Multihull Structure Thoughts

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

  1. brian eiland
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    brian eiland Senior Member

  2. brian eiland
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    brian eiland Senior Member

    An older article I liked very much.

    Eric has now retired from designing and is out on a worldwide cruise with his wife

    [​IMG]
     
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  3. oldmulti
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    oldmulti Senior Member

    Now the following Giles Montaubin tri is only 32 x 23 foot weighing 4000 lbs and displacing 6300 lbs. It has a ketch rig with free standing carbon fibre masts with the sails reefing by rolling around the masts. The sail area is 540 square foot. Why is it interesting? Triskell was built for Stephane Beytrison in 2006 in the Philippines. She sailed it around Asia then it passed to a guy who changed the boats name to Arafura who sailed it to South Africa then it headed to France. In spite of the 6.5:1 length to beam on the main hull, this boat is a real cruiser that has done thousands of mainly trouble free ocean miles pulling 7 to 8 knot averages. The tri configuration, with a good design shape, allows the boat to move well in light airs. The following blog tells you part of the travel story: Arafura http://blog.mailasail.com/arafura

    The tri is constructed from plywood and timber with a light e-glass layer outside. The jpeg tells you more but the keel/bottom plank is 18 mm ply, the chine plates are 12 mm ply, the top sides are 10 mm plywood all covered with 200 gsm e glass cloth in epoxy. The panels are taped together and reinforced with furniture if possible. Each panel has a stringer mid panel. Most of the bulkheads are plywood. This type of structure is similar to the original Jim Brown Searunner tris. The cross beams are plywood boxes reinforced with timber flanges and bulkheads, the cross beams can be demounted from the hulls. Daggerboards are in the floats and the steering rudder is on the main hull.

    The carbon fibre masts for Triskell were built by C-Tech marine in NZ in parts (probably for transport). The 2 part mast had a bottom and a top section that fitted into the bottom section. The foremast has a bottom section of 22.3 foot of an inside diameter of 108 mm with a 6 mm wall at the base tapering to a 4 mm wall at top. The top section of the fore mast is 22.3 foot 100 mm inside diameter section with a 4 mm wall at the bottom tapering to 2.4 mm wall at the top. The total length above deck is 37 foot and weighs 68 lbs. Mizzen mast bottom section is 19.5 foot with a 108 mm with an inside diameter with 6 mm walls tapering to 4 mm at top. The top section is 19.5 foot with a 100 mm inside diameter and 4 mm walls tapering to 2.4 mm wall at the top. The total length above deck is 31 foot and weighs 58 lbs. There is a 6.5 foot 90 mm inside diameter tube with 5 mm walls that fits into the mast section at the joint to act as reinforcement of the mast. The mizzen boom is a 13.5 foot long 50 mm tube with 2.1 mm carbon fibre tube.

    The boat is powered by an outboard and due to the retractable foils can float in 1.4 foot of water. This is a simple fast boat that can take 2 or 3 people a very long distance in reasonable comfort. The jpegs tell you more. the final jpeg is of the 9.4 meter model but shows you the hull shapes used by Giles.
     

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    Last edited: Apr 22, 2020
  4. brian eiland
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    brian eiland Senior Member

    Interesting design, that tri ketch. I wonder what the actual process is on furling the sails??

    Just wondering if a foil shaped, sail holding, outer tube could be make to rotate around a circular carbon fiber inner mast?,.... something like Chris White's mastfoil mast??
    (no probably not, as any slight bend in that tall column would hang things up?)
     
  5. oldmulti
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    oldmulti Senior Member

    Brian. If it follows how Giles does his smaller mono boats the masts can rotate in there mast bases on bearings and you rotate the mast like a furling jib arrangement. My only concern is that there appears to be some "fixed" items on the fore mast with blocks attached and I don't understand the boom on the mizzen mast attachment point and how that would operate if the sail was roller furled. More photo's required. a wing mast shape around a circular mast is possible if either the"frames/bulkheads" supporting the wing shape are spaced apart and could slide independently as the central tube bent or the external wing mast shape is a "loose fit" that would not bind as the central tube flexed. But I suspect it would just be better to do a free standing wing mast in the first place as Eric Spondberg did on a few of his mono's. PS Eric is locked down due to Covid-19 in Bunderberg in Queensland in Australia before he sails on.
     
