Multihull Structure Thoughts

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

  1. oldmulti
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    oldmulti Senior Member

    The following CYBD 44 catamaran is a design study that should be built. The cat is 44.6 x 25 foot that weighs 12,550 lbs. The fractional rig carries a 760 square foot mainsail, 390 square foot self tacking solent and a 1100 square foot gennaker. The hulls have deep daggerboards and spade rudders.

    The designer Corentin Bigot (French) has been involved in many projects and even had a TV show building a 30 foot cat design. He designs both mono and multihulls. He has strong experience in project managing, designing and building boats with composites.

    The CBYD 44 is built from PVC foam sandwich glass epoxy composite sandwich construction. The hulls are multi chine flat panel construction as is the majority of the cat.

    The interesting part of this design is Corentin work on hulls forms, optimisation and VPP performance predictions. The resulting in the hull shape that is interesting with the finer than normal bows but the rocker indicates the center of buoyancy and gravity are further aft than is standard. This is approaching the Grainger racing catamaran hull shapes.

    The VPP performance calculations indicate the CYBD 44 can reach 24 knots and can sail on a reach at wind speed up to 15 knots. This is a high performance cat that will take you far in reasonable comfort.

    The accommodation is a standard 3 or 4 double berth cabins with heads in the hulls. The bridge deck cabin has a dinette, galley, chart table in it. The large cockpit main cabin doorway allows an open feel and nice seating arrangement when weather conditions allowed.

    An interesting design. The jpegs give the idea.
     

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  2. oldmulti
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    oldmulti Senior Member

    STRANGE MAGIC is a trimaran designed and built by Jon Staudacher, a very innovative timber power boat and home built aircraft builder in his spare time. STRANGE MAGIC is about 21 x 18 foot (an estimate) and weighs 1100 lbs with motor and rig (fact). The rig uses a Hobie Cat 18 mast section that was reinforced as required and lengthened to about 30 foot. The sail area is not specified but based on a Hobie 18 rig slightly enlarged the sail area is likely to be about 300 square foot. There is a deep daggerboard and rudder on the main hull.

    Jon has sailed for many years and decided it would be fun to design and build a lightweight, competitive trimaran-using WEST SYSTEM Epoxy-to race with the local sailing association. The trimaran has reached speeds of over 20 knots.

    Jon has a lot of experience in lightweight ply timber structurers. One of his power boats is a plywood hydroplane that can exceed 100 mph. His tri is mainly plywood and timber with fiberglass hull bottoms. The first step was building fiberglass ama hull bottoms from a male plug. The ama bottoms are semicircular (170 degrees) and maintain a semi-circular cross-section from bow to stern. The plywood sides have a shallow bevel where the fiberglass ama attaches to the bottom with G/flex® 655 Thickened Epoxy Adhesive. The semicircular hull bottom gains rigidity because of its geometry. The frames inside of the amas are wooden trusses made from scrap wood (Jon version of scrap wood looks like douglas fir and spruce), with gussets. These minimize weight, uses up the scrap wood, and provides access to see or reach down into the amas when assembling.

    The same wooden male plug used for the fiberglass ama hull bottoms was widened 175 mm at the stern to build the hull bottom for the center trimaran hull. Reusing the mold plug saved time during the building process. The main hull again had plywood sides and decks with scrap timber being used for framing and bulkhead support. You notice the plywood hull sides are cut, scaphed and laid at an angle. This is a smart move as more of the plywood plies can support the longitudinal loads on the hull. This results in either a stronger hull or the ability to use thinner plywood on the hull sides instead of plywood that is laid fore and aft of which 20% of the plywood only adds weight and does not giving additional strength because the grain is in the wrong direction compared to the required load. The cross beams came from a sailboat mast sections and have a stainless-steel water stays underneath for additional strength.

    I will talk more about plywood and how to match the load characteristics to ply tomorrow. Sorry about the limited jpegs but a nice fun tri. The final 3 jpegs are of the plane and hydro plane that Jon built.
     

