Multihull Structure Thoughts

Discussion in 'Multihulls' started by oldmulti, May 27, 2019.

  1. SolGato
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    SolGato Senior Member


    I think you succeeded in your goal of a design that is as easy and fast as Farrier’s, and for a Catamaran a solid floor makes much more sense, so the extra challenge was well worth it IMO. I can’t think of another trailerable Cat that can open and close on the water single hand with an integrated hard deck.

    Have you given any consideration to the feasibility of adapting your system for use on a cruising Trimaran?

    I’ve been toying around with the idea of a Catamaran system that incorporates a legal towing width hard deck with retractable bimini that can swing open to a wide sailboat-like beam to incorporate wing nets for more deckspace and stability. This would be a power boat so no need to worry about mast. The goal is to have the largest amount of deckspace available. The bimini when raised would then have a full enclosure for weather protection.
     
  2. catsketcher
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    catsketcher Senior Member

    No, no attempts at tris - there is no point. Farrier developed an awesome mechanism that is now available to all. My mechanism is now as well, as I patented it and let the patent lapse after many years of designing. My mechanism would be fine for a powercat. It is very stiff as the fore and aft beams are very deep and the mast panel takes any fore and aft loads and is orientated properly for that.

    Unless you have years of time to spend and are besotted with multihulls, I would caution you trying to get cats to fold. There are some very tricky and unforeseen problems with the engineering during folding and a world of intrigue with floors as well. That is why there are very few, (I don't know of any photos or videos of cats folding on the water apart from my previous video) folding cats that actually fold after launch. Even Kelsall's patented method had its version launched fully extended. Simpson had one that I saw with about 5 guys helping to fold it.

    My own point about the sub 8 metre cat is why? These cats exist in a zone where they are almost too small for the ocean, but are too large to be easily trailed. Of course they can sail in a placid ocean for delivery trips but multis derive their safety from the square cube rule and as such the small multis have little stability for coastal sailing, for delivery or for cruising. Waves of a certain size have a certain energy, this is why small boats get knocked down easier than large boats. For multis that must not get knocked down, you need to have more righting moment than a wave has energy to flip the boat. This seems to be around the 30 ft mark. This is not such a problem with monos as small versions can be designed with more stability and of course can pick themselves up from a knockdown. That is the reason I designed the mechanism, to cater for a problem small cats have coastal sailing. Trail the ocean/coast and sail the protected waters.

    Getting caught offshore in a sub 8 metre cat is not what I would want to do. That said, when coming back from Tassie, near Gabo, we passed a little Simpson Woodwind, about 8 metres long. Nice conditions and all good but if things had turned nasty I would rather have been on a larger cat (like ours) or a mono. I never really felt happy offshore in my 24ft Nugget, felt pretty good in my 31 ft Twiggy and belts and braces safe in the 38 footer.

    That said my wife loves sailing our little cats inshore, they are cute and easy, very livable and FUN. She is vigorous and energetic but even our low load 38 footer is too large for her to feel happy with her ability to undertake all tasks on the boat. So a small cat, with its divided layout, huge cockpit and great swim potential is a great concept for some, but I would not recommend them offshore, and I love sailing in different places, and for most cats that means sailing them offshore sometimes.
     
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  3. SolGato
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    SolGato Senior Member

    Well there is Hughe’s Cat2Fold which is a scissoring design, but I believe it requires two people winching in each hull at the same time. Of course it is a much bigger beast, and probably the biggest trailerable cat one would care to have in tow. He also later integrated a neat hinged hard deck into the design that folds and flip up and over the hulls when closed.



    I like manageable designs that are balanced in their offerings and agree that there is no reason to reinvent the wheel with regard to the folding Trimaran. Each popular design has its strengths and weaknesses, and they all get the job done in one way or another.

    My needs are strictly off shore and slow speed cruising via solar electric propulsion, so the design isn’t as challenging as something ocean going. I’ve been sailing my little Farrier Tramp in Pacific Ocean swell off shore launching it off and down waves for years now for which it was not intentionally designed, and I am sold on an overbuilt rigid beam structure that allows the 3 hulls to sail as one. I have been on “flexible” multihulls and didn’t like the lack of confidence I felt in the structure. There was a de-rigged F24 kicking around my island that I considered converting into a trailerable solar electric cruiser, but I would prefer a large bridge deck to a barely usable cabin.
     