  6. oldmulti
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    oldmulti Senior Member

    Motive 25 is 25 x 21 foot weighing 890 lbs. The mast is 35.5 foot high mini carbon fibre wing carrying a 273 square foot lose footed main with a square head, a 80 square foot self tacking jib and a 250 square foot screecher. The boat could be folded/disassembled to 8.5 foot with a CF tube system. The length to beam on the main hull is 12.5:1. It is a completely carbon fibre build. It had a 6 HP outboard. It has a central centre board or dagger board. The Motive 25 was a production tri in 2012/13 but is no longer available. The tri had a least 4 boats built with additional requests for another 8 boats. From the limited information I have this boat was seriously fast and took quite a time to develop to its full potential.

    The build is full carbon fibre. The hulls appear to be foam carbon fibre. The crossbeams are solid carbon fibre tubes appear to be about 150 mm diameter with 6 mm walls. The photo’s etc are unclear as to its “folding” technique. The cross arms appear to slot onto a stub in the floats and push into a tube in the main hull. But I suspect the floats stubs can be pushed into the main hull tubes which would mean that the actual beam tubes are independent and need to be assembled to make it a full width boat. There are rod waterstay under the beams. Originally they were fibre but they stretched too much so it was replaced by number “4” rod rigging. The rudders and centre board evolved with later versions having carbon fibre strengthening inserts.

    Other modifications included “Then there's the new carbon mini-deck which shows the new CB up/down lines sorted out, and with a quick release clam cleat for the down line. Both lines lead to the winches, which is especially critical when lowering the CB and fighting its buoyancy. The new CB has twin carbon rectangular tubes running its full length for strength. The new rudders are mounted to the new Gudgeons I designed and which are much beefier than the previous ones. They're set much farther apart and use a 12mm full length pintle. The tiller crossbeam is now 3 " above the traveller, so the hiking sticks don't crash into the traveller end controls as previously.”

    It is a pity the design was a commercial failure but around the same stage the Seacart 26 and Diamond 23 day tri’s came onto the market with much stronger marketing organisation. Although the Motive 25 was lighter and possible faster than the other tri’s marketing plays a big part in sales success. Does anyone know any more?
     

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  7. brian eiland
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    brian eiland Senior Member

    I imagine that Motive 25 was quite expensive with all of the carbon fiber in her construction. And to keep her that narrow for transportation her main hull had to be very fine,...thus she was just a daysailer with no accommodation like our Firefly 26 which could be a weekender.
     
  8. brian eiland
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    brian eiland Senior Member

    I'm trying to recall exactly how Chris White foil mast were constructed?? My memory is fading. Perhaps someone else can do a more thorough research job?

    I did find this older reference I had made,,
    Catching up with Chris White - Professional BoatBuilder Magazine https://www.proboat.com/2019/07/catching-up-with-chris-white/

    *********************************
    and this from a Sailing Anarchy posting I made,..
     
    Last edited: Apr 24, 2020
  9. brian eiland
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  10. oldmulti
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    oldmulti Senior Member

    Today we will be doing a few loose ends. First is the development of a superb home tri that has gone through many development iterations. The 18 x 13 foot Outlaw tri is a 350 lbs light weight that uses an A class main and a small jib for 170 square foot of sail area. Read his web site listed on the plan for further detail of how he started with a 10 footer that evolved into the 18 footer shown here. This is a fast fun tri.

    Giles Montaubin has been playing around with freestanding rig variations for years. The earliest I can find is a biplane cat built in 1984. Also the free standing wing mast ketch Tricerotops in 2003 looks interesting. Giles needs more investigation.

    While we are on rigs the Junk rig boys are developing their rigs into high performance cheap versions of Aerorigs. The rig shown in the jpegs show a reefable Aerorig type of sail plan that can be placed on any type of freestanding round mast. The AeroJunk Rig was designed by Paul McKay for his boat Miranda. This is an evolution of the Split junk rig designed by Slieve McGalliard. Information is available on the web about these rigs and I will do more about them later.

    Finally, the reason I get worried about the direction of big French cruising cats. The underwing clearance of this boat that is setting out to cross the Atlantic is just a little concerning. Yes, the photo is taken with a small wave in front of the boat but the pods under are still being touched even in relatively calm water. The sound effect and structural impacts going upwind would not be good. How about less accommodation and more performance?
     