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  3. patzefran
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    patzefran patzefran

    Looking at the crews on the platform and the mast, she is much more than 21 feet, at least 25 or may be 30, which is more consistent with the weight and claimed speed.
    Anyway a very interesting design, thanks !
     
  4. oldmulti
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    oldmulti Senior Member

    Plywood and how to match the load characteristics to ply is an interesting topic. Many people assume 5 ply or better for 6 mm ply in marine ply is a good starting point for less than 26 foot multi’s hulls. Yes, it is, but what what does a hull need in load terms? A very big warning here, I am going to simplify the conversation here and the generalizations may not apply in all circumstances. This is the reason you need a naval architect especially if you are pushing the edges of design. EG building an ultralight cat or tri or building a heavy cat with a big rig to drive it etc.

    A tri or cat hull from about 7 to 1 to about 14 to 1 length to beam ratio have between 65% to 75% of their loading fore and aft. Only about 25% to 35% of the hull loading is laterally across the beam. Plywood by its nature if it has 5 equal thickness plies has at best 60% of its “strength” fore and aft with 40% laterally. If its 3 equal plies you have 66% fore and aft 33% laterally. Closer to what is required from a plywood strength versus load situation in a hull.

    BUT not all plywood has equal thickness plies in its construction. Result is 2 thin face plies of higher quality timber encloses 3 thicker plies of lower quality timber. Result you could have a variety of “strength” outcomes depending on the thickness of the plies and quality of timber in the plywood. I have brought several sheets of ply that had equal thickness plies in the plywood but the inner cores were not the same quality as the face plies. When the plywood panel was bent the face ply separated from the core plies. The glue lines were ok the core timber just split.

    Issues like this is the reason a lot of designers specify 6 mm ply for boats that could be built from 4 mm ply. The quality of plywood is variable unless it is from a very good manufacture. Having BS 1008 branding is not good enough.

    Next, we will talk about bulkheads especially cross beam bulkheads. Putting an 18 mm 4 foot high plywood bulkhead between 2 hulls means you are using probably 60% of the “strength” of the plywood, the other 40% is just adding weight. Only the lateral plies are adding strength value with 10% of the vertical timber plies helping holding it together. Several designers understanding this problem actually angle the plywood faces at 45 to 60 degrees across the beam to get all plies sharing the loads across the cross beam. This approach requires more scarping but you can reduce the thickness of the plywood and reduce the weight of the cross beam.

    What is being said here is the quality of the plywood is important. It does not have to be marine but must have marine glue lines and consistent quality timber. The number of plies and thickness matter. The more plies there are and quality consistency the better. Next is the correct application of the plywood to the load paths helps in improving the boats strength overall or you can build a lighter cat or tri for the same strength.

    The major advantage of building in foam glass or WRC glass is that you can build the strength along the load paths by the correct selection of fabrics or unidirectional glass etc. But plywood will produce excellent results also if plywood is sensibly used to match the hull load requirements.
     

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  5. oldmulti
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    oldmulti Senior Member

    “Sandakipper” is a sailing catamaran designed for third world or poorer fishing areas. The cat can be landed on the beach and offer stability and a large platform for fishing. The 16 x 8.5 foot cat weighs 1100 lbs and displaces 2200 lbs when loaded with fish. The rig is a “lug spirit” with a 140 square foot square sail. The 16 foot A frame mast arrangement allows the Sandakipper to tack without having to change the lug sail forward position etc.

    “Sandakipper” can carry half a ton of gill netted fish catch. Hull length to beam is 8.75 to 1 at 1100 lbs and 7.65 to 1 at 2200 lbs displacement. The leeboard on the outer gunnel on one hull helps with windward performance. The rudder is centrally mounted between the hulls.

    The plywood cat that has been constructed with stitch-and-glue methods. The masts and crossbeams are built from locally acquired timbers to reduce costs. Similar sized cats have 6 mm ply skins (Micromegas 5 is built of 9 mm ply) and EG 50 x 160 mm laminated solid crossbeams. The keel lines are solid timber externally for beach landings.

