Multihull Structure Thoughts

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

  1. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    The following 21 foot trimaran is a design proposal from Richard Fraser from Fraseraerospace.. Richard has built a Piver Mariner 25 trimaran (story over 6 pages at: Richards_Arthur_Piver_Mariner_25ft_Trimaran https://fraseraerotechnologycompany.com/Richards_Arthur_Piver_Mariner_25ft_Trimaran.html )

    The proposed trimaran is 21 x 13.3 foot with folding floats that will reduce the beam to 8.5 foot. The weight is unknown but a guess of about 1500 lbs and a displacement of about 2200 lbs. The 30 foot mast will carry about 200 square foot of mainsail and 130 square foot mainsail. The main hull will be round bilge, float shape is unknown.

    The concept model for the 21 foot ocean sailing, 2- place wood and fiberglass trimaran day sailor with forward cubby for one person to get out of bad weather. The tri has a very comfortable cockpit area for beach camping as well.

    Richard runs an aircraft business and as a result understands design and light weight build techniques. The real boats construction would be the latest in simple cold molded construction techniques with epoxy and mahogany strip veneer composite construction. This technique lends itself very well to wooden aircraft construction and is extremely easy and forgiving to the beginner who wants to build a light, very stiff and strong craft. Epoxy used is the West System. The hull thickness would be 6 mm with frames/bulkheads and ribs but very few stringers.

    Floats (amas) would fold down for trailering and the mast is self-rotating. Safety netting would be between the main hull seating and each ama. Forward netting can be optional as this has turned out very beneficial in previous trimarans.

    An interesting concept which I hope was built. The limited jpegs give the idea. There is some development in the jpegs as you will see in the rigs size and main shape.
     

    Attached Files:

  2. oldmulti
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    oldmulti Senior Member

    The Threefold 6 is designed by Dudley Dix to be a safe and lively trimaran to sail singlehanded or with a crew and can be used as a day sailor or comfortable gunkhole cruiser. The Threefold 6 is 19.66 x 16.25 foot in sailing format with a dock beam of 10.9 foot and a trailing beam of 8 foot. The weight is 990 lbs. The 27.5 foot mast (could be a Hobie mast) has a mainsail sail area is 152 square foot and the genoa is 113 square foot. The length to beam of the main hull is 5.5 to 1 on the 18.33 LWL. The draft is 0.66 or 2 foot.

    The accommodation is simple with 2 wing berths, a forward berth, a small galley and a small seat area. It has 4.5 foot of head room but with the moving hatch it will allow 6 foot headroom at the galley when open. Simple and effective accommodation for 2 people for short cruises.

    The performance of the Threefold 6 is best described by Oleg Zelinskiy built in Russia. “In November 2008 he went out in extreme storm conditions to test his boat. With winds of 15-22m/s (30-40 knots) and gusting to 32m/s (65 knots), they sailed with storm jib and deeply reefed main. He reports that she handled perfectly, even with seas washing over the deck through to the cockpit. She achieved speeds of 15-17 knots and was responsive and under full control at all times. He says that stability was perfect and there was no hint of the boat ploughing in. Oleg is very satisfied with his testing of the boat in storm conditions.” And “In September 2009 Oleg reported that in 15-25 knots of wind he and one other crew had sailed 15 miles in one hour, with speeds sometimes exceeding 20 knots.”

    This would indicate Dudley Dix has designed a good sailing vessel and he has some brave clients willing to test their boats capability to the limits.

    The tris construction is plywood, timber and an aluminium cross beam structure. The materials list is as follows:

    MARINE PLYWOOD 1,22x2,44m (4'x8') (preferably Gaboon or Okoume plywood)
    4.5mm (3/16") - 11 sheets (use 4mm if 4.5mm is not available)
    6mm (1/4") - 14 sheets and 9mm (3/8") - 3 sheets

