Multihull Structure Thoughts

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

  1. oldmulti
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    oldmulti Senior Member

    It’s not easy to find jpegs, plans or details of Marc Ginisty's cats but he produces some very interesting designs and builds. He appears to be a limited production designer/builder who now has retired and is cruising on his 49.2 cat. The cat we will talk about is a Kalim called “Marielle” of which I know very little about beyond its length officially. Any other number is an educated guess. Le Kalim is about 49.2 x 28 foot with a biplane rig with 2 carbon fibre 57 foot masts each having a swing wing reefable soft sail rig. The hulls are narrow (length to beam of 12 to 1 or better). The cat has daggerboards and underslung spade rudders.

    Marc Ginisty has designed, built and sailed boats all his life. He sailed across the Atlantic in a boat of his own design when he was young and continued designing and building boats. The jpegs show a Kalim cat of about 42 foot, several 46 foot Kalim cats that are cruising in the Pacific and Atlantic and finally the 49 foot “Marielle”. I am sure there are more boats but as I said details are hard to find. The construction of these boats beyond them being foam glass with some carbon fibre is unknow. He has designed a relatively simple shape that could have a lot of flat panels or minimal curve panels in the build. If anyone knows more could they please advise.

    Now we get to the rigs. The previous Kalim cats had conventional fixed or wing mast rigs that according to one cruising report on a 46 foot version can power the cat to very fast speeds (above 280 miles/day when pushed in near ideal conditions). The 46 foot owner is more cruising orientated and is happy with sub 200 mile days normally. Marc wanted something easier to handle on his personal cruising boat. He wanted a 200 mile day cat not an outright speed cruiser. Theoretically the 49 foot “Marielle” can peak at 24 knots but he has not had to sail that hard to achieve his 200 mile days.

    “Marielle” swing rig appears to be well refined and easy to use. To Quote Marc “Having already sailed quite a bit and built many boats, I wanted for my last cruising cat a simple rig without much effort on the structure and efficient. Result, a biplane rig with two flexible wings. After research, swing wing flexible wings seemed to me to be the best suited. A friend allowed me to meet Guy Beaup, the designer of this rig. I was able to take advantage of his experience and save myself a lot of trial and error. A year after the launch and 10,000 miles later, I am happy with my choice of a light and fast catamaran and the biplane rig with its self-built carbon masts. The lower center of gravity and sails lower center of effort than a Marconi rig also are an advantage. Fearsome efficiency downwind without adding a gennaker or spinnaker. a possible small weak point in the crosswind or the adjustment of the sheets requires particular attention to avoid the winding of the leeward wing.” About windward work he said “A very efficient rig upwind, coupled with an astonishing ease of tacking for a light catamaran. the wings offering little wind resistance do not stop the boat when tacking and start working quickly on the other tack.” All controls are lead to the cockpit. There are a lot of refinements in the rig to minimise the rigs weight, maximise the sail shape and simplify the reefing process. The only time he has to leave the cockpit is to “unlock” the reefing lines at the base of the mast, the rest of the reefing can be done from the cockpit.

    “Marielle” is a very interesting cat that I would like to know more about. The jpegs start with “Marielle” then show the 46 versions and 42 foot model.
     

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  2. oldmulti
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    oldmulti Senior Member

    You want a fun boat for sailing but you have an old Moth sitting in your garage? Here is your solution if you have a boat shaped moth (not a scow shape). The “Mothmaran” was created from a Holland Tunnel Moth hull with stock kit Chesapeake Light Craft amas (normally for canoe to tri conversions). The Mothmaran is 11 x 7.7 foot and weighs an estimated 110 lbs. The sail area in the fat head mainsail is 86 square foot. The fixed prodder fly’s a gennaker on a roller furler. These additions make this tri not allowable to sail as a Moth. But this design was done to race in the 300 mile 2015 Everglades Challenge.