  4. SolGato
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    SolGato Senior Member

    8887D7B2-291B-4963-B2F2-F602EF0D5BBB.jpeg A68AA5A8-D3D8-41D0-A34E-A79F07C21DF2.jpeg 5D70AF4D-4B8A-46CC-BA72-45F5DDFC54C0.jpeg F4114DA8-9333-463C-B424-510F5128EB24.jpeg AFB61BCA-12BB-4C60-8A43-92412DFB075D.jpeg EF78F8BF-7A01-473F-A1BB-D2E52B507FF9.jpeg CE7EC29D-7272-40A9-9E29-D117E5827D0B.jpeg


    Speaking of trailerable multihulls, here are some better photos of the Amas of my Skip Johnson designed demountable Seawing Trimaran.

    There’s a lot going on here with regard to shape not only with the tapering at the socket ends, but also along the leading edges and curvature over length. And after 30 years they still fit perfectly.

    Is it weird that I find these “arms” to be sexy?
     
    Last edited: Sep 3, 2021
  5. catsketcher
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    catsketcher Senior Member

    The Skip Johnson beams are sexy. No need to excuse that thought. The Seawings is such a good looking micro tri.

    As for Cat2Fold, I think you will find they went to twin masts to get rid of the weight of the rig in the middle of the structure when folding. If you were to cut a cat down the middle with a theoretical light sabre, the hulls will rotate top inwards. There is a lot of torque which is fine when the beams are extended but much less so when folding. The pic of Cat2fold half folded has no deck, a light rig, one person per hull in the centreline of the hull and some very high quality engineering in the beams and hinges. Going twin masts got the weight of the mast off the beams and reduced this torque when folding. There may also have been some issues when sailing but it is the folding inward torque that is a real killer. I find it interesting that a good designer like Hughes designed this system and neglected the problems of folding and inward acting torque caused by the weight of the beams and rig impart on the structure. It really is a struggling folding concept held together by excellent composite design and construction. There is also a huge world of pain trying to keep a real rig upright on a folding cat using wires. I had a couple of years spent doing that before I remembered the mast struts we used on 16ft skiffs. They are brilliant, a 3 point system that actually worked first time out. That was not common.

    I would not put hinges in a shallow beam that carries large mast compression loads. Beams like having continuous shear webs and continuous top and bottom flanges. The mast panel on my cat is always in compression and like an arch bridge, is fine with 3 hinges. So if you need to use 3 hinges why not use a system that is well adapted the 3 hinges like an arch bridge (or a tied truss as my mast panel really is)

    Like you I love solidity in multis. My little cats are bridgedeck solid when extended and folded. Simple in retrospect, get the mast compression loads away from a shallow beam onto a tied truss that always stays in compression, deepen the fore and aft beams, put them always in compression too using underwires to restrain the hull extension and make the mast compression panels long fore and aft so they hold the hulls where needed fore and aft. Simple when I say it like that. Took me a few years to work that out.
     
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  6. oldmulti
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    oldmulti Senior Member

    A story about one mans dream of his ideal boat. The difference is he has the resources, enthusiasm and engineering skill to complete the task. He researched options and decided on a one person trimaran and to speed the build by as many components as possible and then assemble them with specialised components as required. His main hull was a Wenonah Canoe that is 18.5 x 3 foot single skin Kevlar structure. Then you talk to the Fulmar trimaran factory and get the floats and folding crossarm structure to graft onto the canoe main hull.

    The tri is 19 x 11 foot with a weight of approximately 600 lbs weight. The 21 foot roller furling mast carries a 93 square foot loose footed mainsail.

    The accommodation is really only one person in a sit down mode that can be converted into a single berth area. This tri has a lot of electronics as the designer builder is an IT specialist. Speed was not the aim, just a practical small cruiser that could be moved around on land with its own wheels.

