Multihull Structure Thoughts

The following is about an aluminium catamaran being built in Thailand by the Aluminium Catamaran Builders Company. The company is relatively new but has built several larger catamarans previously and the following catamaran they built on spec during Covid. It is nearing completion now. The catamaran is 39.4 x about 23 foot. The weight is 12,800 lbs. The 48 foot single spreader aluminium mast carries a 540 square foot mainsail and a 270 square foot self tacking jib. There can be additional sail power as required. The rigging wires are 10 mm. Translation this is a conservative rig on what is intended to be a serious cruising catamaran. The cat has low aspect ratio keels. The cat will have wells for 20HP Tohatsu long shaft 4 stroke outboards to keep weight down and allow a retractable system to get the propellers out of the water giving less drag.

The cat is a prototype 12 metre ocean cruising cat and is progressing well. The brief was for an ocean capable pocket cruiser with adequate performance and slim hulls. Strong but light with straight forward gear onboard and every effort to minimize the need for expensive additional marine equipment. The rig is a safe height, mini keels are fitted for putting her on the beach for antifouling and checking the bottom. The accommodation is pretty standard, bunks and toilets in the hulls with the galley, dinette and navigation in the main saloon and large doors leading to the cockpit.

As you can see from the jpegs the chine hull with axe bow is an easy shape to build and the cat is a nearly an all aluminium build as much as possible. That even goes down to building things like hatches and doors in aluminium. The hatches and windows have 8 mm acrylic sheet and 4 mm aluminium surrounds that are welded to the shell structure to minimise the need for “bolting” things down. Alloy furniture in the saloon, galley (up) cockpit and in the hulls assist in binding the structure together. The entire shell will be X-ray and Dye tested before being finalised and, if required, painted. The great virtue in building in aluminium is the majority of the rig, chain plates etc can be built in house as well and with EG chainplates welded to strong points in the structure. In alloy boat building it’s the skill of the fabricator and welder that determines the outcome. If you are skilled at both and understand how to deal with electrolysis after launch you will be a very happy boat owner.

No performance figures but my estimate is an 9 knot average with 16 knot peak sort of boat. This is a conservative solid cruiser. The jpegs give the idea.

 

This is what happens to old racing cats. This Formula 40 cat that was designed in 1983 by Paul LUCAS and built by the Anitra shipyard was launched in 1984 and raced from 1984 until about 2002 before being purchased in 2003. A small update was done then racing recommenced up until about 2014. It was upgraded in 2015/16 again. That configuration resulted in a 42.1 x 25.6 foot cat that weighed 8300 lbs and carried a 69 foot carbon wing mast and 1400 square foot of sail area in the mainsail and headsail. There are 2 deep daggerboards that draw 7 foot when fully down and underslung spade rudders. Engine power is a 25 HP outboard on the rear beam.

The boat started as a Formula 40 racer but during its time had cabin tops fitted to the hulls which allowed 4 bunks, a chart table, a galley and toilet in the hulls which was all refitted in 2021. The cat now is a very high performance charter cruiser.

The performance is “claimed” to be the “faster than all the catamaran F40’s currently sailing”. I will accept that it is a very fast cat. The build was Airex/glass/epoxy sandwich.

A sistership Boomerang built in 1984 - 1985, competed in several major races then landed in Senegal where it was abandoned. Boomerang was found and a web site started to get funds to rebuild the cat which was successful. The cat is now operational. The last set of jpegs show parts of the rebuild.

2 interesting cats that are fast and now have some accommodation for the occasional short overnight cruise. The jpegs give the idea.

 

This is about the motive power more than about the catamaran. John McGettigan is a New Zealander who likes boating, he previously owned Earthling, a large Greg Young designed sailing cat that was very fast. After selling Earthling he said he wanted “really sailing without sails”. So, he conceived a vessel that didn’t require a crew, was economical and he and his family could cruise on with minimum fuss. The boat chosen was an Alan Carwardine Stealth 36 powercat that was built in Phuket and finished in NZ.

The Stealth 36 is extended to 40 x 18 foot with a weight of 8000 lbs and a draft of 2,5 foot. The hulls are slim. The cat is built from foam glass in epoxy. The hull shape was lengthened to accommodate the weight of the motive power.

Now to the motive power. John is a successful engineer and applied his talents to meeting his requirements of a long range environmentally friendly solution for cruising. His initial idea was to have solar panels and batteries being the primary power. After calculations he concluded that it was not going to work. The weight of batteries, panels etc required a bigger boat that then required more batteries etc. It was a spiral that either required new light weight batteries, more efficient PV panels etc. So, he investigated alternative paths. He still wanted high efficiency and minimum environmental impact. First items were a boat to meet his cruising need, a few berths, a large main saloon for socialising and minimum upkeep requirements. He did not want to “cruise” at speed, he was happy with 8 to 10 knots and he wanted range.

