Multihull Structure Thoughts

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

  1. oldmulti
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    oldmulti Senior Member

    Waterbear. I will try, this is pre internet days but some where I have an article and there is some history.
     
  2. waterbear
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    waterbear Senior Member

    Thanks! I did find this page, but the articles are too low resolution for Google translate.

    http://www.histoiredeshalfs.com/50 multis/G Gautier 1.htm
     
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  3. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    As requested by Waterbear. Gautier 1 was a bold experiment as a racing catamaran for skipper Jean-Yves Terlainto enter and hopefully win the 1980 OSTAR event. The cat was 56 x 37.5 foot displacing 21,300 lbs. The masthead sloop rig carried 1,500 square foot of sail in the basic rig. The draft of the hulls was 4 foot (yes 4 foot) with low aspect ratio keels. The design was basically a pod cat with unique hull and pod shapes.

    Now I am guessing at the logic here but I suspect it was trying to solve many early cat issues at once. The pod was used to as a base for the rig as this cat basically had a triple spreader monohull rig with side stays going down to the side of the pod not out to the hulls. It would have provided a rigid forestay which meant the cat could go upwind well (the Ostar is normally an upwind race). The hull shape is relatively fine ended fore and aft at the waterline and a bit pot bellied (low prismatic coefficient) to carry the weight of the cat, again good for upwind in a slow moving monohull. But early fine ended cats pitched a lot and some wider ones had pitch poled. Gautier was relatively wide for its time and running/reaching on wider cats with fine ends and big rigs increases the chances of pitch poling. My guess (repeat guess) is the designers tried to minimize the pitching/pitch poling by making the hulls and pod very full at the ends above the waterline. All rational thinking at the time, but as with all experiments you can go to far and there were other solutions evolving. After Gautier 1 went sailing, no other designer tried to replicate the broad design concept of square ends for hulls and pod above the waterlines.

    Other designers hulls progressively had higher prismatic coefficients (fuller ends, shallower mid bodies) which have higher top speed potential with less pitching. These hulls also had deep foils with widely stayed fractional rigs that operate better on flexible multihull structures. But the most important improvement in multihulls over time are lighter stronger structures.

    The next issue was the construction, it was all built in aluminum. A modern and some of the older designs around the same size in foam glass or timber were 10,000 lbs lighter with the same size rig. Modern 60 foot racing tri’s can weigh 10,000 lbs and carry 2,800 square foot basic rigs. Gautier 1 had hulls of 3 and 4 mm aluminum with frames and close set stringers. The pod was 3 mm aluminum skin with frames and close set stringers. The 6 aluminum cross beam tubes were each 1.75 foot in diameter running the full width of the beam. This boat was strong and capable of being driven hard in an upwind race..

    The design was for racing so accommodation was an afterthought. The cockpit had a unique feature 2 steering wheels side by side 100 mm apart. Why not a larger single wheel for a single handed racer should be enough.

    Gautier was eventually wrecked in a force 9 storm when it lost its rig and was driven ashore.

    The real issue here is the basic conceptual design of Gautier 1 was flawed. Sorry about the quality of jpegs, if anyone else has any jpegs etc it would be appreciated.
     

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  4. waterbear
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    waterbear Senior Member

    Oldmulti, thank you for this! I was hoping to learn more about the rationale behind the design, but who knows if that could be unearthed. The fact that the boat weighed 10000lbs more than some contemporary designs says everything.

    My guess is someone with money had the silly space age concept before going to a NA and also had the conviction that it should be built of aluminum. NA was happy to take the money and the rest is history?
     
  5. willy13
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    willy13 Junior Member

    Regarding aluminum construction, another possibility is a naval architect interested in conservationism thought it was worth the risk to experiment with a building material that is easy and economical to recycle. In New York State when a fiberglass wind mill blade brakes it is cut into pieces and put into landfills. Clearly aluminum has draw backs regarding strength vs. weight, but as a conservationist I believe we should remain open minded about this building material and be careful to not dismiss it too quickly. But I am not a naval architect, just an enthusiast...
     