    The tri sailed in coastal conditions in a 100 mile test sail. A few problems were found which required an upgrade. Once loaded with all the required Everglades gear water come into the cockpit over the top of the daggerboard trunk - time for a quick redesign! Additions included some fairings for the crossbeam attachments and a massive foredeck coaming to keep water out of the cockpit, plus a higher daggerboard trunk. Next problem for the Everglades Challenge was the tri was too small to sleep on. Minor issues, the owner still went sailing.

    The tri had a standard moth Holland tunnel hull. The floats are made from 3 mm ply with bulkheads attached to the crossbeams initially by 2 bolts which worked loose and were reinforced. The cross beams are 50 x 50 timber with a beam reinforced by an aluminium U channel. In some jpegs have the aluminium U channel on the forward beam, other shots show it on the aft beam.

    The Mothmaran performance in light to moderate airs is good (comparable to non foiling Moths) but when things get a bit rougher its either time to be on shore or to be brave with winds from behind. A fun device for those who cannot afford a bigger option.

    The jpegs give the idea.
     

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  3. revintage
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    revintage Senior Member

    This is another take on reusing a dinghy hull. I quess the donor is a Laser.
    85518763-4D1F-4A64-9023-BA7D2222744F.jpeg
     
  4. jamez
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    jamez Senior Member


    There is a conventionally rigged 42' Ginisty in Auckland. I've seen this sailing upwind in a 30 knot SW with a small jib and a couple of reefs in the main and it was sailing fast and tacked easily. Looked a very nice boat to be sailing on.

    upload_2022-5-10_7-58-53.png
     
    Last edited: May 10, 2022
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  5. oldmulti
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    oldmulti Senior Member

    The following has only a few jpegs but many surprising words. Sam Bradfield said to Dick Newick, a long time friend, that what I’d really like to do as the next step toward developing the ocean capable racer/cruiser trimaran is to see if we could do a successful retrofit of foils. In a sort of “put your money where your mouth is” challenge he generously sent me a package of technical information on two of his boats in that size group. After saying Geez! I’ve done it again! I said: well, I might as well have a go at this and I warmed up the computer and headed out ... computer sailing and optimizing a lifting foil system for Dicks’ ECHO during 2000 in my spare time. The result was a feasibility study of retrofitting ECHO II trimaran as a flying hydrofoil sailboat.

    Who is Sam Bradfield? The absolute pioneer of hydrofoil sail boats. The US navy funded him to produce a sailing hydrofoil boat in 1957. “Monitor” flew fast and continuously. “Monitor” is in the Mariner Museum and is 26 x 21 foot (over the foils) and weighed approximately 800 lbs. The sail are was 230 square foot. The take off wind speed was 13 knots and “Monitor” top speed was over 30 knots in strong winds. It had automatic trim control due to multiple foils, but the foils also had adjustable incidence control while flying. This was a very advanced boat and cost over $20,000 in 1957 (over$300,000 in today’s dollars) . The original design had 2 wing masts (first jpeg) but the final version had conventional rig.

    Sam Bradfield then produced a series of hydrofoil sail craft up to HydroSail’s 25ft EIFO coastal racer. The "EIFO" is a 25 ft racing trimaran with T-shape hydrofoils. She is constructed entirely of carbon fiber and is capable of speeds up to 30 knots. This design can also be produced with daggerboards and rudders instead of foils. EIFO is 25 x 24 foot and weighs 1100 lbs. It carries 495 square foot of sail area.

