Multihull Structure Thoughts

1985 Shuttleworth design the Spectrum 42 is 42 x28 foot displacing 13,500 lbs with all fittings, engine etc and dingy. It has a 56 foot mast with a 550 square foot main and 460 square foot 110% jib. Underwing clearance 2.75 foot. The spectrum is built from Airex, Divinycell foams, tri-axial E glass, carbon and Kevlar fabrics vacuum bagged isophalic polyester and epoxy resins comprise the hulls and decks. Exterior paint is Awlgrip cream and interiors epoxy paint.

The Spectrum 42 could exceed the wind speed in 3 to 5 knots of wind, and top speed was 23 knots in one sailing review. The boat will sail steadily at 18 to 20 knots with no fuss. In fact the general impression by all who sail on her is the apparent effortlessness required to sail the boat. She goes to windward very well with a top speed hard on the wind of around 12 knots.

The Hughes 42 is 42.1 x 27 foot that weighs 9,000 lbs with a displacement of 14,400 lbs. The mainsail is 452 square foot and the blade jib is 270 square foot. The bridgedeck clearance is 3.1 foot. The structure of the hull is composite of 3 laminates of 3mm Akumi marine ply vacuum bagged with West Saturation covered with 200 sgm cloth and epoxy. The deck is 3 mm ply bottom 19 mm baltec AL 600 aircraft pre preg balsa vacuum bagged and 6 mm on top with West System with 200grm fibreglass cloth. The one daggerboard is West System Balsa and ply covering with Carbon Fiber strips.

The Hughes 42 cats have less sail area but can still sail very well with top speeds exceeding 18 knots and some 10 knot averages.

This gives a guide as to the Berckemeyer yacht design Dash 39 cat. The Dash 39 is 39 x 25.5 foot open bridgedeck cat displacing 11,000 lbs (could be weight). The 55 foot mast can be aluminium or some form of wing mast in EG carbon fibre or wood composite with a 650 square foot mainsail and a 328 square foot self-tacking jib and a large 1300 square foot gennaker. There are 2 big daggerboards. The hull can be built in aluminium or hard chine plywood.

Now we have 3 cats of a similar concept. The Spectrum was designed in 1985 and reflected its time with a fine stern but was light and had a big rig. The Spectrum had a brilliant hull shape though, as when the bow pitched down its centre of buoyancy moved rapidly forward due to its inverted bell shaped which minimised pitching. A friend went to Britian to test one in the 90’s and was amazed as to how little it pitched and good it was to windward.

The Hughes 42 was designed later and had a fuller stern and simpler hull shape to build. The Hughes being sold in Coomera in Australia was a boat and the person I spoke to claimed it was a very good to windward. Both the spectrum and Hughes 42 have their accommodation more centered with double berths forward.

The Dash 39 reflects the modern hull shape with a fat stern and finer forward. This again to minimise pitching and allows some of the accommodation aft closer to the pitch centre of the boat. The other feature of the Dash 39 is the more modern rig with a fat headed main and smaller self-tacking jib for upwind work but similar in total size as the Spectrum 42.

You have noticed my emphasis on upwind work. A problem with open bridgedeck cats is the amount of water/spay that gets thrown at you upwind when it gets a bit rough. Many of the open bridgedeck cat have some form of windscreen bimimi top to help protect those sailing these cats. This is the reason Tony Grainger does not design open bridgedeck cruising cats any more as the majority of his open bridgedeck cats had central cabins built on them for more sailing comfort.

 

I think I have already written about the problems of the Spectrum 42 hull shape. I copied the idea of the Spectrum in my little cats and with changes in loading the hull pitches up or down. It sounds good in theory but in practice the change in CB position makes the boat a poor cruiser. Combined with the low flare, it becomes a problematic hull shape for any overloading (and all cruisers get overloaded some times).
My 38 footer started out as an open bridgedeck cat with a small cockpit cover. After the second year of cruising I built an awful looking, but usable open ended cabin (a la Seawind 1000). Then after cruising I built a new cabin from foam with two removable doors and a central window. Also I ensured that one could see outside when seated inside. You can also see from the help, through the open doors and cabin windows.
The open bridgedeck is a pretty silly idea. I quickly worked out that if it was sunny I wanted out of the sun, it if was windy I wanted out of the wind and if it was wet I wanted out of the water. The best idea is a cabin that can be altered as you need, used as a pilot house at sea, a beach house at anchor and as a clear viewed verandah when sailing from the cockpit.

