Multihull Structure Thoughts

Unless you have a specific reason to fold on water I have come to the conclusion that a swing wing trailer with a sango like I section lifting platform is the solution to the trailerable cat.

I saw Kelsall's sliding beams and other systems ages ago. It just seems problematic.

The swing wings achieve the same result as sliding beams on a trailer but won't bind up. The platform sitting on I frames goes up between the hulls when folded in and supports the bridgedeck. Splay the hulls by hand. Use a trailer winch to lower the platform with the bridgedeck. Position and fix the cross beams. Now use the central platform to lift the assembled boat off the wings. Swing them in and you can lower the assembled cat to the ground. Launch in minimal water.

16 pivot points and a hand winch. More complex than a regular trailer but none of it needs to be multihull light stiff and salt resistant.

2c.

 

The microship is a classic case of mission creep. A great idea that just keeps getting heavier and worse every year it stays in the shed accumulating features. For a counterpoint look at the sailing canoe Mead Gougeon entered in the Everglades Challenge. I just love that the old man arrived days ahead of many serious sport boat teams in what looks like a canoe with an easy chair in it! B-B yachts did a follow up boat (with Meads help) but I am not sure they ever sold the design. They did the full Florida challenge and managed to document most of it with video.

 

The following is a story of a couple who enjoy sailing on fast cruising catamarans. Start with several smaller boats then move to a Catana 472. After a time, they decided they wanted more performance and went to Outremer to have a 5X (“Wilding”) built for better performance sailing and comfort. After 3 years of the Outremer 5X they ordered an Outremer 4X as they wanted a smaller lighter, easier cat to handle that was nearly as fast as the previous cat. They built the 4X (“Puffin”) with a lot of carbon fibre in the structure and rig with a minimum of internal gear. The 4X is fast.

“Wilding” is the Outremer 5X in this story and jpegs. The Outremer 5X is 59 x 28.15 foot that weighs 31,100 lbs and displaces 44,800 lbs. The mast is 77 foot with a 1,312 square foot mainsail and a 635 square foot Solent jib. The hull length to beam is about 11 to 1. The draft over the daggerboards varies from 4 foot to 8.7 foot.

The jpegs give a guide as to the build of the 5X. The cat is built with a solid glass bottom below the waterline with localised reinforcements and inserts. All components are resin infused. The hull sides are on the outer skin a CSM mat / vinylester resin then a sandwich of PVC foam core & fibreglass / polyester resin on inside and outside hull components. Deck is infused in a female mould with a sandwich of PVC foam core & fibreglass / polyester resin with various reinforcement (patches and UD strip) and local inserts (balsa). Glued and re-laminated on the whole perimeter of the gasket scheme hull/deck. There is a options of a roof in carbon fibre / Vinylester.

Bulkheads assembly of the 3 main bulkheads are in sandwich PVC foam core & fibreglass / polyester resin, glued and re-laminated to the hulls and the deck. Secondary bulkheads are the same with some plywood inserts as required. “Wilding” was built with optional carbon fibre mast and aft main bulkheads. As you will see the amount of work in a “production” multihull with moulds is large. 10,000 plus hours of work. The PDF contains the specification and option list. It is long and complex.

The jpegs give an idea of the build.

 

Second part Outremer 5X build.

 

The following is just one example of a type of power catamaran that is popular in Australia that can be manufactured as a kit for shipping anywhere and built by a professional or amateur builder with sufficient aluminium welding skills. In this case the power cat is a Chris Tucker design produced by Alloyboats.

The power cat is 24.6 x 8.2 foot over the hulls with a displacement of 6,270 lbs. The hull draft is 1.15 foot. The hull deadrise is 12 degrees on the V hull bottoms. The length to beam of the hulls is about 9 to 1. In power cats the hulls can be closer together as the bow waves down the tunnel help the planning hulls lift.

Hulls need to have wider separation in sailing cats and low powered “displacement” catamarans as the wave patterns create drag in non planning hulls. Richard Woods research found the “balance” point was hull centrelines needed to be about 40% or more of the waterline apart, to minimise drag for eg 10 to 1 or fatter length to beam hulls. When hulls have a 15 to 1 length to beam the hulls can be closer together, but not to close.

