Multihull Structure Thoughts

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

  1. rob denney
    Joined: Feb 2005
    Posts: 722
    Likes: 86, Points: 28, Legacy Rep: 436
    Location: Australia

    rob denney Senior Member

    Still a cool thread. Thanks OM.
    Partly correct. Reducing pitching is about maximising buoyancy x distance from the middle of the boat and minimising weight x distance. The way we do the former is to have zero rocker, full length waterline and a flat bottom. The latter is achieved by not having any more extra hull and deck at the ends than is necessary to keep the bows up while surfing and not having any rigging, fittings or their required beefing up at the ends of the boat. The same applies inside, there is nothing in the ends of the boat.
    By products of this are 1) safety: There is no requirement for the crew to venture further forward/aft than the beams while underway. The shallower draft allows the boat to sit on the beach above the destructive reach of breaking waves. 2) speed: Longer waterline length is faster, flat bottoms can allow planing, pitching is slow and uncomfortable. 3) Easier to build and repair.

    Early harryproas had full ends, not to reduce pitching, but to reduce the nose down sailing that all the 'experts' at the time promised would happen. It didn't, so the bows have become much finer.
    Rocker/overhang makes sense on wide hulls with relatively small rigs that heel. ie minimise wetted surface in light air and in a breeze heel the hull so the waterline length is maximised. The wetted surface gains are mostly negated if the weight of a floor and additional topsides height for headroom are then added.
    If you view a rockered hull from the side, it has a wing shape, with the lifting force pointing downward. A very low aspect wing, but nevertheless, one that pulls the boat into the water at speed. This is unlikely to be fast.
    It is often argued that rocker helps allow a hull to tack. This may be so for highly rockered hulls, much less so for minimal amounts. Regardless, harrys don't tack, they shunt, and have 2 large rudders mounted fore and aft so it is not a requirement.

    The downside of no floor is loss of storage space which is likely to get wet, so not ideal. If the floor is sealed, it increases damage tolerance, but is offset by the difficulty of accessing the damage. Harryproas compartmentalise the bilge with bulkheads and have a flat bottom which is easily repaired, even while the boat is floating.

    An angled bow (at least 3 units of length pre 1 unit of height, starting from the top of the bow) to ride over obstructions is a good idea, but it becomes a large overhang on boats where the foredeck has to be high enough for crew to work on it. Harryproas have the overhang, but fill it in with a replacable section made of impact absorbing foam, backed by a strong, steeeply angled bulkhead. Gives the advantages of waterline length and less pitching plus easy repairability. This can also be done while afloat.

    Comment on earlier post:
    W was an amazing boat and project. A single telescoping beam made from Whitbread 60 sail battens with tricky little joining pieces built in an ex hospital autoclave, 2 hulls free to pitch independantly, an unstayed prepreg carbon mast built in a steel mould at 130C and 6 atms pressure (excess resin poured out), a tricky half mould which worked for all 4 hull halves, kick up beam mounted centre board, single rudder, an owner who never said no to trying new ideas and a workshop next to a couple of exceptional boat builders/sailors who started work at 4 am, knocked off at 3 pm and drank beer/partied/sailed till at least 8 pm, pretty much every day for the 4 months it took me to build the boat. Fun times, doubt i could handle the pace nowadays. The owner was not interested in racing, so it was never developed to anywhere near it's full potential. Not sure where it is now.
     
  2. cavalier mk2
    Joined: Mar 2010
    Posts: 2,103
    Likes: 46, Points: 48, Legacy Rep: 214
    Location: Pacific NW North America

    cavalier mk2 Senior Member

    Cheers Rob!
     
  3. waynemarlow
    Joined: Nov 2006
    Posts: 409
    Likes: 35, Points: 28, Legacy Rep: 134
    Location: UK

    waynemarlow Senior Member

    A better idea of how a ring beam on the TC 601 of Clissolds design fits into the build.
     

