Multihull Structure Thoughts

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

  1. bajansailor
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    bajansailor Marine Surveyor

    Absolutely!
    Everybody is so hell bent on trying to make these beasts as 'green' as possible, that they lose track of reality - and your sentence above sums up the reality of it all very well.
    They would probably have a lot more fun, and 'bang for their buck' with a much smaller boat - but then it would have less pose value.

    Edit - here is the website for the Dragonship -
    Dragonship 25 | PI Superyachts http://pisuperyachts.com/dragonship-25.html
     
    Last edited: Sep 18, 2022
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  2. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Another performance cruising trimaran “So What”, you say. Oh, sorry the name of the trimaran is “So What”, it was designed by a few people, the architect is Erik Le Rouge. The floats were designed by Van Peteghem and research was done by Awentech. There are serious names involved in this design by an interesting path. I cannot be sure, but I think the main hull is a Pulsar 50 with the beams. The floats are off Gitana 11 and matched with Erik Le Rouge main hull and beams. The tri is 59 x 42 foot with a displacement of 13,000 lbs. The 74 foot rotating carbon fibre mast carries a 1,270 square foot mainsail, a 700 square foot solent, a 1,780 square foot gennaker and a 460 square foot storm jib. The draft is from 2.6 foot to 10.5 foot over the main hull daggerboard. The floats have mild C section daggerboards in them. There are 3 rudders, 2 on the floats. The motor is a Yanmar 75 HP inboard.

    The accommodation is 2 double berths, 2 single berths, a single bathroom, a dinette and a large galley. I have included the jpeg of the standard Pulsar 50 main hull layout but the Pulsar 60 “So What” has the dinette forward and the galley aft.

    The Pulsar 60 was a new construction of the Mer & Composites shipyard in Port Napoléon. Equipped with the floats of Gitana 11, the rest of the construction is carbon foam in epoxy under vacuum on a male plug with post-cured epoxy. Carbon beams are glassed on the same plug.

    “So What” provides you with ultra performance, translation 30 knot peak speeds have been reported and 400 mile days possible. This is a seriously fast cruiser. The jpegs give the idea.
     

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  3. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Today we will talk about 2 performance cruising cats’ that are actually the same design by Ker Yacht Design and built by McConaghy Boats. The MC53 (also MC 52) are 52 x 27 foot that displaces up to 37,000 lbs. The 80 foot (optional mast) carbon mast carries a 1,120 square foot mainsail, a 530 square foot self tacking jib (Jib Furler is a Harken 4MKIV), a 1,550 square foot Code 0 and a 2,420 square foot asymmetric spinnaker. The low aspect ratio keel version draws 6.5 foot. The centre board version draft ranges between 3.3 foot to 8.9 foot with boards that can be set in 3 positions. The centre boards are long and thin, hydraulically powered and stored below the hull floorboards. The hull length to beam is better than 10 to 1. The jpeg gives the idea. The engines are 2 x 57hp Yanmar which provide a cruising speed of 12 knots.

    The accommodation is the usual luxury with 3 double cabins and toilets in the hulls. The owners suite is has additional seating to get away from the crowd. The main cabin and aft cockpit are one integrated space with a large door separating them. The galley is large as is the dining seating. The internal helming and navigation position is large. The fly bridge helming position is large and comfortable.

    Polars (attached jpeg) from McConaghy suggest speeds of over 10 knots in a stiff Force 6, at 30° off the true wind. Bear away onto a broad reach and she is expected to manage 21 knots-plus. One test resulted in “The MC53 is a windspeed boat, which means she can approach cruising speeds which are very close to the True Wind. In a 15-knot breeze you will sail at 15 knots. Thanks to a meticulous control of weight owner’s will experience sailing unlike on any other catamaran.”

    The cat is constructed using a controlled vacuum infusion process and pressed panels of E-glass, carbon composite and Corecell for lightweight strength and rigidity. There are carbon fibre bulkhead flanges and other carbon fibre strengthening. There are composite centre boards. Hull and deck painted in high quality two pack polyurethane coating in white as standard, hull is painted grey. Below the waterline surfaces finished with epoxy primer. The internal furniture is composite with veneer paneling.

    I suspect the MC53 is an upgrade of the MC52 to identify a new model with improvements. The jpegs will give the idea of a very well designed high performance cat.
     