cheers

Phil

 

The Manta production cruising catamaran history shows you persistence can pay off. The first Manta 38 was developed in Canada in early 1991. 2 were produced but it was a commercial failure. In 1993 the molds were brought and production started in the US. At its first boat show at Annapolis in 1993 the company sold 5 Manta 38’s. Later in 1997 the Manta 40 evolved by extending the hull length for better performance and handling, with added headroom and other improvements. By 2000 there were 74 Mantas produced. After 2000, several versions of the Manta 42 were produced with at least 10 additional boats were built as well as a power version. The Manta 42 had additional hull length aft and other improvements for more comfort and ease of sail handling. Production ceased in 2009 with nearly 100 sailing versions produced.

We will focus on the Manta 42 which is the same dimensions as the Manta 38 with an extra 4 foot added aft. The cat is 42 x 21 foot with a factory weight of 13500 lbs, a on the water weight of 16500 lbs and a displacement of about 20,000 lbs. The 50 foot fixed aluminium mast carries a fully batten 10.3 oz high modulus dacron mainsail with three reefs and a self-tacking, full batten 8.3 oz. high modulus macro jib with Camber Spar for a total sail area of 798 square foot. The hull length to beam is 10 to 1. The low aspect ratio keels draw 3.66 foot.

On performance, one review said “The Manta 42 sailing in 15 to 20 knots of winds. With her fixed keels provided good tracking on all points of sail and carries its way through tacks. With 20 knots of apparent wind on the beam, she made 9.5 knots boat speed. Close hauled, she made 6 to 7 knots against 25-knot apparent winds. When coming about, her boat speed never dropped below 4.5 knots- not bad for a fully loaded liveaboard cruising cat. Under sail, her top speed for the day was 10.8 knots. Given her speed and her easy sail plan, should arrive at her anchorages early and give her owners plenty of time to relax.” Translation, a reasonable performance cat that will do 7 to 8 knot averages. On deck, the boat has only one electric winch, a two-speed Harken, mounted on the cabin top just forward of the steering station. All reefing lines, halyards, and sheets are labelled and led to this single point in the cockpit, so there's little need to go forward.

The Manta cats are molded in 2 major parts, a full hull bridgedeck mold and a full deck cabin mold that are brought together to form one unit. The structure of the Manta cats evolved over the years but in the later versions the structure has hull, deck and bulkheads constructed of Ferro Super Shield exterior gel-coat with triaxial, biaxial, and unidirectional fiberglass with vinylester, isophthalic resins, and Corcell (hull and deck) and Nida-core (subsoles and bulkheads); all vacuum bagged for stiffness, strength, and reduced weight. The hull/deck joint includes 3M 5200 adhesive sealant and mechanical fasteners on 10-inch centers with glass laminated tabbing. The cat has Kevlar reinforced bow and keels. The twin high density foam/fiberglass elliptical rudders have 52 mm diameter solid stainless steel shafts. The 440 litre water and fuel tanks are made of 4.8 mm epoxy coated aluminium. The 80 litre holding tanks are polyethylene.

The interior is easily maintained vinyl and acrylic, and accented with varnished teak trim and highly durable synthetic teak-and-holly soles. On the bridge deck is a U-shaped galley to port serves the dinette, across from which a serious navigation station sits. The hulls have 2 double berths and a twin cabin and loos. The cockpit has a canvas bimini that covers cockpit over a radar/dingy lifting arch.

The jpegs give the idea, especially of the ever extending stern.

 

Somehow I missed this one.

I'd like to buy these plans, I've spent hundreds of hours researching, researching, researching... and THIS boat hits quite a few of the sweet spots I was looking for... fast compared to a monohull, maybe sacrifice a little speed for bomb-proof (aluminum), and folding to save docking fees.

but I can't find Sylvestre Langevin's website - an old link is dead.
http://www.langevin-sylvestre-architecte-naval.com/
29 Villa Auguste Blanqui, Paris

I found his wife's name (Annick Balaresque), apparently she's an artist, but I don't see she's painted anything lately either, couldn't find anything for sale.

Old Multi, would you know if this guy is still alive, and how to contact him?

Thanks!

