Multihull Structure Thoughts

Came across a photo of BBTT Catamaran’s build of two 73’ Cats.

Looks like they are nearing final assembly.

Pretty impressive build project, and knocking out x2 boats of this size at the same time is pretty ambitious!

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https://www.bambamtactac.ch/

 

OldMulti do you have any information on the following Catamran shown in this 30sec clip.

 

kdifzero. I do not know anything about this cat or "bandoi et lady" or "bandoi double lady". There are several youtube videos of the cat under Yves Nolleau youtube site. the cat looks like ply and a "home design" but an interesting cat. Any other readers know anything.

 

SolGato showed an interesting jpeg and directed us to a web site about Bam Bam and Tac Tac catamarans. These two 73 foot cats were built in Switzerland by Martin Hafner and Patrik Rohrer who were the designers, builders and owners. The cats are valued at 1.7 million swiss francs. ($1.85 million) after 9 years of work. The two cats are 73 x 34 foot with a weight of 56,000 lbs. The 89 foot A frame masts carry a mainsail and foresail on furlers of unknown sail area. The engines are two Fischer Panda 20 kw. The engines are a little small for this size of cat. Other details are unknown.

The accommodation of both cats is similar. Each hull has 3 double berth cabins with attached toilets. The rest of the interior on the bridge deck is also luxurious: a dining area with a bar, a fully equipped kitchen including a wine cooler and humidor, as well as spacious sunbathing areas and a whirlpool in the outdoor area. All internal areas are airconditioned.

Martin Hafner and Patrik Rohrer had a dream, started to do some research, drew an idea and after 3 years of planning started the project and learnt as they built. They were both carpenters so they choose mainly wood for the construction. Marine plywood, fiberglass fabric, epoxy resin and PU foam were used for the basic construction of the hulls. Now I am a little confused. The jpegs seem to indicate narrow strips of plywood on the hull skin but I suspect its strip plank cedar type construction on the skin. The wooden frames are carpentry standard as is the majority of the structure. The structure is based around many frames and skin which is an old approach. Modern ply timber designs have fewer frames and more longitudinal support with stringers etc. The jpegs give the idea. These guys have done good work, but this is a very large project to do with minimal input from professionals. Youth and enthusiasm can work wonders.

A cat this size and weight with an 89 foot rig will perform well if built to designed weight. But the truth will be told when the cat is launched later this year.

The jpegs give the idea.

 

Second item of Bam Bam Tac Tac 73 foot cats.

 

The Castero 42 is a cruising catamaran or daysailer is designed by Sebastián Mazza and Argentina designer. Unfortunately, it appears as though it was a design and production proposal but appears not to be a reality as the design etc was done in 2012.. The Castero 42 is 25.5 x 16.3 foot with a displacement 3,360 lbs. The mainsail is 280 square foot with a 172 square foot self tacking jib. The draft is 1.3 foot over the hull and 4.3 foot over the daggerboards. The design is intended to be trailable but details of crossbeams etc are unknown.

Sebastián Mazza did a lot of work on the hull shape as he wanted a practical boat that could sail well across a variety of conditions. He looked at AC cats and F18 cats concluding the fine forward waterlines were effective at reducing pitching but it was not practical in smaller boats that were intended for cruising. So, he has fine lines down low but increased buoyancy high up. This required the stern to be designed to match the bow shape to reducing pitching across the speed range. Also, the hull shape has been designed to reduce the cat tripping in strong wind conditions.

The accommodation has a practically double berth, 6.5 x 4 foot in one hull and a single berth forward with a galley, sink and stove. In addition, there is a very large locker to store all the things that one always carries on the boat. The other hull has a double berth with a bulkhead and a door that closes the cabin and a private toilet with storage. The bridge deck is open for lounging and sail control.

The intended cat was to have a complete set of moulds with 3D milling that could take between 4 and 5 months. Then the first cat may take another 3 or 4 months. But from the 2nd catamaran onwards we calculate approximately a month and a half of construction. The design was intended to be PVC foam with e-glass in assume vinylester resin.

