Multihull Structure Thoughts

Hi oldmulti. Is it ok if I post a question regarding modifications to the structure of the crossbeam of a Maine Cat 22 here? I know you have already covered the boat on page 38, but I am seeking advice to right some wrongs done to the boat by the previous owner. Also, do you have any information on control systems for rotating masts? The boat was also changed to a rotating spar, but I need to design a spanner to control the rotation.

 

Well that is a blast from the past. I might have to book my own charter!

 

dylan j. Please post your question. I have no great knowledge of the cat but others on the forum may. Please post a photo(s) of the area of concern so others can provide feedback.

 

So, the previous owner of the boat went to great lengths to reduce the weight of the boat. Going as far as removing watertight bulkheads, and cutting into the front crossbeam. I'm not too concerned about the removal of the bulkheads as they were not fully tabbed in, and so not likely structural and by my estimate the boat is buoyant with the volume of the foam core alone.

My concern is that with the removal of most of the rear shear web of the front beam one of the bonded flanges at the base of the beam started to separate. I have reinforced this area, and added some diagonal cross braces to replace some of the lost strength. Right now these diagonal braces are bolted in place, and I can watch and hear as the boat flexes how they begin to load up and limit the flexing of the beam structure. My initial thought was to simply improve on this by replacing these bolted aluminum struts with some carbon tubes that I would glass in place eliminating the movement in the connections. I asked some opinions on this approach elsewhere, and most of the feedback was that it would be a better idea to simply replicate the original structure. Does anyone have any thoughts or examples of this sort of a hybrid box-beam with one face replaced with a truss being used in any other designs?

 

Dylan J. The function of the main mast beam in designs like this is not only to support the mast but also to act as a torque box to minimize the twisting movement between the 2 hulls. The rear beam helps minimize the twisting moment but both the rear and main beam work together. The flexing you are noticing is partially cause by the cut out of the web. The best solution is a replacement of the cut out areas which can be EG a foam glass panel over the top or retro fitted into the same shape and are of the cutouts. This will help with the rigidity. I would be reluctant to put a cross strut as the permanent solution as that is not going to fulfill the need of a Torque box. Any other ideas folks?

 

I am aware of how much more torsional rigidity a box section has relative to what is now effectively a c-channel. I do have a background in mechanical engineering, but it has been more than 6 years since I have had to do these sort of calculations. I am unfamiliar with exactly what sort of load conditions I can expect the boat to experience and to be honest the fact that the all of the structure has been cut in half, and then is bolted back together for the folding system makes the calculations a bit beyond my abilities.. I might just build a 1/4 scale model in order to determine if my current approach is sufficient. I would measure both the deflection under bending and torsion of the original structure, with the enlarged cutouts, and then with the added struts. Would anyone be interested in me posting the results if I do this?

 

For 15 plus years C3 Technologies of La Rochelle, an outcome of CRAIN (Research Centre for Architecture and the water industry), has made technical composite parts for the sail racing boats and some aircraft components. Daggerboards, rudders, foils and other elements for monohulls and multihulls are part of the catalogue but they also offer bracing, partitions, as well as wings and the skeletons of aircraft.

Jean-Marie Buignet, CEO says the core business is producing these elements for racing multihulls or monohulls which require specialist knowledge in the construction of appendages. Jean-Marie Buignet after working in the industry as a composite person went to CRAIN able to develop the composite activity within CRAIN and from 1996 evolve the technological elements for the boating industry. CRAIN was approached by the America's Cup for assistance in structural parts and appendices, and then approached by Multiplast at the time of three catamarans The Race. We saw an opportunity and as CRAIN turned its activities to passenger planes and craft, C3 Technologies became a specialist in technology in high strength appendages etc.

With C3 building, machines, tools, our autoclave, digital die cutting we have developed very specific manufacturing techniques. It’s closer to the aircraft approach of design and manufacturing. On the maxi-trimaran Spindrift, we have manufactured all the rudders, the boards and the foils and we did the new foils for the trimaran Bank Populaire VII. For the foils of the maxi-trimarans, there are 116 mm of solid carbon in some places which requires skill to build especially with radii of curvature of 3.50 metres (11.5 foot). This requires knowledge of fabric and unidirectional layout, type and density of foam cores, resin type, Autoclave temperature and pressure versus time etc. It also needs an understanding of the function of the appendage.

It depends on parts and profiles. For the rudders should retain flexibility because the shovel works in torsion and so a certain bending support. For the foils, load cases are very different and it seeks to achieve a very steep part with little distortion. But now, you have to imagine composite parts with different resistance to torsion modules: there are very rigid parts and other more flexible. We have constraints of mass, load resistance, durability, precision, since most of our parts work dragging in another - a well, a hole... With the speeds reached by boats today we are working in the order of a tenth of a millimeter. 25 years ago, a multihull sailing very fast at more than 20 knots; Today, it is a cruising speed!