  6. oldmulti
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    oldmulti Senior Member

    This is about what can be done if you are ruthless about designing a charter catamaran. It is also about a cat model name that surprises me. It is called the Upwind 50 Eco. The company UPWIND CATAMARAN from Zagreb, CROATIA says: “The aim of the UPWIND 50 ECO design is to provide eco friendly sailing, superior accommodation quality and enhanced sailing speed, especially upwind. While usual charter catamarans can sail upwind only at an angle of around 45-55 degrees, UPWIND 50 ECO has two lifting centreboards which permit sailing close to the wind (upwind) at an angle close to 30-degrees, as a monohull, yet at higher speeds.” Interesting statement.

    The Upwind 50 is 55 length over all including the bow sprit, 49 x 23 over the deck with a Guess displacement of 40,000 lbs (not specified). The 70 foot mast carries a 840 square foot mainsail, 925 square foot roller furling jib, a 172 square foot storm jib and a 2040 square foot spinnaker. That is a fair bit of rig power for a charter cat. The hull length to beam is 11.5 to 1. The draft varies from 5.2 foot over the rudders to 8.8 foot over the daggerboards. The engines are two 40 HP diesels which are fuel economical using 8 litre/hr. There is a 1 kw solar panels array feeding a 1400 amp lithium ion battery bank.

    The accommodation is designed for charter with 4 double berth real cabins with toilets on the bridgedeck. At the forward end of the bridgedeck is the saloon with galley. The saloon has forward panoramic views for the 10 seated guests and crew. The hulls below wingdeck level are mainly used for storage, water tanks engine etc. The cockpit and helm control are on a flybridge above the main bridgedeck accommodation. This is a very comfortable cat. This brings me back to my initial point, we have the accommodation of a charter cat but a rig and foils of a higher performance cat. No performance figures are given but I can accept it will go to windward OK, but at what speed when you are pinching to 30 degrees.

    The hulls, underwing and bulkheads are aluminium construction with some of the bridgedeck cabin. There is some composites in the upper structure but little detail is given. The chine hull shapes are simple and pragmatic for a charter cat. The whole cat is designed and built for a purpose and if it sails well (it should), it has been well done.

    The jpegs give an idea of the cat, an interesting concept.
     

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    Last edited: Jun 5, 2023
  7. peterbike
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    peterbike Junior Member

    Hmm... it appears that beauty was not one of their prerequisite's ? :confused::confused:
     
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  8. oldmulti
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    oldmulti Senior Member

    When a US military shipwright Metal Shark launches a new range of luxury power catamarans you know there is some serious money involved. The Metal Shark M 30 is 100 x 44 foot, weighs 336,000 lbs (150 tons) and displaces 437,000 lbs fully fitted out. The draft of the cat is 6.6 foot over the rudders and props. Now we get to the expensive part, it is powered by 2 x MTU 16V2000 M96L (1939 kw / 2600 BHP) diesels using 2 x ZF 5350 (ratio 4.033:1) Gear Boxes and 2 x 5-Blade Fixed Propellers (58”). Add this to a 60,000 litre fuel tank you get a long range of 7,000 NM @ 10 Knots, a cruise of 4,000 NM @ 16 Knots, a sprint of 2,000 NM @ 23 Knots. Top speed in lightship mode is 30 knots. The fuel economy ranges from 8.6 litres/mile at 7 knots to over30 litres/mile at 23 knots. A quick transatlantic trip at 16 knots will only cost you $100,000 plus in fuel alone. It will be cheaper to higher a 737 jet. Opps, sorry back to the boat.

    The accommodations on the M30 features a beamy, modular spaces across three levels that can become whatever its owners can dream up. To quote the company “Custom configurable interior spaces are designed to comfortably accommodate two owners plus four guests and a crew of four, with ample space for provisions and gear. Metal Shark’s panoramic window treatment allows for dramatic views and an open, airy atmosphere, far removed from the walled-in isolation of traditional yachts.” The M 30 can carry all the required toys to amuse the guests and has a fully integrated Solar array and batteries with inverters to go into “quite” mode overnight when at anchor. Hopefully the parties stop by midnight. The power generators are the day units are 2 x 50 kW 120/240V, 60Hz, 1PH (Paralleled), the night unit 1 x 16 kW 120/240V.

    The construction of the M 30 is mainly aluminum in all structural and skin elements. The interior is between the builders and owner’s interior designer to fit out the vessel to the owner’s taste. Result there is composite panels with fabric or veneer faces etc where required. Sound insulation is liberally used for passenger comfort.

