Boat designer for a steel origami cat?

Discussion in 'Multihulls' started by magwas, Jun 17, 2019.

  1. magwas
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    magwas Senior Member

    My dream boat is an 50 feet steel origami cat with free standing masts on each hull wearing soft wing sails.
    Could you recommend someone who could design it?
     
  2. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    magwas. There are very few steel designs for catamarans. I only know of a 36 foot (11 meter) and 65 foot (20 meter) that were designed in the 70's and no longer available. A 45 to 50 foot ORO or Tehini wharram design was converted to steel hulls but had wooden decks etc. It should be possible to do an Origami cat hulls with a steel deck but you will have to accept the weight disadvantage and have a large rig to drive it. To give you a idea the 36 x 18 foot foot boden steel Catrina bridgedeck cat displaced 25000 lbs (11360 kg) compared to a 37 x 20 foot foam glass ply bridgedeck cat of the same era that displaced 9000 lbs (4100 kg). Maybe talk to brett swain who designs origami steel monohulls he may have suggestions. Look at Multihull Structure Thoughts tread page 2 for more details of the Catrina and look at the design and build concept of Moolabar Fire Truck for a potential idea on how it can be done.
     
  3. magwas
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    magwas Senior Member

    Thank you for the answer. I am aware of the weight disadvantage, but speed is not in the first place for my choice of cat, and my impressions are that (a) it becomes less severe as the size increases, and (b) even this will be much faster than a monohull.
    Do I right on these?
    Brett Swain is well-known (and criticized to death here too) for his attitude of refusing mechanical calculations, and I do not believe that a catamaran can be appropriately sized that way. While I do not think that his critics are right in everything, I would not trust him with a multihull design.
    Could you elaborate more on the history of those two cats you mentioned?
     
  4. oldmulti
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    oldmulti Senior Member

    magwas Do not underestimate the speed of modern monohulls, if they were designed in the last 5 years as a cruiser racer, they are fast, but they heel a lot. Not for me. Oragami steel monohull boats big advantage is the skin is compounded to reduce the amount of framing and therefore the weight. The problem with applying the idea to a cat is cat hulls are round on the bottom and fairly flat on the sides. So unless you plan to have fairly curved hulls above the waterline you will need to support the flat upper panels with a lot of close framing and stringers. You are correct that the larger a boat is the relatively lighter a steel structure is. The main problem of steel is it requires about 3 mm thickness to be welded without ripples unless you are a very skilled welder. Both the boats referred to were built with conventional closely spaced frames and stringers supporting basically flat panels. The 36 foot boat has 3 mm hull plate, frames were 44 x 44 x 5 mm angle sections or 63 x 51 x 5 mm angle sections at 500 mm center lines. Decks and cabin structures were 3 mm steel with a lot of light framing. The 65 foot had 4 mm hull plate and a 100 foot steel cat built in Australia had a 6 mm steel hull and 4 mm superstructure. The 36 footer was designed by Boden boat plans (still on the web) but no longer list the Catrina design. These guys are professional naval architects and may be able to help. But here is an idea for you. A guy built a light fast round bilge 18 foot steel power boat in Australia. He used 1.5 mm and steel panels about 200 mm wide with a 20 mm right angle bend on one edge. He welded up the panels to form a clinker looking hull shape. He was a professional welder and the boat held together well.
     
  5. Rumars
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    Rumars Senior Member

    For metal catamarans you must go to france, there are designs in aluminium there, maybe you can convince someone to do a steel design.

    May I ask why you want to build in steel? If it is for reasons of strenght and cheap available material I would sugest you turn to black locust (robinia pseudoacacia) and cold mold the boat with epoxy. It still will be overweight compared to foam/glass but I think a boat designed for meranti plywood could take the weight. Black locust (fehér akác) should be easy and cheap for you the epoxy is not so expensive either. The end product will be overstrenght and the rot resistance will be way better then rost proofing steel.
    If you want to try a wood core composite paulownia is a good substitute for western red cedar and it is available for moderate prices, but it takes a little searching.
     
  6. magwas
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    magwas Senior Member

    Another reason is easiness of the build and repair. I find cold molding complicated, and I am not sure about glueing black locust either.
     
  7. Rumars
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    Rumars Senior Member

    I do hope you find some designer to take this on in steel. I would ditch the origami requirement, it's to limiting for hull shapes.
    Black locust can be laminated with epoxy without problems. Strip planking is also an option beside cold molding. The easy way would be flat panel multichine with full lenght panels laminated on a table. Basicly making your own plywood.
    Whatever you choose the hulls will be your smallest problem, fitout and finish will consume most of the time.
     
