Multihull Structure Thoughts

[oldmulti]

This is an update on the Vaka 990. The Vaka 990 was designed in 2017 and had a version 2 come out in 2020. Jerome Denlaunay did structural and limited dimensional improvements to a coastal proa with 2 to 4 berth accommodation. The proa can be disassembled for transport.

Vaka 990 Proa is a 32.5 x 18 foot cruising proa with a weight of is 2100 lbs and a displacement of 3360 lbs. Each 30 foot wooden mast (150 mm in diameter) carries a 135 square foot mainsail with a jib forward of 130 square foot for a total sail area of 395 square foot in the schooner rig. The length to beam on the main hull is 10.8 to 1 and the float length to beam is 13,2 to 1 at the waterline. The draft is 3.75 foot over the main hull daggerboard.

The boat is constructed of west epoxy plywood construction. The bulkheads and main hull shell are 9 mm ply with floats bulkheads being 9 mm and the float skin is 6 mm ply. (33 sheets 9 mm and 16 sheets 6 mm 2.5 x 1.25 meter). The 16.4 foot cross arms (262 mm x 240 mm box section) are mainly plywood with 4 x 9 mm plywood webs and a top and bottom of 9 mm plywood. Internal beam bulkheads are 6 mm ply at 600 mm centre lines. The beams can be solidly fixed or attached with ropes for transport.

The "Pod" is habitable and acts as an anti-capsize device and the boat has 4/2 berths, a WC, limited galley with storage. The jpegs give an idea of the Vaka 990 Proa. The PDF is the 2017 study plan of the boat and its structural components.

 

[oldmulti]

Both the world’s largest sailing multihull (58m) and what is rumoured to be the largest ‘proper’ sailing monohull (as opposed to sail-assisted) at around 120m, are in fit-out today and will sport DynaRigs. First seen on Maltese Falcon 25 years ago, these freestanding masts rotate so the yard arms and soft sails can be set to suit the wind angle.

Southern Spars the proven DynaRig is the answer for certain sizes and applications, especially with the 3 latest projects it has in production. In cost and practical terms, it makes much sense – for vessels over a certain size (around 65m+ LOA) and for passage making, it is hard to match.

In the late 1960s German engineer Wilhelm Prölß had the idea to redevelop the square rig style into a more automated and powerful design for shipping. The DynaRig was truly developed by designer Gerard Dykstra for the groundbreaking 3 masted 88 metre Maltese Falcon in 2001. By then carbon composite materials made it feasible, the project team was able to develop rotating, self-supporting masts with curved yard arms that would allow the yacht to sail to windward and tack. Each mast would carry five sails, unleashing a 2,400m2 sail plan in minutes, all controllable by one person. What followed was a fascinating multi-year development of Maltese Falcon’s rig.

DynaRig has been through several brand changes and was then employed on 106.7m Oceanco Black Pearl. Directly inspired by Maltese Falcon, and reuniting its same designers, Ken Freivokh and Dykstra. Black Pearl can up anchor and set its 3,000m2 of sail in eight minutes under the control of 1 crew member.

Now under the North Technology Group umbrella and Southern Spars, a new 5,500m2 factory complete with 90m-long oven in Southern Poland was opened three years ago and will produce DynaRig’s with its 3 latest commissions. Unlike square rigs, there are no gaps in the sails and yards, so they capture all the force and are much more aerodynamic and efficient. With full sail set, each spar’s sail plan works as a single sail that can be trimmed to windward by rotating the mast. DynaRigs are engineered for high loads and equipped with fibre optics and load cells for strain data. Another benefit is the choice of sailcloth. As the sail is supported over its full length, with pressure evenly distributed and there are no high clew loads, conventional Dacron is preferred over expensive laminates or exotic fibres. And as the sails are uniform sizes, minimal spare sails are needed – they don’t tend to flog, but UV is the enemy.

The DynaRig build infuses its superyacht yards in full carbon, the masts built in prepreg carbon in a heated mould. A 14-tonne, 80m-long half-mast shell is cured in a single hit – “surely the biggest structure in the world to do this,” Shaw points out. Shaw goes on to explain how Maltese Falcon and Black Pearl largely used similar technology in their rigs and how their mast sections taper as they extend up, which is hard to build. So, they have redesigned new straighter mast sections, which have a slight weight detriment but are more buildable.