    CEDAR or similar, selected, free of knots, shakes fractures etc
    15x30mm (5/8"x1 1/4") - stringers, framing - 80m (262')
    15x40mm (5/8"x1 1/2") - beams, framing - 20m (66')
    20x20mm (3/4"x3/4") - framing - 94m (308')
    20x30mm (3/4"x1 1/4") - framing, tiller - 67m (220')
    20x40mm (3/4"x1 1/2") - framing - 70m (230')
    20x50mm (3/4"x2") - keelson, sole bearers - 9m (30')
    20x60mm (3/4"x2 3/8") - framing, sole bearers - 4m (14')
    20x200mm (3/4"x8") - companion ladder - 1m (4')
    25x50mm (1"x2") - beams, posts - 9m (30')
    30x30mm (1 1/4"x1 1/4") - sheerclamps - 10m (33')
    30x40mm (1 1/4"x1 1/2") - framing - 6m(20')
    50x50mm (2"x2") - stem, beams - 3m (10')

    This is a relatively easy to build small cruising tri that can sail well and is trailable (with a bit of effort). The jpegs give the idea.
     

    Attached Files:

    Last edited: Nov 26, 2021
  3. Slingshot
    Joined: Aug 2019
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    Slingshot Junior Member

    Good day Old multi.

    I searched the index and did not see any info regarding the Bazapi 50. Do you by chance have any info on the material used for construction and technique of these cats?
    thanks

    All the best
     
  4. oldmulti
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    oldmulti Senior Member

    Slingshot. More information please on the Bazapi 50 cat as I do not know the cat. Eg who is producing or designed it. i can possible follow up from there.
     
  5. Slingshot
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    Slingshot Junior Member

    The Brazapi is a Eric Lerouge design that was produced in Belgium. I have seen info on Eric’s site in the past but never a mention of the resin or core used to build the hulls.
     
  6. oldmulti
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    oldmulti Senior Member

    Slingshot. They talk about the Brazapi 50 and a 51 which were custom builds. The 50 was Foam epoxy glass with kevlar reinforcements and an EG can be found at Brazapi 50 https://www.36degrees.nz/yacht-boat-sales-auckland-new-zealand/boat/brazapi-2
    Next have a look at Eric web site at the 15 meter range and you will find its heritage. Eric design structures are similar across his range. the web site is Erik Lerouge http://erik.lerouge.pagesperso-orange.fr/cat_15.htm
    Finally I have a book Eric wrote in french describing how to build foam glass boats where he describes the build of his cats and mono's. I will find the title tomorrow. hope this helps.
     
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  7. oldmulti
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    oldmulti Senior Member

    Slingshot. The book is by Erik Lerounge and is titled "Materiaux Composites" It was produced by HS 30 Loisirs Nautiques. The book is no longer produced but was written in 1991. presse 50143 issn o47 5017 I cannot even find a second hand version. But it is worth a try. It describes composite construction and in a few chapters mentions cross beam structures for open wing deck and full bridge deck cats. Maybe someone has it around.
     
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  8. Slingshot
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    Slingshot Junior Member

    Thanks for the search Multi. I will have a look for the book.
    Cheers
     
  9. oldmulti
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    oldmulti Senior Member

    I was going to provide Slingshot with some further information on Erik Lerouge 50 foot cats. But I found an interesting website that had Erik giving his personal answers to many questions. Will give some samples of the answers here but if you have a spare couple of hours you can read the site yourself. The site is in French but the translation engines do a reasonable job. You need to get over the heading section to the real comments and Erik starts answering questions about 20% in. Two warnings. Erik favors foam glass and some of the terms used need some understanding. EG CP means plywood etc. Some of the insites are from a designers who has produced 300 plus designs in multihulls and monohulls. He has many production cat designs such as the VIK catamaran or Pulsar trimaran series etc. Most of the very small sample was written in 2007 2008.

    Good idea this forum, it avoids me to always answer the same thing by email and everyone can benefit from it.

    Frankly, I'm not convinced the so-called Quick Methods are that quick. There is mostly a lot of spiel. The realization (creation) of the shell is only one part of the construction, in the large sizes, the finish, the equipment, the fittings represent a lot of hours. There are a lot of methods to get a shell out quickly but this is generally paid for by a finish:
    -Assemblies of flat-panels difficult to mask cleanly. (Mask means cleanly fair joints)
    -Methods without tracing making the cutting and fitting of partitions problematic. - Etc ... After having made 8 personal sailboats, it is certain that the next one will be in a sandwich!

    Then you have to know what you want. The construction of a boat, even badly done, requires thousands of hours and a significant amount of capital, so it is preferable that all this energy leads to a quality result. The compromises made to save a few hours are a drag for the entire career of the boat and a serious handicap for the resale value.