    Back to the Newick ECHO tri. An ECHO is 36.5 x 30 foot with a displacement of 5,600 lbs. The sail area is 600 square foot. The foil system is a T foil on each float just forward of the main cross beam. There is a foil control wand on the float bow to control the flap on the foils for height control. A central aft T foil is on the main hull. According to Sam the ECHO will have completely retractable float mounted foils. The lee daggerboard provides total side force holding capability for windward work. The float mounted foil eliminates the need for a main hull daggerboard installation and significantly increases available main hull space. Newick crash boxes are installed in the floats to prevent serious grounding damage. The transom mounted retractable rudder foil swings up if struck. An 8 to 10 HP long shaft outboard gives seven knots in a calm water. A 25 HP long shaft will permit foilborne powering at 15 to 20 knots in calm water. Echo’s ample aka clearance ensures the absence of wave slam with this boat. And the narrow waterline beam is the secret to easy motion in waves, especially to windward. The lifting foils put the final touch on comfortable sailing to windward by sharing the load with float and main hull. With both main foils extended, Echo flies on beam reaching headings when the wind speed exceeds 10 kts. As the windspeed increases, so does the flight heading range until, with a windspeed of 20 knots, she’s flying all the way from 50 degrees heading to 160 degrees. She’ll be most comfortable flying in the 20 to 30 knot boat speed range in the 12 to 18 knot windspeed range. With Echo’s rig, she won’t be at full power at the top of this sea breeze speed range. She’ll have the capability of doing 30 to 35 knots at 105 to 125 degrees to the wind. As far as I know no ECHO has been modified to fly but its possible according to Hydrosail.

    Sorry I have only seen one drawing of the ECHO foiler and cannot copy it. The jpegs are of the various boats mentioned.
     

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  6. revintage
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    revintage Senior Member

    Last edited: May 10, 2022
  7. oldmulti
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    oldmulti Senior Member

    Revintage. Thank you for the correction. Gordon Baker did design Monitor. Dr Sam Bradfield interest in hydrofoils started in 1963 when he was an aeronautical engineer. His first hydrofoils were done in the 1970's and he developed boats from there. Greg Ketterman the main designer of the Hobie tri foiler said Dr Sam Bradfield's concept which was a refinement of 1957 Hook's planning sensors principle, is the ONLY WAY to make T-foils stable on pitch axis. Sam Bradfield helped develop T foilers, wands and simulation programs for foil performance as well as the designs for the ECHO etc. The attached PDF shows his history and jpegs show a few of his designs and builds including the production 16 x 17 foot Rave foiler.
     

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  8. oldmulti
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    oldmulti Senior Member

    The Holopuni OC3 Sailing Outrigger Canoe is a development from a Hawaiian outrigger paddling canoe. The Holopuni OC3 sailing version is a trimaran 30 x 15 foot with a weight of approximately 250 lbs. The freestanding round carbon fibre mast carries 100 square foot of sail that is reefed by being wound around the mast. A 24" sleeve type mast step is set up forward of the front cross beam to take what can be a free standing mast, or if wind conditions warrant, stays can be added. The length to beam of the main hull is 18 to 1. The floats are 15 foot long with a length to beam of 16 to 1.

    OC3 is a “class” of canoes and several manufacturers produce their own version of the sailing canoes. All have similar design characteristics but vary in their build detail. In the case of the Holopuni brand each canoe is built for its intended task. If it is used in racing it is lighter, if it is going to be used for charter or cruising its heavier in its build. If its going offshore spray rails are built around cockpits to handle spray skirts to minimise water ingress, also you can have the freeboard increased by 75 mm. If the canoe is mainly used for sailing you can have a daggerboard and case installed in the main hull. And if you don’t have enough people to paddle you can even have an outboard mount added. But there is one constant, you have to steer by a paddle.

    So, we have a fine trimaran sailing canoe that can have a sail rig and 3 guys paddling very hard. How fast can you go? Speeds of 8 knots are reasonable but if your surfing down sea waves with strong favourable winds and a brave crew they have been recorded at peaks near 20 knots. The brave crew part means a strong guy with a steer paddle at the back and the 2 crew hiking out on the trampolines. Not exactly cruising but fast. In a cruising mode, it can be sailed in a much more conservatively fashion.

