40 ft cruising cat design. First steps.

Discussion in 'Multihulls' started by bscatam, Mar 28, 2016.

  1. bscatam
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    bscatam Junior Member

    Thanks Dennis. And nice explanations with which I absolutely agree. It will be Med cat with eventual transatlantic sailing to Caribes. My intention was to design 40 ft strictly cruiser with no ambitions for speed, for long term cruising for family of 5. Its normal to make compromises with drag. Which as you mentioned still not been quantified. Still, I think that weight is the main issue for all production cats. So 2-3 tons difference with same sail area how much do you think will make.
     
  2. groper
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    groper Senior Member

    Reducing weight will make it sail faster no doubt about that. However with the same windage, high boom, no dagger boards, this boat will not sail upwind very well- none of the designs like this do, and it's the L/D ratio that's the problem...

    It's not just the vertical windows that makes it look like a lagoon, it's everything... the helm, general arrangement, everything about it...

    What sort of fit out are going to put in her? It will have to be minimal to non- existent to achieve 5.5t. The lagoon 400 is over 11 tonnes dry btw- not 9 tonnes.
    Who has done the structural design for this?
     
  3. UpOnStands
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    UpOnStands Senior Member

  4. groper
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    groper Senior Member

    If you can't discern the differences of your link to this design you have no idea... look at the volume in the hulls for a start, then look at the bridgedeck cabin...
     
  5. UpOnStands
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    UpOnStands Senior Member

    I posted the link to show that a viable cruiser is possible at 5000 kg+ but of course it looks nothing like a Lagoon - much more cockpit and much less cabin -- windows much smaller. No doors - on anything except the cabin.
    Whether it is possible to build the Lagoon style at 7000 kg would be tough to answer.
     
  6. DennisRB
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    DennisRB Senior Member

    Look at the cat in my pic! Its my old boat. I had a Crowther 226A. The A version had a little more accommodations with wing births in a longer brigedeck. No way it was as light as the 6T design weight either, but these were designed structurally to surpass all survey standards. Stuart Bloomfield told me personally the scantlings were super conservative, so weight could be saved for sure. But then again they usually ended up pretty heavy. Although Audacious, a sister ship to mine was raced at 6T sailing weight. Very comfortable and spacious boats. Definitely not a minimalist spartan design, but thought went into the design to keep it light in terms of minimizing surface areas.
     
  7. UpOnStands
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    UpOnStands Senior Member

    from Darth Reapius on Sailing Anarchy
    "226b (or so we'll call it, it was slightly modified, stretched and lightened a bit, dry weight was 5.3 tonnes, sailing weight 6 tonnes"
    close enough

    looks likes yours was sailing well on just the jib
     
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  8. groper
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    groper Senior Member

    Of course it's possible- my father used to own a 43ft CSK built in plywood and spruce, it weighed 4.5tonne ready to sail built in 1979.

    But let's get real here, if you think a design like this will weigh 5.5 tonne ready to sail, including a complete fit out with all equipment installed, then you really don't know what you are talking about.

    The Oram 39 I had built in full sandwich construction was 6 tonne, lower volume than this boat, and it also had virtually nothing in it. The anchor chain, 2 diesel motors, and 8 batteries didn't help the weight tho!

    My father's boat was like a racing yacht, it had nothing in it besides some mattresses, a metho stove, and a little 12v fridge, and 1 hand pumped toilet. That's it. Hulls were like giant Hobie cat shape assymmetric, No bridgedeck cabin, No hot water, no diesel motors, no genset, not even faired or painted inside with no false floors. It was like camping at sea, but we still manged to cruise thousands of miles over the years...damn thing did well over 20kts at times, apples to apples people....
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    Game keeper turned poacher....bless :p
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    ...or the reverse of that, perhaps !
     
  11. DennisRB
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    DennisRB Senior Member

    Not a chance. Lightship maybe, with anchor rope, 200ah battery bank, and empty tanks and next to no fitout. BTW, the DWL loaded is listed at 7400.

    The sailing weight seems to come down to the mentality of the owners. Audacious's original owners were weight conscious racers who oversaw the build, which is why they managed a 6T racing weight on a 43 foot boat far more comfortable than the 43 foot CSK was. Having owned the same boat, and having been aboard charter cats. I can say the space inside the bridgedeck and cockpit was as good, the hulls were narrower inside for sure, but IMO it made little difference to perceived comfort as life goes on "upstairs" in a cat.

    That said, my particular version would have been lucky to be under 8-9 tons in cruising trim. When audacious was sold its weight went up dramatically. So the design as presented in this thread, where the SOR has little to no pretensions to performance will end up just like every other overweight cruiser even if a 6T sailing weight is feasible with little to no real life cruising gear and fit out on board. A fast racer/cruiser may at least bring with it a crew with discipline for weight gain in both the fitout and cruising stage.

    That was another reason I suggested a little extra sailing length, it will help keep the boat trim with inevitable weights getting higher than expected and keep speed potential and motion comfort higher. That said, if the design does end up at 8 or 9T its still a lot lighter than a 11T 40 foot lagoon. Have you guys looked a lagoon from the front? There is almost no gap inbetween the hulls. They almost look like a sailing cube. The design in this thread may look like a lagoon from many angles but it does not like as fat to me.
     
  12. bscatam
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    bscatam Junior Member

    Lagoon 11 t weight. Not surprising. Hulls - thick laminate uderwater and 200 ?mm above WL, core - end grain balsa, bulkheads - marine ply.
     
  13. groper
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    groper Senior Member

    The lagoon weight problem goes far beyond that... the fit out is very intensive, theres lots of furniture, linings, cabinets and upholstery etc and there is also an extensive list of equipment. As you are also a cabinet maker, id imagine you will have a fairly extensive and luxurious fit out inside? Mad if you dont if you have the skills, it will add siginficant value to your project...

    You have a nice set of renders which you can use for cut files and build this boat from.
    But have you a detailed list of equipment and hardware which you will put in this boat to go cruising with?
    Have you tabled all these weights and their respective CoG? Have you used rhino with a function to assign densities to each panel so you have an idea of shell weight and shell CoG?
    Do you realize that there is about a half tonne in weight just to acheive a painted finish youll need to account for? - i didnt realise how much bog and paint i would use until i built and painted one...
    Have you put everything into a CoG spreadsheet and ensure its close to the CoB of the hull so it will float on her lines?
     
  14. bscatam
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    bscatam Junior Member

    Excel spredshit was the first thing even before starting drawing.;) As to furniture for me it is easy to make very light furniture with nice disign. Basically its craft paper honeycomb core between two shits of thin 2 mm ply covered with 0,6 mm veneer all glued in hot press. Edgebanded and sealed with 2-3 leyers of polyurethane varnish. Actualy all furniture could be produced in 1 day.
     

  15. DennisRB
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    DennisRB Senior Member

    How strong and water resistant is this furniture? Seems like an interesting way to make light paneling. I have heard of a very similar technique for boat building before. Do you have a website where we can see some of your work? PM me if you don't want to make it public :)

    All furniture in one day! That I don't believe. I'm sure it would take over a week to design it alone.
     
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