The accommodation is good in the main cabin with a galley seating and steering station. Forward there is limited space for a double berth and a toilet.

This is about the largest aluminium power cat that a home builder can produce that is really trailable. Even so it will require a big SUV or pickup to tow it around. The structure is basically aluminium with the bottom, chine, transom and stringers from 5mm 5083 aluminium. The sides, deck, cabin, etc. are from 4mm 5083 aluminium. The stringers are closely set at about 350 mm centres with frames about every 600 mm. These boats are strong.

The cat is powered by 2 outboards of 100 to 200 HP per motor. There are two 250 litre fuel tanks. This cat under the right power could top 30 knots but I suspect the range would be limited. These cats are mainly used for fishing or commercial applications but could make a reasonable short term cruiser.

Sorry about the limited jpegs. The PDF contains a few jpegs of an actual cat and some good jpegs.

 

Gday Guzzi

I have huge amount of respect for Richard Woods, he is my type of designer - builder and experienced sailor first, designer after - but there are some fundamental limitations with rotating the hulls like the Sango and Wizard.

Chief amongst them is the rotation of the hulls. All of the gear and stowage, water tanks, food, etc are rotated through 90 degrees, including porta potties and the like. Also you have to reduce the total height of the hulls from keel to topsides to less than 4 ft to fit on the standard width trailer. This then forces you into having a little bridgedeck cabin, not a bad thing in itself with the hulls as a small bunk spaces.

One of the nice things about a cat is the ability to have proper divided spaces. Putting everyone into one space is a bit of a pain "Excuse me, would you mind, shift your bum" gets a bit old. That is why cats using the hulls as proper accommodation work so well, everyone can get their own piece or real estate.

We could go away in our little 5.9 metre cat for a week with a family of four and not get cranky with anyone, there was a proper bench for cooking, that was not in anyone's bunk, there was a proper toilet area, 1.5 metres away from the nearest bunk and no one had to lose their bunk for seating. You just don't get that type of easy divided living in a mono or in a Sango. Folding on the water is great if you can work out how to do it as you don't need a special trailer or a deep ramp like you do with the Wizard. You also have very few interior issues with folding beams intruding into the accomodations. There is an easy to build folding cat method, just not too many people wanting small trailerable cats really. Check out the video I posted before - it takes only about 20-30 seconds to fold, which is not a problem.

I don't have a lot of skin in the game anymore, the folding cat thing has cost me a lot of time and a fair bit of money. That is okay, I have a fine day job and enjoy playing with boats. I wouldn't think there are many people who have spent more time thinking/designing/building folding cats than I have. It is an interesting conundrum but design is about fulfilling a need, and there is not a lot of need for a cat that folds. I wish there was more.

 

The trailer I have in mind would neither be expensive nor difficult to build. Assembly isn't instant but it needent be onerous either. Because the mechanism stays on shore it doesn't need to be super light, salt proof or strong enough to take dynamic loads when splayed.

Yes there are limitations to wizard/sango and the toilet problem is the one that killed it for me, but that option suits some people. It's trivial to relocate your porta potty before recovering the boat for example. I want a head.

Your system doesn't look like it can accommodate a bridgedeck cabin, for example, and that's a deal breaker for some people.

Farrier's folding tris have been very successful, but they too have limitations. The accommodation isn't all it could be for example.

If there was a perfect solution everyone would embrace it. What we have instead are choices. At least we have that.

 

A mild update on Mark Grumpecht 22 foot small cruising catamaran. The cat is 22 x 8.5 foot weighing 1900 lbs with 22 foot wing mast as used on the Drifter 17 trimaran. The cat has a lifting centreboard and central rudder. The hulls have a flat bottom “dory” type shape. The cat is really trailable as you can see from the jpegs. The engine is a 6 HP long shaft outboard.

The accommodation has a cockpit 5.5 x 6.5 foot and the cat has a micro galley with a 2 burner propane cook top and small sink. The cat has a custom private head with door on port side and a thetford porcelain marine head. The cat has a double berth with 2 child single berths.

Mark designed and built the cat in one year. It is plywood with light e-glass cloth outside. It uses mahogany wood on the interior. I do not know any structural dimensions but similar cats (Jarcat 20) are 6 mm plywood throughout and the Drifter 17 tri has 6 mm plywood decks.

