Multihull Structure Thoughts

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

  1. ALL AT SEA
    Joined: Nov 2013
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    ALL AT SEA Junior Member

    Have only made it through 2 pages so far, great information... one design I love of the Gougeon 32. 32' 1100lb (500kg) plywood trailerable bridgedeck cat.
     
  2. oldmulti
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    oldmulti Senior Member

    The TRISTAR 24 flush deck design gives you a spacious interior and deck that makes for easy sail handling. TRI-STAR 24 is 24 x 17 foot weighs 2450 lbs and carries 1100lbs with 386 foot of sail.. TRI-STAR 24s' flush deck allows a double berth in each wing. Head room in the main hull is 5 '5" with the hatch dosed and is 6'4" with the "Pop Top" hatch. Tri-Star 24 has the option of being trailerable at 8' 6" width. For trailering the ama's fold up on to the deck. Trailering beam is 16' 5" and the non-trailerable beam 17', the hinging makes the two inch difference per side. Ed Horstman draws designs for both wooden and foam sandwich construction. Double diagonal, 2 layers of 3 mm plywood strips about 450 mm wide are laid over a framework of 18 x 25 mm stringers at 225 mm centrelines, gunnel 50 x 18 mm, keelson, stem, transom and bulkheads of 9 mm ply, all of which eventually became part of the boat. There was not a lot of spiling (planning matched edges to shape) and the layup was quite fast. The first layer is nailed to the stringers but the second layer has to be stapled to the first. Ed Horstman recommended bronze staples which could be left in place. It is important not to allow the staples to penetrate right through as this breaks away the inner surface veneer of the ply skin. The solution is to staple through a strip of webbing, this also assists in removing the staples as the webbing is pulled off. It takes thousands of staples. The deck has upper and lower layers of plywood are separated by timber deckbeams with dense foam infilling the spaces between beams but not glued to the ply above or below.

    According to owners the boat is responsive, tacks easily, steers well and in 19 knots winds virtually self steers at 7-8 knots on the wind. The performance reaching and down wind was 10 to 13 knots. A fun fast mini cruiser.
    Ed Horstman Designs http://www.edhorstmanmultihulldesigns.com/triplans/index.php
     

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  3. oldmulti
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    oldmulti Senior Member

    An interesting designer is Jerome Delaunay. He has mainly designed scow monohulls for river and bay sailing. He did a Scow cat 3D study which is 15.4 x 8 foot displacing 1350 lbs with 10:1 hulls. Jerome did not complete the plans as he though a mono would have more room. But the Scowcat looked interesting even with those blunt bows.

    Jerome also did a full design of a good little plywood trimaran that is trailable. It has Farrier type folding built in ply and uses water stays. The Triops 620 is 20 x 16.4 foot that folds to 7 foot. The tri weighs 1000 lbs and displaces 1700 lbs. It uses a hobie 21 rig of 250 sq foot of sail. It requires 27 x 6mm plywood panels that are taped together with a minimal of stringers. Plywood bulkheads are every 600 mm. There is a T foil option on floats for those who have a need for speed.

    Finally his 420 scow monohull design is free to download. His site is Plywood sailboats plans, pocket cruisers sailboat plan, plywood epoxy boat, DIY boats, junk sail http://www.nautline.com/sailboat_plywood_plans.php
     

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    Last edited: Sep 22, 2019
  4. Slingshot
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    Slingshot Junior Member

    Old multi do you by chance know the laminate schedule of any gunboats. I think the first 2 62’ were glass hulls and then they moved to carbon later.

