Multihull Structure Thoughts

This cat in advertising claimed to be “fastest production weekender in the world”. In 1979 it may have been correct. The cat is a Viva 27 27.7 x 15.9 foot weighing 1750 lbs and carrying a 375 square foot main and 200 square foot genoa. It was designed by Bowie Houghton. This cat was FAST. Its IOMR rating is 1.05. Its real interest is that it’s a genuine trailer sailor. It is not as fast to transition as an F tri but it could still be done in under an hour. The hulls look like an over blown beach cat but still had enough room for 4 bunks. The hulls were built of polyester solid fiberglass with stringers, shelves and bulkheads for rigidity. The folding system is based around aluminium cross beam tubes that have a hinge in the middle. So you lower the mast and winch the hulls together in the water with a rope from each hull pushing the trampoline and cross beam tubes upward. You then float the folded boat onto the trailer. The aluminium cross beam tubes look around 200 mm in diameter. The central hinge brackets look like a U channel about 900 mm long. Very few of these boats were produced. But of the limited reports I have read this boat could sail fast under main alone with the roller furling genoa as the real go fast item. A spinnaker adds further speed. The concept of this boat has been replicated by Thomas Firth Jones in his 23 foot cat and Newick in his Maine cat 22. Pity there are not production versions of this idea today.

 

Sea Falcon was a racing cat used in various races. The boat performed OK but at that stage the French were developing much more aggressive designs which were very competitive. The boat is 70 x 32 foot and displaces 19,000 lbs. The main and genoa totalled 2240 square foot of sail. The real issue with the boat is the 13:1 length to beam ratio on a 60 foot waterline. The righting moment was lower than some of its opposition which means combined with the shorter waterline meant it could not be powered up to the same degree. The boat crossed the Atlantic several times in various races and came 4 th in the Round Britain and Island races. But the real interest for us is the design of the main cross beam. This is a timber ply beam. The beam is very well designed but would require 3 things. Excellent timber, superb specially built plywood, great epoxy and really good builders. Each panel of ply is 6 layers of 2.5 mm ply laid at 45/45, or 15 mm thick per sheet. The multiple timbers are 50 x 85 mm and 50 x 65 mm for the beam structure. For those who aspire to building a large boat figure out how many hours would go into just this cross beam. No wonder foam glass with unidirectionals have taken over for cross beam structures.

 

Dick Newick designed many fast tris but the one that helped him become famous (for the wrong reasons) was Gulf Streamer built in 1973 and came second in the Around Britain and Island race in 1974. The boat was 60 x 31 foot weighing 13700 lbs and carrying 1350 square foot of sail upwind in the main and genoa. The mast was aluminium and 53 foot high. The boat was built of foam glass and polyester resin. Gulf Streamer was capsized by a rogue wave in the Gulf Stream in 1976 and subsequently recovered by a passing Russian ship. Russian sailing enthusiasts rebuilt the boat and sail it now. The boat was built for Phil Weld a newspaper publisher, who after building 2 other Newick tris, eventually won the OSTAR. Just to give you a sense of the development of 60 foot tris over time I have an additional jpeg showing how the latest versions are 60 x 60 foot with 100 foot masts and over 2500 square foot of sail.

 

That beam does look a little strange. I don't get why you would build a beam this (with so many shear webs) unless you were trying to get a beam that could also resist torque. The fore and aft beams are alloy and so would not be hugely helpful in resisting twisting. To design this to be stiffer and easier to build, I suggest modern builders would use a stiff aft beam as well and use more normal box beams instead of the large main beam. Doubling the depth of the main beam increases stiffness by 8 times so adding a little more depth on a normal box beam would have made the beam much stiffer.
Here is the same design with the box aft beam added.
https://www.cruisingworld.com/cat-tale/

 

If you look at the picture where Gulf Streamer is in the snow you can see a rather shoddy piece of engineering, in fact the whole aft end of Gulf Streamer is badly done. The companionway cuts the aft beam. I talked to Dick and he said that you sometimes could not close the companionway hatch because the boat flexed so much, you had to wait for a wave to get it shut. Also the curved cockpit meant that the boat could bend up like a banana from backstay tension. He changed this part of the design when Phil Weld replaced Gulf Streamer with Rogue Wave. Rogue Wave was lighter and much stiffer, and made from wood. Before stitched fabrics and unis, foam and glass was not necessarily the best material to use for boatbuilding.

