Multihull Structure Thoughts

That's an interesting boat!
I've been intrigued by many of Tim's designs and I like his approach.

 

This is a “prototype” trimaran designed and built in Italy in about 1990 for a launch in 1995. "Con Basetta" was then sold to Holland where it’s floats where changed to improve its sailing qualities. The tri is a transportable cruiser that can be disassembled as required. The tri is 28 x 18 foot that can be disassembled to 6.5 foot wide on a trailer. The weight is claimed to be 1900 lbs with a displacement of 2150 lbs. These numbers surprise me as a very similar 26 foot Marples 26 CC weighs 2000 lbs and displaces 2800 lbs. The 26 foot aluminium mast with 5 mm 1 x 19 rigging carries a 161 square foot mainsail and a 124 square foot roller furling jib. The draft of the centreboard in the main hull is from 1.4 to 5.3 foot. The outboard power is 8 HP and can achieve 4 knots.

The accommodation is viable but limited, the main cabin has a seat to starboard (which can be converted to a single berth) and a galley to port. There is standing headroom between. There is a single berth forward with an area fir a portapotti. Aft has a space for a limited berth under the cockpit.

The construction below the waterline in the main hull is 3 layers of 3mm cold moulded wood with stringers sheathed with glass and epoxy. There are frames supporting the stringers. Above the waterline the mainhull is plywood of between 6 to 9 mm with stringers and frames. The crossbeams are timber box construction are removable. The floats are Dart beach cat hulls strengthened at the attachment points to the crossbeams. Why was I surprised at the weight and displacement above? Because the Marples 26 CC has 3 layers of 3mm cold moulded wood with a minimum of stringers and frames in its build due to its Constant Chamber build shape. "Con Basetta" is a similar but bigger boat with more materials used in it structure.

The only performance figures listed is the tri will average 6 knots over a distance in reasonable conditions. I suspect 15 knot peaks under good conditions.

The term “prototype” probably means a home build by a guy who was inspired by other designs. Look at many options before being to inspired. The jpegs give an idea.

 

This is the reason I have a love hate relationship with plywood. The Seaclipper 24 is a good design to fulfil a purpose, it is a creative design that sails well and is a real trailer sailor. It can really be built by a home builder, and there is the problem. First let’s deal with the basics. A Marples designed Seaclipper 24 trimaran has a real swing wing folding system. The 24 x 16 foot tri can be folded to 8.5 foot. The tri weighs 1400 lbs and displaces 2400 lbs. A 29 foot mast (Hobie 18 type) carries a 125 square foot mainsail and 100 square foot genoa. The draft ranges fron 1.1 foot to 3.5 foot over the center board. Power is an outboard of about 6 HP.

It was designed to do extended coastal cruising in coastal waters. It is available in two versions, Daysailer (with cuddy cabin) or Micro Cruiser (with full cabin). Simple 6 mm and 9 mm plywood construction with epoxy adhesives is standard. Flat laminated timber beams are used for swing-wing akas that reduce the 16 foot beam to trailerable width. The hull is light-enough to be towed behind a pickup truck. Expect to spend about about 6 to 8 months part-time effort to complete.

Now we get to my problem. I would call the boat in the jpegs an average build. It looks OK but it was not “finely” finished. Ply and timber are fast build materials but require detailed finishing to achieve good long life results. It is not just about applying West epoxy to seal a surface. Every bolt hole, every friction or abrasion point needs to be well sealed, especially end grain timber. After your epoxy and glass fabric goes on your good quality ply and as clear grain timber you can find, you need to paint and maintain that surface finish.

If you drop an anchor onto a deck or into a hull check it hasn’t broken any surface glass or left a scratch as this is an entry point for water. Always look for leak entry points in the deck, hatches etc, make sure the boat has ventilation, inspect closed buoyancy areas regularly etc. Maintenance is mandatory if you want a long lived boat.

A well done West (or equivalent) epoxy ply finish boat will last as long as you, a poorly done badly built ply boat will die in a couple of years. Do a ply and timber boat well or learn how to fiberglass construction. Fiberglass is more forgiving of bad maintenance but not bad building practices.

The big difference between old fiberglass monohulls is they could be badly built and still survive. Modern multihulls built in any material require good materials and workmanship to survive well.