Sail power is reduced by setting fewer sails, rather than reefing individual ones. “The topsail represents 40% of the bending moment at deck level – so lose that and you’re pretty good,” says Shaw. The rigs can also be twisted very quickly to depower. Each sail is furled one at a time. The yards are tapered so that as you start to furl, the sail is grabbed from the middle, removing the main loads immediately. The captive winches have always been electric. “You have to control four corners of the sail precisely,” Shaw explains. “With electric you get that control, where hydraulic may not do that – hence we spec electric for commercial boats too.”

The DynaRig factory has been building two 60m rigs for the new Greenpeace vessel, as well as twin 60m DynaRigs for a 58m adventure sailing catamaran, both Dykstra designs. The latter is currently in production at Echo Yachts in Australia. This all-aluminium craft will be the world’s largest multihull by some margin when it launches in March 2028, eclipsing the 46.5m Perini ArtExplorer.

As you can imagine all the sail handling equipment and rig sail angles to the wind etc are computer controlled allowing 1 crew member to input desired location and allow the computer slash navigation equipment select the optimum course and sail plan. All no problem if you are spending $50 million plus on your boat. But if you are EG Black Pearl you can cross the Atlantic averaging 13 plus knots.

DynaRigs can be applied to smaller cats or tris as they are no more difficult to sail than a fractional rig sail plan. A DynaRig is about the equivalent of a genoa, meaning to get the best out of a genoa it needs to be adjusted for the wind angle changes etc or just accept less performance and leave the sail at a fixed position. The reefing systems and rotation of the mast can be set up manually on a smaller boat. But please remember you may not get thee optimum performance but you may get a nice cruising rig with adequate performance.

The jpegs give some idea of the rig, its mechanics and some boats mentioned.

 

[oldmulti]

The Tomahawk 620 is a single outboard-engined centre console fishing/workboat with an asymmetric catamaran hull. The Tomahawk is designed by Scott Ramsden in collaboration with marine engineer Austin Kell and is made in Chinderah in northern NSW. It is an alloy cat that has been designed specifically for single outboard engine installations.

The problem with mounting the outboard engine in the centre of the transom in the middle of the tunnel is that the propeller has to rotate in water that is already mixed with air. This creates propeller ventilation with the propeller rotating but getting no grip, or bite, on the water. Propeller ventilation in a single-engined cat will even occur when running in a straight line. And you can forget about taking corners with any speed as the propeller will ventilate, the engine will over-rev, and the boat will go nowhere. The solution to make a powered cat work well with a single centre-mounted engine is to fit a water/wave deflector/breaker in the aft/stern area of the tunnel between the two outer sponsons. This should allow the engine’s propeller to spin in clean, undisturbed water.

The Tomahawk 620 is 20.3 x 8 foot with a “displacement” of 4000 lbs. the hull draft is 1.1 foot. The engine can be an outboard up to 150 HP. Peak speed with a 130 HP outboard was 27 knots, a 150 HP outboard should produce peak speeds of 30 knots. The cat is certified to carry 6 passengers in commercial use.

The Tomahawk is durably built. The hull bottoms/sponsons and transom are welded from 4.0mm plate alloy, while the topsides are made using 3.0mm thick alloy. Internally, the Tomahawk has a 4.0mm tread plate welded alloy floor with giant scuppers at the transom to self-drain water quickly out of the boat. The cat is built from durable 5083 marine grade plate aluminium

In testing the Tomahawk 620 was found to: “The catamaran hull has an asymmetric design along with a wave piercer-like reverse-angled bow and stem shape which is very effective in cleaving through bay chop and ocean swell. Running the full length of the tunnel is the wave breaker/water deflector that not only feeds undisturbed water aft to the propeller but also eliminates tunnel “slap” at displacement speeds. The asymmetric shape of the Tomahawk hull also allows it to corner more easily at speed, whilst maintaining quite a flat and level stance through the turn – cats tend to naturally lean out. Large outer and inner chine flats on each sponson provide lift/buoyancy and more planning surface for improved efficiency, spray suppression and following sea performance.”

An interesting good strong design for serious fishing/commercial or pleasure work. The jpegs give the idea.

