Multihull Structure Thoughts

Today is about foils, daggerboards mainly. Foils on high performance multihulls are to control the boat and resist leeway. The best foils tend to be high aspect ratio and by default are long (deep) into the water. Result occasionally they act as a default depth sounder. The best daggerboard foil shape depends on the capability of the boat. Some boats run 15% foils others 12% NACA sections etc but a well shaped foil improves the performance of a boat especially upwind. Now we come to the construction of the daggerboard. There are several options each have their advantages and disadvantages and more importantly significant weight differences. The main options are Western Red Cedar Core with glass strengthening and coverage. WRC core for about 25% with a balsa front and rear with glass strengthening and coverage. Or a WRC core for about 25% with a Corecell type foam from and rear with glass strengthening and coverage. A full WRC board can be 3 times the weight of a foam glass board and twice the weight of a Balsa based board. In a EG 30 foot cat 2 foam glass boards could be 60 lbs lighter than 2 full WRC boards. The toughest board is likely to be the full WRC, but if done well all the board types can take gentle knocks. Hit the bottom at high speed and you take a choice, have the board break or have the hull bottom damaged. I choose to replace a board not fix a hull. Result I have broken several 10 foot long daggerboards in my life.

There are other ways to make daggerboards for aluminium, steel, plywood, solid glass sides with minimal strength or no cores etc. But I will stay with the main ones for home builders.

We will start with the simplest. Western red cedar core (or other suitable light timber). WRC timber strips are glued together with the grain running vertically to the full size of the board. All timber longitudinal joints are scarfed together. The “blank” is then shaped by plan, router, sander to the desired foil shape. A routed rope channel is done on either side of the board about half way a slot connecting either side of the is drilled through. The slot has a small sheave put in it to allow the uphaul rope to run through. The shaped foil is then has a WEST type epoxy saturation technique applied and smoothed. Now the variations begin. If you have a large thick foil then the back edge can be left as is. But if you are going to touch bottom frequently an aluminum strip of eg 2 mm x 25 mm can be routed in to minimize the rear of the foil breaking.

Next is high density inserts inserted at pressure points. EG when the board is full down the back edge of the foil generally rests on the hull at the exit point. Also, at the front edge of the foil at the case top exit point. Next is the need for lateral reinforcement down the sides of the board. Next decision is are you going to make a sacrificial bottom to your board. If so, the lateral reinforcement stops about 400 mm from the bottom of the board.

The lateral reinforcement requires a shallow indentation (about 40% of the boards fore and aft width) to be routed into the sides of the board to the thickness of the glass used to reinforce the board EG 3 mm. The reinforcing unidirectional glass (or carbon fibre) is laid into routed area to strengthened the board. The depression and glass is faired to the re-establish the foil shape of the board. Then the full board is wrapped in at least 2 layers biax or triax glass in epoxy. Relatively fast but the heaviest approach.

Next is a balsa based board which is constructed in a similar fashion to the WRC board EXCEPT there is a solid insert of WRC in the 25% of the fore and aft width at the maximum chord width. The remainder of the build is the same but you need to do the rear aluminum insert at the rear edge to help prevent damage. Again the sealing and finishing of a WRC Balsa board is important. Water ingress will cause problems ranging from delamination, rotting or worst of all swelling of the timber/balsa and the board not fitting/jamming in the board case. Also antifouling of the inside of the board case helps reduce growth and jamming. Regular inspection, cleaning and maintenance of the board also may save a problem later.

I will do foam glass board construction later as this is getting to long. The jpegs give some idea as to the build and shape of some boards.

 

You can reinforce leading and trailing edges by ripping the relevant strip in half fore and aft and sandwiching in a layer of DB before glueing to rest of the board.
You can do same at maximum chord athwartship on boards to put in some extra DB or Uni. Works on rudders too.

