A PLATFORM FOR TECHNOLOGIES

Not the kind of technologies that frustrate with their complexity and rapidly become redundant, but the kind of technologies that benefit from a steady evolution in modern trimaran design and construction.

Technologies that build light, stiff structures, efficient hull shapes that deliver performance across the wind spectrum, and sails and rigs that make the most efficient  use of the wind.


TECHNOLOGY OF HULL DESIGN

Rocket 44's main hull features full sections amidships to minimise drag in the zone between light weather sailing and flying the main hull. The entry is very fine and the rocker aft is slightly hollow provide a flat release and promote downwind performance.

Trimarans have two sweet spots.

The first is in light air with the floats just skimming the water.

At low speeds skin friction is the main cause of drag and we use a fuller hull shape to minimise wetted area. 

The second is reaching at high speed in fresh air when form drag is the primary drag factor. This is the speed range where a finer hull (effectively a lower displacement to length ratio) is more efficient. It penetrates waves easily and has enough buoyancy to keep the main hull clear of the waves as much as possible.

The challenge in trimaran design is the transition zone between these two modes.  This is the zone where a powered up catamaran has the potential to lift the windward hull and  make minced meat of a tri that is struggling to get air between the main hull and the water.

We sometimes get the call for a flat rocker line in the main hull. But you can't draw the rocker line in isolation of other design parameters.  If you want the floats to be clear of the water at rest (and you should if you want to perform) then you have to provide buoyancy for the full sailing weight of the boat in the main hull without making it too fat on the waterline. 

 

Our goal here is to use sail area to bring the wind pressure forward and boost speed by getting the main hull out of the water as early as possible, and keep it out as long as possible. 

The flatter rocker line will come completely clear of the water at a lesser angle of heel, but while the full length of the hull is still submerged we have more drag holding us back and resisting lift off.

 

In the lulls; as the  heel angle is reduced the full length of a main hull with a flat rocker line is more quickly submerged to close to its full length, whereas a more rounded rocker line will give incremental support at an earlier stage as the power comes off.

 

 



Bare Essentials (left) in ideal trim with the main hull clear of the water. Mad Max (right) was probably able to fly the main hull in less breeze than Bare Essentials and is also able to keep the windward hull airborn for longer periods than the trimaran. Note that Mad Max could drop the traveller a couple of notches without wetting the windward hull and this is where a canting mast is a significant advantage for trimarans.

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