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  4. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    This was meant to be a simple item on anchoring. As I have experienced in real life anchoring is not simple. I am not talking about anchoring in a sheltered location with no waves, we are talking about real cruising anchoring where it may be blowing 25 knots of wind with small waves and an uncertain bottom. So, what do we need? Ideally, an anchor should have the following characteristics:
    • It should set quickly and reset when the wind/current shifts.
    • It should have good holding in all bottom types: sand, mud, rocks, coral, and grass.
    • It should be strong and of good quality—able to handle high loads on any part of its structure.
    • Good holding power, even at short scope.
    • Easy to release from the bottom without damage.
    My model was “the bigger, the better” when it comes to sizing anchors for bluewater cruising. Bigger anchors have more strength to resist breaking, occupy more of a surface area in the seabed to resist pullout, and have more weight to penetrate deeper. Experience taught me the “right” type of anchor that suited the seabed you were anchoring into was as important as the anchor size. An anchor’s ability to create resistance is dependent on its ability to “hook” or “bury” itself into the seabed. It needs to create enough resistance in the seabed to withstand the environmental forces on the boat, i.e., wind and waves. Most modern anchors are very efficient. It’s their holding power, not necessarily their weight, that holds the boat in place although weight usually helps. Some anchors are now being made of aluminum and rely almost entirely on their shape for their function.

    The next real issue in multihulls is “scope” of the rode and the amount of chain you have in your anchor rode. The more, the better in both cases. If the water depth in 20 foot you need at least 75 foot of nylon anchor rope and 25 foot of chain between the boat and anchor. Preferably in bad conditions 175 foot of nylon anchor rope and 25 foot of chain. If you are in a coral area use more chain. I understand that there may be space constraints in an anchorage but if winds are blowing at 25 knots you need scope. Some of the more “popular” anchor types are mentioned next but the real information is some tests below and in the Web addresses, jpegs and PDF’s.

    CQR type (EG The Delta), generally a good anchor and is supposed to have good holding ability in varying bottom conditions, does not excel in any one bottom. The Bruce anchor (Claw) is an excellent all-round anchor. It will hold well in most bottoms, although it performs less well in sand and mud. But has a low holding power to weight ratio, meaning you’ll likely require a heavier Claw anchor than you would require for other styles of anchor. Danforth (Fluke) anchor performs quite well in mud and sand. The downside is that outside of mud and sand, the Fluke has very limited holding ability in bottoms such as kelp, rock, coral, etc. In multihulls weight matters, you need high holding power for weight.

    There is no “perfect anchor” each anchor has its strengths and weaknesses. The best approach is to have 3 different anchor types and at least 3 full rope and chain rodes available with further back up rope available. Also have several backup swivels, shackles and wire to tie of shackles, swivels etc. All of this equipment need to be correctly sized and will weigh quite a bit, but if you are cruising you WILL need it. Marina living is great but real world cruising is unpredictable, I have had to anchor behind islands with wind gusts of 40 knots measured on the wind instruments. I have anchored in a channel with a steady 20 knots of wind for 3 hours before the anchor pulled out and we had to rest everything with a second anchor and chain attached to the first anchor. We had no problem after that.

    Finally, do not underestimate varying wind conditions. If you set an anchor and the wind swings 60 degrees you can lose 90% of an anchors holding power. There are many anchor tests available on the web, please read them and choose wisely. Some extra weight in anchor gear may save your boat and your life.

    Web sites. Anchor Testing and Rode Loads - Practical Sailor https://www.practical-sailor.com/sails-rigging-deckgear/anchor-testing-and-rode-loads

    Anchor Testing | West Marine https://www.westmarine.com/west-advisor/Anchor-Testing.html

    The PBO article (1 of several tests) brief summary of results follows. Best anchor first BUT this is average and depends on the bottom type you are anchoring in.
    6kg spade 24
    15kg spade 32
    4 kg Rocna 21
    16kg Rocna 30
    7 kg Manson Supreme 12
    11 kg manson Supreme 21
    7kg Delta 8
    16 kg Delta 11
    7 kg CQR 7
    21 kg CQR 8
    6 kg Bruce 5
    16 kg bruce 6
     

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    Last edited: Sep 22, 2022 at 2:53 AM
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  5. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    The vessel featured here is part of group of two 99 foot and four 80 foot swath trimarans built by Fjellstrand for Danish shipping company World Marine Offshore A/S. They were designed to act as crew and service vessels for offshore wind farms. We will focus on the Windspeed 25 which is 80 x 31.1 foot with a weight of 76,200 lbs and a displacement of 103,000 lbs. The draft is 15 foot. The engine configuration is 4 Scandia DI 13 main engines, each producing 368 kW at 1800 rpm. The company chose to go for 4 smaller engines instead of 2 large ones to ensure more economical and flexible operation. These are connected in pairs to the two CPP propellers so that you can still use both propellers should there be problems with one of the engines. Gears and propellers are supplied by Servogear, while the 60 kW bow thruster is supplied by MB Hydraulikk. PS there are statements of Gross tonnage of 160 tons, this is a shipping calculation that bears little relationship to the displacement or weight of a vessel, it used to apply to old sailing ships, not modern designs.

