Multihull Structure Thoughts

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

  1. oldmulti
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    oldmulti Senior Member

    The Kinetic Catamaran cruising cat is a very high performance machine. The KC 54 is 54.1 x 27.7 foot that weighs 32,700 lbs and displaces 43,000 lbs. The 69 foot carbon fiber wing or fixed mast depending on the performance option carries a 1,010 square foot mainsail, 590 square foot jib, Code 0 1,390 square foot and a 2,200 square foot spinnaker. There is a 74 foot wing mast performance rig option with about 10% more sail area overall and carries an 1800 square foot masthead Code 0. The length to beam is about 12.5 to 1.

    The foil option come in 3 formats. A swing centreboard, a straight daggerboard and a curved C daggerboard. The designer Maarten Voogd from Simonis Voogd was asked. “How much breeze do you need to fly a hull? ‘It’s hard to be specific, but I would say 15 to 18kts true with a Code Zero,’ Voogd says. And how much of a performance advantage will the C-daggerboards deliver? ‘They will “reduce” the displacement by a solid 10-12 per cent, so you will see a pick-up in upwind speed of about 0.6-0.7kts in ideal conditions,’ he says. ‘Leeway is expected to be the same and the overall VMG will be better by around 0.4-0.45kts.’ I have no doubts about this cats’ performance potential. It should see 25 knots. All sheeting, mainsail tracks etc are done to the coachroof so that the lower decks are clear of sheets etc. The roof based cockpit has access to the sheets etc.

    The yachts’ interiors are fully custom made, so anything is possible. Buyers have their choice of interior and aft cockpit layouts, furnishings, fixtures, fittings, colours, equipment, sound systems and more. To save weight the furniture is foam-cored with carbon backing and wood veneers but corners, edgings and inserts are solid wood. Countertops are milled thin and carbon backed to save weight without sacrificing strength. Removable furniture can be specified if the buyer wants to race.

    The entire vessel is infused carbon construction. The South African builder says. “The laminate is 100 per cent PVC foam carbon infused with epoxy resin, including all webs, floors and structural shelves. The only bit not infused is the tabbing joining components.” All foils are carbon fibre.

    Sheeting sails to the coachroof normally incurs a weight penalty because the structure needs heavy reinforcement to handle the loads, but Kinetic has engineered an ingenious solution. “Apart from the obvious extra reinforcing athwartships, there are two carbon poles below either end of the main track,” Scheepers (builder) explains. “These are strapped onto the main track with unidirectional carbon and fixed through the floor to the bridgedeck. This design feature actually allows us to make the coachroof lighter as the loads are transferred directly to the main structure. We also use these carbon poles as pipes to drain water off the coachroof, to prevent that incessant drip after it rains.”

    This cat is aimed at the Gunboat et al market and is the smallest in the range. This is a well though out design which has many interesting aspects. The jpegs give the idea.
     

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  2. oldmulti
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    oldmulti Senior Member

    The “Neptune” ply cruising catamaran was built 1965 and is 26.1 x 13.1 foot that weighs 2170 lbs and displaces 3360 lbs with crew and stores. The 32.5 foot aluminium fixed mast carries a 312 square foot mainsail and a 84 square foot jib. The length to beam of the hulls are 10 to 1. Underwing clearance is 1.6 foot. The cat does not have keels depending on the deep V shape to provide lateral resistance. The design could have low aspect ratio keels or daggerboards installed which will improve windward performance.

    This cats’ performance is good with 9 to 11 knot averages in very good conditions and capable of handling 25 knots under full sail. The cat sails at about 65% to 75% of wind speed up to 15 knots.