    Developable shapes (flat panel) always lead to a less successful boat. I would not argue on the aesthetic side which is purely subjective. Just a few indisputable mathematical facts:
    -At the same volume, a developable shape represents more plating surface, therefore more unnecessary weight and more material to pay.
    -At the same displacement, a developable form has more wetted surface, and therefore more drag at cruising speeds.
    -The flat shapes are more in the choppy water.
    -At the same volume, the ridges create a higher aerodynamic resistance, therefore a less good meadows.
    -Plane shapes have no intrinsic stiffness, they must be more sampled, therefore heavier and more expensive. This is so true that in all classification society shell structure equations there is a moderating pressure coefficient linked to the curvature of the panel.
    -Flat panel joints like those in plywood pose the problem of structural continuity. It is resolved with gradients or additional reinforcements. Weight and cost.
    -The flat shapes are more difficult to body than a double curvature shape on which it is easier to hide the fabric gradients.
    -Nature which does things well has not made a chine dolphin or an albatross with a beak in the roof of a trawler ...

    Although it's less noticeable on my most recent plans, I used Flat panels and plywood. Curiously, they were less successful than the others ...

    The sandwich offers an incomparable quality of life when traveling. Stiffness, resistance, insulation, ease of repair, low maintenance, rot-proof materials. It is certain that I would like to find an easier implementation but that only seems interesting to me if we border directly on the fittings and we avoid the interior finish.
    My idea was to resume my principle of sandwiching on CP from the deck to the rest of the boat.
    Not yet had time to develop the idea, or even talk about it.

    Erik Lerouge

    In yachting the problem is different. Despite our immense experience of the sea, we still do not know exactly how to define dynamic forces on a boat. The stakes have nothing to do with aviation and the means of study without common measure. We therefore work with significantly higher safety coefficients than in aviation, which means that for the vast majority of boats we do not have to worry about the longevity of the composite which is then very tolerant.

    The problem is quite different in the race because we are trying to be at the limit, but on the safe side ...
    Each new parameter changes the game every time we thought we knew everything:
    -The switch to Kevlar sails seriously increased the efforts (stress) on the beams of the maxi-multihulls of the 1980s.
    -The use of honeycomb caused problems with too steep planks on the 60 'sorting in the Route du Rhum 2002.
    -The use of carbon very high modulus has never been mastered on masts and is now abandoned.
    -The speeds reached in planing by the monohulls with pivoting keels caused flutter problems!

    However, we should not regret the choice of composite. These boats built at the same weight of any other material would not even be able to sail! You just always have to learn, what structural engineers do.

    Erik Lerouge

    Balsa. After having made tests in my beginnings in sandwich I definitively banned the balsa on my boats, except in panels of installations with CP facings.

    The balsa is of course putrescible and on the life of the boat there will sooner or later infiltration. The infiltrations are not only on the outer skin, the interior also especially if it is polyester. Even on the deck, you only have to see the old boats that you can feel delaminated when you walk, usually rotten around the bindings.

    Balsa has double the density of foam, worse it is a real resin pump. The result is a sandwich that is not that light, nor economical. The adhesion to the laminate is not great with polyester. You have to add a bonding mat, hence unnecessary weight and even more resin to pay.

    If the mechanical qualities are excellent, the downside is that in the event of an impact, it is so stiff that the vibrations risk delaminating a large surface of the plating. With a good foam, it remains localized.

    Insulation is inferior to foam. The implementation is easy in female mold but detestable on mannequin (male mould).

    Erik Lerouge

    The web site is: https://www.hisse-et-oh.com/sailing/les-catamarans-derik-lerouge

    Slingshot. Some other info on Lerouge cats are at: Eric Lerouge interview

    An Interview with Multihull Designer Erik Lerouge https://smalltridesign.com/Trimaran-Articles/Lerouge-Trimaran-Interview.html

    Some mould and build shots of a Vik 137 https://butoyacht.com/en/yacht-and-catamaran-construction/

    Bazapi changed to: http://dondra-catamaran.com/about/

    Epoxy glass construction http://dondra-catamaran.com/portfolio-item/epoxy-vacuum-and-linear-glass/

    Bulkheads http://dondra-catamaran.com/portfolio-item/minimum-6-double-bulkheads-and-which-bulkheads/
     

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  10. guzzis3
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    guzzis3 Senior Member

    I agree with a lot of what he says but the statement that fish are not chined is incorrect. Look at photos of, for example, whale sharks. Lots of marine swimmers have ridges along their sides.