 

Derek. France has a rule that is a problem. Unless you are currently working as a designer you are not allowed to sell the your plans. So if Sylvestre Langevin is retired he cannot sell plans according to my knowledge. Probably this is the reason you are having problems locating any source of plans. There are several multi designers who can do aluminum structures but I suspect the price will not be cheap. I agree the Trial 1100 is an excellent concept. Now I am going to be painful because I cannot remember how I got there in the first place. There are plans that were done by a French designer called Sargent that were donated to the museum including a 12 meter aluminum tri. These are old plans but they may give a guide. The start point is Musée Maritime https://museemaritime.larochelle.fr/ then there are some deep links to a plan section of many designer plans mostly mono's. May give a hint.

 

He is probably retired , but still in the directory of IFAN (the association of the french naval architects) :
29 villa Auguste Blanqui – 75013 PARIS -
Tel : 0153612713 Email : langevin.sylvestre@cegetel.net
His recent traces of activity are comments on some of his designs :
Messages 01- S. Langevin http://flot18.free.fr/Message%2001.html
(PS : he is a grand-son of the physicist Paul Langevin)

 

Another possible contact, via Franck Cheysson / spotconcept@online.fr :
Spot'concept - Architecte Sylvestre LANGEVIN http://spotconcept.free.fr/spotconcept/pages/langevin.html
Coordonnées - Spot'concept - Franck CHEYSSON http://spotconcept.free.fr/spotconcept/pages/adresse.html

 

The El Toro racing trimaran is something I would like to know more about. The racing tri is 29.5 x 23.66 foot and will displace 2540 lbs. The rig will be a 47 foot Ctec rotating carbon fibre mast which is located at 50% from the bow. I am working off limited information here but the main has over 400 square foot and the self tacking jib is about 190 square foot. The jib is a self tacker and is hanked on with forestay set back from the bow. The upwind Screecher (guessing about 520 square foot) tacks to the bow with a Facnor 2T internal halyard lock up top and Profurl NEX 2.5 furler down the bottom. The screecher should give this tri with a conservative rig a boost for the 0-10 knots true upwind conditions.

Now I have a problem with the “conservative rig”. If this tri works as designed a near 1000 square foot rig moving 2500 lbs will be anything but conservative. I would consider it down right scary in gusty wind conditions on a broad reach. Initially, El Toro will be equipped with standard daggerboards on the floats, but the possibility of designing foils at a later stage hasn’t been ruled out. Rudders are on the floats.

The main hull looks as thought it has a 12 to 1 length to beam ratio. All the bows are axe or reverse bows. The accommodation in this minimalist multihull is limited as this design is intended for day sailing or coastal racing. The cockpit is large.

The construction is not specified but the jpegs indicate foam glass hulls and floats with removable carbon fibre cross beams. The prodder is carbon fibre as I would assume the rudders and daggerboards. The tri is being designed and built by 4 friends. The design was approved in 2014 with construction starting in 2015. The tri was meant to be launched in 2021 but I suspect Covid may have intervened.

The jpegs give the idea. I hope the crew finish the boat soon and they can afford a really good rig as I suspect this tri will be very fast.

 

This is a story about design persistence. The Notus 50 is a Trimonoran (will explain soon) of 48.75 x 21 foot vessel of unknown displacement and sail area. It draws 4.9 foot. Please look at the jpegs to get an idea of the hull concept first.

When AnwigemA BV started designing the hull the dream was of a trihull that was a better ship than a monohull, catamaran or trimaran in every way. Jelle Bilkert obtained a patent for his revolutionary hull design to produce the “fastest and most stable hull ever”. Bilkert spent almost 25 years developing the design to be stable, safe and comfortable sea motion hull shape for sailors. Bilkert’s multihull design has the outer hulls angled at 45 degrees underneath the deck, making the boat far more compact. In the 1980’s Bilkert developed 16 foot models and subsequently a larger sailing version to test the concept.

In 2010 Bilkert a approached Van Oossanen Naval Architects, who tested and acknowledged the potential of the three-hull design. The result was a design that combined very low resistance with high stability. Van Oossanen compared the Trimonoran against a well-known 50 foot sailing yacht. The Trimonoran slim hulls had little resistance, and the evaluations indicated this model can reach speeds of 20 knots while sailing. The Trimonoran even at considerable roll or heel angles demonstrated good stability. It will not capsize at a 90 degrees inclination.

Some benefits of a Trimonoran according to the designers is a speed gain of up to 50% over standard mono hulls, high stability for safe and comfortable sailing, large deck and hull space, relatively small drag, less water resistance than traditional mono hulls and no need for a ballast weight.