    The Holopuni version is built is e-glass with some foam. The cross beams are magnificent. They are 8 layers of laminated timber that are attached to the main hull and floats so they can be disassembled for transport. Other manufactures use resin infusion, or vacuum assisted resin transfer molding (VARTM), is a closed mold process that also uses the vacuum bagging technique to compress the laminate. Vacuum bagging techniques will normally give you a resin wet out ration of approx. 1:1 ie. for every kg of carbon or cloth used you will use 1 kg of resin. However, with Resin Infusion this ratio drops to 70% ie for every kg of carbon your resin usage is only 700 grams. This represents a weight saving of 15% without compromising the strength. This manufacturer can get a weight of 200 lbs in e-glass. There is also another manufacturer has a carbon fibre version that weighs 160 lbs. The light weight version also has lighter cross beams.

    These sailing canoes can be used in the rough conditions around Hawaii and can be built according to the local need. A well developed excellent solution for a fun sailor. The jpegs give the idea.
     

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    Last edited: May 10, 2022
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  9. oldmulti
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    oldmulti Senior Member

    The final Fred Barret yacht design contribution is an 11 meter timber composite cruising power catamaran with a very fuel efficient canoe stern hull shape initially developed by Malcolm Tennant. The Eco 11 meter is 36 x 18.7 foot with a displacement of about 12,000 lbs (estimate). The hull length to beam is 17 to 1 at the dead waterline and 12.5 to 1 if there is an overload. Translation, keep it light, don’t immerse the chines just above the waterline by overloading the cat. The draft is 2.4 foot. The underwing clearance is 2 foot. I do not know the engine power but it’s a very tight fit in the hulls for things like maintenance. Make sure you have hatches above the engine space to get engines out if there is a problem with the engine or gearbox, also ensure things like oil filters etc are accessible. I have seen one engine installation where to check oil levels and filters etc required acrobatics and removing several parts of the interior.

    The accommodation is not clearly shown but I am assuming a single berth over the engine in each hull. A double berth cabin forward and a toilet in a hull forward. The main saloon appears to have seating, a galley and steering position. The covered cockpit completes the accommodation with a large door leading to the main saloon.

    There is no details of the construction beyond it being timber composite. From other designs Fred has done, it could be strip plank cedar hulls and plywood bulkheads, underwing and cabin decks etc. or it could be foam glass shell with plywood bulkheads etc. Either way this style of catamaran is very weight sensitive and requires to be built to plan. Its not just overall weight, it is where the weight is placed. Malcom Tennant had a couple of his clients try and sue him for a bad design in 50 and 60 foot power cats. In each case the builder and/or owner has added weight in the wrong spot which caused a bow down or stern down situation. One client changed the galley to a different location and used a larger commercial fridge 10 foot further forward and added additional water tanks etc.

    These cats perform very well if they are built and loaded correctly. The economy is only EG 2 litres per nautical mile while running at 10 to 12 knots. If designed and powered correctly you will get peak speeds of 20 plus knots.

    Sorry about the lack of jpegs as I do not think one has been built yet. A good design that hopefully live up to my expectations.
     

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  10. oldmulti
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    oldmulti Senior Member

    An American University, Augsburg, does an interesting educational semester every couple of years. They go sailing for 100 days. This year they went from Saint Paul Minnesota to Baton Rouge (1200 miles) down the Mississippi river. The boats provide the transport and the up to 16 students and 2 staff either camp on the shore, stay in other educational dormitories or motels depending on the locations that are stopped at. Each person is “promised” a shower at least once a week and can carry 30 lbs of personnel gear. The students do a normal semester of education but learn a lot more than most along the way as they meet new people and challenges.

    The fine vessels (yes there are 2) are designed ad built by the university and students. How long does it take? The first drawing of a boat was done March 1, April started construction, the launch of the 2 boats was done early August, the 100 day trip was completed early December.