    Cheers
     
  5. oldmulti
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    oldmulti Senior Member

    Slingshot. No, I do not know a Gunboat laminate schedule beyond "Built by Gunboat in La Grande-Motte, France, operating with the experience and mentality of a race boat campaign, focused on strength and weight; – Top-quality materials that are best suited for every application of the build: Epoxy resin, carbon, corecell foam, and nomex honeycomb to name a few;
    – Processes that match each given material and location it is implemented; such as thermoforming the core, infusing the hull, and the application of vacuum wetpreg for some components and full prepreg for the interior bulkheads;
    – Assembly in our state-of-the-art, temperature-controlled factory, using the very best adhesives and resins from the top suppliers; maintaining a clean, dust-free yard with European safety and environmental standards" to quote the web site.
    The photo's on the Gunboat 68 site clearly indicate a pretty standard carbon foam/nomex structure build. GUNBOAT 68 Internal Structure - Inner Strength | Gunboat https://www.gunboat.com/gunboat68-internalstructure/
    ORMA tri of 60 feet have 1.5 mm carbon fibre skins on 20 to 25 mm cores. The details of the fabric weights, types, direction of layout etc would be the real thing to understand. The closest thing I will be able to tell you, is some detail of 50 footers in a few days.
     
  6. oldmulti
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    oldmulti Senior Member

    Catkadec is a partially conventional small catamaran from France 14.5 x 8 foot weighing 1100 lbs with a biplane rig of 190 square foot (4,46m x 2,50m; 2 x 8.85m², displacement unloaded +/- 500kg, draft 0,15/0,75m). Catkadec is for people with a cruising ambitions but short on money. Simple, fast to build, junty in style and interesting to sail on bays or rivers. It has 7 : 1 hull ratio to carry the weight as this boat will reasonable in performance but not fast. It has a simple rig that can be home made. The wood mast is 14.5 foot above deck 90 mm at base and 50 mm at the tip with 95 square foot of junk sail per rig. The masts could probably 90 x 3 mm aluminium tubes. The majority of the boat is 6 mm plywood with 4.8 mm ply on hull sides. The crossbeams are 150 x 50 mm on transom, cabin and forward bulkheads. Don’t overload this boat as the underwing clearance is only 200 mm. A bit of fun. plan de catamaran http://www.boat-et-koad.com/plan-de-mulitcoques.php
     

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  7. oldmulti
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    oldmulti Senior Member

    Norman Cross is a trimaran designer who was in in aerospace then designed a series of plywood tri’s of which thousands have been built in the 70 – 90’s. Some of his tri’s were advanced and fast for there time. His cruising boats were big and comfortable and very well liked. There are some people today who would build a Cross tri if plans were available. To give an idea of his faster designs I will show you 2 boats The 32 R and 36 R. Both were racing boats which featured Cross’s special fin keel approach which gave a lot of his boat’s good windward performance. Attached is a PDF explaining the theory of the fin keel and how it is integrated with a main hull. The 32 R displaces 5500 lbs is built mainly from 6 mm ply and double moulded 3 mm ply for 6 mm thick hulls. The 36 R displaces 8000 lbs is built mainly from 9 mm ply and has 3 layers of 3 mm ply double moulded for 9 mm thick hulls. Crossfire was Cross’s personal 32 R tri and was very successful race boat in California. It was built after the Newport Esanda race changed the rules to demand 4 crew on a boat. Cross sailing a Cross 24 foot tri had won the previous year with 3 people. Mono people got mean in those days when cheap small ply tri’s embarrassed them. Sorry but your going to have open PDF’s for the study plans etc.
     

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  8. oldmulti
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    oldmulti Senior Member

    The following PDF is the hull lines and table of offsets for a 30 foot multichine main hull and floats of a trimaran. The boat was designed by Leonard Sussman, a man ho designed many light fast tris and did several production tri’s. The design was done for solid glass hulls so could be adapted for ply or foam glass. If there is any further interest I can add to the design details but a lot is given in page 12, comment number 179. TTLF asked for the lines sorry I took so long to deliver the lines.
     

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  9. oldmulti
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    oldmulti Senior Member

    Norm Cross developed many hard chine trimaran designs that were simpler to build than the round bilge models. In the 30 to 40 foot range they ranged from spacious cruisers such as the 10.5 meter, a moderate cruiser like the 37 or an all out racer like the 39 R hard chine racer. The 39 R has simple clean lines but one owner in cruising mode said it was not fast unless it was driven hard. The 39 R appeared to have a “hump” speed that needed to be pushed through. The 10.5 meter proved to be a popular design because of the accommodation but it would only be a reasonable performer due to its displacement for its length and its wide mainhull waterline beam for its length. The forward table would be interesting in a seaway. There were several 37’ built but most were extended to 40 plus feet to provide sugar scoops in the stern that helped their motion. The ketch rig was also upgraded to sloops on several. The 30 foot design was a popular model and was done as an alternative to Piver’s 30 footer. There is also a partial construction plan of the 30. PS this is only part of Cross's design range, it was very large from 18 footers to 80 footers.
     

