Multihull Structure Thoughts

The ancient rig used on this offshore catamaran in Tahiti at the time of Cook's visit had a very efficient high aspect sail. With some modifications it would make the modern fleet much better to windward. I built a smaller 27' replica almost 20 years ago that was reefable and had a similar plan form, I also made one for my 18' Ulua canoe.

 

French builder Advanced Aerodynamic Vessels (A2V) delivered a new high-speed catamaran ferry (for 12 passengers) for use as a yacht shuttle by Monaco Ports Operating Company between Monaco and the Italian city of Ventimiglia. “Monaco One” is a unique aerofoil-shaped hull form that helps generate aerodynamic lift at higher speeds, enabling higher speed.

“Monaco One” is 39.5 x 24.3 foot with a 33 foot waterline. The build shell weight is claimed to be 3,800 lbs and a loaded displacement of 17,900 lbs. The hull length to beam is 9.4 to 1. The draft is 2 foot. The underwing clearance is 1.75 foot. The cat is powered by 2 x Yanmar 8LV, each 260 kW (350 HP) with 2 x ZF 220 gearboxes driving through 2 x Arneson ASD8 surface drives and 2 x France Helices surface-piercing propellers. The range of the cat is 220 miles. A later version has 2 x 300 HP outboards. The builder said configuring the hydrodynamic shape to allow very high efficiency at all speeds and displacements was also a challenge, mainly because the weight carried by the hull varied from 100 per cent to less than 50 per cent of total weight depending on the available aerodynamic lift.

The hull is a stepped V planning shape designed for high speed. Monaco One cruise speed is 45 knots, maximum speed is 52 knots. It uses 120 litres (30 gallons) per hour or about 2.6 litres/nautical mile. To quote the company “Seakeeping is exceptional at high speed, as the vessel is able to maintain speeds above 40 knots even when sailing through waves. In case of rough sea conditions or a technical problem, the vessel still retains its seaworthiness at lower speeds, behaving as a conventional catamaran would, particularly one with narrow hulls and a high cross-section.” About the overall cat shape “We wanted to ensure passive stability through specific mass distribution relative to the center of aerodynamic lift. As with our other newbuilding projects, the aerodynamic center is placed aft of the vessel’s center of gravity. This means that when a gust or a wave increases lift on the superstructures, this reduces trim angle and therefore angle of attack and aerodynamic lift, creating a stable equilibrium.” In short, the designers designed the cat from the start to be a high speed vessel that used stepped hulls an aerodynamic shape to maintain high speed in minimal sea conditions. In rough water, the cat has to slow down and act as a normal cat.

The 12 passengers get a great view of what is coming with the captain having his private steering position. If anyone wanted a very fast cruiser there is enough space to modify the interior to have some light weight furniture etc.

Monaco One is built from foam fiberglass sandwich and foam carbon fibre composite construction. The builders had to do a very accurate weight study of the shell and all equipment to ensure the weight and center of gravity meet the design requirements. Larger versions of this concept have been built but are less dependent on aerodynamics to maintain their speed.

The jpegs give the idea of an interesting concept.

 

Wow! That ferry cat is cool. I have to admit that if I saw it being trucked through city blocks like that and only saw the top of it, I would fear I might be witnessing an alien invasion. It almost looks as if it could double as a space craft.

 

Intersting device. Jeff Morice and later Yves Parlier used previously airplanes stepped hulls on catamarans (hydra planeur).
This catamaran use reduced drag properties of airplanes in the last stage of take off, when hydrodynamics drag is reduced
thanksz to the aerodynamic lift of the wings.Very old story, not a real finding !

 

Sorry I mean Seaplanes !!!!!!!!

 

The first one, named "Evian one" , is in activity in the Leman Lake, Evian-Lausanne line :

 

The only connection between the following 2 designs is the word Hobie. I do not know if Hobie knows about either vessel but at least they have some connection to Hobie even if it is just using the logo.

The first jpegs are from Ross Koball as, I assume, a design study. I could not find any other information on this design and would appreciate if anyone has any information. The concept looks to be inspired by a Harryproa. The telescoping wingsails also look interesting. Ross web site is https://rosskoball.com/Polynesian-Proa

The numbers are a calculated guess. The mast hull is about 29 foot, the accommodation hull is about 20.7 foot, the beam is 18 foot. The masts are about 28 foot high. The displacement is unknown. The accommodation is 2 double berths and a small galley in an area with standing headroom. The structure is unknown but I would assume foam glass. The crossbeams are stated to be aluminium. If Hobie were interested, there could be an interesting design contest between a couple of designers for the contract.