 

[oldmulti]

For those who wonder why monohulls are still preferred by many try this bit of information from 2026 Globe 40 race (yes around the world by the capes) that finished in April: “The newer scow bow boats are in a different league in terms of speed and Belgian Ocean Racing – Curium beat the outright 24-hour distance world record for a 40ft monohull, covering 459.78 miles at an average speed of 19.2 knots, and hit a 31.5-knot top speed. They dominated the fleet on this leg and, having averaged 320 miles a day, held a narrow lead on Credit Mutuel approaching the virtual finish line, but sailed into a calm in the lee of the headland south of Valparaiso, allowing the French boat to catch up. The result was so close that, even after analysis of each boat’s data logs, the race committee had to declare a tie.”

The jpegs show the boats mentioned.

 

[oldmulti]

This is about an inflatable sailing catamaran made by Grabner (Austria), the Happy Cat Star is described as an inflatable multi purpose catamaran. It can day sail 4 people but performs well with 2 crew.

The Happy Cat Star starts in 4 bags, but when assemble and inflated turns into a 15.75 x 7.45 foot catamaran with a weight of 163 lbs for the standard model, there is a full carbon crossbeam etc model available that weighs 143 lbs. The maximum payload s 1100 lbs. The 4 part carbon mast is 20 foot long and carries a Dacron battened mainsail is 86 square feet and has a foot that is cut up on a diagonal, making more headroom for the skipper during tacks. A 37 square foot Dacron jib on a continuous furler completes the upwind sail plan. Because the main is boomless, there’s no danger of a head injury in gusty conditions. The hull length to beam is 10.5 to 1. The draft over the central pod based rudder is 1.5 foot. There is a kickup centreboard under the main beam. The maximum engine power is a 3 HP outboard.

The build of the inflatable hulls is 1100 dtex EPDM-Kautschuk fabric. The cross beam and central spine are either in aluminium for the standard version or carbon fibre for the lightweight version.

The performance is described by one tester as: “We were ripping around the Chesapeake Bay, logging 14 knots of boat speed while the big boats waited out the breeze from the safety of their slips. (The manufacturer reports max speeds over 16 knots.)” Yes, it can sail upwind even in the 20 knot plus conditions and have reasonable performance. If you are towing a caravan to sunny locations this may be a good solution to have a cat as well.

The jpegs give the idea.

 

[oldmulti]

I was reading an article about the latest Mini 6.5 mtr Transatlantic mono racing scow that can foil. An interesting carbon foam epoxy build but the real fun was the statement that they were wanting to get the boat to foil across the Atlantic for up to 100% of the time. Realistically you may foil maybe 90% of the time but the course has been changed this year to include more time in the doldrums.

The real interest is the scow hull design is being optimised for sailing on the foils and less optimisation about sailing on the hull. The hull speed of a Mini 6.5 is 147 miles/day but the 24 hour record of foil borne Mini 6.5 is 352 miles/day (14.62 knots average). To improve this record Sam Manuard (the designer of the 24 hour record holder Mini 6.5) was asked to design a boat more orientated to foiling.

First requirement was a very light strong boat structure. A lot of carbon fibre, foam and epoxy with a very strong support structure for the main lifting foils, swing keel and rudder structures. The point loadings on the pivot points in each of these structures is very important, also required is a stiff structure around each of these points is vital. Any flexibility around the load points can affect the angle of attack on the foils causing performance variations.

Next level is the correct foil section selection. It is not just the macro shape of the foil but how the sectional shape changes along the foil. Minis have limited capability to add flaps etc to foils, so sectional shape is very important.

Next is the surprise. It’s the electronic control system in the Mini 6.5. There are limitations on Chart Plotters and Satellite Communications. The use of Madmtec MAD brain and AI controlled systems used in conjunction with the autopilot systems is designed to improve stability and foiling speed across a wind and sea range. The aim is to get the boat foiling at the optimum height above the water over the longest period possible.

Finally, the Mini 6.5 class restricts the number of sails that can be carried, so you need to get the best combination of sails to suit the foils and course you are likely to sail in the event. EG a non foiling period through the doldrums requires a full genoa, but high speed foiling requires the same sails to have a flatter cut to handle the higher wind speeds. But the same sail may be required to be roller furled to act as a smaller sail for stronger winds.

