Multihull Structure Thoughts

A bargain! What's the bridgedeck clearance on that?

Also, why does the underside of the bridge deck have longitudinal stiffeners? I guess this removes the need for a transversal bulkhead in the middle.

 

The following tri was built in Russia. It is 23.2 x 15.25 foot and weighs 1210 lbs. The custom built main hull weighed 870 lbs. The tri has Toronado floats and rig. The rigs mast length is 9.08 m (29 ft 9 in). The mainsail area, 16.61 m2 (178.8 sq ft). Jib/genoa area, 5.33 m2 (57.4 sq ft). Spinnaker area, 25.00 m2 (269.1 sq ft). The mainhull length to beam is 9 to 1. The centre boards are standard Toronado hull based in the floats. The rudder is a kickup outboard.

The main hull is built from mainly 6 mm plywood with 70 x 25 mm frames. The mast beam framing on the cockpit cabin bulkhead is made from oak reinforced with a titanium corner joiners. All fasteners are made of stainless steel.

The main hull was built and painted in 4 months and the tri was launched 1 month later. 5 months total build time. This guy is good.

The jpegs give the idea of the build and sailing capability. The plan jpeg is all the drawings he did but its is informative. A nice day sailor with some cabin space.

 

The C-Cat 48 was designed by the Yacht Design Collective (François Perus and Romain Scolari) and is a high performance bridge deck cruising catamaran. The cat is 48.6 x 24.5 foot and weighs 21,400 lbs. The double diamond 60 foot high carbon mast carries 970 square foot mainsail, a 570 square foot genoa and a 969 square foot gennaker. There is also a self-tacking jib available. The length to beam of the hulls is about 13 to 1. The dagger boards draw 7.25 foot when down.

The accommodation can be either 2, 3 or 4 cabin versions in the hulls and a galley and dinette in the bridge deck cabin. The entire cockpit and saloon is designed along the “Open” lines. You are protected by a large bimini with the aft cockpit and the saloon on the same level, separated by a large sliding door which connects the 2 spaces into one large open living area. The twin aft helms at the stern and all the running rigging led back so that you can manage the boat without having to leave the cockpit. She´s been designed for shorthanded crews. The C-Cat 48 has an option for an additional interior helm station with an interior wheel which provides protection in bad weather.

There are many construction options, however, they start from a very high standard with a sandwich structure laminated infused with multiaxial fabrics and an epoxy-vinyl matrix. The bulkheads are made of composite with local carbon reinforcements. There is a mainly carbon only option.

This cat has numbers that should provide very high performance. EG 250 mile days should be possible with peaks over 20 knots. The jpegs give the idea.

 

Stienlager 1 was a trimaran that was raced initially in the 1988 two handed, 7500 mile, Around Australia Race. The tri was 60 x 54.1 foot that weighed 11,200 lbs at launch. The 85 foot carbon fiber and divinycell wing mast has a maximum chord of 4.9 foot, designed to withstand an axial compressive load of up to 70 tons. The mast area is about 375 square foot. Stienlager could do 10 to 12 knots under wing mast alone in strong winds. The total sail area including wing mast is 2,400 square foot upwind. There are three Genoa’s and one storm jib, three asymmetrical spinnakers (spankers), the tack attached to a retractable bowsprit. Standing rigging attached to the mast with titanium fittings; the body of the blocks and other efficient things are also made of the same material. The carbon fibre boom has an unusually wide top surface that acts as an aerodynamic platform for the mainsail, limiting air flow through the luff and thus reducing the yacht's inductive drag. The tri draws 10.5 foot with the carbon fibre forward facing dagger board down. The rudder draws 5.5 foot. Each float volume is 200% of the trimaran's displacement, and the float length is equal to the main hull.

With the above numbers, the performance is very good for its time. Stienlager recorded its highest speed - 32 knots, in the race across the Tasman Sea, with a best 24 hour daily run it covered 430 nautical miles. And on a 35-mile section of this passage, the speed did not fall below 28 knots. It won the Around Australia Race by three and half days.

The design was done by Alan Williams and he designed an advanced tri. The tri hulls are made using SP epoxy resins, high-strength aramid (Kevlar) and carbon fibers reinforcing the skins with a lightweight divinycell core.

The final choice of material and technology was helped by the computer: data on the weight of various laminates, the ratio of the weight of resin and reinforcing fiber in them, strength and cost of structures were entered into the computer. Two technological processes were compared: the first was manual molding with the laying of individual layers of Kevlar or carbon fiber fabric into a matrix, followed by impregnation of their layers, and the second was the laying of a pre-assembled and impregnated with a binder package, its compression in the shape of the matrix using the vacuum method and prepreg fabrics in a closed autoclave at a temperature of 75 ° C. The computer showed the advantages of the second method, which achieves a reduction in the weight of the structure by 6-7%, increases the mechanical strength, improves the quality control of the laminate, and reduces the labour of the build.