The wood wing mast is well designed and relatively easy to build. The unrigged mast section weighs 27 lbs for 22′ length, the profile cord is 165 mm before adding the main sail rail, which gives a final measurement of 178 mm long, by 67 mm width (external dimensions). The mast is made out of 1/8″ (~3 mm) plywood and spruce battens, glassed on the exterior with one ply of 170 gsm glass and epoxy. PVC foam was utilized for the rounded forward portion of the mast (leading edge) but balsa can also be used. The forward section is glassed first, then the rest of it, so that the front edge gets two layers of glass. All pieces are joined with accurate scarfs, the interior is epoxy encapsulated, and a 1/2″ (13 mm) glass fiber tube is epoxy glued to the trailing edge and then cut out by means of a circular saw and gig to provide the sail rail. Some carbon may be added to make the whole stronger, but the basic mast is very strong for a boat this size. Two cuts were made on the vertical spruce battens to set and glue the lengthwise plywood stiffener so that it is easier to assemble the vertical “H shaped” structure. Jpegs below.

The history of the cat is Mark built it in 2005, sold it in 2010 to go onto the Drifter trimaran. The next owner sold the cat in 2015 after “not sailing the cat” according to one report. The next owner again sold the cat in 2018 with a few minor problems caused by a hurricane. Again, that owner did not sail the cat and it was stored. This is a good, well built cat that deserves to be used and well maintained.

The jpegs give the idea. The mast details and some jpegs are on Self-Built Mast for Small Trimaran | Small Trimarans https://smalltrimarans.com/blog/self-built-mast-for-small-trimaran/

 

Jarda Suchopar from the Czech Republic decided he wanted to go short term cruising in a trailable trimaran. Like most people he didn’t have much money so he found an old timber Finn mono dingy hull and started to work. The first version ended up to heavy so he found another timber Finn hull and did a second improved main hull using all the other bits from the original tri.

The tri is 16.5 x 11.5 foot that is able to be compressed to 7.2 foot for trailing. The weight of the tri and the trailer is 1,380 lbs. The 22 foot wooden Finn mast is maintained with a 107 square foot mainsail, a 43 square foot jib and a 161 square foot gennaker. The floats are 225 mm wide and the draft is a 2 foot centreboard. The outboard is a 2.5 HP.

A Finn hull and deck weighs 236 lbs. The hull was lengthened from 15 foot to 16.5 foot with glass epoxy resin. The whole hull is reinforced by battens and on the hulls extra freeboard and cabin (deckhouse) is from waterproof plywood – the thickness of the material is 4, 6, 9 and 12 millimetres. The floats are also plywood. The telescopic beams for the amas (floats) which are made from aluminium tubes have diameter 100 x 2 mm for the main hull components. The telescoping beams attached to the floats are 90 x 3 mm aluminium tubes. The floats are bolted to the tubes by bolts. The tri took 60 days to build from the component parts.

The accommodation is basic as you can see in the jpegs, but the main hull can sleep 2. There is extensive shelving for basic storage, and the cabin has enough headroom to be able to sit on a bed and do some cooking. The tri has spent 2 weeks in Hungary in the Balaton lake and 3 weeks in the Croatia in the Adriatic Sea. After a 3500 km road trip to Sweden they sailed 250 miles around the coast over several weeks. The performance of the tri is a 5 to 7 knots sort of boat as the owner wanted an effective cruiser not a racer.

This is a fun effective cruiser that cost Jarda $1,300 all up. This is real value for money and proves if you have the vision and will to build you can go sailing cheaply. The jpegs give most of the story.

 

Part 2 of Finn based trimaran

 

The following is an excellent looking trimaran design from a now defunct “Seagull boatdesign”. Roland König did the “Seagull 20” design and build of the tri in about 2012. The tri is 20 x 18 foot and can be folded by a Farrier type system to 8.3 foot. The displacement is 1,760 lbs with a guess weight of 800 to 1,000 lbs. The rig is of a large Hobie cat with a 29.9 foot mast carrying a 183 square foot mainsail, a 96 square foot jib and a 197 square foot gennaker. The length to beam on the main hull looks about 7.5 to 1. The draft ranges from 1.1 foot to 5 foot if the centreboard is down.

