Multihull Structure Thoughts

What compromises are made when you use the pet vs say a pvc foam?

 

Scuff. A short summary is at Foam Cores PVC vs PET ?? https://www.boatdesign.net/threads/foam-cores-pvc-vs-pet.65018/

This is not a full analysis, but some very good people gave their valued comments. Alik, Bajansailor and Rxcomposites are marine industry professionals and Fallguy is a very competent home builder. All of them suggest you have to design the vessel to suit the product and that the boat will be slightly heavier due to the additional density of PET foam required to get similar sheer strength. Translation, it is possible to Pet Foam as a substitute for PVC or San foam but you have to understand EG the shear strength differences and far more importantly the real characteristics of a product in an actual build situation. Building a polyester CSM woven roving PET sandwich will give entirely different characteristics to an epoxy biaxial PET sandwich. Some products need surface preparation other products will provide a keyed surface out of the box versus the strength of the underlying foam type etc.

 

Today is a story about an interesting high performance tri developed and built in Spain in 2015. The guy wanted a trailable trimaran similar to a farrier but faster. The trimaran “Sefini” is 29 x 22 foot that can fold to 8.2 foot. The displacement is 3,136 lbs. The 40 foot rotating mast carries a 392 square foot mainsail, a 242 square foot roller furling genoa, a 415 square foot gennaker and a 625 square foot asymmetric spinnaker. The draft over the udder is 2.0 foot with the draft over the float based daggerboards is 5.4 foot. The float shape is interesting with a full stern section and a lower freeboard but appears to be full bow section. I suspect the float shape is a compromise for trailering but still appears to work well.

As a comparison an F-28 is 28.5 x 19.75 with a weight of 2700 lbs with a 38.4 foot mast and a 680 square foot main and gennaker. The F-28 has a 5 foot draft. Translation the Sefini has a bigger rig, more beam and may be lighter therefore potentially faster than a F-28.

The accommodation is 3 single bunk beds, small galley, limited seating and fixed toilet. The cockpit can have 6 people.

The structure of this tri is interesting. I do not know enough about it but it is listed as PVC foam and Nomex is used as core materials with Vinylester resin reinforced unidirectional carbon fibres and triaxial fabrics. The cross arms would be unidirectional carbon fibre structures due to the small cross arm sections. The Farrier type folding system would help support the cross arm structure.

As you can see in the jpegs the floats are a good shape and the mainhull is developing a rooster tail in moderate conditions. I suspect the tri would fast but how much faster than an F-28 I am unsure.

The jpegs give an idea.

 

The following solar electric catamaran is designed for day lake, bay and river sailing. The scope of the catamaran is a weekend pleasure boat, an excursion catamaran, a charter boat for corporate events and day trips with a small company of up to 10 people. The catamaran is plywood with fiberglass covering. The cat is designed by Alexander Peregibenko and is 22 x 8.4 foot with a weight 1,570 lbs and a displacement of 4,000 lbs. The cat is powered by solar cells a battery and an electric outboard. The 2400 watts of solar panels are on the cockpit roof. The battery is an intermediate step to the 92 watt outboard in the initial design but the power cat can have up to a 10 KW Woutboard electric motor. The length to beam on the hulls is 8.6 to 1. The draft is 1.1 foot.

The accommodation is a single berth in each hull with minimal headroom. The helm station has a full standing headroom toilet space in it. The cockpit can have up to 10 people seated as required. The jpegs give the idea. The toilet area foot pod is an interesting concept. There could be a BBQ area and limited washing up area available as a mini galley for food preparation or some form of portable fridge for drinks and sandwiches.

The structure is ply covered with e-glass cloth and epoxy. The hulls are covered with 9 mm plywood. The external e-glass cloth covering is 200 to 240 gsm with epoxy. Internal fit out is 6 mm plywood. The stringers are 42 x 30 mm or 50 x 30 mm. The e-glass cloth covering is 200 to 240 gsm with epoxy. The underwing and decks are 12 mm ply. The transoms are 18 mm. The ten 8 foot underwing cross beams are 125 x 40 mm. The components are glued and screwed together with stainless steel screws. The cross beams could be aluminium. This is a relatively simple structure with only the bow shape which will require some effort.

This is could be a good trailable little day cruiser or could be used as a minimal charter machine for a local accommodation place by EG a lake. Interesting concept and appears to be well designed. The jpegs give the idea.