This tri sailed thousands or racing miles before more advanced foil assisted OMRA 60 foot tris made Stienlager obsolete. The jpegs give the idea.

 

I visited the yard in Auckland when Steinlager was being built. It must have been a holiday because Peter Blake was the only person there and had his arms full of frozen carbon fiber walking out of the freezer. He was very kind and informative and gave us the whole tour.

 

My shot when working for Kiwi sailing magazines. Mast never rotated properly; stays went to side of hounds area, therefore reduced power, basic no no.

 

Gary wrote of "Peter Blake was the only person there and had his arms full of frozen carbon fiber". The following jpeg may explain, thanks for the contribution.

 

The following Russian designed tri is interesting in its ply round bilge build. The tri is 23.4 x 14.5 foot with a 1680 lbs displacement. The Tornado mast carries a 215 square foot mainsail and a 75 square foot roller furling self tacking jib. The mast was upgraded later. The main hull at gunnel level is 6 foot wide. The floats are Tornado hulls. The kickup centre board draws 4 foot.

The plan jpeg gives an idea of the accommodation. The real interest in this design is how the round bilge main hull was made from flat 6 mm sheets of plywood. The materials to build the tri is 14 sheets of 6 mm ply for the mainhull skin, decks, cabins and secondary bulkheads. The main bulkheads are 12 mm plywood.

The round bilge hull is made from tortured plywood and if the curves are too tight, darts were cut in the plywood, the edges are then brought together and glassed on the outside with a “stringer” on the interior. The forced curve then can be slightly tortured more to form the round bilge hull. The jpegs give the idea.

The cross beam structure looks light but was calculated and tested by the amateur designer and worked in bay sailing. I would suggest if you are going to sail in heavier winds and waves they be reviewed by a professional. The beams are 60 x 60 x 2 mm stainless steel. The bed 70 x 30 x 2 mm and the support struts are 20 x 30 x 2 mm. The connecting bolts are 10 mm stainless steel. After initial testing there were doublers around bolt holes.

The tri sails well. It is interesting in its build and concept. Jpegs over 2 items.

 

Part 2 of the round bilge Russian 23.4 tri build jpegs.

 

The following is an aluminium cruising tri that was tank tested and built in 1971 and finally launched in 1976. The tri is 39.5 x 24.6 foot displacing 11,650 lbs. The tri has a ketch rig. The 46 foot main mast is circular made from 6 mm aluminium, the mizzen mast is 36 foot high and made from 4 mm aluminium. The sail area totals 900 square foot upwind. The length to beam on the multi chine main hull is 8 to 1. The length to beam on the single chine V bottom float is 15 to 1. The floats buoyancy is 90% of the full displacement. The float based centreboards draw 5 foot when down.

The accommodation is reasonable with fore and aft double berth cabins, 2 wing berths and a galley and dinette in the mainhull. Six foot headroom through the majority of the accommodation.

The hull shapes were tank tested at the Institute of Hydromechanics of the Academy of Sciences Ukrainian over a speed range of 10 to 20 knots and in simulated waves. Result the hull shapes were optimized in both shape and buoyancy distribution resulting in the float centre of buoyancy being 5% in front of the mainhull centre of buoyancy.

The skin structure of the hulls are 3 mm light alloy AMg-5V aluminium was adopted as the main material. Secondary structures (deckhouse, wings) are 2 mm aluminium. The 30 X 40 mm angle sections are used as the side and deck longitudinal stringers throughout. Welded T section frames are located every 3.25 foot. There are three watertight transverse bulkheads. The chines provide additional longitudinal strength. The bow and the bottoms are additionally reinforced with 14 mm aluminium rods. The two main box-shaped beams are 5-6 mm aluminium. The deckhouse decks and the wings have surface corrugations.

At a heading of 140 degrees with 900 square foot of sail in an apparent wind of 16 to 24 knots, the boat speed was 11 to 12 knots. In a steady wind and calm water, the Baida can be close hauled at an angle of 35 degrees to the apparent wind; in waves, this angle increases to 50 degrees. In 35 knot winds and 8 foot waves the cockpit remains dry and the bow deck stays above the water. The pitching of the tri is less than the catamaran he previously owned.

The jpegs are limited but give the idea. For its time, this is a good tri and its aluminium structure is well done. If done correctly aluminium only has a small weight penalty compared other materials. But again you need good welders and electrolysis protection.

 

This is reminiscent of this boat that I came across the other day in an IG post.

It’s always nice to see a boat/design in action, and the video does a nice job of highlighting its features.


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Looks like a fun and functional boat.

 

The following is a day sailing, camp cruiser catamaran called “Timur”. The cat is 19.7 x 11.1 foot with a 1350 lbs weight and a 2700 lbs displacement. The length of the wooden mast is 30.5 foot with a mainsail area is 129 square foot, a staysail of 86 square foot and a genoa of 172 square foot. The hull length to beam is 7.5 to 1. The draft with the board down is 3.25 foot. The underwing clearance is 1.7 foot. The outboard motor is a "Mercury 3.3".

