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

    Would be good if you could pivot the foils forward or aft to trim.

    I think my boat will be faster than you think ))
     
  2. groper
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    groper Senior Member

    The c foils and rudders will have some pivoting range as per the current design trends for these.
     
  3. waikikin
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    waikikin Senior Member

    Hi Groper,

    So the intention is to follow the trend? rather than cut new water. My understanding of the cup boats and similar is to optimise within the rule/size. I'm still amazed that those vessels set up & balance on such a tiny footprint, as I think I understand you dont intend to leave the water but to have a long waterline footprint but wonder how if you bring the special foils into line with the cg/sail thrust vector how that position offers pitch damping. It seems that some great effort/bucks might be expended following this path when simply building a bit longer might achieve similar aims with a more versatile simple platform that works in a greater range of sea states.
    It's interesting from the sidelines to see the evolution of thought, I'm probably well on the conservative side & tend to look at the overall end cost & later disposal/sale result when the funs been had.
    Jeff.
     
  4. groper
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    groper Senior Member

    Yep but i had a think about it and figured its best to leave the pitch damping to the rudder foils. The main foils closer to midship still give good heave damping which is also important.

    Not intending to be fully flying boat here, just foil assist. Will see where it can go once i have better figures on weight.

    Also intend to keep costs down which is influencing a few descisions...
     
  5. DennisRB
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    DennisRB Senior Member

    Loving it. I have just got my 12x6m shed certified. So now I can add another bay to make it 15m ;) My idea was to build a semi open bridgedeck modular design so each hull and the beams could be made separately in my shed and finished to a high degree of fit-out , then assembled at a boat yard. My quick SOR is as follows.

    Simple and inexpensive to build and maintain.
    Must be buildable in a 15 x 6 x 4.5m shed (ie modular construction).
    Semi open bridge-deck ala Mainecat with similar layout and roll or swing down windows. Large hard solar bimini.
    Fully beachable with shallow draft.
    4 doubles plus a few singles (couches will do), this is for my weekend dive trips in my local area.
    Cruising load capable IE dive gear, compressor, paragliders etc for expedition.
    Relatively high performance, less than Gropers ideal, but no prod boat better come close. Maybe a bit more volume and smaller rig.
    One diesel engine in one hull and one electric in the other.

    I have done a bit a of cruising so I don't suffer for the Utopian ideal of the sailboat which never motors and therefore has a $60K electric system with a 20 mile range. Plus I wont be racing. This design will motor at 7k @ 2lph in my estimation going of my last 43 footer which was fairly heavy. The electric in the other hull is just to manoeuvre and maybe play with in terms of propulsion a little. It will not be a commercial marine system which makes it cheaper than a diesel and of course lighter.

    I would choose a smaller rig and to motor a little more often which is coherent with the overall aim of simple and cheap to maintain. A 60m2 main should be ample. This boat will sail far better than any prod boat anyway.

    I participated a fair bit in the central board thread so I still like that idea possibly, or just one dagger in one hull. I don't require any fancy foils etc as it goes against my SOR or cheap and simple. Finish will be work boat. It will be a dive and expedition boat so a little more volume would be required compared to the original racer but overall its very close. Plenty of places to lounge around under the solar bimini like the Mainecat.

    George lost me with his "minimalist" meggayacht. :p This is back on track and very close to what I have had in mind. Nice one Groper.
     
  6. groper
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    groper Senior Member

    Thats nothing - you wait till i explain the building system ive come up with :) this will be extremely fast to build using a variety of methods ive never seen combined before :)

    Ive really been wracking my brains about the bridgedeck house.... really hurts the resale amd appeal to cruisers without a much bigger accom space in the bridgedeck...
     
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  7. DennisRB
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    DennisRB Senior Member

    I can live without a regular "full" bridgdeck, but it would have to be something like this. Just designing it so the option of something like that works would mean it appeals to more people IMO. I'm done standing in the sun and rain and so are most people. I even think the helm position would work for my SOR. I will have a bunch of wet divers all over the boat so this actually works better than a "full" bridge deck anyway. Plus its way cooler with all the options for breeze. Add a BBQ and sink and cooking could be done up there too. This boat is only 41 vs our 49.

    [​IMG]

    [​IMG]

    [​IMG]
     
  8. DennisRB
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    DennisRB Senior Member

    Looking forward to seeing your build system!
     
  9. jorgepease
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    jorgepease Senior Member

    Minimalism is gaining strength but mine is hardly a mega yacht.

    You want if for short expeditions and dive trips, mine is for longer trips, (3-8 months +) in comfort and I also want to charter it a few months per year as a comfy eco charter. Even so, it's not a condomaran, my displacement will be close to the Main Cat 41. Light, Lean, and Long, the roof is optimum shape to reduce drag and Daggers give me good performance into the wind, the rig is where I am struggling but I can go unstayed and still get decent into the wind performance since everything else is working for me. I want to see what you come up with on the centerboard.
     