The jpegs give the idea. The cat was intended to be able to sailed single handed. An interesting design that would have been good for production.

 

The Duo 425 and Duo 480 are day sailing catamarans designed by Bernd Kohler. They are similar in concept and have similar construction. We will focus on the Duo 480. The 480 is 15.75 x 7.5 foot with a weight 157 lbs. The rig is a biplane rig with 2 masts (which can be large windsurfer masts) each carry an 86 square foot sail for a total sail area of 172 square foot. The length to beam on the hull is about 16 to 1. There are 2 versions of the hulls. The initial version was a lengthened Duo 425. After initial sailing the second version of the Duo 480 had its keel plank widen to allow the cat to carry bigger loads. Next is the basic cat can be sailed without dagger boards due to the asymmetric hulls, but many Duo 480 have dagger boards for higher performance upwind.

Both the Duo 425 and 480 have good sailing characteristics and high performance especially for a relatively cheap easy to build catamaran. The 480 is very stable due to its low centre effort of the biplane rig.

The construction is plywood and timber. The hulls are wood/epoxy constructions. The hull sides are made from 4 sheets of 4 mm and the rest of the hull has one sheet of 8 mm plywood for bulkheads, keel planks etc plus 6 kg of epoxy. The rigs are two wind surfing rigs. Vertical rudder is a kick-up system. Sort of "matched hole technique" used to line up the hulls for the build. The construction time is about 200 hours. The cross beams can be aluminium tubes 94 x 68 mm or plywood boxes with timber edge flanges.

This cat is an easy fast build fun boat for 1 or 2 people to sail. The jpegs are of the Duo 425 and Duo 480.

 

Today’s item is about the jpeg tri’s below that were designed in plywood by Ian Farrier between 1974 and 1980. Reason for the item, would you like access to the full plans of these tris?

The 1980 720 is 23.62 x 16.34 foot (folds to 8 foot) with a displacement 2,710 lbs. The 30.5 foot aluminium mast carries 274 square foot of sail. The draft varies between 1.4 foot and 4.3 foot when the centre board is down. The length to beam on the main hull is 6.4 to 1. The structure is plywood timber with 4 mm plywood hull side panels, 6 mm plywood bottoms and 9 mm plywood decks and cabin top on the main hull. The plywood bulkheads have timber backing. The chines are epoxy glass. The stringers and keel line are timber as are the deck beams.

The 1978 680 is 22.3 x 16.4 foot (folds to 8 foot) with a displacement of 2,513 lbs. The 26.5 foot aluminium mast carries 236 square foot of sail. The draft varies between 1.4 foot and 4.3 foot with the centreboard down. The length to beam on the main hull is 6 to 1. The structure is plywood timber with 4 mm plywood hull side panels, 6 mm plywood bottoms and 9 mm plywood decks and cabin top on the main hull. The plywood bulkheads have timber backing. The chines are epoxy glass. The stringers and keel line are timber as are the deck beams.

The 1974 TT 18 is 18.5 x 14 foot (folds to 8 foot) with a displacement of 1,098 lbs. The 23 foot aluminium mast carries 156 square foot of sail. The draft varies between 1.2 foot and 3.75 foot with the centreboard down. The length to beam on the main hull is 5.2 to 1. The structure is plywood timber with 4 mm plywood hull side panels, 6 mm plywood bottoms and 8 mm plywood decks and cabin top on the main hull. The plywood bulkheads have timber backing. The chines are epoxy glass. The stringers and keel line are timber as are the deck beams.

The performance of these tris may surprise you. A well rigged Trailer Tri 720 can match a Buccaneer 24 and a Newick Tremolino 23 in bay racing. A hotted up (with rotating wing mast) Trailer Tri 680 can just about match this group. The TT 18 is Ok in performance but it depends on its fat main hull planning to get real speed. All these tri’s have 100 % buoyancy or below floats. Each of these tris handle well and sail across a wind range well.

