Multihull Structure Thoughts

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

  1. redreuben
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    redreuben redreuben

  2. oldmulti
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    oldmulti Senior Member

    The catamaran WILDFLOWER has proven fast, comfortable, and seaworthy. Her light weight, allowed her to be trailered 3 times from Santa Cruz, CA, 1,000 miles north to Anacortes, WA, to sail and explore the San Juan Islands, the Olympic Peninsula, the Salish Sea, and the Islands and Fiords of British Columbia as far as Princess Louisa Inlet and Johnstone Straits. It also has spent 2 summers exploring San Francisco Bay and its tributaries, and also spent summers sailing Monterey Bay from our homeport of Santa Cruz, CA. Oh it also was being prepared to do the R2AK.

    Today we will discuss the design and build of the cat and tomorrow we will discuss the sailing performance of this cat. The design was done by Skip Allan and Howard Spruit. Skip Allan lived on, cruised and raced a 33 foot mono for 150,000 miles. Howard Spruit is the main builder who has built an excellent Jarcat 5 extended to 18 foot.

    Wildflower is 22 x 8.5 foot with a shell weight of 800 lbs, a weight of about 1200 lbs with outboard, rig, liquids, anchors etc. The sailing displacement is about 1600 lbs. The all up weight for trailering (including the trailer) is about 2500 lbs. The rig is a Hobie 18 mast (older 28 foot version) and a 177 square foot mainsail that had 3 reef points sewn in. The Standing Rigging is Dynex Dux 5mm Spectra. The initial jib was a 90 square foot Etchells jib which is on a roller furler. There is a second hand spinnaker. The hull length to beam is about 10.5 to 1. The single hull based daggerboard draws 4 foot when down. The rudder is a centrally mounted kickup. The cat draws 3 foot when the rudder and outboard is down, when everything is retracted the draft is 1.3 foot over its mini keels. The minikeels is 150 mm x 8 foot long for bottom protection when beaching.

    The accommodation is good for a 22 x 8.5 foot cat. There is a solid foredeck with storage, a double berth cabin with loo on 1 side then a galley area on port and a navigation area starboard. The maximum headroom 4.7 foot in the cabins but the galley area is placed under a hatch that allows 7 foot headroom when open. The cockpit is large and comfortable.

    The build is an extension of a Jarcat type structure combined with “Hartley’s Guide To Boat Builders” as a guide to specifications. Howard Spruits drew over 100 detailed diagrams for the build. The cat took 3000 hours to build over 18 months from mid 2010 to 2012 launch. The cat is basically Meranti mahogany marine plywood and fir timber. The hulls are 6 mm plywood covered with 200 gsm “S” glass fiberglass cloth sheathing in the West epoxy system. The topsides 6 mm plywood covered with 264 gsm e-glass fiberglass cloth. The underwing is 9 mm plywood covered with 320 gsm “E” glass. The hulls have 2 stringers about 45 x 18 mm on the outboard sides and a single stringer on the inside. There are chine and keel timbers. There are 3 main plywood and timber cross beams with an approximately solid timber 100 x 50 mm forward beam for the forestay to attach to. The build is a well thought out structure that has handled 1000’s of miles of trailering and sailing without any real problems. The rig has lasted well without to many issues and has been upgraded with EG a screecher.

    This cat does what it was designed for and does it very well. The first jpeg is Princess Louisa Inlet, British Columbia. The jpegs give the idea.
     

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  3. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Wildflower is a very good 22 x 8.5 foot trailer sailor catamaran. Today we focus on its performance. The theoretical numbers by simple calculation are 4800 foot/lbs righting moment, a full sail capsize apparent wind speed is 15 knots and an average speed of 8.8 knots. The Bruce number is 1.40.

    The reported real performance is “Maximum measured speed to date under sail is 13.0 knots, between 2013 and 2016, with reefed main and jib, in 20 knots True Wind Speed on reach, True Wind Angle of 135 degrees, apparent wind angle (AWA) 125 degrees.” And “Best speed to date on the Velocitek was 11.8 knots under main and jib with TWS of 16 knots and AWA of 100 degrees. After three shakedown sails, the boat handles nicely. TWS all three days off Santa Cruz was 12-16 knots. Boat speed upwind was 6.5 to 7 knots slightly cracked, 9 to 12 knots reaching. We "deployed" an asymmetric in 14-15 knots with 90 degrees AWA. We were making 9 to 11 knots, with two of us sitting on the windward cockpit coaming and the windward hull still in the water.” The simple calculation average speed numbers are similar to the real world performance.