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  10. DennisRB
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    DennisRB Senior Member

    I like your design Jorge. I was just questioning that it is minimalist, well whats minimalist for you might be luxurious for me. Probably just perspective and money! At one stage in the design the hulls were about 12 feet high. Maybe you lost me at that point. I should go have another look. :p For example minimalist for me is walking on the flat bilges so that the hulls are less than 7 foot high, Oram style. Less weight, material cost and build time. Reverse weight and cost spiral.

    Groper and I are experienced cruisers BTW so know what its like to live on various sized boats. My last 43 footer was way big enough. I don't want to go backwards from that, but I am happy if the same space in the "full" bridgdeck is available under a hard Bimini with roll down windows. I expect this 49 footer to have at least as much space and more carrying capacity. I plan on world sailing and live aboard in the same way you do. The 4 doubles and a few singles are so I can sleep as many divers as possible for weekend trips. However the boats main goal is world cruising with say 2 couples expedition style.

    In reality my old boat weighed about 8000+ and it was not slow. So I think the same size or smaller rig would do on a 15m boat that weighs several ton less if the SOR does not include showing all the fastest cruising/racing cats who is boss, which is what it seems Groper wants to do. Pretty sure Groper wants to see Fantasia in his wake, and I think that's doable with this design. I would be happy to arrive not to far behind. We ran a 69m2 squaretop, 39m genoa and 70m2 screecher. We could do 12k in 12k of wind. The same rig on a 15m boat that weighs 2 two or 3 ton less is not going to be slow. BTW we purchased all those sails. Thats 17K icluding a expensive furler. Price seems to go up exponentially from here with 100m2 mains etc. That 69m2 main is the limit I would want to be raising without an electric winch.

    SAXBY
    69m2 Cruise Lminate mainsail 3 reefs 7 battens GST 554.55 6,100.00
    39m2 Cruise Laminate genoa with UV GST 271.82 2,990.00
    70m2 Screecher PX laminate GST 439.09 4,830.00
    Profurl NEX 5 furler GST 309.09 3,400.00

    Here is an idea on the amount of space I dont want to go backwards on.

    [​IMG]
     

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    Last edited: Jun 6, 2017
  11. DennisRB
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    DennisRB Senior Member

    I'm still not 100% sold on the central nacelle with a board. A reverse expense and weight spiral says to just use a single dagger in one hull.
     
  12. jorgepease
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    jorgepease Senior Member

    Yeah my hulls are way lower now. With the camber in the sheer I only have 6'-4" headroom at the end of the forward bath. That is the lowest point of livable space and the sole is now at the waterline. Where I am a bit higher is on the roof because I have the 1.2+ meter deck clearance. You could probably stick my fitout into your boat with no problems.

    I think I agree with you on the one dagger. In a bit, I am going to post on my thread, a thread I found on asymmetrical or just plain daggers. Lots of references to the math and some good logic. The argument for cruisers is to go with a plain dagger and if you're not flying a hull then only one would be enough it seems.

    The power maine cat is really nice below but it's high!
     
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  13. DennisRB
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    DennisRB Senior Member

    Shuttleworth did some calcs on the one board vs two and afaict his conclusions were there are next to no gains by having two unless you are a full on racer. Knowing a few people with Orams with one board the results are excellent. IMO the worst drawback is no redundancy. Also on a big boat the single board will be very large.

    If anyone has the article from Shuttleworth regarding one vs two board I would like to read it again. I can no longer seem to locate it.
     
  14. groper
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    groper Senior Member

    The way oram designed his boats was to give the option of 1 or 2 boards. If you opted for 1 board, then it was to be built a bit larger and he dimensioned both options for you in the plans.

    Dennis- the design of this boat lends itself easily to your requirements and the version ive drawn so far is definitely the sport version. Ive already drawn a bimini roof version and the only other changes is for a slightly higher boom to clear it and a full floor right to the rear beam.
    Inside the hulls- there is considerable volume, easily more width than your old crowther 226 and of course slightly longer too. With a full bridgedeck bimini, its a rather large boat at 15m x 8.5m.

    This is partly why im leaning towards the sport version, simply because its less boat, less money, less time, etc...

    I wanted to power it with twin outboard motors, however there is huge space under the floor there for mid mounted engine rooms like the sig45 setup- which is also better weight distribution. You could do side mounted drives so the boat is still beachable...
     
    Last edited: Jun 6, 2017
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  15. groper
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    groper Senior Member

    Hard bimini, raised boom, full bridgedeck floor, mainsail now 80sqm with a 16m luff length.
    I call it the cruise version with the former renderings being the sports :)


     
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