Multihull Structure Thoughts

Foiling electric powered ferries were an idea, then developed in Europe to be practical. The economics were not good but it was a start. NZ companies started to use some of the foiling and construction technology from their AC catamarans. The result is some very interesting and economically viable foiling ferries. By economically viable I am talking payback periods of under 2 years for the capitol purchase price and running cost for the first 2 years. The following ferry has a 20 year warranty. All this assumes you have an appropriate ferry run with reasonable passenger loads.

The Vessey VS-9 is a 29.3 x 10 foot catamaran foiler that weighs 6,950 lbs. The payload is 10 passengers plus 1 crew, assume a payload capacity of about 2,200 lbs. The draft ranges from 1.5 to 5 foot over the movable foils. The power is 2 EV batteries (guess about 60 KW/battery ) that can cruise the foiler at 22 to 25 knots with a top speed of 30 knots. The range at cruise is 40 to 50 nautical miles in seas of less than 2.5 foot seas. The recharge time depends upon the shore charging stations but if appropriate can be 20 minutes.

The above means if you have a route of say 20 miles, you could do a run every 1.4 hours or 10 runs a day with say 50% load at $25 per person per run, that equals $1250/day income. Small, but your energy running costs are $5/run, your “fuel” expenses are $50/day. Yes, a payback in 2 years.

Back to the Vessev design. Basically, a catamaran hull that has a forward main support foil forward and an aft support foil with a centrally mounted electric engine and propeller unit aft. The foils were done by the same guys who designed the AC and GP 50 cat foils. In short foils that work over a range of about 15 knots to 35 knots that have adjustable flaps on them to optimise take off and low running drag.

The construction of the hull and cabin is carbon fibre foam glass epoxy. The foils are carbon fibre. The hull structure etc meets commercial survey ratings which means it has heavier hull layups than would be required for private use. (PS one of the Vessev VS-9 has been sold as a private cruising foiler). Vessev is the sort of crew that designs and manufactures every single component found aboard this foiler. From the motor, hull, rudders, and the entire electrical system which required a lot of R&D. The price is about $US620,000 for a sea ready launched boat.

The jpegs give the idea of the ferry, maybe short range foiling cruisers maybe a reality soon.

 

You start with a Woods design cat called Wizzer, meant to be a high performance cruising catamaran. Basically a easy to build open bridge deck tube catamaran. Then an owner comes along nad says it needs to have more “cruising” features for more comfortable sailing in Queensland Australia. “Grey Goose” is created.

The standard Wizzer was an offshoot of the Wizard and Sango hull lines. Basically the Sango without a central cabin. The standard Wizzer was 25.3 x 14.75 foot with a weight of 2000 lbs. The sail area was 350 square foot under mainsail and jib. The draft was about 4 foot over daggerboard. The Wizzer we are talking about here is 29.5 x 16.3 foot and a “displacement” of 4,000 lbs. The rig looks about 440 square foot and the draft is 1.6 foot over centerboards (doubt this number). The outboard is 20 HP.

So, what happened? The professional builder in 2006 either stretched the design himself or spoke to Richard Woods and got permission for a larger concept. The hull width remained the same and the open wing deck concept was retained. The real truth I suspect is the hull shape is a SKUA (29.5 foot) hull not a Wizzer/Sango hull shape which was an inverted bell shape.

Next came the “modifications”. As you can see from the jpegs there is a lot of canvas covering of access to the hulls and over the bridge deck to help form “livable” accommodation. The starboard hull has 2 berths. The port hull has a galley and a head. On the wing deck is a double air mattress, a fixed portable table and seating with a helming position under cover. Great for tropical sailing, not so good for wet wind ward work in less temperate conditions. Next you add a lot of stainless steel tube railings to prevent falling over board and then add a electric trolling motor to act as a bow thruster to handle the additional windage when docking.

I am not saying any of this is impractical but the starting concept of a high performance occasional cruiser is lost by the attempt to turn this cat into a cruiser first and a performance machine second.

The construction is strip plank cedar with dynell sheathing both inside and out in epoxy. Aluminium cross beams for and aft and a wooden box beam for the mast support beam.

