Multihull Structure Thoughts

Foiling cats have a great education facility available, the foiling Imoca 60 foot global circling monohulls. These boats can top 35 knots riding on one foil in good conditions. Jpegs attached. The design and engineering of these monohull structures is very well done due to the sponsorship money available.

The 60 foot monohull guys have found that the longer (wider) the foils the potentially faster the boat. But there are some issues. Long foils require some very sophisticated engineering with carbon fibre unidirectional and “thin ply” (150 gsm carbon fibre high strength fabric) builds. For the foils to last for a 30,000 mile race they have to be light well shaped and strong. They also cost $200,000 plus per individual foil. As time gone by the shape of the foil is being evolved. The inner end is a high lift foil then the further out is a lower lift foil with a lower angle of attack for high speeds etc.

But the real issue is not the foils. It is how the foils are integrated with the monohull build structure. Some foils are retractable and are in cases. BUT the foils have to held at specific angles of attack, handle varying fore and aft loads when the boat may be supported only on a foil tip 8 foot from the hull structure. The foils also have to handle hitting solid objects on its global journey.

The designers and builders are finding the foil support structure is harder to engineer than moving keel structures. This is due to the entire boat when flying having a massive point loading at the foil hull interface. The engineers have now integrated the keel support and foil support structures into one “integrated unit” to minimise weight gain in these 60 foot mono’s. But even with all the advanced design and build “Hugo Boss” sailed by Alex Thompson in the 2020 Veendee Globe race has had serious internal structural failures which he currently trying to repair.

Why is this relevant? Because only a few racing multihulls race around the world. The majority of foiling multihulls are at best daysailors that operate close to shore. The 45 knot AC cats only race for 40 minutes in a confined space with power boats clearing the course of debris prior to a race. The global multihull racers have developed strong foils and VERY strong support structurers for the main lifting foils. The rudder foils generally only carry 10 t0 20% of the load. In small cats eg below 25 foot you can do guess engineering and develop solutions that will last, but above 25 foot you need real design and engineering to handle the forces involved in foiling. Crew safety is at stake. A person has been killed in an AC foiling cat. The attached foiling cat jpegs will give an idea of some of the extreme sailig that is being done.

The final problem is foils for monohulls help increase stability. Foils for cats actually decrease stability. Notice how the cats are several feet in the air in the jpegs. They have higher centre of gravity and a raised sail area centre of effort. Both of these items reduce stability. This is the reason why many high performance cruising cats are choosing not to incorporate lifting foils and are willing to “sacrifice” the eg 10% speed advantage of lifting foils. One 80 foot cat designer and builder calculated the cost of semi lifting foils and associated internal reinforcing structure was going to add $500,000 to the build costs of the cat.

 

Tom2x4 requested more information on Post 54. I will quote and upgrade parts of the original entry here. One of the simplest plywood build methods I know of was invented and patented in 1966 (the Australian patent has run out, there was no other patent to my knowledge). It was initially used to build high speed round bilge power boats but could be adapted to any hull shape. The method is basically 600 mm wide plywood strips glued together to form a clinker hull. Now the best part get your 600 mm strips and scarf them together lengthwise to the length of hull. Use eg 3 mm ply for say a 23 foot boat. Put a series of round bilge hull shaped former's on a strongback about 500 mm apart. Place the first 600 mm strip from the keel line outward. Lay the next ply strip about 250 mm from the keel outward covering just over half the first 600 mm strip. Lay the next 300 mm (600 mm ?) wide “plank” 550 mm from the keel line over lapping the 2nd strip and 50 mm of the first strip. Repeat until you get to the gunnel line. Result you have a 6 mm thick hull with a 9 mm thick hull for 50 mm every 250 mm. The 9 mm thick part act as a default stringer every 250 mm. This technique builds a monocoque hull structure that only requires BH's to support the hull shape. A stem, keel and gunnels still need to be inserted. Also, at the keel and gunnel you will have double any eg 3 mm ply to form a 6 mm ply hull. This technique can be used for 4 mm, 6 mm or 9 mm plywood which means it will work on hulls up to 60 feet. Yes, it looks like a clinker ply boat (as Peter Spronk cats were) but it is very fast and easy to do with a minimal need for actual timber stringers etc. The technique can be applied to 3 layers of plywood to give EG 3 layers of 3 mm plywood giving a 9 mm thick hull with a 12 mm thick “stringer” line every 250 mm. The “planks” are wider.