    But the real indicator of the theory against the real world happened of the Santa Cruz main beach. Wildflower was close hauled with 1 reef in the main doing 6.5 knots in 15 knots of wind in 4 to 8 foot swells with a 1 to 2 foot wind wave on top. A 20 knot gust of wind hit as the windward hull was on a larger swell. Wildflower capsized. The crew had released the mainsail quickly as both crew slid from the windward side of the cockpit down to the lee side of the cockpit. Once the capsize commenced the wave momentum finally pushed the cat over. Remember, Skip Allan has sailed 150,000 miles and the crew reacted well releasing the mainsail quickly.

    The theoretical capsize wind speed is 15 knots, the actual capsize happened at 20 knots with one reef in the mainsail. If the gust had happened in relatively flat water the cat may have stayed upright with the main released. The larger swell of eg 7 foot with a 2 foot wind wave meant the sea was larger than the cats beam. Research says a “wave” size larger than the cats beam can cause capsize in the wrong conditions. These 2 factors probably combined to cause the capsize. There was minimal damage in the capsize and recovery.

    This is not a criticism of Wildflower. It just indicating that there are limitations to 8.2 foot beam trailer sailor cats. Wildflower solution was to add a mast head float to the rig to limit the capsize to 90 degrees if possible. The carbon and foam, masthead float (2019) providing 58 pounds of flotation and Windex mount. The float is secured with 3 x 1/4″ machine screws and is easily removable for trailering. A jpeg attached shows the float from Turning Point Design. The only problem with mast head floats is the way a cat capsizes. If the cat is thrown over hard (fast), the masthead float may break the mast tip off a fractional rig and fully capsize. If the capsize is slow with the sails softening the rollover the masthead float may be effective and prevent a full capsize.

    So how could Wildflower stability be improved? Water ballast and having the crew sitting on bench seats further out from the cat’s side would assist. But the main solution would be reefing the rig early. Reefing, plus using sea anchors, in rough conditions will help enormously when cruising. From simple calculations water ballast and people sitting out would allow full sail up to 19 knots apparent wind.

    A good safety feature are two anchors, chain, and rode, oversize for cruising lesser frequented waters. Primary anchor is a Lewmar 14 lb. Delta with 21′ of 1/4″ chain and 179 feet of 1/2″ nylon rode marked at 25′ intervals. Secondary anchor is an 11 lb. aluminum Fortress, 17′ of 3/16″ chain, and 125 feet of nylon rode. There is an extra 300 feet of 1/4″ nylon in a duffel for stern tying to shore. Also Wildflower has a drogue.

    Wildflower is a very good trailer sailor catamaran but it has its limitations as all similar cats. Sail them within their capability and you will have many days/weeks of good relatively fast cruising. The jpegs give an idea.
     

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  4. bajansailor
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    bajansailor Marine Surveyor

  5. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

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  6. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Redreuben asked about Thomas Firth Jones Brine Shrimp in the calculations for small cats. So, we will do a quick summary on 5 small ocean crossing cats. The Tiki 21, Brine Shrimp, Mana 24, Dandy (original round bottom version with sloop rig) and Tiki 26.

    The Tiki 21 is 21 x 12 foot with a displacement of1800 lbs and 210 square foot of sail area. The RM is 7960 ft/lbs and a capsize wind speed of 22.6 knots. Th average boat speed is 7.4 knots.

    Brine Shrimp is 23 x 14 foot with a displacement of 2900 lbs and a sail area of 247 square foot. The RM is 11980 ft/lbs with a capsize wind speed of 26.5 knots and an average speed of 7.5knots.

    Mana 24 is 24 x 12/7 foot with a displacement of 2090 lbs and a sail area of 216 square foot. The RM is 9930 ft/lbs with a capsize wind speed of 24.5 knots and an average speed of 7.65 knots.