    So, what are these 2 fine vessels. Basically, dory cat hulls with a storage box on the crossbeams. The hull length is 24 foot but from here on I am doing educated guesses. The beam may be 16 foot. The displacement is a guess at 5,500 lbs fully loaded. The 18 foot above deck freestanding birdsmouth mast carries a mainsail spirit rig. The hull length to beam at the waterline looks about 12 to 1. The hulls are open in the mid section to allow the motive power, the crew paddling. As the cats are going down the Mississippi the current provides a lot of motive power but the sail rig can provide a significant help when the winds are in the right direction. To quote a crew member “The winds were incredible today. We averaged 7.5 knots and had a max of 10 knots when the gusts were coming the strongest.”

    The hull shape is a very simple box dory shape with a lot of rocker to carry the loads and allow good moveability. The Mississippi river may be wide but it is also heavily trafficked and has many twists and turns. Anny vessel travelling down it needs to be able to manoeuvre around natural and man made obstructions.

    The cat is basically built from big hardware store plywood (probably 12 mm exterior) and Ash timber for the frames, chines, gunnels and crossbeams. The cross beams appear to be 6 layers of 25 mm ash about 100 mm wide. The hulls have a fiberglass cloth in epoxy over them. The central storage box carries each person’s personal gear, spare water, camping gear etc. There is also a small steering cockpit aft on the central storage box. The cats were named Water Strider 1 and 2, and completed the trip with minimal problems bar a rudder needing to be rebuilt.

    The jpegs give the idea initially of the build and some jpegs of the trip. Remember this is what you can achieve in a 4 month build by one person with a little help from inexperienced people. Keep it simple and you can achieve a lot in a short time. This is an early entry because I have other priorities for 24 hours.
     

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  11. oldmulti
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    oldmulti Senior Member

    A short one which is about the jpegs, PDF’s as much as the words. There was a British guy who sold his 18 foot home built trimaran that interested me. He built the main hull as a canoe but added Fyne Boat kits Trika 540 floats and cross beams to convert it into a sailing tri that was simple to trail and launch, A nice tri with good jpegs that show what can be done with a nice bay river cruiser.

    So where did the Trika 540 get the idea of the folding cross beams come from? The Trika guys developed the Trika after Frank Smoot of DIY tri’s first built several versions of it in his brilliant range of 16 to 24 foot trimarans. The plans are now sold by Duckworks under the generic name of Slingshot. Why did Frank get to this design concept. Frank wanted to trail his boat to the water and launch it in minutes not hours. Initially he designed 3 light weight hulls and aluminium tube cross beams which he assembled at the launching location. Frank was not happy with this. He then designed a vertical fold up system for his 16 foot Slingshot. An improvement but it still required some person power to fold and unfold the tri then put up the mast.

    Finally, Frank developed the horizontal folding system that works brilliantly. He can push the tri of the trailer and unfold the tri to full width in 30 seconds. He also has a variation on rig raising that can raise a mast and have the tri sailing in minutes. Total time from first touching water to sailing can be under 5 minutes. The mast raising is not shown below and only works in smaller rigs, but it is a superb total sailing solution for a day sailor that operates in light to moderate winds.

    The PDF’s are free study plans that describe the concept of the Smoot Slingshot tris, there build approach and cross beam options.

    If you want to get into a simple, fast build tri that can be launched in minutes these boats are excellent day sailors. Please look at the PDF’s they are very worthwhile.
     

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  12. oldmulti
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    oldmulti Senior Member

    This is about a French designer who has a varied portfolio of relatively simple designs from monohulls, tris cats and proa’s. Jérôme Delaunay Naval Architect (Nautline) is a creator of plywood-epoxy boat plans designed for amateur builders. The designs we will focus on is the Vaka 600 tacking proa and an update on the Vaka 990 Pacific proa.