Tom2x4. This method ”patent” is over 53 years old and expired under Australian law. The build technique was used in a series of “production” outboard power boats from about 15 to 23 foot. The boats were light and strong with testers reporting they were capable of handling rough conditions. There were 2 failures in prototypes but no known failures in production craft. The only reason this build approach went out of production is fiberglass arrived on the scene. The only downside of this build technique is the exposed edges of plywood in the clinker planking style. This will need good sealing along those edges.

Sorry the jpegs are not clear, but it is a 53 year old magazine they came from. Hope this helps.

 

Escape hatches was meant to be an easy write, then I started to research it seriously. On a cat I owned the escape hatches were on the bridgedeck floor next to hull. They were bolted down by wingnuts and could be undone by a person in an inverted hull.

The modern approach is to have escape hatches on the hull sides below wingdeck level on modern production cats. There is only one small problem as you will see from the first jpeg. It a Helia cat, the Fountaine Pajot Owners Facebook reported it lost at sea off Africa. The Norwegian skipper determined the problem was his starboard escape hatch. He tried many things to stop the inflow of water but ended up being rescued by the Moroccan coast guard and abandoning the boat.

In 2020 Goiot issued a formal recall for Lagoon, Bali, Nautitech and Fountaine Pajot cats using Goiot escape hatches. Boat owners were advised NOT to use their EG Fountaine Pajot cats 2012 to 2018 with Goiot escape hatches until they received new hatches. Source: Fountaine Pajot Goiot Recall Page and Caribbean Multihulls - Press Release: GOIOT HATCHES RECALL https://www.caribbean-multihulls.com/news/press-release-goiot-hatches-recall-2020-02-11

Let’s start with the function of an escape hatch. An escape hatch is to allow people trapped inside capsized catamaran (or tri) to escape from inside the inverted cat. The assumption is the inverted cat will float at a reasonable height (about wingdeck level) with people trapped in eg hulls having some air and are able to move to the escape hatch.

Reality. It is chaos in an inverted multihull, often in rough seas, with eg mattresses, floor boards, clothing and other junk moving around in often a dark space. And I am assuming you have not sustained any injuries. Getting to an escape hatch may be difficult and opening it may be hard if not impossible.

So, we have to position one or two escape hatches in accessible locations that are strong and waterproof with an easy way of opening them. Professional escape hatches initially failed because of there locations, where seas constantly pound the glass/Perspex in the aluminium frames. The bedding compounds used in the hatches brake down over time or there can be significant hits from foreign objects. The position of escape hatches in modern cats should be relatively OK but when you cut a large hatch hole in the side of a hull you lose structural strength and create a point of some structural flexing putting pressure on the escape hatch frame and bedding compound.

A secondary issue is an escape hatch should not be positioned to release trapped buoyancy air out off an inverted cat allowing it to sink lower in the water. This may reduce a person’s chance of being able to survive inside a hull for a period due to less air and space.

What to do? Understand how your boat will float upside down. A designer can provide guidance if you build the boat to plan. Sealed buoyancy chambers should remain sealed, not opened up for additional storage. Once you know how the boat will float inverted, put your escape hatch(es) on or just below inverted waterline. I prefer on a wing deck bottom, preferably near the centre to the rear of a wingdeck. Do not put escape hatches at the high impact load forward end of the wingdeck or in the bow areas. The escape hatch does not have to be a fancy see through escape hatch, a sheet of ply or composite panels will work very well. The lock down mechanism needs to be well planned. It needs to be accessible from the inside AND outside. It can be from bolts with wingnuts to a multipart lever locking device. Also, the locking device needs to be able to be securely locked when the cat is moored.

