Multihull Structure Thoughts

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

  1. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    We have spoken of the M80 trimaran before but the lastest build by Lightwave Yachts is interesting. The M80 is 25.9 x 19.2 foot that weighs 1900 lbs and displaces 3000 lbs. M80 carries a 36 to 40 foot mast depending on the option and carries a 160 square foot self tacking jib and a 250 square foot main. Main hull length to beam is 7.4 to 1.

    M 80 build. For the M80 in build at Lightwave Yachts, the main shell structure, fore and side decks, and cabin sides were built with DuFLEX/foam panels cored with Divinycell H80 structural foam (DuFLEX is 10 mm H80 divinycell with 600 gsm biaxial on either face) in a variety of thicknesses and reinforced with double bias E-Fibreglass skins.

    The cabin top and floats were strip planked with DuFLEX H80 strips with a 450grm uni-directional on either side to achieve the compound shapes and then reinforced with additional laminates to complete the structure.

    The project incorporated carbon fibre and E-fibreglass reinforcement, supplied by ATL, to provide stiffness and to achieve the weight specification for the project.

    The other M80 trimaran option is to build with a stitch and glue system with 6mm and 9mm plywood being the main components. Stitch and glue is an easy method to put a set of hulls together. All glass cloth is 300 gsm with the hull bottom having one extra layer for protection from grounding or running up onto the beach. Epoxy work on the structure is predominantly cove and fillet. The M80 is a folding trimaran that uses standard aluminium extrusions without any welding.

    An interesting discussion happened on another forum about the M80 design and a lighter build option (Wayne Barrett, the designer, only comment was the options would require more framing and be slower builds). The suggestion was a choice of 6 mm plywood or 6 mm foam glass.

    “An 8m tri would only need 400 gsm skins, which are too thin for the Z press (a method of joining Duflex sheets with 600 gsm skins). You would have to join them all by hand, and fair them in afterwards.

    Strength to weight: Boat panels require stiffness, more than strength. Panels that are stiff enough are usually strong enough. Foam/glass is far lighter in both situations. EG 6mm ply/epoxy will have similar stiffness to 6mm foam with 300 gsm glass each side. A square metre of 6mm Okoume/gaboon ply weighs 3.1 kgs and requires .5 kgs (2 x ~.75 kgs/sqm coats each side) of epoxy to seal it. Total 3.6 kgs.

    A square metre of 6mm H 80 foam weighs .5 kgs, plus .2 kgs per side to fill it, .6 kgs of glass and .3 kgs of resin to wet it out (assuming infusion/bagging). Total 1.8 kgs, half the weight of the ply.

    To get equal strength/impact resistance of the 6 mm H 80 foam, make the glass 400 gsm. Weight goes up to 2.1 kgs per square meter.”

    Translation. If you build in plywood you may have a boat that will weigh more than the foam glass version IF it is built with a lightweight version of foam glass EG 400gsm skins. BUT if the tri is built DuFLEX with 600 biaxial skins on 10 mm foam and then the panels are joined with 450 gsm uni directional glass you end up with panels that weigh about 2.6 kgs per square meter.

    The plywood version of a M80 with 6 mm ply with 300 gsm cloth weighs 3.6 kgs per square meter and 9 mm plywood with 300 gsm cloth which will weigh 5 kgs per square meter.

    In short, choose your material options carefully as your boat weight may vary significantly from the advertised weight which will reduce your payload available in your design.
     

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  2. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    This one will be more visual than word based. There are many ways to fold a tri. Farrier folding system is very popular and an excellent solution used by many designers. The other main technique used by an increasing number of designers is swing arms as used by Dragonfly, Brown Marples tri’s and many other designers.

    The swing wing approach depends on good design as the strength of the cross arm depends on a few very highly stressed point loads at the top and bottom of the hinge points that connect either the main hull or float to the cross arm. The pivot pin size is important but the attachment of the pivot pin to the hull and cross arm structure is very important. Water stays help reduce the tension loads on the pivot pins but increase the compression loads. Again smart design can reduce the compression loads on the pins with accurate design is required.

