Multihull Structure Thoughts

The following is a 45 foot day charter catamaran designed by Morrelli & Melvin for 49 passengers. The cat is 45.3 x 24 foot with a weight of 13,600 lbs and a displacement of about 25,000 lbs. The 54 foot aluminium fixed mast carries a 600 square foot mainsail and a 290 square foot fore triangle with a self tacking jib. The headstay and cap shrouds are of 15 mm 1x19 wire. Superior diamonds are 12mm compact strand, inferior diamonds are 10mm compact strand. All turnbuckles and cables are 316 stainless steel. The hull length to beam is 7.5 to 1. The kickup centre boards draw 6.5 foot when down. As a charter catamaran this boat will sail well, but is not intended to be a high-performance racing machine.

According to the designers much thought went into making this vessel as strong and practical as possible to absorb the punishment of high volume day charter business, to minimize down time and to be easily sailed with a short handed crew.

Schooner Creek Boat Works, in Portland Oregon did the first build. The hulls, decks, bulkheads and bridge decks are a composite of bi-directional and unidirectional E-glass and PVC core, utilizing infused vinylester resin. The hulls will be built on a faired female direct mold joined on hull centerline. Final fairing shall be done with “Duratec” vinylester primer, applied in sufficient thickness to form a water barrier beneath the waterline. Two water tight bulkheads are installed in each hull, separating compartments at each extremity. Ring frames are installed in each hull on 5’ centers between bulkheads. Local laminate reinforcement is added to bow, the centerboard case trunk and rudder area for impact absorption. Bulkheads to be installed on trapezoidal foam sections, to distribute compression loading. Monocoque hull and deck construction, with no mechanical fasteners. The hulls are painted with “Awlgrip” linear polyurethane paint.

This is an interesting design that could form the basis of a good cruiser. The jpegs give the idea.

 

A final example of power multihulls is the Oak Hill Marine Design Maine Cat P-47 power catamaran. There are many power cats with similar characteristics in hull shape and design and I have chosen the P-47 as an example. The Maine Cat P-47 is 47 x 18 foot weighs 21,000 lbs and displaces 29,900 when fully laden for cruising. Fuel and deck gear like dinghies, anchors etc add 5000 lbs. The payload for humans and gear is 3800 lbs. The cat draws 3 foot. There are engine options but a normal install could be twin Volvo Penta D3 190-hp diesel engines.

The interesting part of this design is the hull shape that was initially created by Malcolm Tennant many years before. The displacement “canoe stern” hull shape has proven to be very fuel efficient and can produce high cruising speeds in rougher water. This hull shape has been used by many designers and as long as the designer does not produce an overly “full canoe” shape in the stern most of these types of hulls work very well. The P-47 has a hull length to beam of 13.35 to 1. This is an important feature of this hull type as its fine hulls allow the cat to exceed its “displacement hull speed” limits. Dick Vermeulen the builder said “The underside of the wing deck (the fiberglass underbelly of the cabin and deck connecting the two hulls) must stay clear of the water in all but the worst conditions,” he said. In addition, he said, “the bows must be kept light and have ample reserve buoyancy to provide lift in passing waves”

Weight is critical in making the P-47 work well and the Maine Cat uses “Core-Cell” as the structural closed-cell foam core in its hulls and decks which vacuum bags the parts to insure the best fiberglass to resin ratio for strong, but light-weight moldings. In addition, Maine Cat is careful about the weight of absolutely everything that goes into the boat to make sure that all materials and equipment earn their way onto the vessel.

The Maine Cat P-47 is easily pushed with two small diesel engines. According to Maine Cat, at 16 knots the P-47 propelled by twin Volvo Penta 190-hp diesels burns eight gallons (64 L) per hour. That means that she gets 2 nautical mpg or 4 liters per nautical mile. This is pretty economical cruising and much better than typical express cruisers of the same displacement and length. At 23.4 knots, which is the boat’s top speed, Maine Cat says she burns about 18 gph (72 litres per hour) or 1.32 nautical mpg. Maine Cat’s advertising copy says that in the P-47 “…you can skim across the water at an exhilarating top speed of 21 knots.”

A good design that has proven to be a good cruiser. The jpegs give the idea and please study the hull shape especially around the stern.

