Multihull Structure Thoughts

Kiko Johnston-Kitazawa is a Hawaiian Canoe Builder, sailor designer and builder. He is a man who likes to explore the history of proas and other Hawaiian sailing craft. At one point he built a proa named “La ho’i ho’i ea”. The proa is 42 x 19 foot that weighs 2200 lbs. The two unstayed douglas fir pole masts are 31.7 foot high that are 210 mm at the partners tapering to the tip. Each mast has a 250 square foot Hasler McCleod Chinese lug sails. The main hull is asymmetrical with a maximum width of 3.1 foot. The outrigger is 32 foot long by 1.5 foot wide. The proa is steered by a paddle that is 1.5 x 3 foot.

OK, we have a 42 foot boat that weighs 2200 lbs and carries 500 square foot of sail. How does it sail? This proa has several daily sail runs in Hawaii at 15 to 16 knots and it can work upwind reasonably well. The people who have sailed it describe it as easy to sail with the Chinese rig.

Now to the build, 2200 lbs in a 42 footer is light. The main hull is made from 9 mm thick Sitka spruce lapstrake on a 90 x 45 mm white oak keel, stems and steam bent frames. The copper-riveted lapstrake construction of spruce planks onto the frames reminds you of Viking long boat construction. The ama is 6 mm compounded plywood. The timber 19 foot cross beams are laminated timber. There are some watertight bulkheads and some fore and aft decking but it is basically an open boat for day sailing or limited voyaging with skilled crew.

Kiko Johnston-Kitazawa built the proa sailed it for a short time then lent it to Tim Mann for a decade who used it for testing Tim’s proa ideas. Kiko got the proa back and has upgraded it but it still pretty much the same concept. You can contact Kiko who runs a charter business in Hawaii if you wish to explore the design more.

This is a very interesting craft. It shows that many historic approaches to a sailing craft from the design, build and rig can be brought together to form a very effective sailing craft. Sorry about the limited jpegs. The portrait is of Kiko.

 

A scrap of paper (first jpeg below) ended up producing a very rare proa aimed at the Race to Alaska in 2015. The proa “Palindrome” is 30 x 12 foot that weighed 450 lbs at launch and uses a cut down Hobie 16 mast that supports a crab claw rig with bamboo yards and a 195 sq. ft. Tyvek® polyethylene sail. The main hull is 30 x 2 foot with an additional 2 foot “pod extension”. The float being 15 x 1 foot. No idea of the draft over the kickup rudders.

So what makes this proa so rare? Palindrome was designed to be “the most boat we could get for the money”, says Dillon Majoros the designer and part builder. The proa is a creative blend of skin-on-frame hull construction for the main hull and the float a stitch-and-glue epoxy/plywood construction. The skin on frame hull is very light, Dillon said the wood frame and nylon hull was the quickest part to build - no sanding! The frame has 4 stringers per side plus a keel line. There are 10 bulkheads/frames of 12 mm plywood frames with a plywood deck. The skin on frame hull is flexible as the nylon material depends on the frame to provide the majority of the strength. A ply/epoxy deck cabin acts like a stiffening spine giving the flexible hull the stiffness it needs to handle the loads of the sailing rig. The beams are ply/epoxy box section.

The 195 sq. ft. Tyvek® polyethylene sail can be shunted quickly and easy (for a proa) thanks to a clever system of blocks and tackle that pull the yard from “old bow” to “new bow” in a few seconds, with the mast tilt and stays automatically adjusting. Leeway prevention is handled by a single “weather” board in the center. The board pivots fore and aft to adjust the CLR and to avoid damage in groundings. Steering is by quarter-rudders, which also flip up. Only one rudder (aft) is used at a time. The rudders work well and Dillon reports that steering the boat is a single-finger affair, however he’s had a bit of trouble keeping them properly attached.

“Palindrome” sails well. It is controllable, relatively easy to tack and fast on many points of sail according to some comments. The initial power trial produced 9.4 knots from a 4 HP outboard.