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  10. oldmulti
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    oldmulti Senior Member

    Some Cross tri’s became famous but the boat that had the greatest impact was a 52 x 32 foot tri that displaced about 14,000 lbs and carried 1125 sq foot of sail. Th tri was named Crusader and sailed by Mike Kane, the former owner of Spirt of America a 55 foot Crowther tri. The boat sailed very well winning the Newport Esanda race in 1980 and the 1980 single handed Transpac race. After 13 elapsed time records Crusader was eventually “lost’ in 1983 when attempting a sailing record from New York to San Francisco around Cape Horn. The rig fell down due to a $10 faulty shackle, then the Navy vessel sent to “help” rammed the tri. I knew a guy who helped build the boat and he said the timber quality used through out was first class, there were no timber faults in the entire boat. The main hull was “double diagonal” 4 layers of 3 mm WRC with douglas fir stringers and 9 mm ply bulkheads. The floats were 2 layers of 3 mm WRC plus 3 mm of meranti. All external surfaces were covered with 200 gsm glass. The main cross arm was a box beam of 220 mm wide 610 mm deep with a top and bottom flange of 190 x 115 mm laminated Oregon. The rear beam was a box beam of 220 mm wide 510 mm deep with a top and bottom flange of 190 x 115 mm laminated Oregon. This boat was strong. The PDF is a study print. A 78 x 40 foot tri carrying 2350 square foot of sail was a design development of Crusader but I do not know if it was built. The 78 footer had 3 cross beams each about 325 x 600 mm box structure with 285 mm x 115 mm top and bottom flanges. As the boat’s design probably was not finalised assume the beams structure to be an initial guess. The PDF is a study print.
     

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  11. Slingshot
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    Slingshot Junior Member

    I have been following a thread over on SA regarding the new GB 68. This quote is taken from a GB employee
    “ds on the size and purpose of the boat, even in CE you get different design categories that drive structural engineering. I can tell you that our size of boats, built to CE, have to have 1200g/sm skins (that is 1.2mm) on the outside skin. I would never want to go under 1000g for real protection for a 'big' cruising boat. If your buddy has 300g skins, that will hold the boat together, but impact or dock rash strength is very little, so he better baby that boat as much as possible, because: **** happens and that is why CE (Really, ISO Structural Cat A) have these rulebooks, written on top of the graves of plenty of people who kept pushing the limits.”

    I believe in the same thread a former GB employee discussed how HH catamarans does the same 1200g outer skin to comply with CE. HH then removes 400g eglass layer on the out side leaving 800g carbon outer skin.
     
  12. oldmulti
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    oldmulti Senior Member

    Thanks for your valuable input. The Gunboat 68 displaces between 40,000 and 50,000 lbs and I will accept that it has 1200 gsm presumably carbon fibre skins. Orange 2 the 120 foot racing cat that displaces 67,000 lbs has many layers of high tensile strength (681,677 psi) carbon fibre skins that total 800 gsm. But there is a very big difference between “normal” carbon fibre and high tensile strength carbon fibre (as much as 40% in strength terms). For example a 52 foot cruising cat displacing 30,000 lbs will have 1125 gsm Eglass triax 25 mm foam (corecell) 751 triax on the inside in its topsides. The actual hull bottoms of this 52 foot cat are similar in weight glass but are quadax glass. All of the above boats are built using epoxy which again can come in normal and high strength versions. The logic of what the GB employee is saying is correct, you can go much lighter to handle the global strength requirement of a hull structure (I doubt 300 gsm but I get the idea), but the knock resistance is the real issue with a cruising boat. As Catketcher said he thinks 600 gsm is the minimum glass layer over WRC for knock resistance in 30 to 40 foot cat’s even though some have (over 20 years old) been built with 330 gsm e glass skins over foam on the topsides. Once a cat is over 50 feet and above 25,000 lbs displacement then 1000 gsm e glass sounds good for a cruiser. If you need light weight or are moving up in displacement then you should move to higher strength materials. BUT it becomes very difficult to design light, high displacement, high speed multihull structures unless you really understand what you are designing for, can test the materials and the panel strengths of what you are building. Not all manufacturers material performance claims can be meet in the real world. Therefore, in bigger multihulls it becomes harder to just say 1000 gsm skins, you really need to understand what the fabrics are, their layout and the resin type, brand etc and the core material it is being placed on. I liked the comment about HH cats being built with 400 gsm E glass and 800 gsm carbon fibre to meet CE rules then fairing off the 400 gsm e glass.
     