The accommodation is useful for a 20 foot tri with sitting headroom and an effective single berth fore and aft. The tri is outboard powered.

There are no construction details but it would be eg 6 mm plywood taped together with 400 gsm biax tapes and what appears to be a strip plank cedar or double diagonal ply hull bottoms. The exterior is covered by glass with an west type epoxy all over. The cross arms appear to be laminated timber and ply boxes with aluminium folding struts. The plywood bulkhead ring frames at the mast base and forward cross arms attachment points are probably 9 mm ply with additional reinforcements. Roland intended to extensively test his design and refine it, so plans would be interesting for home builders. Since all components are available as CAD files, the trimaran could also be sold as a kit using a computer milling machine.

The only video I could find on the net of the Seagull 20 sailing indicates the tri appears to sail quite well. And initial testing in only force 2 Beaufort showed very good potential: 6 knots was measured on a GPS.

If anyone knows any further details please advise. The jpegs give part of the story.

 

Daniel Charles designed and built over 7 years Epicure an “Indian Proa” which is an Atlantic proa which he launched in 2010. Epicure is 47 x 23.5 foot with a 47 foot long lee hull and a 38.7 foot windward hull that contains the accommodation. The weight complete’ without crew, food or diesel, is 11900 lbs. The rig is a mainsail of 1050 square foot, to avoid the jib problems when shunting, an electric winch does make sail handling easier. A flying jib can be rigged in light air. The lee hull has a length to beam ratio of 18.5 to 1. The windward hull is about 8 to 1 at the waterline. The draft is 3.8 foot over the retractable rudder daggerboards. The Bruce number ranges from 1.46 to 1.99. This indicates a fast boat.

The accommodation is good, she is an attempt at having a live-aboard cruising boat with all the modern comforts (heating, fridge, deep-freezer, oven & microwave, dishwasher, washing-drying machine etc). There are two cabins (one in each windward bow), one with a navigation area (and a 24” computer screen), each with a separate settee and vast amounts of storage and hanging spaces. The lounge with good views and can be transformed into a king size bed. The galley is made of three connected areas: working, cooking, hardware (oven, microwave and dishwasher); floor space there is 22 square foot. A boat you can cruise on for an extended period.

Now we come to the construction. The shell of the proa is aluminum. Daniel Charles has designed many 50 foot plus racing proa’s of many materials but for is personal boat he preferred aluminium. The interior is balsa core sandwich to reduce weight. The rudder daggerboards attachment linkages to the cross beams are engineering marvels. The interior is very well done. This was not a cheap boat costing over 500,00 Euros (about $US 500,000 or $A690,000). Harry proa’s would be cheaper.

Daniel had to sell the proa a short time after the launch due to the cost involved in the build. He stated it sailed very well but deserved an owner who would use it as a true fast cruiser. The jpegs give the idea of a very interesting boat.

 

@oldmulti Epicure does look very fine, with lots of neat ideas.

I love this photo of the mama proa and the tender proa

 

Wow. I got behind a bit on this thread and it took like a week or so to get caught up. I must be honest, I skip over trimarans. They take up too much space for my pocketbook. And mooring even a 17' wide cat is not without challenges; monetary at least. My wife and I purchased property 0.7 miles inland from the Gulf of Mexico with 50' of water and 50' of dock and moorage. So, all my work building the demountable boat appears to be a little bit of an error. Who knew home prices would nearly double in Seattle in 5 years. We will be able to build a dock for the boat, but gonna wait for the launch. I don't have any great pictures to cobble up this thread, but maybe next summer if plans go right. I'm always astonished by this thread. Even the folding business. When I realized the problems with a wide catamaran on the highway, I wondered about folding, but there just is not enough of it to make any informed decision about it working well. I need a bay boat now, for shallow water work. Been considering Wood's 18' Skoota a bit, but those tunnel hulls (almost catamarans) are awfully tempting. I wonder if anyone has ever gone to the extremes in designing cat hulls with a lot of flare and thus reserve. The idea is taking out 6 people and not dropping too far to run skinny. But, a thread creep here. Anyhow, I just want to salute oldmulti for lots of fun reading. Carry on..

 

It doesn't look too comfy from this perspective.