    There are limited jpegs for a few who may be interested.
     

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  9. oldmulti
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    oldmulti Senior Member

    The following is again dream land but an interesting variation. On page 177 we spoke of the Domus trimaran designed by Van Geest Design and Rob Doyle Design who have now teamed up to present a new 30-metre concept catamaran. The Domus 30 is 100 x 53.5 foot with a guess displacement of 220,000 lbs. The rig height and sail area is unknown beyond it being a sloop rig. The hull length to beam is about 12 to 1. Engine power not specified beyond it being a hybrid and there is a very large solar array with batteries etc.

    This Domas 30 is described as a luxury fast cruiser. The design is based around a good structural concept of having full width 7 foot high bulkheads across the full beam of the cat. This is very good structurally and also provides a very large single floor accommodation space on the bridgedeck. This concept has accommodation of house dimensions. The 2 VIP cabins with full ensuites are larger than many house’s master bedrooms. The saloon cockpit space can seat a party and a half, then we get to the hulls. This is where the guests, crew etc have to live in there 10 x 10 foot double cabins with ensuites. There is storage for your spare boats and toys forward of the main cabin. The deck space is very large. The flying cockpits are at each gunnel with several dual seats for passengers to watch the crew sail the cat. There is also a central cockpit with a solid roof over for protection from the sun.

    The structure is not specified but is likely to be foam glass with a lot of carbon or very well engineered aluminum. The design team has been involved in 60 large vessel projects so will have an understanding of requirements. The full beam bulkheads are structurally very good and can be lighter than EG a smaller dimension aluminum tube.

    This is a well conceived design that will sail well if the rig matches the hull design. Pity it will require a crew and electric everything to help it sail around, but as a fast cruiser it will be very good. If only I had a spare $10 mllion plus. The jpegs give the idea.
     

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  10. oldmulti
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    oldmulti Senior Member

    This is a charter catamaran with a distinctive main cabin visual line designed by VK Yacht design. The VK 55 is 55 x 33.8 foot with a displacement of 43,000 lbs. The fixed 75 foot aluminium mast carries a 1,280 square foot mainsail, 936 square foot self tacking furling genoa and a 2,797 square foot spinnaker. The length to beam on the hulls is about 6.5 to 1. The draft over fixed low aspect ratio keels is 5.2 foot. The engine power is 2 x VH4.80-59kW (80.3hp).

    The accommodation for a charter catamaran is good. There are 4 double berth cabins with ensuites and 2 single berth cabins with attached toilets in the hulls. The bridge deck has 4 separate dinettes forward with a large galley and entertaining space. The attached cockpit is large with a lot of seating and 3 tables. The sailing aspects of the cat is done from a flying bridge in the centre of the cabin roof.

    The construction is mainly aluminium. Similar sized cats have hulls of 4 mm plate with 37 x 37 x 3 mm T stringers on 250 mm center lines. Frames are 115 x 50 x 5 mm T sections in the hulls. The deck and cabin plate is 3 mm with 75 x 4 mm with a 25 x 3 mm flange to form a T section deck and cabin frames with 37 x 37 x 3 mm T stringers. The structural cross beams are aluminium but in this design the underwing appears to be main support structure with roof ring frames providing additional strength. I would like o see the detail of this structure.

    There are no performance figures but I do not think anything over 15 knots will happen if I am correct about the hull length to beam. The rig is powerful enough but hull wave drag will be the limiting factor. I suspect the engines will be help keep any charter schedules.

    The jpegs give an idea. A roomy simple cat that will fulfill its function.
     

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  11. oldmulti
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    oldmulti Senior Member

    Just a few odd ball jpegs that I have found. The first is a jpeg of a 20 meter all "carbon" racer cruiser catamaran. I wish I knew more about this design but unfortunately there was no further commentary. The next jpeg gives you an idea of mass production. Many "ships" being transported on a catamaran barge. Each of the "ships" look like boats that go down the Rhine. The Rhine barges can range from 200 tons to 2000 tons displacement. This catamaran barge is carrying at least 17 of these Rhine type boats, so this catamaran barge could be carrying up to 30,000 tons. The final jpeg shows you don't need anything fancy to carry a container, a fine sample of if you have a need you will find a solution. I hope there was no waves or strong winds on the voyage. Back to sanity tomorrow.
     