  13. oldmulti
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    oldmulti Senior Member

    Aikane X5 was a 62 x 31 foot racing cat that weighed 10,000 lbs and displaced 14,000 lbs. It carried 2000 sq foot of sail. It was a CSK design that successfully did transpac’s etc. It held the record at 6 days 22 hours averaging over 14 knots. Finally it was converted to a charter yacht and was wrecked in a Hawaiian storm. The interesting part of this cat was its low tech build and its asymmetric hulls. It’s low tech build was with cold moulded plywood hulls (about 10 mm thick) on timber stringers and frames with aluminium crossbeams initially. The crossbeams were converted to timber carbon fibre at the same stage as an 80 foot Randy Smyth designed wing mast rig was installed. After this X5 did most of its record setting. The asymmetric hulls were over 15:1 length to beam but Roy Seaman, (son of Warren Seaman of CSK) and helmsman on Aikane X5 when it broke the TransPac record was not a big fan of asymmetric hulls. His said that up to a certain speed they make sense. Aikane X5 was capable of speeds above 30 knots. Roy claims that at about 25 knots the boat would 'shudder'. The Randy Smyth designed rig was very powerful and wanted to push the boat faster than 30 knots, but the hulls, being asymmetric, wouldn't go through the water as efficiently as the rig needed. It was a planning issue...he said the hulls wanted to 'break out', but couldn't because they didn't plane at all, like a D-section hull would ala Tornado, Nacra, etc. Roy said asymmetric hulls are great for cruising, not having to worry about skegs, boards, etc and having a very shallow draft. Although, you cannot load up an asymmetric hull as much as a D-section hull.
     

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  14. oldmulti
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    oldmulti Senior Member

    We will now do a series on Lock Crowther catamarans from 28 to 60 feet. There will be a 28 foot cruiser racer, 40 foot racer, 42 foot cruiser, 50 foot racer, 58 foot cruiser and 60 foot racer. All these boats were designed before 2000 but the glass layups, foams etc are still relevant. We will start with design 228 a 29 x 18 foot tube cat that weighed 2500 lbs and displaced 4500 lbs. The 39 foot fractional mast carried 520 square foot of sail. The hulls could be foam glass or strip plank WRC. The foam glass hulls and decks were 650 gsm triax outside 15 mm H80 pvc foam 550 gsm biax inside. The outside laminate was doubled below the waterline. Bulkheads and underwing were 650 gsm biax both sides of 15 mm foam. The cross beams were box sections with foam glass web faces and top and bottom unidirectional E glass flanges. The strip plank hull version was 550 gsm e glass biax inside and out of 12 mm WRC. 550 gsm e glass is used either side of 12 mm duracore in bulkheads and wingdeck. The same cross beam structure’s as in the foam glass boat. The whole boat is taped together with 550 gsm 200 mm wide tapes. The daggerboards and rudders were WRC shaped and glassed over with 550 gsm biax. One boat named Piglet was successful in racing in Queensland and made a fun short term cruiser.
     

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  15. garydierking
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    garydierking Senior Member

    I built the timber crossbeams that replaced the aluminium pipes on the X5. There was no carbon fibre in them just spruce timber and birch plywood. The hull asymmetry was so subtle that you wouldn't have noticed it. Rudy always claimed that they steered better in a seaway with asymmetric hulls.
     
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