    The hull shape is a swath (small water plane area) trimaran, with a large central underwater bulb with forward hydrofoil planes that provide assistance in pitch control and lift when running light. The vessels will be equipped with 40,000 litres of water ballasting systems allowing them to shift between a rough weather SWATH mode and a light weight transit mode. A fixed stabilisation foil adds to the design’s stability - one of a set of permanently integrated motion damping devices that are part of the hull concept and designed to reduce construction and maintenance costs by avoiding complex active motion control systems. The major advantage of this hull shape is to minimize motion at sea in hope of reducing crew fatigue and sea sickness. The water ballast can also reduce motion in heavy weather and settle the tri down when moored at a wind turbine tower for servicing. In both cases the extra weight lowers the hulls deeper into the water to reduce any motion.

    The normal service speed while transiting is 24 knots when loaded with 12 service crew in the 80 foot model. The construction is aluminum.

    The accommodation on is a galley, office, dayroom and lounge with seats for 12 people. Passengers have access to two toilets with showers in connection with the cloakroom. The electronics and hydraulics in this vessel are impressive as this is a real wrk boat that has to meet very high levels of safety and performance in some very rough water at times.

    The jpegs tell you a lot more. Interesting concept that has proven itself in the real world.
     

    Attached Files:

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  6. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    Jeremie Fischer is from Martinique who designed and built his first crab claw pacific proa prior to 2000, it was 16 foot long and very basic. He then developed a more refined larger day pacific proa to get a better understanding of the characteristics and rig handling etc. Now he finalised in 2003 a 39 foot pacific proa for cruising around the Caribbean islands.

    The “Equilibre” is a 39 x 19.5 foot proa with a displacement of 2,500 lbs. The crab claw rig is set on a short 23 foot moveable mast (fixed base but head can move fore and aft) with 430 square foot crabclaw sail. The 30 foot yards are moved from end to end in this design and a shunt takes about a minute. There is a video on the web showing the proa being handled, shunted and moored single handed. The length to beam on the main hull is 20 to 1. Lateral resistance is provided by the asymmetric main hull shape. There are no “rudders” officially listed but in a jpeg in the PDF shows some interesting attachments to each bow that can be raised or lowered.

    The float is 15.5 x 1.5 foot. There are 2 versions of this proa. The original build had a fixed float solidly attached to crossbeams. In later videos and in the attached PDF the float can pitch independently of the beams and main hull. Jeremie was still developing the design as he gained more experience. You can also see the mast base position has moved closer to the main hull is some jpegs.

    The accommodation is limited. The headroom is only 4.5 foot and the 3.2 foot hull width at the gunnel indicates there could only be 2 single berths plus some limited seating, food preparation and a portapotti space available with some storage available.

    The main hull construction is 9 mm plywood covered with a light cloth in epoxy. There are 8 plywood bulkheads in the main hull. The cross beams are box wood construction of 150 x 160 mm. The float attachment varies depending on what version of float you are viewing. There is a “seating” storage box at the midpoint of the crossbeams.

    Performance is unknown but the video shows the boat moving well in light to moderate conditions and is controllable when being sailed single handed. The power to weight ratio and length of main hull indicate the proa should be fast under the right conditions.

    An interesting design. The jpegs and PDF give some idea of the vessel. There is a youtube of the proa at Proa File | Equilibre https://proafile.com/multihull-boats/article/equilibre
     

    Attached Files:

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  7. oldmulti
    Joined: May 2019
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    oldmulti Senior Member

    This pacific proa was designed and built by Jean-Marc Roth a Swiss guy who also is a musician. The proa is named “Sambalaba” and was built over 7 years and was in the “water” in 2015, it was formally launched in 2018 when it was finally finished by the quay side. The pacific proa is 48.5 x 30.2 foot with a 31 foot float. The displacement is 10,100 lbs and the proa has a 59 foot freestanding mast with a ballestron boom to make a fractional Aerorig type arrangement. The sail area is 860 square foot. There are 2 dagger rudder boards that draw from 2.8 foot to 6 foot. The motor is hybrid electric.

    The accommodation is 4 double berths, toilet and large main saloon with seating and galley. The cockpit is large and has a Bimini cover.

    The build is strip plank cedar, plywood and West epoxy system throughout. The 2 hulls and the 2 cross beam structures of the proa were built in a large garage and transported to the water’s edge for assembly. The proa then spent 2 years being finalized with rig, electrics, plumbing interior etc.

    I do not know of any performance numbers, but if the weight is correct and the Aerorig well sorted, I suspect this proa will be a fast cruiser.

    This appears to be a good performance cruiser that has been sailing since 2018. If anyone knows any further detail, can they please advise. Sorry about the limited jpegs. The PDF is a summary of the proa and contains a jpeg of the bow of the proa.
     

    Attached Files:

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