Multihull Structure Thoughts

So, Glenn Ashby (of AC fame) is on television talking about Team NZ wind powered speed attempt. It is sponsored by Toyota, all the usual suspects. He was at Lake Gairdner in South Australia which normally is a salt lake but was recently flooded. Good so far, then he said the proa was designed to hit 250 kilometres per hour. OK. I needed to follow up. What I found was a wing sailed powered land yacht.

Emirates Team NZ wanted to push the limits of design whilst sorting out the next AC contender. Emirates Team NZ updates on the land speed attempt is expected to push the ETNZ design and engineering teams into some "out of the box" thinking, particularly in drag reduction for the AC75 program. As well it is a good workout for ETNZ's in-house construction team to get build processes as streamlined as possible ahead of the AC75 program.

The result is a 46 foot long by about 33 foot wide land “proa”. The driver and wing mast is in the main spar that has a front steering wheel and aft 2 in line single wheels for traction. The windward pod, on a spar, that has a single wheel and lead ballast from 670 lbs to 2250 lbs (acting as a “keel” weight) depending on wind conditions. The 32 x 4.25 foot wing mast appears to be small at about 120 square foot but you need to remember what forces are involved. At an apparent wind of 100 knots (115 mph or 184 Kph) the wind pressure is 134 pounds per square foot or an “overturning” moment of 240,000 foot pounds. If the windward pod has 2250 lbs of lead in it the record proa has a righting moment of 68,000 lbs.

Glenn’s sailing skills will really be tested as he steers a course and sets the wing mast controls to balance the wind loads versus the righting moment. Peak speed is expected to happen in 30 to 35 knots of wind speed. Yes, this machine can sail at 3 to 5 times wind speed.

So what are the rules for the attempt and record. The rules are the land speed record must be set on a natural surface (sand, dirt, salt etc no tarmac) and be on a course that has lss than 3 foot of elevation change. The land yacht must not be push started and move under its own sail power through out the attempt. What speed does the land yacht have to achieve, try 202.9 kph set by Britain’s Rickard Jenkins in 2009. At this speed if anything goes wrong the drivers pod better be strong to protect the driver.

The structure is foam carbon fibre in epoxy with a minimum of metal in the entire build. This land yacht is light and strong but is pushing the edges of structural engineering. The team spent over a year on the design process and development of components, but the build was relatively rapid. The front wheel is a special design but other wheels are standard with slick tyres to obtain maximum lateral resistance.

The record attempts will start in the next few days. The jpegs give the idea.

 

“Kuka Light is the most extreme keelboat I have ever sailed,” explains Mitch Booth. “At 42ft and built in an autoclave she is VERY light and stiff. But when you look at the specifications, she’s special. Around 3,200kg with a beam of 4.6m and draught of 3.5m makes Comanche look very conservative by comparison!” Written by its then skipper Mitch Booth, 4 time Olympian, twice for Australia and twice for Netherlands in the Tornado catamaran to win a Bronze and Silver. Booth is now skipper of the 100ft Comanche, winning the 2021 Rolex Middle Sea Race and 2022 RORC Transatlantic Race.

Why am I interested? This non foiling, legitimate ocean racer with a top speed so far is 34 knots! Ok, how does it do it. It is strong, stiff and light. Kuka Light is 42 x 15 foot with a light displacement of 7,160 lbs. The rotating carbon fibre mast carries up to 1,250 square foot upwind and 2350 square foot down wind. The canting keel draws 11.5 foot with 2 supporting daggerboards for lateral resistance. The dual rudders are attached to the stern each rudder can be raised to reduce wetted surface in light airs or very high performance sailing. The engine is 30 HP and is mainly used for hydraulic pressure to control the canting keel. A high performance non foiling multihull would have similar numbers with one variation, the beam would be 30 foot plus.

This boat is about performance and does not use water ballast. Its accommodation is minimal and minimum food preparation with a minimum toilet. There is a lot of internal vacant space to get thrown around in at high speed.

