Open source 12-15m high performance/semi-cruising catamaran design

Discussion in 'Multihulls' started by groper, May 10, 2017.

  1. jorgepease
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    jorgepease Senior Member

  2. John Perry
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    John Perry Senior Member

    I rather feel that the secondhand value of a one-off home designed and home made yacht is likely to be so low that one might as well forget about it and just build what you want rather than trying to meet the needs of some imaginary future buyer. But I suspect you are right that a big comfortable bridgedeck cabin would improve second hand value, that might need to be a bigger and heavier cabin than you have in mind though.

    Pics below are a 10m cat I sketched a few years ago, its smaller than you have in mind and although it could be stretched to something like 11 to 12m without much change to the layout and concept it probably would not really scale up to your size. Might give you some ideas though. Thinking of a small light bridgedeck shelter I drew a folding cuddy that either partially encloses the steering position, say for watchkeeping at sea or alternatively rolls forward to allow standing at the wheel, say for manouvering in harbour. A human figure is shown standing in the same place in both drawings so in one drawing it pokes through the roof of the shelter. I have drawn this shelter as a canvas on tube structure that would fold away in fine weather or for full visibilty when racing, but it could alternatively be a light weight rigid shelter. Having it folding facilitates the mast lowering arrangement I had in mind, whereby the mast folds aft, although it might well be better in any case for the mast to fold forwards. Please ignore the rig details on these sketches, that part of the design was not finished and I think that in any case a good alternative could be a wishbone boom arrangement as used by Phil here (Catsketcher) - I actually made a wishbone boom rig for a much smaller craft many years ago and it worked well - it was amazing just how light and quick to adjust the mainsheet was compared with hauling on multi part tackles! Also, I expect that an inflateable would be a better idea than the ridgid tender - I like drawing boats and the ridgid tender was just an excuse to draw another one.

     
    Last edited: Jun 6, 2017
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  3. waikikin
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    waikikin Senior Member

    Hi Groper,

    Looks good, nice to have versatility in the design, easy to push the bridgedeck cabintop up a little too & option a back wall/bulkhead & front wall/cabin front into it as well at fairly low weight, even land the sides further onto the hull cabins for the lux/space version, some lightweight removable furniture modules can give race/cruise mode. A lid/containment area will double resale & easily achieved at a later date... it's just an extra composite fabrication or two away;)
    Looks like 5-6 different model options easily.

    Jeff
     
  4. groper
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    groper Senior Member

    You must have read my mind Jeff? After i posted the rendering of my old design with the roof etc i decided to clean it up a bit and ended up doing exactly what you just said above! This was before i read your reply... something about minds thinking alike :D
    Pushed the inner coach roof up a tad and blended in the roof with a forward scallop to lower down on the coach roof forward... makes a good rain catcher too!
    net result;

     
  5. bscatam
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    bscatam Junior Member

  6. jorgepease
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    jorgepease Senior Member

    It is interesting but 1.5 tons in batteries ... only?? That is about 150KW... I can't understand how they are going to get 50KW continuous regeneration when their wind and solar combined gives them around 8kw a day, and why are they figureing 10-16 hours per day on the solar, they will be lucky to get 5

    ... Is hydrogen that much better? I like it, can't see it doing the speed they say 20 knots constant in trade winds and over 3o, not at 36 tonnes in an 80 footer and I don't like the full autonomous mode thing. More stuff to break!!
     
  7. groper
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    groper Senior Member

    Great- shouldnt this be in the other thread tho - has nothing to do with the concept of this thread... PS theres another boat just like this being built in France which is using hydrogen stoarage etc also... very similar concept...

    Jorge - the 50kW is acheiveable through the generation of energy by the propellers coupled to the motors as they are dragged through the water whilst the boat is sailing. Slows the boat down but if there is heaps of wind theres heaps of energy to be harvested... yes there figures are optimisitc, and this project will not see any change from +$10M - very deep pockets indeed...
     
    Last edited: Jun 10, 2017
  8. waikikin
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    waikikin Senior Member

    Hi Groper,
    Just wondering how it would look with the aft connective bulkhead combined with the transoms, a bit more cockpit space, beam notionally gives more control of the platform and a greater spread of the pintles/gudgeon bearings- the trade off is elimination of boarding area but there's other options for that. Might give the biggest "platform" for least structure... of course it might look crap too but only until everyone else is doing it;) - the GB foiler looks a bit like that but not quite. upload_2017-6-11_11-34-12.jpeg
    Jeff.
     
