Multihull Structure Thoughts

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

  1. oldmulti
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    oldmulti Senior Member

    A little bit of history modernised by Lorenzo B. Acompañado II. The Paraw was a trimaran design of a Philippine Visayan sailing outrigger of Sulu sea. As the centuries-old design using modern materials, but the overall shape remains the same and is still fast.

    The Paraw 16 is 16.4 x 16.7 foot with a weight of 716 lbs. The sail area is 86 square foot in a crab claw main and it has an optional jib. The main hull length to beam is 11 to 1. The float is a bamboo tube at least 16 foot long and 125 mm in diameter. The float provides at least 132 lbs of buoyancy at 8 foot from the main hull which provides a righting moment to resist gusts up to 20 knots. The draft is 1 foot over the hull and deeper over the steering paddle.

    The main hull construction is plywood over timber frames. The mast and yards can be bamboo or ex windsurfer spars. The crossbeams are fire-heated bamboo to conform to a desired shape, either in arch or “water spider legs” (elongated letter “M”). The flexibility can be tuned by adding a second beam on top with varied length depending on sea condition and boat loading.

    This is a cheap fun day sailing tri with a historic style about it. A couple of crew could learn a lot about sailing history and be surprised at how fast this style of boat can sail. Just don’t expect it to go upwind well.

    An interesting good knock about design. The limited jpegs give the idea.
     

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  2. oldmulti
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    oldmulti Senior Member

    This next Paraw for review is a common sight in the northern part of Panay island in the Philippines. Again, it is a modernised design by Lorenzo B. Acompañado II. These design mimic the original concept but use modern materials for the main hull as tall trees are not freely available to make a log main hull.

    The length overall is 19.5 x 17.7 foot with a weight of 785 lbs. The 19.5 foot bamboo mast has a crab claw mainsail that has spars that extend the rig height to 24 foot. The mainsail is 150 square foot with an optional 43 square foot jib. The floats are bamboo tubes of at least 127 diameter that have shaped caps in either end. The floats have 172 lbs of buoyancy and can support the rig in 15 knots of wind speed. The length to beam of the main hull is 11.5 to 1. The draft over the hull and stern mounted rudder is 1.2 foot. Motive power is by oar.

    This is an open boat that can accommodate 4 crew for fun days out, fishing or transporting items around lagoons etc. The tri can also be used as a weekend camp cruiser. This is a cheap to build, simple to construct versatile tri.

    The construction is a strip plank WRC mainhull covered with light e-glass and epoxy inside and out. The masts and floats are bamboo. The crossbeams are fire-heated bamboo to conform to a desired shape, either in arch or “water spider legs” (elongated letter “M”). The flexibility can be tuned by adding a second beam on top with varied length depending on sea condition and boat loading.

    Again, this design will surprise you with its speed. There are claims of near 20 knots but don’t expect upwind performance to be a priority. Paraws can use cheap materials for sails and still get good reaching and running performance but tests of crab claw mains show they don’t point high.

    A versatile fun daysailer for semi sheltered waters. The limited jpegs give the idea.
     

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  3. oldmulti
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    oldmulti Senior Member

    A story of a German, Nicolas Harcke, who started designing and building day cats in 1984 (Novacat 15). In 2017 he went on to design and build a bigger day cat for a bit of fun. He asked for thoughts on the web and did an effective design of a day cat. Nicolas has also extended his design and self build range with 2 other day cats and a 28 footer.

    The Novacat 16 is a plywood build of a F16 style cat. The Novacat 16 is 16.4 x 8.2 foot with a 305 lbs weight. The 2 crew should weigh about 335 lbs. The 27.9 foot rotating mast carries a 161.5 square foot mainsail, a 39 square foot jib and a 188 square foot gennaker. The length to beam of the hull is 13 to 1. The draft is 3.6 foot over the daggerboard.

    Each multi chine hull will be built out of 7 plywood hull panels and 3 deck plywood panels and a transom. The hull panels are set up in female molds then the internal seams are stitched and glassed. Internal bulkheads are then fitted with some foam panels laid horizontally to provide additional hull stiffening. Additional timber is inserted on crossbeam bulkheads to support the crossbeams. Then the daggerboard cases are fitted followed by deck stringers to support the 3 panel deck. I do not know the crossbeam dimensions but F16's often use 3mm x 80mm OD tube aluminium beams on the front cross arm with a dolphin striker and a 2.6mm x 80mm tube rear beam.