    The Wenonah canoe people bonded in a pair of 1/2” marine-plywood bulkheads eight feet apart in the kevlar skin canoe coinciding with the distance between the crossbeams of a stock Fulmar 19-foot trimaran. The center hull needed more freeboard than the stock canoe, so 50 mm more freeboard was added all the way around. This adds internal volume and gives a drier ride. Every 2 feet there is a stiffening rib of foam-core material that curves from the gunwale down to join the canoe floor. The added gunwale height was foam glass and below the original wood gunwale in a tapered piece of foam was added to allow our added fiberglass cloth to lay smoothly along the hull, as it refuses to bend around sharp corners. Two wooden strips were added on the forward sides of the hull are for added stiffness.

    The crossbeams from the Fulmar are U-sections, meaning that they are open at the bottom. A structure on the main hull to accept the crossbeams was required. To mold a perfectly mating shape, he built a formica mold shape from scrounged Formica countertop laminate from the dumpster of a nearby cabinet shop turned out to be perfect. Each cross beam nest was given 6 layers of 10-ounce cloth, yielding a final thickness of about .060”. Additional strength was added where needed later, during integration with the boat. The crossbeams were then bolted with 9 mm bolts to the structure with timber inserts to prevent distortion of the crossbeam structure.

    The mast base known as the mast urbator, this accepts the 21-foot freestanding rig, which is then free to rotate on its Delrin bearings. This is glassed securely into the hull. The unit itself began life as a chunk of aluminium tubing with 75 mm inside diameter and 3 mm wall thickness. A set of 4 foldable wheels added to the design for land transport. A peddle powered propeller outdrive was added for low speed manovering.

    The tri can sail reasonably well in trials after its 10 year build but ultimately did not meet the builders requirements. He next got a Corsair 36 tri, then a 44 foot steel monohull which he spent 6 years on then a 60 foot liveaboard power boat which he still lives on.

    The jpegs give the idea.
     

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  7. oldmulti
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    oldmulti Senior Member

    Part 2 of the microship jpegs
     

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  8. jamez
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    jamez Senior Member

    Hi Phil, great to see your little cats getting mentioned again. I remember following (before following was a 'thing') this project with some interest as it progressed nearly 20 years ago. The folding system was designed by Rafael Fraanke the owner/builder. I found the following (communication to a subsequent owner) which explains who was responsible for what at The Boat https://cat2fold.wordpress.com/about/

    Hi Brian Jan 10. 2012
    Nice to see Cat2Fold in her environment doing well, and you guys in the wet and warm environment having good times.
    To straighten things out:
    Cat2fold’s general idea was mine, I hold a US patent for it.

    Rafael Francke,
    Multihulls West Inc.
    84 Cerro Crest Dr.
    Camarillo CA.
    Cat2fold@hotmail.com.

    I came up with the basic design after trial of many different design concepts .
    I hired Kurt Hughes professional service as a navel architect to design the hulls and make load calculations for the folding system. I chose Kurt because of his good name in the business and his wide angle view of systems in general, unlike some other designers that pulled their shoulders in a negative way when first introduced to the Cat2Fold idea.

    Kurt got a spark in his eyes when I came over to his office in Seattle and a small model of Cat2Fold came out of my travel bag and opened and closed on his desk.
    During the design process Kurt offered me a new hull design he had already designed and offered to adopt my folding system to it, which I happily agreed to.
    When Kurt finished Cat2Fold’s folding system calculation, he recommended that we use a company that does computer infinite strength calculation for Boeing Aircraft wings, to test Cat2Fold’s folding beam design, to double check his calculation, “just to be sure” since it was such new approach to catamaran folding beams.

    $$$$$$ later we got the results of this test. Kurt did some minor changes in his calculations and the folding beams were ready for production.
    Note. The folding beams where over designed twice, let me explain.
    First, the beams where designed and calculated to be very strong, then I asked Kurt to change the calculations in order to be able to use the system without the normal “Dolphin striker” you see on all the Catamarans.
    My reason was I wanted the option to moor the catamaran in two adjacent slips, with one floating dock in between the two hulls (below the hard deck, providing there is no pillar at the end of the dock ). This change made a strong beam even stronger.
    More so now when the Bi- plane rig is being used, there is no single mast with all the pressure involved in it, the strength of the beam is way over what really is needed. But it is very safe.

