Multihull Structure Thoughts

This may be the final entry for 2023, I will be back in 1 January 2024, have a happy holiday. Today we will talk about a sailing cat company that will sell you a build slot in 2025. The Lightwave catamaran company produces 3 to 4 “Lightwave 46” sailing or power catamarans per year. Lightwave yachts was established in 1996 by Rodger (a shipwright by trade) and Louise Overell and have produced high quality foam glass mainly sailing cats ever since.

The Lightwave 46 is 45.9 x 24.6 foot with a light displacement of 16,535 lbs and a loaded displacement 24,251 lbs. The 61 foot mast carries an about 700 square foot mainsail and a 487 square foot genoa. This cat is a semi custom with the same basic shell but you can have a performance rig, a cruising rig, mini keels and/or 1 or 2 daggerboards etc. So, I will not do more on the sails but many options are available. The length to beam on the hulls are 11.5 to 1. The draft over the mini keels is 4 foot but with optional daggerboards it can be EG 7 foot. The underwing clearance is 3.2 foot. The engine options are inboard diesels from 30 HP upward.

For comparison of what the Lightwave 46 is about, a Lagoon 46 light displacement is 34,800 lbs and loaded displacement near 50,000 lbs and has a 75 foot mast and length to beams in the 8 to 1 region etc. The Lightwave 46 is a high performance cruising cat with good accommodation for private owners. The Lagoon 46 can sail well but has more emphasis on accommodation and is aimed at the charter market.

The Lightwave 46 has 3 or 4 double berth cabins depending on weather you have the galley down or up on the bridge deck. There is a toilet in each hull. The main saloon can have the galley up stairs with saloon seating and navigation area. The aft cockpit has a large opening door to the saloon to form an integrated area. The helming and sail handling is done from a raised protected area in the cockpit where the helm person can see the sails and has a 360 degree view. Your choice of many interior finishes and fitout equipment. There are many storage areas for additional ropes, gear toys etc. This is a well developed performance cruiser, not a floating hotel.

The build is well developed as a foam glass vinylester resins built under vacuum. The unique monocoque construction method unifies interior composite furniture & parts into one extremely strong structure, highly resistant to torsional loads. This is a well engineered and built design stemming from Tony Grainger with Rogers input.

No performance figure found beyond many happy owners. My calculator says 10 knot averages possible with peaks of 20 knots in the right conditions.

The jpegs give the idea of a very good fast cruiser. See you in 2024.

 

Thank you Old Multi for another year of information. May the Gods of Multihull Knowledge smile on you with Xmas and New Year blessings. I think I can hear a sack full of information coming down the chimney and heading towards 2024. I wonder if it contains something about an exploration of the Ultims about to set off on a RTW race?

 

Thank you Phalmes for your kind thoughts. Just a short one found on the Farrier group web site. A short video testing carbon fibre tubes against metal tubes. Good insites.

 

Yes, it is 2024 where I live and I said I would be back Jan 1. Just a small start before I do a serious entry latter today. There are reasons why people want the PT Eleven Nesting Dinghy from PT Watercraft, it is about the quality of the build and the design. To give you an example of what I mean have a look at the quality of main hull of Russell Browns new tri. Russell has designed and been building the light 29 foot tri for his use over a year or so.

Check the reflections of the fluro lights on the hull surface. That is a very fair main hull (WRC to flair chine point 6 mm ply above). Hopefully the tri will sail in 2024

 

We have done this tri before but recently a Wayne Barret M80 tri came up for sale. Its claim to fame is this “M 80 Trimaran professionally built. Every single item is carbon fibre.” Interesting, then looking at the jpegs shows a well finished tri but with flat panel chine construction in the hulls. This needed some follow up.

This specific M80 is 25.95 x 19.2 foot (folding to 8.2 foot) with a weight of 1230 lbs (standard is about 1900 lbs) and the displacement is 3000 lbs. The standard M80 carries a 36 to 40 foot aluminium mast depending on the option and carries a 160 square foot self tacking jib and a 250 square foot main. This M80 carries a Selen carbon fibre mast and boom. Main hull length to beam is 7.4 to 1. The draft is 1.2 foot to 4.8 foot over the main hull based daggerboard.

Now who did the build. Lightwave Yachts in QLD build light cruising catamarans but the owner Roger Overall occasionally takes on secondary projects. Roger built a foam e-glass M80 for a client and had a lot of the build infrastructure available at his factory. A Melbourne based client did a deal to use the infrastructure and with Roger’s help build an “all carbon” light weight version.

So, what are the build options. A standard M80 is built from mainly 6 mm and 9 mm plywood with a minimum of timber and taped seamed joints at the chines. A square metre of 6mm Okoume/gaboon ply weighs 3.1 kgs and requires .5 kgs (2 x ~.75 kgs/sqm coats each side) of epoxy to seal it. Total 3.6 kgs/square metre.

