Multihull Structure Thoughts

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

  1. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Scuff, I do not know if there are penalties for going further than 200 miles offshore but I am certain an insurance company would say bad luck to you if have a problem over 200 miles from shore and if a person was hurt over 200 miles out you could be charged etc.

    An update on Ping-Pong an Atlantic Proa with a junk rig mast featured on page 66 of this thread. Ping-Pong and is 23.3 x 10.8 foot weighing about 800 lbs and displacing guess 1400 lbs. The single 24 foot above deck mast carries a junk rig carries a 245 square foot sail with a 6% chamber with maximum depth at 45% aft of leading edge. There are 15 x 50 mm batterns sewn into the sail. Ping-pong hulls have a Cp of over 0.6 and a length to beam of 11.7 to 1 on the main hull and 22 to 1 on the float.

    The structure is 6.5 mm pine plywood, stich & glue, taped with 446g/mm2 +/-45 glass and epoxy. Coated simple with white acrylic house paint. The plywood sheets are already waiting for cutting and lengthening at the workshop. The bottom of the hull is v-shaped, the shape is modified to maximise lateral force and a high prismatic coefficent. There will be no leeboards (before sailing test anyway). The sleeve pipes of rudders are connected by bar which changes and locks the rudder positions. The rudders are wired to a wheel in cockpit. Junk rig is used to minimise building costs. It should work well, because the sheeting system is easy to build for a wide boat like proa. Junk rig is easy to reef and it also eliminates caught a back allowing the sail turn in freely. The final costs were about $3500 after 10 weeks and 450 hours of build time. The last two weeks were spent with the rudders.

    The performance evolved with initial trials in 10 to 12 knots winds and 2 foot waves. Three panels of junk sail up and go. Junk sail worked well and is quite balanced so the sheeting force was low. Speed about 5 knots. The shunting angle is about 100 degrees. The Junk rig is cheap (under $400 with mast, sail, battens, blocks, ropes), low stresses everywere, low sheeting force, the easiest rig to reef, all controls in cockpit, safe caught a back and so on. 20 knot winds get maximum speed of 13.5 knots and several times over 12 knots. The buoyancy reserve is OK (quite near 200%). The problem is the drag from beams and nets when the heeling force increases. The ama needs to be deeper. The sail luff and leach are elliptical to minimise losses of upwash-downwash phenomenon. A new Junk sail and rigging will be built using carbon mast and battens to decrease drag and weight and designing each panel to have more camber.

    There was a rebuild of various aspects of Ping-Pong in 2005 which was relaunched after a five week rebuild. The main changes were: 1. Bigger rudders (about 100% more area) 2. Higher clearance (from 30 cm to 50 cm) on the cross arms 3. More camber at the new junk sail. The rebuilt boat was test sailed. Ping-Pong in 10-15 knots winds, course to windward, new junk sail work well, new rudders too. Shunting angle was between 90-100 degrees, satisfied. New rudders could have more balancing area in front of axis line, now they are heavier to steer than the old ones while there is some weather helm. The modified Ping Pong has never lifted the windward hull out of water. Windward hull is quite heavy (with sailors) and junk sail is very easy and fast to reef. We occasionally sailed well over 30 knot winds. Maximum speed was 14 knots and 12 knots when cruising.

    Here you have an easily handled boat that can act as a mini cruiser that can be built in 10 weeks for under $5000 from hardware store materials. It performs reasonably well and can maintain over 10 knot averages. Interesting and fun.
     

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    Last edited: May 3, 2021
  2. guzzis3
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    guzzis3 Senior Member

    I guess the Woods Gypsy isn't a production boat ... 28' plenty of ocean crossings and long term liveaboards...

    Looks a bit narrow and the hull prismatic ?

    Anyway what would I know...

    The europeans do love to regulate don't they ? and you wonder why the poms voted to leave..
     
  3. oldmulti
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    oldmulti Senior Member

    The RS57 is a 56 x 24.6 foot power displacement catamaran “sail trawler”. The 57 weighs 25,800 lbs and displaces 34,000 lbs. The cat draws 4 foot. Its powered by two 75 HP Yanmars driving 3 blade propellers. The claimed fuel economy is 1 litre per engine per hour at 8 knots cruising speed. Very good if the figure is accurate.

    The accommodation is good and set up for the original owner who commissioned the design. The cat has good sound proofing and is very capable of delivering the owners needs. Unfortunately the original owner travelled about 200 hours or 1500 nautical miles before he sold it.