Pity the poor sleep deprived skipper who has to keep up with all these variations and understand the complexity to achieve optimum performance. Give me a simple tiller and some woolen tell tales on the sails.

A few jpegs of a modern Mini 6.5. The last 2 of the grey boat is the 2027 mini version aim at near full foiling.

 

[oldmulti]

Tanton yacht design did aa version of the patented Wingman monohull supported by a large foil design in 1992. It was a sport cruiser with 2 berths and not much else. Jpeg 1 gives the study plan view of the boat. The Tanton “Monomaran” was 24 x 24 foot with a displacement of 1,075 lbs. Sail area is not available. The draft is 9 foot over the central hull daggerboard. The construction of the Monomaran is ply sheets on the sides and decks with cold molded bottom over shaped foam blocks.

Tanton’s description is: “Literally, a single catamaran hull fitted with lateral wings, skimming the water to produce righting moment and the necessary stability; the boat has no keel and is simply fitted with a centreline daggerboard to combat leeway.”

The design was based on Martti Palmquist developed the concept of the Wingman in the 1980’s and patented the concept in 1987. There was a production version available for sail in 1988. Not many were sold. There were 5 prototypes, the early ones reached 15 knots, prototype 5 reach peak speeds of 21 knots and was used as the production prototype. Martti Palmquist died in 1989 and the original prototype 5 sat in a yard unused for 30 years.

Mark Palmquist (son) decided to resurrect the project in about 2016/18 and develop the foiling solution further. To quote Mark: “The foil is super cavitating which means there is no low pressure side. You’re talking about a recent development that did not exist in 1987. The wing operates on the surface not under the water. And there is a small amount of spray that goes forward which the wing then rides over. This is self generating …”

Mark then went on to try other skimming float/foil configurations which he is still developing. Attached are some jpegs of the early Wingmaran and the later version prior to the change of float foil shapes. An interesting idea that help lead us to hydrofoil supported sail boats.

 

[oldmulti]

Founded in 1974 by Yves-Marie de Tanton, Tanton Yacht design is credited with hundreds of completed boat designs and projects. The following is an example of one design concept that went though a few iterations prior to the final design. Little is know beyond the 65.6 foot length and the concept is a sports cruiser. The potential owner had experience with a couple of larger and smaller cats. Features such as a fractional sloop rig, forward and aft cockpits were important as well as a large bridge deck main cabin. Initially there was a forward crossbeam and prodder but as the design evolved the forward cross beam was dropped. This would be a big comfortable cruiser that has some speed potential due to the rig and hull based daggerboards.

The construction was to be aluminium. I don’t know how far this design build went but the 3 separate development iterations are interesting. The red 1 was first followed by the blue version then the black and white hull version third.

 

[oldmulti]

This is about a split stern monohull. That is a monohull shape forward with a catamaran hull shape aft. I have seen 3 versions of this type of boat ranging from 40 to 55 foot. Each sails reasonably well but the concept has been surpassed by monohulls like Comanche. Commanche is the 100 foot racing yacht that is light and wide with a big rig. When Commanche heels the waterlines are relatively narrow as half the wide stern is in the air. Commanche is a dog in light airs down wind and a very fast (30 knots plus) in medium to heavy airs.

The purpose of the split stern in the earlier boats was to minimise roll, narrow the waterline when heeled and add some stability by having a relatively for its beam a wide stern. In this Micheal Pope design it also provided a location for dingy landing and stowage.

The boat is named “Away” and was to be moored in the British Virgin Islands. Away is 44 x 10.2 foot with a weight of 15,000 lbs. The cat schooner rig is on carbon fibre free standing masts. The draft varies from 4.25 foot over the short keel and draws 9.5 foot when the centre board is down.

Away has 2 double berths forward (both placed over 100 gallon water tanks, not always a quite sleeping experience) and a single pilot berth aft. The main saloon has a galley seating and helm/navigation area. The cockpit aft is large but has the split stern to allow the dingy to be raised 2.5 foot when cruising.

The construction is foam glass and is relatively light for this size of boat.

To give you the idea a NZ 50 version of this type of boat could sail at 12 plus knots and could average 9 knots. The WA version was lighter and could sail a little faster but was slow down wind in light weather. The real issue in these designs is the transition from the monohull part of the hull to the split stern. Get the transitional slope wrong and drag is sure to follow.