 

A small update on foilers. The GP F50 foilers are now 15% faster than the AC (America’s Cup) 50 foilers. They are basically the same size of cat using similar rigs and similar weights so where did the performance gain come from?

First the AC 50 is 49.2 x 27.8 foot that weighs 5150 lbs and has a 1175 lbs crew weight limit. The 78 foot high wing mainsail (which weights 997 lbs) has 1040 square foot of area with 3 jib options of 193, 257 and 342 square foot. The hull length to beam is 20 to 1. The foil draft is a maximum of 7.9 foot.

The GP F50 49.2 x 27.8 foot (but over the foils is 28.8 foot) and weighs 5376 lbs with a maximum crew weight of 981 lbs. The 78 foot high wing mainsail (which weights 997 lbs) has 1040 square foot of area with 3 jib options of 193, 257 and 342 square foot. The hull length to beam is 20 to 1. The foil draft is a maximum of 7.9 foot.

Both the AC 50 and the F50 has a 59 foot and 92 foot wing options depending on racing wing conditions. The numbers sound the same because three of the original six GP F50’s were actually converted AC 50 catamarans.

So where did the performance gains come from? Basically it is due to the foils and how those foils are controlled. The AC 50 had limited fore and aft control of their foils which had to be “done” manually (AC being what it is, some boats had “manual” electronic or hydraulic control). The foils were also built to the technology in 2016 which is carbon fibre with sectional shapes developed up to that point.

The GP F50 new foils have been built from a higher modulus (stiffer) carbon than the AC 50’s. This means the F50 foils are thinner and so produce less aerodynamic and hydrodynamic resistance, allowing the boat to go faster. Also the flight control systems have changed dramatically, now the foils are partially computer controlled with now with both main foils and rudders having variable control in 3 dimensions. According to the SailGP website:

“The flight of the boat can be controlled from the twist grips on the steering wheel or from a joystick controlled by the crew member sitting in position 3 (flight controller). The ride height of the boat can be adjusted independent of the fore and aft bow down pitch.

“What seems like miles of hydraulic lines stitched inside the hulls and under the floorboards are used to distribute power to cant the boards to the most efficient angle and activate the rudder pitch control system.

“The helmsman can control the ride height, the jib sheet, and the rudder differential from push buttons on the steering wheel. The helmsman can also adjust the speed at which those functions are adjusted by adjusting a dial in the centre of the steering wheel.”

To control the foils the GP F50 has a lithium-ion battery that provides a 5-hour charge for the hydraulic systems on the yachts. The use of a computerized system makes frequent tacks and gybes possible, eliminating the time it takes for the AC 50 crew to manually charge the hydraulics for foil and rig changes.

The result is the GP F50 is capable of 54 knots when at full speed. The limitation of 54 knots is due to the foil shape and cavitation. Over 54 knots you need super cavitation foils which is an entirely different approach. The outright sailing speed record by sail rocket is 64 knots on super cavitating foils.

Interesting future coming at us fast. The jpegs give the idea.

 

This is about a catamaran design for fishing in Indonesia. The reason for this item is the structure design meets the Fiberglass Reinforced Plastic, Indonesia Classification Bureau 1996 Rules. The 5 GT fishing catamaran 39.25 x 11 foot that displaces about 18,000 lbs loaded. The cat is powered by 2 x 30 hp engines. The results of sea trial had a speed of 9 to 12 knots in following seas and 7 to 8 knots into a head sea. The catamaran fishing vessel designed operational capability is up to 60 nautical miles offshore with moderate and fresh breeze (Beaufort scale 4 and 5; wave heights 4 to 8 foot).

The calculation of the construction of fiberglass boats can referred to the FRP vessel regulations Indonesia Classification Bureau 1996. Mechanical Properties of FRP for ships:

 Tensile strength 85 N/mm2  Young’s modulus 6350 N/mm2
 Flexural strength 152 N/mm2  Shear modulus of 2750 N/mm2

The 5 GT catamaran fishing vessel hull calculations for construction with a Length x Beam of each hull is 39.25 x 4.0 foot and a hull height of 3.25 foot are as follows:

1. Keel/Stem 11 layers combination of Chopped Strand Mat 300 gr/m2 and Woven Roving 800 gr/m2 with 10.3 mm thickness and 5300 gr/m2.