Steve Ladd now owns “Palindrome” and is converting it to a tacking proa named “Pepper” with more cabin space and higher bows. The new tacking proa has the skin removed on the main hull and it has been replaced by foam glass panels using the original framework. Steve Ladd has a you tube channel - Steve’s proa “Palindrome” becomes “pepper”. Type that into google to see his progress.

Interesting proa of unusual construction. Good fun. The final Jpeg is a Diekering Ulura skin on frame proa.

 

This is an update on a B&B trimaran called the “Mini Trimaran”. The tri is 18.5 x 11 foot with a trailering beam of 6.75 foot with sliding aluminum beams. The empty weight is 220 to 240 lbs depending on the quality of plywood and timber you buy. The full load displacement is 610 lbs. The aluminum tube freestanding mast rotating for reefing (with one backstay) carries 100 square foot of sail area with an optional 80 square foot spinnaker. The main hull length to beam is 11.25 to 1. The lateral resistance is a leeboard by the centre cockpit that can be controlled with lines running to the aft cockpit and the stern kick up rudder can be steered by foot steering from the aft cockpit. Additional power can be provided by a Hobie mirage drive in the centre cockpit.

The new "Mini Trimaran" as it is being called (for now) is an evolution of B&B work in small multihulls over the years. It combines elements of the successful Expedition Sailing Canoe and the "kayak trimaran". The tri can seat 2 comfortably or sleep 2 on the "wing decks" which are large enough for sleeping aboard with a cockpit tent.

The structure of this tri is basically plywood and timber with aluminum cross beams. The plywood material list is as follows:

-9 Sheets of 4mm okume plywood

-1 Sheet of 6mm okume plywood

-1 Sheet of 2” Dow “blue board” foam.

-1 Sheet of 3/4” Birch Plywood or OSB (for cradles)

The detailed wood material list is at Trimaran Builders Resource https://docs.google.com/document/d/e/2PACX-1vRWRpKPMBNgduZtcpOd5QmijeB1lWcrL2U7RghSokeVkAPVjCnByqAYCBQssCJtWWBD1M5VVjv3TZyi/pub

The cross beam halves are 50 mm welded aluminum tubes that slide into a central aluminum and fiberglass tube arrangement attached to a hull bulkheads and thick 4 mm ply 52 mm Dow foam 4 mm ply “wing decks”. The foils are solid shaped timber. At the top of the mast is a 340 gram rotating float with a small “plywood gaff” used to provide a simple fat head mainsail sheeting point.

The sailing performance looks good from the video’s but this tri would need to be treated with respect as the float buoyancy is only 275 lbs (about 45% of full displacement). This is a bay sailor more than a coastal cruiser.

A nice design that could provide a lot of fun. The jpeg give the idea. The following web address show you construction jpegs https://photos.google.com/share/AF1...?key=YjJLY010YUxJRjZhZ09TY24zakVMOVp6Vy1weGxn

 

A lot of work ! Looking at the scale in the jbegs of the new mini trimaran the weight is 313 lbs which looks realistic.

 

A short one on a guy who tested glass reinforcement on ply timber corner joins such as chines or deck edges. Seth Miller from Minnesota USA did the testing on “6 mm” plywood and 28 x 18 mm or 18 x 18 mm “chine” timber. The plywood measures 5.25 mm but is sold as “Sureply 6 mm”. He tested the joint with a used a 500-pound capacity force tester to apply a ‘closing’ force to the joints. Warning, Seth does not like epoxy and used Titebond III wood glue as his gluing material for the fiberglass. I do not think this invalidates the results of the next series of conclusions.

The initial joint was like a deck edge with a 6 mm ply panel on top and a 6 mm panel at 90 degrees with a 28 mm x 18 mm “chine” timber join in the corner. Jpegs (Tape 2 Tape 5). There was no reinforcing glass on the joint. Seth found that the un-reinforced joints failed at 25.2-pounds force (lbf) and 32.0-lbf for an average of 28.6-lbf. In both samples the layers of the SurePly separated starting at the outside corner. Separation progressed to near the corner of the chine log, at which point the remaining layers fractured. Jpeg1 (tape3) shows the result of pressure put on the 2 outer plywood edges. The failure was at the edge of the timber which created a “hard” point. There is a reason designers like filleting between a timber EG stringer and plywood panel as it helps distribute the loads more evenly over the ply timber edge.

