Multihull Structure Thoughts

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

  1. YoungGrumpy
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    YoungGrumpy Junior Member

    More specifically, I am wandering if Mr. Kohler has a definitive opinion on the performance of the biplane rigs. He states optimistically the benefits (obvious even to my untrained eye) both in building and sailing.
    The Duo800S shows the plan with the rig, stating that the sloop is an option that would work too. The hulls looks like it could be reasonably fast, and it would be a shame if the Bi-rig would not work upwind well (wide angle or sluggish to tack?).
    I looked on some Pics/videos of the Radical Bay 8000, in addition to the "Original" with two curved Hi-performance -looking one, there are some with small headsails on them.
    Makes me curious if a light cat really needs a headsail to tack reasonably fast.
     
  2. Bruce Woods
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    Bruce Woods Senior Member

    Just to be clear. XL2, in perfect , strong downwind conditions, with full , experienced crew, averaged less than 15 knts when they set the B2G record in the 90's, sailed at times in the standard reckless manner required to win races and set records. (one only needs to look at the trail of capsized racing multis to appreciate this point


    Many precious attempts in less than ideal conditions were no where near this average.
     
  3. oldmulti
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    oldmulti Senior Member

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  4. oldmulti
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    oldmulti Senior Member

    The final article on the Triptyque series of trimarans. Both of these designs may not have been built yet so take them as preliminary designs but I am trying to give the breath of the designer’s work. The first design is the Triptyque 34. A cruising trimaran of 32.6 x 21.7 foot that can be folded to 8.33 foot for transport. The 34 weighs 5000 lbs and displacing 7800 lbs. The 34 carries 740 square foot of sail. It’s a ply epoxy design. This is about the maximum transportable trimaran that I could envisage a person transporting around. I know a guy who owns a F31 and he gets very nervous when he drives through any city streets. Its performance should be OK based on the displacement and sail area etc.

    The next Triptyque is the 38/40 foot. This tri is a serious cruiser that can have its beam reduced for marina’s etc. The tri is 38 or 40 x 26.2 foot capable of folding to 10 foot. The 38/40 weighs 5800 to 7200 lbs depending on the build technique and equipment in the boat. The displacement 10,700 lbs. The sail area is 656 square foot main, solent 365 square foot, mast 55 square foot and gennaker of 800 square foot. Again, the performance of this design should be good.

    Th 38/40 is a big boat and will take a fair bit of effort to build even in plywood epoxy. The cross arms in the 38/40 design appears to be a built structure not a commercial aluminium section which will involve more work.

    The Triptych's hull retraction system cross arm halves are one unit and can withstand significant shocks without deformation. The cross arm halves slide in slots beside each other in structural units in the main hull. The guides and rollers used during the retraction of the side hulls are not subjected to any load once the safety pins are in place. The rigging forces are taken up through the side hulls by retaining sea stay cables taken from structural bulkheads of the central hull to the floats. Once the sea stays are stretched, the arms only work in compression. However, the cross arms have been calculated to resist the bending generated by the boat's maximum righting torque to provide maximum reliability of the system. The rollers are interchangeable without disassembly other than removing the retaining cable and releasing the arm from the slide: just remove them and put the new ones back in place. A visual verification operation must be carried out every year (without dismantling), and the change of the rollers is no longer necessary since the use of a plastic resistant to heavy loads. The reason for the curving is to push the floats down for more stability in the folded mode.

    The designer has many of his smaller designs in the water and according to sailing reports these designs sail well. With this experience his larger designs should, hopefully, be good boats. Jpegs give the idea.
     

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  5. brian eiland
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    brian eiland Senior Member

    I'll drink to that, ....plus you might be able to keep them clean without having to haul the whole boat.
     