    The performance of this cat will be about 6.0 knots averages and capable of carrying full sail up to 22 knots of wind when displacing 1800 lbs. Other cats in this size include the Miss Cindy, Slider 16, Jarcat 5 and Micromegas 5. Each of these designs at times sail faster than their short waterlines would indicate. Both Miss Cindy and Micromegas 5 have crossed oceans and both have topped 140 miles in a 24 hour period.

    Small cats can be ocean capable with the right crew and weather. Do not try and cross the North Atlantic in this size of cat but cruising but around a coast line or around equatorial waters would be OK. The only limitation to small size cats is reduced internal accommodation and limited payload. The Berque brothers who crossed the Atlantic from France to the US in Micromegas 5 quit the cat when they reached the US due to the lack of space.

    A nice concept which could be converted to a small cruiser and playing with the unusual rig could be interesting. The first two jpegs are of the fishing design the remaining jpegs are of the other small cats mentioned.
     

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  6. oldmulti
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    oldmulti Senior Member

    The following camper trimaran was designed by Phil Bolger in 1992. The idea is to utilise your Hobie 16 components and add it to a home built main hull to create a tri. The trimaran is a 23.5 x 12.75 foot tri that weighs 450 lbs of main hull and 320 lbs of Hobie 16 components for a total weight of 770 lbs. The wide main hull of this tri will allow it to carry 1500 lbs easily. The length to beam on the main hull is 5 to 1 at a level waterline. The heeled waterline will be similar. The gunnel width of the main hull is 5.25 foot and with a scow bow the main hull will provide a lot of room for a decent double berth and 2 singles with additional storage space for all those extra’s required for camping.

    Now, the performance of this boat will be OK, but not spectacular. The fat main hull will slow it down, the deep lee board will help to windward but the relativity small rig to the wetted surface will not provide sparkling light air performance. Also, the reverse sheer open front cockpit bow will not help this boat going to windward in any sort of waves. Hobie 16 hulls acting as float also will not provide a lot of buoyancy for heavy weather sailing as Hobie 16 are running at gunnel level with 1100 lbs sailing loads. That means the floats have about 50% buoyancy at the 2200 lbs displacement this camper tri can sail at. Overall, this design is a bay, calm coastal sailor at best. Yes, it will be capable of handling rougher weather but it will not be sailing well in rougher weather.

    The main hull is built from plywood timber stringers and frames. The chines/gunnels are stitch and glue. The Hobie 16 cross beams (from 2 Hobies or cut 1 Hobie 16 beams in half and have a centre hull support tubes) are used as cross beams with water stays underneath. The steering system is using standard Hobie 16 rudders on the Hobie hulls. There was some doubt about the strength and ability of the rudders to steer the camper tri in stronger winds.

    This is an interesting concept that fills the need of a good base of camper cruiser that can allow you to travel to interesting remote locations to set up a shore camp or sleep on the tri overnight. This what I would call a Barrier Reef explorer in Australia. You can sail from island to island stopping/camping as you please. The jpegs are of the initial design proposal and isometrics of the design.
     

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  7. oldmulti
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    oldmulti Senior Member

    In 2014 Jim Brown, the designer of the Searunner series of multihulls, wrote an article about what is a multihull. The full PDF is attached. The following is an edited subset of the article starting with definitions of the multihull types. A. Catamaran. 2 hulls, identical, spaced wide apart. B. Trimaran. 3 hulls, large hull in the center, 2 smaller on each side C. Outrigger. 2 hulls, one large and one smaller D. Proa. Like C but proceeds with either end forward. Sailing Multihulls break into five types:

    A1. Daysailers. These are small, trailerable or car-toppable vessels, normally without overnight accommodations, used for daytime recreation and racing.