There has been much evolution in foil profiles. Flows at 20 knots are not the same as 35-40 knots! The traditional Naca profile has changed to much more sophisticated forms. And we still have more resistant materials with nano-particles incorporated in new carbons. To improve the working life of foils. We can also treat some stainless steels or some aluminium with these nano-particles on the surface, to block the phenomenon of oxidation.

In the autoclave, we can make parts of 12 metres long and two metres in diameter: boards, foils, rudders, partitions etc. The Autoclave can go to 8.5 bars of pressure and 170 ° C temperature, but, in general, it works at 110 ° C and between 2 and 5 bars, according to geometry, constituent material and the thickness of the workpiece.

To build a foil we generally start from the top surface with the outer skin, structural beam, a monolithic party that acts as a bumper on the leading edge, to which add different densities digitally machined and glued foams, skin and Interior after cooking. The technique of the shells is changing because we found one of the big dangers of this kind of build is there are "blind collages", i.e. of the junctions between the two shells cannot be well control, this may impact the foils longevity.

On the structural bar of a foil we have 4 control checks by ultrasound at every stage of the construction since this very thick piece is carried out in several phases. EG The resins used generate such energy calories that it causes significant exothermic phenomena as they are proportional to the mass of the workpiece. Therefore we proceed in stages with cooking differences, it's taken 20 years of experience to develop this technology and at the end, have a finished piece removed from the mould that has the structure perfectly together. In total, there are five controls quality!

Translation of the above. High performance multihull appendages are a specialist area that require very good design and quality manufacturing to achieve their task. The difference is design, material and build techniques for a rudder and a lifting foil was interesting. A few jpegs may help.

 

Do you have enough information to do a post about the 20ft Shark catamarans? From what I have seen it is one of the few cats with a similar folding design to my Maine Cat 22. I would love to know more about the overall scantlings if you have the information.

 

Dylan J. Shark 20 minimal knowledge but this may help. Attunga 20 page 91 of this thread (20 x 10 foot weight about 600 lbs). Years before Newick 22. Folds exactly the same way as your cat.

"Now the point of interest. The cross-beam structures which allow the cat to be folded to allow trailing. The main beam halves are permentaly attached to the hulls. The forward main beam halves are an aft I beam with an attached D front section. The I beam has a 4.5 mm ply web with a 52 x 25 timber both sides top and bottom. Attached to the front of the I beam is a 4.5 mm ply top and bottom wing section with 12 mm ply wing frames on the folding end. The 2 hull beam half sections are joined by metal brackets and bolts. The metal brackets are 500 mm long x 22 mm wide x 3 mm thick SS strap with a 15 mm bolt hole drilled through it at one end. There is a strop on the top and bottom of the I beam and on both sides of the I beam (a total of 4 straps on 1 half). The straps are screwed into the I beam timbers at 30 mm centres. To fold the cat take out the top bolt and fold on bottom bolts. The rear beam again is a I beam with a 6 mm ply web with 30 x 15 mm timber top and bottom on both sides and has 15 x 45 mm bulkheads on each face as there is no forward D section. The connecting straps are 350 x 30 x 1.2 mm with a 10 mm bolt hole at one end. The straps are again attached by screws into the top and bottom I beam timbers."

The first 2 jpegs are the Attunga and the last jpeg is of a very old first model Toranodo cat.

 

Thanks for that information about Attunga oldmulti, I had never seen that design before.

That last image sure looks more like a Shark than a Tornado to me. I had heard that the development of the Tornado was heavily influenced by the Shark design though, so who really knows. I have attached some photos of Shark catamarans from their facebook group. They show the wide variety of build methods for the boat. Cold molded hulls with plywood decks, then fiberglass hulls with plywood decks, and then finally fiberglass hulls and decks. The rear beam and cockpit floor appear to be wood in all three versions, but that's about all I know of the boats.

 

I have been swamped by reality speak to you tomorrow.

 

Sorry, I have an electrician in again who is about to shut down power to the house so I will attempt to do something tomorrow. Life is so unkind, but fun.

 

Skip’s Attunga? If so, a perfect cat. Shark too- what did the class say about it? Like a blown ‘58 Chevy Bel Air…. Better manners and feel than the Sol Cat 18, at any rate- and the folding system was genius.

 

I am confused. The Swisscat, a series of fast cruising catamaran, was stablished by a passionate sailor (Jurg von Ins) in 2009 (or 2007) who produced a limited range of cats in France. Then 3 x S2C 55 and 2 x the S2C 45 were made by a subcontractor in a Turkish shipyard. Swiss Cat Yachts had evolved into a boutique semi-custom builder under the leadership of CEO Philippe Chatel. In partnership with Bay srl, the Swisscat shipyard moved to Italy in 2022, marking a new chapter in our journey. Somewhere in there are comments about buying the Switch catamaran buildings and yard in France. There are several claimed designers RM Design, another person then Francois Perus and Romain Scolari. Let’s get to some “solid Information”.

