Multihull Structure Thoughts

Oldmulti
Bob Perry has requested the link to his book be removed he actively promotes and sells his book through his publisher he has made a start of proceedings to have it removed from the site also. Many thanks.

 

To the Moderator and to Robert Perry, I apologize and the link entries entries have been removed by the moderator.

 

We built a set of beams for Mike Jeff's Tiki 46 We built them to the stock shape and style replacing the wood with Coosa. Coosa does not have the long timber strength. We used unidirectional tows for the top and bottom flange reinforcement . We added local reinforcements as required for cleats and lashing protection and other fasteners. We filled in the "hollows" of the I-baem shape with Divinycell to keep weight down and glassed them. This was three years past.

 

Hello Oldmulti, SolGato and Revintage,

I'am Michel from Germany and I'am the designer of the Husky 6.2, "Mama Cocha" being the prototype. There was a question about the bow up attitude of the amas. To be honest, this was an accident. And the story is as follows ... .Michael, the builder from Brisbane wanted to have a Farrier folding system (ffs), because he wanted to trailer the boat regulary. The Husky 6.2 is designed to use the Sea Rail 19 system which is simple and light. ( youtube search: sea rail 19 setup)
I don't like the ffs, it adds a lot of weight, costs and complication to the build so I refused to modify the design with the ffs. We agreed that I provide the design and Michael would calculate the ffs. To be honest I was a little angry about it and left him alone with the ffs problem. I even forgot to tell him what I knew about the design of ffs. Michael was a carpenter, but no engineer and he did what he could do to make the ffs work. In the end it folded, but only because it stretched the bearings of the struts.
And thats where the bow up attitude comes from. The beamlandings are not properly aligned vertically in the mainhull (due to the reversed sheerline) the bows are showing upwards. Michael later wanted to correct this with some spacers between beam and ama but I don't know if he finished it.

The Husky 6.2 is a very successful design with now 5 completed boats. It's meant to be a camp cruiser and club racer. The development shows that catamarans from (pre wave piercer) Formula 18, Nacra 5.5 and 5.2 are the best way to go. H20 hulls are too heavy and have too much volume. When sailing the Husky 6.2 is a very good and dry running boat, the cockpit offers comfortable seating and is quite protected. The balance is good, it points high and it is damned fast from 7knots wind on.

Other trimaran designs from my drawing board with the upcycled cat concept are two design lines: The "Husky" trimarans with modern styling show reverse (or plump) bows, a convex sheerline and a wedge shaped cabinhouse. Huskies use Nacras and similar cats.
A new line of designs, yet to be named, with a traditional styling feature a strong positive sheer, plump or slightly rounded bow and the flowing lines in Dick Newick style (take a look at the Outrigger 26 to get an impression). These boats give Hobie 18 and Hobie Tiger, perhaps Hobie 20 Miracle a new life. All tri's with this concept are between 6,2 and 7,2m in length

Mainhulls have three panel sharpie hulls with the latest lines providing best hydrodramatics for chined boats. Flat bottom and flaring sides, slightly rounded. The hull is fast, easy and cheap to build. It is quite small in transverse and vertical dimensions, for example 1m wide and 0.8m from bottom to sheer. It's so light that it can be turned over by two people by hand. That means that you can finish the hull including paint on before you continue with the accomodation, wings and cabin house. For accomodation, nearly all parts (floor, centerboard trunk, seats, bunkflats, shelves) can be built in from the outside. That saves you hundreds of in- and out climbs a day, and makes sanding and cleaning faster, vanishing easier.

For more information: Trimaran Projects and Multihull News: The Husky 6.2 club racer trimaran design by Michel Fedisch http://trimaranproject.blogspot.com/p/mamacocha-first-husky-6.html

Have Fun, Michel

 

I am not sure how to classify this boat. It is a foiler, it is a catamaran, it can be a single hander or a double hander and is basically a racer but the hull is only 9.9 foot long. The Mothquito is defined within a new concept, the SIT & FLY, because it is the foiler that practically flies alone. The Mothquito, designed by Toni Blanc of IFS Foiling SL, is 9.9 x 5.9 foot in its basic hull shape but is 18 x 15.7 foot in its full foil configuration. The carbon hull weight is 90 lbs. The 24.5 foot carbon mast carries a 136 square foot mainsail, a 51 square foot self tacking jib and a 33 square foot self tacking jib. The Code zero is 193 square foot. The draft is 3.3 foot over the foils. In spite of its overall dimensions it can be disassembled and transported by a car. Each piec4e is very light.