The jpegs tell you about the idea.

 

Many years ago, I meet Chris Mashford who designed and built many light weight multihull performance cruisers. He proved to me 38 foot tri’s can have 330 gsm skins either side of 12 mm foam and sail fast and last well if cared for. Chris was a creative. He built a 50 foot monohull with a catamaran stern then designed a smaller model for a WA client WA by Bunbury Fibre Glass in around 2000. They called it the Vortex Monocat. This is a big trailable yacht.

The monocat is 33 x 10 foot with a weight of 2,920 lbs. The rising hydraulic swing keel has 660 lbs of ballast in it and can be raised from 9 foot to 1.6 foot. The sail area is unknown on the aluminum mast. The engine is a 15 HP Mercury outboard. This yacht is a real trailer sailor when you have a wide trailer permit in Australia. All up towing weight with the trailer is 4,500 lbs.

The accommodation is a standard V double berth forward, head shower unit next, a main saloon with a galley and a dinette opposite then 2 single berths aft, 1 in each cat hull.

The construction was mainly Kevlar foam glass in epoxy. I am aware several were built but the design/boat was not a commercial success.

Several designers have tried the monocat approach with each having some success but the concept is a half way house. The boats go upwind like a mono and are more stable down wind but in lighter airs have more wetted surface and do not have the stability of a multihull. Also, the aft hull shape has some restrictions on accommodation space.

The jpegs give the idea of an interesting concept that would need to be developed further.

 

You want a challenge to a multihull that is innovative, has a lot of internal accommodation for a 40 footer and the promise of foiling speed, then the following design from naval architects Benoît Marie and Clément Bercault may be want you need. The SKAW (A), the world’s first foiling cruising scow yacht is a collaboration between Skaw Sailing, SHORETEAM, and Sicomin is a high-performance foiling design built from eco-conscious materials.

The SKAW A is 39.2 x 15.9 foot (when both foils are deployed beam is 36 foot) with a weight of 11,200 lbs. The 57.6 foot carbon mast carries a 588 square foot mainsail, a 452 square foot jib, a 1,070 square foot gennaker and a 1,775 square foot asymmetric spinnaker. The draft ranges from 4 foot with foils and swing keel up to 11 foot with swing keel down. The engine is a 40 HP inboard.

The accommodation is very good but has a big problem. In the very bow is a large table and seating. Seating in the bow for a meal in a seaway would be a wild ride. The remainder of the accommodation is reasonable. There is a large galley on one side and a navigation area that can be converted into a small seating area on the opposite side. Aft is 2 large double berth double berth cabins and a larhe toilet shower area. The cockpit is large with a hard cover over the majority of the cockpit.

The build of SKAW (A)’s lightweight construction is from SHORETEAM’s builders. They bio-based epoxies, including SR InfuGreen 171 for large component infusion in the fiberglass/carbon fibre/pet foam hull deck construction and SR GreenPoxy 170 for secondary bonding of internal bulkheads. The internal furniture is plywood with light veneers.

Performance is unknown but the designers claim it will have the performance of a 60 foot catamaran. This statement needs to verified when the SKAW A is tested.

The SKAW A is either a blown up Mini 6.5 racing yacht or a cross between a Mini 6.5 and a 60 foot International Monohull Open Class Association foiling boat. These types of boats are fast, if sailed hard, even upwind but when going fast they are not comfortable boats and some skippers wear helmets for safety.

The jpegs give the idea of an interesting yacht.

 

Part 2 of Skaw A. The following is by student Barbara Guth who was on Team Engineering (Technical Team) as a Junior Naval Architect in the Engineering & Robotics sector. Why is this student interesting? Because she did some of the design engineering for the foils on the SKAW A.

To quote her: “Due to the complexity of sailboats and the small size of the company (SKAW), my role as a Junior Naval Architect spanned across many fields of engineering. Working in tight knit team in a racing environment like Lorient was especially exciting as it is one of the most active areas for sailing and racing innovation in the world.” Also: “My contributions revolved a lot around foils, notably on the design of a mechanism to control their position. This involved measurements, CAD, 3D printing, and structural FEA. I also combined programming skills with new knowledge of aerodynamics to design and analyse wing profiles in foils using software like XFOIL, AVL and grasshopper.”

