Multihull Structure Thoughts

A 50 foot Hawaiian beach charter catamaran is being built by James Bett enterprises. The client started with a 27 foot plywood cat then upgraded to a 44 foot foam glass cat. The client needed a new cat as sailing into the beach 5 or 6 times per day to load and unload 30 customers is hard on the cats structure. So the client spoke to Bett and said he wanted a tough boat. The client choose Titanium.

What is Titanium? It is neither a precious metal nor rare, yet among industrial metals it has the reputation for being very expensive. It's the fourth most abundant metallic element and the ninth most abundant of all the elements in the earth's crust. It is well-named, as the strength of this metal is amazing. It’s 45% lighter than steel, yet it’s just as strong. It’s twice as strong as aluminium, but it’s only 60% heavier. It resists corrosion in sea water. It is resistant to high temperatures, as its melting point is 3,034.4 degrees Fahrenheit (1,668 degrees Celsius). It even resists abrasion, cavitation, and erosion even at high-flow velocities. Price of Titanium is about 2.5 times aluminium, although it in 2006 it was as high as 9 times. It is a very hard metal to recycle (melting point 3000 degrees) so can be found relatively cheaply as scarp if you live near an aircraft factory or an old nuclear reactor (yes, some cheap scrap came from Russia that was radioactive).

Back to the 50 foot cat. The jpegs show parts of the build. Every part of the boat you see in that photo is 3 mm (.125") Titanium as well as the hull plating. Keelson may be 6,5 mm (1/4" instead of 3/8") as Jim Bett didn't like the big difference between the thickness of the two plates for welding. There are lots of pitfalls welding with Ti. In the 50 foot charter cat it would have used 4.8 mm 6061 aluminium weighing 2.65 lbs/square foot verses 3mm Titanium CP2 weighing 2.77 lbs/square foot. The displacement between the aluminium and titanium versions would be very much the same and the much higher strength to weight of the Ti boat should have no problem getting signed off by the Coast Guard.

The 50 foot hulls are asymmetrical with careful compounding of the tighter inner plate at the turn of the bilge at the stern. One of the capabilities that brought the build to Betts is an old Dutch powered feed English Wheel. It takes a lot of pre-forming of a plate to closely match its final shape on the frames and stringers as the Ti is tough and resilient stuff and the Wheel is a necessity. As thin as the plate/sheet is you can't just throw a flat piece on the stringer/frames and draw it down to the frames like you can with aluminium. Look at the substantial strongback and bracing is to keep the hull shape true.

Titanium is an interesting material that is very tough if you want a very good build material. Just do a lot of research on how to weld it and engineer it. Sorry I only have a few jpegs.

 

I've worked with titanium. Absolute pig of a material. Aircraft people are used to it and have the tools and skills to work it but there are all sorts of pitfalls with it.

Bit like solar cells, or photovoltaics. Mostly silicone, doped with bromine. Cheap as chips but growing it into the right sort of crystals takes unbelievable amounts of energy so they are dear as poison. I know about the paper that claims "modern" methods mean they put out more energy over time than it takes to make them. I meant to chase his method to see if it's flawed (I suspect it is) but my strokes happened before I got a chance.

Anyway I'm drifting. Point is unless you have a really good reason titanium is a mad material to make a boat out of.

 

I am confused with this catamaran. It is not an outright racer nor is it an outright cruiser. The ESC 40 is a “40-ft catamaran designed to be two to three times faster than the typical cruising cat – using carbon fibre to reduce weight and provide increased hull strength” according to the advertising. OK. The ESC 40 is 39.5 x 23 foot that displaces 12,000 lbs (ready for sailing with crew I hope). Assuming its well designed and built, that means it should weight about 8,000 to 9,000 lbs. The 55 foot mast carries a 635 square foot mainsail, a 280 square foot self tacking jib and a 1300 square foot gennaker. The hull draft is 2 foot. The rudders are retractable transom hung and with curved retractable daggerboards providing better upwind handling and performance at speed. The length to beam at the gunnels of the hull is 10.3 to 1 which makes the hulls 3.85 foot wide. I am guessing that the length to beam at the waterline is about 11.3 to 1 judging by Hal Whitacre other cat designs.