    Why the interest in this cat? Because its ply and timber structure would be very applicable today. The keel and stem are 40 X 100 mm pine. The frames are made of 20 X 50 mm pine with 6 mm ply either side of any joints. The chines are 20 x 50. The hull stringers are 20 x 45 mm. The hull gunnels are 30 x 120 mm to act as a stiffener at that level. The hull bottoms, decks, transoms and bridge underwing are 8 mm marine plywood. The cabin top deck stringers are 30 x 80 mm with the cabin top cross deck beams are 30 x 45 mm. The underwing fore aft stringers are 20 x 50 mm vertical. The underwing cross timbers are 20 x 55 mm on the flat. The hull sides, bulkheads, internal floors and deck in the stern section are 6 mm plywood. The forward main cross beam is 20 x 70 mm top and bottom of timbers with 6 mm plywood on both web faces. All plywood is fixed with 3X30 screws and glued. The finish internally is several layers of enamel varnish. Now you would use 200 gsm cloth and an epoxy finish externally and a “West” finish internally.

    The headroom in the wing deck is 3.25 foot and in the hulls is 6 foot. The wing deck has a king double berth. The hulls have a galley, toilet seating, a table and single berths. This is a practical short term cruiser that has reasonable performance. The jpegs give the idea.
     

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  3. guzzis3
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    guzzis3 Senior Member

    Gee I was thinking how much like a jarcat it is until you mentioned the headroom. 6ft in the hulls. That's Hirondell territory.

    It would be interesting to compare mini bridgedeck cabin cats back to back. Ray Kendrick's offering, Jarcat, Hirondell and so many others. Similar idea but each has it's differences and merits.
     
  4. oldmulti
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    oldmulti Senior Member

    Construction options and class rules often cause problems especially in Olympic class yachts. The Tornado class racing catamaran is 20 x 10 foot and weighs between 280 lbs and 330 lbs ready for sailing with 235 square foot of sail area in its original fractional rig. The hull length to beam is 17.5 to 1 and the draft with the boards down is 2.5 foot.

    The original design and build was in tortured plywood with a rotating aluminium mast. The cross beams were and still are aluminium. The build details are in the “Tornado build instructions” PDF attached. Later rule changes in 2000 meant that Tornado’s could be built in several materials including fiberglass but the rules effectively prevented high strength materials like carbon fibre to be used in hulls and crossbeams. The masts could be made from carbon fibre from 2000 and as a result all very competitive cats have carbon fibre masts.

    Tornado’s were an Olympic class from 1976 up to 2008 and as a result were popular. But the foiling day cats brigade started to become very popular from about 2015 which means Tornado’s are less popular but they still have an active racing fleet globally. The last major class rule update happened in 2015/2016.

    So, what hull build variations occurred? The original 1976 version had 4 mm to 4.8 mm tortured plywood hulls with thick Styrofoam panels that act as some framing and internal horizontal hull panels to provide stiffness to the hull. There are also some plywood and fiberglass to provide localised strengthening around crossbeam mounting points. These hulls were relatively long lasting in competition when well built and “west” epoxy protected.

    The next versions varied depending on the builder included double molded plywood versions etc. But one of the most successful “wood” build versions was a Gold medal winning western red cedar strip plank cedar version. The strip plank version was built from 200 gsm unidirectional S glass outside, 3 mm western red cedar, 200 gsm unidirectional S glass inside in epoxy. There is some Styrofoam support panels internally in the hulls.

    After 2000 there were many “fiberglass” non carbon fibre hulls produced. They started with a “foam glass” hulls but some were found to be overweight and “soft”. A top racing crew can tell if they are sailing on a plywood or glass hull just by the way the cat sails through the water. The hull needs to be laterally and longitudinally “stiff” not “soft”.

    The high tech versions of the fiberglass hulls were prepreg S glass, Nomex® aramid paper honeycomb core builds that are oven cooked. In 2015 Windrush catamarans built Tornado hulls to maximize the strength and stiffness modulus required despite not being able to use carbon fibres. Windrush says “We have found that the best combination is to use GMS Composites EP-270 epoxy prepreg, which we reinforce using a 200 gram +- 45 deg S glass in combination with a heavily unbalanced 300gm glass cloth that together effectively produces an unbalanced Quad for the outer skin laminates, with a 12mm thick Nomex sandwich core for maximum stiffness, shear modulus and deformation resistance.” The hulls are moulded in an autoclave at low temperature (~100 centigrade/ 212 Fahrenheit) using GMS EP-270 epoxy prepreg and an S-glass cloth multilayer combination.