The innovative patented foil system, the IFS (Increased Foiling System) increase the stability and performance. There are 2 V foils at the front and 2 T foil rudders at the rear. To increase the dynamic beam, the Mothquito incorporates two outward facing V-foils with which the righting moment of the boat increases, increasing the transverse stability and reducing the heeling. These V-Foils are capable of auto-regulating flight height automatically, without the need for dip sticks sensors, and flaps. The V-foils have an adjustment system to regulate the angle of attack according to convenience, for example with little wind the angle of attack is increased to take off from 6 knots of speed. To increase the dynamic length, with the forward position of the V-foils and with a system of extension arms the position of the rudder T-foils increase the longitudinal distance between the support points or foils , increasing the length in flight. This achieves a substantial improvement in dynamic seating and longitudinal stability in foiling mode. The two rudder T-foils also have an angle of attack regulator.

This is a performance machine that takes of in 6 knots of wind and heads toward 25 knots if you are brave enough. According to sailors new to foiling, it is a very easy foiler to learn on but takes experience to get the best out of the boat. The hull shape is unusual as it is meant to be a foiler. Basically 2 surfboard type hulls with a bridgedeck between. This allows a little lift as the boat gets on to the foils, but is high wetted surface shape in light winds. Look for video’s on the web of this boat flying you will be impressed with its controllability.

The build is carbon fibre epoxy with some foam as required for stiffness.

The jpegs give the idea. A very interesting fun device.

 

This is about a pure speed machine. A French company, Syroco, is planning to beat the world sailing speed record in 2023 with a concept that’s “different”. This is the intersect between Kite boarding and hydrofoil sailing. And now things become interesting. The lift of the kite is counterbalanced by the NEGATIVE pull of the hydrofoil. The skill here is to balance the load between the upward lift of the kite and adjusting the foil to pull downward to keep the whole thing moving forward. How do you steer, control the kite and foils etc. Your crew sits in an aerodynamic pod that is half way up the line connecting the kite and foil.

So how do you steer and keep the craft level. By air rudder and elevator as you would in a plane. How effective would the air rudder and elevator be? The aim of this craft is 150 kph, 92 MPH or 80 knots. At this speed the air rudder and elevator will work well. There is a second crew aboard to help control the foil and kite during flight. The current outright speed sailing record is 55.7 knots held by Vestas Sailrocket 2 on November 24, 2012.

The initial idea has been developed by computer simulation but the team decided they needed to test some of the ideas in reality. To prove the viability of their concept the test platform consisted of a fast boat rigged with a 5-meter-high mast system that could provide a traction angle equivalent to the one of the kite. The prototype was strung to this rigging that essentially simulated the kite, and as the chase boat picked up speed, the prototype gently lifted over water. The foil came into action, providing the opposing force as defined in the concept. The pod started flying (jpeg below).

Now we get to the kite and foil. The kite comes in various sizes to match the wind strength, but it is going to need development for the speed ranges and control at 80 knots. The hydrofoil is another world of issues. The foil is working in a speed range where supercritical foils are the only option. Syroco designers have to face the problem of cavitation. That is, the air bubbles that build up around foil as it moves progressively faster through a given fluid. Syroco are aiming at speeds that no sailing vessel has ever reached. “The big challenge is finding a foil shape that works at both high and low speeds,” says Yves de Montcheuil, the other Syroco co-founder. “Our goal is to take advantage of the cavitation and not, like most racing sailboats, fight against it.” “The startup is developing foils that use ‘super-cavitation’ — a frictionless cavitation.” A super critical foil is like a wing foil but the back half of the foil is cut off. It has a "square" back that creates a "vacuum" that helps hold the flow over the front part of the foil. Complex stuff that needs a lot of testing.

The build materials are not specified but a lot of carbon and dyneema etc will be used. The forces here will be large and increasing with speed.