    The Vaka 600 tacking proa is 19.5 x 11 foot and weighs 670 lbs empty with a displacement of 1,460 lbs. The two 16 foot (above deck) free standing wooden masts carry a schooner rig of 2 junk sails of 91 square foot each for a total area of 182 square foot. A jib is optional. The draft over the dagger board is 2.8 foot.

    The accommodation is limited to 2 single berths and just enough bench space for a camping galley and storage. This is a practical camp cruiser for 2 with just enough space for private porta potti.

    The build is plywood and timber. It uses 24 sheets of 6 mm or 8 mm ply with a timber frame every 2 foot in the main hull. The float has 5 frames/bulkheads in a very simple shape. The build uses epoxy glues and West type system throughout with selective carbon fibre reinforcements. A reasonable bay or river camp cruiser for fun with some performance.

    Vaka 990 V2 Pacific Proa is a 32.5 x 18.7 foot cruising proa with 2 berth float accommodation or if the proa is a sports version the float has water ballast and no accommodation. Its weight is 2,100 lbs with a maximum displacement of 4,300 lbs. The two 150 mm diameter mast schooner rig carries 400 to 450 square foot of sail with an optional jib. The length to beam on the main hull is 10.5 to 1. The draft is 3.8 foot over the daggerboard. The "Pod" is habitable and acts as an anti-capsize device and the boat has 4/2 berths, a WC, limited galley with storage.

    The Vaka 990 is constructed of west epoxy plywood and timber framing support with limited carbon fibre. The bulkheads and main hull are 9 mm ply with floats 6 mm ply. (36 sheets 2.4 X 1.25 mtr 9 mm, 16 sheets 2.4 x 1.25 6mm). The cross beam structure in the aka V2 PDF is interesting and fairly simple. It’s worth a look. The rudder and steering system look fairly simple, but I cannot comment on its practicality.

    It was originally Vaka 990 featured earlier in this tread but the new PDF study plan by the designer gives more details of the build and structure.

    The first jpegs give the idea of the Vaka 600 and the Vaka 990 jpegs and study PDF’s (old and new) are next.
     

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  13. oldmulti
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    oldmulti Senior Member

    In 1947 Woody Brown became the father of the modern catamarans building the 38 foot Manu Kai on the beach in Waikiki, Hawaii. It soon became known as the World's Fastest Sailboat. Woody went on to build a few more catamarans before he took charter tourists sailing off the beach. Next came in 1955, the “production” Manu Kai class 20’ catamaran, designed and built by Woody Brown. The boat has the classic design details of an early Hawaiian beach cat, including deep asymmetrical hulls, canoe stern and integrated rudder. The original rig was a homage to the crab claw rig. The mast base is on the fore beam with 2 support struts, forming an A frame, leading to each bow. The boom is connected to the deck amidship. Of the 3 cats that still exist to my knowledge 2 still have the original rigs and only one has been converted to a standard 3 wire sloop rig.

    The Manu Kai (dimensions beyond length are estimates) is 20 x 8.5 foot and is lightweight. The mast is about 26 foot high and carries about 225 square foot of sail. The thin hulls are asymmetric and look about 15 to 1 length to beam. The draft looks about 1.5 foot. The integrated rudders on the canoe sterns I suspect would require long tillers to steer as they appear to be a little unbalanced.

    The cat appears to be a day sailor with a solid bridgedeck. There are some storage lockers in the bridgedeck coaming which helps provides some protection from spray. There is plenty of room for 6 people daysailing. Performance is unknown beyond 2nd hand advertisements saying it is fast. On a reach with those knife like hulls and rig that would be effective reaching, I could accept Manu Kai would be very fast for its size.

    In 1955 Woody was building cats in plywood with timber frames. There was no fiberglass or epoxy in general use in those days. The plywood and timber were top quality and Woody Brown was a first-class boat builder. For cats to last nearly 70 years and still be described as being in “good condition” says a lot. The original fittings were heavy brass components (mast and A frame bases etc). The various mast, strut and beams were all wood. On 1 of the 3 cats have had a glass cloth covering done at a later stage.