    Dandy version 1 round bottoms is 25 x 15.3 foot with a displacement of 2940 lbs and a sail area of 306 square foot. The RM is 16600 ft/lbs with a capsize wind speed of 26.6 knots and an average speed of 8.25 knots.

    Tiki 26 is 26 x 16.1 foot with a displacement of 3000 lbs and a sail area of 285 square foot. The RM is 18000 ft/lbs with a capsize wind speed of 29.4 knots and an average speed of 7.9 knots.

    Do notice the value of beam? Each of these cats can handle 22.5 plus knots of wind speed before capsize. They also require seas of 12 feet before wave capsize becomes a potential problem. All of these cats can be trailed, but Brine Shrimp is the only one that can be folded prior to trailing. All need to be “assembled” before sailed.

    You lose easy trailing but you gain true ocean crossing capability. The price you pay is in the accommodation. The Tiki 21 has basically 2 berths and very limited space. Brine Shrimp, Mana 24, Dandy and Tiki 26 all have 2 berths with some sitting space, small galleys and loo spaces. Wildflower has more internal space than any of the above.

    So, your choice trailability, accommodation space and below 22 knots wind speed capsize and 8 foot wave issue. Versus transportability, above 22.5 knots wind speed capsize and 12 foot plus sea capability. Cost, time to build etc would be similar. Of all the cats discussed in this size I would either choose Wildflower or Dandy original version with sloop rig. Both are very good vessels for their style of sailing.

    Jpegs show the cats.
     

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  7. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Bernd Kohler has produced another fun small day sailing tri for anyone up to 180 lbs. The tri is 13.1 x 7.9 foot and weighs 145 lbs all up. The 19.5 foot mast is a 50 mm aluminium tube which has a 97 square foot sail that reefs around the rotating mast. The mast has some stays but can still rotate due to a mast head bearing to attach the stays, that allows the mast to rotate.

    The main hull is an easy to build 13.1 foot sharpie-shaped hull. More or less an instant build. No stitch and glue. Stitch and glue needs to many work steps, Building on stringers is straight forward operation. The floats work like water-skies and generate dynamic lift at speed, like foils but without the hassle of foils. The Floats have some volume and have static righting moment.

    The bill of materials shows 3 sheets of 4 mm ply for the shell and 1 sheet of 6 mm for transom, x arm bulkheads and hull bottoms. Timber stringers, chine etc are 19 x 19 mm spruce (100 foot) with 10 foot of 25 x 25 mm. Some 120 gsm cloth and UD carbon fibre in epoxy is required. There is a 3 foot mast support tube 60 x 2 mm wall aluminum for the 50 mm mast. The x arm tubes are 40 x 2 mm wall aluminum tubes that are bolted onto the floats and tied with 6 mm Dynema to the main hull. The foils are ply with a centre spar of timber with some carbon fibre and glass wrapped around. The daggerboard is in a case outside the main hull. The rudder is a kickup on the stern.

    Bernd Kohler quote about load carrying and performance is “The construction water line (CLW) is drawn on a sailing weight of 180kg (397 lb). At this weight the boat will be already at 7 knots in plane. The boat will be good for about 12 to 15 knots. I am always wary to give speed prediction for a small and light boat. Wave conditions will play a major role how fast the boat will be.”

    A fun design that will cost little and take about 180 hours to build according to Bernd. The jpegs tell part of the story.
     

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  8. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    This is a story about a yacht conversion. You start of with a 100 x 46 foot foot Alucraft power trimaran. Extend the power trimaran to 111 foot to provide more comfort for the family. Now that you are Nelson Piquet, 3 times world Formula One motor racing champion you can afford to change things a little more. You consult your uncle, a Brazilian naval architect, about some modifications like extending the tri and putting a sailing rig on it. The wife wanted redesign the interior to accommodate the growing family and provide a few luxuries etc. Ok let’s do it.