Next is a Phil Bolger design that is a camping trimaran main hull with Hobie 16 float hulls, rig and rudders. The tri is 23.5 x 12.75 foot and the main hull weighs 450 lbs before you add the Hobie 16 components. The accommodation again can have 2 double berths inside with sleeping headroom and camp gear for cooking etc in the cockpit. A camp cruiser for local waters.

Fun stuff in each case. I just wonder if either were ever built. The jpegs tell more of the story.

 

A frame was my idea.

A frame meeting the top pole about half way along (depending on structural requirments) and a lower pole (boom?).

The A frame and top pole are fixed, all sail tuning and tacking is accomplished by moving the lower spar. Reefing is accomplished by brailing the lower pole upward.

So brailing lines and 2 mainsheets. You need to be careful of teh details. The proportions of the sail, scantlings. But no draft or battens. Get the upper spar as vertical as you can. No standing rigging apart from the spars.

It would be worth teh experiment on a small boat. It would not win races I think but as a cruising rig it should be satisfactory on all points and be dead simple and cheap to build rig (trailer sailer) and operate especially for short handed cruising.

 

Joseph Oster has been a strong proponent of Pacific proas for years. He has evolved his ideas over time to very interesting concept designs. The following is one of latest ideas. The Pacific Proa is 69 x 34.5 foot with a total displacement of 22,400 lbs. The main hull is 69 foot long with a length to beam of 17 to 1 and a prismatic of 0.62. The small hull is 52 foot long with a length to beam of 20 to 1 at the waterline. There is no indication of the foils or rudders in the design study. The sloop rig carries a 702 square foot mainsail, a 457 square foot jib and a 1342 square foot code zero on a 57 foot mast.

The accommodation has 4 double berths, 2 full toilets, galley and full seating and table area.

There is no indication of construction but foam glass with carbon fibre would be the best guess to meet the displacement requirements.

On the subject of performance, the numbers indicate this proa would be fast, very fast if sailed by an experienced crew. The righting moment is over 160,000 foot lbs with a centre of effort 30 foot of the water. That means the main and jib can be carried up to about 30 knots of apparent wind speed. Translation 15 knot cruising speeds and peaks over 25 knots. 300 to 400 mile days possible in the right conditions.

Joseph Oster argues that the righting moment and sail area is similar to a 40 to 45 foot catamaran with but the Pacific proa has a 50% longer waterline with similar wetted surface. The longer waterline alone will provide more speed and the improved length to beam is a real bonus, especially in a seaway. On my simple performance calculator, the 69 foot proa can be up to 35 % faster than a 44 foot cat of similar displacement and sail area in similar conditions.

Joseph has done a lot of sailing miles in many types of boats, so he understands that size helps in a seaway and effective accommodation really matters. An interesting design study. The jpegs give the idea of his latest ideas.

 

1. For someone who spends a lot of time shitcanning Harrproa's , this looks just like a HP but with accom swapped to the other hull.
2. Nice drawing, but it will never get built ; with no weight to wind ward.
His calculator must have been broken when he worked out the righting moments ?
3. Yes it would be fast - just before it went over...

 

Multihulls have on one problem. Everyone thinks they can capsize and they are right. I know cats and tris up to 80 foot that have gone over due to wind, wave action or a structural issue. So, let’s look at what can cause a capsize. Capsize is mainly driven by 3 main causes:

Wave action: be in the wrong place at the wrong time and you can capsize. EG a breaking wave crest has pushed over 57 foot conservatively sailed cruising cat.

Excessive sail area: Simply to much sail for the conditions. This can happen in calm water and 15 knots of wind or 35 knots of wind with a reef in. EG Steve Dashew Beowulf Vl was 38 feet long, 18 feet wide, and weighed in at 2114 pounds in ocean racing/cruising trim (just 1700 pounds in day sailing trim). The hulls weighed 375 pounds each, were solid foam to the load waterline, and segmented into eight watertight compartments. Beowulf VI can capsize in 7 knots of true wind speed. It can also sail at 26 knots in 13 knots true wind speed.

Lack of stability: Either there has been a design problem or there is a secondary problem such as water in a float or being destabilised by an angled wave face etc.

Wave action or crew excesses are problems that the skipper and crew can solve. Design is something that is a naval architect/client issue. There are really only 2 design criteria to consider: Rig overturning moment and Stability of the design. For 160,000 foot pounds of stability from a multihull a 1400 square foot sail area rig with a 28 foot high centre of effort can handle about 30 knots of apparent wind.