    The maximum reported speed so far is 17.7 knots. Videos show a good handling cat that can provide 2 people on a trapeze a lot of fun.

    The jpegs give the idea.
     

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  4. tane
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    tane Senior Member

    I fail to understand the concept of "degressive volume-increase as bow submerges"...
    It will reduce "tripping" over the bow, but at the price of much earlier submerging it (& of course then the reduced dynamic downward force becomes important. With more volume this will become a necessity only with much more downforce on the bow)
    (or is it just a question of "contemporary aesthetics?)
     
  5. oldmulti
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    oldmulti Senior Member

    Tane. There is theory, there is practice and there is fashion. Reverse bows on some fast boats allow a longer waterline that drives through a wave top with less buoyancy up high to pitch the bow up in a a wave pattern. If the boat is designed with a long bow, rig set back and a correct buoyancy distribution, the cat or tri will sail flatter and faster in a seaway. Other designers just add a reverse bow on EG a cruising boat for fashion and functionally makes very little difference to the boat beyond increase its price. But now with foiling being the accepted way of getting performance, reverse bows are less functional in a sailing sense and more a weight and windage reduction idea that is used in multihulls and monohulls.

    Each design needs to be combination of parts that make a sailing totality but a lot of the world buy floating apartments that are fashion items without understanding what is really required to sail. Each to their own.
     
  6. hashtag_laeuft
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    hashtag_laeuft Junior Member

    Hi ..
    thanks for the description of my Novacat 16 project.
    About the negative bow. Of course, the decision was primarily based on aesthetic considerations. "It looks modern, so it must be good". This is certainly the thinking of most people who have no in-depth knowledge of boat design / naval architecture. This configuration offers less buoyancy than a classic bow, that's true. This is also a small disadvantage up wind, as the noses undercut more quickly. At least that's how I feel.

    However, if they do undercut, the water flows off more easily via the bevelled deck. In waves, however, the shape is an advantage as the bow really goes through the waves and the boat doesn't want to go over them. The cat therefore pitches less. The shape of the decks should also provide a better inflow for the jib.

    I have some YouTube videos of that boat. You can find my channel here -> https://www.youtube.com/@novacat_katamarane/videos

    Best regards
    Nicolas
     
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  7. oldmulti
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    oldmulti Senior Member

    The is the final historic modernised trimaran design by Lorenzo B. Acompañado II I will feature. It is based on a boat excavated in the Philippines in the 1970’s and were carbon dated from 320 to 990 AD. The lines of this design were based on Balanghay No 2.

    The Balanghay is 40 x 32.5 foot with a weight of 6700 lbs. The main hull is 40 x 6.6 foot with a waterline beam of 5.5 foot giving a length to beam of 6.5 to 1. The float length is 38 foot with a length to beam of 31 to 1. The buoyancy of the float is 845 lbs. The float righting moment can support 256 square foot in 30 knots of wind or 527 square foot in 20 knots of wind. The 27.5 foot mast and yards used to hold up the mainsail can be custom made timber or large diameter bamboo. There are a variety of headsail options to improve performance. The steering options can be a fixed stern rudder or a steering oar/paddle. The draft is 1.6 foot over the hull and keel strip.

    This tri has 2 single berths in the main hull with a galley, seating, toilet area and chart table navigation area. This is a very practical layout for a cruising couple for an extended period.

    The construction is a basically ply covered with e-glass and epoxy, timber and bamboo. The main hull is cold moulded double diagonal plywood cover with glass and epoxy with supporting bulkheads and timber framing. The floats are also a plywood build. The crossbeam structure appears to be box beam structures with limited bamboo supporting structures.

    This design would be relatively cheap and easy to build but we are reaching a point where small changes would make a safer, faster design. EG larger float would provide more stability and speed but the downside is more weight in the floats and stronger cross arms. I like the simplicity of these designs but once you get to a seagoing vessel safety is more important than simplicity. I am not saying this design is not ocean capable but you will need to understand its limitations.

    No performance predictions, but I suspect 15 knot peaks and about 8 to 10 knot averages in good conditions. Upwind would not be a strong point but reaching and running would be good.

    The single jpeg give a lot of detail of an interesting tri.
     

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  8. fallguy
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    fallguy Senior Member

    Not sure I agree with the less buoyancy remark. Not to tangle with a good designer, but the extended waterline for the same loa or lwl offers more buoyancy and the lcb is also affected by more bow forward (for the same loa or lwl).

