Beam design for a demountable catamaran

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

  1. guzzis3
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    guzzis3 Senior Member

    Depends on what you mean by useable hull volumes. 4' is close enough to sitting headroom. Plenty for sleeping or using a porta potty. The clip on cabins as draawn give 5' headroom. If you want 6' headroom in the hulls you could make the clip on cabins higher. They would still be lower than the sango central cuddy. As I said the problem with sango/wizard is anything permanently fitted in the hulls has to be able to rotate through 90 degrees.

    If you want the side by side route you have a few options.

    A complicated trailer that supports and moves the bits about.

    Several people to move the bits about.

    Complicated or problematic connecting structure to support the bits as they move about.

    Cat2fold can splay or contract on the water, but the beams are complex. Sliding beams can jam or be loose in operation. You can build a horizontal parallelogram to swing one hull forward and one back on the trailer. Makes a long load but means you can have wider than 4' hull beam. A vertical parallelogram can, with the trailer winch, lift a heavy center section up so the hulls can pack in below it.

    Or you can do what Mr Woods suggests for his non folding boats, roll them off a flat bed on dollies, build the connecting structure in the car park, run the boat down the ramp with a rope to your tow vehicle. Only the dollies get wet, and it just keeps on rolling out into the water until the boat floats. Recovery is the opposite. You could build a very light A frame off the bow beam to the car if you wanted better control. Make it as long as you like.

    Every possible permutation has been thought of, and most tried. There is always a compromise and a cost. Wizard/Sango involves very little cost and really only 1 compromise.
     
  2. UpOnStands
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    UpOnStands Senior Member

    This Skoota 28 is very close but no inside access to the hulls
    No swinging arms. Wonder how wide the two hulls side by side?
     

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  3. VadimGo
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    VadimGo Junior Member

    Now,
    I will go and measure the Seawind's hull, just give me a minute or 5
     
  4. VadimGo
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    VadimGo Junior Member

    So, with a reasonable margin of error, Seawind's hull is about 39" inside, right about the point of the hull/deck joint is he widest. As it is an out-lip jointed, plus some thickness of the GRP... inch and a half on each side or less...
    So, it is less than 4 ft.
     
  5. guzzis3
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    guzzis3 Senior Member

    Thank you for that.

    So maybe 45". I'm going to try and get a close look at one locally and make some measurements. The S24 mast beam was the inspiration for my origional post in this thread. They are really common and cheap here so I might buy one and build the trailer as a proof of concept. The design can accommodate the full width beams fore and aft that the seawind uses.
     
  6. fallguy
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    fallguy Senior Member

    The Skoota 28 hulls would be trailerable side by side.

    I am building a Woods Skoota 32 Demountable-powercat. Hulls are also trailerable side by side; about 45" wide each.

    I have considered a trailer; did some mock ups with wood.

    I am convinced the best solution is to launch the hulls conventionally with some temp scissors. So you back to the water and the boat is launched and spreads apart in the water. Then the trailer bunks have slides; like 3/4" ss linear bearings. You'd slide them out with hydraulics and set bunks on them (you cannot trailer on slide bearings-they will fret). You move the trailer back to the water then bring the hulls back on shore.

    Then you lift the cabin up and set the beams and assemble out wide. Back down again. Lots of variables, but it would work. Cost is the issue. You need to model it first to work out the details at 1:10 before building it real and rebuilding it 12 times at full cost.

    For now, the trailer is a maybe for us. I can always hire the boat moved on a semi and assemble it at a marina with a crane.

    If I were building a smaller cat; I'd do the same thing. Put the cabin ahead of the hulls; launch the hulls with temp scissors; move the bunks out; bring the hulls back in wide; cantilever lift the cabin up; retract hulls to home; install beams; lower cabin to home; lower cantilever section; any miscellaneous assembly; back it down.

    For the Skoota 32; the cabin is 13' long; so it is the same concept, but two trailers are needed. The height of the assembly is too high to be safe. The cabin would be rolled off the aux trailer onto the lifting trailer.

    Loadmaster would build it for you for $100k. Yikes.

    The neat thing is you could stay in the cabin on the way if you went a long way. And all the stuff would be loaded aready, etc.

    The Skoota assembly would be tougher because my beams weigh about 120# each. They are not something me and the wife would handle easily at that height; so you'd need some means to lift them as well.

    My friend thinks I need a crane on a trailer; it smells of semi to me to the point I want no crane. Maybe a crane to lift the beams might be good.
     
  7. guzzis3
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    guzzis3 Senior Member

    I am not sure I understand exactly what you are planning but it sounds expensive and complicated.

    If you have say 4' high hulls and a 4' high cabin stacked on top plus axle height the trailed boat will be 10' - 13' on the trailer. In australia our normal height limit is 14'. Remember while the silhouette is huge the weight is low, so from a safety point of view high cross winds are a problem but otherwise that load isn't.

    From what you are describing it sounds to me like you'd be better off with a walk behind forklift. With extended tines you could just position your parts and bolt them together and run the assembled boat down the ramp on dollies with a light A frame to your tow car.

    Something like this:

    Hand Stacker Forklift 2 Tonne 1.6 Meter CtyA Hydraulic Lifter Pallet | eBay http://www.ebay.com.au/itm/Hand-Stacker-Forklift-2-Tonne-1-6-Meter-CtyA-Hydraulic-Lifter-Pallet/222601781021?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D20140106155344%26meid%3D7a2c0bb15aac4decbb9b6ee81ce34060%26pid%3D100005%26rk%3D2%26rkt%3D6%26sd%3D222674405355&_trksid=p2047675.c100005.m1851

    Or an engine crane. I don't know what the 32' hulls and bridgedeck weigh but 2 ton should be plenty of capacity. Each hull and the bridgedeck should weight about 1 ton each, so you could safely extend the tines. It would be easy enough to carry that loader on the end of your trailer. You could pick the hulls from teh side and maybe pick the bridgedeck from the rear.
     