    Tornado’s class is still a really competitive class were some of the ply boats are still capable of winning in local racing. But please note some of the ply boats are lighter than the fiberglass composite boats which means it is a class that has trade offs for high performance sailors. Its “stiffness versus weight” type debate. But when you are sailing on a cat that is capable of near 30 knots you will be having fun on any version.

    The jpegs give some idea. The PDF’s are the build instructions and the Tornado class rules, both virtually give you the build structure of Tornado cats.
     

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  5. oldmulti
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    oldmulti Senior Member

    A small overview of the materials used in the builds of many production and amateur build multihulls. Most production manufacturers have moved to vacuum bagging or resin infusion, with a few of the highest end boats using pre-preg and autoclaves for key components. Over the years almost every manufacture has shifted from solid glass components to foam glass or balsa glass and a minimum of vinylester resin with more using to epoxy. First Production multihulls.

    Asia Catamarans Stealth: Epoxy foam glass with some resin infusion.

    Catana: With a carbon fiber inner skin, Catana also uses Twaron aramid fibers in the sandwiched hull over a foam core. The Bali series are foam resin-infused vinylester.

    Fontaine Pajot: Primary hull construction is resin-infused vinylester with a balsa cored hull and deck. Later cats such as the Excess series are foam resin-infused vinylester.

    Gemini: The Gemini cats are built with a solid hand layup of woven roving and fiberglass mat and polyester resin. Decks are cored with end grain balsa. The Gemini 3200 introduced vinylester resin into the layup to prevent blistering.

    Gunboat: Gunboat hulls are epoxy infused carbon fiber with a Nomex honeycomb core. They build dagger boards and other high load components with pre-preg carbon.

    Knysna: Hand laid, bagged vinylester over an Airex foam core in the hulls.

    Leopard: Built by Robertson & Caine in South Africa, the hull material is vacuum bagged, end-grain balsa-cored E-glass with polyester.

    Prout: Earlier Prout catamarans like the Snowgoose 34 featured hand laid solid FRP hulls and decks. Over time they switched to foam or balsa cores for decks and above the waterline.

    PDQ: Older PDQ boats were made from vacuum bagged vinylester – solid below the waterline and cored with CoreCell foam above the waterline and in decks. Newer PDQ models switched to epoxy resin.

    Manta: All glass is vacuum bagged. Below the waterline is solid E-glass and vinylester. The rest is unidirectional, bidirectional, and triaxial cloths over a Nida-Core polypropylene honeycomb core with isophthalic and vinylester resins.

    Lagoon: Older Lagoons were SCRIMP infused vinylester with and end grain balsa core above the waterline and in the decks.

    Newer Lagoon catamarans use polyester and vinylester resins, also infused with balsa cores above the waterline and solid below.

    Outremer: Beneath the waterline, Outremer uses a single layer, solid vinylester laminate for safety. The hulls and deck are vinylester with a Divinycell foam core. They stiffen certain components with carbon for rigidity and durability.

    Seawind: Foam glass with vinylester resin infusion. Small models aluminum cross beams. Larger models all foam glass.

    Amateur DIY designers:

    Albatross Marine Design (AMD) Dr. Albert Nazarov. Aluminium. Foam glass vinylester. Can do almost anything.

    Rob Denny: Foam glass and resin infusion using vinylester or epoxy. Generally can be done in cheap female moulds.

    Grainger: Mainly foam glass or Duflex glass builds for amateur and production boats. Carbon foam boats for professional one off builds. Vinylester or epoxy.

    Kurt Hughes: Plywood timber in smaller designs and option of foam glass, balsa glass, plywood balsa glass in larger designs. Can also do aluminium and carbon fibre. Vinylester or epoxy.

    Kelsall: Foam glass with polyester resin.

