Multihull Structure Thoughts

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

  1. oldmulti
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    oldmulti Senior Member

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  2. oldmulti
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    oldmulti Senior Member

  3. Russell Brown
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    Russell Brown Senior Member

    I'll download the article. Thanks.
    Stealth Mission looks like a serious boat. Reminds me of Mama Tried, an 8.5 that came from NZ and won the R2AK. It's in SF bay now.
    Anyone know about that one?
     
  4. oldmulti
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    oldmulti Senior Member

    David Wilkins of WILKINS YACHT DESIGN has a small fast fun tri that is simple to build. “Triumph” is 15.25 x 10.2 foot with a weight of 315 lbs without crew. The cat rigged mainsail area is 98 square foot on a 20.3 foot mast. One sensible thought is the boomless mainsail to save your head from being knocked. The length to beam on the main hull is 11.4 to 1. The floats have 640 lbs buoyancy. The draft over the kickup centre board is 3 foot. The hulls are flat bottom dory shapes.

    The accommodation is for one in hopefully a comfortable seat. The steering is foot pedals leaving hands to do rope controls etc.

    The build is plywood with timber stringers. The plywood could be as light as 4 mm but more likely to be 6 mm. The cross arms are timber with waterstays.

    A nice simple design. The jpegs are below.

    Russell, Mama Tried is a trimaran designed by John Tetzlaff (JT) and Tim Clissold and built by JT for his own use in 2010. It was purchased by Pete Melvin (of Morrelli & Melvin fame) in 2012, while in NZ working for Emirates Team New Zealand to use as a fun sailor for his family for his days off. He negotiated a deal that included JT building some new floats that he designed to increase the volume of the floats and also experiment with some hull shape concepts that he was thinking about. He shipped Mama Tried back to the USA in 2014. The boat is demountable and easily fits into a 40’ container. He won the Esanda race at one point before it was sold for further racing adventures. Some jpegs below. Hope this helps.

    A website with background info. https://www.sailingscuttlebutt.com/2014/05/04/pete-melvin-mama-tried-ruled-newport-ensenada-race/

    Russell, just discovered you have been aware of the general history of Mama Tied for 5 years. If anyone has specific build information on Mama Tried could they please help Russell.
     

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    Last edited: Apr 16, 2022
  5. oldmulti
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    oldmulti Senior Member

    A short story about an interesting experiment with a question of why. The claim is the this is a Hobie 16 catamaran with a biplane rig. The cat is 18 x 8 foot with a 28 foot carbon fibre mast placed on each hull. Each mainsail has a wishbone boom on it. Each fat head mainsail is about 120 square foot.

    Now the problems start. The claim is the hulls are Hobie 16 except the hulls are 18 foot long, look symmetrical, round bilge, have daggerboards and are claimed to be built of foam carbon fibre. Maybe it started on standard Hobie 16 hulls then the hulls were upgraded to maybe a Hobie 18 hull configuration. Next, this reminds me of an Australian guy in about 2000 wanted to build a Kurt Hughes 16 foot tri and spoke to a supplier of product who persuaded him to add some carbon fibre, he eventually had the entire tri built from carbon fibre. Cost a fortune and saved maybe 40 lbs in weight. Going on a diet would have achieved the same thing.

    These types of fun boats have no specific racing class that require a minimum weight. Accept they will perform well, but they do not need exotic materials to achieve good sailing performance. If you are racing A-Class catamaran at a peak level then use carbon fibre where EG 18 lbs carbon masts instead of 25 lbs carbon masts means the difference between winning and losing etc. The 18 foot biplane cat described here has several people crewing on it in each jpeg and the weight saving of carbon fibre hulls etc become pretty pointless.

    Many people have a problem then design a detailed solution. Often a deep analysis of a problem will lead to a simple fast solution. EG You want to sail across the Atlantic, why? Is it to experience the sea, challenge your skills, prove to you can build your own boat, think this is what your family wants etc. Depending on the answer you may spend 6 years building a boat or you may walk down to a Spanish sailing club looking for a crewing position on a Transatlantic run. Analyze what is the real problem then act on a solution.

    The description of the biplane cats performance is "fast, fun and stable". Probably says it all. The jpegs give the idea. The final 2 jpegs are of a Hughes 16 foot trimaran.
     