    John Marples contribution to swing wing design in smaller home built tri’s is large. His simple but very effective solutions are appreciated by many. The Seaclipper 20 jpegs are shown. The Seaclipper is 20 x 15.5 foot, folds to 8.5 foot, weight is 800 lbs with 230 square foot of sail.

    The other design shown in the jpegs is the Dragonfly 800 which is 26.25 x 19.5 foot with a weight of 2600 lbs and 375 square foot of sail. There are a few other later model Dragonfly jpegs. The final jpeg is of Oceanbird a production swing wing tri of the early 1970's that is still much loved today by her owners, not fast but is great when it come into marinas.
     

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    Last edited: Sep 5, 2020
  3. oldmulti
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    oldmulti Senior Member

    We now will talk about a car company and a monohull. What? I am interested in sail but even I am surprised at to what some companies will do to minimize their environmental impact. Automotive giant Group Renault is partnering with Neoline to build 2 wind power ships by 2020 and test them on a route from Saint Nazare in France to the eastern seaboard of the United States and the French islands of Saint-Pierre & Miquelon, just off the coast of Newfoundland in Canada.

    So, what is the Neoline solution? An industrial-scale wind-powered freight service. In particular, a 450 x 80 foot ship that weighs 5,000 tons and displaces 11,000 tons. The 4 masts (2 side by side sets) carry 45000 square foot of sail. The 220 foot masts can be folded to 135 foot (the same way you would use a boom for a trailer sailor) to get under bridges etc. She is equipped with retractable daggerboards to improve its sailing efficiency and allow access to a majority of ports. Her port draft is 16.3 foot, offshore 46 foot.

    The main point here is that the sailing ship has the potential to reduce CO2 emissions by up to 90 per cent compared to a traditional cargo ship on an equivalent route. But the reality is a 4000 kw desil electric engine will help keep schedules. The ship will cruise at 11 knots and will have a maximum speed of 14 knots. Everything in the rig is computer controlled with massive power winches.

    The base structure is steel with carbon fibre in the rig. The sails will have companies globally bidding. It will be an ongoing contract that will probably focus the mind of 1 of the 14 crew full time.

    Neoline are planning to have a 690 foot, 3 sloop mast version available in 2030. The jpegs give the idea. Normal transmission will resume tomorrow.
     

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  4. mikef
    Joined: Apr 2015
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    mikef New Member

    Oldmulti, I am trying to find out if there are any similar trimarans to the one I am currently renovating. Amphitrite is a trimaran designed by Derek Kelsall in 1979 and partially built at Sandwich Marina (hulls built by then apprentice Richard Woods). 29' 10" length overall, 28' at waterline, overall width is 25' and draft is 18". She is a bermudan cutter rig with sail area of 550 sq ft. I think she might have been part of a design called 'stripling' that perhaps never evolved. Construction is polyester foam sandwich. This is a fantastic thread and I thought you, or anyone else, might be interested in the pictures.
     

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  5. oldmulti
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    oldmulti Senior Member

    Mike. I will try and find the line drawings I have for the design. I hope our British/European friends may know if any more were built. A relative of the design is the Stride 32 tri which was 32 x 26.9 foot displacing 3000 lbs and carrying 990 square foot of sail. These boats were built in the days when 28 foot waterline lengths were required for the minimum class in OSTAR transatlantic races.
     

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  6. oldmulti
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    oldmulti Senior Member

    On page 24 of this thread we mentioned the Grainger designed Livewire 28 inshore or coastal racing catamaran. Grainger is now providing more detailed home build plans and options. The Livewire 28 is 28 x 16.5 foot weighing 2000 lbs (depends on build skill) and displaces 3000 lbs. The 42 foot rotating carbon fibre mast carries a mainsail area of 384 square foot, self tacking jib 126 square foot, code zero 332 square foot and gennaker 615 square foot. The hull length to beam ratio is 15.5 to 1. The sail area of 716 square foot (code 0 and main) to (115 square foot of hull and 30 square foot of boards and rudders) wetted surface ratio is 5 to 1. This is very high, meaning its light air performance will be spectacular.