I hope these guys succeed as we will all learn something. Sorry about the limited jpegs but there are some videos on the web of the “test” and simulations of the real thing.

 

Always great to hear directly from a designer on a boat design discussion forum.

Thanks for sharing the backstory on how the float angle came to be.

Makes perfect sense from your explanation, and I completely understand your reasons for not being thrilled about incorporating the FFS due to weight, especially on such a small boat.

I love the ease of Farriers system and it makes a lot of sense on a big boat, but the weight and especially the low hanging struts are some of the drawbacks.

When I was shopping for a new Tri I decided I could live with a demountable trailerable design as I only set my boat up and take it apart once a year/season, and found that demountable designs were under valued and a better bargain because most want simple folding, but I also knew if I could find a boat that was lighter than its Farrier/Corsair equivalent and one without low hanging struts, that I would be able to have a lot more fun on light air days and days when our waters see rolling swell.

I also looked up the Searail setup and it looks to be a good compromise that is manageable and overall lighter and I imagine less complicated to incorporate.

Anyway, thanks for sharing!

 

The Hitchhiker 52 sailing catamaran is a large bridge deck cruising cat (52 x 33 foot and displaces about 20,000 lbs) that originally designed and built by John Hitch in 2005 and was sold to Ilan Sebban 7 years ago. The Hitchhiker 52 cat had petrol outboard power but the new owner, Ilan Sebban, decided to install two new diesel Dtorque outboards. IIan has crossed the Tasman sea on several occasions and had two 60 HP petrol outboards. After spending 3 hours using the petrol outboards to hold the bows into a sea in a storm, IIan wanted something more reliable, that used less fuel and could push forward into strong winds and seas.

IIan did a 2 year refit of the cat including installing two Dtorque 111 Nm – 50 HP turbo diesel outboards with state-of-the-art common rail fuel injection and innovative dual counter-rotating crank-shaft design. The engine positions were also moved further forward under the wing deck to ensure the propellers were always immersed.

The cat can, under sail, peak at close to 19 knots and averaged 9.5 knots on longer voyages. Under power the Dtorques’ 50 horsepower output has pushed the hull at up to 10.5 knots during sea trials, (by comparison, the previous 60 horsepower petrol outboards struggled to achieve 6.5 knots at wide open throttle). DTorque engineers claim a fuel burn of less than 12 litres per hour even under wide open throttle. Considering a similar horsepower petrol engine would use close to twice that amount of fuel at full throttle, it is easy to see where the Dtorques start to show their true worth. The engines have a lot of torque (peaking at 111 Nm @ 2,500rpm) but do it low revs versus petrol engines which have lower torque numbers but run at higher revs. HP = Torque x rpm/5252. So the 50 HP at the propeller of this engine is very useful in strong winds etc.

The owner and installer also praised a notable lack of vibration under power from the Dtorques – no doubt helped by the 804cc engine’s dual counter-rotating crankshaft design. they were also impressed by running temperatures of the engines during sea trials that never went above around 40 degrees Celcius regardless of revs. “It’s nice to see smooth, cool-running engines like that.”

An interesting repowering of a cat that has proven to be successful. The jpegs give the idea.

 

Today we will talk about a cat that was designed and partially built at sea, specifically the frames were made on a bulk carrier by the ships master John Sawyer in 1983. John designed and built Double Exposure. The open bridge deck cat was completed on land then sailed successfully. “Double Exposure” was 42 x 24.9 foot and displaced 9000 lbs. The Alspar LP6 tapered aluminium spar has a working sail area was 915 square foot with a triradial spinnaker of 1720 square foot. The length to beam is about 12 to 1. The power is two 9.9 HP outboards.

Now we get to the interesting stuff, “Double Exposure” renamed “TL systems” then renamed to “Tardis” was lengthened to 47 foot. A sister ship called “Fair Curve” was also built. These cats are still sailing with TL systems racing in NZ up to 2018 and is still on the water. 35 plus years of sailing is impressive. But the most impressive part is the performance.