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  6. oldmulti
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    oldmulti Senior Member

    For those interested in Tortured ply construction please remember to read Pages 41 and 42 of Multihull Structure Thoughts where I have done the most research on various boats.

    Also the 28 foot Woods Salish R2AK cat had an interesting comment made by Richard Woods on a blog site "The Salish hulls are made from 6mm ply (4mm topsides optional)." Good quality ply only please. The jpeg and PDF is of Salish.
     

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    Last edited: Apr 16, 2022
  7. oldmulti
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    oldmulti Senior Member

    After investigating Mama Tried the 28 foot JT/Clissold 8.5 trimaran there was a variety of opinions on the floats. I do not know the original float shape but Pete Melvin, when he purchased Mama Tried, asked JT to build new floats to an “experimental” shape he wished to explore. The upgraded float shape caused quite a bit of comment.

    The Melvin floats had more volume, were longer, had a flatter bottom and run. A sailor of Mama Tied said “The amas of their Custom 8.5m trimaran were designed to mirror the hull shape of MOD 70 trimarans… The amas are designed to plane as a single hull, the float”. Pete Melvin replied ”I don’t agree with the description of the float shapes. They are definitely not “mirrors” of MOD70 floats and the shape is very different and unique to Mama Tried. They are an all-new family of trimaran float shape I tried at my own risk that seems to work well in practice.” Another multihull designer commented on Mama Tied float shape “those amas look to me like they were designed for tradewind conditions, not 4 knots true wind speed which happens in the San Juans in the summer. The fat waterplane down low is draggy in light wind.”

    Let’s look at a little history on float shape. Initially designers went for minimum drag shapes which had fairly full sections amidship and a very low drag tail shape as floats would have depressed sterns. The shape was shorter than the main hull, full in the centre and low drag fine shapes at either end, also the floats were low buoyancy EG float buoyancy below the displacement of the tri. EG’s are the JSYD Brittany tri and the F39 tri float shape both designed before 2000.

    Progressively as racing tris became more powerful float buoyancy increased to 150% or more of the displacement of the trimaran. The float lengths started to match the main hull length, then floats became fuller at the ends to gain the buoyancy required. The floats still had rounded bottoms and V shaped sterns to minimise wetted surface in lighter airs. Eventually OMRA 60 tris started to treat a float as a catamaran hull as they developed sailing techniques to fly the main hull for extended periods. These float hulls tended to have a flatter lower hull sections as the 3000 square foot rigs could drive an OMRA 60 tri at 2 or more times windspeed. “Light winds” are relative. EG’s OMRA 60 tris designed after 2000.

    Performance cruising trimarans started to use the fuller shapes to improve performance and safety as exemplified by EG Raw 30, Neel 51, Pulse 600 sports tri and Eric Hensval 18 foot Sardine Run. Eric worked for VPLP and designed some of the OMRA 60 tri's. That 18 foot home build tri has some very advanced shapes for a dory hull.

    Then we come to the Rapido tris designed by Morelli and Melvin. The float shape Pete Melvin did on Mama Tried was done in 2012 prior to the full designs of the Rapido trimarans. The shape suits a high performance trimaran which had some other design considerations. One: the Rapido tris fold, two: the floats need to have a minimum profile laterally and vertically to suit the folded profile, three: by the time the Rapido float shape was designed it was almost standard to have full ends on floats, four: Pete Melvin was willing to push the edges to find out what could be achieved with a different float shape in a practical “cheap” tri like Mama Tried.

    The jpegs give an idea of the transition over time. The Sodebo, Gitana floats where being sold to put more aggressive fuller floats on the tri. The last 2 jpegs are Mama Tried floats notice the flat stern shape.
     

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  8. oldmulti
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    oldmulti Senior Member

    Today is about the design and building of the International 14 high-performance two-person, two-trapeze monohull dingy that is 14 x 6 foot (including any hiking racks). It is a development class so there are few rules beyond the basic hull dimensions and a minimum weight of 155 lbs fully rigged for sailing. The rig has a 25.2 foot mast and 200 square foot of sail area (unlimited spinnaker area). The prodder can be up to 9 foot long to support the unlimited spinnaker area. Another rule requires a minimum hull beam of 3.2 foot. The draft of the foils is about 6 foot. The rudder often has a T foil on a rear extension to help steering control.