Now to access the plans you need to sign up to the following web site using you e-mail address or google, facebook setup, get your access authorised, then look on the left side of the main web page for an item called “files”, click on files and then click on a folder called “plans” 4 items from the bottom. Plans contains 4 items. The 2 two plan items require you to use a ZIP extract program to get PDF plans and build instructions for the 720 and 680. The TT 18 item gives you a ZIP which contains a series of PDF’s for the TT 18 plans. The start web site is: https://fct.groups.io/g/TrailerTris

Have fun as EG the 720 full plans will give a lot of information of how to build a very well conceived small trailable cruising trimaran.

 

I have seen a few very nice examples of those earlier Farrier boats for sale at bargain prices considering the time and cost to build new, and how functional the design is.

And as you mention, some are very good performers while offering a level of comfort lacking in some of the more modern examples.

Like other Farrier boats, there is an active owners group online:

https://fct.groups.io/g/TrailerTris/topics

 

The Scarab 18 trimaran is designed by Ray Kendrick and can be built in foam glass or plywood. The plans offer both versions. The Scarab 18 is 18 x 15.5 foot and can be folded to 6.9 foot. The weight is 1100 lbs in the plywood version or 775 lbs in the foam glass version. The mast is 28 foot high and carries a 178 square foot mainsail, a 68 square foot jib and a 162 square fgoot asymetric spinnaker. The rig can come of a beach cat like a Hobie 16 etc. The length to beam 6.7 to 1 on the main hull. The draft over the centre board is 3.2 foot. Both foils kickup. The outboard can be a 4 HP longshaft.

The tri is aimed at being a minimum camp cruiser for 2 and a daysailor for 4. The cabin provides bunks and a space to get out of the weather and store the camp stove, portapotti and ice box.

The build options are either timber/plywood with e-glass epoxy coverings or foam glass. The PVC foam e-glass in polyester option is lighter, faster and easier to build in this case as the majority of the tri is built from full length flat foam glass panels that require minimal fairing before painting. To quote a builder “The boat is built using flat panels over a male plywood frame. The boat can also be built using plywood laminated panels. The foam was joined to the right length and glass was laid over the length. The resin was spread using a flat drywall spatula. We use peel ply over the resin to give a smooth finish to the laminated panel. The panels for the boat were cut out as you would for plywood joined to the frame with drywall screws and taped with fibre-glass tape. It was very quick to join all the panels. It was turned over and taped inside. The two floats were built in the same way. It took only a day for each float to be joined to the temporary frame and taped on the outside. The bulkheads were added and support for the deck. The beams can be made using a mould that can be knocked up from plywood or form ply. Add the specified number of layers of glass. This boat was built in less than 500 hours and it cost about $10,000 AUD without rig. We used a modified tornado catamaran rig and it should fly.” The jpegs give the idea. Also look at the following web site: Trimaran Building: Scarab 18 folding trimaran Part 1 http://foldingtrimaran.blogspot.com/2008/12/new-boat-new-challenges_07.html

The full detailed plans are currently available at $100 Australian for March 2022 from: Plans for the Scarab 18 trimaran http://www.teamscarab.com.au/Scarab%2018Des.html

Scarab 18 plans. TeamScarab is located in Queensland Australia in an area that has been flooded previously. Queensland Australia has had a major flooding event in the last week so please verify by email if Teamscarab is ok to deliver electronic plans. Hopefully Teamscarad are OK.

Ray has designed many small tris and they all sail well if built to plan. The 18 is an excellent trailer sailor for those who want the occasional weekend away in a well performing tri.

 

A couple of short YT clips of this design.

 

Kurt Hughes designed a rapid build cylindrical moulded plywood catamaran that is 30 x 20.1 foot that weighs 2950 lbs and displaces 5800 lbs. The 36 foot fixed or rotating mast carries a 300 square foot mainsail, a 141 square foot blade jib, a 231 square foot genoa and a 400 square foot spinnaker. The length to beam of the hulls is 11.5 to 1. The draft is between 1.4 foot and 5.8 foot with daggerboards down. The bridge deck clearance is 2.9 foot

The intention was to have a 30' cruising catamaran with full standing headroom in the hulls, but is aerodynamic enough to give great windward performance. The accommodation below has two large double berths, single berth, galley, seating and separate toilet area. The intention of the cat was to strike a nice balance between accommodation, payload and performance. The cat with a rotating mast, deep boards, high wing clearance and minimum windage should be able to sail upwind very well for its size. The construction is the very rapid CM plywood/epoxy technology or an option is a composite version.