Next was second set of sample pieces created with “6 mm” ply on either face with 18 x 18 mm chine timber. Jegs (Tape 6) This time there was a glass tape over the rounded edge down about 18 mm to the edge of the timber on either face. The 18 mm reinforced samples failed at 31.4-lbf and 38.4-lbf for an average of 34.9-lbf. These samples failed in much the same manner as the un-reinforced samples. The plywood failed at or near the corner of chine log. This was to be expected since the reinforcement didn’t extend past that point.

The final set of tests were done on sample pieces with “6 mm” ply on either face with 18 x 18 mm chine timber. Jpegs (Tape 7, Tape 8) The glass tapes covered the corner and extended 50 mm down each plywood face. Therefore, the tape went past the timber edge by 32 mm. These proved to be the strongest joints. These samples failed at 43.8-lbf, 44.0-lbf and 49.0-lbf (pictured just prior to failure below) for an average of 45.6-lbf. These three samples also all failed in the same area and manner. The fiberglass eventually tore and the plywood fractured at or near the corner of the chine log. Seth noticed that the 2-inch reinforced samples flexed much further prior to breaking than did the un-reinforced and 18 mm reinforced samples.

Summary. A tape reinforced ply timber edge can be 90% stronger than a non-taped corner ply timber joint. But the tapes need to extend past any “hard” points such as the edge of timber chine or deck edge. An internal strong fillet between the timber edge and ply face provides a similar dispersion of loads which would help to strengthen a framed plywood structure.

Thank you, Seth Millar for an interesting study that has real applications in the real world. I suspect the results would be similar if there was an epoxy tape joint. The jpegs give the idea.

 

This set of lines for Evergreen is on Proafile; Proa File | Evergreen - a Fast Expedition Catamaran https://proafile.com/multihull-boats/article/evergreen-a-fast-expedition-catamaran
Can any one read the numbers on the lines plan top right, if you can modify it so that they can be read I'd appreciate a copy.

 

Redreuben. 2 paths of action. First expand the line plans on the proafile site then "save as" into your PC. Then bring the line plans up as a picture you can then use the slider to expand the picture and bring up detail. The problem is the underlying diagram does not have high resolution. Second path is to again "save as" then bring the lines plans up as a picture and resize the plan to EG from 500 to 800 (the ratio will automatically fill the second box). This will give a larger plan to look at but again if the original diagram is not good it will not improve the clarity.

 

I know very little about this trimaran and would like to know more. The trimaran “Mongoose 25” was designed and built by George Silva from St Croix. He has designed and built multihulls previously and has a very good knowledge of the design characteristics that suit his sailing area of the British Virgin Islands.

Mongoose 25 is described as an ocean going day sailing trimaran of 25 foot length with a 36 foot aluminium rotating mast with a fractional rig. The tri has a daggerboard and an underslung spade rudder. The floats are high buoyancy. The tri can be disassembled into the main hull and two float cross arms structures. The float crossarm units are slide into slots in the main hull and bolted together with water stays to improve the structural strength.

For any other numbers I am guessing. It looks like a 25 x 18 foot with a weight of 1800 lbs and a “displacement” of about 2500 lbs. The sail area is about 450 square foot. End guessing.

George Silva does his initial designs on table napkins over a beer then formalises the design by hand onto Mylar and enters the design into CAD to allow printed plots for the final build. The Newick’s were family friends and George stated “Back then, to hit 20 knots was the holy grail,” Silva says. “Nowadays boats routinely hit 40 knots. Hull and sail shapes have come a long way. Today, my hulls are very different. By using lifting bodies that rise with forward motion and force water to flow under the hull instead of around it, reduces drag exponentially. With the use of Computer Aided Design (CAD), buoyancy centers can be designed to shift quickly to self-correct pitch. The result is a very stable, very fast boat.” There is a large cockpit with a minimal cabin for storage, probably a loo and a single bunk.