Interesting concept that never really caught on. The jpegs give the idea

 

[oldmulti]

This is about the rig not about the cruising monohull that uses it. The swing rig has been used successfully on a 30 foot Tiki cat for transatlantic sailing and can be done well if you know what you are doing but this is the monohull done by Tanton design takes the concept to another level of technology. This is not the cheap version but interesting.

The monohull is about 37 foot in length and is a true cruiser hull shape. The rig is to be an easily handled with minimal sail controls and loads. The sails are reefable and can be dropped very rapidly.

Have a look at the jpegs you will get the general idea of the concept. The large advantage of the swing wing rig is its variable camber geometry allowing the sail to be flatter for stronger winds to fuller for light winds. Also the wing shape is in theory more efficient than a conventional genoa and main allowing lift drag coefficents of 2 to 3. I say in theory because any wing sail requires the leading edge to be at the correct angle of attack to the wind to the prevailing wind. Unless you are adjusting the wing sail angle of attack by crew or computer continuously you don’t always get the additional sail power out of this rig.

Translation of the above. Swing wing rigs are sensitive to sail trim to get the most power out of them.

The rig components are mainly carbon fibre and plywood on a carbon fibre mast. The individual batten attachment points in this rig have some metal components. This is a more sophisticated than PHA swing rig which has wooden masts and timber battens with simpler attachment points.

Tanton’s swing wing rig will be more expensive and have more maintaince but will provide more power than PHA’s simpler swing wing rig.

The jpegs are of Tanton’s version, the last jpeg is of PHA Tiki 30 cat.

 

[ALL AT SEA]

This is about the rig not about the cruising monohull that uses it. The swing rig has been used successfully on a 30 foot Tiki cat for transatlantic sailing and can be done well if you know what you are doing but this is the monohull done by Tanton design takes the concept to another level of technology. This is not the cheap version but interesting.

The monohull is about 37 foot in length and is a true cruiser hull shape. The rig is to be an easily handled with minimal sail controls and loads. The sails are reefable and can be dropped very rapidly.

Have a look at the jpegs you will get the general idea of the concept. The large advantage of the swing wing rig is its variable camber geometry allowing the sail to be flatter for stronger winds to fuller for light winds. Also the wing shape is in theory more efficient than a conventional genoa and main allowing lift drag coefficents of 2 to 3. I say in theory because any wing sail requires the leading edge to be at the correct angle of attack to the wind to the prevailing wind. Unless you are adjusting the wing sail angle of attack by crew or computer continuously you don’t always get the additional sail power out of this rig.

Translation of the above. Swing wing rigs are sensitive to sail trim to get the most power out of them.

The rig components are mainly carbon fibre and plywood on a carbon fibre mast. The individual batten attachment points in this rig have some metal components. This is a more sophisticated than PHA swing rig which has wooden masts and timber battens with simpler attachment points.

Tanton’s swing wing rig will be more expensive and have more maintaince but will provide more power than PHA’s simpler swing wing rig.

The jpegs are of Tanton’s version, the last jpeg is of PHA Tiki 30 cat.

As demonstrated on Matin Bleu? You've probably covered her previously...
https://voilesetvoiliers.ouest-fran...roisiere-3c153aa2-2f7f-414c-a127-ffda13d4cbdc

 

[oldmulti]

All At Sea. Yes, this is one of the better versions. The junk rig association has several mono's using the swing wing rig. It now has a competitor called the split junk rig which was developed by Slieve McGalliard's 31 foot monohull Poppy -which has a junk sail that has a "jib" component in front of the mast and the remaining junk sail behind the mast. It still can be handled and reefed like a junk sail. It has all the benefits of a balanced junk sail but is more efficient to windward whilst maintaining its advantages on a reach or a run. Slieve originally had flat sails then inserted chamber in each sail component. The split sail was home made in 3 sections of 6oz Terylene, and is 515 sq.ft (47.5 sq.m), the same area as the Bermudan rig mainsail and 135% genoa. This boat sails very well to the annoyance of other Westerly Longbow owners. According to Slieve and results in EG round the island race in the UK Poppy is about 2% slower upwind than her Bermudian rigged sisters but about 2 to 3% faster on all other points of sail whilst being easier to handle under sail. The jpeg gives the idea. For those who want more detail the following web address links to a 2010 AYRS publication describing Poppy and the rig in more detail.

https://www.ayrs.org/catalyst/Catalyst_N37_Jan_2010.pdf

 

[oldmulti]

The Diamond 24 is a very high performance day sailing trimaran. Designed by VPLP, it was conceived as a one design for those who wanted to go fast. The standard model is initially described then we will go onto Francois Gabart modified version done in 2016 to get information about foils etc for the 100 foot MACIF trimarn.