Like Knox Johnston, Weld also re-used the same basic hull shape in his multihulls. Attached is the web page from Dick Newicks site about Rogue wave with a nice photo showing the difference with Gulf Streamers cockpit shape.

Rogue Wave trimaran photos - Dick Newick http://dicknewickboats.com/roguewave.html

When I built a Newick trimaran, we made special effort to ensure the load path aft was continuous. Also we did not cut the beam at the companionway requiring a duck of the head to get inside.

 

I agree with Catsketcher about Gulf Streamer rear end. And as we will see with Rogue wave later today and Moxie there is a progressive development to simpler shapes and improved engineering. The comment about Sea Falcon's beam structure is good. I agree that cats especially need a "stiff" structure at the rear to minimize any torsional movements in the hulls and as has been seen with the Hitch 50 Wired is another approach. Full bridge deck cabins have a similar effect of creating a big torque box to minimse torsional movement in cats. Crowther's open wing cats cross beam structures had a mast support beam of more than twice the "strength" of a rear beam, but the rear beam was generally a reasonably sized box section of lighter materials. Tris have different beam needs based around where the rigging is attached, the dimensions of the main hull structure and the float shape and volume distribution.

 

Rogue Wave was Dick Newicks second boat for Phil Weld. The boat was 60 x 32.5 foot weighing 10,000 lbs and displacing 16,000 lbs. It carried 1450 square foot in its main and genoa. This boat was built as a replacement for Gulf Streamer but tried to fix a few of the areas of concern. As you can see Rogue Wave was 3700 lbs lighter, was 1.5 foot wider, carried 100 square foot more sail area on a higher mast and had a stiffer hull structure. Dick learnt from Gulf Streamer and did significant upgrades, the major being its construction method. As Catsketcher has pointed out the stern of Gulf Streamer flexed requiring a slight redesign and better construction technique. The Gougeon brothers contracted to build Rogue Wave and delivered the boat on time, on budget and on weight. It took just over 10,000 hours to build. The structural details are in the attached jpegs but this is done by some very skilled craftsmen. The bulkheads are 12 mm ply, some float bulkheads are 9 mm ply with ash or spruce supporting frames, hull skins are 2 layers of 6 mm ply, decks are 12 mm or 9 mm ply. The main cabin roof is 75 mm thick with ply either side of a 60 mm Verticell honeycomb core. All done with West epoxy. This boat could seriously sail fast in all conditions (10 plus knot averages, 20 knot plus peaks) and made a great cruiser as well.

 

The final in our trilogy of Newick tris for Phil Weld. Moxie was built because the rules to the OSTAR where changed which prevented Rogue Wave from competing. Moxie was a 50 x 33.3 foot trimaran displacing 10,000 lbs carrying 1150 square foot in the main and fore triangle. This boat with Weld, who was in his 60’s, at the helm won the OSTAR. It was a fast boat that according to Welds book was seakindly as well. It had fuller floats and a finer main hull than Rogue wave. The name Moxie was Welds contribution to a small soft drink manufacturer whose product was liked by Weld. The construction of the tri was basically ply, cedar and timber. Main hull and float skinned with 2 layers of 6 mm cedar cold molded. The keels are 3 layers of 19 mm mahogany with sheers 2 layers of 19 x 50 mm spruce. Bulkheads are 12 mm ply. Decks are 9 mm ply with glass cloth over. A very similar structure to Rogue Wave but with only 2 cross beams. A cruiser version of Moxie was created with a wider waterline on the main hull to take additional berths and pay load. The jpegs are of the original Moxie. The partially built tri is of another Newick design that gives you an idea of the framing involved in a Moxie type build.

 

The attached jpeg shows the difference between 2 Crowther catamarans. The 65 foot charter cat is 65 x 28.5 foot displacing 50,000 lbs with 1800 square foot of sail in the main, mizzen and foretriangle. On the waterline the length to beam of the hulls is 10:1. The 60 foot racing catamaran is 60 x 31 foot displacing 16,000 lbs with 1650 square foot in the main and foretriangle. On the waterline the length to beam ratio is 16:1. Each boat carries a spinnaker of 3500 square foot. Now lets look at what is required to drive the boat at 12 knots under power. The 65 foot charter cat needs two 75 horsepower diesels, the 60 foot racing catamaran requires two 25 horsepower diesels. The engine horsepower requirements reflect how much power is required to push the boat. The rigs are of similar size and would generate similar “power” on a reach but the 60 foot racing would be able to go significantly faster under sail due to a better hull shape and less weight to push through the water.