Hal Whitacre of Whitacre Yacht Design did the design. Oh, Hal also owns and operates another business, Bruce Roberts USA and in that capacity, he has designed over 100 steel and aluminium boat kits in addition to many fiberglass and wood sail and power boats. Most recently, Hal was the chief Naval Architect for Gunboat Catamarans when they were built in the USA. I am now getting more confused. I fully accept the design talents of Mr Whitacre and his capability of designing in carbon fibre foam. But Open Waters yachts said this cat can sail at 2 to 3 times faster than your typical cruising cat. If you’re comparing to a Lagoon 40 that can hit 12 knots maybe 2 times as fast but if you are comparing to an Outremer 45 that can hit 20 plus knots, I question the statement.

The build of this cat is full carbon foam epoxy. The core is a structural-grade foam with a high shear strength characteristic: if the part is of a complex shape, we cut the foam into sections, thermoforming it to the required shape. They use five different sizes and densities of foam on the boat, optimized for local strength requirements. Each cat takes 35 rolls of stitched carbon fibre to complete and the cat parts are epoxy resin infused under vacuum. Final finishing such as taping and sanding is hand done before painting.

The ESC 40 can be had as a kit boat to a fully finished cat. This allows for EG 2 hulls to be put in a container shipped to a location then a final assembly done or have a transportable component cat for transport to new sailing locations.

The accommodation is unusual. A hull has 3.7 foot wide “double” berth aft, either a galley and or a berth centrally and a toilet forward. The wing deck cabin can have either a double berth or a dinette. Plenty of deck space though.

This is an interesting design that has the capability of going fast. But I compare ESC 40 to a Schoinning Arrow 1200 Sport or a Stealth 12 S cats that have better accommodation, about the same sail area and displacement without a full carbon fibre build. I need to know more of the claimed advantages of the ESC 40. Sorry about the limited jpegs. Details can be found at: Open Waters Yachts https://openwatersyachts.com/

 

The WYD 47 is a performance cruising catamaran designed by Whitacre Yacht Design and is being built by Bett Boats in Washington state. The cat is 47 x 25 foot with a displacement of 39,600 lbs. The 61 foot fixed aluminium mast carries a 880 square foot mainsail, 400 square foot self tacking Solent and a 1500 square foot asymmetric spinnaker. The draft over the rudders is 4 foot and the draft over daggerboards is 7.4 foot. The length to beam of the hulls is unknown but I guess about 10 to 1.

The accommodation has 2 double berths on the wing deck forward of the mast. The main cabin contains a dinette, galley and steering position. I would imagine the hulls also contain toilets and extra berths. The aft cockpit is covered and integrated with the main bridge deck cabin. I am seeing approach in several designs of late and if the cat can be controlled from a rooftop cockpit or have control ropes lead into the internal steering position, I see no problems with this arrangement in larger cats.

The structure is foam core with e-glass on either face in vinylester. There is carbon fibre for extra strength where needed EG flanges on bulkheads.

The numbers indicate the performance of the WYD 47 will be good but not ultra high performance. As a cruising cat, it does not need to have very high performance but good cruising speed across the range. If your cat can maintain 8 to 10 knot averages and peaks of 18 knots with a good sea motion you will have a good cruiser. I suspect this cat will be able to do this.

The jpegs give the idea.

 

A short one on how a male mould can be built for a multihull. This approach uses cheap material for a “one off” mould so a production fiberglass female mould can be made. The same approach can be done to produce a “one off” female mould with the framing of the structure on the “outside”. The cat is a power catamaran from Argus boats. We will talk about The Argus 35 cat tomorrow. The cat is 35 x 15.4 foot.

The male mould build is built from MDF. The MDF in this case is CNC cut (could be manually done) into the frame shapes. Either have a concrete floor or good strong back arrangements to hold the framing accurately. The framing is then covered by MDF. This design has a lot of flat panels which makes the covering of the frames relatively easy. Any curved area’s in the hull mould can have the MDF sawed through to a depth of 50% which allows greater curving on the MDF. In the case of the Argus 35 the rounded hull bottoms were built in a separate mould then attached to the basic MDF male mould. You can then do fillets etc to provide the final shape prior to painting and waxing. Once prepared the male mould can be used for a female mould.

Rob Denny Intelligent Infusion does the reverse approach using a cheap MDF mould to provide a female mould for hulls. Check the Harryproa web site.

The jpegs give the idea.