    Second, when Kurt calculated the laminates of the beams it was for HAND LAYED laminates :
    X -layers of carbon = Y- wall thick

    Since the builder was using the latest technology of infusion, the results on a test were different:

    X- layers of carbon = 0.75 Y wall thick
    Now to be on the safe side and to reach the desire wall thickness he did:
    X +.25- layers of carbon = Y wall thick.
    Again the beams where over built, but very safe again.

    During the production, the size of the original single mast sunk into my mind and I did not sleep well for some time, sweating at night from the hard labor of hoisting some 56′ tall single mast, or trailer that long mast in my dreams.
    That brought the design change to a bi-plane rig, after first testing it on a smaller 20′ “Boston Whaler” catamaran, which confirmed my new approach to use two masts, one on each hull, the test boat was called “tester for Cat2Fold” ( pic. available as well as the boat is still in my back yard)

    The placement of the Bi-plane masts was by Rafael Francke, the actual build and laminates were calculated by the builder.
    The masts were designed and built by Van Dusen. Perimeters and basic design by Rafael Francke.
    Wishbone booms were designed and build by Rafael Francke.
    Sails were made by Skip Eliot, perimeters and basic design by Rafael Francke.
    The mast raising system was designed and built by Rafael Francke, whom holds a US patent for the system. The system allowes raising and lowering of the mast with ease.
    The dagger boards and rudders and their placements are Kurt Hughes design.
    Rafael Francke has shortened the Dagger boards after some sea trail, as well as changing the pivot point of the rudder for better tiller feel.

    On this letter I have to include Greg Martell’s name, he was the builder of this unique and high quality folding catamaran, and he did a marvelous job, as well as solved many probles during construction. Sorry to say that with a tough economy, he had to close his doors and and is no longer in the boat building business, which is a major loss for us sailors.

    Brian, I hope that clears a lot of gray areas as for who deserves credit and for what.
    I would suggest to present it as:
    Rafael Francke Designer & Investor ( brainchild, if you prefer to use )
    Master controller and hull design. Kurt Hughes navel architect.
    And if you need to go further:
    Building Hulls and folding system by Greg Martell.
    I would like to add that the long time collaboration between Kurt Hughes Multihull Design,
    and Rafael Francke of Multihulls west allows the option for interested sailors who would like to have a folding Catamaran like Cat2Fold to buy plans and get the proper direction to build one.
    Best to contact Kurt Hughes Multihull Design.

    Brian, This letter has more information that you have asked for but as a sailor with such special vessel and such exposure you should have it all.
    Will the wind blow gentle in your sails.
    Rafael Francke.


    This would have been an expensive project. The hulls were pro-built in Auckland NZ and freighted back to the US where the boat was finished off by the Franke's. It was launched in 2005. They spent the next 2 or 3 years refining the boat. A combination of health problems and the GFC scuttled any plans for production versions. The boat was eventually sold in 2011 for a giveaway price. It was for sale again in 2019 for 75k.
     
    Last edited: Sep 4, 2021
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  9. catsketcher
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    catsketcher Senior Member

    Thanks for that Jamez. I remember it looking like a very expensive project. The change of mast seems logical stated this way, although had he proceeded with a single large mast I think there would have been huge issues with folding.

    Mast length is a real problem for trailerable boats. I put some serious time into a gunter rig. Going gunter with a 3/4 rig would have reduced the mast raising torque by about 45% but I just couldn't do it. As it happened using the trailer winch and using mast struts is a fine option.

    Masts on trailer boats are very problematic. Raising even a Hobie 16 mast is a struggle and getting a mast up on a trailer multi can be very tricky. The original trailertris could have their masts raised by one person's effort whereas the F25 needed trailer winch help. Tall masts are heavy and the CG of the mast gets past the aft mast strut pretty quickly. On my 7 metre cat it gets close to wanting to fall off the mast strut and that mast is pretty short. Then you have the issues of winching up a heavy mast and keeping all in line. So the 56ft mast on Cat2fold would have been a nightmare. Then you would also have to fold it.
     
  10. jamez
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    jamez Senior Member

    I know what you mean, years ago during the grand design quest I became for a time enamored with Kelsalls XKat 26. IIRC the plans were a couple of thousand which seemed OTT at the time for a boat that size, but having just seen a quote of $6k for plans for an 8.2 metre power cat recently, kind of puts that into perpective. You might like this one Guzzi, mast well forward sliding beams if you want them and 'economical' KSS foam/polyester construction.