TL Systems in 0 to 10 knots can beat a Newick 36 foot Echo tri, the boat easily cruises at 12 to 15 knots, goes 10 to 12 knots upwind in any sort of breeze, tacks through less than
90deg and has done 24 knots for an hour or so on a two sail reach. Another owner reported “I remember sailing single handed from Tiri to Kawau and back in 25 knots NE breeze with a metre or metre and a half of chop, I just kept going backwards and forwards at 18 to 20 knots without even spray coming on deck. TL systems was more of a smooth knife than a sledgehammer through the water.” For a simple 35 year old cat this is seriously fast.

The accommodation has 3 double berths in the hulls and a galley and seating area in one hull. There is a toilet forward in one hull. This is a practical layout for sailing but is not a floating house. The open wing deck aft of the mast had a hard floor inserted for more comfort. Open deck design but with cantilevered accommodation inboard of each hull behind the main beam. The main beam is big enough to sleep and crawl through to get from one hull to other hull.

The build is stringer on frame construction with 6mm ply over Kauri frames with Kauri stringers. The underwing is 8 mm plywood. The main beam is a plywood box beam.

An interesting, simple, fun fast cat. Mr Sawyer you produced an excellent cat. The jpegs give an idea.

 

This one is for the technical orientated not about the 6.5 monohull racing boat. The Floki 6.5 a boat currently under construction in La Rochelle will have a hull, deck and structures made from bamboo sandwich panels. The local reinforcements will be made of carbon. The hull, deck sandwich is of Bamboo fibre in epoxy either side of Pet foam. Interesting. I will give the quote of the design team then we will give some quotes from a technical paper I found about Fiberglass epoxy versus a Bamboo epoxy composite.

First the design team. "I tested all the other alternatives to fiberglass and carbon fiber that currently exist: flax, hemp and basalt fiber. Flax and hemp are natural fibers that are quite interesting from an ecological point of view, but have mechanical characteristics that do not allow us to make high-performance boats, due to their high weight. They are relevant fibers for pleasure boats, but not suitable for racing boats. Basalt is not so ecological because it is a mineral heated at high temperature. It is not a recycled or recyclable material, any more than fiberglass says Antoine.

If bamboo is a little heavier than carbon fiber, "but acceptable on a boat dedicated to performance, it is a natural fiber that has sufficiently high mechanical characteristics in relation to its own density and in relation to a finished composite to be used in a relevant way on a Mini 6.50."

The resin is biosourced epoxy and the Pet core is more environmentally friendly.

Now the technical stuff from: Physical-Mechanical Properties of Bamboo Fiber Composites Using Filament Winding https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8433995/#:~:text=The%20tensile%20strength%20and%20tensile,5%2C6%2C7%5D

In order to study the performance of the bamboo fiber composites prepared by filament winding, composites reinforced with jute fiber and glass fiber were used as control samples. The structure and mechanical properties of the composites were investigated by scanning electric microscope (SEM), tensile testing, bending testing, and dynamic mechanical analysis. The results demonstrated that the bamboo fiber composites exhibited lower density (0.974 g/cm3) and mechanical properties in comparison of to fiber composite and glass fiber composite, because the inner tissue structure of bamboo fiber was preserved without resin adsorbed into the cell cavity of fibrous parenchyma. The bamboo fibers in composites were pulled out, while the fibers in the surface of composites were torn, resulting in the lowest mechanical performance of bamboo fiber composites. The glass transition temperature of twisting bamboo fiber Naval Ordnance Laboratory (TBF-NOL) composite (165.89 °C) was the highest in general, which indicated that the TBF circumferential composite had the best plasticizing properties and better elasticity, the reason being that the fiber-reinforced epoxy circumferential composite interface joint is a physical connection, which restricts the movement of the molecular chain of the epoxy matrix, making the composite have a higher storage modulus (6000 MPa). In addition, The TBF-NOL had the least frequency dependence, and the circumferential composite prepared by TBF had the least performance variability. Therefore, the surface and internal structures of the bamboo fiber should be further processed and improved by decreasing the twisting bamboo fiber (TBF) diameter and increasing the specific surface area of the TBF and joint surface between fibers and resin, to improve the comprehensive properties of bamboo fiber composites.

