Multihull Structure Thoughts

Great thread oldmulti.

Firstly the 2% figure does not tell the whole story, or in what conditions the 2% difference occurred.

As Dennis the menace was quoted as saying " Jeeze Brit, even a Turd is tapered at both ends" or words to that effect

Notwithstanding, she was a slow Twelve with big turbulence behind her stern. Neither Ted Turner nor Dennis Conner, (both skippers of Mariner), could avoid her elimination from the Defender Trials of the 22nd America's Cup"

As Catsketcher pointed out a good all round boat for typical cruising conditions should not be dragging an immersed sterns.
Sure, once the speed increase to a point where the flow breaks free cleanly from the stern then this problem disappears.
The reality is this does not occur often enough for any overall advantage for your typical cruiser.




As for current modern production cat design re TS42, we need to remember the manufacturer first and foremost are selling a dream, most owners don't have the skills to utillize small design nuances and the reality of time constraints and weather mean lots of motoring. Marketing hype is just that, and if we really want to own good boats that suit our purpose, then it is on us to learn to sail and take an interest in design.

 

This is an extension to page 37 number 545 about Oceanic catamarans. Oceanics started life in 1963 and was progressively developed into 1990’s. The same basic concept, cruising intent and layout. Just continuous development and many vessels sold to satisfy a market that does not care about all out speed, just the ability to get from A to B comfortably and in safety. The Oceanic 1991 version was a 32 x 16 foot full bridge deck catamaran that weighed 11200 lbs and could carry an additional 6300 lbs payload for a maximum displacement of 17500 lbs. With a sloop rig it has a 42 foot mast and 488 square foot of sail area. O’Brien prefers a ketch rig to lower the centre of effort, but with 17000 lbs of displacement wave capsize is going to be more of a problem than wind capsize. The length to beam on the hulls are 6.7 : 1. The original Oceanics were 30 x 15 foot basically plywood covered with CSM. The later models were solid glass below the gunnel with 12 mm ply CSM glass above the gunnel and bulkheads. These were strong boats. The most famous was Anneliese which circled the globe via the Cape of Good Hope and Cape Horn. Anneliese averaged 116 miles per day (just below 5 knots) for most of the journey with the occasional surf to 12 knots. Anneliese could go to windward slowly. The 1991 version has morphed more into a motor sailor in recognition of the owners saying, reaching and downwind is OK but engines work better upwind. Again, we are talking about what an owner wants versus what is theoretically perfect. This boat is quite refined for what it is EG there are centre boards in each hull to help upwind performance if required and O’Brien has good reasons for the forward deck/wing deck arrangement based on his experience as indicated in the first jpeg.

As I said these boats suit the market they were aimed at and were loved. Anneliese was recently for sale in Queensland and looked very good for a 50 year old boat. The first jpeg is the 1991 model, the second is an older version and a few other jpegs.

 

The Hirondelle catamarans were very popular in a time when multi’s were considered inferior to monohulls. There were several versions of the cat spread over several production runs and manufacturers. They are summarised below.

Hirondelle Mk I – 23 x 10 foot weighing 2300 or 2700 lbs depending on source. In general, the Mk I's had a tall rig with a 32 foot mast and the sail area was 250 sq ft (23 m2) or 330sq ft with the widely used 150% genoa. The Mk I boat has twin daggerboards and lifting rudders and a high percentage of the boats were home completed. The interior layout usually comprises two generous single quarter berths, a large convertible double (cum table) on the bridgedeck and on the starboard side was a small galley and a single berth forward. To port in the bow is the heads - most boats were fitted with sea toilets and a small stowaway wash basin. The Mk 1 had 300 boats built before production ceased in 1983.

Hirondelle Mk II - The important difference between the Hirondelle Mk I and the Mk II was the rig, with the Mk2 mast being about 29 foot. Some minor interior changes appeared, and the cabin windows became slightly larger with a different shape. In the main the design remained the same safe comfortable family cruiser.

Hirondelle Mk III - The major change in the Hirondelle Mk III was under water the daggerboards and rudders were replaced by fixed keels and underslung spade rudders. The new keels are "8ft long trapezoids with NACA-0012 sections, 12.5 inches thick at the base, and with horizontal end plates are now 10 inches wide. These keels are hollow and provide over 600 lbs 0f buoyancy, which is reduced to around 450 lbs of buoyancy when the water tanks in the keels are filled. The effect of these new keels is that the Hirondelle had reduced pitching and minimal leeway. The Rudders, formerly transom hung, have been moved inboard and are now spade rudders with the same NACA section as the keels." Although a greater draught made for less ability to ditch crawl the boat gained in strength and many believe it to be much stiffer under sail. Water tanks could also be sited in the keels.