    Attached Files:

  4. oldmulti
    Joined: May 2019
    Posts: 615
    Likes: 354, Points: 63
    Location: australia

    oldmulti Senior Member

    For a short deviation. Charter cats are required globally to provide tourists with often a day experience to a reef etc. Cats have proven popular having a better motion for non sailors etc. But charter companies want cheap effective vessels that will carry passengers safely. So specialist companies have appeared who provide a fairly standard product. One is the Ocean Voyager series. This boat is the 65 the foot version but you can get a 52 to 85 foot versions of the same cat (the hull shape is shame just extended out with insert sections). At 65 foot the length to beam of the hulls is 12.5:1. Basically, 2 hulls, a hard bridge deck and seating for EG 48 people with a few toilets in hulls and a galley for some food. The Ocean Voyager 65 is 65 x 32 foot weighs 38000 lbs and displaces 45000 lbs. The sail area is a 1100 square foot main and a 500 square foot solent jib. What does this mean? In 20 to 25 knots of true wind gets 9 to 10 knots to windward and 17 knots reaching under asymmetrical spinnaker.

    The construction is equally simple. The hull bottom and deck top come out of the same mould (the deck is cut off aft) and is solid glass 13 mm thick. The hull sides and hard bridge deck is a 32 mm thick balsa sandwich of 25 mm balsa and 4 mm glass water side and 3 mm glass inside. For perspective a Lagoon 38 hull near the fixed low aspect ratio keels are 12 mm solid glass. The cross beams are big aluminium tube sections. Also the 2 x 70 horsepower desils engines on this boat ensure it meets its schedule.
     

    Attached Files:

  5. oldmulti
    Joined: May 2019
    Posts: 615
    Likes: 354, Points: 63
    Location: australia

    oldmulti Senior Member

    There is another thread on plans for an A class cat. I looked into it until I read this article. These boats are getting very advanced. Sorry that in 2 instances you will have to look at attachments for graphs relevant to text. The hull and beam structure are relatively easy. The foils and foil support structures are the hard part to get a controllable A class.

    TECHNICAL DEVELOPMENT PAPER by Martin Fischer. The MayFly is a new A-Class Catamaran design. The boat was designed by Martin Fischer, with help from Jakub Kopylowicz and Woitech Kaliski. The structure of the platform and the foils was designed by Ryszard Partycki. Martin is known for his F18 designs Capricorn and Wild Cat. The boats name is a tribute to the first successful singled handed foiling catamaran named “MayFly” built in the early 70’s and sailed in the mid 70’s at Weymouth Speed Week.

    Hull Design
    Over the last years the hull volume of high performance beach catamarans has significantly increased. Designers found that wider hulls allow pushing the boat harder in stronger winds but don’t slow them down in light conditions. With the design of the MayFly we have of course followed the same direction. The boat has very flat cross sections, little rocker and a very high prismatic coefficient (lots of volume in the extremities of the hull). This provides for good longitudinal stability and reduces pitching, which is always a problem with the extremely light A-Class catamarans. Today A-Class boats are highly sophisticated designs, and in our opinion, it is no longer possible to find a design that is in all conditions faster than the other designs. It is therefore necessary to make a choice in which kind of conditions one wants the boat “to shine”. We made the choice to have a boat that performs very well in medium to strong winds and we were ready to sacrifice slightly the performance in the very light stuff.

    We ran numerical simulations of longitudinal stability and hull drag for a number of hull shapes and compared them to two existing A-Class designs. The graphs below show the relative drag difference of the tested hull candidates with respect to a reference hull (existing A-Class). Values below zero indicate lower drag and values above zero indicate higher drag. Mayfly graphic 1 = Figure 1: Relative hull drag differences for different hull shapes with respect to the reference hull „l_07“ (horizontal line at y=0) as a function of boat speed in knots.

