Why does the HAPPY CAT come with a long centre-board and not with short fins under the hulls?

In short:
• CENTRE-BOARD: When best sailing performance is desired, plus  excellent close haul beating to windward properties, little leeway, precise trimming to suit every situation, highest speed and maximal robustness.
• FINNS: When sailing performance does not matter, so as less windward qualities, less track holding = plenty of leeway, not trimming possible, no longevity/robustness.


Our predecessors the SEMPERIT company with their brilliant designer Eduard Heuzonter experimented already during the 1980s using fins at the hulls instead of boards. We too built prototype  catamarans in 1987 and tested these with fins. At this present state today, to revert to building catamarans to have fins would be a retrograde step of development and bear fundamental disadvantages:


  • Cumbersome and damage prone fixing to hulls


  • The craft is continuously stored ashore resting on fins, with the entire weight pressing onto the fins. When sitting on the catamaran, or wishing to mount a tent on its frame, those fins be better dismounted, and when launching for a sail, to be re-attached. That is bothersome, damage  prone and  a cause for constant  customer claim.


  • Complicated launching of the catamaran and problematic landing. Landing on rocky shores or at high speed can quickly damage the fins.• The belief that fins be better when operating in shallow water is a misconception.  The catamarans rudder still remains fully immersed in water, exactly as deep as a centre-board. To tilt the rudder, so that it does not reach so deep into the water, would create tremendous pressure and render the cat uncontrollable. Apart from that, a centre-board can be tilted so that it does not have such deep draft.


    Using hull mounted fins with little draft does not allow for as good windward performance as that of a catamaran using a profile centre-board reaching deep into the water. Our trials DISTINCTLY arrived at that conclusion. It follow, that beating to windward a fin catamaran needs to tack far more frequent than a cat equipped with a deep centre-board. In offshore wind, this can even be dangerous!


    Compare the wings of a glider plane. They have a short depth, but extreme length (wingspan) The longer the wings the greater the lift, the more efficient the glider becomes. The board of a sail-boat behaves in the same manner. The deeper/longer the profile board is immersed in the water the greater and exerting the velocity of the water flow passing the profile.  The faster the catamaran moves, the higher the efficiency of the board. In deeper water eddies generated by the hulls diminish,  and the effect is greater. Figuratively speaking, the board gets a hold in the water the deeper it is immersed and the faster the craft moves. That allows it to sail closer to windward.


    A centre-board or fins are intended to prevent leeway. The deeper immersed in water the greater the effect. That is why a centre-board is more effective to prevent leeway. On the other hand, when the wind is blustery the centre-board may be set at a calculated angle intended to allow for a measure of drift. That cushions gusts and allows smoother ride characteristics and picking up speed.


    The centreboard is at any time the most effective means to adjust the centre of pressure to suit actual course and situation. When sailing to windward the centreboard may be set in vertical position to be most effective. That increases pressure on the rudder, felt on the tiller, and that is quite important for beating close-hauled. When broad reaching under moderate wind conditions the centre-board may be set at an angle of approximately 20°. That reduces rudder/helm pressure to the benefit of higher speed. When on the run before the wind, the centre-board may be lifted farther off the water to reduce resistance.


    Fins that reach into the water sparsely, have no flow profile and are of flat structure, THEY will generate no pressure, but eddies at the edges. That makes for little performance.
    Added to that the swirls and eddies generated close to and by the hulls, which reduce the effectiveness of the fins further. The point at which leeway is to be prevented is located very high (not deep in the water) and is therefore of very little effect.
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