    Pilar Rossi was extended to 211 x 46 foot, yes, an extra 40 feet on the stern and 60 feet extra length on the bow, the displacement is now 370 gross tons and the vessel has a 7 foot draft. The added schooner rig required two new masts, one 148 feet and another 138 feet high, made by Formula Yacht Spars in Lymington, England, that transformed her into a mega-schooner-trimaran. With hydraulically operated genoa, fishman, staysail and mainsail, she now has 23,600 square foot of sail.

    Why was Pilar Rossi changed so extensively? The question was asked. “But why did Mr. Piquet do this? Why did he have to go through all the trouble of adding and changing things on the boat, instead of selling the old one and getting a new one? –I ask the captain of Pilar Rossi, Ricardo de Fretas, a member of the Rio de Janeiro Sailing Club, a club with 4 Olympic regattas medals.

    – Because he loves the boat. And he is a loyal guy. Maybe he even made a promise to her, and he is the kind of man who keeps his promises. But also, he wanted to create the perfect boat for him and his family and friends to enjoy. The boat is his creation. He is always focused on even the smallest of details. It is incredible how much he cares for Pilar Rossi. Sometimes he calls me from the other side of the world and wants to know if a specific battery in one of the bathrooms works. When Mr. Piquet is aboard Pilar Rossi, he spends much of his time sitting on the large main deck table thinking what will be the next improvement, the next project.”

    Pilar Rossi engines are two 1360 HP / 530 Kilowatts MAN, and two John Deer engines with 90kw each one as generators. What has all these modifications done to the performance of Pilar Rossi. Under sail it will achieve 8 knots. Motor sailing it will achieve a maximum of 15 knots. Cruising under power is about 12 knots.

    The accommodation is spectacular, beside accommodation for 18 guests and 7 crew you need to have you spacious gym, a main saloon cabin that would looks as though it came from a large house. The steering position and “cockpit” are very large. The many toys that can be carried on the aft deck will provide much fun.

    The hull is steel and the super structure is aluminium. The bow extension included a bulb bow and raising the bow freeboard. The outer hulls were extended but the aft deck is where the real space gain was. The modifications were done in Turkey.

    This is a small warning about “modifying” an existing boat to much. Sometimes it is better to build a new boat that design that can more successfully achieve your goals and probably at a lower cost. Each person to his/her own. The jpegs give the idea.
     

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  9. guzzis3
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    guzzis3 Senior Member

    I have to say I am shocked by these numbers. I always felt the jarcat rig was low aspect bringing both slower speeds and more safety. I am really surprised at how the numbers stack up. My seat of the pants impression was the J5 I had was less "hairy" than many of the other boats I've sailed.
     
  10. oldmulti
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    oldmulti Senior Member

    This is not so much about the fast charter catamaran but the materials it is built from. The builders are the Ultimate Boat Company and the designers are TYNC (The Young Naval Architects). The open wing deck cat is 32.4 x 18 foot with weight of 4000 lbs weight and a 6900 lbs displacement. The outrigger seats mean an “overall beam” of 22 foot. The 38 foot aluminum mast carries 513 square foot of sail upwind with a 170 square foot jib and a 343 square foot mainsail. There is 1560 square foot available down wind. There is a central spine from the aft beam to the forestay attachment. The hull length to beam is 13 to 1. The draft of the low aspect ratio keels and rudder is 2 foot. Engine power for manoeuvring is provided by aft solar panels, batteries and two 11 Kw motors.

    Each 2.5 foot wide hull has a berth, a toilet and a lot of storage space. The headroom in each hull is 3.3 foot. Remember it is basically a charter catamaran although it could be a fun day sailor, camp cruiser.

    Jeroen Wats has joined The Ultimate Boat Company (UBC) which builds powerboats for a variety of professional and recreational applications. "The first 2 boats have been built and construction of a 3rd, a RIB, starts in July 2021. Compared to fiberglass, we have gone from a weight of 380 kg to 250 kg with the DANU. This allows us to put the weight where it is useful" explains Jeroen Wats.

