Multihull Structure Thoughts

This is the last of the student conceptual design work for a while but it shows a current trend of a fun catamaran. Kurt Hughes has designed similar cats before but the HD twin power cat design has more French flair and style about it. This cat is for 2 people, in their separate cockpits, enjoy watching the world go past quickly.

The motive power looks like high performance jet ski or snow mobile engines attached to surface piercing propellers which indicates a cat designed for speed. The two shaft propeller drives will create great rooster tails to attract more attention as you speed by. The aero foils behind the sitting cockpits are more for image than practicality as they are almost square and do not have end plates to become effective foils.

The cat is about 30 x 10 foot of an unknown weight. The length to beam on the hulls looks about 15 to 1. With 2 high performance motors each producing EG 200 plus HP we are talking about a 40 to 50 knot cat here. The only issue here is the fine low volume bows. At speed, this cat is likely to drive through waves more than move over waves. OK to a point in small waves but dangerous in larger waves.

The build would be composites and probably be very light. An interesting idea which would be a great fast fun boat for 2. Think of it as a plush jet ski with more comfortable seating. The jpegs give the idea.

 

Lazercat 950 is an asymmetric power catamaran with hydrofoil between the hulls. This power cat can be configured as a charter, fishing or cruising catamaran on the same base hull unit. It is a semi production unit that can be customised (up to a point) to suit your requirements. The cat is designed and produced by Lazercraft in Dunedin New Zealand. Lazercraft have been producing boats since 1984 and have many other monohull aluminium designs some with fiberglass deck configurations.

The Lazercat 950 is 31.1 x 10 foot with a weight of between 8,500 lbs and 9,800 lbs depending on configuration and engines chosen. The draft is 2.2 foot. The engines on the jpeg cat are 2 x Yamaha F300NSB counter-rotating with Helm Master allowing the motors to be independently steered and enabling the boat to move sideways (using a joystick control) without a bow thruster.. The Lazercat 950 is an outboard-powered catamaran configuration based on asymmetrical hulls and a dihedral hydrofoil below the waterline, Lazercat aims to be a smooth-riding hull with the benefits of a foil to improve the ride and fuel economy. The Lazercat’s foil was developed in collaboration with Dr Gunther Migeotte of Icarus Marine Naval architects. The dihedral shape of the foil not only provides lift to reduce the wetted surface (and hence reduce drag) but also continues to provide that lift even when the boat turns sharply.

The performance of the Lazercat 950 when running the engines just over half throttle on 3,100rpm, does close to 20 knots while using 50 litres per hour (2.5 litres per nautical mile). At 5000rpm speed is 37 knots consuming 3.6 litres per nautical mile. The 550-litre fuel tank provides a range in excess of 200 nautical miles, and there is an optional 800-litre tank to extend this even further. It maxed out at 46.5 knots with a similarly half-loaded vessel. After initial test runs and new props installed a cruising speed of 32 knots and a fuel consumption is 85 litres per hour (2.65 litres per nautical mile) was achieved.

The dihedral foil helps as the speeds climb above 27 knots with a noticeably smoother ride at the higher speeds. This is a boat that benefits from more speed in rougher conditions, rather than by slowing down.

The construction is mainly aluminium with a hull thickness of 5mm. The topsides and cabin thickness is 4mm all with suitable framing and stringers. The keel thickness is 10mm and the transom thickness is 12mm. composites are used in the interior furniture and some deck components.

The accommodation is a double berth under the foredeck and the main cabin features a galley on the starboard side – with the dining table and seats and the toilet compartment to port. The galley’s equipped with a fridge and a two-burner hob, plus storage drawers. There is an inside helming position forward in the main cabin. There is a large cockpit for fishing or lounging with an external BBQ etc.

This is a good performance power catamaran. The jpegs give the idea.

 

It's interesting how things go around in circles. I early multihull history initially the 50's and 60's after the Hawaian resurgence of catamarans, the Prouts and Wharram, O'brien and others all advocated catamarans but then the emergence of Piver,Nicol, Newick and Crowther meant that by the mid -60's and into the 70's accepted wisdom was that trimarans were the best ocean multihulls. Late 70's and 80's the pendulum swung back to catamarans again. Now with Rapido and Neel suddenly trimarans are the safest most seaworthy concept. As a trimaran owner I might tend towards that view but the accomplishments of so many catamarans- older and new makes me sceptical of such statements.

 

Akesdesign boat design studio specializes in the design of custom pleasure-powerboats and Rigid Inflatable Boats (RIBS). Akesdesign is located in Sardinia, Italy. The following Powercat 10 features great stability, low resistance, low power consumption, performances, seaworthiness, with reduced weight and superior space according to the designer.