    The simulations were made for a total displacement of 150 kg while the boat is sailing on one hull. The horizontal line “l_07” at 0.00% represents the reference hull and the blue line “ref_02” represents a second existing A-Class hull that was taken as a second reference. All the new hull candidates were designed to have the same longitudinal stability (resistance against pitch poling), which is significantly higher than the longitudinal stability of the two reference designs. The figure shows that all the candidates that were tested have significantly more drag at boat speeds from 0 to 5 knots. From 5 knots onwards, however, the new hull shape creates between 1% and 1.5% less drag than the reference hull “l_07”. With respect to the reference hull “ref_02” the crossing is also at 5 knots of boat speed, but the advantage at higher speed is significantly bigger. An A-Class catamaran achieves a boat speed of 5 knots in about 3 to 4 knots true wind speed (TWS). Thus according to the results shown above our new hull shape should be very competitive from 3 to 4 knots TWS onwards.

    As most of the current A-Class designs the Mayfly is equipped with curved daggerboards. But in contrast to most other designs the boat uses also lifting surfaces at the rudders. Thus, the boat is gradually pushed up if boat speed increases which reduces the hull drag. The lifting rudders provide additional lift, they reduce pitching and they increase the longitudinal stability, compared to a conventional A-Class design. According to our simulations the foils and rudders create about 60 kg vertical lift while sailing upwind in about 10 knots of wind. We therefore tested all hull candidates not only for 150 kg displacement, but also for 90 kg displacement: Mayfly figure 2 a = Figure 2: As figure 1 but for 90 kg total displacement.

    The cross over with respect to “l_07” is shifted to slightly lower boat speeds – about 4 knots – and with respect to “ref_02” it is even at 3 knots. Furthermore, the drag gain at higher speeds is even larger than for 150 kg displacement. From these results we are confident that our boat will perform well from 5 knots of true wind speed onwards. In the very light stuff the boat might struggle at bit, but this can probably be compensated with slightly fuller sails.

    Foils
    It was already mentioned in the previous section that the boat is equipped with curved foils and with lifting rudders. We won’t go into details on the foil and rudder design, just a few hints: The radius of the foils is not constant and they are twisted. The size of the foils and the rudders was set such that they provide a stable configuration for pitch and sinkage variations. Such a configuration enables stable flight in stronger winds, without the need for a mechanical surface sensor as used on the Moth. We have filed a patent for this type of configuration.

    Platform set-up
    The platform set-up was entirely developed by Jakub Kopylowicz. The boat features curved cross beams that are glued into the hulls. Thus, the deck is completely free of any obstacle. Water passes much easier over the deck and the helmsman can sit anywhere much more comfortably, which is an advantage on downwind courses in very strong winds. The curved beams were designed (shape and structure) by Ryszard Partycki. Furthermore, he was in charge of the structure of the hulls and the appendages. The deck layout is very clean, and the Harken traveller rail is integrated into the deck. Cunningham, mast rotation and daggerboard control can be adjusted from the trapeze.

    Construction
    The hulls are entirely built in carbon epoxy with a foam sandwich. The whole hull layup is made with unidirectional tissues. The outer and the inner skin of the hull are made of two layers of UD tissues, oriented at varying angles with respect to the longitudinal axis of the hulls. This provides for better longitudinal and torsional stiffness than hulls built from woven fabrics or biaxial fabrics. We considered building the hulls with a honeycomb sandwich but refrained from it since it is difficult – and expensive in terms of weight – to ensure water tightness of the very thin outer and inner skin of the hulls. Using Nomex honeycomb instead of PVC foam saves about 1kg per hull. However, in order to be sure that water cannot penetrate into the honeycomb core it is necessary to seal the inner skin and to put additional paint onto the outer skin. Thus the total weight of a honeycomb A-Class hull is more or less the same as for a foam hull, with about the same stiffness. But a foam sandwich is more robust than a honeycomb construction which led us to the decision to use foam. The hulls are built with 7 bulkheads and for superior longitudinal stiffness we used high modulus UD carbon layers. The curved beams are a sandwich composite construction without dolphin striker.

