Multihull Structure Thoughts

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

  1. oldmulti
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    oldmulti Senior Member

    The Seawings 24 tri was designed by Skip Johnson an aeronautical engineer in southern California in 1988. The tri is a 24 x 18 foot weighing 1,200 lbs and had a 33 foot rotating aluminum mast with 350 square foot of sail in a fractional sloop rig. The rigging is 1x19 stainless steel wire. The daggerboard is in the main hull and is deep and the rudder is hung on a skeg. The tri is demountable for transport but EG the floats weigh 200 lbs and are difficult to handle with 2 fit people.

    Skip wanted to produce the boat in foam/glass and only 4 boats were made from molds produced from a prototype. The hulls and decks are made from biaxial fiberglass (probably 1708 600 gsm outside) a 9 mm Divinycell core (probably a 400 gsm biax inside). The cross arms are unidirectional fiberglass and biaxial fabrics. The half cross arms are inserted into slots in the main and float hulls. To achieve a 1200 lbs weight, Skip would be using some very good structural design concepts from his aeronautical engineering background. The Seawings 24 molds were given away for free in 2010.

    The people who own these tris comment on the Seawing 24 excellent performance. One sailed from Los Angeles to Hilo Hawaii and returned in 1980, so there is some seagoing capability in the design. Two exist in California, one in the north west of USA and one in Israel. Skip Johnson unfortunately has passed away and plans are not available for any of his multihulls to my knowledge. Skip designed (and had built) 24, 29, 36, 38 and 42 foot trimarans and at least 1 catamaran. Owners of all sizes of his tris comment on their excellent sailing qualities.

    The jpegs show 2 Seawings 24 moored in California, some sailing jpegs, a 24 on a trailer in the Pacific North West and the build molds for the “production version” of the Seawings 24. If anyone has more information Seawings designs, it would be appreciated.
     

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  2. oldmulti
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    oldmulti Senior Member

    This is one man’s cheap and relatively quick way to get a trimaran, or so I thought until I found 2 other versions spread over 3 countries. First, find yourself a Soling monohull racing keel boat. A Soling is 26.9 x 6.2 foot weighing 2270 lbs with 1270 lbs of ballast. A Soling hull is solid glass and weighs about 850 lbs without rig or keel. The keel draws 4.25 foot. Keep the fractional rigged aluminium mast, 147 square foot mainsail and 105 square foot jib. Now find an old Tornado cat and use the hulls as floats.

    Now the fun begins. Each version of a Soling trimaran differs but I will stay with the Austrian cabin version. First cut out the cockpit area of the Soling then add a foam glass cabin. Then add 2 box aluminium cross beams about 19 foot long with water stays for additional strength. These beams slide through a larger aluminium box that is permanently fixed to the Soling hull. The mast has been reinforced with additional spreaders at the original forestay connection point to allow the carrying of a larger headsail on a bow sprit. There is no indication the keel was removed.

    I have raced against a “monohull” Soling and it is a fast boat, so I am willing to accept the Austrian original builders’ comments of a peak speed of 17 knots, the best average cruising speed was 12 knots but on a normal day the average speed is 6 knots. But his best comment on a Soling trimaran is: “the ride was normally fairly dry. But sometimes, during stormy weather with high waves, it was a good idea to wear a surf or diving suit. But riding in the Soling was very, very comfortable!”

    A second Soling trimaran was built in Australia (yellow tri in jpegs called Banana). This Soling had the original decks but had the keel removed and replaced by a centre board. The beams are just low-tech laminated oregon and gaboon ply with double-bias skin. There are no water stays. The floats are home built solid glass csm and woven rovings, all polyester, and weigh about 150 lbs each. This Soling trimaran weighs about 1800 lbs.

    The owner of Banana “my own Soling conversion throws a bit of water around above 12 knots, becoming a fire-hose at 15 knots. In winds above 25 knots, I can go to windward tacking about 100 degrees, footing at speeds of 9 to 10 knots. At speed the spray is blinding - she throws a bit of water around. She is easy and fun to sail.”

    The final Soling trimaran was being built in South Africa but the builder was contemplating using a Etchells rig and hull with the keel removed as the main hull. Fiberglass floats were being built.

    Finally, there are jpegs of a MacGregor 21 trailer sailor main hull with 16 foot fiberglass catamaran hulls as floats. This boat is an inshore cruiser and sails reasonably well with the ballast removed but it’s not fast.