  6. oldmulti
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    oldmulti Senior Member

    To partially answer Young Grumpy about Bernard Kohler biplane rig I present what Bernard says is a high performance biplane catamaran. The DUO 1000 is 32.5 x 20.8 footsemi tube cat that weighs 3600 lbs and displaces 7000 lbs. The sail area is 645 square foot in total on 2 masts. We will focus on the boat sports a biplane (parallel) rig.

    Bernard designed the rig concept in 1983 on DUO 425 then experimented with a bend gaff/yard and sleeved sails on a mast in 1986. The design of the DUO 1000 biplane wishbone rig is different. It is a further development with the wishbone stabilizes only the upper mast part which is the outhaul for the peak of the sail. There is no Aluminium mast profiles and no battens are used, so the rig is relative cheap.

    The masts are made from fiberglass poles as base. They are built up to sufficient strength by adding Unidirectional carbon fiber and fiber glass. Slats are attached to the side of the masts can be added to streamline the rig more. The sail is rolled vertical. The roller construction comprised only of the upper swivel which is direct attached to the sail. As bolt rope a Dyneema rope will be used. The roller at the base of the sail again, is connected direct to the sail.

    Bernard has used the vertical roll sail system successful with a wishbone gaff and has sailed thousands of miles with this rig and it never let him down. The top mast acts as an end plate (winglet) to make the sail even more effective. The mast can rotate to increase or decrease the twist in the sails. The boom is self-containing, so no topping lift is necessary. To set sails is a matter of seconds (typical we needed 20 seconds to set the sail). Compare this to your boat with a normal main sail. Handling the sail is more or less fool proof and is done from the bridge deck.

    It’s a plywood/glass/epoxy structure with timber stringers and plywood bulkheads. The hulls are multichine. The construction time estimated by the designer is 2000 hours. Possible if you have some experience.

    The hulls have the accommodation and the main beam is large enough to allow you to crawl through to get from one hull to another. The big open bridge deck is perfect for handling the boat and lounging.

    Now according to the designer, the boat has a maximum dynamic stability of about 55,000 foot lbs at full load. The speed prediction stops at a wind speed of 25 knots when a hull will lift off the surface of the water. The boat speed will be then about 22 knots. The predictions are made with a safety factor of 60% (wind fluctuation).

    As to its windward performance based on other biplane multihulls it can be good if the rig is efficient. Bernard has more experience with biplane rigs than most designers in the world and this is a good design. I suggest it will be an good all round performer. Jpegs give the idea.
     

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  7. Banzai
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    Banzai Junior Member

    Oldmulti: his name is Bernd, not Bernard. Now we have got that out of the way, please note that image number 10 is in fact from the Duo 480, my boat under construction back when. I think the mixup occurred at Bernd's site. In answer to earlier comments about Bernd's boats please note that English is not his first language which accounts for some of the slightly odd wording in his comments and literature. About bi plane rigs in general: Going to windward is not the issue and is actually one of the best points of sailing. It is flat reaching that is a bit marginal when one sail partially blankets the other. Windward performance is partially dependent on whichever system of leeway prevention is employed. In the case of the Duo 480 it relys on its asymmetric hulls so think Hobbie14/16 : passable . Bernd trys to come up with methods for home building various components as a lot of his customers are from countries where sailing gear is either very expensive or just hard to get. Plywood is still a good system for home building IMO despite Mr Denny's insistent contributions
     
  8. oldmulti
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    oldmulti Senior Member

    Banzai. Thanks for the information and corrections. I apologize to Bernd for the misspelling of his name. If anyone or if Bernd reads this thread at all, any further information on the Maxiweb G32 copy would be greatly appreciated. The Maxiweb and Ocean Swift are 2 cats that have created some interest.

    [​IMG]
     
  9. oldmulti
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    oldmulti Senior Member

    Coast 50 is an aluminium cruising catamaran designed by Philippe Renaudeau of PHR yacht design. The cat is 50 x 25.75 foot that weighs 28,600 lbs and displaces 33,600 lbs. The 65 foot aluminium mast carries 860 square foot main, 450 square foot self tacking jib and 650 square foot genoa. Developed for long term, short-handed ocean sailing in comfort the Coast 50 has several features.

