Planecat - design input / potential project?

Discussion in 'Multihulls' started by silvah, Jan 31, 2017.

  1. CT249
    Joined: May 2003
    Posts: 1,259
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    Location: Sydney Australia

    CT249 Senior Member

    Have you sailed 18 Foot Skiffs and high performance cats?

    1- those yardstick ratings are NOT based on upwind/downwind courses.
    2- the only regular 18 Foot Skiff fleet does NOT sail only on upwind/downwind courses.
    3- Skiffs don't have less EFFECTIVE crew weight, since in these conditions the effective crew weight is a product of crew weight and their distance off the centreline.

    The three crew of an 18 produce about as much righting moment as 9-10 crew hiking from a LS. Where are you going to fit those 9-10 crew while still allowing the bow to lift? Of course, if you load all those people onto the LS, which is a heavier boat to begin with, you now have about half a ton of extra weight on the LS, so it now becomes a heavy boat with a small sail area, which is slow.

    You still end up with a skinny sharpie-type boat, and as classes like the Australian Sharpie in the vid show, they are much slower downwind than a high performance cat in strong winds.

    4- Re "He did not claim it would be faster than a Skiff. Only faster than a C Class". Have you ever watched a C Class race against 18 Foot Skiffs in strong wind and then interviewed the fastest Skiff sailor and asked them about their boat's performance at high speeds? Having been lucky enough to do that the only time it ever happened, I don't believe that the difference between the peak speed of the 18 (which was a Grand Prix 18, even faster than the boats in the vid I posted) and the C Class was anything like the difference between the C and a LS.

    5 - 18 Foot Skiff and good catamaran designers spend a lot of time designing their boats and rigs so they don't pitchpole at high speeds - just ask them. Bolger, on the other hand, is highly unlikely to have designed the LS so that it didn't pitchpole at the 20knots plus speeds we are talking about. Not only that, but the lessons that the dinghy and cat designers have learned over the decades show that for high speed craft, the LS shape is not particularly good at resisting pitchpoling.

    6 - the best known racing LS, in its best race when it was downwind all the way and records in many classes were shattered, was well beaten by a 1950s designed 20 foot catamaran. The cat that beat the LS was much slower than a C Class. The LS was also beaten by a 14 Foot skiff, which would be slower than a C Class. The Light Schooner finished slower than a J/24 would have, and it's ludicrous to think that a boat that is slower than a J/24 downwind in a breeze would beat a C Class cat in such conditions.

    To get back to the original point - the concept of a hard-chine planing cat has been tried time and time again and it has been proven slower in most conditions time and time again. Top cat designers are not ******, that's why they don't usually hard-chine design planing hulls.

  2. sailhand
    Joined: Jan 2017
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    Location: australia

    sailhand Senior Member

    the planecat looks like it has potential to me, the guy was definitely onto something. I played with cat designs for years and came up with the opposite to what I was told would work. my hull shape has proven to be very efficient for its size. I have a full flat self draining deck that you can sit a queen size mattress on and walk around it, and it planes with a three hp (pics posted on this forum), contrary to what everybody told me. the algorithms in many of our software packages available seem to fail to include the effects of hydro dynamic lift in some hull shapes as speed increases, and its effect reduces resistance. the planecat hull shape looks like you could do something with it, and I think the guy was onto something. I have found similar results however as yet have not had the chance to scale it up. that will prove out the efficiencies of the concept once and for all. after all its not that long ago you were derided for even owning a catamaran and I remember being told by a guy on a mono that if I didnt own a cat I could get a lift to town with him. its ok though I towed him off the beach the next day,. I am actually trying to buy a mono at the moment though so I hope Im not "hullist".
    Last edited: Feb 13, 2017
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