    Anything is possible if you are determined to get a cheap boat but you have to accept some limitations. The above boats can all sail reasonably well but each has its own weaknesses, such as throwing a lot of water around at speed and not pointing as high as their original monohull versions do. But if you want cheap fun look at the jpegs.
     

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  3. oldmulti
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    oldmulti Senior Member

    The Typhoon trimaran was designed by Derek Kelsall as a main hull unit that could use your Tornado catamaran hulls as floats. The cross beams were also your choice. The overall design was intended to be 25 x 17.5 foot and weigh 600 lbs. The main hull unit was designed to weigh 272 lbs. As this design had many variations depending on who owned the tri displacements went from 1300 to 2000 lbs. The green hull Typhoon in the jpegs weighed 1200 lbs in full sailing mode prior to crew.

    The rig was meant to use a standard Tornado rig with a 29.75 foot (135 x 76 x 1.8 mm) carrying a 190 square foot mainsail, a 186 square foot genoa, 92 square foot jib and a 52 square foot small jib. Derek Kelsall said about the mast “This has always been a question mark on this design. When we started, we were well aware that had we designed a rig for a wide tri, we would have gone for a larger mast section. We decided to try the standard mast and we were surprised at how far we could push it. As far as I know no masts have folded. The wider stay base obviously helps.” But some builders widen the beam to 20 foot which required additional diamond spreaders on the mast to stiffen the rig. The rigging was originally 1 x19 stainless steel wire but many builders upgraded to Dyform rod rigging.

    The main hull is foam glass with minimal bulkheads inside and “support tubes” for the cross beams. Depending on the version it either had a centreboard or daggerboard in the main hull or some people maintained the centre boards in the Tornado hulls as lateral resistance. One builder installed a stiff deep carbon fibre daggerboard. A kick up ruder was on the stern of the main hull. The Tornado hulls ranged from the original 4 mm tortured ply versions to latter foam glass versions. The cross beams on some versions were 138 x 112 mm aluminum mast sections on edge while others have used 125 mm to 150 mm aluminum tubes. All versions I have seen have water stays for additional rigidity.

    The main hull had minimal comfort with 2 berths and not much else. Headroom on the standard version was 4.25 foot.

    A modified version with a modified Tornado mast, daggerboard and deep rudder goes upwind at about 11 knot speeds, pointing high. Other owners claim they have gotten “close” to 20 knots. The reports on performance vary according to the owner and version of the tri they are sailing. Some were “standard” and sailed quite well. Others were modified with wider beams, stronger rigs, bigger sails and deeper foils. Some tris worked very well indeed, other needed a lot of “tuning” including replacing a mast after 5 minutes of sailing due to an unstrengthened standard rig on a heavy 20 foot wide version.

    The jpegs are of several versions of the Typhoon. The first line drawings are of the standard version.
     

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  4. oldmulti
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    oldmulti Senior Member

    The following trimaran “Majando” was designed and built by a New Zealander Doug Barry-Martin. He may have been inspired by John Westall’s 40 x 28 foot Matamona trimaran. Majando is 40 x 31 foot that has folding cross beams to reduce the beam to 15 foot. The tri displaces 13,500 lbs. The 45 foot high lattice mast is made from three 60 mm outside galvanised tubes with short 25 mm tubes as “bulkheads”. The mast carries a 10 oz, 400 square foot mainsail, a 130 square foot self-tacking jib and a 260 square foot self-tacking outer jib. All standing rigging is 9 mm 1 x 19 galvanised wire. The main hull length to beam is 8.5 to 1. There are main and aft withdrawable centre boards that can be trimmed for self-steering. The under slung rudder has a trim ab arrangement for a wind vane.

    As you may have gathered this is an original design done by a creative mind. Majando left in 1975 on a 4,500 nautical mile return voyage from New Zealand to French Polynesia and the Cook Islands. The tri sailed well and could reach reasonable speeds on passages. Its peak speed was 18 knots with 14 knots more achievable. The tri can tack through 90 degrees. The motion is comfortable in normal conditions but in big seas the tri can pound and if the tri is moving fast some movements can be shape and jerky.