This high lights the effect of weight in multihull design. Weight costs money. Both boats are foam glass with some Kevlar in the racing cat. But I would ensure you the build and fitout costs of the 60 foot racing cat would be a lot lower than the 65 foot charter cat if done by professional builders. Adrian Rogers who built the 60 foot racing cat built most of the boat with himself and one other guy and occasional assistance of a student. Basically a full time home build. The 60 foot racing cat was a relatively cheap boat.

But you say the real difference is in the accommodation. Yes agreed. But in the world of 52 foot bridge deck cats that have similar accommodation, the cruising displacements can range from 25,000 lbs (Raku 52) to 57,000 lbs (Lagoon 52) with hull length to beam ratio’s of Raku’s 12:1 to the Lagoon 7.2:1. The lighter (25,000 lbs) cat would be cheaper to build for a home builder, fitout (smaller engines, winches, ground tackle etc) and would be faster under sail. The Lagoon being a full production cat with moulds would take less manhours to build but being a composite core boat would still cost more in materials as the structure would require more materials to take the additional 30,000 lbs of displacement. Translation light boats are often cheaper and faster. The jpegs are of 60 foot racing cat now used in charter. I cannot find a photo of the charter cat.

 

This is the final in a series on Newick for a while. This 1980 cat is very interesting on many fronts. The cat is 44 x 22 foot weighing 12,000 lbs and carrying 690 square foot of sail in the main and foretriangle. This is a charter boat with a deliberately small rig.

The cats interesting feature. Its simplicity of build. Build a 24 foot long by 6 foot wide frame with stringers as a former. A 6 foot circular radius is put across the 6 foot width of the former. You then lay and glue together 3 layers of 6 mm cedar or ply onto the former to form an 18 mm thick panel. Create a second panel scarf them together and you have half a hull. Create another half hull and after a little shaping join the two halves at the keel line insert some 12 mm bulkheads and you have a hull shape. Tape inside and outside at the keel line and up the stem. This is a fast build method that can use cheap materials to get a hull shape. The hull will have minimal stringers and framing as it is the equivalent of an 18 mm thick monocoque hull similar to a constant camber hull build. The half hull panels can be “tortured” fore and aft by about 300 mm to form the full hull shape.

Compare this boat to say a Raku 44 by Grainger. The Raku 44 is 44 x 23.5 foot weighing 13,000 lbs and carrying 1010 square foot in main and jib. The Raku 44 has a 12:1 length to beam. The Newick 44 has a 13.2:1 length to beam. The Raku has a better hull shape for reduced pitching with lower wetted surface. The Newick 44 would have a softer ride through a seaway. The Raku would be faster due to its additional sail area. The Newick 44 could have higher mast with another 300 square foot of sail without a problem. In cruising mode, these boats would probably be minutes apart after a day sail.

But the big difference between a Raku 44 and the Newick 44 would be the amount of hours and cost to build the boats. The Raku 44 is a modern composite foam glass build with all its associated fairing etc. The Newick may be wood but if done well with a deck cabin will achieve the same outcome in less build time. Unfortunately the downside to the Newick would be at resale time. The fiberglass Raku 44 would get twice the money of the wood Newick 44. The other downside is the equipment and fitout of both boats would be the same costs for a similar finish, so you may save 50% on the hull structure cost but you will only save about 20% on the total cost of the Newick. There are no jpegs of the cat.

 

We have spoken about this boat before but the following has more detail. The following cat is how you take a concept to the limit. The Tornado 20 foot cat is a tortured plywood design using 4 mm ply. Walter Beadling and Bob Cruger decided to take it to the limit and build a 38 foot cat using 9 mm ply. Most people thought 6 mm ply was the maximum you could torture. The cat is 38 x 19 foot weighing 8000 lbs and carrying 700 square foot. The plywood for the hulls were manufactured into a 40 x 8 foot sheet of 9 mm Util mahogany. 4 ply panels were laid together then cut to size. The gunnels of 65 x 65 mm were glued to the deck edge of the ply. 3 mm copper wire was then tied every 150 mm along the keel and stem line. The panels were then set apart at 120 degrees (the text says 180 but 120 is correct) from the centre line to the stern. The keel had an epoxy slurry poured inside then glassed. The hulls were turned over then glassed on the outside. Then the fun part, Spanish windlasses were used to persuade the sides to a hull shape. Then the stern and 3 bulkheads were then inserted into the hulls and taped to the hull inner surface. The exterior of the hulls was lightly glassed. The remainder of the boat had 2 timber cross beams and a ply bridge deck attached. The boat was intended to be a coastal cruiser and had a successful sailing time including some brushes with sea ice. Interesting concept.