Please review your escape plan if your multihull inverts. In larger multi it includes escape hatches. In small beach cats I know a person who drowned because he got caught below the trampoline and ropes of an inverted Hobie. A knife may have helped. The jpegs give some ideas. The second last jpeg is a 38 foot cat, without escape hatches, that 3 people died of exposure 7 miles off the coast. The final jpeg is of a cat that left its escape hatch open for ventilation, unfortunately the waves built up and water washed in through the escape hatch, result one hull sinking.

Finally, you can read for further information. Helia 44 Escape Hatch Failure - Cruisers & Sailing Forums https://www.cruisersforum.com/forums/f136/escape-hatch-failure-194102.html

 

The following is a 1998 concept for a Yachting Monthly magazine design competition. Dr Albert Nazarov of Albatross Marine design drew this cat in his early years. The design competition wanted a “Starter Boat” and out of the 212 entries this design was in the final 6. The cat is 21 x 16.1 foot. The displacement is unknown but a rough calculation indicates about 2500 lbs. The mast is 31 foot with a mainsail of 175 square foot and a fore triangle of 72 square foot. The length to beam of the hull is about 9.2 to 1. The hull at the gunnel is 3.5 foot wide and the small wing increases the internal hull beam to 4.1 foot. The headroom would be 4.5 to 5 foot. The hulls have centreboards and external kick up rudders.

There are no structural specifications but it could be built in moulded timber, solid fiberglass or foam fiberglass. The crossarms are 150 mm aluminium tubes. The cat may be trailable if it had an expandable trailer to allow the beams to be inserted. I do not know if this design was finalised or if any samples were built. The cat was named “Summer Twins 21” and would be a great starter boat.

Who is Dr Albert Nazarov? He is Russian by birth and has designed boats for over 20 years. His current design office is in Thailand which he started in 2006. His design work ranges from small monohull yachts, multihulls, powerboats to larger commercial ferries. His design work is good and to give you an example, please look up the free full plans for his plywood Kavalier 800 26 foot monohull trailer sailor and his plywood Pilgrim 590 a monohull 19.3 foot trailer sailor at the following web sites KAVALIER 800 Designed by Albert Nazarov, Maxim Kovalyov, Dmitry Dolinsky & PILGRIM 590 Designed by Albert Nazarov & Maxim Kovalyov https://www.boatdesign.net/NYD/ and KAVALIER 800 Designed by Albert Nazarov, Maxim Kovalyov, Dmitry Dolinsky https://www.boatdesign.net/nyd/K800/

Over 10 of the 26 foot trailer sailors have been built and the owners appear to be happy with them. There are several 19 footers also have been built.

Sorry about the limited jpegs, but an interesting cat design. The last 5 jpegs are on the 26 and 19 foot trailer sailors.

 

Another excellent (as always) post - thanks Old Multi.

Just tagging Albert here - @Alik - in case he does not see your post.

 

We have spoken of Frank Smoot DIY tris previously, but today we will focus on his twin mast 24 foot day sailor. The tri is 23.75 x 18.1 foot weighing 360 lbs and carries two 18 foot above deck freestanding rotating aluminium masts. Each mast carries 85 square foot mainsail. The main hull has a 600 mm waterline giving a 12 to 1 length to beam ratio. The main hull is 760 mm wide at the gunnels. The main hull has 2 lee boards for lateral resistance and a kick up rudder on the main hull. The initial floats were only 12 foot long with some LAR keels. They were later modified to 16 foot long to provide more buoyancy.

Frank reported “Just two days ago we managed an astonishing (to me) 9 mph close hauled – about 45 degrees off the wind. And you know what? I think that’s plenty! We zipped past a close-hauled monohull like he was at anchor. Whoever says tris don’t point and cat-ketch rigs don’t go upwind is welcome to come along next time we go out. We also managed 12 mph on a reach in 12 mph of wind.”