    Bernd Kohler: Plywood timber in most designs. Some designs use EG PVC pipe for floats. Foam glass in larger designs. Excellent easy build designs.

    Mark Prescott: Strip planked cedar glass. Foam Glass vinylester

    TeamScarab Ray Kendrick: Plywood timber in smaller designs. All designs have a foam glass option with PVC foams and vinylester resins. The ply designs also have heavy glass layups. The majority have fiberglass crossbeams with metal folding components.

    Bruce Roberts: Solid glass, foam glass in polyester or vinylester in mid range cats. Aluminium in mid range to larger cats.

    Schoinning: Are now more about kits and plans but they prefer Durakore and Duflex Panels glassed over for home built designs. They will do other options at special request. Vinylester or epoxy.

    Tennant: Tortured plywood. Plywood timber, strip planked cedar glass, foam glass in epoxy or vinylester.

    Wharram: Plywood wood epoxy coated with some light fiberglass.

    Chris White: Constant Chamber plywood timber earlier models, foam glass later models. Carbon fibre on specials.

    Richard Woods: Plywood/timber in smaller designs, solid glass hulls in some designs to 30 foot, foam glass and ply in larger designs. Polyester, vinylester or epoxy.

    There is no consistency to the material in multihull builds and it mainly depends on material availability, cost and the intended purpose of the multihull. Most amateurs can build in plywood and foam glass but do not have aluminium welding skills. Professionals using moulds can do foam resin infusion and aluminium easily. If the multihull is well designed you can use any of the above materials to build it. It is more about your preference and skill. The jpegs are some samples of designers.
     

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  6. oldmulti
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    oldmulti Senior Member

    The Antares 44 is a performance cruising catamaran that was designed by Ted Clements. The original 44 cat was built by PDQ Canada in 2001 and from 2008 Antares has built about half a dozen boats annually at its facility in San Fernando, Argentina, situated on the outskirts of Buenos Aires on the Río de la Plata. There are at least 62 Antares 44’s sailing. The Antares 44 is 43.5 x 21.75 foot with a 19,500 lbs and a displacement of 24,000 to 26,000 lbs depending on the model. The 54 foot fixed aluminium mast carries a 614 square foot mainsail, 243 square foot jib, 473 square foot genoa and a 732 square foot screecher. The hull length to beam is 12.5 to 1. The low aspect ratio keels draw 4 foot. The underwing clearance sailing is 2.5 foot. The righting moment of the 44 is 192,000 foot lbs. The mast compression is 18,300 lbs and the bulkheads and mast are designed to carry 3 times the load or 55,000 lbs.

    The accommodation on the cat is good with a 3 cabin layout. The owners double cabin and toilet in 1 hull and 2 double cabins and toilet in the other hull. The boat can be customised but normally the galley is in the hull. The bridgedeck cabin has the dinette, chart table and storage cabinets with a washing machine. This is a serious cruising catamaran.

    The construction of the 44 is basically foam glass from production moulds. The Antares hull has 3 molds – outside left hull, outside right hull, and the inside hulls and bridgedeck. The molds have an orange gel coat then a 330 gsm omni-directional mat is applied to form the skin coat. The skin coat provides adhesion between the gel coat and the layers of fiberglass that follow. Bonding putty is evenly spread on the hull and foam core is laid on top. The core is vacuum bagged. The air travels out through the pinholes in the foam to ensure a secure bond that’s free of any air pockets. Antares hulls have solid glass below the turn of the bilge. Should damage occur below the water line, the solid fiberglass is more easily repaired. Solid fiberglass also facilitates high integrity thru hull installations.

    Once the 3 separate components are cored and glassed, the outside hull molds are aligned with the inner hull and bridgedeck mold section. The structure is taped and sealed together with 8 layers of biaxial fiberglass are applied to the seams to create the hull structure. The complete hull is now removed from its mold. The hull structure is then sanded and components are ready to be installed.