Hirondelle Family - The Hirondelle Family 23 x 12.5 weighting 2500 lbs and carrying 245 square foot of sail area was born as a result of a Hirondelle Mk III owner, David Trotter, and the original designer Chris Hammond, modifying the Mk III moulds in 1990. The most important differences were a wider beam (about 600mm extra), more freeboard (allowing more comfort in the cabin), the starboard forward berth was removed and replaced by a larger functional galley, the heads became much bigger and even had a shower. The underslung rudders enabled "sugar scoop" transoms to be used. A major improvement in space was achieved by the new bridge deck nacelle has been added to the underside of the wing deck. This increases strength, helps prevent slamming, and gives extra legroom underneath the dinette table, which allowed more foot room at the central table. An Aero Rig was also fitted to some Hirondelle 'Family' boats in place of the conventional sloop configuration. Even though the “family” is larger than the Mk 1 version, at 2500 lbs, it is 200 lbs lighter, owing to the of plus/minus biaxial stitched cloth over a 12 mm balsa core. Solid laminate is only used blow the water line.

The jpegs below give an idea of some of the versions of the Hirondelle. Later today I will talk about the boats structure and performance differences of various rigs.

 

I would like to thank all the people who have contributed to the thread, without your kind words and updates this thread would not be as useful. EG waynemarlow, manuhai who added value after short mentions of their boats. Also, to the builders, designers, researchers etc whose published information has added value to the thread, thank you.

We will now focus on the Hirondelle Family which started production in 1991 by Swallow yachts and production was eventually outsourced to Prout catamarans in 1995 and built to Prout ISO 9000 standard of construction. The Family is 23 x 12.5 foot weighing 2500 lbs and displacing 3500 lbs under normal load. The standard sloop rig had 250 square foot of sail, the Aerorig version had 217 square foot. Although the Aerorig had 33 square foot less sail area than the standard rig it was faster and handier with a margin of about 1 knot (windward) – 2 knots (off the wind in light airs) according to tests (Yachting World/ Practical Boat Owner) between the Aerorig and the standard rig Hirondelle. The length to beam on the hulls is 8:1. One owners’ description of his USA based Hirondelle “She is a joy to sail with her peppy response and comfort. This is an extremely capable cat that has sailed across the Atlantic from England to the United States. The sailing performance of the Hirondelle was excellent in its day, and is still good for a boat of its size, particularly in Mk I form.” I cannot verify the Transatlantic statement but I would not advise it as a regular event.

The structure of the boat is solid fibreglass bottoms, balsa sandwich topsides and decks. The hull bottoms are 300 gsm CSM 3 layers of 720 gsm triaxle solid (approx 5,5 mm thick) from waterline down. The top sides are 100 gsm surface tissue, 600/300 combination mat (600 gsm biax, 300 gram CSM), 10 mm balsa core, 2 layers of 600/300 mat. The hull bridge deck is moulded as one unit, the deck is moulded as a second unit. Under the mast step there is 18 layers of unidirectional glass. The main bulkheads were plywood but I do not know if they were changed to foam glass later. A great small performance cruiser. The initial jpegs are of Mk 1, Mk 3 then the Family version.

 

For those who need a project for the odd day off and want a boat, here is a fine trimaran. Its 16 x 12.35 foot displacing not much and carrying 90 square foot of a few bed sheets or a plastic tarp stitched into a triangular sail. You will have to spend 8 hours building it, but as a 2 person shallow lake or river crosser you should have a bit of fun. Go down to your local hardware store get 3 sheets of 6 mm ply (4 mm if your game) add some 25 x 50 mm (planed all round will probably be 22 x 47), 60 x 40 mm and 50 x 50 mm plus something like Gorilla glue or exterior liquid nails.

Cut the ply according to the indicated plan use some wire to stitch the bottom of the sheets together use the liquid nails to glue together the pieces. The structure is 6 mm plywood, main hull keel is 21 x 21 mm, gunnels are 18 x 34 mm, Float gunnels is 21 x 21 mm, no keel, liberal use of glue fills the gaps. Cross beams are 58 x 38 mm. The A frame mast is 50 x 48 mm. The lanteen spar is 4 pieces of 18 x 48 mm overlapped so the centre attached to the A frame is 4 units thick and the ends are 1 unit thick. Some spare 18 x 34 mm is used to frame the rudder stock with some spare 6 mm ply used as the rudder. A couple screws are used as the rudder attachment point. Some cheap lengths of rope and some cheap exterior household paint and away you go. PLEASE use safety vests (PFD’s) and test in water you can walk to shore. A bit of fun.