The above is NO criticism of Mr Marples design. It is a very good design. It is a statement about how home builders build boats and occasionally cut corners. The jpegs give an idea of the tri.

 

I did not realise that I had not done a formal item on the Seaclipper 24, so we will do more detail today. The Seaclipper 24 is a good design by John Marples and Jim Brown that has a real swing wing folding system. The 24 x 16 foot tri can be folded to 8.5 foot. The tri weighs 1,400 lbs and displaces 2,400 lbs. A 29 foot mast (Hobie 18 type) carries a 125 square foot mainsail and 100 square foot genoa. An option is to use a 32 foot mast and a 7/8 rig with 600 mm diamonds with a J24 main or Star main and a Echelles jib. The draft ranges from 1.1 foot to 3.5 foot over the center board. Power is an outboard of about 6 HP.

The Seaclipper 24 was designed to do extended coastal cruising in coastal waters. It is available in two versions, Daysailer (with cuddy cabin) or Micro Cruiser (with full cabin). Simple plywood construction with epoxy adhesives is standard. Flat laminated timber beams are used for swing-wing akas that reduce the 16 foot beam to trailerable width. The hull is light-enough to be towed behind a pickup truck. Expect to spend about 6 to 8 months part-time effort to complete according to the designer.

The PDF’s below give the accommodation layout of the options but both layouts have a single berth forward. The longer cabin version has room for a small galley and a seat. The short cabin version has a longer cockpit. This tri is more of a camp cruiser than a mini cruiser. Functional for a single hander for a week long cruise. Very cosy for 2 people.

The construction is plywood and timber which has 300 gsm glass in epoxy covering the exterior. The dory shaped main hull has 6 mm ply hull sides on ply timber frames and stringers. The mainhull bottom is 12 mm ply. The floats are 6 mm plywood sides with 10 mm ply bottoms. The decks are 12 mm plywood, Marples prefers thicker plywood on decks to minimise framing support infrastructure. The mainhull transom is 12 mm plywood but there is a second 19 mm kickup plywood transom which has the rudder mounted on it. Cabin sides are 12 mm plywood and the cabin top structure, cockpit floor and internal bunk/seats are 9 mm plywood.

The crossbeam structures are in 3 parts. The forward crossbeam centre components are 3 laminations of 37 x 295 mm with the swing arms being 2 laminations of 37 x 295 mm by 6 foot long. The aft beams are 3 laminations of 37 x 240 mm for the centre section and 2 laminations of 37 x 240 mm for the swing arm sections. The swing arms pivot on stainless steel bolts. On the deck of the floats at the pivot point is a plywood disc to provide more support for the pivot bolt.

A builder of a Seaclipper 24 said: “I went with the larger cockpit which is very comfortable for four people, yet my wife and I have figured out a way to sleep comfortably enough for a couple nights. As expected, she takes about an hour to set up to launch with two of us, though it helps to grab a curious onlooker to help us raise the mast.”

As mentioned, the PDF’s provide layout and sail plan details. The jpegs give an idea of the tri. A simple alternative to a really trailable larger trimaran.

 

A good tender is very useful for a lot of sailing. Unfortunately, they are very desirable for others as well, result, you want a good tender that can be replaced cheaply and quickly if someone decides your tender needs to borrowed on a long term basis. The tender is 7.35 x 3.9 foot with a weight 60 lbs. The tender carries a small optional rig but can be built without the mast, daggerboard case and rudder etc.

The tender served Bernd Kohler of K-designs well on his 11 year journey on his 36 foot PELICAN catamaran. He could row it in up to wind force 7 winds when at anchor.

The construction is 2 sheets of 6 mm plywood and I sheet of 9 mm plywood. There is a minimum of timber. It is a simple effective professional design.

The full plans are in the attached PDF along with a few jpgs. A good little boat.

 

The following is a pure ”image” power catamaran. But it has a few interesting features. ERYD Design did the MAKAI M37 power catamaran and it is built by MAKAI Yachts Ltd. The M37 is 36.5 x 15.2 foot overall with a hull length of 32.5 foot. The displacement of 19,800 lbs. The length to beam on the hulls are 6.7 to 1. The draft is 1.8 foot. The standard engines are 2 x 320hp Yanmar with surface drive propellers or 2 x 370hp with outdrives. Maximum speed is 38 knots. The fuel tanks total 1100 litres.