All good so far. The only difficulty is almost every low windage semi open bridge deck cat design I know ends up with some form of wing deck cabin structure on it to “improve” its accommodation. Richard Woods resisted for years before he designed a small removable add on accommodation pod on his open bridge deck cats. Tony Grainger virtually gave up doing semi open bridge deck cats because everyone just added a central cabin that in some cases, degraded the visual appearance and performance. Kurt Hughes focused more on full bridge deck design cats after the earlier designs etc. The attached jpegs are of the initial 30 foot simple rapid build design then an example of what one 30 footer was completed as. This is not the only example of this design having a bridge deck cabin added. This cat’s central cabin was relatively well done but it added weight and windage. The hull shape above the waterline was also modified to allow the double berths to be placed in the hulls. This adds a lot of work to an existing design to obtain “improved accommodation”. Please speak to your designer upfront about your real wants/needs. I know from experience changing one thing on a design can have cascading effects through out the build process and you end up doing a lot of extra work that could be eliminated up front by having a clean design, not a partial design and modifying on the fly.

The jpegs give the idea.

 

Seaflier is a hydrofoil proa that was designed and patented in the late 1970’s and early 1980’s by Patrick Cudmore and built by Ted van Dusen in about 1984. Details of the design and build are limited so take the next part as a guess at best. The Seaflier is about 16 x 8 foot, with an unknown weight but guess of 300 lbs. The cantilevered, articulating wingsail provides lift and drive. The wing sail area is about 120 square foot. The arched foils at either end of the “proa” are probably Ogive sections (symmetrical fore and aft) as the foiler could sail in either direction. The build is foam glass throughout. The articulated wing rig was difficult to build and required a lot of development.

The foiler when sailing had 3 modes according to Patrick “operates at three performance levels: in buoyant or displacement mode at speeds under 5 knots, in hydrodynamic mode at intermediate speeds to 14 knots as the majority of lift develops on the top surface of the foil, and in hydroplaning mode as the underside of the foil achieves lift near the water's surface at high speed." Under ideal conditions and with adroit sheeting and foilborne, climbing up 2 feet vertically, the proa could reach or exceed windspeed in two or three boat lengths.

The issues with the proa where interesting. In its original form "Seaflier" has no rudders. Steering control when foilborne is achieved by rolling the craft sideways. Rolling to windward turns the boat away from the wind. Rolling to leeward causes it to round up. The steering response was too slow to deal with gusty conditions. Although rudders were initially eliminated to minimize drag, it became obvious in early sea trials that some form of low-speed steering control was necessary. The yellow boat jpeg shows a later “catamaran” version with 2 rudders and a sloop rig for better control. Testing of the original version in a variety of conditions would have a typical flight cover anywhere from 100 yards to 1/4 mile. The boat climbed onto its foils in windspeeds of 8 to 10 knots and demonstrated considerable pitch and roll stability in flat and rough water. There were some very impressive speed runs, but the need to develop the rig and control systems in the “proa” format caused the modifications to a catamaran model at one point.

After a few years of testing and upgrades the project was sidelined. Patrick Cudmore passed away in October 2001. The jpegs are limited. The expired patent is in the PDF (under a meg).

 

Just quick question about ideal weight distribution in trimarans? Does it make sense to keep weight out of side hulls and try to back most of the load in the center hull?

 

calevi. Try to centralize weight and keep it as low as possible in a trimaran design. If you have good hull shapes then weight in the center helps reduce pitching and "snap" rolling. Older trimaran designs that had heavy floats with deep V shapes tended to be slow to react to wave action and in some heavy reaching and down wind conditions would have floats that drove under a wave top because the float did not lift up fast enough. OK in most cases but in some instances caused the tri to trip over. Keep floats light and design them with more than 100% buoyancy of the fully loaded displacement of the trimaran.