    A2. Ocean Cruising Multihulls. This type includes interior, overnight accommodations for the crew, and usually some form of auxiliary power. Many of these vessels have achieved extended ocean voyages, their crews (sometimes families) living aboard for years at a time. The catamaran yachts, especially, have proven quite commodious, with great privacy achieved in the outer hulls and communal living in the bridge deck between. Such craft contain all the systems needed to support comfortable habitation and satellite navigation, and are now the vehicles of choice for “term chartering” with or without a professional crew. A major portion of today’s recreational marine business is in this type of for-rent, “condo cruising,” and activity in this type of multihull represents a growth area.

    A3. Ocean Racing Multihulls. Very lean, lightweight, Spartan versions of A2 with huge sail plans, these craft reach 150’ in length, and now hold all the major ocean racing records (at least where they are allowed to compete). The technological development of these vessels has advanced rapidly since the 1960s to now commonly utilize aerospace materials and engineering. They can cross oceans at ocean liner speeds, sail much faster than the ambient wind is blowing, and are sometimes fitted with hydrofoils to make them “fly” above the waves. The trimaran type currently prevails offshore, but catamarans are chosen for inshore competitions such as the Americas Cup. Indeed, multihull ocean racing has sparked fierce international rivalries, and contributed greatly to the overall advent of modern multihulls.

    The current thrust in hydrofoil-borne, sail powered, racing multihulls is focused on speed, but the future of this technology addresses the number one problem of commercially transporting human beings on water; seasickness. Hydrofoils, when combined with the steadying effect of sails and the inherent stability of multihulls, can achieve by far the smoothest ride of any surface vessel type. This makes large, commercial, wind powered, hydrofoil-borne multihulls of special interest in the energy efficient future.

    A4. Excursion vessels. Called “day charter” boats, that approach 80 foot and are Coast Guard certified for carrying up to 150 passengers on short excursions for snorkeling, dining, whale watching and sunset partying.

    A5. Sailing workboats. In the 1980s, the author and others conducted several boatbuilding training projects in developing countries. Sail power was used on multihull vessels to minimize running costs for peasant watermen working in artisanal fisheries and transport routes.

    Technology. The initial technical advance for modern multihulls is light weight. After WW II, strong, light materials like plywood, aluminium, fiberglass and synthetic fibers for cordage and sails, all became commonly available. These together with increased understanding of hydro-and-aero dynamics, and the multihull’s easily driven, narrow individual hulls, all contributed, but by far the most meaningful advance was the reduction of weight. Moreover, the wider beams leading to greater stability vastly increases the utilization of wind power in the sails, and because performance is a function of power-to-weight, reducing the vessel’s weight and greatly increasing its power profoundly affects performance.

    Many other technical advances have been spearheaded in multihulls, including the use of aerospace materials, computer-aided design, and the coming of rigid wing sails and hydrofoils – each a compelling story in itself – but the main technical advantage of the multihull is its combination of light weight with great stability and shallow draft.

    Cruising multihulls for voyaging, whether local or trans-ocean, are distinctly different from the racing type. Designed to carry much more weight, they include large tanks for carrying water and fuel, at least four anchors and ground tackle, equipment for fishing, diving and water sports, plus the myriad amenities required and desired for extended living aboard. Failing to contend with this weight by naively optimistic designers and sailors has led to many overloaded cruising multihulls with consequent structural and safety problems. Furthermore, a cruising payload seems antithetical to the basic multihull premise of light weight. Nevertheless, with a crew that respects the “back packing” nature of multihull cruising, and when their vessel is properly designed, built and operated, such craft can achieve significant trans-ocean voyages, including circumnavigations, and even serve as extended family homes.

    Passage times for cruising multihulls are often somewhat faster than for their monohull counterparts, but speed, per se, often is not the main attraction in cruising. More than any other type of vessel, proper cruising multihulls enjoy an unprecedented combination of superlative seakeeping properties together with shallow draft.