    X-Kat 26.jpg
     
  11. peterAustralia
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    peterAustralia Senior Member

    In regards to the microship, they are packed with electronics, Steve said one was for sale, asking $50k use (ouch). A couple notes, the wheel system (they can go on land) is super complicated, better to go with a little cart made from an axle and a couple pieces of wood, add a small castor wheel for the bow.

    Secondly they sail stern heavy, because the occupant is sitted aft, the canoe is light, thus the trim is off. Better to build your canoe with wider sections aft to cater for the weight of crew. Because the starter craft was a Kevlar Canadian canoe, double ended, it lacks the wider stern sections, thus the trim is way off.

    For the time it was very innovative as the new wave of micro trimaran s had yet to arrive
     
  12. jamez
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    jamez Senior Member

    While it sounds a retrograde step the lug rig has some good potential, particularly on boats that are never sailed to windward (that's not as stupid or unlikely as it sounds). Dick Newick drew a boat called the B2 which was a home builder version of the Argonauta, folding and all, with an optional lug rig. I have a drawing of it somewhere. Sounds daft but it is a powerful rig, and very low aspect, the mast just being an alloy tube on the B2. I think it could also be a good rig for a motor sailer type power cat.
     
  13. oldmulti
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    oldmulti Senior Member

    Jamez. Page 49 multihull structure thoughts Back to Basic tri. Also a 48 foot newick tri that is actually sailing. Jpegs attached.
     

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  14. oldmulti
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    oldmulti Senior Member

    A story about a series of Russian transportable catamarans. We start with a 26.3 foot cat that was that was not built to my knowledge but was the basis of a 32 foot cat. A 30 foot version was initially built in 1994 and raced under the Gazprom banner for several years.

    The design diagrams of the Ivan 8 meter are the first group of jpegs. The cat is 26.3 x 16 foot with 3.3 foot wide hulls.. Guess displacement 3200 lbs. No rig specifications. Draft 4.3 foot with daggerboards down with a hull draft of 1 foot. The length to beam is 13 to 1 at the waterline. The accommodation appears to be 2 aft single berths and some 5 foot headroom cabin space.

    The structure of the 26.3 foot cat is not specified but the remainder of the cat series are PVC foam carbon fibre with fore and aft aluminium tubes cross beams with a short structural centre mast beam that slots between the hulls.

    The Ivan 30 foot Gazprom is a tube racing cruiser racer cat with a bit more accommodation due to the bell shaped bottom with low chines. The Ivan 30 catamaran is a 1994 design by Vitaliy Belykov and Pavel Tkachev. The cat is 30 x 22 foot with a weight of 3790 lbs. The 36 foot rotating mast carries 640 square foot in its rig. As you can see it also carries spinnakers and screechers etc. The draft over the daggerboards 5.4 foot. This cat has raced under Gazprom sponsorship in many European races including the Fastnet.

    The accommodation is a bit more useful with 3 single berths and a small dinette and galley. Again, the build is likely be PVC foam glass. There are fore and aft aluminium tubes cross beams with an aluminium centre mast beam with a dolphin striker that slots between the hulls. This cat looks like a solid structure.

    Finally, The Ivan 32 was produced which is 32 x 20.5 foot and weighs 3,350 lbs. The wing mast is 48.2 foot and carries 580 square foot of standard sail and up to 900 square foot under light weather sails. The draft over the boards 5.4 foot with a hull draft 1.25 foot. The underwing clearance is 3 foot. The cat is demountable and able to be trailed or shipped in a container. This is not a weekend trailer sailor. It requires hours of assembly or breakdown.

    The accommodation is single berths reasonable headroom and a small galley. The build is claimed to be 100% carbon fibre PVC foam. The fore and aft beams appear to be box sections as does the mast beam and I suspect they will also be carbon fibre as this is a large cat for its 3,350 lbs weight. Again this cat is used in racing and the builders/owners are wanting advertising to help pay for the cats running costs.

    An interesting series of cats. if anyone knows more details, could you please advise. The jpegs give the idea.
     

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  15. oldmulti
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    oldmulti Senior Member

    Ivan 32 cat extra jpegs.
     

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