Now we get to the hulls. They are asymmetric. The outside of the hull is wider than the inside (tunnel side) of the hulls. The hulls are V bottom. In power cats there are 2 paths, thin hulls with limited power that can achieve up to 30 knots or wider V bottom planning hulls which become efficient at planning speeds. The M37 choose the wide V bottom planning speed hulls. Next is the “low” tunnel height. In planning cats the air cushion created by the tunnel shape helps smooth the ride of the cat as it rides on a “cushion” of air (in theory, reality is it an assistance not a solution).

Finally, we get to the outdrives (inboard outboard) versus the surface piercing propellers. The outdrives are understood and easily installed. Surface piercing propellers advantage is the drag of the propellers shaft and support leg for the propellers shaft are not exposed in front of the propeller. Result less drag and interference to the propeller. If you use 5 blade propellers you get similar blade area with half a prop as you do with a lower fully exposed 3 blade prop. But surface propellers need very good design that is well matched to the hull. The faster the boat goes the more effective surface propellers are. The company describes surface props as: “Surface-piercing propellers sit almost half-in and half-out of the water, just behind the transoms. Those transoms typically disturb the flow of water exiting the transoms, so propellers work inefficiently while in that wash. So having the propeller at the water surface means more of the lower part of the propeller occupies “clean” water, while the upper part must only pass through the atmosphere and not water - reducing drag and draft, and making surface drives such as ours suitable for many applications where the owner is looking to reduce fuel consumption, increase speed and create a more efficient vessel.”

The accommodation is designed for marina living overnight or cockpit use when underway. The 2 forward double cabins have their own toilets. The bridge deck salon/cockpit has the main seating with a small galley and dinette. There is good helming and social seating.

The build is a full female moulded hulls & decks, exterior gelcoat finish with molded-in non-slip surface on deck areas. The hull laminate is infused polyester resin laminate with vinylester tie layer. The hull core material: PVC closed cell foam core. The deck laminate: Vacuum formed polyester resin laminate with a PVC closed cell foam core.

The jpegs give the idea of an interesting design.

 

In the diagram 'Air-Glide.jpg' surely the labels on the colour legend should be the other way round - green should be for higher pressure and red for lower!
At 38knots the airflow stagnation pressure will be about 230Pa, that sets an upper limit to the pressure that could be acting on the underside of the hull right at the bow, the pressure will be less further aft. That gives an idea of the lift force from airflow under the hull - it is not enough to have much of an effect on a boat weighing about 8 tons.

 

Today we talk about 2 sisterships with slight variations. John Hughes of Cat Spec designed both high performance short handed cruising cats. They were both built using the same moulds by Partridge yachts KeriKeri. Catenza and sistership Zephurous were built in 2002 – 2005 period. They are 45.9 x 26.2 foot with a build weight of 12,300 lbs a launch weight of 13,900 lbs (including rig engines etc) and a loaded sailing displacement of 17,500 lbs. The 60 foot aluminium mast carries a 755 square foot mainsail, a 355 square foot jib on a Profurl furler and a 833 square foot screecher. The hull length to beam is 13.5 to 1. The underwing clearance is 3 foot. The draft ranges from 1.5 foot to 7.2 foot over the daggerboards and daggerboard rudders (more on them later). Catenza runs 2 x 36 HP Yanmars inboard, Zepurous runs 2 x 20 HP outboards in their own wells. In both cases the cat cruise at about 7.5 knots and can run 10 knots at full speed.

The accommodation is 2 lateral double berths just forward of the main beam and a double berth aft in the starboard hull. The cabins have attached toilets. Forward in the port hull on Catenza is a full workshop for running repairs. The main bridge deck saloon has a large galley to port and a dinette to starboard. There is a navigation and entertainment area on the saloon cockpit bulkhead. The cockpit is small but effective for the sail handling. John Hughes was asked for a performance cruiser and minimised the open space to maximise the performance. The exact opposite to charter cats.