Result. John went hybrid, choosing two German Molabo electric motors that power Earthling soundlessly, fed by a huge coachroof-mounted solar array supporting a 45kWh Lithium batteries system, supplemented by two 8.5kW Whisperpower DC Charge Genverters. All system components are dual redundant are leading edge European technology. The generators, which use only 2.5 litres of diesel per hour, propel Earthling at ten knots.

Says John, “The boat is optimised at this weight – it’s so easy to push.” So Earthling, with a full battery charge, has a range of up to 40 nautical miles on storage alone at slower speeds; around 20nm at 8 knots and 18nm at 10 knots, the sweet spot. As with any power boat, high speeds take a lot of energy, so the design concept of ‘Sailing without Sails’ allows easy passage-making at comfortable speeds. But at anchor under sunny skies it would take around three days to fully recharge the batteries from the 2 KW solar panels. Result the need for the on board generators.

The two Molabo electric motors, from a German start-up company, can provide up to 50kW of energy continuously, though John has limited the drives to 30kW. At Earthling’s cruising speed of 10 knots, the motors draw 15kW – 7.5kW each. If running on one engine, simply run at 15KW – part of a complete dual redundancy platform. With fully depleted storage the Genverters provide the 15kW (2 x 8.4kW) to continue the passage at 10 knots. Peak speed can be 18 knots but only for short periods.

The accommodation is 2 double berths and 1 single in the hulls with a toilet. The main saloon has the inside steering position, galley, seating and access to the fore and aft cockpits. All domestic electricity on board is 230 volt standard supply provided by inverters from the batteries. The power required to boil water or heat food etc is small in relation to the power generation capacity of the total system.

The Earthling Stealth 40 has already done many longer range cruises and has meet its targets. But it has also been helped by John’s management software for the total power package which allows him to balance power inputs with power outputs to obtain the best performance for a given set of conditions. Very innovative.

The jpegs give the idea.

 

The HopYacht 30 is a Dutoit Yacht Design built by HopYachts.co.za. It’s a “slimline” cruising catamaran designed to fit into a monohull berth. The HopYacht 30 is 30.7 x 11.3 foot with a weight of 5,730 lbs. Displacement is unknown. The 33 foot aluminium mast is a mast aft rig that carries a 320 square foot roller furling jib. The draft is 2.3 foot over the fixed keels. The genoa sheets are led to one winch at the helm station, making sailing single-handed possible. HopYacht conducted research that showed that a high percentage of holiday sailors choose to sail under headsail alone. There is less to worry about, and less experienced sailors find this easier in stronger winds. The design brief was to keep the HopYacht 30 sail plan simple and easy to manage. With a single furling genoa, the mast is moved further aft to ensure good all-round performance.

The cat is powered by 2 E-Propulsion Evo 6.0 - 6kW (9.9hp) Pod drives and two 14kWh Lithium Ferro Phosphate Batteries with built in battery management. The result is at full throttle 2.3 hours for each motor. At cruising speed range increases significantly to over 8 hours. This excludes power from the 4 x 400W solar panels inset into cabin roof. This requires 4 x Victron Smart Solar MPPT 100/20-48V solar controllers and Victron Cerbo / GX Touch monitor onboard and remote. Also Victron MultiPlus-II 48/5000/70-100 230V inverter/charger with 2 x Victron 48V Lynx distributors.

The accommodation is comfortable for 2 and viable for 3 or 4. The forward queen berth cabin has an island bed. Aft is a proper bathroom with an inside 2 seat dinette arrangement. Aft in the cockpit with hard roof is the galley, a 6 seat dinette and a steering position. The mast aft rig needs the solid roof to support it. The roof also holds the solar panels.

The construction is laminated with VAIL - Vacuum Assisted Infusion Lamination technology, which improves strength, mechanical and chemical properties of the composite parts. The Lloyds approved, Isophthalic NPG Gelcoat and Isophthalic infusion resin used to optimise chemical resistance against osmosis. Sandwich construction structural laminates make use of multi-directional fibreglass reinforcements as well as a structural closed cell foam cores as engineered by the design/build team.

No performance numbers but this boat is not intended to be a racer, it is a pure cruiser that can fit into a monohull berth for cheaper mooring etc. The thin hulls and relatively light weight help but going upwind or reaching in strong winds will need an alert crew as this cat has a high centre of gravity and a lot of windage for a 30 foot cat. Finally, the hulls can be separated from the bridgedeck pod to allow transport to a new location in 2 containers. Instead of ocean crossing put the cat into containers.