 

Brian Schmitt said he wanted a bigger power catamaran than his existing 57 x 25 foot cold moulded wood John Marples designed power catamaran he owned from 2003. Schmitt and his wife, DD, ran “Hippocampus 1 (or H-1)” and maintained it themselves, often leaving H-1 in the Bahamas and flying back and forth. But a 57-foot cat could never act as a support vessel for all Schmitt’s toys includes a 26-foot Calcutta catamaran, a 17-foot Twin Vee, a Robinson R44 helicopter, a two-man Nemo submarine and a mini four-wheel drive, four-door vehicle that weighs 2,000 pounds. Schmitt, now 67, longed for a bigger boat that could take him, his family and all his possessions further afield. So, Brian Schmitt started with a requirement list and again went to John Marples and Herrin.

The result was initially an 85 foot power cat but ended up as a 110 x 35 foot aluminium power cat design. “Hippocampus 2 (or H-2)” displaces 330,000 lbs fully loaded, carrying 12,000 gallons fuel. Powered by twin 1,600-hp MTU diesels, the analysis predicts the boat will run over 20 knots with a fast cruise of 17 and an economical sweet spot of 13 knots for a range of 5,000 miles.

The accommodation has a giant salon and galley, four en suite staterooms, including a full-beam master, and an office that converts to offer more sleeping quarters. There’s also crew’s quarters and a second galley. The 600-square-foot aft deck offers an outdoor galley and entertainment space which is covered by a helipad. There are cranes and dive lockers and a level of redundancy you don’t often see on a recreational vessel. It’s being built to cruise to the poles and anchor out in the Galapagos—it’s totally self-sufficient.

Brian Schmitt then found a 300 x 80 foot shed, fitted it out with tools computers etc and hired the entire Herrin crew to build the aluminium cat. The team purchased raw ingots in 10,000-pound increments at commodity prices. The ingots then had to go to a smelter to make the 8-foot-wide, 35-foot-long sheets used for the transverse bulkheads. More than 12,000 parts were cut from aluminium sheets of various thicknesses. Each part received a serial number so they could trace it back to the original ingot should they need to hunt down any irregularities. All told, the project will require more than 140,000 pounds of aluminium to construct. They started by laying the keels, which are 75 mm inches thick, 200 mm high and 110 feet long pieces of aluminum. The keels were laid in 2017, and then the crew began installing the frames and decks like an erector set. Schmitt wanted a wooden interior and purchased 10,000 square feet of mahogany and brought in expert craftsman John Lombardi to run the wood shop. Nearly five years into the project, the hull is now in primer, and the engines, gensets, solar panels and most of the other systems are in place, but no one wants to be pinned down on a launch date. And through it all, Schmitt maintained control, but he also floated the shop and the men putting his dream together.

Schmitt says. “Everything you do is a compromise in a boat. In a catamaran everything is very weight dependent. Overload them, they will be dogs and not perform. It’s a struggle between what you want and the associated weight. You have to manage that. This process has allowed me to build it for less, and I know that I am going to get what I want. I specified every little piece of equipment, you name it.” He also said this will be his forever boat. He won’t charter, and he won’t ever sell, unless of course someone makes him a ridiculous offer.

A well planned vessel built by a determined man with the resources to do it properly. A very interesting vessel. Jpegs give an idea.

 

The following is about an Austria guy, Willi Prenninger, who wanted a sail. He built a 16 foot day sailing proa and found it fun. Later he saw an article about a 20 foot cruising proa “Port Madison” in Duckworks Magazine. He wanted something a little bigger and brought Tiki 26 plans. He then said this is too big and it is not a proa. next he did a 10% sized drawing of what he wanted and started to build.

The result is a transportable proa of 24.6 x 14.75 foot with a displacement of about 1800 lbs. The crabclaw rig size is not specified but my guess is about 200 square foot. The daggerboard rudders draw about 4 foot when down. The jpegs of the rudders show a good version of the concept.

The accommodation has a 4.5 foot headroom with 2 single berths and very little else. The 6.5 x 3.25 foot cockpit (tilted up in jpegs) provides a good steering position and easy access to the rig. There is little detail on ow the rig will be controlled beyond the curved timber from bow to stern over the cabin top. More development required.