The Powercat 10 is 32.7 x 17 foot with a length overall of 37.7 foot including outboards. The weight is 10,300 lbs and the displacement is 16,800 lbs. The engine power can be from 2 x 115 to 2 x 400 HP inboards or outboards. Speeds range from 20 knots to 50 knots depending on engine configuration. The performance on the test boat was up to 35 knots @ 5200 rpm with a load of 12 people and 2 x 250 HP Evinrude E-tec outboards.

The hull shape is very asymmetric with wide hulls and a narrow tunnel. The hulls are focussed on planning with the tunnel providing a ram air cushion to soften the ride at high speeds.

The accommodation is mainly hull based with a double berth master cabin and toilet shower in the port hull and a single berth aft. The starboard hull has a single berth forward, a galley next and a dinette with 6 seats midships and a single berth aft. The main saloon has a helming seat forward then an integrated mainsaloon, cockpit aft to take any form of seating desired.

The design can be home built but is more intended to be a semi-custom design for professional builders. The design is intended to be aluminium but can be done in composites. Akesdesign can make the design changes required.

An interesting design, the jpegs give the idea.

 

I think you need to devout some time to these vessels built by SafeHaven Marine,..

https://www.safehavenmarine.com/home

 

Just one of their designs,...

 

The following is a smaller version of yesterday's Powercat. The Powercat 9 was again designed by Akesdesign which is located in Sardinia, Italy. The Powercat 9 is a base design that can be used built as a charter cat, fishing cat but is best suited as a performance power cruiser.

The Powercat 9 is 32.3 x 14.1 foot with a weight of 10,000 lbs and a displacement of 13,400 lbs. The maximum number of crew is 16. The draft is 1.6 foot. The hulls are single step, large-deadrise with deep tunnel for rough seas, and has been developed using latest CFD analysis for 40+ knots speed. The engine power is 2 x 200 to 2 x 350 HP outboards which provide speeds from 35 up to 50+ knots depending upon the engine options. The design category CE: B.

Aft there is a large cockpit, with flush deck, suitable for fishing or as relax area; inside the cabin a big kitchen, 8 persons seats with large table, 1 double cabin + 1 single cabin, toilet room; big sundeck is at the bow and a flybridge to helm from.

Powercat 9 is made of thick aluminum alloy and can be customizable to other layouts and build materials. The jpegs give the idea of the design.

 

The following is a South Korean design done in about 2016 of a large aluminium cruising cat. The design was a speculative effort therefore and little detail is available. The jpegs give the idea.

The Sarsat 6 (not actual name but blog entry) is 78 x 36.5 foot with a displacement of 156,800 lbs. The 100 foot fixed carbon mast carries about 3,500 square foot of sail upwind. The draft over the hull is 4 foot and over the rudder and fixed keels is 8.5 foot. The proposed engines are from 2 x 250 HP to 2 x 300 HP inboard diesels.

Each hull has 2 double berth cabins with ensuite toilets and a single berth cabin. The main saloon is large with seating, galley etc. The main sail controls and helming is on the flybrige above the main saloon.

The construction is mainly aluminium for the hulls, underwing and decks. As you can see from the Xray frame structure there are a lot of frames and stringers with some full width bulkheads to hold the structure together. The main saloon cabin structure is foam glass composite.

An example of the number of components and work just to get a shell together which is about 35% of a total build time of a cat like this. The jpegs give the idea.

 

The Cat Flotteur 42 is a robust and seaworthy catamaran designed by Michel Joubert and constructed in 1996 at the renowned French shipyard Prometa. This vessel boasts a Strongall construction featuring thick aluminum plates, offering durability and safety for ocean crossings.

The Cat Flotteur is 42 x 21 foot weighting 21,000 lbs and displacing 26,000 lbs with 1100 square foot of sail. The 3 reef mainsail full batten is 570 square foot, the self tacking jib is 280 square foot and the genoa is 516 square foot. There is a sorm jib and spinnaker also available. The draft is 4 foot over the hulls and fixed mini keels. The engines are 2 x Yanmar 4JH4 54 HP with SD 50 sail drive transmissions and 18″ J-Prop feathering propellers. There are 2 diesel tanks of 250 liters. There is a total of 1000 W solar panels, a 400 W wind generator that feeds 800 Ah AGM batteries. There is a 1500 W pure sine inverter with a 300 W inverter at chart table.

The accommodation is the almost standard 2 cabin with a double or 2 single berths and a toilet shower in each hull. The bridgedeck cabin has seating, table and a good galley. There is a large practical cockpit.

