TT Scow från Thomas Tison

Det är kul med nya designidéer. Foiling har väl varit hetast de senaste åren, men även scow-konceptet dyker upp allt oftare. Vem minns inte David Raisons trubbnosiga mini som vann Trasat här om året.

Thomas Tison har bland annat jobbat med Mascalzone Latino, Team Origin och är nu på Artemis designavdelning i San Francisco (bor med Fredrik Lööf).

Nu ligger han bakom en superlätt enmansjolle med ostagad mast som kan lutas 15 grader till lovart. Frågan är om det är för hightech i en traditionell värld, eller om detta segment numera tillhör Moth-jollarna?

Thomas Tison and Nomad Composites (Benoit Quemener) are to launch an extreme and innovative single handed dinghy this winter.

The TT Scow has been designed with only speed in mind. It is the only recent dinghy to have an unstayed canting wing mast for improved aerodynamic efficiency. It also has a scow hull shape for improved form stability. Buailt to a high standard in carbon fibre, it is the ideal dinghy for adults, especially those who like to sail fast, with minimum constraints and on a nicely finished and exclusive boat.

The prototype has been built and will be undergoing testing this winter in France. It will then be on display in Europe and in the USA.

The main features are:

– High stability
The scow hull shape and the hiking wings make the boat as stable as a skiff. It can therefore carry a large and well proportioned sail plan without trapeze.

– Efficient
The unstayed, canting and rotating wing mast ensures the flow on the mainsail is clean and that the mainsail is well in the wind, at any heel angle. The hull shape helps initiate planning early and the long bow overhang increase waterline length upwind.

– A stiff, robust and lightweight structure
No E glass is used in the construction. The boat is built using carbon sandwich laminates only. The foam core and the outer skins are designed for robustness where it matters, while keeping the overall displacement really low for a boat this size.

– A unique style, carefully built and engineered
The boat was engineered in Germany, and carefully built in France by Benoit Quemener (Nomad Composite) who has, amongst other things, taken part in the construction of Sail Rocket. Thomas Tison is a naval architect currently working for the America’s Cup.

Thomas har ju lagt fram en del scow-designer tidigare, utan att de blivit förverkligade. Bland annat den här 14.2 meter långa racern. Även Reichel/Pugh hade ju en maxi på ritbordet för ett par år sedan.

Nedan försöker han reda ut fördelarna.

The main benefit of scow hulls is form stability which is a cubic function of hull beam. Hull beam in this case is taken as the average hull beam i.e. a hull will be beamier from a form stability point of view if it has a constant maximum beam compared to the more triangular shapes induced by the standard vertical bows. More form stability allows to carry more sail area, and therefore create more drive force, for the same weight (improved power to weight ratio). Typically a scow hull shape, for the same hull length and maximum hull beam as a standard hull shape will create 30% more righting moment.

The other positive point is that the tendency of hulls to pitch by the bow (bow down) is much reduced. This bow down attitude is due, on standard hull shapes, to the volume above the waterline, by the transom, which goes under water when the boat heels. This effect is what drives the transom shapes of TP52s and mini maxis currently. Scow hull shapes however, being equally wide all along, do not have more volume in the back when the boat heels and it is therefore possible to push the boat harder, in some cases also reduce sailing displacement as some classes use water ballast for this purpose.

Another key point is that using the bow overhang and the capacity of scow hull shapes to behave well when heeled allows to design two specific hull shapes. On one side, an upwind hull shape (large heel angles) with the increased waterline length provided by the bow overhang, with rounded sections for minimum wetted surface area. And on the other side, a reaching hull shape, with flatter sections to create lift at lower heel angles.

One thing which is clear from the lines above is that scow hull shapes must heel, and using a canting mast therefore makes a lot of sense.

(I wrote an article about scows for seahorse some years ago (published in June 2011) which could be a good reference)