So, what sort of performance do you get? With Catenza, it matches wind speed to 15 knots, surfs at 15 to 18 knots for hours with peaks of 27 knots and has done 276 miles day run when fully loaded for cruising from NZ to Fiji. The average speed for the whole trip was 8.3 knots. The sail plan for most of that trip was 3 reefs in the main and a partially furled jib. They were running/reaching in 7 foot seas with some 16 foot seas, winds ranged from 25 to 45 knots. Its sistership Zepurous in initial trials did 14 knots in 15 knots of wind, peaked at 22 knots and was close winded.

I spent time on a very similar cat in Australia that in racing mode did a 320 miles day and did over 22 knot average for 4 hours. Cats like this are seriously fast. They also have one down side, they require very strong sails. John Bertrand a North sail maker who won the America’s cup for Australia was amazed when a mainsail he made stretched out of shape after its first sail even thought it was made with the strength of a 65 foot monohull mainsail.

The construction is epoxy e-glass, carbon, Kevlar hybrid and triaxial fabrics vacuum bagged in strip planked chipboard female moulds. High Modulus did the structural engineering. They used Herex foam above the waterline and Airex foam below the waterline. The rudders are a lifting foil in a 500 mm rotating tube bearing drum in stern steps.

This is a real good fast cruising cat design that achieves its aims. The limited jpegs tell the story along with a few pages of some magazine articles. The last jpeg has a photo of the barrel dagger board rudder in the top left corner.

 

On page 123 of this thread we featured a 50 foot charter catamaran being built in Titanium. We don’t know much about the cats dimensions beyond it length. We know a little about the build. The jpegs show parts of the build. Every part of the boat you see in that photo is 3 mm (.125") Titanium as well as the hull plating. Keelson may be 6,5 mm (1/4" instead of 3/8") as Jim Bett didn't like the big difference between the thickness of the two plates for welding. In the 50 foot charter cat it would have used 4.8 mm 6061 aluminium weighing 2.65 lbs/square foot verses 3mm Titanium CP2 weighing 2.77 lbs/square foot. The displacement between an aluminum and titanium versions would be very much the same and the much higher strength to weight of the Titanium boat should have had no problem getting signed off by the Coast Guard.

Two things Titanium is a good structural material but is a problem to build with as there are lots of pitfalls shaping and welding with Titanium. So, it was interesting to find comments from the designer of the Titanium cat, J Culbert, and his thoughts on the cat. Quote from here:

“Because the client had already worn out an epoxy/marine plywood catamaran which was replaced with a larger aluminum Harris design cat in the Waikiki Beach day sail trade. The aluminium cat was built with daggerboards instead of the pivoting centerboard that the designer had intended. They hit a whale or sea turtle on one side and the USCG had to take off sunset sail passengers. The boat was anchored off Waikiki overnight to try and salvage the next morning but with the weight of the water in one hull it dragged onto a reef and the swell came up by morning and there wasn't much left to salvage.

The replacement for that cat was a homegrown Rudy Choy designed composite cat, in fact the last design of Rudy's long career. It has carried no telling how many vacationers over the decades and the Coast Guard has threatened to pull its COI many times as they have been doing to the older Waikiki cats in an effort to upgrade the fleet. The Titanium cat (50') is my design and 'why ti' was my first question to the client. He had the impression that the strength and corrosion resistance would provide him with a legacy boat that was indestructible. The guy who referred me to him had been trying to sell the US Navy on titanium use on warships for several years and tried to dissuade the client from building in Ti but the client must have 'drank the koolaid' and I started design work on it just over 9 years ago! USCG has been a huge obstacle and I am not sure they have signed off on the submitted plans to this day. I chose the wrong old school professional engineer as our USCG liason guy and he never held up his commitment and I think the young Southhampton NA who now works for Betts is having sort out all the false starts with the Coast Guard. I worry that the client will not live to see the TiCat in the water and frankly wonder if I will live that long either! I get photos occasionally but if any of you readers here get a chance to see the boat please post here.”