    Rig
    The boat comes with a Fiberfoam carbon mast and with Landenberger sails. It is of course possible to choose a different mast or sail. We are also working on a wing mast that represents about 30% of the total sail area. First tests have been made but it is too early to draw any conclusions.

    1st Sailing test , report by Fischer: “Over the weekend I was in Poland and we tested the Mayfly. We had 3 Mayflys on the water and there were about 6 or 7 other A-Cats. The wind was shifty and gusty between 12 and 18 kts, the strongest gusts may be 20 kts. Downwind the MayFly was clearly quicker than the other boats. With the MayFly it was possible to do the downwind course on the trapeze, whereas the others were already limited due to nosediving. The speed difference was very clear. Upwind the boat speed was good, as quick as the others, sometimes may be quicker, but not as superior as downwind. Overall it was a very promising first test for us. The set-up of the lifting rudder surface was not 100% right, so we are confident that we can improve the downwind performance.”
     

    Attached Files:

  6. oldmulti
    Joined: May 2019
    Posts: 615
    Likes: 354, Points: 63
    Location: australia

    oldmulti Senior Member

    A class boats are being home built by some. John Lindahl LR6 A class uses Corecell M-80, 3/8" thick with 5.8 oz (200 gsm biax) IM carbon skins, laid on the bias on the inside and 0-90 on the outside. Proset Epoxy resin. Also added some tight weave 3.7 oz. glass in some spots. Beams are filament wound from Forte. Beam attachment is carbon fibre wrapped under the beam onto the hull as well as over the beam to the hull. Creates a stiff boat. The board passes through a slider at the hull bottom bearing pivot and the angle of attack (AOA) can change from +4 degrees to -2 degrees. The rudders complement the foils in stabilising the ride. The ‘L’ solution adopted does away with the junction drag associated with ‘T’ or ‘+’ foils and the angle of the tips is carefully optimised for dynamic effects. L rudders are also a more practical solution than kick-up rudders. The jpegs give an idea of the build process. Look at LR 6 https://lindahlcompositedesign.weebly.com/lr-6.html

    Another A class builder Larry Woods, a friend of Lindahl said: No real drawbacks to using strips vs larger sheets since you glue each strip and the clue is generally stronger that the foam. Corecell is easier to work with wet layup than with nomex, wet lay up is more difficult to get even fillets around each honeycomb. Nomex is stiffer and a little lighter, but realistically the longest unsupported section of the hull is about 6 to 7' So in my opinion, not enough hull flex to worry about. The water issues are not a problem with the closed cell nature of the corecell. I bought my beams last time around, but I think I would build my own on the next go around. I will build a female mold and use an inflatable mandrel to make my own beams in the future. The right amount of uni-directional carbon and some woven sleeve materials will be fine. Putting a curve into the beam and then bending the ends down and burring them into bulkheads in the hull really stiffens up the beams and the entire platform. Wrapping uni around the attachment points and down the sides of the hull helps stiffen and spread the twisting forces. Next time will build the curved beams as mentioned and attach to bulkheads.

    For comparison the bench mark in the A class is the DNA Fx1 an 18 x 7.5 foot with 150 square foot of mainsail area. The Fx1 weighs 120 lbs and has a recorded top speed of over 29 knots. Hulls and beams are made of carbon prepreg, cured in one production run to avoid secondary bonding. The main and rudder foils have rake control. The rudder/foil rake control cylinder can be seen in the jpegs. Z-boards and L rudders - are carbon prepreg, autoclaved.
     

    Attached Files:

    Last edited: Jan 7, 2020
  7. patzefran
    Joined: Feb 2011
    Posts: 184
    Likes: 13, Points: 18, Legacy Rep: 10
    Location: france

    patzefran patzefran



    May fly is one of the first design of foiling A cat, she was discontinued because she didn't reach claimed expectations. Main problem was steering, as the foil was way too forward to balance the CoE of the sail !
     