 

This cat was built by Prout (yes the cruising catamaran people) as an experimental racer cruiser built in 1978. It raced successfully in Britain for several years. The full bridgedeck cat is 40 x 19 foot weighing 5000 lbs displacing 6000 lbs carrying 610 square foot in the main and fore triangle. Yes, the weight for a 40 foot bridgedeck cat is 5000 lbs. Study the attached jpeg and you will start to understand why. EG the hull skin is 4 mm ply with 19 x 38 mm tapered stringers at 150 mm centrelines. There is a 6 mm ply shelf in the hull at bridgedeck level. There are 6 mm ply bulkheads. Gunnel is 70 x 19 mm. Decks are 6 mm ply with stringers. The main crossbeam bulkheads are 7 mm ply with a timber matrix inside with an EG 22 x 22 mm basic top flange with a doubler 22 x 22 mm over the centre 10 foot. Time spent studying the detail of the jpeg will be useful. This is not an offshore boat but it could do coastal sailing well. It is possible to build a really light plywood timber cat if you use good materials and sensible design.

 

Alex Kozloff was a pioneer in many aspects of beach racing catamarans and over time moved up to C lass cats and then developed D class cats. D class cats have one rule 500 square foot of sail area. Any thing else is optional length, beam, number of hulls, sail configuration, mast height etc you choose. The jpegs is an article about Alex's design process for a D class cat, design detail, structure thoughts and rig configuration. There is a lot of design detail in this article and you could build a D class from it. The hull specs done today would probably be a lighter stiffer layup and the aluminium cross beams would probably be carbon fibre but the concept would be very similar. The cat is 32 x 18 foot weighing 850 lbs and carrying 500 square foot in the mainsail and wing. A modern “substitute” layup for the hulls could be a 400 gsm 0/90 carbon fibre 12 mm airex and a 400 gsm 0/90 carbon fibre if it was done in a female mold. The wing mast could be lighter also. D class cats have done Newport to Esanada races but I would stay with around the bouy racing myself. A good article. The final jpeg is of a later D class that Alex designed and had built.

 

An interesting site showing some build photo’s of a Looping 50 catamaran. Very few details but showing the build process from TomCat custom boat building. http://tomcatboats.com/custom-projects/ Another site featuring the same build is Building: The Looping 50' — Steemit https://steemit.com/blog/@thebongdruid/building-the-looping-50 The boat is a corecell build with plywood box beam with timber strips for rear beam and a plywood timber frame build for the main beam.

 

John Patterson has designed since the early 1970s. John’s work has involved small trailerable tris and cats that utilize innovative folding and righting strategies. His 44’ live-aboard tri is “Buddy”. Buddy is for sale, It’s “Fast and beautiful. I've lived aboard my 44' cruising-racing trimaran “Buddy" for 17 years. Buddy is well maintained and loaded with all the proper gear to take you on your next adventure. Rig is a true cutter, mainsail, stay sail and genoa can all be set at the same time. Dagger board forward and low aspect ratio fenced keel insures great upwind performance. If you have owned a cruising catamaran and didn't like the performance then this would be a great boat for you. It sleeps 6 in 3 cabins, queen size aft, double forward and 2 singles in the main cabin.”

Why is Buddy of interest? Because John designed a 21 foot tri that have threads pleading for the design to be published. There were 5 of the 21 footers built and John is willing to let the design plans be published if anyone has a copy. John will not provide any builder support if plans are found.

Back to Buddy. The 44 x 31 foot tri weighs 9800 lbs carrying a 54 foot carbon mast and 1326 square foot of sail in main and genoa. The boat was built of 600 gsm 45/45 e glass 15 mm WRC 300 gsm 45/45 e glass epoxy. The hulls were built from a “master” section shape that simplifies building. The tri has 200% floats. The boat has done thousands of sea miles and is very comfortable. The attached jpegs give the idea of Buddy and the small tri.