I DONOT care if it is a trimaran, catamaran, Pacific proa or a Harryproa. As long as they generate 160,000 foot lbs of stability and have the same rig they will all capsize in about the same wind strength irrespective of their configuration.

The Oster 69 foot Pacific proa total displacement is 22400 lbs and has a float displaces of 5600 lbs. It is 27.6 foot righting arm from the main hull centre of buoyancy point, therefore produces 154,600 foot lbs of righting moment.

A Grainger Raku 40 catamaran displaces 19,712 lbs and has a 168,000 foot lbs of righting moment.

A Grainger TR 42 trimaran displaces 10,200 lbs and has 153,000 foot lbs of righting moment.

A theoretical Harryproa of about 55 foot displacing about 12,000 lbs would have a righting moment of 160,000 foot lbs (20 foot righting arm with 8,000 lbs accommodation hull weight).

The simple performance calculator says the Harryproa and the Pacific proa would be about equal in speed with the TR 42 trimaran closely behind. The Raku 40 would be fast but in this company would be about 20% slower. The Pacific proa is the longest and heaviest but has the best displacement length ratio. The Harryproa is very close in displacement length. The trimaran is the lightest but has a displacement length is twice the Proa’s. The cats displacement length is 4 times the proa’s. Translation, if a boat is relatively heavier for its length given the same rig the slower it will be.

Please remember, this comparison is a little unrealistic as I have used a common 1400 square foot sloop rig. The Harryproa is theoretical and would probably have a smaller 1100 square foot mainsail schooner rig. The real TR 42 tri has a smaller mainsail and a large genoa. The Raku 40 cat has a smaller mainsail and its largest headsail. Surprisingly the mast heights on each boat are not that much different in the real world.

Summary, the Raku cat is a 270 mile/day boat, the TR 42 tri is a 320 mile/day boat and the proa’s are 350 mile/day boats under this common rig. The jpegs give an idea of the actual boats.

 

Harryproa designs are constantly evolving as more boats are built and sailed. Many customers have specific ideas and requirements they want included. As a result Rob Denny has unpgraded accomodation, rigs, steering systems etc. to meet the customer needs. The C50 is the latest version of which at least 2 are under construction in Brazil and Sweden.

The C50 is 50 x 25 foot with a 50 foot long mast hull and a 33.5 foot accomodation hull. The weight is 4,480 lbs with a payload capacity of 4,480 lbs for a total displacement of 8,960 lbs. The mainsail only schooner rig has a total sail area of 946 square foot. The masts are freestanding carbon fibre. The draft rudders up is 1 foot, with the rudders down 5 foot.

The rudders are 2 way sections, that are closer to the hull and do not have to rotate through 360 degrees. They are liftable for balance, shallow water or storm survival and kick up in a collision. In terms of drag and spray, they are a significant improvement on previous versions. The rudders are also stronger and easier to lift and lower.

The designer claims the C50 will sail at wind speed, without extras, between 5 and 20 knots, tacking through 90 degrees and with no limits on downwind sailing angles. The unstayed carbon mast need no maintenance apart from a coat of paint every 15 years or so. The wishbone booms are light.

The accommodation in the windward hull has two queen size bunks in separate cabins, complete with their own toilet and shower. The saloon has two tables for 8 and a galley on the same level to allow the cook to see out and be part of the socializing. The lee hull has 2 big single bunks in a single or separate cabins, one of which could be made into a shower/toilet or used for storage.

The C50 construction is based on “intelligently infused” molding using foam and fibreglass. Intelligent infusion includes as much of the build as possible in the infusion. All the work is done using dry materials in a simple mould which does not require sanding or polishing. Intelligent infusion aims to do as much of this as possible using dry, easily cut and handled materials (glass and foam) in easily made low cost moulds. Once everything is prepared, a vacuum bag is placed over it and resin sucked in (infusion). The entire job is wet out, with the perfect amount of resin, no voids and minimal waste. A hull half can be done in one 40 minute resin infusion shot. Some of the tasks that can be included in the infusion are: perfectly fitting doors, hatches and windows and all the edging and rebates that these require; landings and edge treatments for the bulkheads, shelves and furniture; male/female joins for the hull components; solids and/or variable laminates and core thicknesses where required. All surfaces can be ready for painting or gluing, with the option of including fancy (timber, woven carbon, melamine, etc) finishes. Built time can vary but the claim is 2250 hours which is impressive for a 50 foot boat.