Now a small warning about this tri. Frank builds day sailor tris for Florida conditions, Frank did not push this tri hard and Frank by his very nature builds light weight structures that achieve his trailable day sailing goals. Yes, his boats work well and are strong enough, but do not assume the 24 foot specifications are suitable for a coastal cruiser.

The tri’s main hull is built by scarping together 3 sheets of 3 mm ply and cutting out the 23.75 foot sides to shape. The gunnels and chine strips are glued on. A transom is made. Now the sides and transom are stood up and the bow is pulled together with plastic ties. The hull sides are forced apart to the required shape. Deck beams and frames are pushed into the hull to hold the shape. The main hull bottom is 6 mm ply. Four layers of 50 mm blue Styrofoam is glued to the bottom and shaped to provide rocker and a round bilge shape. The blue foam was initially covered with 4 oz glass, and then the whole hull was covered with 6 oz glass. Additionally, the 6 mm ply floor was covered in the cockpit areas with 6 oz glass. The 5 bulkheads in combination with the foam “enclosed semi-circle” make a sturdy hull. The mast base support is a PVC tube glued to a mast base structure and deck. The leeboards have a “lifting” system so the person controlling the boat can steer with their feet, control the sail sheets and lift the leeboards without leaving their comfortable sailing seat.

The cross beams are 18.2 foot wide single units made from a 12 foot long 75 mm aluminium tube with a 65 mm tube inserted in either end to form the full 18.2 foot width. The cross beams are bolted to the gunnels of the main hull and floats. The initial floats were from a smaller tri and were built from 3 mm ply. They floats were lengthen to 16 foot.

This tri is very easy to build (shaping the foam would be a bit of a pain), is light and simple. Frank has modified his smaller tris (eg last jpeg tri on trailer on left side) to have a very simple folding system which could be adapted to the 24 footer which would make this boat a very good trailable day sailing tri. More details are at New Page 1 http://www.diy-tris.com/2012/10-24-footer.htm

 

This is about dreams, money, some knowledge and reality. The initial owner of this boat wanted a performance trimaran based on his reading of Nigel Irens information suggesting 16 to 1 length to beam hulls have very low resistance. His logic was low resistance means low HP engines and smaller sail areas. So, he designed and organised a professional ship yard to build his 75 foot aluminium trimaran. The initial drawing gives you the idea of what he wanted. The tri also needed 9 cabins for guests when chartering.

The draft of the design was to be 800 mm for sailing in Indonesia and being able to beach the tri. The rig is a fully suspended lanteen that gives the tri almost double the off-wind driving power of a Bermuda rig, while keeping the overturning moment low for those small outriggers.

Now the reality. The next jpegs show the initial aluminium build with minimal “overhang” steps on the main hull. Then I suspect someone at the professional ship yard did some serious calculations and suggested some additional buoyancy would be needed to support the weight of this boat. In the final jpegs you can see the buoyancy addons on the main hull to support the weight. The length to beam on this main hull configuration would be about 6 to 1 with a lot of the addon buoyancy also helping the righting moment because the “small floats” did not have sufficient buoyancy. The floats also had raised ends to help the righting moments. The tri now travels at about 10 knots under engine power with some assistance from the lanteen rig. The tri was for sale for $695,000 a couple of years ago.

The message here is if you plan to design and build a multi above about 30 foot please understand what you are doing. As Kurt Hughes said you will save the designers fee in reduced material costs alone if you have a good experienced designer in the preferred type of multihull. An inexperienced designer builder will often over or underbuild a structure which will require later modification to get it nearer what the person wanted.

Dream the dream but please do the serious research first before you consider doing a reality. Any 40 foot plus multi is not a by guess design process as you can get into real trouble with them. The jpegs tell a story but don’t be to inspired.

 

Thanks for this - the aluminium work looks good, but the design itself is a real abomination.