Now a short comparison to a “conventional cat or trimaran” with clearly separated hulls that are vertical and with minimum wetted surface. The Trimonoran hull shape has a fine central hull but angles the outer hulls at 45 degrees to allow them to pick up buoyancy as the hull form heels. Excellent for stability up to 90 degrees but the design picks up a large amount wetted surface in the process. Also, as the design heels there would be an increasing wave interference in the “tunnel” between the main and outer hull. Translation: Agreed it would be faster than a cruising monohull but not a good cruising cat or tri of the same length. A modern racing monohull would probably outsail the Trimonoran. But the Trimonoran is not just about speed and is designed for other features such as increased stability and comfort over a more conventional cat or tri.

The Notus 50 has 30% more space than a mono hull of the same length with three comfortable cabins. There is a large master cabin in the bow with own bathroom. Other cabins using the general bathroom in hallway. The saloon with open galley and navigation area included. I have no idea of the structure.

This is an interesting concept that could suit a market segment who want a cross between a mono an a multi. The jpegs give the idea.

 

The following is about an 18 foot home built foldable sailing tri with a mast aft that is intended for fishing. The tri’s main interest is in its folding beam system which is simple but reasonably thought out. The tri is 18 x 16(?) foot that can be folded to 8.2 foot. Displacement is unknown but the 26 foot aft mast carries a 130 square foot sail.

The structure of the hulls is foam glass. The daggerboard case is solid glass and the daggerboard is a sheet of plywood with 10 mm PVC foam on each face shaped to an aerofoil then glassed. The cross arm are square PVC guttering down pipes that have unidirectional fiberglass coverings for strength. The aft mast started as an aluminum section but proved to flexible. A stiffer vacuum bagged resin infused glass mast was made to make the rig practicable.

Now we get to the folding system. The cross arm halves are hinged in the middle with strong stainless steel large “door” hinges. The cross arms are controlled in the folding process by single simple control arms per cross arm halves. When the cross arms are unfolded and full width the arms are bolted to a central channel in the main hull. The cross arm halves are permentaly bonded to the float hulls. The owner stated “The main hull does want to tilt when the arms are not up or down, but if I stand inside the hull, I can hinge the ama's in and out without any problem and still keep the main hull upright.”

The owner built this tri to practice his resin infusion technique and to get an understanding of the folding system as he intends to apply the idea to a 32 foot transportable folding cat he is contemplating building.

An interesting concept that appears to be simpler than a farrier but with a little less control. I still think Frank Smoots DIY tri folding system is the best small tri folding system I have seen. Jpegs give the story.

 

This is a design that used boat sales people speak really highly of. The cat sells almost immediately a spouse visits the boat. After 3 months, the person who enjoys sailing often starts thinking about selling the cat. The design is the motor sailor Catfisher 28 and subsequently extended version Catfisher 32. The Catfisher 28 is 28 x 13.1 foot with a weight of 8,500 lbs with a displacement of 11500 lbs. The ketch rig has a 30 foot aluminium main mast, a 23 foot mizzen mast with a 147 square foot mainsail, a 56 square foot mizzen, 156 square foot jib and a 260 square foot genoa. The length to beam of the hulls was about 8:1. The design has a low aspect ratio keels.

The Catfisher 32 is 32 x 13.1 foot model is almost the same accommodation layout and main cabin shape. The weight is 8000 lbs due to better construction but the displacement is about 12,000 lbs. The sloop rig has a 32 foot aluminium mast with a 170 square foot mainsail and a 300 square foot genoa. The design has the same low aspect ratio keels as the 28. There were 18 Catfisher 32 made.

The Catfisher 32 is just a Catfisher 28 with a 4 foot platform stern added to the rear end of each hull. There are some changes mainly in the rig and construction but the accommodation etc is very similar.

Now we get to the joy of the design that sells to any person who wants comfort. 6.2 foot headroom throughout, 2 double berths, good size galley, lots of “wood interior”, internal steering position, proper loo and a nice cockpit.

Now, we get to the down side. When sales people “test sail” the cat they motor upwind and set sail reaching or running in flat water. The Catfisher’s can sail at about 45% of wind speed running or reaching in winds up to 20 knots. Impressive for what is effectively a “block of flats”. When the new owner of a Catfisher 28 sails out over a bar into the real ocean and heads upwind 3 things happened. The cat pitched and hobby horsed, the underwing was slapped by any seaway and the pointing angle especially with the ketch rig almost demanded the engine be fired up to make any sort of headway.