  8. oldmulti
    Joined: May 2019
    Posts: 615
    Likes: 354, Points: 63
    Location: australia

    oldmulti Senior Member

    We will go back in time to the Yachting World magazine 1967 Multihull Design Competition Joint Winners. This is to highlight just how far we have advanced in multihull design and structures in 50 years. The designs were advanced for there time and the first tri “Inca” could be built today (hopefully in modern materials) and probably would perform well. The second tri “Dorado” shape may not work as well but it has a feature of an angled retractable foil set at 45 degrees in the floats that designers today are still perfecting.

    “Inca” is a 42 x 25.25 foot trimaran that displaces 11700 lbs and carries 720 square foot of sail in main and foretriangle on a 50 foot mast. The main hull length to beam is 6:1. This was fairly standard cruising tri ratio’s at the time. The major changes over the last 50 years in trimaran hull shapes has been in the forward with waterlines going to the bow tip on the main hull and floats and becoming fuller. The structure of this boat is where the main changes have come. EG the main hull skin from the outside is 3 layers of 600 gsm CSM, 3 layers of 800 gsm woven rovings on top of expanded polyurethane foam of 0.8 lbs/ cubic foot topped with 5 mm gaboon ply and 1 layer of 750 gsm CSM. The foam is weak and would soak up water and crumble over time, but the heavy fiberglass external skin would probably good enough to hold the boat together. The cross arm structure would need some serious work but it did have a balsa core deck of 12 mm with 750 gram CSM on either side. The concept and accommodation is very good but the structure and hull shapes do not compare with modern tris which are much better in structure and performance.

    The second design is “Dorado” a 36.5 x 20.9 foot tri that displaced 5000 lbs and carries 600 square foot on a wing mast. This boats fully battened main on a wing mast with float foils was seriously advanced thinking for its time. Features that have been developed further even today. But this boats float design and total boat structure are not as advanced. The hull structure is 7 layers of 3 mm timber with 2 x 225 x 37 mm longitudinals running half the bottom length and many 100 x 19 mm stringers also supporting the bottom. Seriously over specified. The coach roof is 6 mm solid glass. This structure would probably be heavier than the optimistic displacement figure. Now the float foils they are 4.75 foot long by 1 foot wide and made of solid stainless steel. Partially bullet proof and heavy. Again the ideas are good the design concept and structure not so good.

    As you can imagine there were several letters to the editor in the next couple of issues criticising both tris but the major concern was Dorado’s foils with one person saying the tri would not go fast enough for the foils to work and they would not create any lift as the tri would shake the foil so much it would suck air. Hmm. Times have changed. But I also give you the page in Yachting World which followed the design winner announcement. Draw your own conclusions.
     

    Attached Files:

  9. oldmulti
    Joined: May 2019
    Posts: 615
    Likes: 354, Points: 63
    Location: australia

    oldmulti Senior Member

    The following 40 foot cat is designed by S Langevin, a french designer who designed the Edel 26 and 33 production cats and a variety of multi’s from racing tris to 80 foot charter cats. The cat being discussed is 40 x 20.3 foot displacing 12500 lbs and carrying a 420 square foot main and 440 square foot genoa on a fractional rig. The length to beam on the hulls is 10:1. The boat in the jpegs was built in 1996 by an amateur in France. The design can be built in foam sandwich or aluminium. This boat was built in foam and balsa sandwich. Another design I will show later was built in foam glass but shows the creativity of Langevin.

    The reason for the design being shown here is the accommodation layout which in the plan is interesting but as per usual the builder became creative and built his version of interior. Wood features heavily here. This is a sensible conservative design that will be good for a cruiser.
     