Translation: The jpegs below are some of her design work and give you details of one of foil shape used in the design process. The foil profile is informative as to the profile required for good performance in a seaway. These profiles were developed from ‘Nicomatic’ the Class Mini 6.50 racing boat that was fast and successful in Mini 6:5 racing. Barbara also helped designed the foil support in the hull of the SKAW A.

It takes a lot of skilled engineering to make a large foiler to work ranging from understanding of the best foil profile, the foil carbon fibre design to the foil support structure and then you must design the rest of the hull and rig structure. What do you mean I have to understand high level maths, have computer skills, have an understanding of weather and sea conditions and have time and money to test this stuff before I can build.

The jpegs give an idea of Barbara skills. The jpegs are large and may take a few seconds to load.

 

O/M - this "skaw" is very interesting & 'may' become the future of monohulls. ?
'Maybe' it will cross over to multi's too ?

 

since my interest in sailing took over my life in the mid 70s, multi- & monohulls have come a long way...

 

The final item on scows for a while. This monohull scow was aimed two-handed offshore class that was originally scheduled for the 2024 Olympics. It was designed by Finot-Conq Architectes but this Olympic yachting class never happened in this financially constrained world. The other designs were about 30 to 32 foot of more conventional monohull designs.

The Olympic 32 is 31 x 11.5 foot with 4,850 lbs weight and has 2015 lbs of ballast on a 8 foot deep keel. The 43.3 foot mast carries a 418 square foot mainsail, 320 square foot genoa and a 1452 square foot asymmetric spinnaker. The draft over the slim fin keel with a bulb on the bottom is 8 foot. The bow spirit was to be a tacking unit but there was some debate about this.

The accommodation is minimal, sleep on sail bags, camp stove a good navigation spot with good electronics. The cockpit is large for sail handling etc. This is a racing boat first anything else second as is indicated by the light displacement.

This design has not gone into production as the Olympic class did not happen. The performance concept of this design is to act like a catamaran when healed with the outboard chine acting like a slim hull with a slightly blunt bow. The concept works well in Mini 6.5 scows.

DANU recyclable composite is specified for the hull, deck, structural bulkheads and keel fin. As a result, it already exceeds World Sailing’s sustainable agenda that requires 90% of the weight of a boat to be recyclable by 2030.

Sorry about the lack of jpegs but I think the design fell into someone’s bottom draw after the class was cancelled.

 

The following is a great idea, good it is being done with catamarans and uses a lot of theoretically possible semi proven technologies. The idea is to have sailing catamarans go around the Atlantic dragging a propeller generation system to produce enough power to electrolyse seawater into hydrogen and oxygen, store the hydrogen and sell it at a profit. The entire electrolyse happens on board the cat and about once a week the cargo is unloaded. Initially the cats will be manned by 6 crew but after a period a fleet of 20 plus cats will be fully automated and autonomous guided by computer software.

The cat and computer software are the easy parts. The generation of the power and hydrogen production is the hard part. To get it all to work on a production scale is going to take a lot of refined engineering. This is the reason China cannot produce very high end computer chips, no single company in the world can inhouse can create the production equipment, manufacture the source materials, do the production and the software. EG TMSC company is vital in the manufacture of high end chips and virtually no one else fully understands what and how TMSC do their part.

DRIFT Energy has revealed its all-new concept MVY, a 190 foot sailing catamaran that represents the first in a "new class of true green, fuel-generating vessels." MVY is 190 foot long about 70 foot wide and carries 4 masts 156 foot high each mast carrying a 5000 square foot wing sail. A total of 20,000 square foot of computer controlled sail area. The cat are then course controlled to optimised the sailing speed. The faster the cat goes the more power is generated by the water generator. How much power 1 to 2 MW/day. This will provide the power to produce 154 tons of green hydrogen a year per catamaran. The cat has onboard storage for about 7000 lbs of hydrogen in pressure containers.

