Multihull Structure Thoughts

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

  1. Hell_Bent
    Joined: Sep 2021
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    Location: Vancouver BC, Canada

    Hell_Bent Junior Member

    Here's an interesting one. Zephyr, an Antrim 40 featured here on Antrim Associates' website has just caught my eye in Reno, Nevada. 40ft LOA and WL and 34ft 1in beam, she was designed to break records while still having reasonably comfortable accomodation for her crew compared to other racing tris of her size. The cabin trunk consists almost entirely of plexiglass, so there would be plenty of natural light below, especially given the stark finish of the interior. She even has a nice big swim platform off the stern with an offset outboard on a track similar to Learn to Fly. Also, did I mention that she's fully demountable for road transportation? Needs one hell of a flatbed (or two) to haul her around though. She is not the only one of her kind which as far as I'm concerned is not a bad thing as I find her and most of the other antrim tri's to be quite fetching.

    According to Antrim, her other specs are as follows:

    Displacement: 4,620lbs
    Draft: 7ft 11in board down/4ft 6in board up/1ft 4in rudder up (casette rudder)
    Air Draft: 62ft 8in

    Main: 741 sf 68.9 sm
    Wing Mast: 71.8 sf 6.66 sm
    Jib: 217 sf 20.1 sm
    Genoa: 494 sf 45.9 sm
    Spinnaker: 1456 sf 135.3 sm

    Berths: 2 doubles, 1 single
    Outboard: 15hp designed, but later upgraded to 20hp
    Fresh Water: 30gal (when the boat is this fast, you don't need a lot)

    Tons more pictures on the Antrim site at the long provided. I will include the link to the listing which has more current photos here.
    [​IMG] [​IMG] [​IMG]

    Also I'm kind of new to this forum, so if there is a better way of embedding images or creating a gallery please let me know
     
  2. oldmulti
    Joined: May 2019
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    Location: australia

    oldmulti Senior Member

    Fritz Roth has progressively developed pacific proas for more than a decade. He started with a monohull, a cat and a tri before he started with a 23 foot pacific proa to test some idea’s. he then developed a 30 x 13 foot pacific proa to further develop and test his idea’s. The 23 and 30 foot pacific proa’s have proven themselves after being tested for over 4 winters, sailing the Strait of Gibraltar in up to force 10 winds. Also, the smaller proa’s sailed off beaches with breaking waves that were as wide as the proa. He was so convinced about the safety and performance of the smaller proa’s he started to build his dream pacific proa and 88 foot long version. The idea behind the 88 foot concept is to have a boat as long as possible for comfort underway & anchoring, because one can anchor almost anywhere there is no need to go into a marina. The proa is to have good cruising speeds with as little as possible of a sail area, a 1000 square foot with no need to reef or change sails up to force 8 going to windward and force 10 running and be safe from any breaking freak wave or gust. All this is good in theory, now let’s look at the suggested design.

    The 88 foot pacific proa is 88 x 35.6 foot with an estimated displacement of 25,000 to 30,000 lbs. The schooner rig twin fixed masts are 44 foot high with a total sail area of 1000 square foot. The low centre of effort in the rig helps make this proa relatively stable. The main hull length to beam 16 to 1. The main hull is 6.5 foot wide at the gunnel with additional room on the wing cross arm structure. The float hull is 34 x 2.2 foot with a length to beam of 16 to 1. The draft over the hull is 2 foot and over the rudders is 3 foot. As a basic proa these numbers would indicate real performance but there is an additional design feature that will add substantially to performance under some conditions.

    The base proa is intended to have a foil attached to its windward hull to hold it down. This is a high performance version of the Bruce foil. The foil does not provide lift but is design to pull down when the float hull is to windward. Bruce foil proa’s with the same configuration up in Scotland worked as planned but, in some seaways, the low aspect ratio foil came out of wave as it worked through a seaway. This required rapid crew action as near capsizes was the result. Fritz solution is to use a longer higher aspect ratio deeper foil that will keep part of the foil in the sea as it works its way through a wave.