The jpegs give the idea.

 

The last two designs are some of the better purpose built solar electric catamaran examples I’ve seen.

The Earthing in particular has a very functional layout and a serious propulsion system that has some extra cushion built in. Too often I see designs with systems that rely on optimal performance to meet the output specs, when in reality sun and battery capacity will dictate usability. And it sounds like the owner/designer has embraced this by closely monitoring power in/power out and adjusting “driving habits” to allow for good efficiency.

The HopYacht is also interesting as its propulsion and charging system have been optimized for slow speed cruising, as well as its sail plan. I can see the appeal of a rental boat like this and this kind of use is where solar electric propulsion makes a lot of sense, provided of course it is being operated in an ideal environment.

It would be interesting to know if the sail plan gives good enough performance to take advantage of EPropulsions hydro generation.

I don’t know what the rental behavior is of the targeted users, but from my days or working at a lake renting houseboats and pontoon boats, I could see the specs of this boat working well for day, long weekend or weekly rental use without having to return to the dock for shore power charging provided users are sailing/motoring to an anchoring destination where they set up camp much like they do on lakes.

 

The following is about a 34.3 foot tri that was designed by Georges Auzepy-Brenneur naval architect for a French guy. The tri “Tricky” is 34.3 x 23.6 foot with a displacement of about 10,000 lbs. Rig size unknown. The length to beam of the main hull is 5.9 to 1. The float length is 27.5 foot with a length to beam is 12 to 1. The main hull draft is 2 foot with a total draft of 3.1 foot over low aspect keel and underslung spade rudder.

The accommodation is a double berth forward, a separate toilet area, then the main saloon. There are 2 single wing berths with a small galley area and navigation area aft before the cockpit. The saloon is quite roomy with a jpeg showing the saloon occupied by 5 adults and 5 children.

The build of the round bilge hulls is cold molded wood (double diagonal) with sheet plywood above the waterline on the main hull, decks and cabin area. All this is supported by frames, stringers and bulkheads. Please look at the PDF for details. The interior seating floor etc are 8 mm plywood with cabinets 6 mm plywood. The cross arms are an aluminum box section bolted to the floats.

There is limited additional information about this tri as it was a one off. The owner is a very happy man and enjoys his cruising. The PDF contains a side and top construction detail plan which gives a lot of insites into how these tris are built. Sorry about the limited jpegs.

 

Folks, I need help. I found the first jpegs which is of an interesting trimaran with swing wings. The tri is 37.7 x 21.6 foot tri that can be folded to 12.8 foot. Displacement unknown. The tri has a mast aft rig that has a 485 square foot genoa and a 300 square foot staysail. The draft is 2.5 foot over the 2 L foils on the floats. The design looks as though its plywood. I suspect the design was done by Gilles Montaubin, a French designer who may have retired by now.

I cannot find any further detail bar that jpeg. Some of the other design I think, repeat think, Gillies has done are in the other jpegs. He did do a lot of monohull plywood yachts as well. Can anyone verify or know if the 37 foot swing wing tri “Fiftri” design went beyond an initial study plan.

 

Francois Lucas does many interesting designs in both monohulls and multihulls. The following cruising cat is a sample of a larger charter catamaran or floating home designed to be ocean crossing capable. The TMB 58 is 57.4 x 28.2 foot with a weight of 49,300 lbs. The displacement is 60,400 lbs. The near full sloop rig has a 76 foot aluminium mast which carries a mainsail of 1160 square foot, a genoa of 760 square foot, a self tacking staysail of 345 square foot and a gennaker of 1720 square foot. The hull length to beam is about 10 to 1. The draft is 5.4 foot over the low aspect ratio keels and rudders. The motive power will be diesel with a solar array to support the electrical needs to provide power at anchor to reduce noise and fumes etc.

This is a solid cruiser with some performance capability and is primarily designed as a cruising home that is occasionally chartered out for a few weeks a year. The accommodation has an owner’s master suite with 3 other double berth guest cabins and crew quarters. The main saloon contains all the usual seating, entertainment, bar etc with a large doorway to the cockpit with additional seating. The flybridge is the major sail control and helming area and has a solid roof for sun and rain protection.

The construction is mainly aluminium for the majority of the shell. The multi chine hull shape should be a fast build. Some parts of the cabin structure are composite construction to reduce weight and provide inbuilt insulation properties. Details are not available as this design has not been finalized yet.