The real virtue of this cat and the reason it sold in 2026 for $200,000 US for a 1996 build cat, is its construction. This is a “Strongall” aluminum construction. Thick aluminum. The dory hull bottoms are 12 mm thick, the hull sides are 10 mm. Deck and superstructure are 8mm. Base plates of mini keels are 20mm. There is minimal framing in the hulls with the monocoque hull shell carrying most of the loads. The underwing is also thick with some stringers. The decks and cabin structure have some framing and stringers for additional support. If electrolysis is kept at bay this cat will outlive you. Also this is as close as you can get to a “bullet proof” boat build method, even better than steel, but a rocky shore, coral or a bad fitting can sink anything.

These cats are good cruisers with averages of EG 8 to 9 knots but peaks are only in the 15 to 16 knot region. This is due to the weight, limited sail area and to a limited extent, the chine hull shape with a lot of rocker.

These are very good cruising cats that will look after you on a global trip. The jpegs give the idea.

 

“By October 2015 the time spent on the project had risen to about 8,500 man-hours. By the launch (Sept 2016) the final figure was 10,450 man-hours. I estimate this is accurate to plus or minus 50. The elapsed time was 5 years 2 months.”

This is a statement of a home builder of a Richard Woods Eclipse performance cruising catamaran. This item is more about the home builders web site as he describes the build process well. For those who aspire to build a “large” cat (a 32 foot bridge deck cat is not that large) this is a realistic indicator of what it takes.

The Eclipse is 32 x 19.5 foot with a weight of 6,100 lbs and a displacement of 8,200 lbs. The sail area of the mainsail and fore triangle is 615 square foot. The draft is 3 foot over the fixed keels or 5.5 foot over the daggerboard version. The engines can be 2 x inboard diesels or an outboard.

The build is a combination of strip plank cedar lower hulls, plywood hull sides, plywood frames bulkheads and decks.

The web site of the Swing Cat - a Catamaran Odyssey is: Swing Cat https://www.swingcat.co.uk/index.htm

The What , Why and How tabs provide some very good insites into the build.

Woods Web site about the Eclipse is: Sailing Catamarans - Eclipse - 9.9m performance cruiser https://sailingcatamarans.com/index.php/designs-2/5-catamarans-over-40ft/184-eclipse

There are a few Eclipse jpegs and build jpegs from the site attached.

 

About 20 years ago I had the honour and privilege of going for a sail along the coast here on Richard's original Eclipse, after he had arrived here from the Canaries on a textbook fast crossing that was without any drama.
And I thought that she was wonderful. A nice accommodation layout, and very deceptively fast, even in full cruising mode.

 

"...the time spent on the project had risen to about 8,500 man-hours. By the launch (Sept 2016) the final figure was 10,450 man-hours. I estimate this is accurate to plus or minus 50. " - this should be a warning for all "I'll build myself a 50'er..."
and hats off: "The elapsed time was 5 years 2 months." - this is dedication!

 

The builder of the Swingcat, the Woods Eclipse 32 foot catamaran featured yesterday also did some additional PDF’s about various areas of the catamaran construction. Again the builder did the appropriate research to facilitate a solution and documented it for others to benefit. These PDF’s are mentioned in the website but are not obvious. The electrics, plumbing and gas information is very useful. Construction and Bulkhead details provide some good guides. These documents were created by the builder and may differ in some details to what Richard Woods designed.

Attached are the PDF’s.

 

This is the final on the Woods Eclipse 9.9 metre performance cruising catamaran. The design of this cat was done for Richard Woods personal boat. He sailed 15,000 miles in the cat including trans ocean voyages. There are several construction options based on the same design including a round bilge and a hard chine option. The sail plan and internal layouts are the same in each build.

The Eclipse is 32 x 19.5 foot with a weight of 6,100 lbs and a displacement of 8,200 lbs. The sail area of the mainsail and fore triangle is 615 square foot. The hull length to beam on the hulls is 10 to 1. The draft is 3 foot over the fixed keels or 5.5 foot over the daggerboard version. Underwing clearance is 1.75 foot at its lowest point. The engines can be 2 x EG 18 HP inboard diesels or 1 or 2 EG 9.9 HP outboards. Under power the outboard version will cruise at 5.5 knots and motor flat out at 6. In comparison the twin diesel version reaches 7+ knots flat out.

The accommodation layout is a double berth cabin aft in each hull, forward in 1 hull is a toilet shower and in the other hull is a full in hull galley. Forward in the bow is a single berth. The main saloon is basically a dinette. The cockpit is useful and contains helming positions and sail controls. There is claimed to be full headroom throughout. Full headroom in this case is 5.8 foot (1.75 metres) in some areas.