Silva explains. “I still prefer old fashioned drafting with my curves and a pencil. So, I pull out the Mylar and draw a scale picture. Then, I enter those lines in a CAD program and refine them. After that, I print full size patterns and build the molds. I built the armas first in reversible half molds and then the main hull. This boat is foam core, so the sheet foam is cut into strips and bent or heated into the mold then fiber-glassed. Essentially, it’s built from the inside out.” The structure is directional fabrics with west epoxy over vertical strip M80 corecell foam that are vacuum bagged. A second builder designed his own oven for heating the foam. The second builder is doing his beams and mast in unidirectional carbon and pro-set epoxies. Depending on who is building the tri it can take from 1 to 3 years to build. George Silva has sold plans for the design.

The performance is good according to its rating of 1.000 when racing. As I said I would like to know more about this design. Sorry about the limited jpegs.

 

The Taenga 16 trimaran is one mans specific build to suit his requirements. A small cruising trimaran that could be stored at home and trailed to the water. The tri was intended to be a folder but as the build developed, he choose to keep it simple and made it a solid build.

The tri is 16 x 8.2 foot with a weight of about 700 lbs. The displacement is unknown but judging by the waterlines would be about 1400 lbs. The 19.5 foot rotating aluminium mast and sails are from a KL 14 catamaran with a hand sewn roller furling jib. The floats are the KL 14 hulls which are 14 x 1 foot and have low aspect ratio keels and kickup rudders. The buoyancy of the float hull is approximately 1000 lbs.

The main hull of “Taenga” is a Prindle 18-2 hull which has been cut down to 16 foot by reshaping the bow and cutting part of the stern off. The hull centreboard was retained. The deck was cut in several points to allow the installation of cross beam slots and building a centre cockpit area.

All modifications (except the plywood crossarm slot boxes) were done in PVC foam glass. The aluminium cross beams are 8.2 foot long 100 x 5 mm aluminium tubes that are bolted to the main hull and floats.

There are several storage areas under seats and forward in the main hull but there is no real internal accommodation.

The tri took about 4 years to complete due to the builder having medical issues, but the build was well thought out and done well. The tri sails well with moderate performance and with careful handling can do limited coastal sailing.

A design for a specific purpose to suit 1 mans need. It utilises many “spare parts” from second hand and unloved boats to build a ice tri.

 

Another home built tri using product cat parts to eventually form a fast day sailing trimaran. The tri is 20 x 17 foot. The weight is a guess of about 600 lbs with a sailing displacement of about 1000 lbs. The 33 foot rotating aluminium mast carries a 160 square foot mainsail and a 100 square foot self tacking jib that he modified from a larger sail.

Jim Gallant the designer builder built a few small tris first then wanted a fast foiling trimaran. He used a Supercat 20 hull as the main hull. Added a 17 foot aluminium cross beam, 2 small planning floats and 2 main foils and a T foil rudder system. This tri could foil in 13 knots of true wind for 20 or 30 seconds at a time but was very twitchy when it got onto foils. The tri was a bit of a handful requiring 2 people to control it. (First set of jpegs) The tri could go 20 knots but kept breaking parts due to the rotational forces through the structure. Jim decided to enjoy sailing not rebuilding all the time. So he used his main hull and rig and added Nacra 5.2 cat hulls as floats.

The new non foiling tri has a Supercat 20 main hull with dagger board and rudder and Nacra 5.2 cat hulls as floats. The cross arms are 17 foot long 115 mm outside diameter 6061 aluminium tubes with 3 mm walls. The cross beam have a stainless steel water stays on the forward beams and a 1x19 stainless steel water stay on the aft beams. The dagger board is 5 foot long and is a foam carbon fibre structure with a hardwood timber spar core. He made his own mesh trampolines after he found out the price of professionally made units.

After 2 initial trial sails of the tri (google jim gallant diy trimaran for a youtube of some sailing) he built a self tacking track and frame for his headsail to make the tri less of a handful to sail solo.