The accommodation is simple with 4 berths, 2.6 foot wide at the head and 1.5 foot at the base, all 6.5 foot long. The cabin has 4 foot headroom with 3 foot over the bunks. The cockpit can sit 6 comfortably.

The construction is waterproof plywood and timber (spruce or pine) including the main, fore and aft cross beams, mast, boom, “solid decking” instead of nets and fore and aft support beam. The hulls are 6.5 mm plywood with 45 x 22 mm frames at 3.2 foot centres, 45 x 22 mm chines, 90 x 22 mm keel line and stem. The bunk support frames are 45 x 22 mm with 6 mm ply bunk tops acting as a hull stiffener as well. The transoms are 10 mm plywood. The deck framing is 35 x 22 mm with 35 x 22 mm cab top/sides fore aft support. All frames have 6.5 mm plywood corner backing. The hull decking/cabin roof are 6.5 mm ply. All external surfaces are covered with 200 gsm cloth and epoxy resin.

The cross beam structures are framed with 45 x 22 mm timber. The main box beam has 10 mm ply on the sides and bottom with 6.5 mm ply on the top face. The cockpit floor and fore and aft bridge deck decking is 10 mm ply. All fore and aft beam frames have plywood supports on either side and timber intersections. This also applies to the fore aft support under the plywood fore deck. The mast is timber framed with plywood sides as is the boom.

The central crossbeams and cockpit arrangements are bolted to the hulls and can be disassembled for transport or trailing to new locations. The engine mount details are good as you will see in 1 jpeg. The centreboard mountings are on the tunnel side of both hulls and are simple and effective as the jpegs show. The centreboards and rudders are timber.

The build takes Waterproof plywood 1250x2500 mm: 6 mm - 19 sheets, 10 mm - 8 sheets. Glass cloth: 200 gsm, 100 meters long. Epoxy resin: 20 kilograms. Waterproof wood glue: 5 kilograms. Timber for frames (for 2 hulls) etc pine, spruce: 45x22 mm – 130 foot, 35x22 mm - 40 foot, 90x22 mm - 40 foot. Stainless steel metal brackets and bolts as required.

The owner describes the cat as “In general, the catamaran turned out to be very successful: comfortable and spacious in habitation, durable and seaworthy, develops high speed, easy to control under the engine and sails.”

An interesting design that has achieved the owners needs. The jpegs tell the story.

 

Part 2 Timur cat 19.5 x 11.1 foot. build jpegs.

 

The SC 48 is an aluminium bridgedeck cruising catamaran. The cat is 47.5 x 25.5 foot that weighs 40,300 lbs that displaces 47,000 lbs. The 62 foot aluminium mast carries a 935 square foot mainsail, 470 square foot self-tacking jib and a 970 square foot gennaker. The hull length to beam of 8.8 to 1. The low aspect ratio keels draw 4.7 foot.

The Garcia SC 48 (formerly Alumarine Sailing Cat 48) is a sailing catamaran that has been designed for customer use or as a charter catamaran. The naval architect is Pierre Delion who paid particular attention to the position of the equipment. EG the water and diesel tanks are cantered and placed under the floors of the hulls. The bridgedeck is relatively short with fore and aft cockpits. The navigator seated at the chart table has a clear view forward (two deck hatches, slightly aft, also allow the mainsail to be seen) and all the necessary repeaters to the roof based cockpit ensure to smooth sailing operations. The accommodation is 3 or 4 hull based double cabins with toilets. The bridgedeck cabin has the galley, dinette and chart table. There is an option of an internal helming station next to the entrance to the forward cockpit.

The hulls are round bilge with a thick aluminium skin (about 8 mm) with heavy framing at 670 mm centre lines and stringers at 180 mm centre lines as you can see in the x ray jpeg. The cabin and deck structure aluminium skin (about 6 mm) is again heavily framed with longitudinal stringers. This is a heavy well structured build that is typical of Gracia. Again, comparable quality aluminium cats of the same length have slightly lighter framing and thinner skins eg 5 mm for hulls and 4 mm for cabins. The SC 48 cats are designed to be tough and capable of handling most things you can throw at them.

And the other aspect of this cat is its focus on safety. The hulls of this catamaran have two crash boxes (at the bow and at the stern) and two watertight bulkheads (one forward of the engine / rudder room and the other aft of the forward hold) to prevent full flooding in the event of an impact with an object like a rock, log or container. Finally, the mainsheet has a fuse on it to protect the rigging from excessive strain.

The SC-48 was superseded by the Explocat-52 after 2015. But the SC-48 was a good design that could sail well and do as its advertising said, act as a global capable catamaran. The jpegs give the idea.

 

Part 2 SC-48 cat.