Beam design for a demountable catamaran

Discussion in 'Multihulls' started by guzzis3, Dec 21, 2016.

  1. basil
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    basil Senior Member

    Simplist and best catamaran folding system yet. Yeah kinow Richard Woods has the same thing but here the trailer is the key

    http://www.s-boat.com.au/
     
  2. guzzis3
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    guzzis3 Senior Member

    Well on sango the trailer is the key aswell.

    If I wanted a FOLDING cat I'd get a sango or wizard. I was just pondering a way to overcome the hull rotation issues.

    I suppose I'm missing something important, but many other people place more emphasis on performance than I do. I want a boat with a level of comfort I can be happy with, a boat that's easy (ish) to live with and that's pleasant to sail. I've spoken to Mr Surtees at length and I find him a very pleasant gentleman, but his boat does not appeal to me. To each their own.
     
  3. UpOnStands
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    UpOnStands Senior Member

    for Guzzis3, for "fair" sailing, what would be reasonable freeboard, draft, bridge deck clearance?
     
  4. guzzis3
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    guzzis3 Senior Member

    That's a hard question to answer concisely. To me it's a boat that makes decent progress across a days passage, sails ok on all points, has good manners and isn't too wet or harsh.

    There is nothing wrong with a fast boat but it often comes at a cost, and not just in the buying. If your sailing on a knife edge that's exhausting. If it rides hard and pounds in a seaway that's painful. Most of all if you've sacrificed your accommodations that's uncomfortable.

    I watch the australian market pretty closely. Most boats take a long time to sell because most owners are optimistic about what the market will bear, but from what I see (it's hard to say definitively) boats with limited accommodations are a niche. There are the racers that love that stuff but a decent cabin seems to command a decent premium in sale price. I suspect there is a broader market for a decent sail boat with good accommodation.
     
  5. Beamreach
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    Beamreach Junior Member

    "The idea is:

    A complex trailer with swing wings rather than sliding beams to spread the hulls, and a central section which raises on a parallelogram using the tailer winch. Swing wings mean no binding, the arms work in your favor about the pivots rather than the size of the hulls working against you to bind up."

    Taking Guzzi's idea for making a Swingwing trailer to use on R Woods 24' Eagle.
    I'm wondering what materials for building the hinges would stand up to use.
    The hulls are 750 lbs (341 kilo) ,I 'm not good with metal welding,I am good with glass ,or hard wood . Would this be a good use of Carbon/ wood ?Have a quite bit of carbon uni unused.
    Suppose a metal hinge is ideal ,would prefer a composite glass one as I can build that way....
     
  6. guzzis3
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    guzzis3 Senior Member

    Heavy duty galvanised gate hinges are the simplest solution, remember that 350 kg is distributed over 2 pairs of hinges.

    I'm curious where you got that figure. The total empty weight is quoted as 600 kg. Are you including cruising fitout ?

    Anyway you could get pivots fabricated, with or without radial roller bearings. Bushes would be fine. It's a trivial problem for any metal fabricator.
     
  7. Beamreach
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    Beamreach Junior Member

    Empty displacement for Eagle 24 =650 kilo.
    True ,hulls will be less ,I just divided by two ,so there can be stuff in hulls .
     
  8. guzzis3
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    guzzis3 Senior Member

    I've had another idea :D No doubt someone here will tell me why it won't work.

    As I mentioned in my other thread I've been a bit busy so that is on hold, but I was thinking about crowther international 23's and had a series of ideas that might be worth considering.

    Some (frustratingly not all) inters were made with fiberglass sleeves running through the hull, which allow the oval beams to slide. The hulls can be pushed together for an 8' trailering beam and spread apart for sailing beam, probably 13' or thereabouts. The hulls don't come completely together, there is a gap to accommodate the mast step etc. The gap is about 10" I think.

    So my first thought was to exploit this by fitting a permanent nacelle. The nacelle does 2 things, it holds all the heavy stuff like motor, battery, fuel so you don't have to assemble all that every time you launch.

    The second thing is it's the support point during assembly and launch. When trailering the hulls sit on their LAR keels. When it's time to reconfigure for launch a cradle under and around the nacelle lifts, probably on a parallelogram using the trailer winch so the LAR keels clear the wheel arches. The hulls are now hanging free and you can shimmy them out to sailing width. The hulls now clear the wheels so you can lower the boat until the keels are almost touching the ground. This reduces the depth required to launch.

    So then something else occurs to me.

    Sliding beams in hulls have always been a bit problematic. They misalign and stick, they can be loose.

    Instead of having the beams slide in the hull how about they slide through a 20" long box on the front of the nacelle (for the mast beam, rear of the nacelle for the rear beam). The beams are square section each 8' long and glassed into a hull. They are offset fore and aft by 1 beam width. There is a sleeve with about 3mm clearance all round to allow the free end of each beam to slide through the opposite hull to facilitate trailer width. This sleeve does nothing except keep water out of the hull. Pull the hulls out and the free end of each beam comes to 10' from the centerline, so they overlap 20". You then bolt both beams to the aft face of the central box (mast beam), which in turn is glued to the front of the nacelle.

    Now there re some obvious problems with this. First you are restricted to about 15' beam. The big problem however is the loads while the whole boat is hanging in mid air suspended from the nacelle on supports about 18-20" wide. I don't think the boat would tip while you are pulling out one hull, but once out you have potentially 500 kg of fully fitted out cruising hull at about 7' from the centerline. There is going to be friction to overcome and there will be significant loads to consider. I've got some ideas on that but I thought I'd run it past you all to see if there are more problems I have overlooked.