 

Continuing along the let’s do an easy boat theme, we will discuss one person’s solution. There are many versions of this type of tri but this looked easier than most. The guy said I have a used Hobie 18 but want a bigger4 boat with a small cab for fun. He said he will use the H 18 hulls as floats and use the H 18 rig. So the solution was to design a main hull and use as much of the H 18 as possible. The tri design ended up being 21 x 16 foot weighing 800 lbs and displacing all up 1250 lbs. The main hull is 21 foot long with a beam at waterline of 2.1 foot giving a main hull length to beam of 10: 1.

The designer did a rough calculation of the basic materials. 4 mm or 6 mm ply (prefers 6 mm) for the sides, 6mm ply for the bottom and deck, marine grade Okume approximately 10 sheets (could be good 5 ply exterior), stringers will be nordic fir (or what you have in your area that is light and cheap). Following his experience, you will need around 30kg of epoxy. (West 105 or similar) and 200 gsm cloth for the exterior. Two more sheets of 4mm ply for the interior, some paint, consumables, bits and pieces. He did not specify the cross beams though.

There are many solutions to the same problem. EG Woods Striker series of tris, the Typhoon which uses Tornado hulls and rig etc. But be warned beach cat hulls are designed for a different purpose and when there used as a float they have 2 problems. One the centre of buoyancy is often not in the right place and if the tri is capable of speed make sure the hulls is longitudinally stiff as a lot of pressure can be put on an unsupported bow. Most Hobie cats are tuff.

 

These 3 are information only, 2 old (12 and 14 foot) and one fairly modern (12 foot) design. The Hobbykat surf cat is a ply imitation of a Hobie 14 and the 12 foot Cats paw is a full flat deck extremely simple cat. If you want a fun cat look on EG E-Bay and buy a Hobie 14 second hand. You will often get one for less money than the materials to build one of these 2 boats. These boats were designed in 1970’s for magazines like Popular Science, Popular Mechanics, Boat builders handbook etc. who occasionally had special boating editions. You will find these types of plans (mainly mono) on many web sites ranging from 8 foot to 30 foot and the plans are direct copies of the original magazine articles. There is also a 20 foot trimaran plan out there but it is so old in concept that it would be difficult to build.

But if you still desire to build a small modern plywood 12 foot catamaran look at this web site of Chris Tucker and his DS 12 cat. http://www.ctmd.com.au/DS12.pdf The plans are pretty detailed but there are no building instructions. As a learner cat for the young for both building and sailing, it could be a good thing. The reverse bows look modern and the structure is how modern cats are built. Have fun looking at the ideas.

 

Vudu or F 12 cat is 12 x 6.5 foot and weighs 230 lbs. The Vudu and the DS 12 mentioned above, both were designed around the same time. There is a big difference though, the Vudu is foam glass construction and has different cross beams. Both cats were aimed at them same market as a youth trainer for people of about 80 lbs to about 140 lbs. The build process for the Vudu is described in the following web site and the build ideas could be applied to a DS 12 cat.

Kiwi F12 Build Pics https://www.catsailor.com/forum/ubbthreads.php?ubb=showflat&Number=243944&page=1

The Vudu cat beams are 60 mm tube x 2 mm wall bent on a 3.15 radius. The initial boat had 63.5 mm tube x 3 mm wall. The foam is 10 mm divinycell with 2 layers of (guess) 200 gsm e glass on outside with a 200 gsm e glass inside with local reinforcement. Polyester would do but vinylester is better. The jpegs give an idea of the hull shape and style. I think the DS 12 plans will fill in a lot of detail.

 

This is some information for TTLF and others who may own desire to own a Newick Tremolino trimaran. They are relatively fast boats in standard 23 x 16.5 foot 800 lbs weight, Hobie 16 floats and rig trimarans. The Mk 4 designs with larger volume floats, 1000 lbs weight and 18 foot beam were genuinely fast boats. But many owners were unhappy when trailering their tri with the set up and take down time of either of the “fixed wing” models. So John Odin (builder) introduced the Tremolino T Gull (and 2300 more upright bow and 25 foot variant) models. Each had folding cross arms to make the boats a lot more trailable.