    The second problem with this configuration applies to fast boats. A fast boat can be doing 15 knots and run into the back of a wave slowing it to 2 knots in seconds. A proa depending on a EG 1000 lbs down force at 15 knots from a foil will only have EG 20 lbs of downforce at 2 knots but still have the same overturning moment in the rig. A recipe for a capsize. When you do the maths on the stability of this proa, the foil will help, but if you had no foil and EG 1500 lbs of water ballast in the float you will achieve the same increase in stability as the foil pulling down 1000 lbs. The big advantage of the water ballast is it has very predictable stability characteristics and not subject to speed or wave effect load variations of a foil. And 1500 lbs of extra weight on a vessel of this size will have a minimal effect on overall performance. Finally, the cost of a high aspect foil will be many times the cost of some water tanks.

    The accommodation should be OK even for a thin hull as 88 foot provides room for many cabin spaces along with the wing cross arm structure providing additional space.

    There is no mention of the structure beyond the jpeg of plywood frames. I do not know if the 88 footer is complete.

    The jpegs give some idea. The first jpeg is the 23 foot and the second is the 30 footer. Interesting project, I hope Fritz can complete the 88 footer.
     

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  3. Hell_Bent
    Joined: Sep 2021
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    Location: Vancouver BC, Canada

    Hell_Bent Junior Member

    I had forgotten about these proas. Very interesting ideas, but I agree that water ballast would be a better option than the vector foil, with the added benefits of increased reliability and reduced cost. Adding extra weight to the windward hull could also help to settle the boat down a bit in heavy seas, especially if the swell is on or close to the beam and could potentially reduce the risk of capsize due to wave action. Vector foils are interesting, but I think that they are best used when lightness is the ultimate goal, such as with smaller proas. For cruising, water ballast is a tried and tested method that is cheap, low risk, and easy to maintain if done correctly and corrosion prevention is adequate.

    The aka of my proa was designed with water ballast in mind and the tanks actually extend over top of the ama. The lowest point of the tanks is still over open air and as such drains could be fitted to quickly and easily drain the tanks into the sea in any conditions. The pickup and pump assembly would be housed in the vaka and controlled from the cockpit so that the tanks could be filled or drained in any conditions. As with the real life proa she was based on, the aka also houses the potable water tanks and the ama houses the batteries and watermaker. There are plenty of necessarily heavy things aboard crusing boats that could be moved out to an appropriately sized windward hull and used to generate righting moment, rather than just being lugged around in the bilge. If I opted for an internal combustion engine instead of an electric drive (which could be a servoprop saildrive under the vaka to generate both thrust and regeneration in both directions), the fuel tanks would likely be fitted in the aka to simplify the fuel lines, which could also be entirely gravity fed.

    I've recieved the first set of models of my design from the 3D printer and, while the vaka and aka need to be re-printed, it's nice to finally have something to hold and manipulate after a couple of months of just staring at a screen. I haven't connected the hulls with the struts yet because of the reprint, but the renders give the idea.
     

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  4. Florent
    Joined: Jan 2022
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    Location: Swizerland

    Florent New Member

    Hello,

    Do you think it's dangerous to have an exit at the bottom of the mast ? In case there is strong wind sailor could get hit by the boom.

    I'm new with sailboat and I really like catamarans with forward cockpit like this Windelo 50.

    Thanks!
     
  5. Hell_Bent
    Joined: Sep 2021
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    Location: Vancouver BC, Canada

    Hell_Bent Junior Member

    Fortunately there is pretty much 0 risk of that happening. The forward cockpit walkouts are designed with sufficient clearance and, since you are so close to the gooseneck, the movement of the boom will be relatively slow compared to the outward end.
     
  6. Florent
    Joined: Jan 2022
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    Location: Swizerland

    Florent New Member

    Yeah, that makes sense.
     