They were asking $695,000 a couple of years ago - good grief. This is probably still a fraction of her building cost, even in Indonesia. And it is only worth now what somebody is prepared to pay for it - but if nobody wants it, it is not worth much.

I think that this example (especially with a hull form that is so critical re extra weight added) illustrates clearly the importance of doing a very accurate weight estimate early on in the design spiral.
I have seen a few boats here where their designer owners ignored any thoughts of weight estimating - all they were concerned about was lots of deck space for fare paying passengers.
One of these boats (a power cat party boat) was launched just before Christmas one year - the Owner proudly told me that he had bookings for Christmas parties, hence he really went into overtime to get the boat finished by then. Earlier, he had ignored suggestions by myself and others that he did not have enough buoyancy in the hulls.
And on launch day, with no people on board, the vessel floated with about 6" of freeboard........ her owner quickly hauled her out again and set about rebuilding the hulls to make them wider. An expensive lesson learnt the hard way.

 

I think you nailed it with “weird tri”
I think this one is headed for the smelter.

 

The following is about a day sailing trimaran that originally designed by Mark Zolitsch of Bellingham, WA. Only 2 or 3 were built. The original version was called the “Adventure 24”, had two large windsurfer rigs on it with a small jib to form a schooner. There are video’s of this boat sailing very well on the web. The original 2 or 3 trimarans were built with 200 gsm biaxial e glass, 2 or 3 mm Soric core (Lantor Soric is a hexagonal flexible infusion medium that holds its thickness under pressure) 200 gsm biaxial e glass resin infused with vinylester. The advertising described the tri as “Adventure Trimarans are the fastest adventure sailing canoes on the planet. Designed for coastal cruising, adventure races, expeditions, day sailing, or getting a tan on the lake, they are part sailing outrigger canoe, part beach catamaran, part sea kayak, and part trimaran sailboat.” All things to a few people.

The second owner of the Adventure 24 molds made his version of the trimaran. It is 24 x 14 foot and weighs 400 lbs all up. The mast is a 25.3 foot aluminum rotating mast with a Hobie 18 mainsail and jib. The mainsail is a Whirlwind Super-R tri-radial mylar laminate. The jib is dacron 3oz. The rig is stainless wire. The mainsail had 2 reef points inserted in it after initial trials. The rig is more than powerful enough to drive this trimaran. The rudder and daggerboard are carbon fiber.

The second mold owner built the jpeg tri’s hulls and decks with 200 gsm biaxial e glass, 2 or 3 mm Soric core (Lantor Soric is a hexagonal flexible infusion medium that holds its thickness under pressure), a 3K carbon fiber fabric. There also is some Kevlar in the bows of all 3 hulls. Also, there was an extra 3” strips of carbon fiber tape at hardware attachment sites, and hull-crossbeam hardware sites. The jpeg version was resin infused with MAS epoxy resin. Any bulkheads, daggerboard case, hull deck joints and addons were done with West epoxy. The jpeg builder learnt most of the resin infusion process from online sources. The Fibre Glast Development videos were very helpful. He followed their suggestions closely. The jpegs give some idea of the infusion process but further detail jpegs are available at Modified A 24 Trimaran. FOR SALE https://www.modifieda24trimaranforsale.com/

The crossbeams are 95 mm outside diameter with 3 mm walls. These are spindle wound high strength carbon fibre composites produced by CCDI in California. The crossbeams are held down by stainless steel saddles and bolts.

This tris hull shapes may not be perfect but the shape will be good enough to produce good performance. The initial jpegs are of the original Adventure 24 tri followed by some rough drawings of the second single mast version and the associated some associated build jpegs. An interesting build.

 

Raphael Censier was 16 in 2010 when he started to dream of an A class cat that could really fly on foils. He decided to build his own A class after building a canoe and hovercraft. He is creative and went his own way in a methodical (engineering) type of approach. The end result was an A class that flew on foils. An A class is 18 x 7.5 foot that can weigh under 170 lbs all up with 150 square foot of sail area.