    The bulkheads require high strength-to-weight ratios. There are 3 primary bulkheads that provide structural integrity to the hull, there are also numerous others that are used throughout the hull. The three major bulkheads are: Mast bulkhead: to support the mast & balance the stresses imposed by the rigging. The companionway bulkhead: forms the division between the cockpit and the saloon. The steering bulkhead: provides support across the stern and forms the watertight division between the aft cabins and the aft lockers. The bulkheads are foam glass resin infused. The mast bulkhead is an “I-beam” where the bridgedeck and hull are the top and bottom flanges and the bulkhead acts as the web. Next are the secondary bulkheads are glassed in place.

    The interior of this cat is all hand-built with TriCell Honeycomb with veneers for lightweight construction. The head modules are the only GRP liner type units in the boat. After the furniture is installed the upholstery, vinyl work, and the more than 65 hand-crafted cupboards and drawers are installed. The vinyl head liner goes in as a finish surface covering up all the wiring and fiberglass. It also acts as a sound insulator.

    The cockpit hardtop carries the mainsheet track, which is subject to high loading – in this case, approximately 10,000 lbs. Stainless steel tubular supports are bolted to the deck and bimini to prevent the force of the mainsail from pulling the bimini off. The traveller track is mounted on a carbon fiber beam that’s laminated onto the hardtop. This carbon fiber structure prevents the beam from bending. The rudders have two sides of the rudders are constructed from fiberglass with a core center. This core center significantly reduces the weight of the rudder. The two sides are bonded to extended stainless steel arms that are welded to the rudder stock. The steel is made of 316L stainless that’s highly resistant to corrosion. The skeg, the tubular casing for the stock, and the rudder are assembled as one unit, adding strength to the overall construction.

    The performance of the cat is good. They are 250 mile per day boats if sailed hard. The cat under normal sailing circumstances will achieve 65% of win speed up to about 20 knots. Some reports say “We sailed at 9.3 knots in 14 knots of steady wind” and “As we sailed closer to the equator we encountered bursts of unsettled weather with heavy rain and winds gusting close to 40 knots; boosting our peek velocity to 14.8 knots and propping our SOG average to 8.6 knots.” The PDF from the design team giving the sailing polars of the cat.

    This is a well designed and built cat that has stood the test of time. The jpegs give the idea.
     

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  7. oldmulti
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    oldmulti Senior Member

    Antares 44 cat part 2.
     

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  8. oldmulti
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    oldmulti Senior Member

    A short one about 2 aluminium work boats that have very different displacements and power requirements, but the basic structural materials are the same. The cats are “Rokat” a 32.75 x 11.5 foot crew work boat that weighs 13900 lbs and displaces 18900 lbs. The underwing clearance is 2.1 foot. It is powered by 2 x 300 HP outboards with 30 knot cruise and a 35 knots sprint speed. It carries 1000 litre of fuel.

    “Rokat” Structure is: Bottom Plates 5 mm. Side Plates 5 or 4 mm. Main Deck Plates 5 mm. Foredeck Plates 4 mm. Superstructure Plating 4 mm. Nominal Frame Spacing 650 mm. Stringers are also built in for the hulls and decks.

    The ‘Spirit of Turmarr’ is based on a new design from GMD, featuring a near-vertical stem for increased waterline length, a high tunnel clearance, high volume hulls, and a fine waterline angle of entry. The final delivered vessel was to a very high standard, ably meeting the performance requirements of the client. The vessel has Jet drives and has good sea keeping and is a very capable and fuel efficient work boat for its intended application.

    The cat is 39.33 x 14.9 foot, weighs 34,400 lbs and displaces 44,350 lbs. The draft is 2.25 foot. Underwing clearance 3 foot. Fuel Capacity 2 x 1200 Litres tanks. Engines are 2 x Iveco C90 550 hp. Sprint Speed 25 Knots. Cruise Speed 21 Knots. Cruise range 225 miles.

    “Spirit of Turmarr” Structure is: Bottom Plates 5 mm. Side Plates 4 mm. Main Deck Plates 5 mm. Foredeck Plates 4 mm. Superstructure Plating 4 mm. Nominal Frame Spacing 700 mm.