Some people “beef up” the structure and do a plywood version of a M80 with 6 mm ply with 300 gsm cloth (double below the waterline) weighs 3.6 kgs per square meter and 9 mm plywood with 300 gsm cloth which will weigh 5 kgs per square meter.

But if you want to go lighter you can do a 6 mm H 80 foam and 400 gsm skin either side hull deck structure. A square metre of 6mm H 80 foam weighs .5 kgs, plus .2 kgs per side to fill it, 0.8 kgs of glass and 0.4 kgs of resin to wet it out (assuming infusion/bagging). Total about 2 kgs, half the weight of the ply.

Now if you do an “all Carbon” version you could do 300 gsm carbon skins on 6 mm H 60 foam which if built well by infusion would lower the skin weight to about 1.6 kgs/square metre. This version will have to be infused and the surface of the foam “prefilled with a light weight filler” to minimise resin take up. Also, the surface finish should be a very good paint job to minimise any water ingress (very light skins can be porous if not infused fully).

As you can see there is a large difference in shell weighs between the standard plywood and full carbon fibre build weighs. The main difference in use will be the plywood tri will take knocks but be slightly slower, the Carbon fibre boat will have to be treated very carefully near land and on a trailer but will be a faster tri when sailing. In short choose if you want a cruiser occasional racer or a racer occasional cruiser.

Those who have sailed the M80 are happy people reporting good all round performance.

The jpegs give the idea. The jpegs are from several different boats but the majority are of the CF build.

 

Nice boats the m80 ,a "farrier like " folding tri but a much simpler build I considered building one at one point, the orange one in the picture was built in Brazil I believe...the m80 website seem to be down atm hopefully not gone forever

 

An update on an entry on page 63 of this thread. Kurt Diekmann is an air plane constructor and yacht designer from Munich Germany. His tri Archeopterix was built in 1999 and has crossed the Atlantic with its good sailing performance. The tri is 32.75 x 20.35 foot capable of folding to 7.5 foot wide (whilst on the water). The draft ranges from 5.5 foot to 1.5 foot. The tri displaces (probably weighs) 4500 lbs. The sail is a sloop with a mainsail of 290 square foot (has 3 reefing points) and a furling jib of 215 square foot sail area. A 33 square foot storm jib is available with a sea anchor: a 280 square foot parachute is used as a sea anchor and holds the bow into the wind in any condition. There is no traveler in the cockpit to take up space, instead the mainsail is controlled by 2 sheets, each with a triple pulley setup for perfect control. The engine is a Yamaha F9.9 AEML high-thrust outboard in a center well location.

The construction is Marine Plywood with Epoxy West System, and a light fiberglass external finish painted in white epoxy paint. But the absolute joy of this tri the simplicity of construction. Look at the internal jpegs. Minimal framing and stringers depending on bulkheads and internal furniture for reinforcing of the “monocoque” hull structure. The hull shape does a lot of the longitudinal hull reinforcing with its fiberglass taped chine lines. My GUESS is the hulls are from good quality 9 mm plywood. The cross arms are simple aluminium mast sections with a simple to construct folding system. Judging from the jpegs its effective as well. This keeps things simple to build and maintain allowing lots of time for exploring and sailing. The initial tri was built in 2 years part time, a second boat was done in 1 year 4 months from start to finish by mainly one guy.

Now the update. There were about 10 of the “Clou 10” trimarans built. This specific tri was built between 1995 and 2000 in Germany and sailed to the Caribbean where it was purchased in 2015 by a Dutch guy. The Dutch guy returned it to the Netherlands sailed it for a year then decided to refurbish the tri and rename it to “Chilli con carne”. The jpegs give an idea of the work involved which in parts was a strip back to basics and redo. In 2021 it was relaunched for sailing.

The jpegs give an idea.

 

Oldmulti, in another thread by myself i asked about timber epoxy beams for my trimaran i'm building 30ft x 22.5 ft 2200lbs and being similar to a bucc 28 .I found back in post 177 , you said.....
"Next is a plywood trimaran. The trimaran plan is for a 28 foot tri that could be easily be extended to 30 foot. The structure of the tri would be the same for a 30 footer. So I will use the full plans for the Buccaneer 28, a high performance tri with aluminum cross beams. The plans are available at MediaFire https://www.mediafire.com/folder/aaltgc3owsb1u//Buccaneer%2028 If you want to have timber cross beams another tri of the same general size and displacement has a forward beam with fore and aft 9 mm ply webs, 240 mm high in the middle, parallel over the mid 1.5 meters and tapering at either end to the thickness of the flanges. The top and bottom flanges are 2 layers 140 x 19 mm clear oregon. The cross beams bulkheads are 30 mm thick every 700 mm with the cross beam bulkheads at gunnel edges of the main hull and floats 100 mm thick. The rear beam is the same structure but the webs are only 200 mm high."
Which kind of answers my question i asked from my thread, Do you remember which design you quoted from for the wooden timber ones you describe ... was it maybe the seaclipper 34 or 28