But the real interest of Rapheal’s A class is the hull build. Initially A class hull’s were built with 3 or 4 mm tortured plywood and aluminum beams. Next came foam glass hulls with 195 gsm cloth 5 mm 75kg pvc foam 195 gsm cloth in vinylester or epoxy. Later A class hulls have lighter carbon fibre skins with 5 mm pvc in the ends but 8 mm pvc foam around the main beam and daggerboard/foil cases. The cross beams, wing masts and most of the deck gear are carbon fibre. In this class grams count to get under the weight limits, especially with the developments of long lifting foils and structural cases that are heavier than old rudders and daggerboards.

Rapheal started to do some experimentation on how to make a lighter hull layup and found that building a foam glass sandwich structure was heavier than anticipated because of the resin and microsphere weight absorbed (read filling the foam surface) by the foam in the build process. The weight gain in the foam glass version in the resin and microballons used on the foam is about 30%. Remember, the skins are very light and the foam glass interface is a “relatively” higher proportion of weight gain than if you have heavier glass skins.

His experiments and calculations concluded there would be sufficient strength in a single carbon fibre skin, with fibres running in 4 directions, and if it could have a supporting frame structure to stiffen the hull both laterally and longitudinally the hull would be stiff enough for racing. Combine with the internal structure with a rounded hull shape there would be enough hull stiffness for A class racing.

The rounded hull section was relatively easy as some A class hulls are symmetrical top to bottom. Just produce a mold for the bottom half of the hull and use the same mold to produce the deck. The hard part of the thin shell no foam approach is the internal “frame” structures. The frame structure needs many small components made and fitted to the hull structure with associated bulkheads around cross beam and lifting foil case points. This is easy for the bottom half of the hull as it just takes time. The real skill is when you have to put the top half of the hull onto the frame structure and bottom half of the hull. You have to “glue” the top half of the hull to 15 plus frame or bulkhead connection points as well as the gunnel joint all around the hull without any internal access to the hull. Each frame and bulkhead connection point has to match the shape of the top half of the hull very closely to allow an epoxy glue joint to develop full strength.

The cross beam basic hull tube structure also has to be built into the hull prior to the top half of the hull shell is installed as well as any reinforcements for eg rudder pintails, deck gear, trampoline attachment points etc. This is a major design and logistical build technique that takes longer to produce than a “conventional foam glass hull”. This is the reason no production manufacturer would use the thin shell internal frame technique.

The result? A stiff, strong, light weight (170 lbs) A class that after 2 sets of foils flew very well and was controllable. The jpegs give the idea and sorry about the size of some. Interesting.

 

Additional A class thin shell build jpegs.

 

Sodebo is presently trucking along at over 37 knots ( been doing that all day on the tracker ) in rough water just below Capetown SA, which together with debris in the water, has knocked out some of the competitors through damage in this years vendee globe.
News - Vendée Globe - En https://www.vendeeglobe.org/en/news

 

Today will be about the Raku 44 designed by Tony Grainger and his team. The Raku 44 is 44.25 x 23.5 foot and weighs with aluminium rig, 45HP diesel sail drives and ready to sail 13,800 lbs. The displacement can be 23,500 lbs including a maximum payload of 9,700 lbs. A sign of the times. Once payloads for 40 foot cats used to be 4500 lbs, now with big engines, fuel, water for showers every day, battery banks air-conditioning etc you need the extra capacity. I hope its reliable gear as you will be spending a lot of time moored doing maintenance and not cruising. Sorry, I am sounding like a broken record (if your young ask your dad what they were), but it was Tony Grainger who said all he needed was a well maintained simple boat, a good compass, some extra rope, food and water and he would go cruising for 6 months.

Back to the Raku 44. The hull length to beam is 13 to 1. The hulls can have either low aspect ratio keels or daggerboards with underslung spade rudders. The rig is a 61 foot mast which can be aluminum or carbon fiber fixed or a carbon fibre wing mast. The mainsail is a fat head of 745 square foot, a self tacking jib of 327 square foot, a code 0 of 575 square foot and a Gennaker of 994 square foot. All the above numbers indicate a 20 knot speed potential with 8 to 9 knot averages over 24 hours.