So how did it perform? This is a high performance day sailor. It sails very well upwind and goes well on all other points of sail. To quote Jim “The boat has tremendous speed potential. I should have reefed the main given the gusts. I was sheeted out to shed wind most of the time so as to not scare myself. I didn’t have an app or device to gauge my speed, but it seemed very fast. Probably over 15 knots at times. Acceleration is alarming. I almost went off the back of the boat one time after jibing and getting the main sheet set.”

This is a daysailor bay or river boat with minimal free board and good performance levels. It is now a more reliable boat that Jim enjoys more sailing on and less rebuilding. Jpegs give the idea.

 

One of the higher risk things you can do is reading Russian boating message board sites, they can be long, boring and contain a level of abuse that would surprise you. But occasionally they can contain real information from very competent amateurs and professionals.

Fedor Konyukhov is a 68 year old Russian adventurer and survivalist who has done 2 circumnavigations, rowed across the Atlantic and done many other extreme adventures. His latest adventure is a Solar power catamaran which will do a Transatlantic run as a warm up before he does a 100-day solo Transpacific trip of 9000 miles from Chile to Australia that will be exclusively powered by PV power (solar panels and batteries).

The catamaran "Nova" is designed by Englishman Phil Morrison. The cat is 37 x 23.8 foot that weighs 5000 lbs. The cat is powered by 710 square foot of flexible heterojunction solar panels and 26 Li-Fe-phosphate batteries for a total capacity of 60 kWh. The batteries weigh 1200 lbs. The power consumption of the two electric motors to achieve the designed speed is 1.5kW requiring a supply of 36 kWh to run 24 hours. The battery capacity of 60 kWh allows for the motors to operate continuously for 40 hours without recharging if there is overcast days etc.

The total surface area 710 square foot of the primary solar modules include 550 square foot with a peak output of 9 kilowatts laid horizontally laid on the upper deck, and an additional 160 square foot of PV on the outer hull sides to capture any sun rise/sunset rays. The 2 electric motors consume 1.5 KW to achieve a speed of 5 to 7 knots in reasonable conditions. The cat can go faster or use more power to maintain speed in stronger wind conditions but it effects range.

The cat is a carbon fibre PVC foam build throughout. The cat is designed to be disassembled and able to be put in a single 40 foot container for ease of transportation. The 2 hulls are independent units with a series of cross beams with the solar panel modules on top. The quality of build looks good judging by the jpegs. An ocean crossing 37 foot cat that weighs 5000 lbs including 1200 lbs of battery is pretty good.

The accommodation is for 1 man and has the basics. I hope he has a few toys to play with whilst sitting there for 100 days as this is one of the easiest ways to cross an ocean if you can avoid corrosion of the wiring etc. The jpegs give the idea.

 

Re the electric cat above - it is impressive, but I have to ask what is the ultimate purpose of this expedition?
It seems to be that it will be more a test of the skipper's endurance re sitting for 100 days on a flat cat while pootling along at 4 knots or so.
I hope that he will be allowed to have at least a bimini awning (or 2) to shelter him a bit from the sun.
And I wonder what the budget for this project is?
I would be a bit skeptical about 1.5 kw pushing this cat at 5 knots - maybe in a flat calm sea, with a very clean bottom.
And any wind behind him would help certainly.
Maybe the bimini awnings could help a bit as sails......

 

bajansailor. The web site is Pacific Ocean crossing aboard the solar-powered catamaran “NOVA” - Fedor Konyukhov https://konyukhov.ru/en/project/expedition/crossing-pacific-oceans-aboard-the-solar-powered-catamaran-nova/

He appears to be a professional "sponsored" Russian adventurer who gets deals done with sponsoring companies to promote products. EG The boat is equipped with an 11 kW PV system built with flexible heterojunction solar panels developed by Russian module maker Hevel Solar. “The cost of solar elements plus labor and without the storage system was RUB 1.1 million, which makes up to €12,000,” a spokesperson from the manufacturer told pv magazine.