  7. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    This is an update on page 38 of this thread. The Wadvogel 38 is a simple catamaran designed by Janbart de Jong in the early 1980’s that had several copies built. The cat is 37.25 x 21 foot that weighs 8500 lbs and displaces 10,500 lbs with a 270 square foot main, 96 square foot self tacking jib, 300 square foot furling jib and a 860 square foot spinnaker in a 7/8 fractional cutter rig. The mast is a 40 foot aluminium tube. The 38 is an extension of a successful home build 33 foot version of a semi wingdeck boat. The hulls are dory shaped and have a length to beam of 12.5:1 at the waterline. The flat bottom hull shape has minimal pounding and pitching if the ends are kept fine according to the designer. The draft is 1.7 to 5 foot depending on the draft of the daggerboards. The steering rudders are quite shallow but of the limited sailing information I have there are no complaints about steering. The engines are 2 x Torqeedo 48V electric outboards, a 10 KW diesel generator and solar panels.

    The cat has simple accommodation in both hulls 3 cabins with 5 bunks, a small dinette and well equipped galley. There are an additional 2 berth s in the bows if you were sailing in sheltered water. The centre-deck harbors storage space, a navigation-cabin with 4 seats that can be converted to a double bunk and a wide sheltered cockpit. The design has proven to be a fast and seaworthy yacht in various offshore races and voyages to the Shetlands, Scandinavia and the Med. The normal sailing speeds are between 6 to 15 knots. The Texel rating of the 38 is between 118 and 128. To give a comparison a F24 tri Texel rating is between 118 to 128. The 38 can sail well.

    The construction is based around the designer’s experience of sailing in shallow water. The flat bottom is 56 mm thick, laminated from 56 x 40 mm battens. The edges are rounded off to give a better waterflow. The sides are 12 mm ply panels scarfed together with stringer support. The decks are 10 mm plywood with deck beams and a layer of 3 mm teak veneer laminated on to reduce maintenance. There are plywood and timber main structural box cross beams. The forward 2 aluminum cross beams are used to anchor the forestays. There are Western red cedar covered with glass daggerboards and rudders.

    The jpegs give the idea of a simple, easier to build, good performing design.
     

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  8. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    The ELB (Extremely Light Boat) project began withs friends Don and Fred talked about how to make a very efficient powerboat. Don and another friend, Mike, decided to take action, and removed the amas from Don's Multi 23 trimaran, built a deck and created a prototype for the ELB. Don's comment: "With a 2 hp Honda we made 7.7 mph speed and about 70 mpg. Next prototype should be less crude." The new ELB (soon called Expensive Little Boat) is a 27 x 8.5 foot power catamaran that weighs 1000 lbs fully loaded without crew with a single engine 10 HP outboard and 1200 lbs with 2 x 10 HP outboard engines. The hull length to beam is about 13.5 to 1. The draft of the cat is 1.3 foot over the outboards when powering along. The underwing clearance is good. The ELB can be trailed on a “standard” snowmobile trailer.

    After talking to Don, Fred used AutoCAD 3D to loft the hull sections. They had a hull shape drawn to created a male form over which the hulls would be created. Before too long Mike's cow barn was filled with corecell foam dust as they made and glued up strips of structural foam core. This core had carbon fiber cloth laid over it and then epoxy vacuum infused through a vacuum bag to create a strong, lightweight hulls. The ELB new nickname is “Cowmaran”. So, we have the general concept of the cat. The ELB is being used as a general day cruiser around Florida and acts as a support boat for local dingy racing. As you have already concluded this is a group of guys who just want to have fun on the water and have designed the most fuel efficient cat to achieve this.