Now the build options for this design. First the Eclipse can be built with a strip plank cedar round bilge lower hull and plywood timber stringer hull tops sides, decks, bulkheads and cabin tops. Next is a foam glass hull bottoms and plywood timber for the rest. Next is a full foam glass shell with plywood bulkheads and beams. The next option is a hard chine Eclipse known as a “Tamar 31” which is an all plywood and timber stringer, frame design.

The performance of this cat is good. Eclipse sailed across the Atlantic to the West Indies in 18 days. Normally Eclipse is reefed in 25 knots apparent wind. Under double reefed mainsail and a much reduced genoa, Eclipse has day-sailed to windward in 50 knots. Offshore, Eclipse coped well in over 40 knots when crossing Biscay. A top speed of 21 knots has been recorded, and the Eclipse is capable of 8.5 knots to windward tacking through less than 90 degrees. For a 32 foot cruising catamaran, this is excellent performance.

Eclipse Materials List Materials List for Strip Plank cedar version. Building in foam sandwich is feasible, please ask for more details when ordering plans.

Hull Planking Below Knuckle - 35 sq m western red cedar either rectangular 25mm x 12mm
or profiled 32mm x 12mm eg "Speed Strip". Note both sizes are finished sizes, ie after planning.

Topsides - 32 sq m western red cedar 12mm thick (planks can be up to 70mm wide) OR if plywood topsides used,
18 sheets 9mm ply plus 80m 2" x 1" timber gunwales 40m 3" x 1"

Glass - (cedar topsides) 600g biaxial 120 Kgs (or use 430g UDWR on inner skin - 35 Kgs plus 95 Kgs 600g biaxial)
-or-
Glass - (ply topsides) 600g biaxial 70Kgs plus 300g cloth 10Kgs, Epoxy glue 200Kgs
Note you can use polyurethene glue for making the strip glue joints

Bulkheads and Beams - 6mm ply 9 sheets, 9mm ply 9 sheets, 3" x 2" 50m, 3" x 1" 20m, 2" x 1" 40m, 4" x 2" 8m

Interior - 6mm ply 7 sheets, 9mm ply 9 sheets, 1" x 1" 40m, 2" x 1" 100m

Bridgedeck - 9mm ply 11 sheets, 12mm ply 6 sheets, 2" x 1" 25m, 3" x 2" 30m,

Decking - 6mm ply 2 sheets, 8 or 9mm ply 20 sheets, 12mm ply 3 sheets, 2" x 1" 70m, 2" x 2" 40m, 3" x 2" 15m

Coach Roof - (Layup as hull bottoms) 15sq m western red cedar, 20Kgs 600g biaxial glass, 30Kgs epoxy

Sheathing decks - 300g glass cloth 50 sq m

Note: All plywood to be best quality marine grade gaboon, sheet size 8' x 4' (approx 2440 x 1220). All timber to be sitka spruce, douglas fir or similar.
Dimensions given are "Planed all Round" PAR (eg 2" x 1" has an actual finished size of approx 45 x 20mm)

The attached jpegs give the idea. The Eclipse is shown first and the Tamar 31 hard chine hull option in the last jpegs.

 

This 31' trimaran design was done by Kurt Hughes and was commissioned by a group who wanted to see if a better design could be created to compete with the heavily marketed folding trimarans (read Farrier Corsair etc). It had to be able to fold as easily as the heavily marketed ones, look much better, have a more level ride. Most importantly it had to be able to improve safety by being wider and having larger amas. The design was wider and had fuller floats etc and met all the criterion, but the economics of a saturated market just were not there. It would have been roomier inside due to the ergonomic "double shuffle" top sides than say a Farrier 31.

The Hughes 31 is 30.9 x 24 foot with a weight of 2550 lbs and a displacement of 3950 lbs. The folded beam is 8.33 foot. The aluminium or carbon mast carries a 380 square foot mainsail, a 122 square foot jib and a 670 square foot screecher. The length to beam of the main hull is 10.6 to 1. The draft is from 1.33 foot to 7.9 foot with to daggerboard down. The engine can be from a 10 HP outboard.

The accommodation is not specified but if it is similar to Hughes other designs it will have a double berth forward, a toilet then the main saloon which is likely to have a galley down one side and a dinette opposite. The cockpit is next followed by an aft double berth cabin.

The build is foam glass in epoxy with carbon fibre at strength points and in the cross arms. The folding system can either be aluminium or carbon fibre if you can afford the cost.

The performance is unknown but Kurt rarely designs a slow trimaran. His basic mantra is to have efficient, high performance cruiser racers and very fast racing trimarans.

Nice design, hope one gets built. The jpegs give the idea.