    Multihull Design. There is no magic in designing multihulls, but there are some significant differences relative to monohulls. The sprawling platforms can produce severe global torsion, the added stability causes far greater mast and rigging stresses, and higher speeds severely tax rudders, centerboards and hydrofoils. Analysis of the “free body,” and fifty years of experience, has reveals certain unexpected failure modes, and multihulls have substantiated the old engineering axiom, “The more sophisticated the design solution, the more catastrophic the design failure.” However, our increasing understanding of these challenges, together with the marvellous new materials now available (like epoxy, carbon fiber, Mylar sails and spectra cordage) have imparted a remarkable security to the robustness and durability of modern multihull structures.

    Multihull Construction. These boats have been built in many settings worldwide. They began by being built entirely by their owners, often in back yards or in makeshift shops, then by professionals on a custom, one-off basis, and finally by organized production builders. All three methods are still used, but now the production builders predominate; most are located in France. Production methods vary from the wood /epoxy technique popular with owner-builders to full-on aerospace composites of foam, fiberglass and carbon fiber. Welded aluminium is used in the large, commercial and military vessels.

    I hope the above is reflecting the original intent of the PDF. Please read the original PDF to get the full story.
     

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  8. garydierking
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    garydierking Senior Member

    And the Searunner 37.
    [​IMG]
     
  9. oldmulti
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    oldmulti Senior Member

    The following is based on information from Dr. Richard Jagels, an emeritus professor of forest biology at the University of Maine.

    According to various sources, wood that’s kept relatively dry, maintained at moderate temperatures, and protected from deteriorating influences such as decay or insect infestation will retain its original mechanical properties for at least a few centuries. EG redwood trees can be centuries old. Research studies comparing strength properties of wood from centuries old buildings in Europe and Japan generally show little or no loss in strength and often an increase in stiffness, or modulus of elasticity.

    Some changes in hemicellulose content and lignin bonding to cellulose can occur after many centuries of aging, but these changes have only marginal effects on strength. Within the time period of one or two centuries, the greater risk for loss of strength would be the nature, duration, and magnitude of loads that are applied to wood structures and the extent of moisture and temperature fluctuations. Duration of load and constant stress on wood reduces its ultimate strength. If a beam has to carry a continuously heavy load for a long time, it will fail with a much smaller load than that needed to cause failure before the long-term loading.

    Constant stress over time leads to an exponential loss of strength. By 10 years, wood may be induced to fail under a standard static test load that is only 50 to 60 percent of the load that would have caused failure if the beam had not been stressed for 10 years. The loss of strength is a consequence of creep, where the elastic properties of wood are slowly eroded, leading to inelastic deformation—a sagging beam, for instance. If the same load is applied intermittently rather than continuously, then the time to failure is extended. EG if the load is applied at varying intervals that add up to a total of 10 years over a 100-year period, then the beam would reach the 10-year level of strength loss after a century is reached under conditions of non- fluctuating temperature and moisture conditions. Large cyclical changes in either of these factors will increase the rate of creep. Changes in wood moisture content are quite common in boats, particularly those that are hauled out periodically. Further, wet wood is more prone to creep under loading stresses.

    What does this mean? The relative strength of standard timber beams (with 12% moisture content) that is loaded over time is as follows. Timber beams that have stressed for 10 years have about 50 to 60% of the strength of timber that have not stressed for 10 years. Timber beams that have stressed for 1 year have about 70% of the strength of timber that have not stressed for 1 year. Timber beams that have stressed for 10 days have about 85% of the strength of timber that has not stressed for 10 days. Think about wooden cross beam. The jpeg indicates the above.

    Impact loading on boats which are often exposed to rapidly applied forces of short duration like pounding in rough water or bouncing against docks can be handled. Studies on wood-framed aircraft in the 1920s revealed that during diving manoeuvres of a few seconds’ duration, aircraft could survive forces that if applied over a longer period would have led to certain failure.

    Working out safe working stresses for timber needs some adjustments. EG modern “higher grade” timber often has defects in like small knots, defects and lower ring counts per inch for some “rapidly” grown timber. Result modern timber may have less strength than “high quality” timber provided to the market 50 years ago.