 

The Argus 35 power cat is a displacement cruising cat, designed by Roger Hill of New Zealand, that has good fuel economy. The cat is 35 x 15.4 foot and displaces 9400 lbs without fuel, stores and crew. The hull length to beam ratio is 13.5 to 1 with its round bilge full displacement hull. The underwing clearance is 1.75 foot. The cat draws 2 foot with its outboard motors. The twin 90hp Suzuki outboards on the demonstrator consume 28 litre/hour at 16 knots, equating to 1.75 litre/nautical mile. Top speed of 20.5kts results in 65 litre/hour. An Argus E35 cruising cat did a 6500 nautical mile circuit of Australia using less than $10,000 worth of fuel in 2015.

The accommodation has 2 double berth cabins, featuring queen-sized beds with European-style slat bedding, forward of midship, a galley in one hull, toilet in the other with a dinette and seating in the bridge deck cabin. The steering position can be forward in the bridge deck cabin and/or on a flying bridge. The cockpit is large and can be integrated with the main cabin to provide a large space.

There are engine options with diesels available but the preferred, cheaper and lighter option is 4 stroke outboards which are easier to maintain as well. The fuel tanks are 600 litres which allow 340 mile range at 16 knots. If the cat is slowed to 8 to 10 knots it can travel 600 miles on a tank. There are 400 litres of water and a 50 litre holding tank.

The Argus 35 has a solid e-glass fibreglass bottom, with vinylester resin below the chine, and composite foam e-glass vinylester resin construction above the waterline and on the decks. There are lateral and fore aft watertight bulkheads just in case, and structural foam-cored fibreglass keels that let you rest the boat on the dry without damaging running gear.

One test report said: “Designed with narrow hulls and a deep forefoot, the E35 rises slowly in choppy conditions so the hull slices through waves rather than bouncing over the top providing a comfortable ride combined with outstanding fuel economy.”

An interesting design that appears to be a very good coastal cruiser. The jpegs give the idea.

 

The Albertza 40 catamaran was designed by Dutoit Yacht Design of South Africa for charter work for an owner operator. The cat is 40 x 23.8 foot with a weight of 15,400 lbs. As a charter cat I could imagine a 6,600 lbs payload so an all up displacement of maybe 22,000 lbs. The 54 foot fixed aluminium mast carries 845 square foot fractional rig. The headsails are not self tacking due to the forward cockpit. All headsail sheets go to the coach roof. The cat hulls have a length to beam of about with 8.5 to 1. The draft of the low aspect ratio keels is 3.25 foot when empty and underwing clearance of 2.46 foot.

Dutoit Yacht Design of South Africa may not be well known but think about the Balance catamaran and Knysna catamarans as other examples of this design houses work. The accommodation layout of this cat is spacious and comfortable to suit the charter needs. In each hull there is a queen size aft double cabin with a toilet shower room and a double berth cabin forward. The bridge deck cabin has a dinette, galley, saloon (?) and chart area/bench space available. There is a forward and aft cockpit. The aft cockpit has all sail controls lead to it. This cat is seriously comfortable.

The construction of the boat is semi-custom using the moulds of an existing hull and adding a customised deck, superstructure and interior. Material used is GRP and balsa core for the hull, deck and bulkheads.

If anyone knows if this vessel was completed and have any idea of its performance I would be interested. This could be the basis of a serious cruiser with reasonable performance. The jpegs give the idea.

 

The following power semi foiler cat was designed by Bieker Boats for a Florida client who wanted to build the boat himself for recreational boating. The cat is 29.5 x 9.1 foot weighing 2,950 lbs and displacing 4,600 lbs. The hull length to beam ratio is 10.3 to 1. The draft is 0.9 foot. The underwing clearance is 1.25 foot. The power is two 90 HP Suzuki 4 stroke outboards. The cat can run in displacement mode and the foils can be retracted. With the flip-up main foils down combined with the “moustache” foils mounted to the motor drive legs theoretically reduce displacement 40% when down giving faster cruising speed and better stability in a seaway. The main foils can be manually adjustable for trim over ±2 degrees.

Bieker started with his commuter cat hulls as a template since they had performed well then added features suitable to warm weather boating in Florida, like a larger deck, minimal cuddy cabin, forward seating and a permanent hard top for shade and paddle board stowage. The cabin contains a double berth, a toilet in a hull and storage in the other hull. The wing deck headroom is 4.5 foot with the hull headroom of 6 foot over a short floor length. The cockpit has good seating and an effective sun shade hardtop. The forward area has some forward seating and netting.