    This show that there is effectively a minimum effective size of materials used in aluminium builds that is more a constraint of the build process. Those constraints the welding capability of thin materials. 3 or 4 mm thick aluminium is about the minimum that can be welded by an average welder without creating a distorted surface, 2 mm or below requires really skilled welders.

    The frame spacing and stringer structure differs in the designs but the underlying material is the same for a cat of double the structure. This may give a hint why foam glass is more popular in sailing multihulls as its material weights can be more easily varied. The jpegs are of the 2 cats.
     

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  9. oldmulti
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    oldmulti Senior Member

    This is an explosive story about Don Richardson an Australian who had a dream of owning an aluminum monohull. The “Gelignite” is 35 x 12.6 foot monohull that displaces 10,400 lbs. The fixed aluminum mast carries 620 square foot of sail. The keel draws 6.5 foot with a keel that weighs 3,500 lbs.

    This boats construction technique is the really interesting part. It is a version of explosive stamping. First dig a hole in the ground, then drop a steel copy (mould) of your hull supported by 20 x 20 mm steel support bars. Pour concrete in any gaps between the hole and steel mould. Line the steel shell with plastic surface (equal to waxing a female mould). You are ready for hull production. PS find yourself an explosive expert and some explosive.

    Next get a 5 mm 5083 N321 sheet the length of the hull circumference of the boat, 16 x 5 foot wide, place it in the mould bending it roughly into position, fill the mould with water, place in an explosive and bang. You have 20% of your hull shaped perfectly in 0.15 of a second. Repeat the process for the next panel in the next section of the mould. The 7 transverse sections are welded together. That is 6 lateral welds no longitudinal welds.

    The 5 mm aluminium was found to be capable of elongating 10% allowing the final explosive shaping to form an accurate hull shape. Then a framing system is installed. Don Richardson changed the usual aluminum hull design as he refused to weld stringers to the skin. The bulk of stringer welding has been replaced by adhesive joints.

    The cladding was reinforced with longitudinal stringers made of extruded aluminum “hat” profiles with flanges along the free edges. Having laid the stringer along the marking on the skin. Then both flanges are glued to the skin using VHB (Very High Bond) adhesive tape on an acrylic base. Such a tape has high adhesion to metal: the connection is quite strong and elastic, does not lose its properties under the influence of oil products, sea water and temperature drops. VHB tape is already widely used in aviation and space technology, maritime transport, and packaging of various goods. The stringers run continuous along the entire length of the body and are spaced approximately 200 mm apart. They are supported by 7 frames made of I-beams, which are installed on top of the stringers and do not touch the skin. The frames are welded to the stringers with short tacks. Reinforcements of keel floors are welded to the bottom skin for keel support, as well as in the area where the mast and engine are installed.

    A standard plate deck and deck house structure is joined to the hull. There were at least 10 boats produced by this method in 1992. They raced and cruised well according to those who have sailed on them. They were described as basic in their fit out. One was still sailing in 2014 which indicates a reasonable lifetime.

    This concept could work very well for shaping an aluminum hull bottom of a catamaran as the “mould” would be small compared to the entire hull of a 35 foot monohull.

    The jpeg give some idea.
     

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    Last edited: Jun 6, 2021
  10. oldmulti
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    oldmulti Senior Member

    The Tiki 31 was designed as a work boat initially but has been built by many as a tough little cruiser. The Tiki 31 is 31 x 17.5 foot that weighs 3000 lbs and a displacement of 5200 lbs. The mast and mizzen are 25 foot high 150 mm x 3.5 or 4 mm wall aluminum tubes. The masts can be made form 25 mm timber walls. The gaff wingsail mainsail is 162 square foot, the gaff wingsail mizzen is 140 square foot, jib 90 square foot and a mizzen staysail of 140 square foot. The gunnel width of each hull is 4.8 foot. The hull length to beam is about 11 to 1. The draft is 1.75 foot. The rudder is stern attached and also draws a maximum of 1.75 foot.