  8. fallguy
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    fallguy Senior Member

    Hulls are 6'2, cabin is 6'2 plus base with vee say 8" min, 13' without trailer and if you set the cabin atop; only with a crane. 18" trailer is 14' 6".

    Max height is really about 13' 6". Otherwise if you turn down some side street; cabin is trouble by a good foot.

    Too high.

    Expensive to have a third party build.

    I can get linear bearings for $4000 or less; hydraulics for 2, basic trailer for 7. I figure 25k for all worst case. And I don't weld.

    Vessel is ?6500#
     
  9. UpOnStands
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    UpOnStands Senior Member

    Water is cheapest fork lift.
    During transit the full cuddy sits on the vertical hulls side by side. (this is for the 24-26 foot boat of OP :p)
    Back the trailer into the water until the hulls provide some lift.
    A scissor frame raises the cuddy off the hulls.
    Back further until the hulls float.
    Separate the hulls - solid scissors arms needed
    Lower the cuddy onto the registration pins in the hulls, tighten up on the center pivots of the scissor arms
    Raise mast off the cuddy and rig.
     
  10. fallguy
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    fallguy Senior Member

    My boat is a power cat. But the cabin is hooked to the beams; not the hulls. And too high as I said.

    However, the water is the place to make simple moves for sure.

    Not meaning to hijack; just help.
     
  11. UpOnStands
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    UpOnStands Senior Member

    Your 32 sounds like a transport once only deal. Or once every few years. Sounds very expensive.
     
  12. fallguy
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    fallguy Senior Member

    Well, a good trailer would make it easier, but we plan to move to the coast someday.

    Only cat trailers are a special deal, so a fun challenge.
     
  13. UpOnStands
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    UpOnStands Senior Member

    Don't get me wrong, a 32' power skoota would be an awesome boat. Good luck with the fishing.
     
  14. guzzis3
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    guzzis3 Senior Member

    I don't mind you hijacking my thread. Any thoughts on the trailerable catamaran problem are welcome. Having said that I am interested in boats 7 - 8 meters and they present a completely different class of problems. For one thing the hulls and bridgedeck are going to be about 250 kg each not a ton.

    There are many solutions. None are perfect. Trying to fit a 32' catamaran on a trailer, take it off and assemble it is a mammoth task no matter how you approach it. I've not looked at the power cats closely but the fixed skoota 32 quotes an empty weight of 3 ton. Gypsy, which I assume is similar to the 28' version is 1.8 ton. For that extra 5' you are paying for a 66% increase in weight, so apart from the cost of building it you have 3 pieces each about a ton instead of about 600 kg.

    If the boat is too high with the cabin on top of the hulls then you have a whole other problem to address before you start on the assembly.

    If you can work out how you want the boat on your trailer then you could for example mount each part on a dolly and use an electric caravan mover or electric trailer winch to get them down the ramps on to flat ground to assemble. Having assembled the boat and having it on dollies you would still want an A frame to back it down the ramp. A caravan mover would not be safe for that.

    Floating bits off the trailer and assembling on the water sounds good if you say it real fast, but how do you control 1 ton of boat hull in any sort of cross current or wind and when there are potentially stupid people all around you ? Even assembling on flat hard ground is problematic if a gust catches the hull side on or gets under the bridgedeck. Try pushing a small car around with no motor, power steering or brakes... try wading out 32' into any body of water to shove the other end of that boat. Are you planning to motor a single hull around ? A hull 4' wide 6' high and 32' long ? thats designed to work as half of a catamaran ?

    To overcome the sango hull rotation problem you could start with a conventional boat (like eagle/elf/even gypsy),mount the hulls on dollies and winch them off using a trailer winch and wheel them to each side of the trailer. The center section could be mounted on a sango like trailer and lowered to the appropriate height to connect to the hulls. With the boat assembled you could use the parallelogram to lift the whole boat enough to back down the ramp launch and float away. The parallelogram would need to be strong enough to carry the whole boat and you would be getting the trailer wet, but it would maintain control throughout.
     

  15. fallguy
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    fallguy Senior Member

    I will have a better idea when we flip the hulls, but the hulls are likely not capable of staying in the water on their own; they would almost certainly roll. They are slight vees with some rocker, but flatten out aft. So they might actually float alone. I have 1:10 scale model hulls that are not done. Once they are; I will know better. I am building the boat; so model less important.

    So, yes, you'd need safe harbors, good weather, low crowds. The scissors beam would need to work well enough to move the hulls out without failure or breaking. You aren't launching in a river current or narrow landings, etc.

    The easiest place to move the hulls is on water. I think they will come in at 1500# or so each, but with fuel tanks full 400 more. Engines are 270# each. You don't move them far; they never leave the shore but a few feet. The vessel is about 18" draft midship near zero for'd. The trailer comes out; bunks moved out and you bring it back up. The process is less than 10 minutes done right.

    Dollies require ramps. Dollies for a ton probably require drive motors. But motorized dollie might work.

    Another tool that might work is hydraulic rams that lift the hulls with the beams. So, the hulls are out; somehow. The beams and cabin are assembled and set upon four rams and go up hydraulically. The hulls then retract; cabin and beams set in place.

    One beam in the middle of the boat will be especially tricky as it slides into the hulls midships. The others will drop in. 3 beam boat... another reason for rams would be holding that beam in place and moving the hulls; not the beam. But this becomes a possible death nail for the entire trailering concept if I must crane the cabin to get above the middle beam, or if my hydraulics would punch that beam through their sockets.

    Tricky-that is why I will model it.
     
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