The design was done by Doug Schickler of ST Yacht design who was told by the owner to ignore all rating rules and make the boat as light as possible, period. The aim was to design a very high performance boat that can be sailed by 6 people that can outperform the current 40 foot class, match TP 52’s and occasionally embarrass 60 footers. A task it has achieved frequently racing against 50-60-footers in events like the Rolex Giraglia and Middle Sea Race. The design and build were done in 2012 and Kuka Light is seriously fast upwind, reaching and when broad reaching or running spectacular. The jpegs give the idea.

To the build. The owner said light, the designer said we need to choose people who can build light. The carbon honeycomb core hull as far as possible would be autoclave cured at Martström in Sweden, Martstrom autoclave could “cook” half a hull side at a time and most other parts were also manufactured in the autoclave. This gives access to huge pressures during cure and allows prepreg’s with far higher fibre to resin ratios than is normally possible. These construction techniques ruled out in AC and IMOCA yachts, except for the masts and appendages. The weight savings were unattainable any other way. The bowsprit, foils, and mast are also be produced in this same hi-tech fashion. The lightest core material is from aramid honeycomb. The core properties allow the designers to reduce weight further. Aramid cores, though hard to master, have higher stiffness and strength than conventional foam cores, but at about half the weight per square meter. Further weight saving came with a carbon keel spar, titanium keel ram, and carbon/ titanium drive shaft. Practicality played a role in the decision making as well. In places, carbon cloths were added to given the primary laminates additional resilience and foam cores were used in places to allow for damage without water infiltration. This pragmatic decision making reinforced the boat is an ocean racer, not a specialty light air flyer. The Martström parts were then transported to the Cantiere Soleri in Italy, who assembled the parts, created the internal structures and fitted out the essential systems and interior furnishings

This boat cost over 1 million Euro’s in 2012 but the owner is more than pleased as it gives 60 footers a hard time and occasional wins races on handicap even though it is a pure speed design. Again multihulls can learn from mono’s especially how to build very light fast boats. The jpegs tell part of the story.

 

Today we talk about one of the best mini cruisers I am aware of, the Bernd Kohler DUO 480C. The 480C is 15.7 x 7.5 foot (can be up to 8.2 foot depending on your local road rules) and weighs, if well built, 400 lbs. “Jigsaw” a NZ build weighs 500 lbs ready to sail. Maximum displacement is 1000 lbs. The biplane rig can be 2 windsurfer masts (with some lengthening and strengthening) and sails or two specially cut 86 square foot sails on round carbon fibre tubes. If the sails have vertical or near vertical battens, they can be roller reefed around each mast to reduce sail area. At the base of each mast is a “drum” that is used like a roller reefing headsail for simplicity. There is an alternate Gunter biplane rig available. The hull length to beam is 13.5 to 1. The draft is 1 foot. The hulls are asymmetric so no lateral foils. The rudder is central, bridge deck mounted and a kickup. The engine can be a 5 HP outboard. The cat is very trailable.

The DUO480 has a small cabin for gear and a toilet. With some provisions, two persons can sleep on the boat. The big cockpit will seat 4 when day sailing etc. There is a “long version” option with a double bunk in the cabin. This is a mini cruiser and has minimal headroom inside but is it is sufficient for 2 to get out of the weather when moored for a night or a weekend.

The DUO 480C is easy to build in good quality plywood and timber. No strong back is needed as the asymmetrical hulls are self aligning during the build. The hull keels and underwing are 8 or 9 mm ply, forward underwing is 2 layers of 4 mm plywood, the bulkheads are 6 mm plywood, hull sides are 4 to 6 mm ply and deck 6 mm and 9 mm plywood. Transoms are 9 mm ply. This is a light boat, select your plywood (eg Gaboon) and timber carefully to minimise the weight of the build. Timber framing is as indicated in the jpegs, but bulkhead frames are EG 19 x 19 mm. Epoxy saturation is used throughout. A very light fiberglass cloth layer (EG 190 gsm or less) is used outside.