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    Last edited: Jun 8, 2023
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  12. Andrea Wasserliebend
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    Andrea Wasserliebend Junior Member

  13. oldmulti
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    oldmulti Senior Member

    Andrea. I will do a bit tomorrow on the Mattia, but I do not think I will be adding much value.
     
  14. oldmulti
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    oldmulti Senior Member

    This is about a support catamaran for someone who enjoys using his submarine. Yes, this cat has a rear deck crane to rise and lower his submarine from the water. Thunderbird 2 was designed and built in Turkey by Brilliant Boats and B and B yachts. The cat is based in the Caribbean. Thunderbird 2 is 70 x 33 foot displacing 161,000 lbs (72 ton) at full load. The draft is 3.8 foot. Maximum speed is 22 knots from the two Yanmar 8SY engines and Hamilton waterjets. At 10 knots Thunderbird 2 has a Transatlantic range.

    The cat carries a 3 passenger 1000 nautical mile range Triton submarine on the aft deck which has an 8.5 ton crane capacity to lift the sub in and out of the water.

    The accommodation has a master cabin in 1 hull and a guest cabin in the other hull with space for crew forward. The main saloon is area has the galley and a spacious lounge entertaining area. There is also an office for navigation, administration and monitoring of the sub when launched.

    The build of Thunderbird 2 is mainly aluminium. The jpegs give a good insite to the structure. This is a structurally complex build especially around the submarine deck which has to support a 6 ton plus load. A combination of a raising and lowering platform plus the crane arms for initial control of the sub puts impressive loads on the aft hulls and roof structure. I don’t know any structural dimensions.

    A very interesting design for a specific task. The sub name is Thunderbird 4, do you remember an old puppet television series where Thunderbird named submarine, rocket etc used to save the world? Study the jpegs, they will provide a lot of information.
     

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  15. oldmulti
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    oldmulti Senior Member

    As indicated Andrea I can only add an analysis of what and probably you have found on the Mattia e Cecco built Enrico Contreas designed Mattia 39. The Mattia 39 is 38.4 x 15.75 foot with a weight of 8400 lbs and a displacement 15,000 lbs (varies according to the boat). The 44 foot fixed aluminium mast carries a mast head cutter rig with a 340 square foot mainsail and a variety of headsails. The maximum sail area is about 900 square foot with main and fore triangle. The draft can vary between 2 and 6 foot with the centre boards. The engines vary from 20 to 80 HP inboard diesels. Now we get to my analysis. I could be wrong here, as there is not much information on this design.

    The Mattia 39 is a design of its time. It has 34 foot long waterline with a bow over hang. The hull shape looks classic moderately fine ended semi pot bellied (low prismatic coefficient) design and shape of the late 70’s. This means if the length to beam is about 11 or 12 to 1 it will be a reasonably fast shape but there will be more pitching than a modern design. Think 18 knot peaks 8 knot averages in reasonable conditions.

    It has a long wing deck which provides internal accommodation and a strong base for the rig. Being a Spanish/Italian design they tried to make it attractive with a lower main cabin top. Result there is a pod on the underside of the wingdeck which acts as a foot well for the main table but far more importantly provides a strengthening structure for the mast base which goes through the main cabin roof. The pod extends forward to where the forestay connects to the forward end of the wing deck.

    The structure says GRP. It looks like solid glass for the hulls, maybe balsa or foam glass for the decks and underwing. I suspect the internal bulkheads and fit out are well done plywood. If I am correct the builders are very experienced in multihulls and if the boat has been well maintained these cats should be still a good vessel. But please have a survey done as some of these cats were used in Charter as was the one you are looking at.

    The accommodation is to quote 1 advertisement. “INTERIORS 2 cabins, 2 bathrooms 1 Master cabin aft with double bed, private bathroom with electric toilet and shower
    1 Guest cabin aft with double bed, separate bathroom towards bow with electric toilet and shower. 4-burner galley with double gas cylinder, electric oven, microwave oven, internal fridge and freezer Large convertible dinette with dining table and sofas.” Reasonable but berths across the boat are not always comfortable upwind.

    Summary, a reasonable cat that if well maintained and should be a good value boat. It is better than the old English designs (Catalac etc) but is not as good as the modern lightweight performance cruisers. Sorry about the limited jpegs.
     

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    Last edited: Jun 11, 2023
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