Each 190 foot cat is proposed to cost $US24 million. For this you get a fully integrated production unit sailing the high seas. These cats will be developed in collaboration with catamaran support specialists ShadowCAT in order to bring the design to the leisure market. A 190 foot 4 wingsail leisure cat will something to see. I do not know the length to beam or displacement but the MYV cats look light and have narrow hulls which would indicate with the sail area, 20 knot averages and peaks in the 30 knot range may be possible in the right conditions.

These cats will be something to follow in the development. The jpegs give some idea.

 

sounds like a very roundabout way to produce hydrogen.
Why not have windturbines on stationary platforms, maybe floating ones, anchored in deep water, & have the H2 produced there. Collected each fortnight or so...must be way cheaper & more efficient than those cats.

 

The Tricat 6.90 was the European Yacht of the Year 2022 and uses a hinged float-folding mechanism similar to that of the Dragonfly. This means it is a viable trailer sailor tri that has is built by a company that understands small to 30 foot trimarans. The naval architect is BE Tricat’s Jack Michal.

The Tricat 6.9 is 22.66 x 15.1 in sailing configuration and 24.9 x 8 foot in folded configuration for trailering. The weight is 1,587 lbs and a “light” cruising displacement of 2,100 lbs. The 30 foot fractionally rigged mast carries a mainsail of 237sq ft, a jib of 116 sq ft a gennaker of 258 sq ft and a spinnaker of 366 sq ft. The floats are large in volume to help with stability. And have a length to beam of about 12 to 1. The draft ranges from 1 foot to 3.9 foot over the float based daggerboards. Outboard engines can range from 3.5 to 6 HP.

The accommodation is small but effective as is any 22 foot trimaran. There is a V berth forward a small galley next either side in the central hull and then 2 seats/quarter berths with a table in between. Translation mum and dad forward and 2 kids on the seat/berths will fill the boat when weekend cruising. The porta potti will slide from under the cockpit. The aft section of the main hull is full to handle the weight of the crew in the cockpit.

The Tricat takes about 2 hours by one person to launch or retrieve mainly due to the trampolines and rig set up. It takes a lot less time if you have another person.

The structure is vacuum infused GRP Corecell sandwich, and the foils are carbon fibre, while the float arms are aluminum with a GRP cowling. Also, the crossbeams have water stays for extra stiffness. This is a fairly sophisticated build for a relatively small fast cruiser.

The performance of the Tricat6.90 is good. One test report had 10 to 16 knots of boat speed in winds 20 to 25 knots. Another report claimed 8-10 knots boat speed upwind with a peak of “almost” 20 knots in a gust while reaching. From the video’s on the web I am convinced that this tri can sail well and is relatively easily easy to sail even single handed.

This is a well thought out 22 foot trimaran that sails well and can act as a good weekend cruiser. The jpegs give the idea.

 

The Nacra 17 is a performance catamaran. It was designed in 2011, went into production in 2012 and has been the focus of multihull sailing at the Olympic Games since its conception. The Nacra 17 was converted to a hydrofoil for the 2020 Tokyo and 2024 Paris Olympics.

The Nacra 17 in its original form is 17.2 x 8.5 foot and weighed 381 lbs ready to sail. The 30 foot carbon fibre rotating mast carries a 172 square foot mainsail, a 43 square foot jib and a 192 square foot spinnaker. The hull length to beam is 13.8 to 1. There were straight daggerboards. The combined crew weight is best between 270 to 310 lbs on the twin trapeses.

The next variation was the introduction of Z foils to replace the straight daggerboards and T foils on the rudders. This significantly increased the speed capability of the Nacra 17 and increased the difficulty of sailing these cats until crew gained experience.

Next variation of the Nacra 17 was full carbon construction. Originally the Nacra 17 hulls/decks were around 410g per sq meter skins with a 5 to 8 mm PVC core in polyester resin. Next came an epoxy foam e-glass version. In about 2024 there was a full carbon fibre hull/deck version. All versions a full glass epoxy space frame to handle all those loads. All foils are in carbon fibre. The mast was a full prepreg carbon fibre also had a substantial additional carbon mast bands and added additional carbon and other exotics in appropriate areas. All Nacra 17’s in epoxy are “post cured”, that is they are initially cooked at a moderate temperature, cooled, then heated again for a longer period of time so as to achieve the best practical cure within the available time frame.