The designer says an average amateur can built this boat in around 300 hours. A Finnish guy built his in 10 months building on weekends while studying full time. He reported there weren’t any major difficulties with the build and got good support from the designer and from other builders on the web. Another builder in Thai land said: “It’s been built by a “wood butcher” whose main desire is to get out on the water with a boat that is strong, cheap but close up, is not a thing of beauty. The Duo took 2.5 months to build, all ply epoxied and 200 GSM to the gunwales. Cost $2000 AU and 10 weeks.”

The performance of the DUO 480C is good. The maximum speed reported by 1 sailor is 14.4 knots with 6 knot averages when sailed by 2 people on a moderate wind day with 4 to 5 foot waves. The underwing had minimal wave slap. Higher speeds of over 15 knots have been recorded but I do not know the conditions. The only issue appears to be the size of the rudder which works well at lower speeds but can be a bit sensitive at higher speeds due to its size. This is only a bit of refinement or a “kickup daggerboard rudder” (possible but needs some good design).

A cheap fun day sailor to weekender that can be stored in your garage. A very nice design for bay sailing or short coastal hops. Look up the build of “Jigsaw” done by a NZ guy. A good boat done by a competent builder. The jpegs give the idea of several boats.

 

Jeremy Fischer of Martinique, who built the 40 foot proa EQUILIBRE some 10 years back also built a second proa which is UNNAMED PROA (referred to as “Noname”), a near 60 foot racing design with a crab claw schooner rig. Jeremy intended to enter the Route du Rhum with the proa. Now we have a problem. Jeremy is very "organic" in the way he builds his boats. He can probably tell you the length and width, and how much sail approximately it has (he is a professional sail maker, so he just sew the sails he needs) but everything else would be utterly vague, based on his experience and experimentation. So, any numbers here beyond its length are calculated guesses.

The unnamed boat is a pacific proa of 60 x 32 foot with a crabclaw schooner rig (initially). The displacement is unknown but I am guessing in the 6 to 7000 lbs range based on his previous 40 footer. The 2 masts are 30 foot high with 2 yards (booms) 34 foot long. The sail area in each sail is approximately 400 square foot for a total sail area of 800 square foot. The float is 38 foot long and can twist on its mounts as it drives through a seaway. The length to beam appears to be over 20 to 1 and the hull appears to be slightly asymmetric. The bows were designed to be wave piercing. There are no “rudders” mentioned but in the final jpeg you will see fore and aft trimming boards.

The schooner rig has the base of the yards running on a track to simplify shunting. Now we get to issue number 2. The unnamed proa has changed to a single mast and single crabclaw sail. After the 40 foot Equilibre was split in two by an unlucky combination of low tide and high waves and the new 50 foot one got badly damaged during a tropical storm. Jeremy rebuild the 60 foot version using parts of both ships, so, in essence, it's still Equilibre, albeit a longer version of itself.

The new rig single mast is 30 foot high with 42 foot yards and a sail area of 630 square foot. Jeremy went back to a single sail as shunting the two sails was proving to be too much of a hassle and barely doable single handed.

The accommodation is basic with space for several single berths and other basic requirements. The construction is plywood and timber. The 2 main crossbeams appear to be some long narrow tree trunks. The rest of the beam structure is probably laminated timber.

Performance unknown but a video shows it moving very well in light airs. If the numbers are close to the above, this boat could be fast but its limitation is its righting moment. The proa does not have a pod used by other pacific proa’s like Jzerro etc to help righting if it is overpowered.

Jeremy is a very creative man who is willing to design, build and develop his ideas. Well done. The initial jpegs are of the original build. The final jpeg is of the proa in late 2020.

 

Oh my! I have never seen a reversible sail like that. What?!

The no name is an awesome proa. I am looking to build something similar in a trimaran format. Something about a long slim hull like that. That's what I have been wanting build for a very long time.