    So, what is the performance of the ELB? How about 12 knots maximum on a single Tohatsu 9.8 hp engine with a fuel economy of 4 miles per litre. With 2 x Tohatsu 9.8 hp engines the ELB can reach 16 knots and cruise at 13.5 knots with appropriate propellers. The fuel economy with twin engines is about 3 miles per litre. To quote the owner “With a 15-20 knot headwind and harbor chop tall enough to smack into the crossbeams under the deck, the engines wound up to about 5,200 RPM and the boat went 15 knots.” The ELB rides relatively smoothly with the fine bows. Again, a quote: “We did not even feel the little waves as the bows sliced through them” but this is not an offshore cat in a serious seaway.

    To the construction. To achieve light weight the ELB has been built from corecell and carbon fiber cloth that is epoxy vacuum infused through a vacuum bag. The 4 full length carbon fibre cross beams are 150 x 6.4 mm square tubes. All bulkheads and bridge deck etc. are carbon fibre foam. The deck console is a plywood structure. The outboard supports have timber reinforcements. The deck rails are aluminum tubes.

    This is an interesting cat that shows a long light boat with minimal HP engines can achieve good cruising speeds and be very economical. The friends have had many hours of fun doing day cruises and supporting dingy races in the local area. A good design. The jpegs give the idea.
     

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  9. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    The only issue I have with the elb is draft. 16" is too much and this is the classic problem for these higher performance teeny cats with axe hulls.
     
  10. SolGato
    Joined: May 2019
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    SolGato Senior Member

    I find the Elb design particularly interesting and am surprised there was no mention of electric propulsion since lightweight tall narrow efficient hull shapes like these translate to longer range and runtime with electric propulsion as well.

    Interesting to hear the prototype was built using Multi Amas. Lately I’ve been eyeing my Seawing Amas wondering what kind of power cat they might make.

    One thing about the deep draft as fallguy pointed out, is that at slower speeds I have found that lightweight shallow draft buoyant hulls tend to get tossed around a lot in swell. Having the bow knife edge it’s way through the water might be partly why the boat is reported to have good ride characteristics considering how light it is.

    Anyway, an interesting design that would probably shine with a pair of electric motors.
     
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  11. Ron Badley
    Joined: Aug 2020
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    Location: Madeira Park, British Columbia, Canada

    Ron Badley Junior Member

  12. Ron Badley
    Joined: Aug 2020
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    Location: Madeira Park, British Columbia, Canada

    Ron Badley Junior Member

    Also see the Gougmaran.... www.epoxyworks.com/index.php/birth-of-the-gougmarans/ ...I think the hulls were designed by Newick. The concept has much appeal for warm weather cruising.


     
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  13. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    The Grainger TR 36 trimaran design has been featured on page 128 of this thread before. The tri is 36 x 27 foot with a weight of 6500 lbs for a “standard” build. There are all carbon build options which would be lighter. The 49 foot mast (from fixed aluminium to a rotating cardon fibre) carries a 505 square foot mainsail, a solent of 281 square foot, a code zero of 493 square foot and Gennaker of 1102 square foot. The length to beam at the waterline of the main hull is 10.2 to 1. The length to beam on the float hulls is 16 to 1. The draft is 5.5 foot over the daggerboard. The rudders are kickup on the floats.

    The accommodation is a double forward and head. The main cabin contains a good galley, 2 narrow single berths and a small dinette. Aft can have a small double berth cabin and a reduced cockpit or a large cockpit. This tri could be seriously cruised by a couple but any more would be interesting after a week. I have cruised sailed a 36 foot tri with 3 to 4 people for a month and life got interesting.

    The “standard” build is a plan and a precut duflex kit using e-glass and vinylester resins. Professional builders use from duflex or PVC foam cores and epoxy with e-glass or carbon fibre. The Waarschip Composites build has used duflex on the hulls with e-glass. PVC foam on decks with carbon fibre outside and some Kevlar inside. The cross arms main strength structure is in a carbon fibre box section with a PVC foam glass fairing. All chain plates are glass and/or carbon fibre depending on the rest of the build. Current Marine in South Africa has done an all carbon foam build. Again, you can build in many materials so you can build in the material you understand.