    The Coast 50 has swing up centre boards and rudder blades. Each keel has replaceable fuses which allow the keel to swing up if it were to strike a submerged object to minimize damage. The Coast 50 is built in aluminium and according to one builder is much stronger, at a cost close to that of a fiberglass catamaran of the same specification.

    When you look at the build jpegs you will find 2 versions of this cat. One is a full aluminium version with the deck house is in aluminium, the second was going to have a composite deck house fitted. As you can see building an aluminium cat may be a fast method but it involves thousands of pieces that have to be welded together. The speed of an aluminium build comes from using simple cutting and shaping equipment to make the parts, and the speed of the welding. If you leave an aluminium boat unpainted you have a really fast build. Fair and paint an aluminium boat and you will be back to a similar build speed of a foam glass boat.

    Also for safety reasons, there are the crash boxes in the bow, the 2 swimming ladders that can be opened from the water (in the event of a fall) but also the 4 (!) Spaces provided for life rafts, 2 of which are accessible from the bottom of the hull in case of overturning. The front beam is also equipped with 2 complete anchors ready for use.

    Designed for oceanic sailing with a small crew, the Coast 50 design emphasizes comfort, with a large open and spacious cockpit / lounge deck. The owner's cabin is located in one of the hulls, and includes a double bed, shower room and wc, as well as a storage / workshop area. The other hull includes a cabin with two beds as well as a cabin with a modular bed according to the number of guests. The two helm stations are placed under the aluminium bimini and benefit from good visibility. The bimini and deckhouse have been designed with a rainwater collection system, which can be channelled directly into one of the tanks.

    This design is a solid cruising catamaran of which several have been built. A nice global boat.
     

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    Last edited: Aug 4, 2020
  10. oldmulti
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    oldmulti Senior Member

    Folks seek and you will find. The Bernd Kohler Maxi is a homage to Meade Gougeon and his G32. I have limited (and occasionally conflicting) information on the design but the idea is very clear.

    The Maxi is 26.25 x 8 to 8.5 foot wide depending on where you live for trailing. The boat weight is 1700 lbs with a displacement of 3300 lbs. I do not know if the displacement figure includes the optional water ballast of 570 lbs in each hull available for extra stability in stronger winds. The mast is a 180 mm carbon fibre tube that has no spreaders to allow the 160 square foot mainsail to roll around the mast. The mainsail has semi vertical battens to hold up the fat head. The head sails range from 120 square foot to 170 square foot. Now there was an earlier version of the rig which had a roller furling boom for the mainsail. I do not know if this is in the final design.

    The length to beam of the hulls are 16 to 1. The hulls are easy to build Sharpie (flat bottom with a slight lift of chines at bow) hulls. The build will be plywood and wood in epoxy and glassed over, as with Bernd’s other designs. Bernd’s build time estimate is 500 hours. The rudders and boards are kick up in case you run aground.

    Now we come to the elephant in the room. It’s a narrow cat for its length. Bernd designed a fold out seat to let a person sit out further and add to the stability. The water ballast when used appropriately will add to the stability and performance. Bernd did some calculations (shown in the jpegs) about stability and performance. There was a light displacement mode where the cat would average 9.1 knots lifting a hull in 17.44 knots of wind to a heavy displacement mode where the cat would average 8.94 knots and lift a hull in 19.18 knots of wind. I do not know if the numbers include water ballast or not.

    The Gougeon 32 forum very clearly indicates these types of cats are sailor boats. The skill of the helmsman and person who trims the sails really make the difference between a fast cat and learning how to self right a G 32.

    Now when it comes to self righting the Maxi is very similar to the G 32. They are designed to be self righted after they capsize. The Maxi has a mast head float and which keeps the mast above the water when capsized. The water ballast and weight of the boat will right the boat one rigging on one side has been released (eased) 10 degrees. The jpeg gives the idea.