 

A follow up on an early Prout racing catamaran called Phantom Wake built in 1978. Phantom Wake was designed by Roland Prout. It raced successfully in Britain for several years. The full bridgedeck cat is 40 x 19 foot weighing 5000 lbs displacing 6000 lbs carrying 610 square foot in the main and fore triangle. Yes, the weight for a 40 foot bridgedeck cat is 5000 lbs. Study the attached jpeg and you will start to understand why. EG the hull skin is 4 mm ply with 19 x 38 mm tapered stringers at 150 mm centrelines. There is a 6 mm ply shelf in the hull at bridgedeck level. There are 6 mm ply bulkheads. Gunnel is 70 x 19 mm. Decks are 6 mm ply with stringers. The main crossbeam bulkheads are 7 mm ply with a timber matrix inside with an EG 22 x 22 mm basic top flange with a doubler 22 x 22 mm over the centre 10 foot. This is not an offshore boat but it could do coastal sailing well. It is possible to build a really light plywood timber cat if you use good materials and sensible design. Time spent studying the detail of the jpeg will be useful.

Paul Redman was General Manager of Prout Catamarans at their yard in Canvey Island, Essex, said: “Roland Prout was ‘way ahead of his time’ with a 40 footer called Phantom Wake, which had vertical sided hulls and which made speeds of 25-30 knots.” 30 knots is possible although I think its unlikely, a peak of 25 may have happened but we are talking about 40 year old rig design technology here. The accommodation is practical but not spacious, EG there is limited headroom.

Now the update from “Sackville” an F-27 owner who purchased Phantom Wake. “Phantom Wake was an experimental boat. His experiment was to minimize drag from wave interaction in the tunnel and astern, for the penalty of some extra wetted area & leeway. To achieve this the hulls were asymmetric - vertical on inside face. On the outside, the hulls had a hard chine. It didn't take much wind to get the windward float almost flying, and the boat would be planing on the narrow hard chine of the leeward hull, with very little wetted area ....... and going very fast. It was kind of predecessor to foiling, using the materials of the day (sheets of marine ply sealed with epoxied glass.) Leeway was addressed by 2 deep, high-aspect daggerboards. Between the hulls and astern there was almost no wave development at all, hence her name, "Phantom Wake".

“Phantom Wake won many races but was retired from the Round Britain Race with damage. After she broke up in the Pacific, I realized that I probably could have avoided the accident by raising the boards, which acted as levers that the sea used to break off a hull (the hulls were bolted onto the bridgedeck by hundreds of bolts, copying the way the wings were attached to Spitfire aircraft). But I was young and inexperienced at the time. Now I try to avoid such seas or if I do meet them, I turn back and wait for better times.”

The jpegs give the idea of Phantom Wake. There are very few photos of Phantom Wake on the web, if anyone has a jpeg it would be appreciated.

 

This is about what is possible when you want to win in racing. You start with an owner wanting a winning tri without spending much money. DERICK REYNOLDS Design Services produced plans for an 8m (26.2 foot) Micromultihull for Micromultihull racing initially in Britian. The trimaran is Ozone 2 a 26.2 x 26.6 foot with a weight of 1080 lbs. The rotating wing mast is 33.5 foot high with a chord length of 1.8 foot. The mainsail is 260 square foot with a 100 square foot and a 350 square foot spinnaker. The draft is from 0.7 foot to 5.5 foot over the float based daggerboards, the rudders are kickup on the floats.

The accommodation is minimal, 2 single berths at best and some stowage area. This is a racing machine with only the basic accommodation required by the rules, no luxuries like a toilet or galley.

The details of the build are unknown beyond the basics. The main hull is strip plank cedar (guess 7 or 8 mm WRC with 300 gsm or less biax cloth on either side in epoxy). The floats are fibre reinforced plastic (guess foam glass maybe 9 mm foam with 300 gsm outside 200 gsm inside in vinylester). Plywood bulkheads. The crossbeams are aluminum with water stays. Initially they were bolted onto the main hull and floats for transportability. A later version (blue boat) has an integrated crossbeam arrangement of unknown material (looks like composite or wood).

I cannot find any racing results but the numbers indicate a 20 knot peak speed type of boat. With such a wide beam and relatively fine ended floats driving this tri hard will take a lot of attention. John Shuttleworth once said you need to design a boat that will capsize either over its bows or side at about the same time. Very wide beam tri often can pitch pole sooner than capsize sideways.

This would be a wet boat for the 2 crew but I am sure they would be having a LOT of fun.

The jpegs give the idea. If anyone knows more details can they please advise.