Performance unknown but my simple calculator says in the right conditions 200 to 300 miles days with peaks approaching 20 knots. I hope the winches are electric because this is a big rig and a powerful boat that in cruising mode will still require a few strong people to handle her.

Sorry about the limited jpegs.

 

A while ago we spoke of the CK 72 from Squalt Marine. Today we will talk about its smaller sister the CK 64 cruising catamaran designed by Francois Lucas in about 2016/7. The CK 64 is 64 x 30 foot with a weight of between 57,000 and 64,000 lbs depending on the options included. The 73 foot fixed aluminium mast carries a 1,290 square foot mainsail, a furling in 1,400 square foot genoa and a 3440 square foot spinnaker. The hull length to beam is about 10 to 1. The draft is 5 foot over a minimal fixed low aspect ratio keel. The engines are 2 x 140 HP inboards.

There is another rig option provided by Francois Lucas. The biplane rig with 2 free standing carbon fibre masts that have reefable wing sails. The rig will be tricky to handle with the masts being closer together than most biplane layouts. Interaction between the sails will require careful adjustments to get the best performance.

This is a pure cruising or charter cat with luxury accommodation. Each of the double berth cabins have their own entrance, seating area, desk and ensuite toilet. These are apartment size areas. The main saloon has a very large galley/bar area, multiple seating table areas, entertainment/navigation area and a large rear door to a lower cockpit that has outside under cover seating. The flybridge is covered and is where the main sail handling and helming is done from. Electric winches please or 2 very strong crew. The 2 crew cabins are in the bows.

The build is mainly Sealium (high performance aluminium alloy) with frames and stringers as required. The jpegs give an idea of the number of components required to build the structure. Also look at the building shed. Those overheads cranes etc are required because even the frame structure of 1 hull would weight several thousands lbs. It also helps to have talented welders and fabricators. The internal furniture is mainly honeycomb with veneer finishes to minimise weight.

A solid global cruiser for those who can afford such luxury. There have been several built and are selling used for over $1.5 million US. The jpegs give the idea.

 

This is about a Waller 880 cruising catamaran. We have written about this boat before but this is a construction update. The Waller 880 is 28.8 x 16.2 foot with a weight of 6,900 lbs and a payload of 2,200 lbs. It can be overloaded to a maximum payload of 4,400 lbs in good sailing conditions. The 40 foot fixed aluminum mast carries 387 square foot mainsail and a 161 square foot foretriangle. The hull length to beam is 9.2 to 1. The draft is 2.7 foot over low aspect ratio keels (daggerboards are optional but take up internal space and for a cruiser less needed). The underwing clearance is 1.95 foot. Outboard power of about 10 to 15 HP.

The Waller 880 is a full length bridge deck catamaran designed for family coastal cruising, with the “occasional foray further afield”. The accommodation is designed for a family of 4, but can sleep 6 if required. There is a full sized double berth in its own cabin forward with 2 separate single berths aft in the hulls. Forward in the port hull is a large 'bathroom' cabin, with WC, a vanity unit with sink and room for a shower. The center portion of the port hull has a chart table area. To starboard, the center hull area contains a large and functional galley. On the bridge deck is a large dinette, with a table which drops down to form another double berth if needed. The cockpit allows ample room for day sailing and entertaining.

The construction is a mainly strip plank shell with plywood bulkheads, furniture etc. The hulls and underwing are 400 gsm e-glass 12 mm paulownia (or western red cedar) strip planking 330 gsm e-glass in epoxy. The deck is can be 400 gsm 12 mm core 330 gsm or 16 mm duracore with glass either side. Cabin sides can be 9 mm plywood. The secondary bulkheads are 9 mm plywood with 31 x 31 mm timber edge framing as required. The main mast full width bulkhead is a 45 mm thick ply timber ply sandwich. The mast bulkhead has 6 mm plywood with a top and bottom flange of 65 x 31 mm, a mast compression post three 31 x 65 mm posts with 31 x 42 mm diagonals and 31 x 31 mm edges around doorways. All the timber is then covered by another sheet of 6 mm plywood. The aft beam is a 9 mm full width plywood panel with a top and bottom flange of 31 x 65 mm with diagonals and verticals of 31 x 42 mm. Another plywood panel boxes in the majority of the rear beam. All external plywood sheets are covered with 200 gsm e-glass in epoxy.

The 880 has proven to be capable and seaworthy in all weather conditions, and is easily steered in heavy weather. Her full bridge deck in heavy weather provides a good, solid platform from which to work the boat, and significant increases in buoyancy forward which prevent her from burying her bows. One owner commented “The WaIler 880 has on several occasions clocked up daylight daily runs in excess of 80 nautical miles in a 10 hour period, and has recorded a timed run of 18 nautical miles in 90 minutes. This is a family cruising boat, and high speeds are not the main design priority. These figures show, however, that the 880 is capable of excellent average daily cruising runs.” Translation, the 880 can average 8 knots plus (200 mile days) and probably peak at over 15 knots. Good for a solid cruiser.