Width = distance girth hull chine left to right = 2300 mm Keel width = 400 mm.

2. Shell/Hull Side 7 layers Chopped Strand Mat 300 gr/m2 and Woven Roving 800 gr/m2 with 6.3 mm thickness and 3100 gr/m2.

3. Frame/bridge deck/Girders-Sandwich System (Polyurethane core) 7 layers Chopped Strand Mat 300 gr/m2 and Woven Roving 600 gr/m2 of 50 x 70 mm with 5.67 mm thickness and 2700 gr/m2. Frames are at 500 mm spacings.

Please remember this is for a solid fiberglass hull using e-glass and polyester or vinylester resin. More sophisticated structurers could be built with PVC foam sandwich and higher strength glass and resins. The solid glass structure is for economy and simple, long life, low maintenance operation.

The limited jpegs give the idea of the shape of the cat with some eg’s of the frames.

 

Malcom Smith and Ian Sargeant produced the Mi6 Proa for a 1993 design competition. The Mi6 design was the winner out of 80 entries. The Mi6 proa is an Atlantic proa, but due to its free standing rig, can be sailed as a Pacific proa. Mi6 is 19.5 x 8.2 foot with a 20 foot aluminium mast, the lower section of the mast is large diameter and tapers sharply up to the spreaders at wishbone level. Above that level it's just a conventional mast section and about 150 square foot of sail in a balanced or 'swing' rig to reduce sheet loads. The rig plugs straight into the mast box of the main hull, to allow 360° rotation. The rig uses a wishbone boom to which is attached both the clew of the mainsail and the tack of the jib. The jib is an unusual delta shaped 'lop sided hang glider wing'. There is no jib sheet and the slot is trimmed by adjusting the clew position with a simple control line. The sail plan is of modest area for ease of handling. The design of the proa is intended to carry a family of 4 for day sailing.

The main hull and outrigger are the same length with the outrigger having enough volume to carry twice the displacement of the boat. The outrigger is the same length for speed and also to provide maximum diagonal stability in Atlantic mode.

The construction of the simple, dory style hull shapes was decided upon for its ease of construction as well as providing a very useful flat floor to the cockpit. To enhance the hull bottom, a 100mm wide chine plank was introduced. Made from 16mm thick cedar or Oregon this plank is shaped to provide a soft chine. The rest of the hull is nominally 11m foam cored Coretech panels for lightness. The highly cambered "end decks" were added at each end of the boat mainly for appearance. These would be constructed from 4mm ply. The construction technique is identical to that of the main hull and also incorporates a rounded chine plank.

The cross beam structure consists of two 125mm OD x 3.0mm wall aluminium tubes. Stainless steel 'S' simply hook over the tube wall at the outer ends of the cross beams. Both hulls are pulled together against these hooks by the tensioned trampoline. The cross beam supports in both hulls are of 16mm plywood. To dismantled the boat for trailering if required, the trampoline is slackened, the beams are unhooked and the cross beams are then ready to slide out.

The Mi6 was initially sailed for about 20 hours in winds up to 25 knots. It only capsized once in initial sailing due to rig and rudder issues. The rudders were modified as a result with a better shape and interconnectivity. Once sorted it sailed well.

The jpegs give the idea. An interesting design for fun sailing.

 

Malcom Smith and Ian Sargeant produced the Mi6 Proa then designed the Mi12 proa. The Mi12 is a cruising Atlantic proa that was claimed to be self righting under certain circumstances. The Mi12 main hull is 37 x 9 foot at gunnel level. The waterline beam of the main hull is 4.6 foot. The length to beam on the main hull is 7.5 to 1. The float is 42 x 2 foot with a 20 to 1 length to beam ratio. The total overall beam is 20.5 foot. The displacement is 7,900 lbs. The 48 foot wing mast has an area of 80 square foot. The mainsail is 570 square foot and the jib is 250 square foot. Again it is a balanced wishbone ballestron rig and double edged linked rudder system for easy shunting.

The interesting part of this design is its ballasted dagger keel that draws 8 foot when down. The ballasted keel and buoyant wing mast allows the proa to self right. The reason for my comment about self righting at the start is that the rig needs to be in place after a near capsize to help the self righting.