J. Culbert 111
C3Design
251-545-3664
www.c111design.com

A later update from the designer J. Culbert. "The client insisted on US produced titanium as he thought that would be needed to not run afoul of the Jones Act. The hollow stringers you see were flooded with argon and there was a lot of trial and error to get the welding gun shield just right. I was concerned at how the builder wanted to run the longitudinal seams for the hull plating in the middle of the stringers so they were one sided welds. They later injected dye into the stringers and used clear vacuum bag on the outside which would let you see any leaks in the welds. I don't know if the Coast Guard had a 30' proctoscope to visually inspect the inside of those welds. Some sample welds with the stringer section were sent out to a testing lab who repeatedly broke their pull testing machine. Mostly 1/8 CP2 in the hull skins. Some elements such as the bridge deck were built in carbon fiber but think that the CF components came out heavier than the original Ti scantlings."

The jpegs below show the build, I do not know if it will be launched.

 

I really like the shape of the hull. Very pretty! That rudder assembly is awesome.

 

The QE IV was custom designed and equipped for the rough 40-mile ferry route between St. Croix and St. Thomas in the U.S. Virgin Islands. The tandem-catamaran hull arrangement was conceived and tested by vessel owner Warren Mosler, to provide passengers the most comfortable ride possible while remaining affordable due to low fuel burn. This vessel has been used as a ferry for 5 plus years with high patronage. The designer was Roger Hatfield of Gold Coast Yachts who built the vessel. The QE IV is 103.1 x 17.5 foot with a weight of 30,000 lbs and a displacement of 47,200 lbs with 58 passengers and crew. The draft is 2.6 foot. The power is 2 x 380 HP inboard diesels. She cruises at 19 knots with an average fuel burn of about 6.7 litres/ nautical mile. Peak speed is 24 knots.

The hull shapes of the “quadamaran” was intended to provide a more comfortable ride for paying passengers. The canoe forward hulls are slim to pierce waves and not react to quickly to waves. The aft hulls again are slim but have transoms to minimise pitching effects. Result this vessel is partial swath partial cat with a long “beam” cabin connecting the demi hulls. If you understand the average sea height and frequency you can optimise the vessels length to minimise pitching etc.

To keep the fuel consumption and weight down, the entire vessel was constructed from carbon fiber. The Gold Coast engineering team, along with subcontractors, conducted the most through engineering review the USCG has ever seen. That review included a complete Computational Fluid Dynamics study followed by a Finite Element Analysis for the entire vessel. A traditional first principles analysis was also conducted independently. All studies were then verified through Data Acquisition, which included measurements of strain and accelerations in various wave heights, heading, and loading conditions. With air-conditioning, comfortable ferry seats, and a smooth ride, passengers can enjoy a quiet crossing between the islands.

The build is basically infused carbon fiber offers several advantages over wet-bagging or carbon prepregs. Wet-bagging tends to yield heavier laminates. It doesn’t remove excess resin, leaving the cloth resin-rich and increasing the potential for thousands of microscopic air bubbles that weaken the structure. As the name implies, prepregs come already pre-wet-out with the correct resin ratios. A potential problem is that they have a finite open time when the material is brought out of cold storage and begins its thermally driven cure. Also, any gaps in prepregs that were not perfectly prefilled in the core remain as voids. With infusion, the time pressure is eliminated. The various laminates are simply laid in place, and once the bag is down and the vacuum pulled, you can pick when to infuse, introducing the freshly mixed resin and catalyst. The actual infusion of liquid resin under vacuum fills every microscopic void before it cures.

Because carbon fiber has a thinner thread than E-glass, it is harder to wet out. We used carbon cloth developed over several years by Bravolab. It included a 6-gram nylon micro-web as the transfer medium between every 200 to 300 grams of carbon. When we created and maintained a powerful vacuum of 24+ Hg, we created the lowest resin-to-cloth weights and were not restricted by the number of laminates we could infuse in one operation. This vacuum demands a tight mold, a near-perfect seal between the mold and the bag film.

The primary structure holding the tandem catamaran together is a long, hollow box (beam) running fore-and-aft, also serving as the passenger cabin space. The two forward hulls and the two aft hulls were to be connected to this long box, each with the conservative, proven pair of crossbeam bulkheads typical of catamaran construction.

Below are jpegs of the very successful vessel. One jpeg show a part of the vessels carbon fibre layup schedule, it is amazing that this vessel is the same weight and length as the French 30m (100‘) Ultime maxi-trimarans and half the weight of Comanche, the 100‘ ocean racing maxi monohull.