    I-14 boats are capable of sailing in rough open water, but are optimized for protected waters. For racing, they are rigged for the expected wind conditions, usually with a maximum wind speed of 20-30 knots. With the 2 crew on trapezes these boats require real skill to obtain the best performance. The best total crew weight is between 350 to 380 lbs.

    Paul Bieker has designed and built composite I-14s using autoclaved prepreg carbon fibre with Nomex honeycomb cores in hull moulds that are post cured in an oven. These boats are stiff, strong, meet minimum weight and are expensive. Paul wanted to make the I-14 class more accessible to more people and has designed the Bieker B6. The B6 is a less-expensive ambient-cured, vacuum-bagged wet laminate with a foam core. “A well-built vacuum bag part is about 60-70% of the strength of a prepreg construction.” But in I-14 racing these small skiffs are subject to intense and rapidly changing loads imposed by wind, water and the swiftly moving crew of two, “the prepreg boats are a little lighter and a little stiffer, but both types of boats can be competitive.”

    Bieker’s B6 calls for a hand-built, vacuum bagged wet laminate, and specifies standard-modulus, mid-grade carbon fiber primarily in 200 gsm 0/90° plain-weave and 300 gsm unidirectional fabric, with knitted double-bias cloth for use as additional reinforcement patches in the layup. The resin is Gougeon Pro-Set 125/229 epoxy is the laminating resin. The B6 design is as close as possible to the minimum surface area allowable under the I-14 class rules, to reduce both the laminate’s area and its weight. EG there is no foredeck on the B6 which reduces the surface area. There is also an option for an E-glass version that can be vacuum bagged.

    Bieker thinks the B6 molds would also work well for resin infusion, but says he hesitates to infuse something so light. “The skins are so thin — typically the outside skin is on the order of 400 gsm of material, and significant areas of the inside skin only about 200 gsm,” he explains, adding that the core (light cores have open pores that soak resins) for reliable resin infusion can be pretty heavy for such a lightweight layup. Vacuum bagging is preferred.

    The B6 mast is a high-modulus prepreg carbon tube 7.7m long, with an outside diameter (OD) that tapers from 74 mm at its root to 42 mm it its tip. The prepreg features HR40 carbon fiber, “high-modulus HR40 carbon fiber produces a more rapidly responding mast and less energy loss as wind gusts blow through.” The masts are made on a tapered mandrel that has a sheet of unidirectional (UD) prepreg that combines HR40 carbon fiber (640 ksi tensile strength, 54 msi tensile modulus) with a semi-toughened, 250-300°F (121-149°C) cure epoxy matrix rolled around the mandrel. Areas of point loading are reinforced with a prepreg plain weave 33 msi carbon fiber in HexPly F515, 250°F-cure epoxy. The outside of the mast is a Hexcel prepreg of 7781 woven E-glass that is wrapped around the mast. The finished laminate is then wrapped with shrink tape to apply high pressure during cure. The amount of tape and tension applied is controlled to result in 60-80 psi when heat is applied. Professional masts are preferred for sailing consistency.

    The standing rigging for the mast are commercial pultruded carbon rods with end connections created by Henderson Boat Co., using braided SK-99 Dyneema.

    These are serious high speed dinghy’s for highly competitive racing. The build technology can vary for the hull and still be competitive but anything above deck level should be purchased from professionals to achieve competitive results. The jpegs give the idea.
     

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  9. Russell Brown
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    Russell Brown Senior Member

    I built about 130 sets of foils for Bieker I-14's, about half of those had hydrofoil rudders. It drove me crazy in the end, but starting a kit boat company wasn't any better.
     

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  10. oldmulti
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    oldmulti Senior Member

    In 2009 a prototype Competition Cat 30 was designed by Thadeaus Bierza, built by Wingfox and launched. It was refined and optimized by 2011. The 30 is 30 x 17 foot over the hulls but is 39.5 x 25.5 foot over hiking racks and bow prodder. The 50 foot carbon fibre wing mast carries a 570 square foot mainsail, a jib of 270 square foot and a Gennaker of 872 square foot. The weight of the 2011 version is 1450 lbs fully rigged. The Cat 30 is designed to carry 3 crew with a total weight of about 550 lbs. The length to beam of the hulls is about 16 to 1. The draft is (guess) about 6 foot over the boards.