The jpegs give the idea.

 

The following is about a Navy catamaran that is a ship to shore landing craft. The cat has an unusual lifting centre platform that allows it to function as a cat at sea then lowers its central platform at the shore to allow the up to 100 ton load to move to the shore. The L-Cat is 107 x 41.3 foot of unknown displacement. Capable of carrying a 100 ton load on its 21 foot wide central moveable platform. The length to beam of the hull varies between 10 or 11.5 to 1 depending again on load. The draft varies from 5.9 to 8 foot depending on the load.

The L-CAT can travel at 15 knots cruise with a top speed of 18 to 22 knots depending on the load. The 4 x MTU 12V 2000 M93 engines that produce 1370 KW. The engines drive through 4 jet drives. The range is 800 nautical miles with 22,000 litres diesel.

A Mark 2 version has a higher top speed with the assistance of a foil between the hulls forward and a bit more power. Top speed of the Mark 2 now is 35 knots.

The vessel structure is basically aluminium with composite component to help reduce weight.

The L-CAT works with a mother ship to move loads from ship to shore. Initially the Navy tried hovercraft but found they were high cost, high maintenance and could not carry a big load. The L-CAT performs the task very well. The L-Cat has a retractable steering cabin to allow the L-CAT to moor in its mother ship.

An unusual cat that may give others’ ideas. The jpegs give the idea.

 

The following is a design study from Michael Schact Designs intended for production after a few details are worked out. EG hull material layup etc. Take the ideas as they are, and I hope the details are worked out to allow full production.

The modular pod cat called ARGO. The version we will initially talk about is ARGO 1 which is 30 x 18.1 foot with a loaded displacement is 6,660 lbs with a gaff rig sail area of 442 square foot on a 34.2 foot mast. The hull length to beam is 9.2 to 1. The draft over the low aspect ratio keels is 2.4 foot.

The accommodation has 4 “double” berths (if you think 3.5 foot wide is a double berth) in the hulls with a portapotti. The galley and dinette are in a separate pod between the hulls. The cockpit is attached to the central pod. This is in the 30 foot version. The headroom in the hulls is 5 foot and in the central pod under the roof extension 6 foot. It is possible to extend this design hulls to EG 40 foot or create a proa version with differing accommodation layouts using additional molded components.

The designer says “Argo 1 is an ocean crosser and is not designed for top speed, though I think she will be no slouch, especially in the trade winds for which she is meant. She is designed for load carrying because - have you ever seen a small cruising cat that is really out there doing it, that floats on its lines? Me neither. Argo is a capable load hauler.”

Now the interesting part and the reason I said it was a modular pod cat. The entire cat is intended to be female moulded from 2 molds, one 10 foot long half curve straight mold, the other an 11 foot long bow shape mold half the height of the hull. The body of the hull is an elliptical tube section. The bows and sterns are identical, and are also identical top to bottom. You’d make a molded part for the bottom, and make another one, and then turn one over and bond them together at the gunnel. You’d need a half tube mold, and a half bow mold, and that would be it. The pod is made from the same hull molds, plus some extra flats, etc.

You would need 8 bow parts and 4 body parts for the two hulls, plus 3 body parts for the pod. It is mass production on a personal scale, and it makes spending time on the molds worth it. In exchange for the molds, you get a real fiberglass boat, with all the virtues of the material. The cross beams are undecided as yet but they will either be over sized mast sections or fiberglass pultrusion’s are being investigated. The jpegs show more of the concept.

The major design issue is the joining of all these components. Molded components allow for good finish and lighter components, but if you have to fiberglass tape each joint you either have to mold flanges into the components or you have to fair each tape joint. And in this design concept there are many joints that have to be taped together. Also judging by one of the jpegs there are a number of secondary bulkheads in the hulls which have to be added. In the 30 foot version there is at least 250 linear foot of 150 mm wide taping per hull. One of the advantages of build large single piece components is you can make them lighter and often stronger due to less secondary taping required.

I am sure Mike and the group assisting who have provided their time and insights to the project: Paul Cheevers, John Dalziel, John Pugh and Robert Wise will address these issues. This design components are intended to be built by a home builder in their garage and then can be assembled in their backyard or near a shoreline.

The jpegs give the idea. Interesting concept.

 

I can think of several well documented Woods cats that have done a lot of ocean work from thee 28' Gypsy up. I know there are a lot of marinaramans out there but not all cats sit around gathering weed...