At one point the following appeared on a web site. “I could sell you a kit to convert your Tremolino into a T-Gull 23, it would make things much easier allowing you to leave the mast stepped, you could use the extra hour and 55 min. to work on making more empties. Also for those interested the displacement #s for the T-Gull 2300 are 2206lbs for the ama in saltwater and 1583lbs for the Vaka in saltwater. Bill the builder Tremolino boat company.” As the Tremolino boat company no longer exists other options for converting a standard Tremolino to a folding Tremolino need to be considered. On page 33 number 489 is a dutch tri that has a nice idea of how to do folding. John Marples 20 foot folding tri (page 28 number 410) is another approach. Also located on the Tremolino owners web site was an option imitating a Farrier folding beam arrangement. I suspect it would have heavier than standard beams but very doable.

The production T Gulls were 2300 version 23 x 18 foot 1400 lbs dry weight displacement 2200 lbs with 267 or 285 square foot of sail area. The 25 foot production T Gulls were 25 x 19 foot 1950 lbs dry weight carrying a Hobie 18 rig of 310 square foot of sail. The jpegs are a combination of 23 and 25 footers the final 2 are some one’s home conversion to act like a farrier, very similar to a Marples 26 tri.

 

Tremolino T Gull meet some market demand but there were requests for a more liveable version. Next came the Argonauta. The tri is 26 x 20 foot with a 6 foot main hull beam at gunnels. The length to beam on the main hull waterline is 8.7:1. The beam folded on the trailer is 8.5 foot and it weighed 1400 lbs with a 330 square foot sail area. The 26 foot versions displaced 2500 lbs and it was claimed they could go as fast as the wing up to Force 5. I need some verification of that.

The Argonauta is a comfortable trimaran suitable for a vacation cruise for a couple or small family. The aft cabin has a full sized double bed (4'6" x 6'4”) and space for a small galley. The center cockpit offers good visibility and the boat can be piloted from the cockpit or from inside the cabin. The bow has a cuddy cabin that can act as a dry locker for sails and rope, or could be converted to a single berth or a porta potty station, and anchor and chain locker. Access is through a large hatch forward of the windshield.

The outriggers are symmetrical (22' feet long) and swing aft for folding for trailing. The outriggers rounded shapes and V'd bottom provide easy motion in a seaway. Each has watertight compartments plus foam buoyancy. Folding and deploying the outriggers is a one person job and deploying the boat from the trailer to the water, ready to sail, takes about 1/2 hour. The hull & deck are a sandwiched construction with bi-directional fiberglass and closed cell PVC core of 4.5 lb. density, reinforced in special areas as necessary with unidirectional glass fibers (Kevlar & Epoxy), folding fiberglass cross arms on which pivot fiberglass outriggers with three flotation chambers.

According to owners the boat is very easy to sail with the wheel steering, sail controls, dagger board controls are in the cockpit within easy reach of the skipper. She is easy to trailer and very stable in high winds with good all round performance.

 

NZ Gray Treadwell design was awarded first prize in the Royal Institution of Naval Architects Concept Boat 2002 competition. His winning design is Jasmin, a 31 foot multi-hull that he calls a bimaran. It folds its 19 foot beam to 8.5 foot for trailering. The boat weighs 2350 lbs and displaces 3700 lbs. The bimaran has an unstayed mast on the “float” hull instead of the centreline like conventional catamarans. The Aerorig has a 280 square foot main and a 160 square foot jib. The bimaran concept is a one direction “Harry Proa” with all accommodation is in one hull and the “float“ hull has the rig in it. Treadwell has owned a 28 ft Great Barrier Express followed by a 43ft Bladerunner but "However, it was a bit of a mission to find someone who wanted to design an asymmetrical yacht. Eventually I persuaded Rob Denney to take a break from proas and we traded ideas till we had a design for a 40-footer W”. W has an unstayed balanced rig and a single telescoping beam, which allows the hulls to pitch independently and vary the beam from 23 to 13 foot beam. W displaced 1350 lbs.