    The cat is constructed from three main techniques. Strip planking, is used in making the bottom of the hulls. It is made up of strips of red cedar in 20-30mm strips, stuck together and then covered with a biaxial fiberglass cloth impregnated with epoxy resin. Plywood is used for the bulkheads and side planking. Digital cutting is used to save time. Each individual element arrives pre-cut, according to the design, thanks to computer software which can be connected to a digital, industrial cutting machine. All of these elements are then pieced together on the floor like a giant puzzle. Using aligning pins and scarf joints allows for an optimum fixing of all the individual elements. Other elements are then added to the base of the hull, (transversals, bulkheads and other reinforcements) before everything is lined up using a laser. It required three people working for two weeks to line up the frame of the RS57. Before, the external sides of the planking is pre glassed under vacuum on marble to reduce the amount of finishing and sanding down needed. The interior is then impregnated with three coats of epoxy resin, meaning that even over a long time, humidity cannot penetrate. For the bridge and the deckhouse, we think that the well-known technique derived from the sandwich is the most appropriate. For the RS57, we did the following: for the outer layer a sheet of fiberglass. The middle layer was a PVC foam, and the inside layer was plywood. The plywood used as an interior facing, can be lacquered without too much tedious sanding and rendering work. The PVC foam ensures excellent thermic insulation, and the external glassing rounds off the general solidity of the build.

    All the parts of a modern multihull are glassed using strips of cloth, which is usually biaxial. From the main partitions to the transversals and to the lowest levels, every part contributes to the overall structure. The result is there for all to see: a lightweight structure with exceptional stiffness. By adding small quantities of carbon fiber at strategic points (mast bulkhead, beams, appendages) we can improve technical performance still further.

    The progress in wood composite techniques over the last 30 years, coupled with all the different ways that they can be used, means that they represent an interesting alternative to other materials that are currently in use. External maintenance has been made easier through the systematic use of cloth and epoxy resin as an outer coating on the whole of the boat. By using this system, the boat is well protected from humidity, and apart from a fresh coat of paint every 10 years, the upkeep is no more intensive than for any other material.

    An interesting cat that is well built. The jpegs do not do the design justice. I have attached a xray of the 65 foot version of this type of cat showing the structure for the ply timber construction.
     

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    Last edited: May 5, 2021
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  4. oldmulti
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    oldmulti Senior Member

    The pacific Harryproa type proa IS is still being built so a minimal amount of information. This will be more of a jpeg story. IS is 29.5 x 14.75 foot with a crab claw sail. The hulls are slightly asymmetric with flat dory bottoms.

    The guys met to initially build a 20 foot proa/cat with a crab claw rig in the Marshall islands using stitch & glue technology. The 20 foot proa/cat was funded by GIZ (German International Corporation) as a project “Transitioning to Low Carbon Sea Transport” (or TLCSeaT) prototype workshop in January to April 2020. Rob Denny also produced his 24 foot cargo proa for the same prototype workshop.

    After the protype workshop was complete the guys went home to Germany and decided to build a 29 foot “cruising proa” which may have been inspired by Denny’s thoughts. IS is built from ply and timber with ply bulkheads timber frames and stringers. Ply skin panelling is fiberglass covered. The decks are ply with timber stringers. The cabin roof is moulded ply. The cross beams have timber top and bottom flanges and are timber framed with ply web shear faces.

    The crab claw sail is a polytarp type of sail with many used windsurfer masts stuck together to form the upper and lower spars and a mast. The rudder arrangements are on a folding frame on each cross beam.

    The jpegs tell more of the story. Could be an interesting minimal cruiser for 2.
     

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  5. SolGato
    Joined: May 2019
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    SolGato Junior Member

    It’s cool to see so many designs adopting the “Crab Claw” sail.

    I have been designing my own hybrid version for my solar electric HobieCat.

    I saw an AquaCat for the first time years ago and was impressed with the sail system from a trailering, stowing and deploying standpoint. It looked to me to be the star of the show, while the low volume hulls and undersized support structure left much to be desired as far as beach cat designs go.

    One thing I have been considering with my setup is installing a track and a car along the front crossbeam where the sprits will be anchored to in theory allow better tacking angles. I don’t know how it will work, but it will be an easy modification so I figure it’s worth a try.