    The cat is built from foam glass with an option of carbon glass. Similar cats have hull layups of 12 to 15 mm PVC foam with 400 gsm e-glass biax or eg 270 gsm Kevlar or 200 gsm biax carbon fibre in vinylester or epoxy. The layups are double over the bottom. The more you pay the faster you are likely to go.

    The 2 cross beams are aluminium mast sections of 271 x 180 mm. You can have carbon fibre beams.

    The central spine is a rigid structure that allows you to crank on the forestay and mainsheet tension for optimum upwind performance. If you’re running a screecher or Code Zero to windward the central spine provides the ideal platform for sheet blocks so you can rig a bridle or a barber hauler between the hull and the spine. It also serves as a secure storage pod for anchor and chain, and other items that need to readily accessible from the deck. It’s also provides firm mounting base for the outboard auxiliary while concentrating the weight close to the centre of buoyancy.

    The Livewire 28 is a very fast open deck cat for racing with minimal accommodation for “cruising”. This would be serious fun for the young at heart. Jpegs give some idea but the hull lines give a lot of information.
     

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    Last edited: Sep 7, 2020
  7. Slingshot
    Joined: Aug 2019
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    Slingshot Junior Member

    So, what was this cruising cat built from? 6 mm plywood, high density foam and e-glass. The cross beams are aluminium tubes with a dolphin striker on the main beam. You could build a boat like this at your home. The hulls are basically a plywood boxes with a shaped foam bottom added on covered by e-glass and epoxy. At the daggerboard box exit a ply support V structure was built to reinforce the daggerbox bottom. The hulls had 6 watertight ply bulkheads and deck beams. The final hulls weighed 375 lbs a piece. The approximately 22 to 1 length to beam hull shape was done by Norm Riise who, in his spare time, used a mainframe computer at Jet Propulsion Labs to optimized a boat hull shape. This was the first time a computer optimization was done on a boat like this."

    Old Multi this post got me thinking about the construction technique of a symmetrical length wise box with a foam bottom. In addition the mold infusion Harrypro uses could be incorporated to make hulls very quickly.

    My question is would half box hulls with foam bottom be faster or better than the Kesall system of a half hull flat panel with a foam strip bottom then join? One plus is you have a foam crash bottom but could be heavy. Thoughts.
     
  8. oldmulti
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    oldmulti Senior Member

    Slingshot. Short answer depends on the type of foam you put on the bottom of the box. Polyurethane low density foam is a pain to work, seal and glass but low coat and high maintenance. High density PVC foams is better to work and glass has lower maintenance but ends up being more expensive. There is a trade off point in this approach where the fairing of a block of foam takes more effort than building a male or female mould to form a shape and glass it inside and out.

    As to hull shape. The closer it is to a rounded shape the better as it minimizes turbulence etc. BUT and I mean a big BUT, a well designed chine hull shape will be faster than a poorly designed round hull shape. Also chines in the aft end of a hull often shed water at high speed better than a round bilge shape. But again it depends on the length to beam, speed length ratio and intended purpose.

    As an example, the Livewire 28 hull shape is great for high speed sailing with the center of buoyancy and center of gravity aft allowing the fine wave piercing bow shape. This hull shape should not be used on a cruiser as a cruiser needs as much buoyancy as possible in the ends to allow for overloading and eg running downwind in big seas to minimize the chance of pitch poling.

    Summary. The build technique for Dashews 38 foot cat is very good and would be appropriate for similar style cats, but if your going to build a cruiser you may find it better/easier to use more conventional build methods. Sheet plywood, tortured ply, aluminum or Denny's intelligent infusion are all relatively fast build methods. After that it depends apon your experience of a material and you access to equipment that can simplify the build. I know of one 17 foot plywood mono mini cruiser design that I saw a person put one together in 8 months from start to launch. I know another person who has spent over 4000 hours so far to do the same design and is still a few years away from a launch. The materials are one thing your skills are another.
     