    The accommodation is 4 separate cabins which can either have narrow “double berths” (really are singles) or EG a head space or a galley space instead of a berth. Because the design was aimed as a workboat the mid cockpit in each hull is large and separates 2 cabins. Some builders put additional roof space over the cockpits.

    The structure is ply timber. The hulls have 8 mm plywood sides with 10 mm plywood bulkheads. The keel lines are stitched together, have epoxy slurry poured in the glassed inside. Bulkheads and a few stringers are positioned and bunk and floors are placed in the hulls. Deck cabins are attached. The 4 main cross beams are built and attached.

    This is a “standard” Wharram build but is heavier than EG a Tiki 30 which is 1 foot shorter, displaces 1000 lbs less and is built from 6 mm ply skins. The Tiki 30 has more effective internal space than a Tiki 31.

    A Tiki 31 builder reported it took 2500 hours to build the boat according to plan and an additional 1500 hours of work not on the plan (EG electrics, engines install etc) and assembly time of 200 hours. A total build time of 4200 hours. Another builder said it took 3 years off husband and wife part time.

    Tiki 31’s performance is OK. They can go to windward at 55 degrees with the V hulls. One owner report said “with some wind, it goes very fast, and the TIKI 31 tends to go very well to windward by using the mizzen, while offering multiple combinations: it will sail with jib and/or main alone, or jib and mizzen.” This cat is a 50% to 60% of windspeed type of boat that is a moderate performer in light winds.

    There are many Wharrams out there doing serious long distance cruising. The Tiki 31 can cross oceans as long as you don’t want full headroom or luxury accommodation. The jpegs give an idea.
     

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  11. oldmulti
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    oldmulti Senior Member

    part 2 of Tiki 31 build, sail plan.
     

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  12. oldmulti
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    oldmulti Senior Member

    The following is a 2 person camp cruising catamaran that almost anyone can afford. I am sorry but I have very little real detail on this cat, but I know some dimensions as per the jpeg. “Leste 350” is 11.5 x 8.3 foot with a displacement of 1000 lbs. The weight is a guess of 450 lbs. The 19.3 foot wing mast carrying 100 square foot mainsail, a 25 square foot jib and a 120 square foot spinnaker. The length to beam of the hulls is 6.5 to 1 at the waterline. Draft is 1.8 foot over the low aspect ratio keels.

    The hull headroom over the berth is 2.25 foot with a 0.75 foot well. The berth in each hull is 6 foot x 1.85 foot. There is also a storage space forward in each hull. The trampoline/deck area could also have a 2 person tent pitched on it for a “double bed” leaving the hulls for storage.

    Now we get to build options. Nothing is specified but you could build the hulls from 4 To 5 mm ply with 6 mm bulkheads with 19 mm timber edging under the main beam and transom. If the hulls were tortured ply a 25 x 19 mm stringer at bunk level going to the bow should be adequate with 30 x 19 mm gunnels. Decks and bunks should be 6 mm plywood. The decks should have 2 stringers the full length of the hulls. The deck beams sold be 40 x 25 mm. The exterior could be covered with 200 gsm cloth and epoxy.

    If you wish to spend more you could do a round bilge foam glass model. EG 6 or 9 mm PVC foam with 330 gsm cloth on either side in polyester or vinylester. A 6 mm ply bulkhead, transom and bunk panel will still work if you don’t want to do foam glass panels. An additional layer of 200 gsm cloth should be laid on deck in any area sat or walked on. If you do a strip plank cedar version you could d a 6 mm WRC covered with 200 gsm cloth either side with epoxy. Cross beams could be 100 x 50 mm timber or 75 mm aluminium tube. These are oversize but it’s an area I like strength. The keels and rudders are WRC covered with glass.