    The overall idea for my application is that the sail rig can remain assembled on the boat resting forward over the trampoline and bow when under electric propulsion, then if sailing is desired, the A frame can be erected and the upper sprit hoisted to unfurl the sail. To reef, the lower sprit is raised up to the upper sprit. The upper sprit remains fixed but is able to pivot on a swivel.

    And instead of Polytarp construction, I purchased a new Sunfish cruising sail that I intend to cut down.

    Around here in Hawaii, Crab Claws are of course great for cruising in our trades, I kinda like the idea of combining the old technology with the new. Plus the Craw Claw design is a great way to keep the deck clear of a low swinging boom making it more comfortable for passengers.
     
  6. oldmulti
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    oldmulti Senior Member

    The Czech Republic based Independent Catamaran company has produced RAW, a very high performance catamaran with some hull based accommodation. The IC36 is 36.1 x 20.33 foot that weighs 5,500 lbs (stripped) to 6,500 lbs depending on options chosen. The 46 foot high-modulus carbon wing mast from Pauger (optional) carries a 452 square foot mainsail, a 194 square foot jib and a 495 square foot code 0. Gennaker and spinnakers are your options. The hull length to beam is 15.5 to 1. The hulls have a bulbous flair above the waterline for accommodation. There are daggerboards that draw 6.6 foot with kickup rudders. The cat is also transportable being able to unbolt the cross beams etc to fit inside a shipping container or on a trailer. the underwing clearance is 2.65 foot. The design is done by Tomas Jonas Yanda.

    The reason for weight options is a stripped version or a Pacer model that has a coach roof, cockpit tent, more storage and cooking and freshwater systems. The Pacer model can accommodate eight people in the hulls, with a fridge and two-burner hob to port and a shower/heads to starboard. Or you can opt for a fridge and hob in the folding cockpit table.

    Construction is in epoxy-glass composite with local Kevlar reinforcement and foam core, helping to keep weight down to less than 6500 lbs. And there are three buoyancy chambers in each hull, which makes the boat unsinkable. The very forward cross beam for example weighs 55 lbs and can be loaded to 29,500 lbs before breaking.

    The light weight and high-performance rig mean you can sail at up to 1.4 times wind speed according to the advertising. Expect reaching speeds of 20 knots plus. The light-weight carbon-fibre rig is made for performance and high speed with minimal pitching. Light composite stays support the mast, along with top-of-the-market Facnor drum furlers and other state-of-the-art fittings all contribute to a boat that combines great performance with ease of handling.

    The jpegs give the idea.
     

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    Last edited: May 6, 2021 at 7:37 PM
  7. oldmulti
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    oldmulti Senior Member

    The Santorini 65 was designed in 1997 by Michel Joubert, Bernard Nivelt and built in 1998 by the Prometa shipyard. The 65 is a long range power cruising catamaran. The 65 is 65 x 24.25 foot catamaran that weighs 44,800 lbs and is powered by two Perkins Saber 6 cylinder 135hp (7 litre displacement) engines driving 45 mm outside diameter stainless steel shaft lines attached to 610 mm four-bladed propellers. The chine “canoe stern” hull length to beam at the waterline is about 14 to 1. The cat draws 4.5 foot.

    The great virtue of this cat is it can have any accommodation layout you would like but the design has been conservative layout using only 7.5 meters length of bridge deck accommodation with some hull based accommodation. No full length, double story bridge deck which adds weight and windage.

    The advantage of these long thin hulls with minimal windage is this number, 1.65 litres of fuel per mile at an average of 11 knots. This average consumption was measured over 1000 miles in a variety of weather conditions. The 7,200 litre total fuel supply allows a range of 4,000 nautical miles. It also allows you to spend $6,000 to $12,000 US dollars per fill of the fuel tanks depending on where you fill up. If you desire to use power to travel long distances EG a quick trip around the Pacific and the Atlantic, maybe 25,000 miles, you are going to be up for $35,000 to $70,000 in fuel costs alone. The cat can travel comfortably in 35 knots upwind or down. It slows down in 50 knot winds. Top speed is 15 knots.

    The structure of the Santorini 65 is aluminum. Thick aluminum. The hull bottom is 12 mm, the sides are 10 mm and the decks and coach roof are 6 mm aluminum. There are minimal stringers and framing using this build technique. Prometa has specialised in this type of construction in monohulls and some multihulls for years. To give you an idea a 60 foot Crowther aluminum power cat would have a 5 mm plate hull with 115 mm deep 5 mm plate frames and 40 x 40 x 3mm T stringers at about 400 mm centre lines. The deck is similar construction. The Crowther cat is not that much lighter than the Santorini 65.