Result of all this development is cat that in original format could reach 20 knots, after the Z foils and carbon fibre improvements, the boat speed can reach speeds up to 30 kts (55 kph), and can sail steadily at 25 kts (46 kph) in the right conditions.

An analysis of Nacra 17 foils is available on the web is at: https://www.researchgate.net/public...GFnZSI6Il9kaXJlY3QiLCJwYWdlIjoiX2RpcmVjdCJ9fQ
It is on researchgate as a free download. This is a 23 meg download but shows the foil section and how sensitive the foils are to the correct angle of attack when sailing. The drag profile can increase with a 2 degree change angle of attack.

The jpegs give the idea, the web has a large range of jpegs and video’s of Nacra 17’s in full flight.

 

The following is a German manufactured power cruiser that is designed for European canals as well coastal open sea work. This is a pure cruiser with reasonable accommodation. The basic design can be as short as 32.7 foot or up to 42.7 foot with the same beam and overall structure. The version shown here is 36.5 foot.

The BB 37 is 36.5 x 14.7 foot with a displacement of 10,780 lbs (likely weight). The length to beam on the hulls is 7.8 to 1. The draft is 1.5 foot. Power total is about 120 HP with twin 60 HP outboards. The hulls are semi planning V chine hulls.

The accommodation is 2 single berths forward in the hulls with a double berth in the hull/wing under the saloon seat. The main saloon has a helming seat forward, a galley to starboard and a large dinette that can convert to a double berth. There is an external semi flybridge and a stern cockpit. A practical layout for both canal and coastal work for a couple.

The BB37 loft catamaran is built in GRP sandwich lightweight construction with an extra reinforced keel sole. All windows are double glazed for the northern climates of Europe.

There are no performance numbers but my estimate is a 10 to 15 knot cat that will probable cruise at 8 to 10 knots.

This is a “loft” or floating apartment for long term cruising around or through Europe and Baltic. A nice option. The jpegs give the idea.

 

The following hydrofoil power boat came about because an owner of a 52 Spirit monohull sailing yacht decides to upgrade to a 111 foot Geist Spirit monohull yacht. Spirit produce timber composite, lightweight modern underwater yachts with “old world” looks above the waterline. The owner next asked for an environmentally friendly chase boat so some good camera shoots could be done on EG the Around the Island Race in Britain. Now we get to the featured boat which is a fully electric, foiling power boat by Spirit Yachts in collaboration with BAR Technologies. The Spirit 35 electric foiler (E.F) is capable of delivering a range of 100 nautical miles between charges. The first Spirit 35 E.F holds the record for the fastest time around the Isle of Wight in an electric yacht (50nm in 1 hour 56 minutes).

The Spirit 35 E.F is 35.4 x 7.5 foot with a weight of 5,376 lbs all up excluding crew. The draft is 2.5 foot to 4.7 foot over the retractable foils. The 80 KW engine is driven by a 120 KW battery and is an all electric system. The take off speed is 16 knots and the EF will cruise from 18 to 22 knots. Peak speed is 30 knots. Its stand out feature is the EF can cruise at 22 knots for 100 nautical miles. The battery, cooling and power management system is fully integrated into one package and the engine drive system into a second system that is managed as an overall package. Equipmake designed, developed, and manufactured the electric drivetrain, which features an adapted version of its lightweight, power-dense, high-performance HPM-400 motor producing a peak power of 80 kW with an integrated gearbox. It also features Equipmake’s HPI-450 IGBT (insulated-gate bipolar transistor) inverter and a 120-kW·h battery pack.

Using America’s Cup simulation and design expertise, the 35-ft electric flying boat features a trio of active and retractable foils to help minimize drag. An electric foiler requires a fraction of the power of a non foiling boat. The actual power figure is 15%: ie the foiler consumes 15% of the energy of a conventional speedboat going at the same speed.