    I've lived the nightmare of not having enough forward buoyancy and I've stared at the front of my boat and basically see reverse bows with a cutaway.

    ps I changed the angle of the extension to to positive angle
    IMG_0976.jpeg
     
  9. peterbike
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    peterbike Junior Member

    Fallguy, iirc you built a woods skoota ?
    Did you change anything from original design ?
    Peter
     
  10. SolGato
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    SolGato Senior Member

    Speaking of bow design, I came across this sea trials video of the T-2000 Voyager that OldMulti did a post about a while back:

     
  11. fallguy
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    fallguy Senior Member

    I'm not interested in critiquing the design on this thread. I made a few changes, but they were not the heart of the issues. Anytime a builder endeavors to build a boat, they will build in the absence of detail and make minor adjustments for locale. One example is the windows are tempered and I have 106 pounds of solar just for'd of lcg atop the cabin. Richard has some exceptional designs. If you'd like to discuss it privately, once you have direct messaging rights, message me with your real name and location and I'd be happy to tell you about it.
     
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  12. oldmulti
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    oldmulti Senior Member

    This is an update of the L20 trimaran feature on page 14 of this thread. The L20 was designed was finalised in 2017 and was designed by Lorenzo B. Acompañado II.

    This is a very aggressive day sailing trimaran design at 20 x 20.2 foot weighing just 885 lbs with a 29.75 foot high, a 22 square foot wing mast with a 160 square foot mainsail, 64 square foot jib and an optional 260 square foot spinnaker. The mainhull length to beam is 13.5 to 1. The floats are 18 foot long with a 670 lbs of buoyancy and a length to beam of 24 to 1. The righting moment of this tri is about 6,400 foot lbs (excluding crew out on a wing seat) which means full sail in 20 knot plus wind speeds. The draft is 4.9 foot over the main hull daggerboard and 4 foot over the kickup rudder.

    These numbers equal speed. If the conditions are right, peaks of 20 knots would be possible. This is a wind speed boat in light to moderate conditions. Upwind will be very good. The limitation here will be the courage of the crew, if the tri is well built.

    The Vaka (mainhull) panels requires 6 sheets (3 per half-side) of 3/16″ [5mm] thick marine plywood with 200 gsm e-glass and epoxy over. The location of the scarf joints need to offset from each succeeding panels, in order to attain a stronger hull. Each scarf requires a feathered length of 4″ [102mm]. Glass tapes hold the hulls together. The floats are 5 mm ply also. The cross arms (aka) have 5 mm webs with bulkheads with 25 x 25 mm timber on the sides. The top flange is 51 mm wide x 29 mm laminated timber. The bottom flange is 100 mm wide 19 mm thick laminated timber. The bottom panels of the cross arms will be the last part to be installed. The interesting part of this design is it will be rig limited if it uses a standard Tornado rig but if it uses a well designed wing mast and appropriate rigging you should be able to power the tri up to its full capability.

    The jpegs give x-rays of the structure, panel layouts and the PDF the materials list. This should be a fast fun boat that will give a few local fleets a bit of competition.
     

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    Last edited: Apr 6, 2024
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  13. oldmulti
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    oldmulti Senior Member

    This is about an area of catamaran design that has been tried many times and in theory should work but in practice it does not work well. The planning sailing catamaran. These boats were developed by EG Nick Parkyn, Yves Parlier Hydraplaneur and the boat featured here by Bernhard Kohler. Bernard was commissioned to do this design and was “sponsored” by Tenson.

    The Tenson 5 metre is 16.4 x 13.1 foot (over the wing seat extensions) and weighs 265 lbs. The 26.5 foot rotating mast carries a 140 square foot mainsail. The length to beam on the hulls is 14.28 to 1. The draft over the hull based daggerboards is 2.5 foot.

    The purpose of the cat was to explore planning catamarans as a fun daysailing cat. The designer did some initial sailing and suggested it need some modifications such as an additional 22 square foot of sail area, modifications to the rudder efc and was inviting any future clients to experiment more.

    The construction of Tenson is ply some foam and light glass. The hull sides and deck are 5 ply 2.7 mm plywood covered with 80 gsm glass and epoxy. The hull bottoms are 2.7 mm ply with a layer of 20 mm Clarkfoam and covered by a layer of 60 gsm Kevlar in epoxy. There are frames and bulkheads inside the hull structure. The foils have an NACA 63 profile and are hollow with ply sides and carbon fibre strengthening. The hulls weigh 50 lbs each.