The designer of the Catfisher 28 and 32 was Terry Crompton who designed what the Catfisher organization wanted but Rod Gibbons a seller of the Catfisher range said “The Catfisher's designer, Terry Compton, told me that after about hull #25 (of the 54 Catfisher 28’s) or so, the pitching motion (due to the builder's request for canoe sterns to match those of the Fisher monohulls), was severe enough that the builder thereafter added something like a vestigial swim platform at the aft end of each hull, at water's level, to dampen the pitching.

Terry tells me it was a discernible, but modest improvement. If I recall correctly the LWL for the CF28 was about 24'. Conversely, the CF-32 had completely redesigned transoms that, like today's modern cat designs, were convex in shape, thus ADDING 4' of extra waterline to the boat. The bows still lifted noticeably when heading into a seaway, but the "rocking-horse" motion of the 28' was almost eliminated. And, the longer waterline increased performance under sail and under power. In essence, the CF-32 was the same boat as the 28, with simply an extension of the aft ends of each hull.”

The Catfisher 32 could sail moderately well upwind but was still a motorsailer. The next problem was the high centre of gravity of the whole design due to the height and windage of the central structure and narrow beam. There are no known capsizes of the design but in big winds and waves you had to be careful with your sailing technique.

What the above is trying to say is do not push the edges of the design envelope. 6 foot headroom is nice with big main cabins but if its put on to small a cat, especially with fat heavy hulls you may end up with a design that may not perform as expected. I reiterate that Terry Crompton designed what he was asked to, not what he would have liked, this is not a designer problem per say. The Catfisher 28 and 32 suit a certain segment of the market who want good accommodation in a small package and don’t mind running an engine.

And finally I will quote one owner. “In 1996 I bought the above Catfisher 28. I had always liked to look of the boat & accidentally came across one in Kip Marina when looking for a motor sailor. My wife fell in love with it as soon as she saw it, & after a trial sail with a sweet talking Kip salesman, we bought her. I decided to move her from Kip to Largs which is when I found what a pig it was, wouldn't sail for toffee, when motoring the noise inside the wheelhouse was horrendous…. After three months I decided she wasn't for me, sailed her to Troon, then on to Pwhelli via Loch Ryan Isle of Man, Holyhead. Put her up for sale, first guy to see her bought her…. The only good thing about the design is the accommodation...” Stearman65

 

The following trimaran is a design study but I am certain it is or will be built. The tri is the CBYD 27 racing trimaran of 26.9 x 25.6 foot weighing under 3000 lbs and displacing 3580 lbs. The rotating (assume) carbon fibre wing mast is 44 foot high and carries a 405 square foot square head main, a 215 square foot solent jib which is self tacking at very narrow angles and a 655 square foot code 0. This is a very powerful rig for a wide moderate displacement tri. The foils in the floats add to the righting power of this tri. The length to beam on the main hull is 10.5 to 1.

The rudders are on the floats and there is a deep daggerboard in the main hull. This tri should have no problems going upwind or keeping the large rig under control with this amount of foils available. My only concern is the cost and maintenance of all these foils. I also think this design is meant to be sailed on one float as much as possible to get the most speed possible.

I suspect the comment of the designer about a top speed of 26 knots plus is possible. The attached polar of wind speed versus predicted boat speed jpeg also clearly indicates the tri is capable of sailing faster than wind speed up to 20 knots wind speed range reaching. This is a seriously fast tri.

The designer Corentin Bigot (French) has been involved in many projects and even had a TV show building a 30 foot cat design. He designs both mono and multihulls. He has strong experience in project managing, designing and building boats with composites. The CBYD 27 is built from PVC foam sandwich glass epoxy composite construction.

Sorry about the limited jpegs but it is an interesting design.

 

The Allures company has been producing aluminum monohulls for years. They decided back in 2017 to also do catamarans. The Allures C 47.9 is 47.8 x 24.1 foot bridge deck cat with a weight of 26,800 lbs. I suspect the cat could carry a 6000 lbs payload. The sloop rig carries a mainsail of 730 square foot, solent 590 square foot and a 1235 square foot gennaker. The hull length to beam is about 12 to 1 and the hulls have low aspect ratio keels. The performance of this cat should be good with a reasonable amount of sail power for its displacement and good hull shape.