The construction is basically plywood hulls and bulkheads with PVC foam carbon fibre for underwing and cabin roof. The hulls have 6 mm plywood sides and the hull bottoms are 9 mm plywood. The hulls have 200 gsm and 300 gsm e-glass cloth in West System Epoxy inside and outside. The 18 x 10 foot wet deck and hard top has 20 mm PVC cores with 3 layers of carbon vacuum bagged on both faces. Structural reinforcing details are carbon composite. For tapes and reinforcing 400 gsm double bias carbon fibre and 300 gsm unidirectional carbon fibre in epoxy is used. The forward crossbeam tube is carbon fibre (ex boom of a 6.5 mini mono). The hull build jpegs give the idea.

The foils have a main spar of 167 layers of pre-preg 190 gsm unidirectional carbon fibre to form solid foil plank. 144 layers are at 0 degrees with the remaining 23 layers dispersed though out the layup at 45/45 degrees. The foil is cooked at 120 degrees C in 5 or 6 separate runs as the entire 167 layers of prepreg material could not be laid up in one run. This foils took one person several months to complete including the molds. The jpeg gives the idea.

The performance is good. At a non foiling cruising speed of 20 knots @ 4,200 rpm, the fuel consumption is 12 Litres/hour (3.1 gal/hr). The cruising range is 320 nautical miles.

This is an interesting design that should provide a lot of fun. Part of the way through the build the builder decided he would use the boat as a prototype for a production cat. Jpegs give an idea.

 

Etoile 65 power trawler from Mayday Boat designed by Patrick Balta with help from Bob Escoffier as a real ocean crosser. The cat is 65 x 28.2 foot with a weight of 67,000 lbs unladen and a displacement of 110,000 lbs ready to cross oceans. There is 14500 litres of fuel and 3500 litres of other liquids aboard that weigh 35,000 lbs alone. The draft is 4.8 foot and its underwing clearance is 4 foot. The two 260 HP Iveco diesels can drive the cat at a maximum speed of 17 knots but its normal economical cruise is 10 knots.

The Etoile 65 is an expedition voyager and nautical home. The profiling of appendages and the optimization of the propellers increased its speed by 10% and allowed a moderate consumption of 1.5 litres/nautical mile per engine at 10 knots and if the weather is kind, 1 litre/nautical mile per engine at 8 knots. Realistically, this cat has a range of 5000 miles if it has full tanks and reasonable conditions. A true transatlantic cruiser.

The accommodation is very comfortable if you are the owner with 750 square foot on the bridge deck available for the galley, kitchen table and seating, a lounge area and an owners cabin with ensuite area. Also there is the inside steering position. Down in the hulls are 3 double cabins with attached toilets storage, tanks and 2 full size engine rooms. Look at the jpeg, this is how it should be done, full headroom space to access the majority of the engine, really good insulation and a full camera system in the engine room that allows the person at the helm to view the engines while underway.

The entire cat is insulated with over 2000 lbs of insulation. The main bridge deck cabin roof has 35 mm of foam and then additional insulation in it. The extraordinary acoustic thermal insulation allows the cat to be cosy in winter and northern countries as well as very good in the tropics.

The structure is plywood, laminated with glass/epoxy with timber frames and stringers. For one-off construction, the material is ideal. Light, strong, easy to work with and has no electrolysis or osmosis. The boat was cut out by a digitally controlled cutter, directly from the plans. The manufacturer delivered packages of itemized parts, to be assembled as a kit directly in the yard. Not everything is made of plywood, the structure is in solid wood EG keel and bow parts, stringers, crossbeams, deck beams etc. The timber used is Hemlock although Spruce would have been preferred but the 8.5 cubic meters of Spruce was not available in a reasonable time. Think about the 10,500 lbs of timber is used in this design combine that with at least 300 sheets of 9 mm plywood (to form a laminated skin thickness of guess 18 mm). Each engine and gear weighs 1700 lbs and there is an 800 lbs generator.

Now we come to the need for a good designer. Beside the structure requirements you need to know where to place the weight. EG each of the 4 fuel tanks weigh 7000 lbs. Where do you place them so they will not significantly alter the trim as they empty? Patrick Balta designs his power boats with a hull centre of buoyancy quite far aft, and very slim forward sections, which don’t create big bow waves. His hulls, thus designed, damp pitching movements rather well and do not ‘dig in’. One of the hardest tasks for designers is to accurately assess the weight of a design and then have the weight correctly position to match the buoyancy distribution of the hulls. The hulls have a length to beam of about 10 to 1.