    Attached Files:

  10. oldmulti
    Joined: May 2019
    Posts: 615
    Likes: 354, Points: 63
    Location: australia

    oldmulti Senior Member

    S Langevin produced many other designs so I will focus on 2 interesting ones. Both are 50 foot cats. The racer is the junior model to the 70 foot Roger and Gallett racing catamaran. The racing cat is Catapulte 50 and is 50 x 27.9 foot displacing 7800 lbs and carrying 1430 square foot in main and genoa on a fractional wing mast rig. The length to beam on the hulls are 18:1. This is a foam glass boat with a fabricated aluminium box mast and rear beam with an aluminium tube fore beam.

    The cruiser is 50.8 x 29.5 foot displacing 10000 lbs. The 59 foot aluminium mast carries a 785 square foot main and a 700 square foot genoa. The length to beam on the hulls are 14:1. This cat is built from full foam glass in the hulls and crossbeams. The main mast cross beam is of very large dimensions allowing 2 double berths in it. The large rudders are also kick up. Very useful for cruising. The accommodation layout is good. A couple could go long term cruising in this boat if there were electric winches, furling headsails etc. This is not a roomamaran, it could really sail and 300 mile days would be possible.

    I would have liked to see a race between these 2 boats. I suspect the cruiser would perform very well against the racer.
     

    Attached Files:

  11. oldmulti
    Joined: May 2019
    Posts: 615
    Likes: 354, Points: 63
    Location: australia

    oldmulti Senior Member

    The next 3 Langevin cats just show the variety of his designs. The small “demountable” 26 x 16.25 foot cat weighs 1570 lbs and carries a 280 square foot main and 204 square foot genoa. The basic cat can be built in ply or foam glass. The hulls length to beam ratio is 10:1. This is a simple fun boat that with that amount of sail on 2200 lbs displacement would go very well. The accommodation is basic but comfortable. The next boat is a 48 x 23 cat cruiser displacing 22500 lbs. It has a 52 foot mast carrying a 500 square foot main and 610 square foot genoa. The hulls are 10 :1. A simple aluminium cruiser that will da a reasonable job. An d the final cat is one of his smaller (yes he did 80 plus feet ones) charter cats. The charter cat is 66 x 32.8 foot weighing 34000 lbs and carrying a 915 square foot mainsail and 1076 square foot genoa. Combined with the 11 : 1 hulls this boat would sail well whilst carrying its 10 paying guests. Notice the rudder arrangements. The charter cat rudder jpeg is attached and you will find it is a substantial structure. The cat can be built in aluminium or foam glass. The final installment of Langevin multi’s will be a few interesting tris from 25 to 50 feet.
     

    Attached Files:

  12. oldmulti
    Joined: May 2019
    Posts: 615
    Likes: 354, Points: 63
    Location: australia

    oldmulti Senior Member

    The final on S Langevin multihulls is a sample of his trimarans. Again they range from small tri 25 x 17.7 foot foldable to 8.1 foot that weighs 1568 lbs and carries 344 square foot in main and genoa. The real interest in this boat is it is built in aluminium. The folding mechanism is different but having to lift the floats into the road position would require some mechanical assistance. The accommodation is limited but serviceable. The next tri is a 32.8 x 26.6 foot that weighs 5600 lbs and carries 699 square foot in sail area. This could be a minimalist cruiser for 2 over long distances. The floats are a little dated but the concept is good. A choice of foam glass or aluminium.

    Now we get into the serious cruiser. This tri is 50 x 30 foot weighing 19000 lbs and carrying 1470 square foot of sail in a ketch rig. There would be no problems sailing with your closest 10 friends anywhere you wanted to. There is enough space to escape them if required but you would be sharing a loo. Hmm, let me think about this. The hull lines give you an idea of what was an acceptable older hull and float shape of what would be a very comfortable cruiser. The sail area gives a hint of reasonable performance even though it is split over 2 masts. Structurally this boat would be strong due to the full wing deck shape and would be a welders delight being of aluminium construction.