The Allures yard has also drawn expertise of its partner Outremer Yachting (builders of Outremer 45 cat etc). The naval architects Christophe Barreau and Frédéric Neuman designed the aluminum hulls, bulkhead structure etc to deliver optimum performance. I am sure Outremer provided some guidance on the foam glass composite deck structure.

The hull as indicated in the jpegs is an aluminum stringer on frame construction with aluminum cross beam structures. The composite deck is resin infused foam glass to minimize weight. The mast is aluminum.

The interior has the galley and dinette in the bridgedeck cabin and the hulls contain 3 double berth cabins.

This is a serious ocean cruiser that has the additional comfort of a knock resistance of an aluminum hull. Notice I said increased knock resistance not bullet proof. The Allures C 47.9 hull plating is probably 4 mm aluminum. The only aluminum cat I know that is near bullet proof is the 10 mm thick aluminum hull of Antoine's 41 x 21 foot Banana Split built by Prometa that displaces 26,800 lbs.

The Allures C 47.9 will out perform eg Banana Split (Antoine has sailed over 20 years on his cat very happily). But when you are long term cruising outright performance is low on the priority list. Crew comfort, ease of handling, ease of maintenance and comfortable performance are the most important things to the majority of people.

The jpegs tell you more about the Allure C 47.9. The final 2 jpegs are of Banana Split.

 

More on the unusual. It is called a Twin Foil catamaran. The design concept is done by Lawrence Meacock at the following site Twinfoil Catamaran Designs https://www.arton.co/twinfoilcatamaran.html. I can find little information about Mr Meacock design credentials, but I will assume this is a serious design attempt. The design shown here is 45 x 16.3 foot sailing version. The length to beam on the hull is 17.5 to 1 on the 32 foot waterline. The underwater bulb is about 45 foot x 5.1 x 1.8 foot which gives an approximate displacement of 40,000 lbs including the hull components for the Twinfoil. The sloop sail area is unknown. I suspect this is a motor sailor design. It is claimed the idea can currently be used up to 100 foot long.

The best I can do is quote from the designer’s information “The basic concept of the TWINFOIL Catamaran design is based on having two horizontal linear foils running the full length at the base of the two narrow waterline-width low-wave-resistant catamaran hulls. These provide the necessary underwater ballast requirement, and additionally each also acts as a “Flopper-stopper” resistance to vertical wave motion.

It has been generally established that the surface wave motion resistance on a hull provides the greatest hull resistance through the water, slowing down the whole craft. The surface wave motion even exceeds that of a large wetted surface area displacement area. Catamaran twin narrow width hulls provide a faster passage with minimum forward resistance. However, there is still a requirement for some extra ballast needed in the water to adequately support the craft, as does the extra hull surface area provided by the two linear foils in this design concept. Such a combination will result in a high degree of hull efficiency, along with higher speeds using less fuel, and a greater comfort provided by the twin linear foils giving a high a high degree of lateral stability at sea.

Construction materials envisaged for the 40-50ft range of TWINFOILS would be of fiberglass inner and outer moulded surfaces with a sandwich construction of 2-inch high density internal foam, along with twin linear internal keels constructed of laminated wood for extra strength and damage control. Having a total beam of 16’.4” (5m), they could also be built in two 8’.2” (2.50m) halves with interlocking centre-line surfaces which can be bolted together to provide suitable road transport capability for assembly at such areas as inland lakes.”

Now folks, I suspect that the designer is being selective about his information. Yes, hull drag is more important above certain winds/boat speeds in a sailing catamaran, but below those wind speeds the wetted surface drag is far more important. In this design concept you have high wetted surface for a given displacement. Also having narrow waterlines means that when the Twinfoil heels it picks up additional wetted surface quickly. All this wetted surface will slow the vessel down even if there are narrow “low drag” hull shapes.

The concept of wide flat bottoms on the hulls will reduce roll and pitching moments but will also limits the Twinfoil ability to react to EG head seas which could be the reason for the long high freeboard overhangs fore and aft. The concept of additional water ballast I suspect is a “balancing” device for varying loads and/or weather conditions. Also, the bow thruster openings would not help water flow around the hull.

Again, a design idea to solve a series of problems but not a complete solution for an all-round high performance sailing solution. The jpegs give the idea.

 

Seems he's trying not to use the term/word SWATH.
As the images pretty much indicate this. But it really depends upon how much buoyancy is in those lower tubes as a ratio to the WPA. ..as a unit of measure for a Swath hull.