 

I love unconventional purpose designed and built vessels like this that are conceived to solve a problem or perform a specific task well.

I’ll admit though that at first glance before reading your summary, I thought someone had built a water version of the tractor trailer rig.

 

The following is about one basic design but developed into 3 different models. We have spoken of the Palma 30 open bridgedeck before but Palma now has produced a Palma GT with a rigid coachroof on the wingdeck. The Nicolas Purnu design is built in France in Charente-Maritime. The basic design is 30 x 18.7 foot with a displacement of 6,900 lbs for the open wingdeck version. The Palma GT rigid coachroof has a weight of 7,400 lbs and displacement 9,200 lbs. The 42.5 foot Z-Spar mast carries a 333 square foot main, a 183 square foot self tacking jib, a 300 square foot genoa, a 387 square foot Code 0, a 538 square foot Gennaker and a 755 square foot spinnaker. There is a performance package delivers extra power with a 46 foot long mast, a bowsprit, three high-end Aramide & CZ laminate sails. The draft is 3.2 foot over low aspect ratio keels. The power can be 2 x 15 outboards and inboards or a hybrid electric version.

Palma GT catamaran offers two aft cabins with 4.5 x 6.5 foot double-berths and 6.1 foot headroom and may add smaller single berth cabins forwards, directly accessed from the companionways. Each yacht is equipped with a full bathroom on Starboard and may host a second bathroom or a small office on Port. The Palma GT offers two choices of kitchen configuration: U-shaped behind the mast or L shaped at the yacht centre. An owner's dressing room is also available on Starboard hull.

The hull and deck structure is vinylester resin infused foam sandwich using PVC foam. All work is done in female moulds.

There are no known performance figures but I would suggest 7-8 knot averages and 16 knot peaks for the Palma GT. The open wingdeck Palma 30 with the optional higher rig would be faster.

The jpegs give you the various cruising Palma GT options. This is a well designed, smaller cruising cat that could carry a smaller family far.

 

Hi Oldmulti,

The biplane wingsail rig on this boat is quite similar to what I envisioned building. Is there more information available on it's performance and utility?

Great thread, thank you.

 

This is a sportier wider, lighter version of the Palma 30 basic catamaran. It uses the same hulls as the Palma 30 and Palma GT featured yesterday. The “Ventio” open bridgedeck version is 34.75 x 20.33 foot with a hull length of 30 foot (the bow spirit is 16 foot long). The weight is 5,500 lbs with a displacement of 9,000 lbs. The basic rig is 36.5 foot aluminium tube mast with a 355 square foot mainsail, a 172 square foot self tacker, a 398 square foot Code 0, a 473 square foot Gennaker and a 753 square foot spinnaker. An optional rig has a 42.5 foot rotating mast that carries a 419 square foot main, a 193 square foot self tacking jib, a 300 square foot genoa, a 430 square foot Code 0, a 538 square foot Gennaker and a 840 square foot spinnaker. The length to beam on the hulls is on the hulls is 8 to 1 with an underwing clearance of 1.65 foot. The draft is 3 foot over the fixed keel or 6.9 foot over the hull based centreboards. The cat can be disassembled for transport in a single container if overseas locations are required.

The accommodation is basically limited to the hulls with each offering a central cabin: large double berth, large clearance at the foot of the companionway and side furniture (can be fitted as wardrobes, galley, chart table, etc.). The large hold located under the cockpit is directly accessible and offers considerable storage space. The foredeck, accessible from the deck and from the inside, can also be converted into a large single cabin. A Bimini can be installed to protect from the sun in summer.

The hull and deck structure is vinylester resin infused foam sandwich using PVC foam. All work is done in female moulds. The rear beam is made of aluminum while the front one is made of composite to integrate lockers and a protection for the nacelle. The centreboard case is under the hull double berths with the berth tops acting as a structural stiffener.

So how will this version perform. The peak speed may only be a little faster (maybe 18 knots) because of the 8 to 1 length to beam. The real gains will be in light to moderate airs and upwind where the better sail area to weight ratio and deep centreboards will be a real advantage. Also having a 10% wider beam than the Palma 30 gains the extra power to support the rig.

The jpegs below give an idea of the design. A bit of fast fun for limited cruising. Interesting design.