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  11. oldmulti
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    oldmulti Senior Member

    The fine tri I will talk about now is Bernard Kohler’s Little Tri. The tri is 15.4 x 12.5 foot weighing 170 lbs and carrying in its “standard” Sunfish rig 85 square foot but other rig versions have carried rigs up to 140 square foot. Construction time is about 120 hours and it can be built for under $1000 US if you can find a cheap rig. The tri is according to the designer a quick build, he used PVC irrigation tubes as low volume amas. The rest is easy. The hull is a plywood/glass/Epoxy composite sharpie hull. The easiest shape to build. The rig used is a low cost Sunfish rig.

    According to the designer “The boat is fast, easy to sail also for beginners. The boat has proven itself for coastal cruising and can handle wind and waves well.” The PDF plans cost $76 US available from the designer direct or Duckworks.

    But the interesting part for me is the fact that the base design has been used for many sail and rig experiments all of which with a little development have appeared to work well. The initial design with the Sunfish lateen rig has been shown in many video’s and the Little tri appears to sail very well. The next variant was a lug rigged version done by a guy who wanted a simple rig without too many battens that could sail well. But the next version got my interest the most, which was a variation of a split junk rig done by a guy who wanted to sail it in some longer distance local races but required some reefing capability. The total sail area (minus the split) is 130 sq feet. Each reef removes 28 sq ft (it has three reefs). That is a lot of area for a small 15.5 foot boat, but the Little tri handled it well. The reason is that the tri could sail under full rig in lighter airs and be easily reefed in heavier airs to allowing the Little tri to handle bigger winds and waves.

    This is a little design that can be used for a lot of experimentation and learning whilst being able to handle day sailing for 2 or short cruises with some camping equipment. The jpegs tell most of the story. The construction guide PDF was done by the designer and came from the Duckworks web site. A fun machine.
     

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  12. oldmulti
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    oldmulti Senior Member

    The Searunner 25 tri was/is a genuine small sea vessel. It would take an experienced person but it can cross oceans. The tri is 25 x 16.5 foot (foldable to 8 foot) that weighs 2000 lbs and can carry a payload of 500 lbs. The mainsail is 122 square foot the staysail is 79 square foot, the jib is 113 square foot with a 210 square foot genoa. The rig is a cutter on a 28 foot mast. The length to beam n the main hull is 7:1. People who have sailed the boat say its very responsive and can perform well with its deep centreboard that draws 4.5 foot. The main hull at the gunnel is 3.75 foot wide. The floats are 21.5 foot long and have over 150 % buoyancy.

    The tri is plywood with timber stringers and frames supported by plywood. The main hull has a 12mm ply keel plate, 9 mm chine plates and 6 mm topside plates. The stringers are 25 x 19 mm. The chines have taped joins inside and outside. Timber frames 19 x 75 mm are on the ply bulkheads. The floats are 6 mm ply with 9 mm bulkheads. The centre case has 12 mm ply sides. The decks are 6 mm ply with deck stringers. The aluminium crossarm tubes are either 48 mm scaffold tubes with thick walls or square sections of unknown dimensions. The diagonal timber cross beam sections are 50 x 140 mm. The rudders gudgeons are 3 x 32 x 75 mm stainless steel with 12 mm pins. The centre board and kickup rudder is Western Red Cedar covered with glass. The original mast was a timber box section. A 5 hp outboard provides the power.

    The accommodation layout is based around the central cockpit with single bunks fore and aft. There is a small galley and not much else. This is an excellent coastal cruiser and is a good sea boat. The basic structure has been proven for over 50 years and would form the basis of an excellent cruiser with a few accommodation mods.
     

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  13. catsketcher
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    catsketcher Senior Member

    I love Searunners. I almost built a 31 and had the plans but saw a Twiggy next to a 31 and bought one. We then almost bought a 37 after the Twiggy but couldn't find an epoxy one and I wanted one with epoxy. The resorcinol one we looked at was still going strong years later. Great boats and a fab manual for construction. All proper sea boats.
     