    Woody Brown had a few friends like Rudy Choy and Warren Seaman that further developed the catamaran concept and popularised the catamarans globally. The Manu Kai was the first step with orders for the Manu Kai coming from several US states and the cats were built and delivered to the new owners’ homes.

    We owe a great deal of gratitude to Woody Brown for his vision and skill to produce such quality “production” cats. I do not know the total number produced (probably under 10) but at least 3 still exist. Des anyone know any more detail?

    The jpegs are of the various Manu Kai cats I have found.
     

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  14. oldmulti
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    oldmulti Senior Member

    This is a story about a man desire to build a proa. He was inspired by the Madness proa design created by John Harris of CLC boat, design and kit manufacture. He purchased a Madness pacific proa plan and wanted it slightly bigger and built in a different material. Madness is 30 x 20 foot with a displacement of 2400 lbs. He then said it should be 45 foot long, so he scaled everything by 1.5 times. This would allow a 4.5 foot wide double berth in the pod and a full headroom bridge area with viewing ports. Translation, I want more accommodation in a fast boat that it still relatively cheap to build. His logic was a proa will achieve this.

    Also, he will build it from aluminum. With no engineering and limited welding skills he thought this was a good idea. To try and understand more he went onto the web to ask a few questions. He initially thought about just using the plywood thickness as the thickness of the aluminium sheets he should use on the hull skins. Logic was that aluminum is stronger than plywood therefore should be strong enough for the increase in size. The 4 different web sites he blogged on provided differing advice from full encouragement to some professionals suggesting he needed to rethink what he was doing.

    Next came a set of jpegs of the initial build of the main hull with the following set of specifications for both the main hull and float. The hull sides are aluminum 6 mm plate. Decks, cabins 4 mm and on the mainhull a 10 mm bottom plate. The bulkheads are 6 mm. The initial jpegs showed a lack of bulkheads and minimal to no stringers. According to those who know aluminum welding the quality of welds were not good. The professionals and experienced builders became less kind and basically suggested he really needed to get some advice. The inexperienced people wanted the builder to continue. Little on the proa build has been seen on the web since.

    What were people suggesting some professional advice? The 45 foot version if scaled from Madness plans by 1.5 would be 45 x 30 foot with a displacement of about 7000 lbs. The structure of a plywood 30 footer proa would have EG 6 mm plywood which is relatively stiffer for its weight than aluminum. Therefore 6 mm ply would require minimal framing and stringers with bulkheads about 3 foot apart. If you scale the design by 1.5 to 45 foot and still only have the same number of bulkheads, the bulkheads will be 4.5 foot apart. To support the 6 mm aluminium, you would require more stringers not less as aluminum is not as “stiff” for its weight. Also, aluminum requires more intermediate frames to support the stringers.

    Yes, you can reduce framing, bulkheads and stringers if you use 10 mm thick as in Strongall type build but the weight of the aluminum would be more than the total displacement of the 45 foot proa. Aluminum as a build material is not the problem, the reinforcing structural detail is the down fall here for a boat that has minimal displacement. EG a proa this size could have 3 or 4 mm skins but would need frames every 600 mm and stringers every 400 mm. There was no mention of the cross beams etc and how they were going to be designed or built.

    As I have often said, a good designer is the cheapest investment you can make. Increasing the length of a design up to 10% may be OK, but expanding any other dimension requires professional assistance especially if you are increasing any beam dimensions. It takes a good designer to engineer a 7000 lbs 45 x 30 foot proa especially if its in aluminum.

    The jpegs are of the initial build. If anyone knows any more please advise.
     

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  15. bajansailor
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    bajansailor Marine Surveyor

    I am pretty sure I saw him posting on this Forum a while back about this proa - do you have a link please to the thread that he started then?
     
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