The objectives of the Mi12 proa concept design are to achieve high cruising performance and comfort at low cost, and with safety equal to or better than any comparable boat. The wide main hull gives internal room for accommodation as indicated in the jpegs, but there is one downside. When going upwind the forward double berth is effectively in the “bow” and would be uncomfortable. The galley is also a little limited. The cockpit is vast.

Flat panel 'stitch and glue' construction uses pre finished cored composite panels. The panels could be PVC foam glass, Balsa glass or Duflex balsa with thin wood panel faces. Also, a strip planked cedar option could be possible.

This is an interesting concept but I do not know if any were ever built. It would be interesting to see if such a design could live up to its self righting claims. I suspect the performance would be good for a cruiser but the wide main hull and moderate sail area would not indicate very high speeds.

The jpegs give the idea.

 

Today we talk about a catamaran that has a 128 foot BEAM. Your local marina should be able to accommodate this cat at a moderate mooring rate! The ‘NEMESIS ONE’ is claimed to be the World’s Fastest Luxury Foiling Sailing Yacht, able to break the 50 knots speed barrier, while flying on computer controlled hydrofoils.

Nemesis One is 332 x 128 foot of unknown displacement (guess over 150,000 lbs) with a 280 foot carbon fibre, AYRO's patented ‘OCEANWINGS’ reefable wing sail of 11,500 square foot in area. Length to beam of the hulls are about 25 to 1.

The designers are VPLP, who have the credentials to design such a beast and also have experimented with the modified 'OCEANWINGS' wing sail automatically adjusts it’s angle of attack, camber and twist, eliminating any need for manual sail trimming. Additionally, the reef and furlable wing sail is claimed 2.6 times more efficient than a conventional sail plan of equal size.

The excessive speeds the yacht (anticipated to be up to 50 knots) will be capable of under sail, required the Nemesis team to completely abandoned the classic operating concept of: ‘Pulling lines and handling sails’. The designers have implemented state of the art hydraulic and electric controls throughout the design. Replacing bulky winches and line cluttered cockpits. Nemesis One will be equipped with the latest generation of smart LiDar (laser radar) sensors, precisely capturing the yachts surroundings. The current sea state, especially wave height, shape and frequency, will be live monitored by LiDar as well. All gathered data will be processed by the yacht’s mainframe and translated into precise control commands for the automated hydrofoils and rudders, making the yacht exceptionally stable & safe at any given speed.

The accommodation layout is anything you want, and is modular to allow you change it to suit the locations of the world you are sailing in. The cat is a zero emission vessel. Powered by a retractable hydrogen-electric propulsion, the yacht has no need for any fossil fuel. In addition to the hydrogen fuel, up to 8073 square foot of solar panels, will generate up to 150kW of power, to recharge the yacht’s batteries.

This is beyond dream land with a base price of $90 million US, but I hope someone buys one to find out if it is a 50 knot “cruiser” that is basically computer controlled. We will all benefit if all this technology works. There are several “smaller versions” a 60, a 100 and a 200 foot versions if you cannot afford the $90 million US. The jpegs give the idea.

 

Well. Not sure if you can call a superyacht with a footprint of 1 acre green, but it sure is impressive!

 

A short one about a man inspired by the experiences and life philosophies of Bernard Moitessier and Joshua Slocum. Michael Fuchs designed a pacific proa in 2016 as his mode of transport for some serious sailing. The proa is 36 x 25.4 foot (including pod). The displacement is approximately 5,000 lbs. The mast is 35 foot high and carries a 200 square foot mainsail and a 315 square foot fore triangle. The main hull length to beam is 14 to 1, the float has a 13 to 1 length to beam at the gunnel. The daggerboard rudders draw 4 foot.

Michael sized this Proa for a couple to comfortably live full time while long distance worldwide blue water cruising. The aka accommodates a full sized galley, head with shower, and large storage areas. There is ample room for a normal queen sized bed in the overhanging lee pod. I suspect this design has been strongly influenced by successful similar sized ocean crossing pacific proas.

Michael hopes to have very high cruising speeds with this design. I wish him success. There appears to be no further details or plans and I do not know if he built the boat.