  9. oldmulti
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    oldmulti Senior Member

    This is the dream boat. Unfortunately, even second hand they bring $US 1.7 to 2 million, that’s if you can get one of the 6 owners to part with their boat. What is it, the Gunboat 48 built between 2004 and 2009. The Gunboat 48 is 48.3 x 24.3 foot that weighs 17630 lbs and displaces 22500 lbs. The 64.3 foot carbon fibre mast carries a 980 square foot mainsail, 390 square foot genoa, 1390 square foot gennaker and a 1560 square foot spinnaker. The cat also has carbon fibre boom and spinnaker poles. Unidirectional aramid fiber shrouds and Aramid forestays (x2) with custom Facnor furlers. The hulls are 6 foot wide at the gunnel and has a 4 foot underwing clearance at full load. The hull length to beam is about 12 to 1.

    Morrelli and Melvin are the architects after Peter Johnstone approached them for a smaller Gunboat after the highly successful Gunboat 62. The accommodation has a main salon with galley, lounge, and folding dining table. There are three queen size cabins and 2 heads with dedicated showers. There is a forward cockpit for sail and mast control and a spacious “back porch” aft cockpit with caulked teak deck dedicated to lounging and outdoor dining.

    The build of the Gunboat 48 is a vacuum-bagged, oven-cured monocoque hull epoxy foam sandwich and Nomex aramid honeycomb with carbon fiber inner skins and Kevlar outer skins for impact resistance and a foam sandwich deck utilizing epoxy, biaxial with unidirectional glass and Kevlar plus carbon fiber, daggerboards, lifting rudders, stringers, ring frames, and crossbeam. Even the Edson custom steering wheel is carbon fibre.

    What does all this technology give you? A tacking angle of around 100 degrees going to windward and a boat speed of between 7.5 to 9 knots. Head off the wind and you will sail close to wind speed with the right sails up (gennaker, code 0 or jib), tacking downwind again at 90-100 degrees for the best VMG (velocity to waypoint). When the 48 hits 12 knots, she really starts to fly. In the right conditions sailed properly, you should be seeing speeds in the 20s.

    To quote a TP52 owner who has sailed a 48. “Upwind, we sailed at 7.5-9 knots in the big seas. The ride was comfortable and dry even though Cam Lewis and I did get some spray in the trimming cockpit in front of the front salon doors. Downwind we saw 19 knots on our practice day with the chute up. In the long distance race, we saw 21 knots on our only spinnaker leg but then hit 24 knots on a Code 0 reach on the downwind leg towards the finish of that race.” But to put this boat into perspective this TP52 owner said “I can tell you for sure that a TP52 will kill a Gunboat 48 upwind in all conditions and that a Gunboat 48 will probably only come close to pacing the TP52 in over 10 knots reaching and downwind.”

    This is a fast catamaran cruising catamaran. PS the first Gunboat took 35,000 hours to build. The jpegs give the idea.
     

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  10. Rumars
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    Rumars Senior Member

    Oldmulti, while I agree with the above in principle, let's not forget it's 2020. Carving foam by CNC is commonplace, you just have to adjust your segment sizes to the machines bed size. As long as the design is available digitally and one is prepared to pay for the machining this method is fast and easy, just have the shaped foam delivered, ready to be glued to the plywood box. A thrifty person could even laminate the foam with polyester and only glue and tape it to the rest with epoxy.
    But, and this has to be said, foam is heavy and the finished article will probably weigh more then all ply construction.
     
  11. trip the light fandango
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    trip the light fandango Senior Member

    Low density cheap polyurethane foam could be used to create the form and then removed, adding watertight bulkheads as you go., while leaving some for an ice box... Profiles to fit stations can be cut to check your progress while shaping. Polyurethane is very delicate but a joy to work with I think. Having no access to the inside skin of the hull isn't ideal, cutting into the plywood and making water tight hatches means that re enforcing the hull with glass from the inside can be done well with out the fairing standard necessary on the outside.
    Foam is handy for floatation and as a crash box in the ends but it is better to have a bilge where you can monitor and drain any water ingress in the foam at least.
     