The bamboo fibers isolated and prepared from bamboo have good mechanical properties. The tensile strength and tensile modulus of single bamboo fiber can be more than 1.43–1.69 GPa and 32–34.6 GPa, respectively, and the elongation at break of single bamboo fiber was 4.3–9.7%. Based on these properties, bamboo fiber is regarded as natural glass fibers

The table in the attachments is only showing below and when clicked on will black out. Please review the original paper to get details of the table in a readable format.

* TBF-NOL: NOL composites made of twisting bamboo fiber; JF-NOL: NOL composites made of jute fiber; GF-NOL: NOL composites made of glass fiber. The standard deviations are listed in the parentheses.

The tensile strength, shear strength, and bending strength of TBF-NOL was 5.15%, 48.78%, and 12.72% of GF-NOL, respectively. It can be concluded by activation energy that the interface of the TBF and JF circumferential composite was superior to that of the GF circumferential composite. The glass transition temperature of the TBF circumferential composite was the highest, which indicated that the TBF circumferential composite had the best plasticizing properties and better elasticity.

As a result, the interface between the bamboo fiber and resin can be improved by reducing the TBF diameter and increasing the specific surface area, making the composite possess high mechanical properties, which can provide the technology guidelines for the process and application of TBF.

Translation. Bamboo fibre can be used in boat building. It is lighter but has lot lower strength and bending strength but its shear strength is reasonable. The bending strength is less of a problem in a sandwich structure, the shear strength is OK for a foam structure. The elongation and strength are the issue that will require good design analysis.

 

Be warned, the following is generalisations. To help in calculating the thickness of a fiberglass layup the following tables may be of value. Often a designer will specify a fabric layup but not advise how thick the layup is. This can cause a problem if you want to “seamlessly join” a layup with eg plywood panel and need to rout the plywood surface to allow a smooth surface with minimal fairing.

The blue tables below (from West) give the thickness of a fabric that has resin impregnation fabric that has a hand layup. Being West products they expect you to do a good job with a high fiber weight fraction. The fourth chart is a company recommendation with a higher resin lower fiber fraction. The PDF is another companies fiber thickness and some other details.

The final chart is NOT accurate when it talks of thickness. The other details beside price are useful. Use the first 5 charts only for thickness calculations.

Hope it helps.

 

I saw that article from WEST. They didn't mention how metric makes it dead easy: every 100 gsm. of cloth equals .1 mm of thickness. Five layers of 200 gsm. cloth equals 1 mm of thickness. This only works with bagged laminate.

 

Sometimes I am surprised at the skill people apply to solving problems. The following is about a working catamaran to gather seaweed. Why? Look at the first jpeg. This is on the shore of a Caribbean Island that depends on the tourist trade for its income. They need to clean up the seaweed (or Sargassum) which rots on the shore line emitting foul smelling gases. The task to design a clean up solution involved Lucas Guessard, 54, founder, owner and chief engineer of Aventura Boats in the Dominican Republic. The CleanCat 42 (12.8m), a sargassum harvester is based on his tourist Arawak 42 cat used by many holiday resorts. The CleanCat 42 is 42 x 18.5 foot with weight of 17,000 lbs empty. The maximum payload of seaweed is 22,500 lbs. The draft is 2.35 foot. The power is two Yamaha 250 hp outboards. Maximum speed is 24 knots, cruising speed is 15 knots and loaded speed is 10 knots. With the Arawak 42 cat cruises at 18 knots and recommended dual Yamaha 300 outboards running at 3,450 rpm, makes 1.2 nautical miles per gallon.

As you can see in the jpegs, there is the basic catamaran hull and wing deck shape with a high flying bridge control station. There is a forward ramp that has a stainless steel conveyer belt that is used to scoop up the seaweed onto the bridge deck area. The cat when loaded goes to shore and unloads the seaweed onto a trailer for processing onshore. The good news is that sargassum has value. One of sargassum components is alginic acid, which the food industry can use as a thickener and emulsifier. Other components can be employed to make paper or ethanol. It also makes excellent fertilizer, and agriculture is an important sector in the Dominican Republic and Mexico. Guessard’s task was to build a tool matched to the task of harvesting sargassum before it gets onto the sandy beaches.