 

I concede defeat. This is the latest design from Julien Melot and built by Zen yachts, a Spanish yard. Why defeat? This is another multi story cat with a lot accommodation in a 50 foot package with a minimal rig and a vast solar array that provides motive power. A modern motor sailor catamaran. As I said previously, I prefer cats that really sail and less accommodation. The Zen 50 is 51.5 x 27,5 foot with a weight of 36,000 lbs. The “rig” is the VPLP developed “Oceanwings” reefable multi part wing rig of 345 square foot. The draft is 4.3 foot over low aspect ratio keels. The motor component is electric powered by a 16,000 watt solar array. The panels feed a 160 kWh battery park gives the catamaran a high autonomy. The two 40 kW engines ensure a cruising speed between 6 and 10 knots on average, with peaks at 14 knots, a constant maximum speed calculated under sail and with engines at full throttle. Under engine only, the Zen 50 reaches a maximum speed of 10 knots and 5 knots continuously.

The layout of the Zen 50, it offers several versions. The owner's version reserves the port hull for the owner's suite. Two other versions are suitable for family or charter use with 4 double cabins and 4 private bathrooms or 4 double cabins, a single cabin and a cabin with bunk beds. In the saloon/cockpit, the layout can vary according to the owner's wishes. There is a choice of a lounge, a dining room, a large chart table. The interior will be more in a minimalist style, with freedom in materials and arrangements for the customer. The Zen 50 is offered in 3 versions: Racer, Cruiser, Explorer (depending on the options chosen) with or without wing.

"We realized that solar works very well as long as the surface of the panels is sufficient while keeping the boat light” Said Melot. The first 36,000 lbs Zen 50 is built made from a carbon fiber sandwich with a foam core in vinylester and epoxy. The cat will be in full production in 2023. The first unit is being built and is sold.

The total concept is to be a serious cruising vessel that will produce minimal pollution. The solar array powers the cat during the day and the wing sail assists during the day with it acting as the main power overnight with some support of the electric motors via the battery pack. Lets hope they aren’t running air conditioning and entertainment systems overnight.

I think this is a creative design that will find a market. The jpegs tell part of the story. The web site is: https://www.zenyachts.com/zen50

 

The irony oldmulti is in the name.
Zen my arse.

 

In my opinion the only thing the mast and sail would be good at is shading the solar panels.

 

In a cyclone, that thing could fly pretty well.......

 

This is the style of performance cruising catamaran that I prefer. The Seaquest 46 is a collaboration between Carkeek Design Partners and builder Eaton Marine based in Dubai. The Seaquest 46 is 46 x 24.6 foot with a weight 18,400 lbs and a working displacement of 24,000 lbs. The 63 foot mast carries a 770 square foot mainsail, a furling self tacking 645 square foot jib and a 1,722 square foot spinnaker. Spectra soft standing rigging and soft shackles are used throughout. Options include carbon fibre mast, electric main traveler, electric furling jib, and detachable or permanent electric furler for the code zero. The draft is 4 foot over the rudders and 8.3 foot over the C curved daggerboards. Located a little way forward of the boat’s centre of gravity, the C boards generate dynamic lift as well as lateral resistance, raising the bows when the boat is powered up. The daggerboards’ lift allows the bows to have very fine entries without the usual drawbacks of pitching and burying, while the aft sections are wider and flatter than you might expect. The result is a boat with more longitudinal stability and thus a more comfortable motion, potentially more boat speed and better load-carrying ability. The underwing clearance is 2.4 foot.

The SQ46 is powered by two Oceanvolt 15.1 KW electric motors. Available in either a fully electric or hybrid option with a traditional diesel generator. Standard battery capacity provides a range of 120 nm on a single charge at a maximum speed of 7 knots. Alternative propulsion configurations are available.

Available in a three cabin layout with port side owner’s hull with the option for a traditional four cabin layout with mirroring hulls. Forward staterooms feature athwartship queen berths. Aft staterooms have fore/aft queen berths and opening hatches in the headliner and aft facing port lights. Each cabin contains a hanging locker and storage under the berth as well as LED downlights, reading lights, a fan, and low profile hatches above the berth for light and ventilation. The Seaquest 46 offers queen size berths, but they do not have walkways on both sides of the berths to have slim hulls that are more hydrodynamically efficient. The above-average size of the saloon containing the galley, seating, table, navigation and entertainment area is integrated with the cockpit for a larger space for relaxing.