The jpegs give some of the build details.

 

The usual story arrives again, a client of Neo yachts said he wanted a fast catamaran. Neo yacht then had Lorenzo Bergamini, naval architect and by Architect Marco Colangiuli of Neo Yachts do interiors and aesthetics of the new cat. The requirement was for a light fast performance catamaran with cruising accommodation. And it was to be built in carbon fibre foam. The difference is the design started based on in-depth hydrodynamic concepts, but above all on the comparison of the VPPs of other cats with the VPPs (speed prediction programs supported by real data). This allowed optimisation as the design developed.

The Neo 410 is 41 x 25 foot with a weight of 9,600 lbs of the build shell and a weight of 11,870 lbs with all equipment and rig aboard excluding crew water and food. The 59 foot fixed or rotating carbon fibre mast carries a 775 square foot mainsail, 366 square foot self tacking jib, and a 970 square foot Code 0. The bow spirit is 6.5 foot and is retractable. The Length to beam on the hulls is 10 to 1. The draft over the hull is 1.6 foot, the rudders is 4 foot and the daggerboard is 8.9 foot. The underwing clearance is 2.7 foot.

The build is not complete so no performance numbers yet but my calculators say this cat will be fast. 300 miles days, 12 knot averages with peaks of over 20 knots should be possible. This boat when powered up will require several strong alert crew to sail it well. When cruising with the self tacking jib should be easier but you will still need to reef that large fully battened mainsail. Big rigs on light boats equal speed but also a fair bit of work if you don’t have electric winches etc.

The accommodation is the same main cabin with galley, seating and direct access to the aft cockpit which contains sail handling and helming facilities. The difference is in the hulls. Version 1 is the owner cabin in I hull with a double berth and single berth cabin in the other hull. Version 2 is 2 double berth cabins and a single toilet in each hull. The double berths are full width of the hulls. This is a comfortable minimal practical fitout cruiser. Less stuff, less weight equal more speed.

The construction is epoxy, foam, carbon fibre. The cat is fully moulded using prepreg multiaxial and unidirectional carbon fibre which is then cooked in an oven at 70 degrees centigrade. Neo yachts have produced a lot of large light weight racing monohulls and know how to build light. EG All the interior is foam glass and are structural components, not just add ons.

One quote I liked was “The small chord rudders allows the use of simple tillers for excellent speed of response to the control, much appreciated in race pre-starts or when flying on one hull.” Even the builder wants people to have fun. The jpegs give the idea.

 

Okay, I almost like that cat, but I find it amazing how much power it takes to drive a cruising/racing cat. It's not at all surprising that they are prone to capsize, but there's very little talk about that. It seems like a serious side-effect of trying to have it all; the condo-like accommodations on a boat that sails really fast. Am I wrong?

 

Russell do these Condo cats have large(r) boards to combat the windage adding to the wetted surface side of the equation?

 

Later today I will load an updated index, so no item today. Russell, I like the Neo 410 as well. I used to sail on a 42 cat off very similar dimensions with a measured weight of 13600 lbs excluding crew. It was fast, 300 mile days were done on several occasions, 22 knot averages over 60 miles and could sail very well in light winds. BUT the power of the cat and loads on the rig when it had a 60 foot wing mast were amazing, upwind with a large genoa meant 2 people winding hard on a very big winch. The 2000 square foot spinnaker was a nightmare for the 7 crew going down wind in a rising wind etc. I fully agree large sail areas on 40 foot cats is a problem and as Redreuben mentioned the deep daggerboards are a problem. On that cat we broke 5 because we hit things at speed.

The reality is if you have a smart designer and you were willing to limit the accommodation a bit, you could build a lighter cat with 14 to 1 hulls and a smaller high efficiency rig. What I am talking about is a 40 x 26 foot cat with thin hulls and an all up displacement of under 10,000 lbs. The mast would be a wing of 50 foot or less with a self tacking jib, fat head main etc and a few larger light headsails. We are heading toward what Bob Oram used to design with a little more beam. Unfortunately, it still would be more boat than I would like as my greatest fun has been on boats about 30 to 33 foot. A lot less effort to sail and still give double berths etc. EG a Raku 32 type.

I will post the indexes later today.

 

Test load of updated index for all items up to page 212 of MST. If load is OK could the moderator please place them on page one to overwrite the existing index.