The structure is e-glass cloth covered plywood. The main hull dory bottom is 10 mm with the rest 6 mm plywood. The structure is stich and glue. The cross beams are a curved version of the Tiki 26 cross beams. The cross beams are strapped on as a Tiki 26 cross beam would be. The float is the main hull of the 16 foot proa.

No perform figures but an interesting design. The PDF’s are of the “Port Madison” proa which is 20 x 12.5 foot with a displacement of 900 lbs and a 150 square foot crab claw sail. 6 mm ply structure mainly.

 

Reefable wing sails are an interesting topic, but Rob Denney wanted real world experience. Lets talk about Bernard Fecot Tiki 30, PHA, that crossed the Atlantic with his reefable swing rig, which was then converted to a 2 part reefable wing sails. Bernand then built a Tiki 46 which had a 2 part reefable wing sails. He sailed Grand PHA a few miles before the 2 part reefable wing sails battens exploded. The battens were replaced were replaced by single unit battens built in aluminium. Similar to the Gallant rig. He then sailed PHA around the world including a 3 months plus stop in Melbourne Australia to see his son and grand children. He has some experience in this topic.

Now a few quotes: “I climbed inside the mast to see one pulley with balls has been damaged and blocked the haylard. After to have solve the problem I descent with the sail and next days I replaced the pulleys with other larger ones without balls.” “Grand PHA The Saturday after to have made temporary corrections to reduce the frictions with the mast we sailed with one sail to Morgat and according the point of sail we helped with one engine when it was necessary to head against the wind with a light wind with speed between 3 and 5kts.” “The Monday 15th October, we were sailing north heading in the Chenal du Four with a W-SW wind of 15-20kts to join the isle of Wight. We sailed at 60° of the wind with a speed of 10kts. When the wind become a beam I opened more the port sail and we heard a sound of broken wishbone. So we immediately dropped the sail to don't damage it and I decided according the wind and currents to stop in the Aber Wrac'h river in sailing only with the starboard sail. But a few miles latter when changing of heading after passing the light of the Four, we were downwind and after to have adjusting the sail I looked below the sail to see the inside in order to check if all was OK when the wishbones broke suddenly pushing me violently outside.”

“Although I have oversized the section of the wishbones (the plan said to use an aluminium tube of only 25 mm, the same as for my previous Tiki30) they don't accept a wind of 20kts with gusts of 25kts and even the upper articulated wishbones at the top of the sail were broken.” “For me it was a cold shower because after my tests aboard our Tiki30 PHA I had a very great confidence in the Swing wing rig offshore, but unhappily for a bigger boat this system is not enough reliable and as I've now any confidence with it I decided to give up the wishbones with articulations to get sails able to accept heavy conditions offshore sailing without damages.” “The rig will be from outside very similar with the Galant rig with aluminium wishbones without articulations. The main difference is that each wishbone will be connected to the sheet system. Sure the sails will not be so much powerful than with my previous articulated wishbones, but they will be very reliable with strong wishbones.”

“I only waited to approach the traffic lane corner offshore of Cap Finisterre to cross (the channel). To cut the traffic lane at 90° I had to close the wind at 70° and the wind increased with gusts at 30kts, so we hauled dawn all the starboard sail to continue only with the full port sail. We sailed between 7 and 9 kts with waves abeam. It was a good test for the mast and the boat who passed very well on the waves (which cleaned very perfectly the decks) and the mast didn't have too much bending (the only problem was the friction of the wishbones with the mast it's the problem with this rig). After to have crossed the traffic lane the wind decreased until 20kts and the next hours until no wind. We motored one hour until to get an east breeze of 10 kts. We sailed 653NM in 4 days and 8 hours at an average speed of 6.2kts.”

Grand PHA “Yes all the first parts of all the double wishbones broke due to too much curve (which generate a very high force in the middle of the sail) and due to a section not enough big to absorb the efforts.” “I was tired with this too long time to build the boat and at the end I haven't taken enough time to check it was OK. With the good experiences with our Tiki30 PHA. But all is very different with the efforts on a 30' and a 46'....”

PHA could average 6-8 knots at sea when conservatively sailed and peak at 14 knots. Grand PHA had similar performance with higher peaks of about 17 knots.