    Last edited: Sep 10, 2020
  12. oldmulti
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    oldmulti Senior Member

    The Exploder 25 trimaran was designed by Richard Partyckiego. The tri is 25 x 22.9 foot with a claimed built weight of 1000 lbs but the only one built and was weighed, loaded for racing, at 1550 lbs. The 40 foot tilting rotating carbon fibre mast carries a 345 square foot main, 65 square foot jib, 160 square foot genoa, a 345 square foot code 0 and a 540 square foot gennaker. The tri’s speed is increased by wide beam, alloy angled foils in the floats and a mast that tilts from side to side with hydraulic rams on the shrouds. The mast tilt in effect “reduces” displacement of up to 220 lbs (less sail pressure pushing down) and simultaneously allows the sails to be more efficient. The Exploder 25 has relatively large foil areas to improve efficiency and rudders on the floats. The floats have 200% buoyancy.

    As you have already noticed this tri is nearly square. The lateral stability is high allowing the tri to power up and go fast, the down side is that the lateral stability is so high which may over power its fore aft stability. In short, you can pitchpole the tri over the bow. Twiggy a 32 foot Crowther tri was nearly square as well and needed a Mark 2/3 version with much fuller bows to minimise the tripping tendency and fully use its lateral sail power.

    The Exploder 25 is designed to act in 3 modes: as a “beach tri” with the crew of 3 - 4 people on trapezes, a coastal tri with 3 crew for 2 to 3 day maximum duration or a long distance ocean racer with 2 crew for a maximum of 2 weeks in moderate conditions and seas. That is, no North Atlantic crossings.

    There is a minimal cabin with one fixed berth, two seats and a navigation/cooking table.

    The Exploder 25 is trailable which brings a second advantage. With a little work you can self-right the tri if it is capsized so 2 crew away from the shore could continue sailing. This would not be an easy option but may be a life saver. The Ex Capsize recovery jpeg gives the idea of the recovery technique.

    The hull, floats and beams are constructed entirely of carbon-composite sandwich epoxy with structural foam and honeycomb Nomex cores. The beams have unidirectional top and bottom flanges. The bows of the hulls have two transverse bulkheads creating water tight zones. The boat had production moulds etc but the cost of producing a carbon tri in 2005 was prohibitive (about $US 120,000). A lower spec e-glass was contemplated but the weight gain was over 10% and that was still going to be too expensive for owners.

    Gwenc'hlan Caterine the owner of the Exploder 25 said it started life as an Exploder 23 and after testing gained a two feet extension on the stern. He said “I can confirm it is really an adrenaline machine with impressive top speed and accelerations. And at the same time very seaworthy.” He intended to participate in the 2006 Route de Rhum (cannot find entry). He claims the tri with a 4 person crew reached 24 to 26 knots in coastal racing. The TCF is 1.297 for the Exploder 25. For comparison the TCF for a F-25C (carbon fibre 25) is 1.161. The Exploder 25 is seriously fast for its size that would have to be treated carefully as its wide beam would generate a lot of power. The jpegs give the idea.
     

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  13. Slingshot
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    Slingshot Junior Member

    The funny thing is I look at the Livewire 28 and think scaled up to 18 meters with a small cabin house would be a perfect cruising boat. Take on some French culture and have a speedo as the main crew uniform and all is good :)
     
  14. catsketcher
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    catsketcher Senior Member

    I must admit I find boats like Gunboats boring. It is easy to get fast if you throw huge amounts of money at something. Interesting design for me comes from balancing conflicting design requirements - such as room, economy and speed. Putting 35 000 hours and millions of dollars into a boat is something most mortals cannot contemplate. I can't see any real design lessons in way out boats, it is easy to make something good at only one thing, or to spend money. Designing a classic, like an S and S 34 or Piver Lodestar or Irens 1986 ORMA trimaran requires a constant juggle of competing priorities that can push design philosophy forward. Gunboats are 10 times as expensive as a mid sized cruising cat for twice the speed - it seems like a bad deal for someone like me.
     
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  15. rob denney
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    rob denney Senior Member

    I could not agree more.
     
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