    The construction of the cat is Carbon-Airex-epoxy sandwich in a vacuum process. Wingfox manufacture carbon masts as their main business so the wing mast is carbon fibre.

    This cat can be disassembled and is transportable in a container. The 50 foot wing mast is a 2 part structure with an insert at the join point (jpeg attached).

    Performance of this cat is very good, wind speed or better up to about 15 knots, peak speeds in the 20 plus knot region. But although the design is good, WingFoX with SAY was planning to establish a One Design Class the concept was overtaken by the GC 32 foiling cats which were just being designed and about to be manufactured.

    A very good high performance sport catamaran. The jpegs tell the story.
     

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  11. revintage
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    revintage Senior Member

  12. oldmulti
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    oldmulti Senior Member

    Revintage. The site did not have a working link to the 30 ft cat mast but from the information below I would guess it is the S carbon wing of 100 x 277 mm but I cannot tell you the wall thickness. The righting moment of a powered up Cat 30 with people on the hiking racks is similar to the righting moment of a powered up F22 with crew on the floats. The F 22 carbon fibre wing mast section (102 x 185 mm with 3.5 mm walls) is shown in the yellow jpeg. The F22 section has a web cross inside the mast, The Wingfox S section has thickened walls for additional strength. The jpegs are of the Wingfox sections, specifications and the F 22 section. The insert length would be a guess but rough scaling says about 900 mm long. Hope this helps.
     

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  13. revintage
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    revintage Senior Member

    Thanks! Seems like we have different printouts of Wingfox sections, the one I guessed for is at down right on your(older?) copy.
    900 mm seems like a good guesstimate. Used a 600mm insert when I joined and shortened a broken Flying Phantom, Adam Hall mast to 8m.

    image0.jpeg
     
  14. oldmulti
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    oldmulti Senior Member

    The Free Flow 8.5 is designed by Stanton yacht design. The aim was to create an Australian catamaran that would fit the NZ 8.5 rules. The Free Flow is 27.9 x 17.7 foot with a 2000 lbs “displacement”. The 37.7 foot fixed carbon fibre lightweight mast carries a 355 square foot mainsail, a 183 square foot jib, a 377 square foot genoa and a 807 square foot masthead screecher. The hull length to beam is about 14 to1 with a hull draft of 1 foot and a foil draft of 5.3 foot. The cat is designed to be transportable on a trailer or in a container.

    The fixed carbon mast was done to minimise weight, minimise maintenance and minimise rating penalties under OMR racing. The fixed mast also allows narrower sheeting angles. The carbon fibre prodder was designed to allow tighter forestay tensions for better windward performance.

    The accommodation is minimal with 2 single berths, camp galley and portapotti. Cockpits are 10 foot long for the maximum number of crew to sit to windward for maximum stability.

    The construction is infused multi axial glass over foam build using epoxy or vinylester in female hull molds preferably to minimise weight. The aluminium or optional carbon fibre beams fit into moulded recesses for speed of assembly from a trailer. The tramps are mainly preset and then are tensioned when the cat is assembled.

    The Free Flow 8.5 is claimed to be capable of 300 mile days according to the designer. This cat will be fast but like all 8.5 cats they need to be driven to win races which means flying hulls in heavier weather. Fun, but doing it to achieve 300 miles in 24 hours is a little tiring.

    The limited jpegs give the idea. One was being built in 2011 but no reports of a complete boat.
     

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  15. Lucifer8.5
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    Lucifer8.5 New Member

    A bit more on the Stealth Mission & Momma Tried story... there were three of them built. Stealth was the first, then Lucifer and lastly MT. Each had variations, rig, float designs, beam placement and more.
    IMG_5877.jpeg
    This is one of the few times Stealth and Lucifer were on the same racetrack together.
    IMG_2486.JPG
    Lucifer got a bit crashed but is now well on the road to recovery and will be racing in our winter series (NZ).
    IMG_5743.jpeg IMG_6589.jpeg IMG_6858.jpeg
    The 4mm stressed ply floats were as badly damaged as the main hull but surprised us how well they took the impacts. The ensuing puncture wounds and were reasonably easy to repair.
     
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