 

Would love to get more info and detailed photos of this all out racing tri, that is totally to my liking, even if the beam width is a little over the top.
Suppose it was built in the 70´s or 80´s, anyway before square top mainsails?
Wonder if the center of the rudder tie bar is connected with a track and traveller?

 

Where do you get one of them transparent blue sails?!?! What is that, vinyl?

And what's up with that trampoline, is it also transparent green?

 

About the trampoline it is both cheap and simple to find ;-) .
Covering net | Container covering net | Trailer net https://www.lasi24-shop.de/en/area-of-application/container/covering-nets/104/covering-net-container-covering-net-trailer-net?gclid=CjwKCAjwqJSaBhBUEiwAg5W9p9ETz4mWx2w8RlJDkdhWtmidFQLpqk3t1Eigw1ScD0okt9zo9iE3iBoCKWgQAvD_BwE

 

Oh. Hehe. I guess the photos made it look different.

 

Revintage. As i said I do not know much detail. Micromultihulls started mid 80's and I suspect Ozone was designed in he 90's. We need someone who was micro racing around that time to give more info. Also MOCRA used to run some racing featuring this size of boats and they may have some results, start at mocra Archives - The Multihull Centre https://www.multihullcentre.com/tag/mocra/ but there is also there is some older magazine issues on the web. An e-mail to Richard Woods may produce some clues as he was a major driver in Micromultihull racing in he 80's and 90's. Also
MOCRA Newsletter 01 17.cdr
John. For sails look up Mylar sail materials, this is just a start. Sail materials range from conventional Dacron cloth to carbon fibre material on a substrate if you have real money. The triangular sails used on the proa were developed 2 to 300 years ago in the Pacific. The rig type is meant to develop a lot of power from a very simple shape. The only problem is the sail handling, reefing and tacking of the sail. PS Welcome to the thread.

 

Thanks for the info. Wonder if Derick Reynolds have more to add?

 

Thanks for the mylar. I searched it for an hour and there were no sources on what transparent sails were made of. Looks like it has a short stretching life.

 

Broadblue catamarans design and produce some very interesting multihulls. The Rapier 400 is a fast cruiser with a semi open bridgedeck cabin. The cat is 39.34 x 21.98 foot with a weight of 11,020 lbs. The either aluminium or carbon fibre mast carries a 624 square foot mainsail, a 300 square foot self tacking jib, a 860 square foot gennaker and a 1,070 square foot spinnaker. The draft is low aspect ratio keels that draw 3.7 foot. The 2 x 40 HP Diesels are optional can be substituted by 30 HP engines.

The accommodation is 3 double berths cabins in the hulls with 2 toilets and a navigation area. The main bridgedeck cabin contains a galley forward under cover and some seating but is integrated with the cockpit to form an open living space. The aft end of the main cabin can have a canvas tent to enclose it for some protection. This boat is a good moderate weather vessel but sailing in Alaska may not be the most comfortable.

The construction of the Rapier 400 was initial done in Poland and the hull and deck are vacuum bagged foam core with woven matt construction and solid GRP (done in polyester) below the waterline. The deck has an integrally moulded non-slip finish. The hull-deck join is fully bonded and protected. All of the structural bulkheads are of vacuum bagged foam core construction. The Rapier 400 is virtually unsinkable due to its water tight bulkheads and buoyancy compartments fore and aft. The low aspect ratio keels are sealed off from the hulls forming a “double” bottom. Interior Construction: White internal mouldings with Marine grade plywood/ sandwich panels finished in oak. Teak and Holly platforms.

The performance of the Rapier 400 is good as indicated by the 2 class wins in the UK Round The Island Race. Also one of the owners commented on his first delivery trip “On the first journey home we encountered a F10 subtropical storm in Biscay...sub-tropical storm Stephanie. We had 6-7 metre seas, with occasionally waves breaking over the top of the vessel. All the covers were on and we were interior in standard clothes… safe and dry!” Race winning performance and able to handle Force 10, a good enough recommendation.

There have been quite a few Rapier 400 produced as the jpegs indicate. This is a well thought out vessel that would make an excellent high performance cruiser.