The shell is constructed with vacuum infused E-glass with a high-density foam core and extra multi directional E-glass below the waterline. Carbon fiber frames running across the bridge deck supporting foam cored bulkheads linking both hulls. Externally visible frames and structure finished in gel coat. Two Carkeek engineered, curved daggerboards designed with state-of-the-art computational fluid dynamics software. The deck is vacuum infused E-glass with high-density foam core on all flat sections. Extra E-glass for all high loaded areas. Non-skid finish on all deck walking areas with the option to upgrade to alternative deck surfaces. Sensibly for a world cruiser, it’s built mainly in e-glass which can easily be repaired by a local boatyard or an amateur boat owner in a remote part of the world.

Carkeek’s VPP suggests that even when sailed conservatively, with sails well reefed, more than 200 miles a day can be expected. With a bridgedeck clearance that’s higher than most plus a low centre of gravity, it shouldn’t be slowed down unduly by choppy seas or ocean swell. When fully powered up and actively sailed in performance mode, about 360 miles in a day should be easily achieved. The attached jpeg of the performance versus windspeed and wind angle gives the designers estimates. Maximum speeds of over 25 knots on a broad reach is theoretically possible according to the designers.

This is a very thought-out serious cruiser built of practical materials and is designed to be maintainable. EG the steering system has a minimum of solid rods etc and is mainly based on Spectra rather than solid links to allow easy replacement. The jpegs give the idea and is now in production. The ‘frame” jpeg is the base for the wooden hull plug.

Finally this cat is at full displacement is 20,000 lbs lighter with more sail than either of the multistory cats mentioned previously. Result slightly less accommodation but up to 10 knots more peak boat speed under sail and capable of crossing an ocean in days less. My style of cat.

 

This is a comment on fiberglass fatigue and failure. It came from reading a thread about a Farrier F27 that had a beam failure whilst sailing in winds about 15 knots and waves of 1 to 2 ft. They were on starboard tack, on a close reach, doing 10-12 knots. with full main and a storm jib. There was a "crack" sound, and the port ama slowly folded out while the boat gradually heeled more to port and came to a stop. The boat was in good condition and was well maintained. The F27 made it back to a trailer after some very good reactions by the crew. This is not a criticism of the F27 or the owner of the vessel. The F27 was over 20 years of age and we do not know the history of the vessel whilst being towed or if it “hit” anything in its 20 plus years of sailing.

The jpegs tell part of the story but the possible underlying issue could be fatigue and microcracking of the structural fiberglass beam structure. There have been a few other F27 beam problems reported in the Beam Care Bulletin (attached PDF) of cracking and some delamination. The Beam Care Bulletin suggest how to inspect and repair any issues that may be found. Now we go into 2 separate issues.

Issue 1. The F27 beams were considered very strong and built by a reputable company from 1985 to about 2000. The beams design/build approach had a few iterations over time but in the jpegs, it looks like the “strength” is in the skin structure with the foam acting as a filler more than being a structural component. If so then the shell of the beam is expected to take all the loads and any cracks in that shell structure can lead to a progressive failure with a EG microcrack progressively expanding leading to delamination between layers.

Issue 2. Microcracks can lead to the failure of any fiberglass structure. If a fiberglass panel is designed correctly, it will be strong enough with a safety factor of EG 3 to 10 times. The safety factor depends on the function it is being designed for. If you are in a temperature-controlled environment using vacuum infusion and a post curing oven with known tested products, a safety factor of 3 may be OK. Home builders in uncontrolled environments hand laying fiberglass require a design with safety factors of 10 designed in, as the build quality could vary significantly between each person..

There have been extensive studies on fiberglass composite layups fatigue factors and microcracking since the aircraft and wind farm industries are using composites for many components. There are defined life spans for aircraft components and wind turbine blades as a failure in either could cost lives. The marine industry is not there yet but is improving as Finite Element Analysis tools etc being used to help design boat structures and provides guides to high stress areas etc.

Please do not assume your multi is fine because it is built by a “reliable” manufacturer and has a reputation as a “strong” boat. If boat is seriously used in a seaway over a long time, they constantly structurally move and develop problems. I have been sailing and hit a log at speed in a coastal trip. It only damaged a daggerboard but it may have fractured the outer layer of glass in the foam glass structure. We looked at the area 6 months later when it was slipped and found water under the skin. Sailing is fun but maintenance is not. But careful inspections and early maintenance may save a lot of problems later.