Jasmin has the same concept of hulls pitching independently of each other, within limits, which allows them to walk over the waves for smoother, drier sailing. Treadwell claims the result is a lighter, stronger boat. Treadwell "The engineering looks radical, but high modulus carbon structures and kevlar ropes mean we have to adjust our vision to what looks right. Sometimes things look undersized when actually they are way over strength. And vice versa. There is no substitute for detailed engineering analysis. "

"Putting the mast in a hull means you don't need a stiff structure between the hulls to get good sail shapes. You need only one beam, which can pivot, and this removes torsion loads and minimises fatigue. Also the stays between the hulls can have some stretch, again reducing peak loads, and you get a simpler folding mechanism. Conventional wisdom is the hulls must be exactly parallel. So we ran some actual comparison measurements. These proved you go faster as the hulls walk over the waves rather than pushing through."

The jpegs give the idea. The first is of W the Denney initial design. The remainder is from Gray Treadwell Jasmin. The final jpeg is of 40 foot folding Harryproa designed by Denney.

 

While I am the folding multihull thing I get frustrated that there has been no real success with folding cats since the Stilletto series. The Stilletto’s suffer from the usual problem of sliding tubes that they bind a little as you fold or unfold them. But here are alternatives shown before on this thread. The Clissold TC 750 folding cat was another sensible attempt. The 24.5 x 18 foot cat could be folded down to 8 foot for trailering. The boat weighed 2100 lbs and carried either a biplane rig which keep the masts light and easy to handle, and keep sailing simple or a conventional sloop rig. According to Tim Clissold the beams and mounts would essentially be carbon fibre, so no reason for them not to be more reliable than alloy. The lower strut is still 300mm above the water line, similar I would suggest to many (accepted) folding trimarans. This is above a spray rail, so some water will be deflected down in that area. The hard floor at centre is below the water when folded; a compromise to get sailing beam, and depth into the centre cockpit. The intention is to put the boat on the trailer once folded. The hard deck would provide diagonal rigidity.

Tims words from here “I have an 8m cat design (Hard Drive) built from 4mm plywood, ie is very light, that has been thrashed around the Hauraki gulf for ten years and is still in one piece. Construction is mostly flat panel, or developable panels for quick prototyping and production. Either plywood or foam sandwich is fine. Its a performance sailing catamaran designed for comfortable cruising, and club racing. The hulls feature forward raked bows for wave piercing, and chine rails to reduce spray at speed. Inside there are berths for up to six, with two cosy double berths aft. There is a galley to port and head area to starboard. Rig options include a conventional 3/4 sloop rig, or twin cantilevered masts out of each hull, as shown. The mainsail(s) are square topped, and are boom-less for crew safety.”

Now I do not know if the carbon fibre folding system is available but I hope so as it would with a biplane rig as it may be as easy to launch and recover as a Farrier. The jpegs give an idea. The TC 750 first, 2 of an TC 850 sailing and the last 2 are of a Stilletto 30.

 

I have been playing around with folding cats for about 18 years. I used to have ideas about selling plans but that market has dried up. Still I developed two folding cats that work well. It usually takes me about 20 minutes to get from the launch ramp to pushing off and motoring away from the ramp. The boats work really well.

One of the problems with folding cats is that the designs that look good on paper, like the Takeaway and the Clissold design above use pivoting beams that work reasonably well when fully extended. When folded the structural integrity of the beams reduces dramatically. Think of a book half closed and then you try to rip it apart - it will do so rather well. On my designs I need to include a forebeam to stop the weight of the floors and folding mechanism to stop the inward rotation of the hulls. Also the folding truss shown is marginal in supporting the huge load of the mast compression in dynamic situations. It is better to use an inverted vee in my opinion. That part of the design has never given me an ounce of concern and is pretty much bulletproof.

You learn that there are lots of little known loads pretty soon when you actually build and use a folding cat. The designs seem much harder to design than a Farrier type tri. This is because you need to work out the folding floor mechanism and some sort of mast support that all work in all extensions from fully out to fully folded. On a tri all you have to design is the folding mechanism, in a cat, there are floors and the mast system, which took me years to work out.

For those who are interested I have a video showing my folding cat. I have tried to find a builder who is keen to build these, or a version of them but this has proven tricky. Anyone keen to build these can contact me on philthompson67@gmail.com

 

Nice looking boat Phil. I remember there was a brief period when you had a website up and were offering plans. Did any others get built? Looks like the sort of concept that should be commercially viable. Any idea how a production version would have compared price wise with the obvious folding tri competition?

 

I jumped the gun with the first website. It took a while to get what I thought were mere wrinkles, sorted out properly. There is another 7 metre sistership building. As to cost, I have no real idea. I thought it would be about the same, as the beams are much simpler than Farrier style beams but there are two interiors to make.