 

Adrian. The tri being "quoted" was a theoretical 30 tri, not a real tri. The cross beam dimensions for safety would have come from a Seaclipper 34. In your tread you have a part plan of a Seaclipper 28 cross arm that would be more than adequate for your proposed tri if it is built to the weight you anticipate. The righting moment of your tri is only 10% more than the Seaclipper 28. Mr Marples designs strong structures to allow for home builders so when he specifies hulls he uses EG 9 mm where others use 6 mm ply. The same applies to cross beam structures. Never have I heard of a Seaclipper 28 structurally fail unless it was due to poor maintenance. A few jpegs below of a Seaclipper 28.

 

Thanks again OM

 

Seaclipper 28 beam and good example of a simply constructioned counterlever beam

 

This is about what it takes to get a commercial vessel certified under Det-Norske Veritas' rules for high-speed light craft. The following is only part of the certification process and clearly indicates the reason why small craft naval architects stay with there craft and commercial craft Naval Architects charge a lot of money for there designs. Small craft architects design a boat based on some calculations and a lot of experience. Commercial boat designers have to prove to certification authorities that a craft is correctly engineered prior to the vessel being built.

In modern production sailing catamarans design firms like VPLP have the in house resources and technical capability of meeting EG Det-Norske Veritas' rules but the majority of small vessel designers cannot or choose not to meet the Det-Norske Veritas' rules as a client could not afford the expense required. Please understand many small craft designers will do an excellent design job but don’t expect a perfect design.

Back to this design study of an 80 metre (262 foot) aluminium power catamaran that can be a cargo ferry. The overall length of the K50 class vessel is 80m. The vessel is powered by four Ruston 16RK 270 diesel engines, each rated at 5,500 kW, and using a propulsion system consisting of four steerable KaMeWa 80 waterjets. This gives a service speed of 47 knots and a sprint speed of 53 knots. The main deck is configured for up to 89 vehicles. The aft deck is capable of carrying large heavy vehicles such as buses or fast freight. The second deck accommodates up to 400 passengers with all essential services.

The company doing the verification of the design study is Strand7 consulting using a software package called Strand 7. The software package does a complete three dimensional global strength analysis on high-speed catamaran vehicular ferries more than 50m in length. The software only has to analyse 10,179 nodes, 8.625 beams, 12,781 plates and do 60,990 equations on each run. Yes, some computing power is required. The result of the global strength analysis was to evaluate the allowable global stresses and the buckling capacity of various plate panels, stiffeners and girder systems. Remember, this is only part of the verification of Det-Norske Veritas' rules.

The real purpose of this work is to verify the design is capable of going through a seaway without a structural failure due to twisting and bending through a seaway.

The jpegs give an idea of the concept design and its structure. The twisted cat structure is an extreme example of the theoretical limits the design could reach (not realistic).

 

Indeed.
Not many people realise this...nor the amount of work required in doing such.

Not just FEA of global strength. Even simple things like crane foundations are now required by Class for approvals:

 

This is a Russian design that started out being a canoe that could be broken down into 3 components for storage and transport. The original design was to be a round bilge fiberglass design but the designer converted the canoe to a chine plywood version and said there would be minimal impact on speed and be easier to build. The ply canoe design was 16.9 x 3.15 foot but later floats were added to form a sailing trimaran. The 17 foot aluminium tube mast carries a 57 square foot mainsail and a 26 square foot jib. Later a 65 square foot “flying jib” was added. The leeboard draws 1.7 foot when down.

The canoe was converted into a collapsible sailing trimaran which according to the author is significantly safer and practically faster, since when the wind increases, a relatively large area can be carried. This is a 2 to 3 person design for sailing. The reported sailing speed is 6 to 9 knots when sailing in moderate conditions in 1 foot waves. As you will see with the structure this is a sheltered water design not intended to be pushed hard.

The construction is ply timber with aluminium cross beam and mast tubes. The floats are Styrofoam shaped as required. The keel is 40 x 70 mm, 6 mm plywood shell with 40 x 40 stringers and 45 x 45 mm gunnels. The 3 hull components are joined by 8 mm bolts on each corner of the join. The 6 foot long shaped foam floats are covered by 1.5 mm of fiberglass. The cross beams are 40 x 2 mm aluminium tubes. The rudder and lee board is a wooden foils. The mast is held up by 2 mm stainless steel wire.

The drawings give a lot of detail. A Russian dictionary helps but boating terms don’t always translate. An interesting design for someone who has a minimum of storage space.

 

The pictures are the four jet units on the queen Beattle been fabricated from scratch and me also standing Infront of the Queen beetle when it was turned around and had and to have the deck part placed on top then returned the shed.






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Austal Hull 396 - Queen Beetle - Showcase Video - YouTube