The PV were cheap for that size of flexible PV panels and all associated equipment. I agree with your reservations on the power to push the cat especially in rough conditions but Phil Morrison is an excellent designer and engineer. My problem is where does the design and engineering finish and the promotion team hunting for funding take over.

 

I have to agree about the electric cat being underpowered for its size and use as an open ocean cruiser and have to wonder if both motors consume a combined 1.5kw, what do they actually produce in propulsive power?

Now if each motor pulled 1.5kw and were of brushless design with say an 80% efficiency at cruising speed, I could see a speed of 5knots sustained achievable provided a bimini or anything else isn’t added that would create windage. The weight of those batteries will really help keep the boat on point.

Also with a boat this size out in the open ocean, it would be better to spin a larger diameter more aggressively pitched prop at a lower RPM to reduce cavitation and give better bite. Problem is this often requires some sort of gear reduction which adds even more inefficiency. But with two motors and the right hull shape, it will should move faster and track better than a single motor being a Catamaran.

It’s definitely a cool design and an ambitious project, and I commend the builder for challenging themselves with this adventure.

And along those lines, have a look at this wild inflatable tubular framed sailing Trimaran that just set out on its journey:


More here:
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I think the same guy has built an inflatable Catamaran and smaller inflatable Trimaran in past that he sailed long distance.

 

The Hanstaiger X1 is a limited-edition trimaran cruising yacht. John Ordovas , who was searching for the perfect yacht for himself and family couldn't find a design to suit, so he decided to create something that met his expectations. The tri is 64 x 32.5 foot weighing between 80,000 and 90,000 depending on the build option with 2600 square foot mainsail and a 1100 square foot self tacking jib. There are electric winches to control all aspects of the sails. In the sailing version there are 2 Volvo IPS 300 hp engines. The power version can have 2 Volvo Penta IPS 810 HP engines which will give 30 knots. Engines are located in the floats as are the rudders. The tris draft is 3 foot with the keel retracted.

Before we go further, a hint about this tris function is the headroom throughout ranges between 7.5 foot and 10 foot. This is a floating home that has accommodation on 1 level including an 830 square foot lounge area. The jpegs tell you a lot. When a spa and a grand piano are part of the furnishings you know this design was inspired by Piver, refined by Horstman ideas then extended into a new design dimension of luxury first, sailing capability second, power third and after that, the $5 million I paid allows me ignore any other requirements.

The main deck of Hanstaiger X1 is a single level, with the exception of the owner’s stateroom, running the length of the yacht and separated into sections: the owner’s suite, two VIP staterooms and two crew staterooms. Furthermore, there is a 830 square foot lounge space that comprises yacht’s main salon and galley. The owner’s suite also is divided into sections. These include an upper level with a large bed and an office, a mid-level where the en-suite bathroom with his-and-hers sinks, a dressing table, a hydromassage cabin and sauna are found, and a lower level with a large glass dressing room and another WC. One VIP stateroom is located to port. It features a comfortable bed, a sofa and a large en-suite bathroom. The second VIP is located to starboard. It has two reclining beds, a roll-up TV, a private dressing room and an en-suite bathroom.

The structure is interesting. The hull structure from the mid line down is a PVC carbon fibre or E glass structure depending on the option is chosen with vinylester resin that is vacuum resin infused as one piece then cooked for a final cure. The topsides, decks and bulkheads are all carbon fibre PVC foam and epoxy again vacuum resin infused and cooked for a final cure prior to final assembly with the lower hull. This is a very interesting build if they are doing a 64 x 32,5 foot one shot resin infusion for the lower hull. Additional structural reinforcements is done with titanium filaments.

The tri is painted black, which is a heat generator, but this is dealt with a powerful 120,000 BTU air conditioning system, powered by 24 lithium-ion batteries. Oh, the epoxy resin in the topsides is a very special high temperature formulation that will not soften in high temperature direct sunlight.

I don’t know what to say. This is a valid build, but it is so far removed what I consider a fun sailing vessel that I wonder if a power tri or cat would not be better. The jpegs give some detail.