    The accommodation in the Maxi is similar to the ECO 5.5 cabin (2 jpegs attached). An interesting design. As I said I am working off some secondary information sources so this may not be the final version of the design.
     

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  11. catsketcher
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    catsketcher Senior Member

    I think the comment you quoted is an example of cognitive bias. I can't think of many (any?) times a crewman has been hurt by hitting something with a daggerboard and stopping. There are thousands of daggerboard boats and very few (none?) examples of people being hurt by sudden daggerboard stopping. I think we sometimes see what we want and there are heaps of daggerboard boats doing great work and none of the people I know have been hurt by this. Surface piercing foils are often more prone to ventilation and the pivoting bridgedeck centreboards found in early off the beach cats were almost all replaced by daggerboard cats (I think in Australia the Arrow still has the boards, but it is a rarity nowadays although it used to be more common ).

    Cleaning a daggerboard is really easy. You pull it out, clean it up, antifoul it and put it back in. All good.
     

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  12. YoungGrumpy
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    YoungGrumpy Junior Member

    It is the case/slot that is a pain to keep clean, not the board! Not best example of the breed is the Seawind 24 I've got. I keep the boards on the deck, clean and smooth. In the fertile waters of NE USA if I am away for more than a week, I have a hard time to push the board back. (antifouling the insides is another spring time exercise!)

    But. To quote a more educated person "most of what we know of fluid dynamics was discovered by trial and error". I'd love to see somebody to do the direct comparison of two identical cats... you understand.
    Up to that point, I would say, that both arguments sound quite convincing, however, I remember reading some article about Stiletto 27 if I am not mistaken. The boat was originally with one board from the bridgedeck. New owner refitted the rig, and put a pair of boards in the hulls, going after performance improvement. Was it because the original was poorly designed/engineered or was it inherently inferior to the Board-from-the -Hull? I do not know
     
  13. oldmulti
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    oldmulti Senior Member

    After yesterday’s Maxi, a homage to the Gougeon 32, we will talk about the Gougeon 32. The Gougeon 32 is 32 x 8.3 foot that weighed between 1200 lbs to 1400 lbs depending on when it was manufactured. Most cats weighed about 1600 lbs with motor and rig. The displacement is 2200 lbs. Now the fun begins. The G 32 also can optionally carry water ballast of 600 lbs per hull. So you could end up in heavy weather, with a “displacement” of 3000 lbs if you had full water ballast and a 2 person crew. The original aluminium mast carried a main sail of 187 square foot, a jib/genoa of 109 square foot of sail area. The jib has roller reefing and the mainsail rolls around the boom. The foils are of a centerboard type that will retract if they hit something.

    The hulls length to beam is 20 to 1 and are wave piercing . Why so fine? When you have cat hulls relatively close together for the cats length, wide length to beam hulls (eg 10 to 1) drag waves and create a combined wave pattern between the hulls. Richard Woods did research and found this wave pattern slowed a cat down until the hull centrelines are about 40 % plus of the water length apart. The other way to reduce this wave pattern appearing is to have extremely thin hulls (greater than 16 to 1) which minimize hull created waves. Result you see jpegs of the G 32 travelling at speed with virtually no hull waves.

    Also, the fine hull ends on the G 32 are another feature of 16 to 1 plus hulls. Hugo Myers did tank test work and found fine end hulls had no effect on performance once the length to beam is greater than 16 to 1.

    Now the structure of the G 32 was subject to more research than most other production boats. I won’t go into all the options, but the final structure was done in molds and used infusion techniques. The hull layup is a polyester gel coat then a 495 gsm biaxial e-glass with 225 gsm CSM 9 mm balsa 600 gsm 0/90 e-glass in epoxy. The underwing was similar but with 12 mm balsa. There was some ply in the bulkhead crossbeams and some foam. There were 14 boats built before the cost of producing the boats exceeded the sale price.