    Being aluminum, you really need to understand electrolysis and how to deal with it. As Redrueben once said, he sailed on an aluminum 40 foot yacht that had a nickname of Pill as it was dissolving that fast.

    The Santorini 65 was sold for 25% of its build cost in 2010 to a guy who “reorganized it” and subsequently the 65 ended up being owned by Bernard Nivelt one of the original designers. A mast appeared on the cat as an auxiliary rig which would help increase the long distance cruising range if the wind blows in the right direction.

    This is a strong excellent long distance cruiser that is a good model for long distance power cats. The jpegs give the idea. The yellow cat is the Trawlivarius 65 which is the latest production version of the Santorini 65 being produced by Prometa.
     

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  8. guzzis3
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    guzzis3 Senior Member

    Have you considered featuring some of the boats that got it terribly wrong ? One example that comes to mind was an attempt by beneteu I think to build a catamaran. They were pretty ordinary.

    Just a thought..
     
  9. bajansailor
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    bajansailor Marine Surveyor

    I think that this was the Beneteau Blue II?
    I remember seeing one on the Hamble river in England 30 years ago, and thinking it was lovely - I wonder why they didn't 'take off'?
    Blue 2 Volume and excitement! - Multihull - Multihulls World - Multihulls World https://www.multihulls-world.com/practice-catamaran-trimaran/blue-2-volume-and-excitement

    This might be the boat that I saw back then -
    Beneteau Blue II Catamaran For Sale, 10.40m, 1987 https://hamble.boatshed.com/beneteau_blue_ii_catamaran-boat-14676.html
     
  10. Coastal Ogre
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    Coastal Ogre Junior Member

    I've heard (2nd hand of course) that the Blue II's suffered from early design & construction issues of various degrees. Hopefully someone with direct knowledge can comment. Charles Kanter seemed to think the world of them in his books.

    Having said that, I have seen one actively cruising in Guadeloupe back in 2016. A nice unit that appeared (visually) in good shape. I was never able to connect with the crew. But the cat looked to be frequently used.

    I would like to second Guzzis3 comment on perhaps expanding this thread/starting a new one that would examine some of the ideas/designs/whims that did not go 'according to plan'. Should be enlightening and beneficial :)

    IMG_5218.JPG IMG_5224.JPG IMG_5226.JPG IMG_5229.JPG IMG_5230.JPG
     
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  11. oldmulti
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    oldmulti Senior Member

    OK folks we will expand the thread to include some of the missteps or errors that can happen in multihull design and construction. We have to be careful to stick to facts and not identify some people who may still be working in the industry. The following is not a criticism but a warning about dreaming a fast cruising power catamaran.

    After a few displacement power catamarans, we will look at a “planning” power catamaran that can cruise at 18 to 22 knots with a peak speed of 26 knots. The Lynx 16 meter cat be built from 12 to 16 meters depending on needs with the same hull cross sections. We will stay with the lynx 16 meter which is 52.5 x 20.66 foot and weighs from 54,000 lbs to 74,000 lbs depending on configuration and intended purposed of the vessel. The hull shape in the diagram is a V planning shape which at higher speeds is intended to be more efficient. The length to beam on the hulls are 10 to 1. The cat draws 4 foot. With planning power cats research has shown that the gap between the hulls can be narrower without effecting performance. With displacement hulls the gap between the hulls needs to be further apart to reduce drag interaction between the hulls. But there are downsides.

    The power to drive these planning hull cats are large. Try 2 x Scania DI16 43M main engines with a total power 2 x 588 kW (2 x 800 hp) attached to water jets 2 x Hamilton HM461. This will provide the 26 knot speeds but at 260 litres of fuel/hour, if you cruise at 18 knots you will only be using 160 litres/hour. Using our mythical 25,000 nautical mile Pacific and Atlantic cruise you will only have to pay between $220, 000 to $500,000 for fuel to do the trip at 18 knots depending on where you buy the fuel.

    Again, the accommodation is anything you want. The diagrams show a work boat layout and the majority of this company work is in work boats for offshore work built to European regulations so they will be well built and seaworthy.

    Most of these designs are built in aluminum but could be built in foam glass or adapted to steel. I have no build information.

    The jpegs give the idea. The PDF is the general arrangement line drawings of the Lynx 16 meter in the jpegs.
     

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  12. guzzis3
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    guzzis3 Senior Member

    Please read this carefully and don't extrapolate on what I actually type.