    The construction of Majando is plywood and timber with steel cross beams. The main hull has a 25 mm plywood bottom, chine panels and lower topsides are 12 mm ply and top sides are 9 mm ply. The decks are 9 mm ply. There are main bulkheads are placed every 6.5 foot. There are stringers and internal plywood furniture that provide additional stiffness. The floats are 9 mm plywood. There are galvanised steel frames in the main hull and floats at the cross beam connection points. Now we come to the folding cross arms and an education about the forces on a trimaran. The structural tube crossbeam halves worked well with no problems. The 30 mm stainless steel pins in the hinges worked well. Now the problem. There is 10 mm solid steel connecting plates attaching the cross beam hinges to the hull attachment points. One of these 10 mm steel plates split. Read the metal did not crack it tore. The 10 mm metal component did not fail at a weld. All the 10 mm steel plates were reinforced and gave no further problems.

    After Doug had his fun in French Polynesia, he sold the tri to design and built a monohull which he was sailing to South America but he had heart problems, passing away in 1985. Majando, the tri, was used as a charter and advertising tri in Nelson before being sold again. It was anchored and was blown onto rocks in a gale never to be sailed again.

    An original design with many good idea’s that would be possible to replicate today with some modifications to the rig and cross beams. The jpegs are of the drawings of Majando, 1 jpeg of the tri sailing, the cover of Doug’s book “Trimaran to Tahiti” (out of print may be available second hand) and the final jpegs are of the tri after hitting the rocks.
     

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  5. oldmulti
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    oldmulti Senior Member

    A story about a “production” trailable catamaran that only 2 cats were produced before a fire damaged the molds. The Little Barrier Express (LBE) is a John Brown design (it looks like a Malcom Tennant cat but Brown designed it as he produced Great Barrier Express 28 foot cats in Australia). The LBE is 20 x 8.25 foot that weighs 1,200 lbs as a shell but sailing weight is about 1,700 lbs. The mast is 25 foot high (weighs 65 lbs) and carries a fractional rig with 175 square foot of sail. The cat has low aspect ratio keels with a centre board that draws 3 foot and transom hung rudders fixed shallow rudders. The length to beam on the hulls is about 10 to 1. The underwing clearance is 1.15 foot.

    The accommodation is a double berth on the bridgedeck and a kids berths in each hull aft. There is room for a Portapotti and a fridge. Sitting headroom only. For a 20 footer it has good accommodation but a Jarcat 20 has more space. These boats are a few weeks at best, near shore types of cruisers.

    The performance of the LBE to quote the USA owner “I regularly do 6-8knots, in 12knots of wind, but can go faster with more wind or when I fly the big sails”. A test sail (the attached PDF) stated the builder had hit 14.3 knots in 20 to 25 knot winds under spinnaker. The test found the cat could do 6 knots in 10 knots of wind with 2 crew. The cat sails well upwind and is relatively dry.

    One LBE is still in Australia but the other ended up in the USA and is currently being used as a charter catamaran by “skint for life” (web name) and can carry 4 crew for $600 for 3 hours or $1000 for a 6 hour charter. This cat second hand, cost him less than a couple day’s charter fees. That is value for money.

    The structure of the cat is solid glass in all curved area’s and some form of coring in flat panel areas. I would think it would be coremat for low coat and building efficiency. The glass layup is hand laid biaxial fabrics with some CSM and a gelcoat surface. One of these boats could be built in 6 weeks from order to delivery.

    As Richard Woods said in smaller cruiser racing cats the thickness of the outer fiberglass skin on a foam sandwich hull is only slightly less than what is required for a solid glass skin. Result no need for the foam for very little weigh gain. Single solid glass skins make the cost of producing smaller multihulls cheaper.

    LBE is a good looking, genuinely trailable cat that can sail well. The jpegs give the idea. The PDF is a “sales” brochure and test report.
     

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  6. redreuben
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    redreuben redreuben

    Couple of points on the Little Barrier.
    I’ve got little respect for manufacturers who rip off their designers work. This guy and Tennant, Corsair and Farrier, Samsung and Apple etc etc.
    Construction; yes at this size you can lose the foam to coremat but you also lose the buoyancy. Of course $ wins every time.
     
  7. oldmulti
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    oldmulti Senior Member

    The Starter 800 catamaran is a home builder design with the assistance of Bosgraaf Yacht Design built in 1999. The Starter 800 is 26.25 x 16.4 foot with a designed weight 1700 lbs but had an actual built weight of 2300 lbs and a sailing displacement of 3100 lbs. The 41 foot fixed aluminium mast carries a 226 square foot mainsail, a 120 square foot jib and a 450 square foot genoa. The rudders are transom hung daggerboard type. There are also hull based daggerboards. My guess is the hull length to beam is about 12 to 1 judging by the jpegs. The hull shape is a deep V with a slightly rounded bottoms and fine ends. The cat can be broken down into 3 trailer loads for transport.