The standard Diamond 24 is 23.75 x 18.4 foot displacing 1020 lbs. It carries a carbon wing mast that is 210 mm x 100 mm by 37.75 foot long and carries a 236 square foot mainsail and a 107 square foot jib. The draft is from 2.6 foot over the rudder to 5.25 foot over the daggerboard. The build is foam with carbon fiber and epoxy covering. The cross arms are carbon beams in a glass/pvc sandwich, that have 4 bolts to attach them to the hull structures. The assembly is relatively fast as each component is relatively light.

The Macif & Francois Gabart version of the Diamond 24 was used to test new developments for the 100 foot Macif Tri. The Francois Gabart version had initially C foils in the floats then moved to J angular foils in the floats and lifting rudders. This required structural modifications and strengthening which then required a slightly more powerful rig. Result is, the modified Diamond 24 displaced 1,130 lbs and carried a 40 foot rotating carbon wing mast with a 258 square foot mainsail, an 87 square foot jib and aa 398 square foot Gennaker.

This version could reach 30 knots peak speed and 15 knots upwind. The first development was to check the stepped version of Artemis first flying AC45 foil design against the simulation model projections. The objective is to validate the performance and maintenance of the new foils for the bigger Macif Trimaran. When the flying balance etc was sorted out then Francios developed the auto pilot functions whilst foiling. It far cheaper to crash land a 24 footer than have a 100 footer go out of control. The research work was very successful as the 100 footer seems to work very well.

A jpegs below of a standard Diamond 24 then the 3 jpegs of the foiling version.

 

[skaraborgcraft]

This is a Diamond Cat.

All the design charm of a 60s design and a rare find these days. They make Wharrams of the same length seem very claustrophobic.
Not owned a multi, but Jeromes Vaka did have me pondering for some time, a non-shunting proa seems to have upsides.

 

[oldmulti]

We are going to talk about a 1967 catamaran design done by Ernie Diamond. A home builders design based on a previous 20 foot catamaran. This design was a plywood timber chine design that was covered with polyester (later upgraded to epoxy) glass intended for home builders. It was a cruiser with accommodation for 5 to 7 crew.

The Diamond 24 catamaran is 24 x 12 foot with a weight of 2,500 lbs and a displacement of 4,200 lbs loaded. The 30 foot fixed aluminium mast carried a 160 square foot mainsail, a 96 square foot jib, a 140 square foot genoa and a 35 square foot storm jib. The length to beam on the hulls is 7.8 to 1 (the shallow V hulls are 3 foot wide at the waterline). The draft over the fixed low aspect ratio keels is 2 foot. An 8 to 10 HP outboard will drive the boat at 6 knots plus with less than a 1 litre per hour fuel useage.

The accommodation is 3 single berths in the hulls with one hull having a head forward and the other hull having a galley. The main saloon has a dinette that converts to a double berth. The headroom in the hulls is 6 foot with the main saloon having 4.5 foot head room. The cockpit has sufficient space to sleep 2 people if required.

The original Diamonds were built from 6 mm plywood over plywood and Columbian pine frames and stringers (about 45 x 18 mm), glued together with Aerolite and gripfast nails. This was later changed to epoxy glues when they became more available. There was one Canadian Diamond 24 that was built with a foam glass shell over plywood bulkheads. The majority of Diamond 24’s are still sailing if they were well built and maintained.

The Diamond 24 had an outright peak speed (no extra gear on board) of 18 knots but normal peak speed was about 12 knots with an upwind speed of 6 to 7 knots upwind reefed down in 30 knot winds. Not to bad for a simple cruiser.

This design was very good for its time and a simple build, it’s a pity there are not many of these simple designs available anymore. It's not always about speed.

The jpegs give the idea.