    Performance would be 10 knots max sort of boat but would be a lot of fun for camp cruising for 2 people in bays or rivers etc. Sorry, there is only one jpeg of the “Leste 350”. The second jpeg is of Dudley Dix 12 foot “BigaKat” cross section for a hint of cross beam attachment. If you want a free guide plan of a 12 foot cat (DS 12, lighter but will give some good hints) is at: DS12| Chris Tucker Marine Design https://www.ctmd.com.au/ds12.php.
     

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  13. oldmulti
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    oldmulti Senior Member

    Aquanima 40 is claimed to be a blue water electric power catamaran capable of ocean passages. The Aquanima 40 is 43.5 x 19.6 foot that displaces 15700 lbs. The 600 square foot roof top solar array generates power to the 60 KW Lithium-ion phosphate batteries. The 2 electric motors are 10 KW each. The length to beam of the hulls is about 10 to 1. The draft is 2 foot.

    The performance claims are an unlimited range at 4 knots with a maximum speed of 8 to 9 knots for the pure solar electric version. There is also a hybrid version available. The builders claim the motors are virtually maintenance free for 20,000 hours.

    The basic structure is aluminium with tough glass windows and appropriate internal furniture with timber or timber veneer finishes. There is a 4 double berth version or 3 doubles and 2 singles. The bridgedeck cabin has the steering position, galley, seating etc. The solar panel roof top can be used as an upper deck. The base cost of the cat is 523,000 Euro ex ship yard.

    An interesting design. Please reference the following web site for video’s and further detail: https://www.azura-marine.com/aquanima-40

    I will add one thing. I want to see how this craft would handle a day of 50 knot winds and 20 foot seas, especially if the intended port is upwind. This is my major reservation about this design.
     

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    Last edited: Jun 9, 2021 at 9:45 PM
  14. Burger
    Joined: Sep 2017
    Posts: 19
    Likes: 3, Points: 3
    Location: Australia

    Burger Junior Member

    In a Cat 4-5 cyclone it could probably fly a fair distance.......
     

  15. oldmulti
    Joined: May 2019
    Posts: 1,293
    Likes: 692, Points: 113
    Location: australia

    oldmulti Senior Member

    The cruise cat is a plywood motor sailor of Russian design. The cat is 23.6 x 9.7 foot with a 3600 lbs weight and a displacement of 5400 lbs. The 23 foot square mast is 115 X 90 mm glued from pine boards 17 mm thick; its weighs 45 lbs. The sail area is 225 square foot. The hull length to beam is 9.5 to 1. The underwing clearance 1.5 foot. The outboard power can be as low as 10 HP but can go to 50 HP. A 20 HP engine was initially chosen.

    The accommodation is good with 2 double berths forward and a dinette double berth in the main cabin. The steering position is also in the bridge deck cabin. The bridge deck cabin headroom is 4.5 foot. The galley bench is on the bridge deck but the footwell is in the hull providing 6 foot headroom.

    The construction is plywood and timber. The hulls are 6 mm plywood the external keel is 40 x 40 mm, the internal keel is 80 x 30 mm on flat with an 80 x 25 mm vertical on top. Chines are 35 x 30 mm. Stringers are 20 x 20 mm. Frames 80 x 20 mm with 4 mm ply backing plates at joins. Gunnels 60 x 15 mm. Underwing stringers 25 x 20 mm with a plywood underwing of 6 mm. Wing cross beam are 30 x 60 mm. Cabin top 5 mm plywood 20 x 20 mm stringers and 1.5 mm plywood internally. Cabin top deck beams are 40 x 20 mm. Deck 6 mm plywood with stringers 20 x 20 mm. Bulkheads are 6 mm plywood with timber surrounds.

    With 10 HP the cat can do a maximum 9 knots with 50 HP it can achieve 15 knots. Under sail with a moderate wind, the speed on a reaching course will achieve 7 knots, and to windward 5 knots. This cat is designed as a motorsailor and mainly is motor powered up wind. Reaching and downwind is where the sails are mainly used. After initial trials a 3 foot extension was placed on the sterns to improve motoring performance.

    A fun design for a mini motorsailor. The limited jpegs tell a bit of the story.
     

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