    I have never seen a blue2 in the flesh. I saw one advertised at what I initially thought was a good price years ago and looked closer. I quickly became concerned by many elements of the design and subsequently had an interaction, possibly on this forum, with someone with direct experience with them. That person confirmed my concerns.

    The hull looks like it was designed by a monohull designer. Lots of skin area, big draggy mono style keel. The boats demount to fit in 3 containers. The beam connections and probably the beams also are flexible and apparently noisy. By all accounts they don't sail particularly well, are flexible and the layout isn't all it could be. I don't recall if any have actually broken, but I think it would need to be very cheap to tempt me.

    2c.
     
  13. oldmulti
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    oldmulti Senior Member

    The Phillipe Briand designed Beneteau built Blue 11 cruising catamaran has been subject to some discussion. So, let’s look at the basic cruising cat. It is 34.2 x 19.65 foot and weighs between 6,700 to 7,300 lbs depending on the information source (and I suspect the options). The 42.5 foot aluminium fixed fractionally rigged mast carries 440 square foot heavily roached main with many batterns, a 145 square foot self tacking jib and a 260 square foot genoa. The hull length to beam is a bit problematic as the waterline length varies between 29.25 foot to 33 foot due to fore and aft overhangs being depressed. The length to beam is about 9 to1 and goes to 10 to 1 when sailing hard. The large low aspect ratio fixed keels draw 3 foot. There were 48 of these cats produced.

    When this cat was designed this was the first catamaran design from Beneteau and Phillipe Briand was a very successful monohull designer. Result he designed a cat that would suit the perceived Beneteau market. Shapely ends that had some overhangs and fixed keels that were large to ensure some reasonable upwind performance. Result was a boat that had a semi “monohull” hull shape and keel.

    The impact of this varied but let’s quote the February 1987 Sailing magazine sailing review. “In heavy airs the Blue 11 … will travel at 12 knots. In more moderate airs it can move along at 7 knots easily” To quote Multihull World magazine “Yes, a catamaran weighing hardly three tonnes will experience a few difficulties when sailing to windward in a force 7…” And “But it suffers from its long keels to windward …, slams easily in the waves, because of its excessively low bridgedeck (it’s noisy too!) and pitches generously, through lack of sufficient volume in the ends... So it’s true, the Blue 2 isn’t a boat for sailing to windward.” Other reports say the Blue 11 can sail downwind at up to 18 knots. I suspect the fine ends and low prismatic hull conceived to ensure light air performance did not help the cat upwind especially in a seaway that induced pitching. Result, less than good upwind performance. For monohull owners looking for a performance catamaran in the 80’s, the lack of upwind performance may have been a down side.

    The next issue with the Blue 11 was its ability to be broken into 3 parts for container transport. The cat was basically an aluminium beam cat that had a central bridgedeck pod and cockpit unit added for sailing. This is OK in normal weather, but all reports I have read make comment about the noise of moving parts in a seaway. Finally, the accommodation layout was different for the time. It had a big full headroom main saloon but the galley, toilet and 2 double bunks were squeezed into narrow hulls.

    The Blue 11 was fiberglass with some foam glass components and aluminium cross beams bolted to the various hull components. If you are interested in one second hand, I would check the crossbeams very closely as corrosion and fatigue would be a major factor over its lifetime. Also, the masts were foam filled in the original versions which would need to be inspected.

    Now Beneteau learnt from this experience and years later started a small side company called Lagoon. It became one of the biggest cruising catamaran producers in the world. Now Beneteau produces the Excess line of catamarans. The later Lagoon and Excess cats can sail well and have large amounts of accommodation.

    The jpegs give the idea. In summary the Blue 11 was a brave attempt for its time, but lacked the refinement in hull shape, construction and accommodation that we have come to expect.
     

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  14. guzzis3
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    guzzis3 Senior Member

    Yes good on them for trying, but it's an object lesson in choosing the right person for the job. Get a cat specialist to design cats, not a mono designer, maybe think twice before using a trimaran specialist. If they had handed the brief to a good cat specialist it could so easily have been a brilliant boat.
     
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  15. Dejay
    Joined: Mar 2018
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    Dejay Senior Newbie

    Well that boat is from 1985, think of all the books that have come out and the internet with all it's info, forum, email, mailing lists and videos. Culminating in this here thread ;) And software. Today you still need a good designer to build a decent boat but maybe not a specialist. Best of times, worst of times.
     
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