The following web sites give more detail: Quand une poulie coince la drisse de grand voile , par maheyo - Site de Marie-Hélène et Bertrand http://maheyo.free.fr/spip.php?article82

Sailing with "PHA" Tiki 30 n°119 http://wharrambuilders.ning.com/profiles/blogs/sailing-with-pha-tiki-30-n119-1

Sailing with "GRAND PHA" Tiki46 N°2 Part 1 : From Brest (France) to St Martin (Caribbean) http://wharrambuilders.ning.com/profiles/blogs/sailing-with-grand-pha-tiki46-n-2

 

This is a story about Jose who wanted a house in or near Paris. He could not afford the price so he said I will build one that will float on the Siene river. Jose approached a naval architect but did not agree with the build approach being discussed, so he said he would design and build the boat himself. The catamaran “Coalescence” is 75 x 28.2 foot that displaces 90,000 lbs. The cat has 2 electric motors mounted on shaft lines. Forklift batteries are used to power the engines. There are 10 KW of solar cells to help charge the batteries but the real recharging is done by shore power. The range of the cat is 15 kilometres when fully charged. This cat is a floating river house not a sea boat. The underwing clearance is 2.3 foot.

The accommodation is large with 1290 square foot available. There is a small cockpit without a formal steering station. As Jose is a computer specialist he can control the cat with his smart phone or a computer. The internals of the boat are built from house building materials so the walls etc can be laid out as required into rooms etc. with house hold equipment like stoves, refrigerators, lounge chairs etc.

The build was going to be a problem as Jose only had a garage to build the cat. So he produced 15 x 4 foot hull sections in his garage and transported the 10 hull sections to a boat yard near the river for the final construction. The hull components to the bridge deck level are waterproof ply, above that level commercial timber and plywood is used. Once the hull segments were joined to form two 75 foot hulls the underwing and roof components were built. The timber sections are large and I suspect the naval architect would have said they structure could be built lighter with more marine focussed building materials. Jose did a reasonable job over the 10 year build project.

Jose and his family spend 10 months a year living on the cat near Paris. The regulations required to live on a boat near Paris would be interesting but barge owners appear to be able to do it.

An interesting concept aimed at being a floating house on a lake or a river. Well done Jose.

 

The CC 30 power catamaran is a design by Col Clifford for home construction. Col Clifford has been designing for 55 years and has produced 500 designs, most of them custom designs. He has done both power and sail. The CC 30 is 30.9 x 14.9 foot with a full load displacement of 7800 to 8900 lbs depending on the build materials. The length to beam of the hulls is 8.2 to 1. The draft is 1.6 foot.

With motors, fuel, water and crew on board will displace less than 9000 lbs. Two 25 HP outboards will produce 8 to 10 knots cruising with a top speed of 14 knots. Two 50 HP 4 stroke outboards with a 10 to 12 knots cruise speed using 1 litre of fuel/nautical mile. Top speeds are 18 to 20 knots with the 50 HP outboards.

The accommodation is a saloon cabin with a spacious U shaped galley and breakfast bar and a dinette opposite. Forward is a steering position with entrances to each hull which contain a toilet ensuite and double berth cabin. The cockpit is setup for fishing with a cutting board and washup sink and plenty of room.

Now we get to the in construction. The CC 30 is an aluminium frame with a choice of plywood, fiberglass or foam glass panels. Col Clifford has patented a series of aluminium joining units which clip onto square tubes or pipes. You can set up an entire aluminium frame with the joining units, make sure it is accurate and true, then pop rivet the join units to the aluminium square tubes or tubes. Once the frame is established then you can cover the frame with your chosen shell material. Looks good so far, but please remember a fast frame build does not mean a total fast build. A frame is 10% or a build time. Attaching the shell material to the frame is the start of the work. By the time you have done the internal fit out, external finishing and equipment you are doing 90% of a normal boat build. I have no criticism of this approach any many cats up to 45 foot have been done using this technique. It does speed up the build but is not a total solution. Col designs most of his boats with either chines or conical sections to make the build easier. The jpeg of the CC 30 show a chine hull with mainly flat panels.

An interesting build technique that is well proven by a designer who has optimized the technique. The jpegs are of various designs Col has done.