We will focus on the Swisscat SC 55 is 55.4 x 26.9 foot with a weight of 31,100 lbs and a displacement of 42,500 lbs. The carbon mast length is 73.8 foot and carries a 1086 square foot mainsail, a self tacking jib of 624 square foot, a Genoa of 753 square foot, a storm jib 300 square foot, a gennaker of 1720 square foot and a 2690 square foot spinnaker. The draft can either be a 4 foot deep fixed fin or daggerboards that draw 9.35 foot. The underwing clearance is 3.25 foot.

Francois Perus designed a modern and powerful hull shape with a low rocker to promote good acceleration and create dynamic lift to reduce pitching and heeling. The displacement takes into account the load requirements for a blue water cruiser, good balance is achieved by keeping the weights centered and trying to keep the bow and sterns empty. This design focus is intended for fast cruising on the open sea: to sail in any sea in comfort and safety, with a fast cat, and extremely easy to steer. The result is a high-performance, wave-resistant multihull with excellent sailing properties.

There are 2, 3 or 4 sleeping cabin versions available (see jpegs) that are very well equipped with high quality decor and fittings (finishes, upholstery, colors, cabinetry etc). These are semi custom cats that can be made as you require within the basic shell structure. The deck layout is centralized around the roof, and the 2 rudders (single rudder model also available) are located in the cockpit area well protected from the weather and positioned for excellent visibility fore and aft. Remote electric control options are possible.

The structure was optimized by the specialized firm Rivoyre Ingénierie with the use of carbon fibers wherever reinforcements are needed. The SC 55 is constructed using EPOXY/CARBON sandwiches, using vacuum infusion. An isolated room allows post-curing of the infusion. The hull and deck are painted in polyurethane paint. The build takes around 8,500 hours (i.e. double that of a mass-produced catamaran) but Swisscat says it improves the quality and longevity of the construction. The internal furniture is lightweight veneer panels and several components are structural. Now for aspiring home builders of 55 foot cats 8500 hours in a factory with production moulds and knowing exactly what they are building means a home builder would take maybe 15,000 hours to do the same type of cat. Have you 6 or 7 years full time available to build a 55 foot cat?

Performance with sail area and displacement numbers like this are good to very good. 300 mile days are realistic in good conditions with peaks of over 20 knots. Cats like this have one very large advantage, you can dial in the speed and or comfort level you want to get somewhere. In some conditions you want comfort upwind at 8 knots in other conditions you want 15 knot reaching speed to get somewhere. Accommodation cats don’t give you the speed options, performance cats allow you to have the choice of speed versus comfort.

A very nice cat, pity I cannot afford one. The jpegs give the idea.

 

An update on the Tricat 30 trimaran designed by J.Michal / A.Houdet from CN Tricat France. The Tricat 30 is a sport cruiser, swing wing transportable (to wide to be trailable) trimaran. The Tricat 30 is 30.2 x 23.3 foot and can be folded by swing wings o 12.5 foot. The weight claims range from 4000 lbs (original brochure) to 5000 lbs (several test reports) with a displacement of 6500 lbs. The 36 foot aluminium mast carries a 430 square foot mainsail, 215 square foot jib and a 485 square foot gennaker. The main hull length to beam is about 8 to 1. The hull draft is 1.6 foot and 5 foot over the float based daggerboards. The floats are 29.5 foot long and have very full square sterns. The outboard is 10 HP.

The accommodation is a forward and aft double berth with a separate toilet area. The main saloon has a 7 foot galley with a dinette opposite. There is also a fold down chart table with seating. This is a practical cruising layout with 6 foot headroom in the main saloon. A couple could cruise this tri for a month in comfort. The cockpit will handle 6 people with all sail handling available.

When this tri was being developed by Tricat, they did a 3D CAD design then built a full size plywood model of the tri to sort out the ergonomics and any sail handling issues, winch locations sheets leads etc. It is far cheaper to change things on a cheap plywood structure than modify a production mould.

The structure is mainly foam glass. It is a polyester foam glass vacuum infused structure but the second tri, at the request of a customer, had the hulls vinylester foam glass vacuum infused. There are solid glass areas but any flat panel has foam cores. All the elements of the Tricat 30 are made by infusion (carbon epoxy for the arms and the appendages, glass polyester for the hulls) The crossbeams have stainless steel pivot pins. For the hulls of the T30, Tricat outsourced to Marsaudon Composites in Lorient, as trusted sub-contractors.

From a performance test report 10 to 14 knot winds. “Our speed ranges between 9 and 11 knots, and the tiller is precise, enjoyable and doesn’t require much effort.” “An offshore chop was now settling in and the breeze maintained at 12-13 knots, with regular gusts to 15-16 knots - the ideal scenario for our test. The T30 is easy to get slipping along at 12-14 knots (the maximum we hit on the day was 14.5).” This tri can sail at near wind speed, tacks well, points high and has peaked at 20 knots. Then Martin Fisher assisted in the design of a Tricat 30 PERFORMANCE with a new lighter rigging and asymmetrical daggerboards. The upwind performance was improved and the Tricat won a few local races. In short it can sail well on all points.

This is tri is a practical fast cruiser that can sail far if required, at least 10 have been launched. The jpegs give the idea.