    The increase in wetted surface is trivial and there has been some speculation that the chines do something to assist windward performance. I'm not supporting that claim as I don't know enough to be sure, but people cleverer than I have said there might be something to it. I know enough about fluid flow to know how little I know.

    Also remember that sail boats crab through the water, very different problem to the way fish or marine mammals move.
     
  11. oldmulti
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    oldmulti Senior Member

    The SOUBISE 70′ Carbon Line designer is Philippe TOURNIER with structural analysis done by Team One. The cat is built by TOURNIER MARINE. The SOUBISE 70 is 70.5 x 34.5 foot with a weight of 40,000 lbs to 45,000 lbs depending on the version. The displacement is 45,000 lbs to 56,000 lbs depending on version and function. The carbon fibre wing mast is either 85 or 92 foot with a 2,070 square foot mainsail, a 1,540 square foot genoa, a 1,030 roller furling jib, a 2,120 square foot drifter and a 3,180 square foot asymmetric spinnaker. The length to beam of the hulls ia about 13 to 1. The bridge deck clearance is 3.8 foot when loaded. The draft over the rudders is 5 foot and over the dagger boards is 9.2 foot. The engines are 2 x 84 HP Diesel Saildrives.

    The designer wanted to create a cat to offer to owners a fast sailing and comfortable cruising catamaran. The accommodation is 5 double cabins with attached ensuites in the hulls. The central cabin has a full galley, large seating table and full inside steering position with navigation area. The attached cockpit is large.

    The cat is all carbon fibre and foam in epoxy resin. The mast, rigging and sail cloth are also carbon fibre based. The jpeg showing the internal details give an idea of how complex and how much structure is required to build a large cat. The majority og the bulkheads, shelves, floors etc add to the structural integrity of the vessel.

    The designer claims the Soubise 70 will be able to cruise at around 5 knots in light winds, and up to 20 knots in steady wind. There is active on-board navigation, with computers and forecast reception so you can either find the best winds, or move away from them if you want.

    The jpegs give the idea. TOURNIER MARINE produces cats from 40 to 70 foot with the most popular size around 46 to 50 foot.
     

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  12. oldmulti
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    oldmulti Senior Member

    The Kiwi 18 is a design by Richard Fraser that is a day sailing tri. The tri is 18.4 x 10.1 foot with a displacement (weight) of 380 lbs. The mast is 24.5 foot high with a mainsail of 127 square foot the fore triangle is 62 square foot and the genoa is 101 square foot. The rig could come from a Hobie 14 or similar. The draft is 1.4 foot over rudder and 3 foot over the daggerboard.

    The cockpit can carry 4 crew but the design is intended to be sailed by 1 or 2 people. The seating is 6 foot long allowing camp cruising if required. The tri is really a fast simple day sailor.

    The 3 hulls are built as a prototype in timber strip construction using thin plywood or cedar strips (variation of double diagonal timber construction) with compound curves to exactly duplicate the weight of a production version to be manufactured from all fiberglass and polyester or vinyl composite resins. The total skin thickness is only 0.25 inches (6 mm) and is far stiffer than those made from fiberglass and polyester. No screws or nails have been used in the construction. The cross arms are aluminium tubes that look like Hobie 14 or 16 cross beams.

    The aft deck has been installed and the water tight lazarette can be seen for access to the spade rudder bearing, rudder removal shaft pin and storage area. This craft is totally epoxy bonded and has an outside colour finish coating on top of the epoxy with extremely hard linear polyurethane. The spade rudder can just be seen below the hull.

    The jpegs show the initial design and the main hull but I do not know if the tri was ever finished. No production version was done to my knowledge. An interesting concept.
     

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    Last edited: Nov 29, 2021
  13. Scuff
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    Scuff Senior Member

    That's a cool looking boat
     
  14. oldmulti
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    oldmulti Senior Member

    Doug Brookes in St. Kitts, W.I. has designed and built large catamarans several decades. His cats are light, fast and built initially in plywood and timber frames and stringers. The cat being discussed is a Brooks 62 charter catamaran. The cat “Spirit of Barbados” is 62 x 28 foot weighing about 20,000 lbs. The rotating timber wing mast carries a mainsail of 664 square feet, a jib of 463 square feet and a genoa on a Profurl C420 furler. The wing mast area is about 200 square foot. The draft with boards up is 3 foot. The claimed underwing clearance is 4 foot, very doubtful more likely 2.5 foot. The hulls are at least 13 to 1 length to beam.