    Finally a racing trimaran 50 x 40 foot weighing 7840 lbs and carrying on its 59 foot mast 1600square foot of sail in its main and genoa. This tri is aluminium with a single large cross beam carrying the small floats and t foils beneath. This boat was built and raced with some success but as Derek Kelsall and Langevin found early aluminium foils had cavitation problems at certain speed ranges and also due to the cavitation the foils developed pitting in the metal and became less effective over time. Two major things have helped foil development. Better sectional shapes and better materials which resist surface foil erosion. As you can see S Langevin was a multi-faceted designer who could turn his design mind at many styles of multihull.
     

    Attached Files:

  13. oldmulti
    Joined: May 2019
    Posts: 615
    Likes: 354, Points: 63
    Location: australia

    oldmulti Senior Member

    The following cats are closely related and I will deal with them together. Dudley Dix is an ex South African designer who now resides in the US. He has designed mainly mono’s but has done some very good multihulls as well. His main focus is wood construction but has done metal and foam glass. The 2 cats are The Dix 470 a 46.75 x 25.33 foot cat displacing 23300 lbs and carrying 1099 square foot of mast head rig main and jib. The second cat is the Dix 430 a 43.1 x 22.6 foot cat displacing 22700 lbs with a masthead rig carrying 911 square foot main and jib. Both cats displacement is very similar and the length to beam on the hulls are about 8.8:1 on both boats. These boats are best described as performance cruising catamarans capable of carrying a family a long distance.

    The structure of these boats is the main focus as they are very similar. The hulls are 22 x 44 mm WRC stringers at about 225 mm centre lines on 12 mm ply bulkheads and 18 mm ply bulkheads for attachment to the main cross beams. 9 (10) mm ply covering the majority of the hull with radius chines. The chines are 3 layers of 3 mm ply over a short former then cut to size to fit the hull shape. The decks are either 3 x 3mm ply or 9 mm ply depending on the deck cabin curvature on very closely placed deck beams about 225 mm centre lines on cabin roof or deck stringers on fore and side decks. The underwing is 9 mm ply or forward 3 x 3 mm ply BUT it has an internal framing matrix and another layer of plywood on the inside for a total thickness 60 mm. There is Styrofoam inserts between the stringers in the underwing.

    The cross beam structures are 18 mm plywood with 2 layers of 600 gsm biax on either face and an additional 2 layers of 600 gsm biax at 45 degrees on the joints between the 18 mm hull bulkhead and bridge deck cross beams. There is additional 44 mm wide by 88 mm deep timbers on the bottom and top flanges of the 18 mm ply beams. The rudder shafts are 73 mm schedule 80 stainless steel pipe. They are put inside a 90 mm PVC pipe wrapped in 8 layers of 450 gsm biax tape. One boat has a hydraulic steering system shown in a jpeg.

    Folks these are well engineered boats but the are complex things to put together. You literally have thousands of bits of timber and ply to cut, fit, glue, sand, West, fillet, glass, fill and paint. This is where I start to think a flat panel foam glass structure for EG the underwing would be a lot faster to build and finish. The final cost of this boat may be slightly cheaper than a foam glass version but in boats this size it’s the equipment costs that make the real total cost difference. A luxury fit out will be much more expensive than the build materials. The jpegs are of the 2 designs and the build of a Dix 470.
     