 

An update on the Coral Cove 31 cruising catamaran designed by Mike Waller. The cat is 30.9 x 19 foot displacing 7800 lbs with a maximum payload 2200 lbs. The sail area is 540 square foot for inshore or 480 square foot if the cat is intended for offshore work. Both are fractional rigs with a 40 or 42 foot aluminium mast. The length to beam on the hulls is 9.4 to 1. The draft over the low aspect ratio keels is 2.9 foot. The underwing clearance is 2 foot.

The cat is plywood and timber with in the initial design a box section main mast crossbeam. After many were built with bridge deck cabins a Mark 2 option appeared with a full panel crossbeam and integrated main cabin structure. The box section cross beam allowed the components of the boat EG hulls to be built separately and assembled closer to the water. The hulls are 9 mm ply with a layer of glass over a ply bulkheads and timber frames and stringers as shown in the jpegs. The box section main beam has 18 mm ply webs on either side of timber top and bottom flanges with vertical and diagonal timbers between the webs and flanges. The rear beam is a similar structure but longer.

The accommodation options are as per jpegs. The Mark 2 version has full headroom throughout. The update is the jpegs of a build. With a 28 foot waterline this is the effective minimum size for a serious long term offshore cruiser in my opinion.

 

Part 2 of jpegs of Coral Cove 31 by Mike Waller.

 

Thanks OM. It's good to see some wing sail results.
My interest in wings for the prototype 24m/80' cargo proa is more towards ease of build and use, longevity, low cost and buildable by the boat builder. If it performs as well as a conventional set and forget cruising sail, it will do the job. The design has been an interesting puzzle.
I have zero confidence that a wing rig will reliably weathercock at anchor or in big waves and I have not seen any wing rigs that could be lowered that did not suffer dimpling on the leading edge or high halyard loads, so it had to be lowerable. The result is a solid fibreglass fairing on the leading edge and 10 telescoping sections per mast, each 1.25m/50" high. Each one pulls up the one below it. The non solid parts are lightweight, unshaped sailcloth in easily tensioned batten pockets.
The masts are unstayed for low maintenance and no tuning. They had to be large enough diameter to support the beams and vice versa without loading up the low hull (insufficient bury). There is a significant weight saving involved here as the beam loads are taken by the mast, not the hull.
Untapered masts to make it easy to build from pultruded carbon strips. Consequently, windage (but not weight) is high, so we decided to make them telescope. This also helps with stepping and unstepping in crane free locations and gives some options for light weather extensions to the masts.
Non rotating as bearings are expensive, require occasional maintenance and a lathe to make a mould for the bearing shells. Result is the wing must rotate, which has lower loads, but requires more complex sheeting and halyard arrangements.
Twist control. Twist is pretty easy to include in a rotating mast arrangement, but difficult to control. Batten sheeting resolves this, at the expense of more string.
Batten sheeting also means the loads are spread, resulting in lighter ribs. The sides of these are reasonably easy to move relative to each other using the sheets, imparting assymetry to the foil without complexity. They also open at the trailing edge, making it relatively simple to get inside the lowered wing for adjustments, prior to the planned replacing all the strings with fixed components, eliminating maintenance and adjustment.
A tail may be added to make trim automatic.

There are several challenges still to be resolved, but none look like being terminal. We shall see.

We have made a couple of sections and the results are good enough to move into production of the components. Unfortunately, the photos of the tests are in the photographers's computer, at the back of a shipping container mired in a very wet paddock awaiting a truck. When they are liberated, they will be on the cargo proa build blog at Cargo Ferry Prototype – Harryproa http://harryproa.com/?p=3788 I have included a rib photo showing how the NACA 0012 shape changes to a cambered section and an early complete section.

BTW, the rudder arrangement on Willi Prenninger's proa is flawed. The centre of rotation is aft of the centre of pressure, meaning the boards will want to align across the flow. The solution is to rake them aft or move the pivot forward, neither of which looks possible on this design. Another option is to link the rudders to negate the forces, but this removes the option of lifting one of them. On bigger boats, hydraulic steering solves the issue, unless/until it fails at high speed, with spectacular results.

 

“Sanderling” is a Wharram Oro 46 that was started in 1976 and launched in 1978. The original ORO 46 is 46 x 20 foot with a waterline length of 35.3 foot. The design weight is 7,850 lbs and a payload of 6,600 lbs for a total displacement of 14,450 lbs. The original rig on the ORO design was a bermudian ketch rig of 750 square foot. The hull beam at the gunnels was 7 foot and about 12 to 1 at the waterline. The draft is 2.2 foot over the keel hull and rudders. There are no foils on the hull. The original ORO built in ply was possible to build for $1000 US dollars according to the designers 1977 advertising brochure.