    Calculating safe working stresses for boats with wood-composite construction creates entirely different design criteria. Boats built using safe working stress reductions and good design principles should hold up for many decades if properly hauled, stored, and protected from decay and marine borers. Insufficient hull support during storage probably has the greatest potential for inducing creep, which can lead to hogging and other structural distortions that progressively weaken a boat. Small craft that are stored upside down and only supported near stem and stern are particularly prone to progressive hogging.

    Translation. Design timber multihulls under the assumption that timber strength declines over time and constant loads. This is especially important in wooden cross beam design in cats and tris. Timber strengths used in calculation may only be EG 20% of the theoretical maximum strength of the timber. Trust your naval architect, if they say 150 x 75 mm beams are required and you think 100 x 25 mm will work because some else has done it the architect may be thinking about your long term safety.

    The following web site leads you to an interesting paper on wood fatigue done by Meade Gougeon for NASA and Department of Energy. It is big 13 meg 156 pages. The attached 2 page PDF shows a subset of some of the results. Loose translation of document, compression capability of wood reduces under load. Structural properties of laminated Douglas fir/epoxy composite material (Technical Report) | OSTI.GOV https://www.osti.gov/biblio/6492500-structural-properties-laminated-douglas-fir-epoxy-composite-material
     

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  10. oldmulti
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    oldmulti Senior Member

    Nathan Caves decided he wanted a tri so he created “3 Bags Full”, a Franken-tri made from a Nacra 5.8 as a main hull, Cobra cat floats. The tri is 18.9 x 14.5 foot that weighs 550 lbs. The tri has a F18 mast and main sail with a Cobra cat jib. The rigging is 4mm dyneema. 3 Bags Full has a top speed of 20.5 knots in flat water in 25 knots of wind and she has done about 10 knots in around 14 knots of breeze. 3 Bags Full “can reel in those F boats” around a race course.

    The Nacra mainhull was cut down the centre and widened by 150mm at the transom. The halves where canted out slightly. The shears were raised by 100mm. The Nacra hull single rudder and board were strengthened. He used 20mm 100 lbs/cu ft density core cell for the beam bulk heads with layers of Biaxial and unidirectionals on either side. The sockets on the Nacra mainhull are now 8mm thick carbon fibre only 400mm deep to take a 100mm x 3.5mm round alloy cross beam sections. The Cobra cat float hulls (3mm ply) were wrapped in carbon for additional strength. The Cobra cat hull centre boards were removed and bows modernised. The majority of the glass work was done with vinylester resin.

    Two fit people can lift her unrigged and she can sleep 1 adult in the cockpit. There is a full width deck tent that is used for overnight camping that can accommodate 4 people if required.

    This is a very nice tri built from left over components with a bit of creativity and work by a determined man. It did not cost much and is fast. It can also be used as an effective camp cruiser. You can access more information on 3 Bags Full trimaran and you will find several video’s on its build and sailing capability at Homemade small tri http://forums.sailinganarchy.com/index.php?/topic/195719-homemade-small-tri/

    Jpegs give the idea.
     

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    Last edited: Nov 7, 2020
  11. oldmulti
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    oldmulti Senior Member

    Moderator. Sorry to do this, but I have redone the indexes and could you please replace the indexes of the Multihull structure thread on page 1 with the following. They have been broken into multihull type and an additional index of structure rig and other items.
     

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  12. Boat Design Net Moderator
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    Boat Design Net Moderator Moderator

    No problem at all. Will do so in a moment.
     
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  13. oldmulti
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    oldmulti Senior Member

    Moderator. Thank you. I hope this will help everyone.
     
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  14. oldmulti
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    oldmulti Senior Member

    This is a story about a man, David Vann, who had a dream of sailing around the globe single handed via the 3 capes from California, he hoped to do it in 120 days. He built an aluminium tri at his home to do this task. The tri is 50 x 30 foot weighting about 9000 lbs (estimate) and has a 50 foot mast with about 1200 square foot of main and fore triangle. A genoa adds more sail. The mainhull length to beam is about 20 to 1. The floats are even narrower. The rudder is outboard and lifting. The keel appears to be a fixed shaped foil, again cheap and effective. PS the default tri name was "Tin Can".