So why the interest in this proa? It is due to the Michael Fuchs employment. Michael Fuchs is the Chief Mechanical Designer at Stratolaunch (read Virgin rocket ship stuff) for the past 18 months and for the prior 11 years worked a Scaled Composites as a Mechanical Design Engineer doing design, build, and flight test prototype aircraft and spacecraft. He was a Design Engineer on the Virgin Galactic SpaceShipTwo (2008 – 2013). There may be more substance behind the structure of this proa design than first appearance.

The limited jpegs give an idea.

 

The VAAN R4 and R5 series of catamarans are being built from Hydro 75R alloy, made of minimum 75 percent recycled post-consumer metal. Translation these cats are built to be mainly recyclable from the start of their lives to the end of their lives where they can be recycled again. The VAAN R4 is a cruising catamaran that is 42 x 23.15 foot that weighs 24,500 lbs. The displacement is unknown but assume at least 33,000 lbs. The 56 foot aluminum mast carries a 592 square foot mainsail, a 323 square foot jib, a 915 square foot genoa and a 1450 square foot gennaker. The hull length to beam is 6.6 to 1. The hull based daggerboards draw 6.1 foot. The rudders are spade.

The performance polar jpeg gives the estimate of performance with a maximum of 10.5 knots in 20 knots of true wind. The displacement and hull length to beam limits performance to about 50 to 60% of true wind speed. This is a true cruising cat that will match the performance of the heavier French cats. The designers of the cat are Dyskstra Naval Architects, a very serious design group that knows how to design mainly mono’s from 20 to 300 foot. Their performance prediction programs are generally accurate.

The VAAN R4 has spacious accommodation in the hulls and on the bridge deck and uses natural materials, such as lyocell (an alternative to silk), a plant-based alternative for leather made of pineapple leaves, cork, linen, and certified wood. Again, this yacht build is based around minimal long term impact on the environment.

The build, as you can see from the jpegs, is mainly aluminum with multiple stringers and frames. Aluminum is one of the faster ways to build a boat if you are a competent metal worker. But the real time saving is the fact that you do not have to paint the finished shell structure ever. Unfortunately, most people want a pretty colour and a glossy smooth finish. Result all the fairing and finishing minimises the build time savings.

A global cruising cat that is environmentally orientated. The jpegs give the idea.

 

Astus has produced a 14.5 foot trimaran or proa depending on your desire. The tri version is 14.5 x 7.9 foot with a weight of the main hull of 56 lbs and each float weighs 16 lbs for a total tri hull weight of 88 lbs plus cross beams and rig. The proa version is 14.5 x 4.95 foot with a total proa hull weight of 72 lbs plus cross beams and rig. The maximum crew payload of either version is 290 lbs. The rigs on both versions are the same, with a 2 part free standing mast with a total height of 15.4 foot. The mainsail is 54 square foot and a genoa of 54 square foot. the draft is 2.4 foot over its daggerboard. The main hull is 1.9 foot wide giving a length to beam ratio of 7.65 to 1.

The Astus 14.5 was designed by VPLP designer Jean-Hubert Pommois. It can be sailed as a Pacific or Atlantic proa or with 2 floats a trimaran. The Astus 14.5 was conceived as a proa or trimaran that was light and easily transportable on a car top, if required, that provided the simple pleasure of being on water under sail or paddle.

Tests of the Astus 14.5 state the proa or tri version can sail well upwind or down in 5 to 15 knots of wind. The 14.5 has been sailed in 25 knots of wind in initial production testing without any failures. The 14.5 depends on crew weight to assist its stability in stronger winds but its sailing qualities in video’s indicate it has good qualities in light to moderate conditions.

Astus build these tris from a combination of solid polyester fiberglass in the hulls with some PVC foam glass components. The cross beams are aluminium tubes of about 50 mm diameter which are bolted on the central hull and tied by ropes on float(s). The daggerboard is aluminium. The rudder is a kickup.

This is a fun, fast bay or river sailor that you can store and transport easily. It is relatively cheap at about $US5000 or euro’s. The jpegs give the idea. There are a couple of videos which give a good idea of the performance.