    The Starter 800 offers 2 bunks of 6.8 x 4 foot, a small galley + lockers in the port hull with a wc, hanging-locker and 2 bunks in the starboard hull. The headroom in the hulls is 5.6 foot. A cockpit-tent in three parts greatly enlarges the accommodation and covers the cabins and the bridge deck (11 x 7 foot).

    The hulls are built in plywood, timber stringers with ply timber frames. The hulls have an epoxy glass layer over. The deck and cabins are foam glass composite construction. The cross beams appear to be timber ply construction. The concept of plywood hulls and foam glass decks is very good. Many timber ply boats rot from fresh water leaks above the waterline not from leaks below the waterline. Having a composite deck structure reduces the chances of leaks.

    The Starter 800 has been used for cruising and local racing with the owner “satisfied” with its performance. The jpegs give the idea of the cat.
     

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  8. redreuben
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    redreuben redreuben

  9. oldmulti
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    oldmulti Senior Member

    McGowan Design did a tri recently. Laurie McGowan also co-designed the Evergreen 20 foot tube cat which has had good critical acclaim. The trimaran is a small racer/cruiser “Zip” which is 23 x 20 foot and can be disassembled to 10 foot for trailing. The cruising version of the tri weighs 1000 lbs with a displacement of 1400 lbs in the cruising version that has a non-rotating aluminium or carbon mast with a mainsail of 215 square foot, an 87 square foot jib and a genoa of 267 square foot. The racing version weighs 900 lbs with a displacement of 1300 lbs in the cruising version. The racing version has a rotating carbon fibre mast with a mainsail of 280 square foot, a 96 square foot jib and a genoa of 354 square foot.

    The floats are 145% of displacement (2000 lbs of buoyancy). The main hull has aft 2 small steps in the hull to probable promote planning and help reduce pitching. The cruising version has a single daggerboard with rudders on the floats. The racing version has additional C lifting foils in the floats. The 20 foot beam, float foils and 2 or 3 crew trapezing will provide a lot of upwind power, so this boat if built to the planned weight should perform very well if handled correctly. The racing Bruce Number is claimed to be 178, this is fast.

    The living space includes 4 berths: 2 singles (a settee and a bow berth) plus a double under the cockpit, a galley, and camping head (read bucket or portapotti).

    Construction is of epoxy/wood/foam core/biaxial glass and a little carbon fibre. The demountable (not folding) cross arms are bolted together at the centreline, and are socketed through the main hull side, creating a lighter, stronger and wider setup than with a folding system. These features reduce weight and increase strength in the cross arms. The cruiser version may be all-plywood and timber construction cover by a light glass cloth and epoxy covering.

    This tri could be a local racing weapon in the right hands. But this tri has a lot more lateral stability than fore and aft stability. You will need to understand after a screaming fine reach turning downwind will require some sail adjustments or you may find yourself cartwheeling in the wrong conditions.

    The jpegs give the idea. The web address is: Zip Tri https://mcgowanmarinedesign.com/Zip_Tri.html

    While you’re on the McGowan site have a look at Hull Speed document which gives an insite in the characteristics and speed capability of EG dinghies. The web site is https://mcgowanmarinedesign.com/Home_files/Hull Speed_ 2017.pdf
     

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    Last edited: Feb 12, 2021
  10. redreuben
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    redreuben redreuben

    There is no plans prices on the McGowan website that I could find.
    I know the Evergreen catamaran done with Schacht was just a concept, which is a shame because the hull shape with just 5 panels is exquisite.
    It’s hard to tell these days with the proliferation of rendering software just what are designs with actual plans and what is “vapourware”.
     
  11. oldmulti
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    oldmulti Senior Member

    The Maxcat 48 is high performance racer cruiser designed by Paolo Portinari and H3o. The 48 x 27.6 foot weighs 11,900 lbs and displaces 14,110 lbs. The 70 foot rotating carbon fibre wing mast carries a 900 square foot “fat head” mainsail, 485 square foot jib and a 1,720 square foot gennaker. The daggerboards draw 8 foot and the rudders draw 4 foot. The length to beam is about 20 to 1. These numbers indicate speed over accommodation which supports the designers claim he was inspired by AC cats.