    This tri’s performance is fast in any option but can be made faster with a lighter base build and taller rig. To give you an idea one builder claim is “The hull is also narrow enough to cut through the water before the trimaran starts to ‘fly’, 24 knots is achievable with 17 knots’ wind!” There is a video of Waarschip TR 36 sailing and it is very impressive. I could accept above 20 knots is possible.

    This is a very good design that is worth consideration. The jpegs give an idea of the design and build. The jpegs have some repeats and some new items.
     

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  14. Hell_Bent
    Joined: Sep 2021
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    Hell_Bent Junior Member

    I guess I didn't actually properly state that in my earlier post. I did link the ad with an embedded link like this though. I regularly browse west coast classifieds and that's how I found her.

    That TR36 is a beauty and a beast. I love how Grainger does the very pronounced flare above the waterline that gets even more dramatic as it approaches the stern. That was one of the first design cues that I tried and failed to copy in CAD when I was just getting started.
     

  15. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    The CC 37 is a constant chamber build cruiser racer trimaran designed by John Marples in the 1990’s. The CC 37 is 37 x 24 foot with a weight of 7500 lbs and a displacement of 9500 lbs. The 46 foot aluminium mast carries a cutter rig with a 322 square foot mainsail, a 183 square foot furling jib, a 485 square foot genoa, an 860 square foot screecher and a 1,200 square foot asymmetric spinnaker. The standing rigging is 8 and 10 mm 1x19 stainless steel. Running rigging is 12mm + 14mm + Spectra. The length to beam on the main hull is 7.5 to 1. The float length to beam is about 12 to 1 when sailing hard. The draft over the centre board is 5.75 foot when down and 2.75 foot when retracted. There is an optional low aspect ratio keel. The engine can be a 15 HP inboard diesel.

    The accommodation has a double berth in a stern cabin and bow cabin. The main saloon has 2 settee berths, a good galley, navigation area and there is a toilet area. The cockpit has the engine under. This is a practical layout for a cruising couple with the occasional guest.

    The performance of this tri is good. It won its class on handicap in the 2005 OSTAR. In 2006 it came second in its class in the Round Britain Race. The Texel rating of CC 37 is 104. A Farrier F28 or F82R rate around 101 to 108. This tri can sail. The owners quote: “She sails great and is a very good long distance cruiser/racer. Her speed very much depends on all the stuff (cruising gear) you have to take with you. In racing mode (as light as possible), with a flat sea, all sails up and in a good force 5 to 6, she is doing 15 plus knots, sometimes up to 20. When the lee float is immersed enough (when you push her hard till the deck of the lee float is almost under) she will accelerate because the main hull is lifted a bit and her speed comes in the much higher (15+) regions. Actually, it is not necessary to touch the helm much because she is in a completely balanced situation. The buoyancy of the floats, especially in the bows is big enough to withstand the tendency of burying even when you surf into a wave trough.” The featured boat also has cruised the full length of the Med. Another interesting quote from the owner: “I never used my parachute anchor but under 40knts+ conditions I followed the tactic of waiting for better conditions under bare poles as long there is sea room enough of course. She behaves like a raft and although drifting sideways, the ama floatation prevents her from capsizing.”

    The construction is basically wood, plywood and epoxy. The constant chamber mould system is used to make curved cold moulded panels 12 mm thick for the main hull and 9 mm thick for the float hulls. These panels are joined together and mildly tortured into a hull shape. There is very little internal timber stringer support but several bulkheads are in each hull. The framing on the timber cross beams is complex but easy to do. The jpegs of the cross beams are from a 40 foot CC tri. Constant Chamber is one of the easier ways to build a multihull but you have to compromise a little on hull shape. The decks and bulkheads are mainly plywood.

    John Marple’s knows how to design a reasonable hull shape using constant chamber and as you can see from the above performance results these tris can be very fast. The jpegs are mainly of the CC 37. There are 2 CC 40 study prints to give an idea of the hull shape and as said the cross arms are of a CC 40. A good practical design.
     

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