    Attached Files:

    bajansailor likes this.
  14. Tony.Ellen
    Joined: Nov 2019
    Posts: 5
    Likes: 1, Points: 3
    Location: Sweden

    Tony.Ellen Junior Member

    Oldmulti
    Excellent thread you have created.
    A bit of information in video form from my friend the builder JJ and designer Dudley Dix and his DH550 built in South Africa. It is a short documentary he made. It is high quality given his professional backgrounds. Explains those thousands of little bits of wood well.
    18 month professional build from memory.
    DH550 basic spec
    Length/Beam ratio floating at DWL is 8.96. She is a fast cruising cat, not a racer. That said regularly reported by owners on passage averaging up to 12 knots with one owner achieving 300/24 passage so performance hulls doing their intended job as you mention while carrying the home safely.
    Calculated lightship displacement is 12200kg and loaded displacement is 17000kg.
    She can dry out on a sandy beach. Contact points would be the toe of each rudder and hull centreline about 500mm aft of the front of the bridgedeck. The props will be clear of the ground.
    Structure was intended from the beginning to be BS1088 okoume (gaboon) plywood.
    Dudley will draw any layout design changes and supply the drawings to Exocetus so that they can adapt their kit files to the new layout etc. A side note Dudley has a 50' version of the 470 in build from a kit he redrew for the owner so a very versatile design.
    Full kit options are available including preformed radius chine materials from Exocetus in UK with an Australian contract cutter available for local market. Enjoy
    Kits http://www.exocetus.net/kits.html

     
    Last edited: Jan 10, 2020
    BlueBell likes this.

  15. oldmulti
    Joined: May 2019
    Posts: 615
    Likes: 354, Points: 63
    Location: australia

    oldmulti Senior Member

    We will now talk about one of the fastest boats in the world. Hydroptère is a 60 foot long x 74 beam foiling trimaran that was launched in 1994. Alain Thebault pushed the concept and got the design done by VPLP. The design is based on experience from a range of hydrofoil sailcraft that Thébault built in cooperation with Eric Tabarly since the 1980s. On 5 October 2008 she reached a record speed of 52.86 knots (97.90 km/h; 60.83 mph), however this was over a shorter distance than the 500m necessary to qualify for an official world record. On 21 December 2008, the Hydroptère briefly reached 56.3 knots (104.3 km/h;60.8 mph) but capsized shortly after.

    In 2015 Hydroptere took 11 days to do the Transpac in light winds, it did 35 knots on the first day but conditions went light. The boat was abandoned in Hawaii and subsequently sold by the harbour authority for under $20,000.

    In 2010 Thebault built Hydroptère.ch a Franco-Swiss development foiling catamaran as a precursor to the Hydroptere maxi being proposed to circle the globe in under 40 days. CH was 36 foot long x 49 foot beam and capable of carrying 2200 square foot of sail. The boat worked well but it was a development version exploring the use of T foil rudders on floats of a larger boat. The next proposal was started in 2008 and was for a Maxi Hydrofoil project, which consisted of creating the fastest trimaran in the history of navigation. Alain Thébault wanted to beat the speed record (pass 50 knots) and go around the world in 40 days

    The hull and the floats of the foilers were made of several layers of carbon fibers and separated by honeycomb structures (NIDA or NIDAPLAST) The whole hull is covered with a layer of Kevlar.

    Hydrofoils also use the same materials, the lateral foils also having a leading edge in carbon composite (replacing the aluminium of the first versions). On the Maxi Hydroptere they measure six meters, weigh 240 kgs and are terminated by vertical foils. The lateral foils are held at an angle of 42 to 45 ° by titanium arms. The amount of the rear foil measures 3.30 m and it has a flap of 55 cm which controls takeoff.

    One feature used on all versions is a clipper or force damper Hydraulic cylinder invented by André Sournat. A hydrofoil sailboat, like the Hydroptère , is carried by the dynamic pressure of the water on its foils (It is the lift). There comes a time when this force becomes very strong and can damage the boat, hence the idea of placing a shock absorber, the clipper. This allows the foils to fold a little if the lift becomes too high, so this force decreases and becomes normal (sufficient to make the boat fly). The jpegs show the 60 foot version the CH version and the proposed Maxi. I suspect AC foilers and other maxi tri foilers finally killed the Hydroptere concept.
     

    Attached Files:

    bajansailor likes this.
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.