    The design was for a “habitable catamaran”, with four cabins and two bathrooms that had very high performance. The speed sought and “obtained” was 16 knots downwind and 10 upwind in 14 knots of true wind and 7 knots downwind and 9.5 knots upwind when the wind drops to only 8 knots. Being a cruising catamaran, the designer thinks he has the right balance between power and lightness. With so much power to keep under control, the water lines and weight distribution needs to be matched to the immersed volumes to reduce pitching. The wave-piercing bows also help to reduce dynamic pitching in rough seas and to avoid the tendency to nose-dive in crash-gybes.

    The structure is a Kevlar PVC foam composite with carbon fibre in selected parts of the hull structure. The cross beams and foils are carbon fiber epoxy. Now we get to my confusion. The crossbeam structure is very curved which helps minimise weight and flexing combined with the dolphin striker being in tension. This can lighten the cross beam structure but in this design I would not like to be a crew winching at the mast base when sailing fast upwind.

    The concept and execution of this cat will result in a very fast cruising cat. My only reservation is that at speed, in a seaway, this cat may not be a comfortable cruising cat due to spray and motion. The jpegs give the idea.
     

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  12. oldmulti
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    oldmulti Senior Member

    The Maxcat 54 is a bigger sister of the Maxcat 48 representing the cruiser evolution. The Maxcat 54 is 54 x 27.6 foot and has increased displacement (not specified) but my guess is 18,000 lbs. It has the same 70 foot rotating carbon fibre wing mast carrying again a 900 square foot “fat head” mainsail, 485 square foot jib and a 1,720 square foot gennaker. The daggerboards draw 8 foot and the rudders draw 4 foot. The hulls are slightly wider and deeper to carry the increased displacement and internal volume. Again, the length to beam is about 20 to 1 with the slightly increased length and increased volumes of each hull.

    The Maxcat 54 performance will still be very good, but with increased internal space. The new central bridge deck superstructure provides a galley, dinette and chart table to starboard. The hulls have three cabins and three bathrooms, the port hull has the owner suite, the starboard hull has 2 cabins for guests.

    There is also more comfort for controlling the cat with the cabin providing some protection and increased covered cockpit space which will improve the ease of handling. Other changes include using steering wheels, not tillers, an improved forebeam and the carbon T-Top covering part of the cockpit.

    Again, the structure is likely to be a Kevlar PVC foam composite with carbon fibre in selected parts of the hull structure. The main crossbeam structures would be different.

    This should be a very fast cruiser that will be more comfortable than the Maxcat 48. The jpegs give the idea.
     

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  13. Mark.V
    Joined: Feb 2021
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    Mark.V New Member

    I read some, or actually all the thread, on the Crowther cats. I am considering buying an Alowplast Crowther 47 and was wondering what your thoughts might be. I am somewhat concerned that the bridge height might cause slamming. Anything I should look for and pay close attention to? Should I even consider it? Any comment is welcome...
    Mark V. - (an aged cat enthusiast)
     
  14. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Welcome to the Forum Mark.

    Re the cat that you are interested in, is she similar to this one?
    2017 Alwoplast ATLANTIC 47 Catamaran for sale - YachtWorld https://www.yachtworld.com/boats/2017/alwoplast-atlantic-47-3140079/
    If she is similar, she appears to have reasonable clearance under the bridgedeck in the photos (although she is very light in this condition).
    But I will be interested to see what Old Multi thinks.
    Certainly Chris White is a highly regarded catamaran designer.

    Here is another Crowther 47 cat for sale, in the USA -
    2002 Crowther 47 Multi-Hull for sale - YachtWorld https://www.yachtworld.com/boats/2002/crowther-47-3660022/
    One of the photos shows her sitting in a Travel Lift hoist, and the underside of the bridgedeck appears to be about 12" at the most above the painted waterline.
     

  15. oldmulti
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    oldmulti Senior Member

    Mark.V The 2002 Crowther 47 for sale is a "normal" 47 that appears to be very heavy. EG two 100 HP engines, Very large freezer, timber fittings etc. The bulbs on the bow should just be underwater not well under and the aft sections also appear to be deeper in the water. The "step down aft" on either side of of the aft underwing is where double berths are placed on the wing deck. Normally they are higher off the water and on a lighter (read 16,000 lbs on the scale) 46 foot Crowther I sailed on, did not pound. Alowplast normally produced good boats but this one looks as though its has all "mod cons" which really adds weight. The only real way of knowing is taking the boat on a real test sail, in stronger winds, upwind. If the current owner is reluctant to do that consider other options.
     
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