The jpegs are of the F27 and a sample of microcracking. The jpeg of strength versus cycles gives an idea of the fatigue characteristics of various materials. The PDF is the Farrier Beam Care Bulletin. The next PDF is an analysis of various composite failures in boats.

PS The surveyor said the broken beams were due to "fatigue failure", and therefore it is not covered by insurance because they say that is "normal wear and tear". The owner found a broken F27 which had 2 good beams and has replaced them.

PS 2. If anyone knows anything about the laser based trimaran in the last jpeg can they please tell the thread.

 

A small item on what are very popular production catamarans. The Isla 40 is a development of the Lucia 40 catamaran (over 400 sold in 6 years). The Isla 40 is very similar to the Lucia 40 and currently has a 18 month waiting list. The Isla 40 is Fountaine Pajot built “entry level” cruising cat is design by Berret-Racoupeau Yacht Design. The Isla 40 is 39.1 x 21.7 foot with a weight of 21,000 lbs. The displacement is unknown but I suspect the Isla 40 could carry a 6000 lbs payload. The 55 foot fixed aluminum mast carries a mainsail of 635 square foot and a genoa of 388 square foot. The length to beam of the hulls is about 8 to 1. The draft is 4 foot over the low aspect ratio keels. The power is 2 x 20 or 30 HP diesels. With the 30’s, the Isla 40 can maintain an average speed of 7 to 8 knots without pushing it.

The real story of the Isla 40 is seen in a few of the jpegs. The bow is moderately fine with an “inverted” bow (fashion statement) but if you look closely you find in the underwing tunnel bumps just above the waterline fore and aft to provide additional room for double berths and toilets in the hulls. The length to beam may be about 8 to 1 in flat water but in a seaway reaching you will find a length to beam of a hull of maybe 7 to 1. This cat is focused on cruising.

The Isla 40 model main feature is the upgraded accommodation layout compared to the previous model. The hulls have either 4 or 3 double cabins and a bathroom in each hull. The main bridge deck saloon has a large galley, dinette that can convert into another double berth, a navigation and entertainment area. The large glass doors aft lead to the cockpit which can be “integrated” into the saloon space when the doors are open. The steering, sail handling cockpit is a step up on the starboard side of the cockpit and goes through the cockpit roof. The majority of winches and rope clutches are easily accessible from the cockpit. The cat is orientated toward accommodation over performance.

The performance of the Isla 40 is best described by owners as “sailing at about 50% of windspeed up to 25 knots of wind”. A formal test reported “In a slight sea, 5 to 15 knots of south easterly winds for the test. There, with 8/9 knots of wind, we strode along at 5 knots at an angle of 50° off the true wind. No need to head up any further - the Isla 40 prefers the sails just a little open.” Translation 100 degrees between tacks upwind and reasonable performance across a wind range.

The construction is a sandwich with a balsa core and skins made of multiaxial glass cloth in vinylester resin. The hulls built using infusion process are made up in three sections: the underside of the nacelle, the inboard topsides and the outboard half-hulls. The deck and the coach roof are injected parts - vacuum infused lamination in a two-sided mould. The internal components are mainly moulded parts with timber laminates etc added as required. The aft cockpit roof top carries the loads of the mainsheet traveller and requires 2 stainless steel poles down to the cockpit floor for additional support.

The Isla 40 is the size and type of cat that the majority of the market wants. Performance is not the priority but good accommodation and an easily controlled cat is required. When the wind is in the wrong direction or not blowing strongly enough the engines will allow you to meet your schedule etc. This is a good cruising cat designed and built from a lot of experience and according to owners who have sailed them for over 10,000 miles fulfilled their requirements well. The jpegs give the idea.

 

She looks very nice.
I wonder if it is possible to have a bimini canopy over the helm station.
Or even if a tall helmsperson standing up would be at risk from being clobbered by the boom?