    Now we learn more about 30 year old cats. The polyester gel coat on some of the G 32 cracked letting water into the epoxy balsa structure resulting in rotten balsa in some area’s. The areas varied depending on whether the boat is trailed or not etc. Result some owners had to replace rotten core in several areas and several went through the pain of chipping off all the exterior gel coat on the G 32. The result was a 100 lbs boat weight reduction after you applied an epoxy paint system. Russell Brown did an excellent blog on his refurbishing of his G 32 “G-Wiz”. Russell also changed to a carbon fibre mast and made other carbon components to lighten and enhance his G 32. Result G-Wiz is lighter than other G 32’s which probably helped him win the solo division in the Race to Alaska. PS Russell is a very good sailor and seaman but even he has capsized his G 32 when hit by a mechanical failure, but he was able to self right it with only getting his boots wet. There are Gougeon 32 promotional videos “Part 1- Gougeon 32 Catamaran 1991 Promo” and “Part 2 - Gougeon 32 Catamaran 1991 Promo” shows the process in reality. It only takes 10 minutes from capsize to sailing again.

    2 jpegs show the sail versus wind chart recommended by the builders. The performance of the G 32 is spectacular. We have a boat, that if it is sailed by a good crew, can exceed 20 knots boat speed. It can handle 30 knot winds plus when reefed down. The reefing systems on the boat allow you to dial in the sail area required to maintain speed across the wind range. You need to be attentive but this boat rewards good sailors.
     

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    Last edited: Aug 6, 2020
  14. oldmulti
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    oldmulti Senior Member

    Sail power can come in all forms but one of the more unusual is Flettner rotors, the sail devices were originally invented in the 1920s.

    Flettner rotors are vertical cylindrical structures that are installed on the deck, often with horizontal disc-shaped blades at the top and sometimes down their length. As the name implies, they are free to rotate around a mast, and do so under the influence of the wind. This rotation creates a thrust due to a phenomenon called the Magnus effect, in which a spinning body in a moving airstream generates a force perpendicular to the direction of the airstream. A German engineer Anton Flettner launched the first experimental ship in 1924. Jacques Cousteau built a hybrid diesel-Flettner ship called the Alcyone in the 1980s and has done thousands of sea miles. Flettner rotors are powered to make them spin to create the Magnus effect.

    In about 2008 a serious experiment was done to understand if Flettner Rotors would work on a trimaran. The tri chosen was a Brown 34. Any reasonable cruising tri or cat could have this modification as long as the boat can handle the weight aloft and especially the weight in the ends of the boat. We will focus on the rotor build and powering.

    Two 4.5 foot diameter rotor core tubes were built. The forward (main) one was 27' long and the aft (mizzen) was 21' long. The rotor cores had 8 foot diameter discs placed on the cores 3 foot apart. They were sized and positioned to center the lift in a similar place to the sail-powered version of the Searunner 34. A 48 DC electric motor (10 HP golf cart motor) powered each rotor from a bank of batteries wired through a speed controller. The controller throttle access was conveniently positioned in the cockpit for the helmsmen. Battery charging required a shore power plug-in at the dock. The batteries to power the Rotors can in this tri last about 8 hours without recharging. If the tri had solar panels and bigger batteries or a small generator the tri would no require any additional shore power.

    Each rotor was a large, smooth cylinder, supported by ball and roller bearings. Since the surface area of the fences and cylinder was quite large, a foam/carbon fiber sandwich construction was chosen to keep the weight down. We made each cylinder in a cylinder mold in four longitudinal sections with joggle seams at the joints. Coring foam was beveled at the edges and omitted at the joints and bulkhead attachment areas. The 27'-long panels weighed about 25 lb and the 21'-long panel about 19 lb. The rotors were supported on the boat by aluminium tube stub masts that went half way up the rotor to the mid bulkhead. A pin on the mast top supported a roller bearing, carrying the full weight of the rotor. Another larger ball bearing at the bottom maintained the rotor alignment on the mast and provided an attachment point for the cog belt drive system. We added major structural reinforcement to the boat deck, cabin top and flooring to support the weight and bending moment of the rotors. It was crudely done using multiple layers of plywood to resist the side loads created by the rotor lift.