The boat has 2 options, a 2 seater or an open cockpit version that can carry about 6 people. There is not much else beyond storage and a cooler.

The build is interesting. Spirit yachts love wood and strategically use carbon fibre. Result the Spirit 35 EF has a 12 mm wood core with carbon fire either side and then being covered outside in a 6mm layer of sipo veneers, and then varnished to great effect. The bottom of the boat, which would be subject to the most pounding, was strengthened with a layer of hemp saturated in epoxy on the outside, and a layer of carbon fibre on the inside. Spirit said: “The carbon fibre is there mainly just to stiffen the timber,” says Sean. “We find that if we take the timber scantlings down to where they’re absolutely strong enough, they then get a little too flexible, so we sandwich them with a little bit of carbon to stiffen everything.” The finished bare hull of the Spirit 35, without any of the propulsion system or fit-out, weighed just 595kg (1333 lbs). The 3 retractable foils are all made from titanium. A T-foil rudder aft controls the pitch and yaw (or ‘angle of attack’) while the two forward foils are joined by a fixed bar with trim tabs at either end to control the roll.

Performance has been mentioned above but a few other issues. “A boat that’s foiling is inherently unstable. It’s like an upside-down pendulum,” says Simon from BAR. “It’s like balancing a broom on your finger and you have to keep moving your hand to keep the broom up. That’s effectively what we have to do the whole time to make the boat fly. It doesn’t want to fly; it wants to fall over because the centre of gravity is all the way up in the air.” To stop the boat ‘falling over’, BAR have developed a flight control system – its so-called Foil Optimization and Stability System (FOSS) – which can read the state of the sea and adjust the foils accordingly. The Spirit 35 (F) is fitted with five sensors, which determine how high the hull is off the water, as well some monitoring equipment to calculate the boat’s inertia and acceleration. Between those sensors, the on-board computer develops a mathematical picture of what the boat is doing and what the sea surface is doing around it. From that information, it adjusts the foils to correct for roll and pitch movements according to the size of the waves. If it’s just a bit of chop, it just skips pass them, but if it’s a longer wave it will follow it.

There is a lot to learn about foiling boats. Probably the reason the first Spirit EF 35 cost over 1 million pounds to build. The jpegs give the idea.

 

BAR technologies do a range of interesting work. This will be about a new 98.5 foot crew transfer vessel for offshore wind farm work. The vessel can also carry up to 3 x 10 foot containers for equipment etc that may be heeded for maintenance work. I will call this vessel a power proa that can carry up to 26 workers to and from wind farms etc.

The BARtech 30m CTV (also known as Seacart) is 98.5 x 35.7 foot that weighs 174,500 lbs and displaces 224,000 lbs when fully load with crew and 3 containers. The draft is 5 foot in “light” mode. The hull shape is interesting. It appears to be a proa with a narrow main hull. The proa float hull appears conventional but underwater is a swath hull (long tubular hull with a thin support structure to the above water proa hull). Also there are hydrofoils to assist pitch and stabilization control.

The accommodation has on the top deck the helming and control position for deck work. The lower level is accommodation for up to 26 wind farm workers. On the external forward deck is the space for up to 3 x 10 foot containers plus the crane for moving equipment on or of the vessel.

The reason for the design is fuel efficiency. The proa is capable of 30 knots and can cruise at 15 knots depending on the engine power options. In most cases the proa is between 30% and 50% more fuel efficient than other types of crew transfer vessels. With the swath outer hull and hydrofoils the 30 meter Proa reduces vertical accelerations by between 35% and 70% allow more comfortable travel in 8 foot plus seas. Why is this important, any offshore engineering personnel beset by sea-sickness in travel to a project must be returned to port – meaning in practice that a vessel transporting up to 24 engineers must cease its transit to a project site – resulting in expensive downtime for the project owner. PS in some offshore wind farm areas the crew boats are limited to 10 knots due to whales etc being in the area.

The structure appears to be aluminum with suitable reinforcing for decks and bows for nudging up to wind turbines and carrying containers etc.

The jpegs give the idea. An interesting design.