This is a very serious cruising cat that has already crossed the Atlantic twice. It has “cruised” into 50 knots winds and associated waves. The owners said it was comfortable with no underwing pounding. If big winds are behind the cat it can “surf” down waves at up to 20 knots. This is a cat you can really live on and cruise widely and it can be yours for 1 million Euro. Back to reality tomorrow.

 

The One Off 45 catamaran is not a one off, there were 2 built. This cat was designed Christophe Barreau in 1998 as a high performance cruising catamaran for the needs of a client. The cat is 45.2 x 25.9 foot with a displacement of 14,110 lbs. The 61 foot fractional wing mast carries a 385 square foot fore triangle and a 800 square foot mainsail for a total sail area of 1185 square foot. The length to beam on the hulls is 12 to 1. The draft of the daggerboard is 7.5 foot down and 3.7 foot when up. The underwing clearance is 3.1 foot. These numbers indicate a performance catamaran that will exceed 20 knots and be capable of 300 mile days under the right conditions.

The accommodation contains 4 double berth cabins with the doubles on the wing deck and a share toilet in each hull. The main bridge deck cabin contains a dinette, galley and chart area. The only real issue is a product of the design time, the steps between the hulls and main cabin requires you to bend over to get up and down. Modern cats ensure you have full headroom on those steps. For short term cruising 6 people could live comfortably and for long term cruising 4 people could live well. The cockpit is a little cramped but effective.

The structure is basically PVC foam (H75) Twaron (brand name, kevlar, can be woven with carbon fibre) in polyester with selected carbon fibre reinforcement as required. The foils are unidirectional carbon fibre over a polyester Twaron foam core. The French jpeg gives the idea. The wing mast is foam, carbon glass.

This cat is what a fast cruiser can be. It has the required berths and cabin space without being spacious which allows narrow hulls, minimal wing deck and a big rig. Result a fast cat that can sail well according to test results. The jpegs give the idea.

 

Today a bit of Voodoo. Voodoo is a wave-piercing, partially planning displacement hull catamaran, with a very low draft and drag coefficient. Voodoo is 56.9 x 25 foot with an assumed weight of 27,500 lbs and a displacement of 33,600 lbs. Why do I say assumed weight and displacement? Here is where the Voodoo comes in. The hull lines looked familiar after some investigation Voodoo was found to have a Gunboat 55 hulls (modified) and underwing.

I could imagine the owner team sitting around a table talking about a new charter cat that could carry 30 people around the Virgin Islands. The water is occasionally rough so we need a good hull shape, I have seen a few sailing cats with wave piercing bows go well. Great idea how do we power it, sail is too unpredictable and I am sick of losing a day of charter fees while trying to fix up an engine. Let’s use outboards, we can change them in an hour but they cost a fortune in fuel. How about diesel outboards. Ok lets talk to David Walworth Design Inc. Dave said we should talk to Hal Whitacre who worked with Gunboat. Hal said we could use the Gunboat 55 hull moulds from Croswait Custom Composites with modification.

Back to Voodoo. The Gunboat 55 hulls aft had a carbon fibre shoe that is wider and flatter fitted and forward had a small addition in the bows to allow trimming water tanks installed. So, it’s basically 90% of a Gunboat 55 hull with a few mods to handle the outboard weight and power requirements. The two OXE 200 diesel outboards have 2 litre turbocharged engine and each engine weighs 784 lbs complete. The fuel consumption of each engine is 40 litre per hour when developing 200 HP which is about half the fuel a petrol outboard would use.

The design includes using 17″ custom Sharrow Marine propellers. These props generate another 17-20% fuel savings over conventional models and give us lower end, mid-range and top end speeds, as well as less cavitation and vibration. When Voodoo is doing normal charter cruising it runs between 20 to 22 knots. The efficiency of the modified Gunboat 55 hulls is very good. Also, Voodoo was equipped with ballast tanks in the forward bow compartments so from the helm, the captain can fill the tanks with sea water rapidly to adjust the trim of the boat.

The cats hull and bridge deck structure with the modified hull shape is composite construction of vacuum-bagged carbon fibre skins over Core-Cell foam sandwich core, infused post-cured Gougeon Brothers Pro-Set epoxy resins. The hull bottoms at along the keel lines have up to 16 layers of carbon fibre. New deck house structures and bulkheads are foam glass with some of the fit out like seats etc being plywood.