The structure of most of Grainger’s cats now are basically foam glass or duracore glass preferably built from kits supplied by specialist companies. Tony has developed his hull and deck shapes to maximize the use of flat panels with only a minimum of shaping work required in hull bottoms and around the deck cabin roof. Cats of this size generally have 1200 gsm e glass biax or triax on the outside, 20 mm PVC foam cores and either 800 gsm e glass or 1200 gsm on the inside. Most cats do vinylester but some do epoxy resin. The bulkheads are foam glass with heavy triaxial faces and have unidirectional glass top and bottom. The deck cabin roof requires extra reinforcement and an understanding of your deck gear layout for reinforcing "solid" inserts to be placed where ever there is going to be bolts etc. The underwings are reinforced with multiple ribs or have thicker cores. Do not underestimate the amount of electrical, plumbing and gear fit out work in a cat this size. The hull shell is only 35% of the work.

A good design that will perform. The jpegs give the idea.

 

This is a two part story about a tri that Greg Lynn designed and had built. The tri is the GF 42, a 42 x 32 foot tri that weighed 5800 lbs. It has a 64 foot carbon fibre rotating wing mast with single spreaders. The upwind sail area is 1211 square foot and can set 2061 square foot downwind. The length to beam at the waterline of the main hull is about 12 to 1. The daggerboard in the main hull draws 7.4 foot. The floats have C curved foils and lifting rudders on them.

Greg Lynn is an architect who is recognized globally as a pioneer in applying digital technology and computer numerically controlled (CNC) machinery in design, Lynn has also been a leading advocate for the use of composites in architecture. He has likewise championed composites in collaborations with BMW, Disney and others. This tri was a “one off” design he used as a promotional item to highlight the use of CNC tooling and composites manufacturing techniques. The fact he got a fun fast tri as well was a bonus (possible tax write off as well). The project also served for the USC School of Architecture “a vehicle for introducing architects and students to composites and how they can actualize digital designs and allow exploration of new paradigms like tension-based structures and designs which integrate structure and surface.” Study the jpegs, the cross arms are part art and part structure.

What sort of performance? In 17-18 knot winds the trimaran does a steady 22 knots. In true wind speeds (TWS) 10-12 with the boards down 75-100% the boat points very high (higher than a monohull if we want to sail at 12-15kts) but VMG is faster if they bear off to TWA 50 and sail at 15-17kts. The fastest speed is 28kts on a delivery trip in TWS 18 with the main and genoa. This tri is fast and can exceed wind speed across most of the speed range.

The C foils can provide lift up to 80% of the tris displacement. The foils are designed to provide a couple of tons of vertical lift at +20kts and are engineered to break at 6600 lbs, so the boat is never meant to be fully foiling. It is early days, but yes, 80% is real. If anything, they underestimated the vertical lift provided by the foils. When fully deployed upwind they were lifting the leeward float out too much. They adjust the foil alignment as they sail. The foils are adjusted by changing the UHMWP blocks at the top of the foil case (it is a mechanical operation involving a CNC mill not an adjustment done while sailing). But between the "C" and the winglet tips they are providing at least 80% lift.

The tri has “accommodation” for 3 berths a minimal galley and loo. Greg says it has about the same accommodation as a 32 foot tri. This tri is more a racer cruiser than a cruiser racer.

Greg Lynn also combined with Frederick Courouble of Courouble Design & Engineering who did some of the design and engineering work. Frederick has been involved in AC and other high-performance monohull yacht builds. They partnered with Westerly Marine to make the CNC cut foam female tooling and produced the major parts (with the exception of some small parts) supplied to the builder for assembly. More on the construction tomorrow.

The jpegs are of the concept, the study diagrams of the rig airflow and of the trimaran GF 42 “Girlfriend”.