  9. groper
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    groper Senior Member

    I like your ideas Jeff - they always make sense :)

    The only reason i had not already designed it like that was to allow for some davits off the rear beam and have room for a tender such that it didnt make the LOA further than the aft extremity of the rudders for berthing in a marina etc... The solution might be to simply haul the tender onto the rear deck whilst in the marina or similar?

    Ill draw it out soon and see how it looks - im sure it will look fine and it would certainly speed up the build and simplify it...
     
  10. UpOnStands
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    UpOnStands Senior Member

    If you can, drop the fixed davits and try the rotating type that pivot on the aft supports of bimini/solar panels. The idea is to use the davit arms to swing the tender inboard for Med style marinas and transits.
     
  11. waikikin
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    waikikin Senior Member

    If your tender was designed somewhat scow/punt/cat like it could strap down aft there as another integrated piece of cockpit furniture, kinda borrowing some seating style from Rob Denneys or another little cat tender on here but with seats/lounges down either side/kids playpen/whatever(?). An extension to the boom-like a ringtail or stuns'l extension but using modern materials maybe with an underslung track to ship it inboard- or just a really really really long boom- some cats used to use a track under for the main to give similar sheeting to curved track with mainsheet to load the cargo unit.., and or some simple sliding telescoping beams to sit it on aft of the aft beam.. All starting to sound like complexities though & escaping the scheme... of course you could drop the dinghy through the cockpit sole Thunderbird 2 style;)
    Jeff
    [​IMG][​IMG][​IMG]
     
  12. jorgepease
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    jorgepease Senior Member

    I like the full deck too. The swinging davits is a good idea, keep them out while you are running and swing them in if you need to at the Marina. Here is what the full deck looks like, I will try to draw the roof. I notice you can't pull the red foil completely without hitting roof.

    15_28.jpg 15_29.jpg 15_30.jpg 15_26.jpg 15_27.jpg
    15_26.jpg 15_27.jpg
     
    Last edited: Jun 12, 2017
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  13. DennisRB
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    DennisRB Senior Member

    Nice renderings! How much does moving the rear beam back affect weight at the stern?

    I have always thought that boards with an inward angle (opposite to what is designed here) would have the benefit of adding a bit of lift. But also in the event of wind or wave capsize conditions they would be safer. I imagine a wave hitting the side of the boat. With inward angled boards the windward board would dig in and the leeward one would want to rise. That may help a bit to prevent capsize. With outward facing boards the opposite would occur! Sideways movement would create an overturning moment from the angles of the boards.

    The effect is probably not great, and its obvious with this design that the slots are in a very easy place to manage in this location and would be difficult to access if it were the other way around. Plus there is hardly any cabin intrusion. With the planned lifting foils at the front you don't need the lift plus having them cant in seems good for upwind performance.
     
    Last edited: Jun 13, 2017
  14. groper
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    groper Senior Member

    I dont think weight at the stern is too much of a problem other than the inertia in it and its effect on pitching. The rudder horizontal stabilizers will take care of that - and no i still havnt done a proper weight analysis yet - ive been busy.

    I also think a "thunder cat" lifted up by the main boom through the cockpit floor just in front of the rear beam is tempting - no davits at all and no weight and expense of cockpit floor to build either.... The thunder cats have a low profile and flat deck not too uncomfortable for lounging on, so could work well - i think we just eliminated more unessesary junk and cut more costs from this project :)
    [​IMG]

    The daggers and foils are a work in progress - im really starting to second guess the feasibility of having 3 or 4 different boards which is where this thread started. A single lifting and leeway board- like a large C board or L board, with a good strong set of rudders and stabilizers at the stern is probably the best option - likely why you see this configuration on cats already, not 100% convinced either way tho. Id really like some decent L boards but having them able to be withdrawn from the top and not looking too ungainly on the exterior of the hull is proving difficult...
     
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  15. Ad Hoc
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    Ad Hoc Naval Architect

    The pitch stability is dictated by the waterplane area inertia. The mass distribution affects the radius of gyration.

    You must do a weight analysis before you go any further. Otherwise you will have no idea what you're aiming at...in terms of:- will she float..will she float up right..and will she float on the draft expected....etc. You need a datum.
     
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