    Performance was aimed at planning in Force 3 or above. Now we get to the issue many attempts have been made to get a fast all-round sailing planning cat. On some points of sail each one of the cats mentioned sailed well but they were not consistent. The long thin round bilge “displacement” hull cats could sail around a course at a higher average speed. Planning cat sailing design is now of minimal use in a world where foiling is the way to achieve speed. An interesting deviation that just was not as practical as the theory suggested.

    There are 3 jpegs of Tenson, 2 of Nick Parkyn designs and Yves Parlier Hydraplaneur.
     

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  14. oldmulti
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    oldmulti Senior Member

    The following is about an interest development in monohull power boats but could help solve some issues in power multihulls or if you are creative solve some an issues in a sailing multi.

    A company in Holland has designed a rear hydrofoil (they call it a Hullvane) that improves the sea motion and provides lift in the rear of a hull (minimising squatting in power boats) that has proven to improve performance and improve fuel economy. HullVane developed this appendage about a decade ago as a spinoff from research originally conducted for the America’s Cup.

    How large a boat? Try Dutch Navy patrol vessel size. From the Hullvane Company “Depending on vessel type, design, and speed, efficiency gains can reach up to 25%, according to Hull Vane”

    Using a lift-generating profile, the wing converts part of the stern wave’s energy into forward thrust. Because the lift force is angled forward, it has a forward-pointing horizontal component that adds wave energy to the vessel’s propulsion. In shallow water, vertical lift reduces the squatting effect, thus boosting top speed.

    A wing-shaped profile creates an accelerated flow of water across its upper surface, which leaves behind a zone of low pressure to interact with the wake and suppress energy-sapping stern waves (similar to the bulbous bow reducing the bow wave).

    Horizontal wings also mitigate pitching motion, which reduces wave resistance.

    The sea trials conducted on the Dutch patrol boat on a 2 way transatlantic run that produced an 18% reduction in fuel use and a 1.5 knot increase in peak speed (19.5 to 21 knots).

    The Hullvane foils are constructed to suit the need. Big ship units are in steel, luxury motor yachts like the 138 foot Alive have either aluminum or carbon fibre aft foils. Over 60 vessels have been fitted with the Hullvane foils including some monohull sailing yachts.

    The jpegs give the idea.
     

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  15. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    This is about how to build in wood in a different way. A Dutch company is building curved wood pieces that can be assembled into a full boat. Business partners Roelof van der Werff and Henk Bergsma wanted to develop sustainable wooden boat construction using woods like bamboo and radiata pine wood. They have hull sections of this wood bent into three-dimensional shapes. With this procedure, we create panels that together form a hull. Yacht builders should start using the renewable materials that grow all around us.

    A 24 foot old style monohull power boat have been developed and launched and a 39 foot demountable catamaran is currently being built. The hull panels are built on a computer controlled series of actuators that can form any shape required. Over this shaped mould is are placed double moulded cheap timber strips that are vacuum moulded together. This formed a preshaped panel that may form a quarter of a boat hull shape. The 24 foot power boat has a 10 mm thick skin. The hull skins are then laid over the hull frame structure.

    The advantage of this system is any hull shape designed on a computer can be input to the computer controlled actuators in seconds then you can immediately place the cheap timber strips over applying epoxy resin next and then vacuum bag the hull part. Each hull part is accurately produced so it fits together like a jigsaw puzzle.

    2 separate issues. Excellent you can use cheap timber types is a thicker skin matrix and achieve a strong enough part to build a hull skin in a cheap efficient way. The epoxy provides the waterproofing the timber strips provides the bulk (read in this case stiffness with thickness and curvature).

    Second issue. The idea of a cheap thick vacuum bagged curve skin was created by Jim Brown/Dick Newick with there constant camber mould and panel technique. The 2 dimensionally curved mould allows panels to be glued together then tortured (to a limited degree) into a hull shape. A later development was laying the panels at an angle over a mould to produce an asymmetric shaped hull. (read about Silver Gull dingy on a constant chamber mould). The constant chamber method limits the hull shape but is a far cheaper method of building a mould. But if a designer is good enough even a cheap mould will produce a good hull shape.

    The real advance here is the use of bamboo and radiata pine build materials in thicker panels to give a hull skin. There is till a need for some framing and bulkheads in most designs. Stringers are generally not required with thicker hull panels.

    The jpegs will give an idea of the computer controlled mould, hull panels on the mould, hull panels and 24 foot power boat, the start of bthe catamaran hull. The second set of jpegs shows the constant camber moulds and panels. The pdf patent application gives a lot of detail of the constant chamber process.
     

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