The accommodation is basic with heads, a minimal kitchen area and a lot of seating.

This is a very interesting conversion that has achieved its aim very well. The use of diesel outboards is a great thought for charter use. The jpegs give the idea.

 

This is a story of a cat where the first one was abandoned with a rig failure and found upright without a rig a year later, the company went bust producing hull number 9 and the hull “owner” had to recover it and had it rebuilt by others, story at now that's a rebuild. oops, we mean two rebuilds. – Sailing Anarchy https://sailinganarchy.com/2018/08/28/now-thats-a-rebuild-oops-we-mean-two-rebuilds/

After this several more GUNBOAT 55’s were built after the success of her earlier sisters, and is a performance cat for those interested in “day sailing and coastal cruising” in the Gunboat series. The Nigel Irens Design cat is 56.9 x 25 foot with a weight of 27,500 lbs and a displacement of 33,600 lbs. The 78 foot mast carbon mast carries a 1345 square foot mainsail, 430 square foot jib, 1505 square foot Code 0 and a 2520 square foot asymmetric spinnaker. The hulls length to beam is 12.8 to 1 with a underwing clearance of 2.8 foot. The draft is 9.2 foot over the swing up centreboards when they are down. Several owners have ordered daggerboards or had a rebuild to have daggerboards installed.

The accommodation varies according to customer needs and I have a least 3 different layouts on the bridge deck. The hulls contain 3 double berth cabins with attached toilets. In one set of jpegs there is a galley in a hull, in another cat the galley is on the bridge deck. The main feature of the design is the sail controls and steering are at the forward end on the main cabin so those controlling the Gunboat 55 are protected from spray and sun whilst sailing.

Performance of the Gunboat 55. I will quote. “Heading upwind, for example, she felt stable and stiff, with no movement inside. We averaged 10-11 knots (at just under 40°A), up to 13 knots by cracking off 10°”. “Basically, we aim to get her sailing at close to wind speed, said boat captain, Chris Bailet. Sure enough, in 7 knots of wind she clocked an easy 6 to 7 knots; in 12 knots, with the screecher deployed, she made 11 knots on a beam reach.” “Her only motion is forward with ease. Her high wing deck will prevent wing slams in all but the most severe conditions.” “Rooster tails began to rise off the transoms. A fine spray fired off the leeward bow as a gust hit. We carried it downwind as the apparent wind shot forward, feeling the surge and watching the speedo rise from mid-teens to 20 knots”. Gunboat 55’s will sail offshore sitting on 8-14 knots for days and deliver higher daily averages for shorthanded cruising crews than just about any other owner-operator cruiser.

OK this cat can really sail. But the most telling comment came from another test “Past Gunboat models such as the 62 and 66 have a defined transition zone. Like a powerboat struggling to get on the plane, once they hit 13 knots they fly into the early 20s. The 55, however, consistently made 15-20 knots reaching, comfortably, stably, easily, whether in waves and big winds under jib or asymmetric, or on flat water with the furling R1/screecher sail up.”

The latest Gunboat 55’s (or 57 which has 2 foot added to the back) have hull and deck made of a composite of carbon fiber, epoxy resin and Corecell foam, bound together in a sophisticated vacuum infusion process. The hulls and bridge are molded as a single unit, which makes the structure extremely stiff and strong and allows the forward crossbeam to be eliminated. Constructed in female molds, the hulls, built in epoxy sandwich using infusion, are post-cured in a kiln, and benefit from carbon tissue and reinforcements wherever necessary. Carbon for the shroud chainplates, the daggerboards, the spreaders, the boom, the compression beam which finishes as a bowsprit. At 12.5 tonnes unladen on the scales, the Gunboat 55 is at the bottom of the range of weights for a catamaran of this size. The bows are sacrificial for 1.5 meters, with a watertight bulkhead aft.

The Hall Spars mast and boom, and in the interior furniture, which is made up of carbon/Divynicell-foam composite panels. All the systems are planned out to use a minimum of material in order to shave off critical weight. CNC routers cut out the individual parts to exact tolerances. Standing rigging is aramid fiber; the inner and outer forestays are tacked to a jutting carbon fiber beam that is braced by aramid stays taken to the hulls. These, in turn, are strengthened internally by long stringers of carbon fiber, stiffening the hulls to make up for the lack of a crossbeam.