 

Bajansailor. There is a bimini canopy option available. Some sailors have used it and it limits the mainsail view but otherwise OK. I do not know if it has full standing headroom. Later addition, found jpegs, boom does clear person in cockpit and bimini is useful.

 

Carbon fiber comes in many strengths and the higher the strength the more expensive it becomes. Basic boat building carbon fiber is about $12 per pound and can go to $900 per pound for ultra high strength options. There have been 2 break throughs in carbon fiber base components and manufacturing that may significantly reduce the cost of carbon fiber to about $3 per pound.

First breakthrough is the base product used in the manufacture of carbon fiber filaments. Currently most carbon fibers are produced from a polymer known as polyacrylonitrile, or PAN, which is pretty costly. The price of PAN makes up about 50% of the production cost of carbon fibers. The new feed stock being investigated, and proven to work, is petroleum residue (pitch). A waste material left over from refining petrol that is often sent to landfill. The carbon fiber produced from this method has advantages other than lower cost of manufacture over traditional carbon fibre, it can have higher compression strength, meaning it could be used in applications with higher load bearing.

Pitch is the general name for the tarry substance that is highly viscous at room temperature and has very high carbon content. It is a complex mixture of many hundreds of aromatic hydrocarbons and heterocyclic compounds with an average molecular weight of 300–400. It can be produced from natural sources by destructive distillation of petroleum and coal or from synthetic sources by pyrolysis of polyaromatic compounds and polymers. The composition of a pitch varies widely according to the source of tar and the processing conditions. Pitch can contain more than 80% carbon, and as the aromaticity increases, the quality of the product carbon fiber increases.

The researchers at MIT used computer simulations of the dynamics between molecules in the pitch (the way that bonds form and crosslink between them) to develop a way of predicting how different processing conditions could affect the resulting properties of the fibre. They identified the key chemical and processing parameters that determine and control the formation of pitch-based carbon fibers. Lead author Asmita Jana, at MIT. “To the point where companies could take those graphs and be able to predict characteristics such as density and elastic modulus of the fibers.” Their results showed that by adjusting starting conditions in the production process, carbon fibres could be made that were not only strong in tension, but also in compression.

Next development is PAN fibers have to be heated to 200-300 degrees Celsius to oxidize them. Next, they must be heated to 1,200-1,600 degrees Celsius to transform the atoms into carbon. Finally, they have to be heated to 2,100 degrees Celsius so that the molecules are aligned properly. Without this series of steps, the resulting material would lack its needed strength and stiffness. The development is to add trace amounts of graphene -- only 0.075% concentration by weight -- to the first stages of this process allowed the creation of a carbon fiber that had 225% greater strength and 184% greater stiffness than the conventionally made PAN-based carbon fibers. The flat structure of graphene helps to align PAN molecules consistently throughout the fiber, which is needed in the production process. Further, at high temperatures graphene edges have a natural catalytic property so that "the rest of PAN condenses around these edges".

Finally manufacturing techniques have improved in the production and weaving creation of carbon fiber fabrics which requires less heat and processing to achieve the final product. All this adds up to potentially stronger carbon fiber for less cost. The mass use of carbon fiber in aircraft and starting to be used in cars will help mass manufacture of carbon fiber which will also help reduce the price. The demand for mass manufacture of the above is significant so it is likely that cheaper carbon fiber will be available very soon.

The jpegs are of the new product. The first jpeg is of the Pitch based carbon fiber strands. The second jpeg is of a human hair (the vertical strand) and the thinner angled strand of the carbon fibre beside the clear ruler edge. You can google “cheaper carbon fiber” for the sources of the information.

 

The following is about SVR-Lazartigue, an extreme Ultim racing tri. The tri was designed by VPLP and is for François Gabart, the current world record holder for around the world sailing. The tri is 105 x 75.5 foot displacing 33,000 lbs. The carbon fibre rotating wing mast is 109 foot high and carries 4,574 square foot upwind and 6,940 square foot downwind. The majority of the sails are on furlers as this boat can be sailed single or dual handed. The draft over foils and boards is 14.6 foot. The tri was designed to be a foiler from the start as a result the floats are narrow and have lower buoyancy than a non foiling racing tri. The foils extend from the float inboard 13 foot.