Now we will talk about “Sanderling”, an aluminium hulled ORO 46. Sanderling weight is not specified but its draft is 3 foot fully loaded which indicates its fully loaded displacement would be about 20,000 lbs. The builder chose to build in aluminum for a long life, low maintenance, and strong cat. Wharram intended his original designs to be built cheaply and easily by amateurs, and be fully seaworthy. The Wharram’s are seaworthy but the plywood boats often had a short life and high maintenance. “Sanderling” hulls are built of 4 mm 5086 aluminum alloy. The hulls have 7 bulkheads with stringers on the hull sides with some furniture also supporting the hull structure. 5086 alloy is strong, easily welded, and very resistant to corrosion in salt water. Sanderling was launched 43 years ago and has never been painted and is bare aluminum, above and below the waterline, and is still in excellent condition. Sanderling has no bottom paint. Its beached and scrubbed with a pressure washer to get the bottom clean. The builder took great are to isolate any other metals from any aluminum hull structure. There are sacrificial anodes which are replaced regularly. The windows are 6.4 mm tempered glass.

“Sanderling” took perhaps three times as long to build as would have been required in plywood or fiberglass, but is stronger than a standard Wharram plywood design. The 4 main cross beams are factory-laminated glulam beams are slightly oversized from the Wharram plan, and were fully pressure treated. The bolts attaching the beams to the hulls are oversized stainless steel. The beams sit on rubber inserts to allow some flexibility in the design. The deck between the hulls is spaced cedar boards on the cross beams.

The rig is a Junk Rig ketch. Similar to Hasler's design, but the sails are rectangular. Sails are blue polyethylene tarps. Making a new suit of sails consists of buying two large tarps, putting a multi-layer hem around the edge, and screwing on the battens. Blue tarps work well for junk rig, as the stresses on the sail fabric are very low. Masts are tapered, free standing island fir trees, cut by us on Stuart Island, WA. They are finished with wax and mineral spirits. Mast steps are 6.4 mm aluminum, 4 foot high by 1 foot square. Mast steps are anchored with welded aluminum brackets to the beams. Running rigging is solid braid nylon rope. On the Junk rig, the loads on running rigging are small. Halyards and sheets are multi-part purchases, so no winches are needed. Reefing is easily done by lowering the sail by one or more battens. Masts are easily recoated with wax and mineral spirits from a bosons chair, using running rigging, no need to remove any finish, just put more on.

The accommodation is 2 double berth cabins and 2 single berth cabins all 8 foot long. There is a galley and seating in a hull and a toilet area in the other hull. The walls and ceilings are lined with Styrofoam and painted for insulation and sound reduction.

“Sanderling” has mainly lived on anchor for its 43 years requiring minimal maintenance. It performs well and is very seaworthy according to the owner. There are at least 5 aluminum Wharrams that I have read about but this is the longest lasting and has been built effectively at a relatively cheap cost. The jpegs are of “Sanderling” except the final peg of a 30 foot aluminum Wharram with a deck cabin.

 

Re Sanderling, I am intrigued by how they still used timber cross beams, despite the hulls being built of aluminium.
Surely it would be a lot stronger (and more homogenous) if everything was ally?

 

Bajansailor. My impression was the builder built the boat to a budget with an aim of doing minimal maintenance. He appears to be a good thinker but does not claim to be a boat designer. Result, he had confidence to change the hull materials but kept the concept of timber crossbeams as per the original concept. I also suspect he had access to cheap beams and the timber masts that were easily accessible. Again his logic could have been I can replace a beam or mast if required but a hull is a much bigger problem to replace therefore make it long lasting, I am just guessing here. The slightly increased cost of hull materials would have been offset by a very cheap rig and relatively low cost beam arrangement. Also the engine arrangement on the bridge deck with a long tail is relatively cheap. My guess is this cat would not cost any more than a ply timber 46 footer built to the original plan. The big gain is he has had a low maintenance. low cost to own cat for 40 years. It may not match modern designs in performance but it has served well as a long distance and long term cruiser.