Gybing centerboard and Mini-Transat

Discussion in 'Sailboats' started by pogo, Apr 21, 2015.

  1. pogo
    Joined: Mar 2010
    Posts: 342
    Likes: 9, Points: 18, Legacy Rep: 73
    Location: Germany Northsea

    pogo ingenious dilletante

    In the late 70s Jean-Louis Noir drew a little trailersailer for the french yard Dufour.
    T for trailering , 7 for her length in meters--Dufour T7

    The boat featured a centerboard , was bilgeballasted and had an aft cabin, which meant space for max. interior space ( berth).
    For such a small cruiser an aft cabin is not the worst concept.

    One might think that such a small bilgeballasted centerboarder with aft cabin has been designed only for trailering, family cruising in sheltered waters and that she can't be not seaworthy .

    Haven't few years before some centerboarded Quartertons shown that the concept with internal ballast can be unsafe ?

    However , the Dufour T7 was another generation , not sticked to the IOR-rules.
    The boat had little rocker , was more flat-bottomed , tended to plane, surfed faster, while still being roundbilged, with seakindly ( pretty sharp) forefoot.

    Designer and Yard where convinced of the boats potential and so the french racing-sailor Daniel Gilard ( who searched for a good "upwinder" took part in the second Mini-Transat in 1979 with the prototype.

    The boat proofed to be very stiff, performed upwind in a seaway very smooth and was fast.
    In the 1979 Mini-Transat The fleet of 49 boats had to sail thru three storms w. more than 8 Bft. .
    The Dufour T7 finished third !!

    Apart from being a small seaworthy centerborder , the most intereting feature of the Dufour T7 is her gybing centerboard .
    It can gybe, ' cause it's overbalanced.
    Pix explain it very well:

    Dufour had the T7 only for three years in production, about 250 have been built.
    The moulds were sold to ???? and the boat was produced as Rhodes 24 until 1993.

    Nowadays Dufour T7s are mainly used for coastal cruising, often in shallow waters. Nearly all of them have trailers.
    T7s are genuis safe trailersailers . With their shallow draft and the possibility to dry out they widen the cruising grounds ( dunna the exact english word;).
    Most owners don't know anything about the seaworthyness of the boat. A lot of second, third , fourth owners don' t know anything about the gybing , no " loose" centerboard, which often someone has " repaired " .

    Nice underestimated boat, i love her.
    Each time when i see a T7 i admire her. I'm jealous about her owner ;)

    However , nearly all T7 still fulfill the duties of their owners ---safe (family) cruising and/or trailering.
    That was also the designer's aim.
    Here an interview w. Jean-Louis Noir , he explains why and how:

    "At first glance, the Dufour T7 is different from any other boat, so we reveal the thoughts of her designer Jean-Louis Noir, who explains the innovations of this yacht.

    VM: Jean-Louis Noir, why design a total centreboard boat?

    JLN: This type of boat allows total independence from marinas and other costly moorings. A simple trailer allows its transport and launch into water without any external aids on any beach. The total absence of any projection below the hull allows one to beach anywhere you want and without beaching legs. Briefly, the centre boarder allows you to beach at any time of day or night. On the other hand, a fixed keel, in a foaming sea on the beam is rather uncomfortable, whereas with the with the centreboard, it can be raised and therefore remain more stable. This fact was noticed by Daniel Gilard during his Mini-Tranat race.

    VM: The great innovation with the T7 is its adjustable centre-blade – can you explain how it work?

    JLN: It is effectively thanks to this system that the T7 has attracted so much interest. The principle is simple: a traditional fin keel must obligatorily slip sideways to be effective. As the yacht no longer progresses along its true axis, there is a resulting loss of speed and angle of sailing of over 4°. The variable angle centreboard reduces these losses by controlling the water flow in a manner similar to a “trimmer”. It allows the boat to progress along its true axis without leeway. The improvement leads to better sailing angle when close hauled, which in turn leads to improved efficiency of the sails, increasing speed because of less drag and therefore improved overall performance by between 20 – 58% in the case of the T7.

    The progressing angling of the centreboard can be seen from the diagram (Not available at present). By using this system we have been able to win the Micro Cup two years running. After little more than one years development, this technique is fully proven and has been put into mass production of the T7. This makes the T7 the first total centre boarder equipped with this variable angled centreboard in mass production.

    VM: Finally, what are the advantages of the centre cockpit?

    JLN: It allows us to bring all the weight into the centre of the boat, thus reducing pitching and a much smoother motion through the waves is achieved. In the event of being pooped, the trim of the boat is maintained and as a result the cockpit empties very efficiently via the engine well.
    Finally, the cockpit splits the yacht into two. The aft cabin will become a kid’s haven or that of friends. During my summer cruise on the T7, the kids made it into their playroom. The saloon will become the owners cabin. Each person’s privacy will be respected. Furthermore, a cockpit canopy spread above the cockpit will transform this into another room.

    Tss, ....
    There are a lot of concepts for boats.
    I believe that the T7 is one of the few boats that...... She is a masterpiece ---in HER concept.
    I don' t know any boat of that size that is so .....

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