 

Trevlyns (web name) is an amateur designer and builder of a 23.6 x 18.7 foot Pacific proa. The weight is listed at an optimistic 270 lbs with a displacement of 1,350 lbs. The Gibbons/Dierking lanteen arrangement rig has a 12.5 foot mast with a 30 foot yard and a 172 square foot sail. I would imagine a lot of used windsurfer masts in this rig. The length to beam on the main hull is 11.75 to 1. The length to beam on the ama is 22 to 1 at the waterline. Steering is being done by a steering oar. The lee partial accommodation pod helps prevent a capsize. It’ll heel to 28 degrees before the extra lee pod buoyancy kicks in.

A nice feature is the “ballast box” mounted on rails on the beams. The “ballast box” which contains heavier items like batteries, tools, anchor and chain and water canisters. As a proa always has the wind on the same side (the ama side), this arrangement allows ballast to be shifted in either direction for stability. Also, as the ballast box is shifted to windward as the wind picks up, the mast support which is attached to it also moves and cants the mast to windward – moving the direction of drive (and overturning movement) away from the horizontal towards the vertical. This feature sounds good, but will require some engineering to ensure the rig ballast box stays attached to the beams and under control.

The accommodation is 2 single berths and a small 8 foot galley bench area in an area that has 4.75 foot of headroom. The cockpit is on the windward side.

The build is being done with ply and timber. The builder doesn’t like joining plywood sheets so he is building the main hull in 3 separate 8 foot modules and bolts those modules together with stainless steel bolts and then sheathed the hull with fibreglass cloth. This eliminates the need to scarf the plywood sheets. The ama is made up of two modules. The reason I am worried about the weight is that C Class racing catamarans weigh about 300 to 350 lbs and are of a similar size but use some of the most advanced honeycomb or PVC foam carbon fiber epoxy construction in the world. 6 mm or 4 mm plywood panels are much heavier than a C class composite panels. The quoted 270 lbs for this proa is optimistic at best.

An interesting design with a few interesting concepts. The jpeg drawing gives the idea and some build jpeg. I do not know if the boat has been completed and sailed.

 

That seems a lot of faffing about to avoid joining ply. Butt straps would have sufficed instead of scarfs.

 

The Aventura 34 production catamaran is designed by Samer Lasta. The Aventura is 32.7 x 17.4 foot and weighs 10,100 lbs. The 54 foot ZSpars mast carries a 495 square foot mainsail, a 312 square foot genoa and a 516 square foot gennaker. The fixed low aspect ratio keels draw 3.6 foot. The hull has a fine bow with an inverted bell curve shape that provide a step/chine that improves accommodation space and provides forward flare for added buoyancy. These shapes operate well but have one down side, if you are moored and small waves pass by there is a constant slapping sound that come from the close to the water chines that is very annoying after a while.

The whole concept of the design is a good performance cruising catamaran that is below 33 foot long and can be easily handled by one or 2 crew. The boat is capable of sailing offshore up to 200 miles and up to force 8 winds (about 40 knots) according to its European B category. The design is labelled as the smallest liveaboard catamaran available. The accommodation has a wide double berth aft and a forward double in one hull. The other hull has a wide double aft and a proper toilet area forward. The bridge deck cabin contains the galley, dinette and chart area. There is a steering and sail handling cockpit above the aft cockpit.

Comment on European standards. There intent is good, but when good sailors can sail 21 foot catamarans around the world you start to question what they are rating. The real issue is often the skill of the crew. Yes, some boats are badly designed and built but the majority of the problem is often not the boat or the sea conditions, it is the competency of the crew. The “nanny state” exists everywhere.

The 34 is built with quality equipment and hardware EG epoxy resins, water-repellent woods, stainless steel A4 316 ISI, Harken and Spinlock hardware, Elvström wardrobe, ZSpars rigging, Raymarine electronics etc. The basic structure is polyester sandwich construction with epoxy resins on the underwater section and other components. The cat is built in Tunisia as are many other smaller boats as the costs are lower.

The only tests I have read suggest a reasonable handling boat but the helm lacks feel. This cat is a cruiser not a racer, but sails well up and down wind. The low aspect ratio keels are large enough to get reasonable upwind pointing.

The jpegs give the idea. A good design for a serious cruiser or live aboard.

 

Oldmulti, what are the consequences of sailing further than the category b 200 mile limit? Will you be imprisoned for such an offense?