    As a charter cat there are few berths but 2 big toilets. The galley and bar are on the wing deck in an undercover cubby. There is a lot of deck room for many guests. Sail controls and steering happens on the aft deck.

    For those who don’t trust plywood you are looking at a cat built 23 years ago which has been used continuously in charter. Effective, but minimal maintenance has been applied to keep her in reasonable condition.

    The boat structure has 9 or 12 mm Bruynzeel plywood and has timber stringers every 150 mm with frames every 4 foot. The hull is covered with glass in epoxy. The wing mast is 6.3 mm Douglas fir with EBX 1200 biaxial cloth inside and outside in epoxy. There is a 6.3 plywood web across the mast with a stringer the full length of the mast on either side of the web on either internal face of the mast. There is additional timber reinforcement for reinforcement at the leading and aft edges with extra reinforcement at shroud attachment points. Brookes believes wooden wing masts (in 2010) are cheaper than aluminium.

    This cat will sail in the 10-15 knots range very easily and her twin 34 HP Yanmars will push the boat well over 8kts when the wind is absent. The peak speeds are 25 knots even under her conservative rig.

    The first set of jpegs give the idea. The next set of jpegs starting with Eagle are other Brookes catamarans. Brookes initially worked with Spronk before he went out on his own. Plywood can last if well maintained and has a West type system used. A web address about an article on Doug Brookes is at: Professional BoatBuilder - 119 - Jun-Jul 2009 https://pbbackissues.advanced-pub.com/?issueID=119&pageID=31
     

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  15. oldmulti
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    oldmulti Senior Member

    Northwind Yachts is a Spanish monohull manufacturer that over its 40 year history has built many semi-custom monohulls and a few custom multihulls. They wanted to add a new product to their company in 2016 and explored a catamaran option. They approached François Pérus and Romain Scolari to do the concept study with the assistance of Jonas Hertwig, who is a yacht designer, for the interior design and he also did some of the exterior design. Gonzalo Redondo, managing director of D3 Applied Technologies, designed the hull bottoms and the appendages, and co-worked with the architects for performance optimization, using the latest hydrodynamics and VPP knowledge. The result was the North Wind 55 catamaran designed at the limit between racing and cruising.

    The 55 cat is 55 x 28.9 foot with an approximate displacement of 47,000 lbs (calculated guess). A 76 foot carbon wing mast carries a 1100 square foot fully battened square head mainsail and a 590 square foot fore triangle with a self tacking jib and a 1700 square foot asymmetric spinnaker. The length to beam on the hulls is 10 to 1. The hull shape features the latest trends in hull design with negative rocker aft and flat sections fore and aft improving pitch stability. The underwing clearance is 3 foot. The draft is over the rudders and daggerboards is 7 foot but variable with T foil rudders and Z foil daggerboards. The numbers suggest this cat will be fast but not an outright racer.

    The bows are inverted and the sail plan set back enough to accept a self-steering jib. Two versions were proposed: an e-glass fabric, vinylester resin with some carbon reinforcement and a high-performance version in mainly carbon and epoxy resin. The foils are carbon fiber in either version. The daggerboards can be fitted with either curved or Z-shaped daggerboards. The latter, a kind of foil, associated with T rudders, should help to support the hull (but not to make the boat fly). According to Gonzalo Redondo “The main advantage of the Z foils is that in case of flying/jumping they have better heave stability than C foils. The biggest difference of Z foils is dynamic stability and control… Some static VPPs might tell you that a C board with winglets are better.”

    The accommodation suits the style of previous North Wind owners with excellent owner and guest double cabins with attached ensuites in the hulls. The main saloon contains a large galley, entertainment area, seating, a dinette and internal steering navigation area. The associated cockpit can be “integrated” by the use of a large door between the 2. The external steering and sail controls are on each gunnel.

    The jpegs give the idea. I do not think Northwind built the cat and it remains a concept. Interesting.
     

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