    The tri was meant to cost $25,000 and be built in under 6 months with supplies from Home Depot. Now my confusion really starts. Yves-Marie Tanton was the naval architect, Yves is a very good and creative naval architect of monohulls. His design portfolio is large and excellent. This design hull shape is literally a slab sided box with pointed ends. A fast build but not the best hull shape. There is one advantage of this shape is it can have a very high prismatic coefficient (read full ends) and with slim hulls you can have a canoe stern with minimal pitching impact.

    As you can see from the jpegs its built from aluminium. The hulls and decks are of 9 mm aluminium with framing about every 400 mm. The float hulls were foam filled. The lattice crossbeam structure is an X beam with about 125 mm top and bottom tubes welded together with compression tubes between them. The structure was rapidly built with long hours done by David Vann, his wife and friends. Most people were amateurs although David Vann had been involved in a 90 foot aluminium charter catamaran previously.

    The build cost of $25,000 in 2008 is questionable even with all the free labour. Either he brought a lot second hand or had substantial gifts from others as the safety equipment, deck equipment and rig alone would have eaten most of the $25,000. To quote David “The plumbing and electrical systems inside the boat are complete, as are the foam and paint. And the boom's up, winches mounted, wind generator, liferaft, Monitor windvane, steering system, etc. For a simple boat, it turned out to be fairly complex.” The accommodation is minimal and would have been difficult to live in in a seaway due to the noise of being in a flat-bottomed aluminium box.

    How about performance? This tri was quick in its short sailing career. Quoting David “But it sails faster than the wind in light air, cruising along even when the sea surface is reflective. It feels insistent. You set the sails to a faint breeze, then try not to touch the helm at all as the boat comes alive, surging forward to accelerate off the wind of its own forward movement. In 5-10 mph of breeze, it will jump so quickly from 6 mph to around 13 mph, you can feel your seat pressing into your back. It's a lovely surprise after the months of work and doubt.”

    David set out and sailed about 300 miles when “The crossbeams that hold the three hulls together are a complicated structure that I have worried about ever since the initial stages of planning and building. I wanted a ladder-like design that would have low wind and water resistance and light weight. But the beams also have to be strong enough to resist enormous stresses. What I found after a day at sea was that although the beams themselves, the primary structure, were still intact, the secondary support structures I had added—five vertical compression posts where the beams meet at the main hull—were cracking out.”

    The circumnavigation attempt was abandoned and I do not know what happened after that. The jpegs give the idea of the tri and the last 2 jpegs show weld problems. Rope chafe after 2 days of sailing is also concerning. The idea was interesting but this tri needed a lot of refinement before it would be a viable racer/minimal cruiser.
     

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  15. oldmulti
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    oldmulti Senior Member

    Tin Can current status is can be found at the following web site with a copy of a Coastguard report.
    Crew wanted http://forums.sailinganarchy.com/index.php?/topic/216116-crew-wanted/

    Tincan appeared to be modified to provide more accommodation (first jpeg) and bouyancy in bulges in the bow area. It was then "chartered" into the Pacific in mid 202o. It was rescued by the Coastguard "HONOLULU — The Coast Guard and crew of the merchant vessel Mahi Mahi rescued three mariners from the disabled 50-foot trimaran Third Try 825 miles northeast of Oahu, Wednesday." with one person saying "So, they made it to Hawaii (towed it in after the rescue?). It has cracked beams and no rudder... oh and a king size bed. priorities!"

    Tincan (Third Tri) now appears to be under modification to a "motor boat" in the final jpeg.
    An extra jpeg of the 90 foot cat David Vann built. The 'story' of part of that build is at Review of David Vann's (Tin Can man) book "One Mile Down&quot http://forums.sailinganarchy.com/index.php?/topic/67570-review-of-david-vanns-tin-can-man-book-one-mile-downquot/
     

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    Last edited: Nov 8, 2020
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