These cats performance is spectacular. The designer Nigel Irens and current builder Croswait Custom Composites in North Carolina are producing a light strong cat that can sail across a wind range very well. Pity I cannot afford the $2 million US plus required to buy one. The jpegs give the idea.

 

The CM²46 is claimed to be primarily designed for the purist and an adventure sailor who wants a lightweight owner cruiser racer or for the performance charter owner an efficient fast performing sailing design that is spacious due to its open plan saloon and cockpit. A Swiss army knife of sailing.

The cat is 46.2 x 24.3 foot which weighs in the foam carbon fibre “racing” version 10,300 lbs, in the CE approved foam glass “standard” version weighs 11,200 lbs. The maximum displacement of either version is 15,700 lbs. The standard mast can be a fixed aluminium 56 footer or a 62 foot rotating carbon fibre wing mast (produced in house by Current Marine). The mainsail is 626 square foot, the Solent jib is 333 square foot, the staysail is 151 square foot and the Code 0 area is 677 square foot. The hull length to beam is 12.6 to 1 and the underwing clearance is 3.1 foot. The daggerboards draw about 6 foot and I imagine fixed low aspect ratio keels are an option.

The accommodation is 3 double berths and a large toilet in the hulls. The bridge deck cabin contains a dinette and galley. The large door between the cockpit and main cabin allows a larger space when cruising. The steering positions are in the aft corners of the cockpit to allow a clear view of the rig and sea conditions around the cat. Good for racing but make sure you have good self steering gear for cruising as continuous exposure would not be nice.

The Standard CM²46 built using epoxy resin infused composite E-Glass, 80-130kg/m3 Foam core achieving optimal weight and strength. Carbon used extensively in locally reinforced structural areas. The “racing” Carbon CM²46 built using epoxy resin infused composite Carbon, 80-130kg/m3 Foam core achieving optimal weight and strength. Externally-spray finish Awl Craft 2000 / Alex seal in light solid colour of choice / Anti-slip/ Anti-fouling barrier coatings. The foam cored furniture is built by lamination and infusion process to deliver an excellent base-level interior furniture surfaces, which is faired and painted. This adds many man-hours but avoids the weight penalty of rougher internal laminate with the cosmetic need for paneling to hide it.

The hull and cabin top shapes are designed to keep the weight down, with simple curves in most areas allowing the use of un-scored foam. Complex curves require scored foam to bend to shape and these scores open up, fill with resin and add hundreds of kilos for no structural benefit. Finish Like Gunboat and HH cats, the CM’s hull is finished by fairing and spraying. Awlgrip paint saves several hundred kilos over gelcoat. There are many colours to choose from and, after five years in the sun, painted epoxy boats tend to look much smarter than polyester gelcoated boats.

The designers’ predictions of performance are interesting. Cruising speeds of 12 to 16 knots and a top speed of 25 knots plus. Motoring top speed is 11 knots. 2 points. These speeds would be under optimum conditions in a possible racing situation. When cruising I will suggest you will want to sit on 8 to 10 knots even though you can sail faster to keep you comfortable and able to cook meals, sleep etc.

This is a well designed cat that appears to be well built in the first carbon fibre version. The second cat is a more standard version with a carbon fibre mast for a couple who owned a Pogo 12 monohull. The jpegs give the idea.

 

"and is a performance cat for those interested in “day sailing and coastal cruising” in the Gunboat series."

55' daysailer and coastal cruiser. FFS... Here I am wondering if going from 25' to 32' is excessive....

 

I think you're being overly complementary to the designer here. Since this is the MO of all designers, not just this one, otherwise the boat wont float correctly!
It is the first task for any naval architect when designing, get the balance right from the outset...

That is merely a function of a fine angle of entry, nothing else. One shouldn't read into things which are not there, merely because a sales blurb states so!

Damping , in pitch, is complex, but more beam and less draft along with more of a 'V' section helps.



But in his case the main reason is the that the freeboard at the bow in greater - shown by the red arrow - and the cut-away of the raft section - shown shaded in yellow - prevents the digging in as you cite it. Or Deck diving or bow diving.
There has been a significant body of work on this subject. I draw your attention to the excellent work by the MCA their research study report 502 back in 2005 on this subject...which mirrored our own in-house research too..