapering back so that it passes from its own wake as painless as possible. What worked for the Vikings, still works. A little but though, it should not become too heavy. More about this later.

So for it to have a so lightly driven hull as possible it should therefore be as slender as possible. Catamarans have such hull with length/width ratio over 10, with the disadvantage that there must be two hulls and that it is not self righting after one turn around. So focusing on as "slender as possible" mean that stability characteristics for this hull is a high priority. Large breadth give large stability (initially) but also large resistance, so we stick to a narrow boat. Now, let's become even more out of date. Water line width does not differentiate itself especially greatly from width in deck. So even if width over all is small is the working water line width relative looking fairly large. And it is there you have it, stability that is. Comparing with modern boats which is narrow in waterline, it demands of crew to sit on the gunwale, this can have ballast tank at the gunwale and/or have a keel with a weight in the bottom, and this we do not want. The boat should be shallow going and be stabile by herself. In short: cross section of midships will more resemble a shoebox than a half circle. Proof: compare the experience between standing on a timber log with that of standing on a float.

The concept slender should also include that the boat should be light compared to its length. This is achieved by consequently using a sandwich construction in all the boats parts. Comparison with the unibody construction of a car is illustrating, where all the parts contribute to the strength. The end result is a light, strong and easily driven boat that does not require especially large sails to reach its top speed.

Configuration with the centerboard far forward and a rudder far back give special characteristics. Course stability is exceptionally good as the rudder is almost as effective as the centerboard in preventing leeway. As compared to a "hot" dinghy is it possible to do a calm and worthy turn in class with considerably bigger and heavier "normal" keelboat. If one releases the rudder completely, the center of lateral resistance goes drastically forward and the result is like hitting the breaks. On the other hand, one can draw up the centerboard, tie down the rudder and the boat becomes directionally stable downwind. Between these there are an endless number of combinations. As they say in America, the boat has a unique underwater configeration, VCLP (Variable Center of Lateral Pressure) that makes it possible for one by himself to determine how well the boat will balance! It would be interesting to build a 10-12m boat according to these principles.

Rolf Eliasson