  14. oldmulti
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    oldmulti Senior Member

    The following design got half way around the world before being wrecked. A new version of the same design was built to the same dimensions but just lighter. So the cat is 21 x 13 foot weighs 900 lbs has no cabins is an open bridge deck “beach cat” with special equipment for global sailing. The cat initially started with 2 people but was single handed after the initial leg. And yet, 20 months after setting off, Yvan Bourgnon has succeeded in completing the impossible: going around the world in a sports catamaran, via Panama and Suez. To be able to sail the 55,000 km with 20 stopovers; the crossing of 3 oceans and 13 seas; one destroyed boat following a running aground; 2 capsizes and 2 falls into the sea; 7 storms; 420 freeze-dried meals and 30 tubes of sun cream. Yvan's average overall speed was 5.67 knots and his longest single crossing was 3,326 nautical miles between the Galapagos and the Marquesas Islands. His average sleep time was 15 minutes at a time throughout the voyage with periods of up to 3 days with virtually no sleep. He sails "old fashioned", with a sextant and paper charts, ensuring his own navigation.

    Yvan Bourgnon built the boat in foam glass with much carbon fibre in 2000 hours. The replacement boat was made lighter to allow more speed in lighter airs. The boat had up to 600 lbs of load when ocean crossing. The cat can reach 18 knots when conditions are good and Yvan was up to it. This man has courage and a lot of sailing experience.

    This is proof positive you do not need a large boat to travel the world but I suggest 2000 hours of build time will get you a slightly bigger boat with a cabin and it will probably average the same sort of speed around the world. Stunts are one thing boats for real global travel are another thing. I admire the man and his achievement, but there are better ways which we will discuss later. The second last jpeg is of the wreck half way around the world.
     

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  15. oldmulti
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    oldmulti Senior Member

    The following boats have all done at least 3000 open ocean sea miles in cruising mode. They are all home built and less than 26 foot long. Its possible to travel far in a small boat if you have a well designed and built boat. It also requires the skipper to have real sailing experience built over time and a common sense attitude.

    The boats are the Searunner 25 (25 x 16.5 foot) which has sailed from LA to Hawaii. Original Klis (22 x 14 foot) which sailed from England to New Zealand. Cooking Fat Tiki 21 (21 x 12.5 foot) which has sailed around the globe and has done many Trans Atlantic’s. Tiki 26 (26 x 14 foot) which has done many Trans Atlantics and done a lot of the Pacific. The next boat is Brine Shrimp (23.3 x 14 foot) a later design of Thomas firth Jones who sailed 2 smaller Wharram type boats across the Atlantic including surviving a full hurricane. But the absolute grand champion of a small long distance cruising boat is Miss Cindy (16 x 8.5 foot) that cruised Mexico down the Baja, was truck across South America, then sailed from Nicaragua to Cuba then to Florida. All of these boats can be transported on a trailer (or car topped 3000 miles in the case of Miss Cindy) for home storage or maintenance etc.

    The accommodation is limited in each design but you have at least one legitimate bunk, a galley, a spot for a loo bucket and in all bar the Tiki 21 sitting headroom. Klis 3 has 6 foot headroom. In short you can get away from the weather and get some form of proper rest. Each of these designs can handle about 1000 lbs of load except Miss Cindy (only 16 foot long) who could only handle a load of 600 lbs. Most of these boats had windvane self steering.

    Performance is interesting. Klis could peak at 15 knots and averaged about 5 knots. Cooking Fat averaged 110 miles per day from England to the USA and averaged 170 miles per day from USA to England on a Trans-Atlantic run. Miss Cindy top speed was 15 knots with 3 to 7 knot averages over its 4000 miles. All these boats are doing 40 foot monohull ocean averages.

    All of the boats carried 2 people for sections of there voyages, but many voyage sections were done single handed. You do not need a large boat to travel far. You just need enthusiasm, a good attitude and sensible seamanship. Also, most of these boats were built in backyards for less money than the mooring and maintenance cost of a 40 footer for a year.

    What do you really need? A dream with 4 double berth cabins that will take 10,000 hours to build or a boat that can sail far with 2 on board that can be well built and stored in your back yard after a 1500 hour build. Those extra 8500 hours of sailing time can literally be life changing fun. I will get off my high horse now. All these designs have been spoken about previously in this thread. The jpegs are of either the original Klis, Miss Cindy, Cooking Fat or later models Klis 3, Brine Shrimp, Tiki 26. The Searunner 25 is in a previous post.

    PS I did not mention Wharram’s initial 23 foot cat built in 1954 because the boat was not a long term sailor. It worked as “a raft” across the Atlantic.
     

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    Last edited: Apr 28, 2020
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