    The cylinder mould Panel construction employed a metal surface, partial cylinder mold and vacuum bag layup. Cylindrical accuracy for the finished rotor was crucial since it was intended to operate at 400 rpm. (That equates to a surface speed of about 65 miles per hour.) Minor weight differences between panels could cause significant imbalances in the finished rotating structure, so we need the lay-up consistency to be as accurate as possible.

    The mold surface was .040 aluminum sheets, 4' wide by 6' long. Each sheet was butted to its neighbour with self-adhesive aluminum foil tape was used to cover the butt joints on the molding surface, rendering them air-tight. The panel construction consisted of 6 oz plain weave carbon fiber cloth on each side of ½"-thick H-80 Divinycel contour core foam. We started the layup with nylon release fabric against the mold, then used squeegees and roller to wet out carbon fiber cloth. The foam core was precut to dimension and coated with a light mixture of epoxy and 407 Low-Density Filler to fill the surface voids. We transferred the wet foam onto the carbon cloth and positioned it. That was followed by release fabric, baby blanket (quilt batting) and finally, the bag (4-mil poly film). The vacuum manifold was already in place and covered with masking tape. We pulled the tape off the manifold and the vacuum seal and attached the bag, with the pump running. Soon the bag was compressing all layers and the vacuum gauge normally showed about 23" of vacuum. Next, the three ½" plywood bulkheads were positioned and epoxied in place, followed by a third panel. Next we added more ring frames and mechanical gear, then glued the last panel in place. We duplicated his work on our rotors with 8' diameter discs added on 3' centers.

    A crane lifted the rotors into position and slowly them lowered onto the mast. The rotors had to be threaded onto the mast perfectly vertically so that the bearing pin at the masthead would engage the bearing bore on the middle bulkhead, which was only 1½" diameter. The bearing pin had a machined “dunce cap” nut to help hit the target bore. It all worked very smoothly, thanks to the expertise of the crane operator Each rotor was powered by a 10 hp, 48-volt electric motor with a speed controller and a bank of 6-volt batteries. The motors were mounted to the mast on clamp brackets of welded aluminum. A cog belt using pulleys to achieve the correct speed ratio spun the rotors at 400 rpm maximum.

    The initial trials were run in light airs. At first, the boat bounced around in the light chop and swells, but as soon as the rotors started turning, the boat stabilized and became very smooth. It achieved 6 knots boat speed in 6 knots of wind at the best run of the day. The demonstration sailed with about 8 hours of powering time for a single charge on the batteries. Since the winds were light and the rotors only rotated to less than 200 rpm, we had over 12 hours of running time. An interesting concept, although it is what I would call “powered” sailing. I would also like to know how it would perform in heavy airs.
     

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    Last edited: Aug 7, 2020

  15. brian eiland
    Joined: Jun 2002
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    brian eiland Senior Member

    Yes its the slot in the case of a daggerboard,..then the slot and the board itself in the case of the centerboard arrangements.

    There is a long subject thread here that touches on the Stiletto situation as well,..
    Bridgedeck centreboard why don't they work???
    Bridgedeck centreboard why don't they work???
    Bridgedeck centreboard why don't they work??? https://www.boatdesign.net/threads/bridgedeck-centreboard-why-dont-they-work.57051/

    BTW, here was my particular suggestion,..posting #47
    https://www.boatdesign.net/threads/bridgedeck-centreboard-why-dont-they-work.57051/page-4#post-795051
     
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