The design philosophy for Guessard boats derives from “a sailor in a universe of powerboats.” He designed his semi displacement hulls around fuel efficiency and seaworthiness—as defined by the capability to take out passengers even during the moderately rough conditions often found at Caribbean beach resorts. All his boats are designed to embark passengers from a beach.

Hull construction is solid fiberglass, averaging 1⁄2″ (13mm) thick below the waterline and about 3⁄8″ (10mm) above, with superstructures in composite sandwich stiffened by NidaCore. Plywood is still being used for some bulkheads, but as Aventura gets ready to begin production of third generation models, Guessard said he plans to replace all wood with NidaCore or polyester foam coring, as appropriate. Platform to hull construction is strengthened by the company’s practice of bonding all furniture and other superstructure components instead of fastening them with screws.

This is an interesting cat that is strongly built for its task. The jpegs give the idea. The final jpeg is of the Arawak 42 cat used in the tourist trade.

 

The following cruising catamaran was designed by Alexander Verheus of Verheus Multihull Design for short handed cruising. “Sunday Child” is 36.75 x 19.7 foot with a displacement of 8000 lbs (probably weight). The aluminium mast is 44 foot high with 325 square foot mainsail, a 365 square foot furling genoa, a 280 square foot high aspect furling genoa and a 987 square foot gennaker. The draft is 2.3 foot over the low aspect ratio keels and rudders. Power is 2 x 9.9 HP outboards.

The hull shape is inverted bell bottom. That is narrow waterline with flair topsides to increase hull accommodation. The jpegs show the narrow waterline but the hull double berths are wide. This is a good hull shape for sailing and if done correctly, helps provide good speed and a smooth ride in a seaway.

The accommodation in the main saloon is a J-shaped Dinette with varnished table and a navigation desk. There is a spacious galley in the starboard hull with a double berth aft and a single berth cabin forward. A double berth cabin aft and a head forward in the port hull. The mast base is in the front of the cockpit (like older Prout cats) for ease of sail controls with the helming position close to the mast base so it's easy to control the yacht single handed.

The yacht was built in 1998 in New Zealand by M&M Boatbuilders and is listed as GRP. I suspect this cat has either strip plank cedar or a foam core judging by the clean interior with a minimal of interior framing. My bet is on Strip planking.

This is an interesting design; I do not know any performance numbers but I suspect it will be an 8 knot average sort of cat with peaks in the 16 knot range. In short, a very good cruiser. The jpegs tell the story.

 

The TC1040 cruising trimaran is the largest really trailable (it folds to 8.2 foot) trimaran I know. It was designed by Tim Clissold of TC Design Ltd for a guy in Holland who had it built by M&M Boat builders at Drachten. “Nova” was launched in 2007. Nova is 36.9 x 26.9 foot and can be folded to 8.2 foot with a farrier type system. The weight is 5600 lbs and the displacement is 9000 lbs. The 46 foot Sparcraft aluminium mast carries a 548 square foot mainsail and a 290 square foot jib on a ) Facnor FX 7000 roller furler. The draft over the rudder and Catri foils in floats ranges from 3.2 foot to 6 foot. There are also foils on the back of the main hull and floats help with lift and stability at speed. The Hybrid Kubota D722 diesel-electric propulsion. Powering the system is 144V is by an electric engine on a sail drive set up and 4 bladed Piranha propellor drives the tri at 5 to 6 knots using 2 liters/hour.

The yacht offers two double cabins and a dinette that can be converted into a third double bed. There is a large galley has all electric appliances, rather than LPG, in the main saloon. The head is right by the main hatch, while the shower is forward. The cockpit is where all sail controls lead to and the helm is a tiller steer. The claimed sailing speed of the tri is 8 to 15 knots. Realistic.

The construction of the PVC foam-glass-epoxy sandwich yacht. The amas are rounded, using the stressed foam method in two vertically split hull moulds, while the main hull has flat panels for ease of construction above the chine line. The crossbeams are large section aluminum tubes with control arms.

The jpegs give the idea of this tri. Only problem I see is the mast raising, a 45 foot mast with its bits would weigh 200 lbs plus, quite a control problem when being raised.