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  8. magwas
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    magwas Senior Member

    I do not consider origami to be too limiting for hull shapes. Basically any developable design can be converted to origami sheet layout easily.
    Thank you for the hints about black locust. It is a great, very durable material. I was playing with the idea of using it for months, but I have decided for steel origami.
    It has its compromises, and maybe not among the best methods for the task, but I LOVE how two dimensional sheets are formed to a 3D shape.
    Hopefully now comes the part when I will not just know, but feel how much bigger task the fitout/finish is than creating the hulls ;)
     
  9. Rumars
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    Rumars Senior Member

    In theory you are right, any developable design can be converted to origami. In practice it saves only a few meters of welding and you have to deal with full size panels at once without precise control of the resulting angles. Doing a multichine design in origami would probably be slower then conventional. You will have to go multichine to achive the needed volume for the heavy material.
    Here you have a link to something better, the pictures are self explaining. Much simpler and cleaner then origami.
    Selbstbau-Stahlyacht Motu 42 / 44 (Anton Luft) - Teil 1: Rumpf und Deck https://klabauterkiste.de/selbstbau-stahlyacht-rumpf/
     
  10. oldmulti
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    oldmulti Senior Member

    magwas. Fitting out a steel boat is harder than most other materials unless you design it very well. Wood or fiberglass hulls you just glass tape a panel to the side of a hull. In steel yo have to have a tab welded to the hull to bolt too or weld a stringer or a frame as required. If you do good design you can overcome most of this problem by sensibly positioning any stringer you need for strength. In bigger cruising boats I have built or seen built the hull/deck is about 33% of the time, the internal furniture fit out is about 33% of time and the remaining time spent on electrical and mechanical systems, engine, deck gear, rig etc. For a 50 foot boat if you are really good home builder you may do it in 5000 hours but its likely to be a lot more.
     
  11. guzzis3
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    guzzis3 Senior Member

    strucell foam cheap as chips, polyester resin half the price of epoxy (or less) and get your eglass from www.utekcomposites.com about $1 a kg. I don't know about shipping to europe.

    As said hulls are about 1/3 of the build but not mentioned if you build in steel you will need to insulate! Or condensation and cold will kill you and your boat.

    Don't forget the cost of rustproofing everything inside and out. You end up with a catamaran with no resale, heavy, slow and will take as long to build and as much money.

    I am a metalworker by trade and building in steel would be so easy for me, but I'd never do it. I hate to discourage you but better stop now than get into it and realise you've thrown your money away.

    And as oldmulti said don't assume a slow cat will be faster than a decent mono, especially if you are comparing cost for cost rather than length for length. There are plenty of big yachts available now dirt cheap and some can be very quick. The old macgregors for example..
     
  12. magwas
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    magwas Senior Member

    Progress so far:
    I have asked a lot of designers for a quote. I have received some 8 answers. Most of them was "no", only one quote so far. A couple of replies included the same considerations for weight as in this thread, and I am specifically warned that the boat would not be able to sail windward in any sort of wind conditions, which is a safety risk.
    I am considering to go with aluminium. Dreams are nice, but reality is a beach.
    Thank you all for the discussion.
    Let's talk about what would be the minimal size of this kind of boat which would make sense. 100ft? 200? No such size? What is the way to come up with a well informed guess?
     

  13. guzzis3
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    guzzis3 Senior Member

    Well there are a few considerations.

    As mentioned 3mm plate is your minimum so a square meter of 3mm is 7.8x.003= 23.4 kg so your break point is about where alternatives are about that.

    Then you need to look at build cost. Yep the hull skin might be cheap but the other stuff, rust, insulation etc impacts practicality and cost of build. 50' is already insanely big for a cat, what do you plan to do with this boat ?

    I disagree about sailing to windward. I don't understand their basis for that. A properly designed cat should be able to sail to windward no matter the hull material. Yep it'll be heavier and the increased wetted surface will make it a bit slower but it should still sail.

    Aluminium is lighter because it's half the density of steel so you can build sufficiently thick/stiff/rugged skins at reduced weight. Aluminium has problems though which is why so few boats are built from it now. Corrosion and condensation for a start.

    The reality is many cats have been built over many decades and the marginal methods have fallen by the wayside just like the poorer compromise in design. People have tried all this stuff and it just doesn't work, which is why no one builds in double diagonal anymore either. Even before you look at complete lack of resale value the reality of building boats this way and the ongoing hassles of living with them have consigned all those "alternative" methods to history. It's also why no one home builds 50' cats. The man hours to finish that sort of boat are astronomical as is the cost. You will just never finish it. I estimate more than half the bridgedeck cabin cats 11 meters or more never get finished. People get the hull done then realise the incredible amount of work left to do and the cost and move it on at a huge loss.

    Consider building a small cat first, something around 20-25' or at most a 30' bridgedeck cabin design, or a farrier trimaran. Do a conventional popular design so you can sell it for something when you finish. That will give you a good idea what you are getting into and you can sail it an get a feel for where you are going.
     
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