This tri is all about performance. To quote Gabart. “The apparent wind created by the speeds reached is “mind-blowing”, says Gabart. “This is the most impressive thing about this boat. We have never had these apparent wind figures on other boats. “Here, we regularly reach speeds of over 40 knots at less than 90° true wind angle (TWA). In certain conditions, such as 25 knots of wind on flat seas, at 65°-70° off the wind, you’re doing 40 knots. That’s 60-65 knots of apparent wind speed. The maximum AWS in our log is not far from 70 knots”. SVR recently did a training run where the tri averaged 37 knots for 200 miles on a reach. Think about that, 200 miles in 5.5 hours. SVR has done 820 miles in a day and its averaged 24 knots over 7,500 miles. Numbers like this are the result of a lot of skill in design, engineering and building skill. It also requires really good sailors. In this case 2 people. And you thought double handling your 30 footer was hard.

So what magic is designed in this tri. Try 23 hydraulic cylinders to control things like foil rake, mainsail outhaul pressure etc. This helps control aspects of SVR quickly while sailing BUT you can only use human input to build up hydraulic pressure, so each time you wind the 43 cm (1.4 foot) diameter winches you are also building pressure in the hydraulic reservoir. This is a very demanding tri physically. SVR electronics are vast but the most important item is the VPLP developed VPPs (velocity prediction programmes) are much more than simple polars with the speed targets. The charts displayed in the cockpit, recommend theoretical settings for foil depth, rake and flaps under the various wind conditions and angles. As conditions change the setup of the tri has to be changed to maintain optimum speed. If the crew does not react resetting the configuration not only will the tri slow but also could be damaged by EG incorrect foil setting for a given condition.

The total design of the SVR tri was optimised aerodynamically to minimise air drag. For instance, the traditional canopy over the helm station has been ditched, while the living quarters and the cockpit have been integrated into the central hull. This makes for a bulkier hull, but nothing protrudes above deck. The boom is as low as possible, skimming the deck, and reduces windage to a minimum. When you are sailing at 40 knots disturbed air not only creates drag but also effects the rigs setting to obtain the most power. But the most important components for pure speed are the foils. The main foils are particularly complex, between the L-shaped lower section and the S-shaped vertical upper section that run on a free ball joint that gives a degree of freedom in the foil boxes to be able to raise and lower them. The upper foil section moves longitudinally, allowing the rake to be adjusted. Each main foil weighs 880 lbs of crafted high strength carbon fibre. Say goodbye to over $100,000 for each foil just for the build process let alone the material costs.

The build is foam/nomex prepreg carbon fibre post cured in an autoclave (one of the 3 autoclaves measures 82 x 13 foot) when making these large parts like foils beams and hull components. The build took 150,000 hours of work, some 40 months of work and around 20 local companies were involved in the project plus a lot of design time prior and during the build. This is a $20 million plus boat build and campaign.

The jpegs give the idea. Do not underestimate the technology and build skill involved here. This is not remotely home builder technology here. It is a very specific design for specific tasks that would cost several million a year to campaign. We all learn something from these machines.

 

Yes, Aventura catamarans exists since 2000, it seems to be a French-Tunisian company with the shipbuilding yard at Bizerte (Tunisia) , they built a 28' from 2002 to 2017 but not sure it is the one showed on Solgato picture.
The company : À propos de Aventura Catamarans https://www.aventura-catamarans.com/en-au/apropos
Aventura 28. Aventura 28 - voilier du chantier Go Catamaran - Fiche technique Bateaux.com https://www.bateaux.com/plaisance/voiliers/aventura-28-REFv4CDIKxsHvE,

 

.... more info on Aventura Catamarans : the company was created in Tunisia in 2000 by Frenchmen Eric Roger and his son Romain Roger. They started with a remake of the Camping cat 23 and thé Diabolo 28 under new names Aventura 23 and 28, then in 2007 they propose their first home design Aventura 20, then 33, 44, .... They are now in a production of ~ 25 catas / year (2019) :
Aventura, le constructeur de catamarans en pleine croissance https://www.boatindustry.fr/article/29211/aventura-constructeur-de-catamarans-pleine-croissance