    I did some drawings but my USB stick isn't playing at the moment. I will try to upload them later. Meanwhile any thoughts ?
     

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    Last edited: Oct 25, 2017
  9. VadimGo
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    VadimGo Junior Member

    O the Holy Grail of catamarans!
    Just recently I saw this
    27 Catamaran Design http://multihullblog.com/2017/08/27-catamaran-design/
    And my reaction was, "if it has a center cabin/cuddy, and could be put on/off reasonably fast, as to be "trailerable", I want one!" I am waiting to see if Mr. Hughes will come up with some answers that I like.
    Meanwhile, Guzzis, friction and especially, weight issue is there, if you do not support the hulls (weren't there trailer swinging arms under each hull?). Btw, do you consider the even Holier one, folding to 2.5m while still on the water?
    I have my Seawind'24 put out (it is getting cold around here), and I expect an "I want a bigger boat" bug to get me again this winter.
    As I an not qualified (or, smart enough) to come with the solution, I am watching the developments and new ideas with hope and anticipation.
     
  10. guzzis3
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    guzzis3 Senior Member

    If you are considering building or buying a boat you should first decide what it is you want to end up with. Mr Hughes has some great designs as does Mr Woods. The 27' sliding beam cat you point to is a completely different boat to say a sango. The one that is right for you depends on what you want to end up with.

    If you want to fold a cat on the water you would probably need to get a cat2fold. I am not sure why you would want to do that.

    If you have a seawind 24 you are probably aware of the strengths and weaknesses of that design. There are maybe 6 for sale here in australia at the moment under $10k, and a few over, and few if any are finding buyers. Most other boats on market aren't either. I am not saying seawinds are bad boats. My point is that the second hand cost of boats atm makes building or buying something new or expensive difficult to justify. It would make a lot more sense to buy something second hand for almost no money and modify it to suit. The trick of course is finding a good starting point and a not unreasonably optimistic seller.

    I have always personally preferred the inter 23 to the s24. There is one for sale atm for $5k. Unfortunately it's 2 days drive from me, so a week (and $1k) turnaround by the time I rent a trailer, drive, load, drive home, unload. And that assumes after I've driven for 2 days the boat isn't a disaster. I could have had one about half the distance from me for $3k with an 8 hp 4 stroke but it was one of those built without the sleeves in the hulls so it can't collapse. Has to be spread and taken apart to trailer. Quite annoying...very disappointing.

    "And my reaction was, "if it has a center cabin/cuddy, and could be put on/off reasonably fast, as to be "trailerable", I want one!" "

    Why then wouldn't you want a sango ?
     
  11. UpOnStands
    Joined: Nov 2015
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    UpOnStands Senior Member

    Any one know how the Sango is refolded for retrieval? Wood's web site is not that informative and there are no videos on Youtube?
    There is one cryptic comment "Generally make boat as light as possible by removing loose gear."
     
  12. redreuben
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    redreuben redreuben

    My understanding is the cabin platform is winched up and the floats fall in underneath.
     
  13. UpOnStands
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    UpOnStands Senior Member

    Thanks for the reply.
    Can't see how it works though unless the trailer has a massively strong cradle and some big muscle to swing it up.
     
  14. guzzis3
    Joined: Nov 2009
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    guzzis3 Senior Member

    This is a skoota 20. Same principle as the wizard and sango. Skoota is a power cat version.



    Photos of sango on trailer here:

    Sailing Catamarans - Sailing Catamarans http://sailingcatamarans.com/index.php/component/content/article/313

    The bridgedeck sits atop a platform. The platform raises and lowers using the trailer winch. If your ramp is steep enough you just untie the oat, back down the ramp and as the transoms immerse the hulls float up and out. Recovery is the opposite, line up the bridgedeck with the platform, motor up onto the trailer, winch the boat into it's proper position, drive up ramp and as hulls come out of water they rotate in and down.

    It is a beautiful system and works well. The origional wizard was built in 1993 and many many happy owners have been building and sailing them since. The are said to be VERY fast, dry for their size.

    So why aren't I building one ? The ONLY problem I can see with them is fitting a head (as opposed to a porta potti) in the hull and setting up a permanent galley in the otehr hull. Mr Woods design has a dinette which converts to a double in the central pod and aft of that a galley. The hulls have 4' headroom, 4 singles and you can fit a porta potti, removing it before recovery. If you would be happy with that accomodation then a sango, or a wizard (22' 100 kg lighter, shorter mast) would be perfect trailerable cats. Options include hard chine ply, foam sandwich, strip plank, clip on cabins for the hulls to raise headroom.

    I don't suppose anyone knows EXACTLY how wide a seawind 24 hull is do you ? I realise they demount to 8' for trailering, but are the hulls exactly 4' wide or a bit less ?
     

  15. UpOnStands
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    UpOnStands Senior Member

    Thanks for the Skoota video.
    Re. the 4 foot high hulls
    I tried a non symmetrical swing arm arrangement (tuck the hulls in vertically staggered arrangement) to get great hull height but of course supporting the cuddy becomes problematic.
    The vertical hulls side by side with the cuddy traveling on top seems to be the only way to get usable hull volumes.
     
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