    Now we get to the build materials. I cannot give details as the material developers have patent applications on them. The following is from several sources. “DANU is comprised of a combination of styrene-free resin and sustainable fibres producing a material said to be stronger and lighter than glass fibre and less brittle than carbon fibre.” And “UBC is clear on all the benefits that using DANU can bring. The company claims it is stronger and lighter than fiberglass and less brittle than carbon, so boats made from DANU are built to last a lifetime. This super-tough sustainable material maintains its technical properties and strength indefinitely, so can be reused over and over again, completely re-cycled, upcycled or re-manufactured. Crucially, its cost is comparable with traditional materials, and no additional manufacturing or labour costs are required.” Followed by “UBC has dedicated considerable effort to ensuring that the production method closely resembles conventional vacuum infusion yacht building. This has the added advantage of reducing production waste and requires less raw material. Plus, switching production to Danu incurs minimal manufacturing process changes and zero incremental labour costs – making it an immediate and affordable alternative. The core material used in Danu is natural. At end of life, the constituent components can be reversed to their virgin state without losing any technical properties. Most crucially though, the material maintains its technical properties and strength after each recycle.”

    Translation of all of the above a styrene free epoxy type resin combined with EG a University of New South Wales developed tough material from hemp fibers that have a higher strength-to-weight ratio than steel. “In addition to flax, almost 300 parts used across Ford’s vehicles are derived from sources such as soybeans, cotton, wood, jute and natural rubber,” she tells WardsAuto. “For the parts of the vehicle, we used a lot of natural fibers such as hemp and flax and recycled fibers, as well as biodegradable polymers such as polylactic acid, recycled polymers and biopolymers.”

    We need to follow the development of DANU to see if it is a viable home builder material if it has better strength and lighter than fiberglass. It helps that the material is less brittle than carbon fibre. The jpegs give the idea of the cat.
     

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  11. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    I may not be adding anything to the thread until August 3 2021 due to some building issues. So this will be a short item about a monohull, not for the hull shape but the rig and construction method.

    The IED 40 is 40 x 14.4 foot with a 11200 lbs displacement. The wing keel has a moveable lead bulb that slides to either end of the wing keel. Also the galley unit rotates on a pole in the main cabin to move the main galley weight to the windward side. The galley movement is driven by hydraulic rams. Both significantly increase the righting moment of the boat. There are twin lifting rudders on the stern.

    Now we will discuss the rig. The 55 foot high, 2 part wing sail has an area of 1210 square foot (on 1 side total area of both sides is 2420 square foot). The leading edge of the wing mast is a rotating carbon fibre structure covered with Spectra and some flexible solar cells on its surface. The aft part of the 2 part wing sail is a flap which is constructed of carbon fibre internal structure with a Spectra sail covering. The wing sail is reefable. The rig is claimed to be 15% more efficient than a normal sloop rig.

    The construction of the majority of the yacht is built in bio-composite composed of 3D flax fiber, cork core and bio-compatibles resin. The cork core is tree cork. The fabric is EG Bcomp Switzerland has Bidirectional fabrics with fibers oriented at 0° and 90°, suitable for manufacturing fiber reinforced composite products with a high performance and a low environmental impact. ampliTex® 5040 has a very good drapability and is ideal for complex shapes.

    High laminate stiffness is obtained due to the low crimp twill 2/2 weave as well as zero-twist yarns. Performance advantage Considering that glass fibers have a density of 2600 kg/m 3 and a tensile modulus of 70 GPa, the flax ampliTex® 0°/90° 300 gsm can replace a 495 gsm glass fiber 0°/90° fabric to have the same stiffness in tension. In compression, the performance of flax is a bit lower, thus the flax ampliTex® 0°/90° 300 gsm can replace a 410 gsm glass fiber 0°/90° fabric to have the same stiffness. This fabric is ideal to be combined with the powerRibs fabrics 5019 and 5020, replacing a 600 gsm carbon fiberlayer with same performances in bending. Processing guidelines · Great compatibility with epoxy and polyester · Near zero CTE, hence good processing compatibility with carbon fibres · Compatible with infusion based processes (vacuum infusion, RTM), wet layup · Flax fibres always contain some humidity at ambient conditions. · Fibre weight fraction of 50% can be reached with process pressure > 5 bars. However, the fibres absorb a lot of resin when hand-laminating the fabric and it tends to look “dry” (unless too much resin is used) before pressure is applied.

    An interesting concept. See you in a week.
     

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