Multihull Structure Thoughts

Nice bunch of photos and looks like a well-built boat. Thanks.

 

This is the final part of Andrew Stransky's design and home built 51 foot fast cruising catamaran “Fantasia” (full plans were drawn and called “Seven Seas 50” but I do not know if they are still for sale). We will focus on the decks, cabin, interior and launch.

The interior furniture is started to be placed on the bridge deck as required. Most appears to be Gaboon ply with EG seats adding strength to the structure and in some instances performing a function of a seat and a water tank. If you do the interior properly and finish it well at this point you will save yourself a lot of time later. Next comes the plywood bridgedeck cabin sides which define the limits of the foam glass decks.

The decks and cabin top are foam glass with timber inserts in high load areas. Planning is required as you have to know were each stanchion base, turning block, water/fuel tank port, winch base, headsail track bolt position etc is going to be for the timber inserts on the deck and cabin top. Also do you do the majority in vinylester resin and each hole you drill through timber has epoxy resin put in it or do you use epoxy throughout when you glass and drill. Starting to understand why these boats take 1000’s of hours to build.

Next comes the installation of the forward beam and netting. The daggerboards are WRC and glass in epoxy. Several boards have been required as Andrew likes racing and things “happen” when you push hard. Also, Andrew had to rebuild about 2 foot of one bow when in a racing series.

The launch was relatively easy as Andrew lives on Russell Island in a bay off Brisbane Australia. The locals gathered as the tractor dragged the boat down the local roads to the water for the launch.

4.1 years after the start of the build, the cat hit the water. This is how you do a big home build cat for fun and travel. Dedication, a helping family involving mum and dad, the wife and daughter helps enormously. Also having many contacts in the local boating industry and multihull clubs etc also helps. Well done Andrew and his father for a good design and build.

The jpegs again give the idea.

 

Final Fantasia jpegs.

 

Been following the R2AK? There's an Australian Cochrane designed trimaran in the lead. Race to Alaska R2AK 2024 - YB Tracking Race Viewer https://cf.yb.tl/r2ak2024
The boat's name is Dragon and it started life as an 8.5m class. Now sailed and owned by Canadians.

 

Cochrane is a New Zealander lives near Tauranga. Dragon was built in NZ a long time ago (1990's?), before the 8.5class . Underwent several iterations over its life.
Cheers Tb

 

Russell made a comment about a trimaran Malolo which was competing in the Race to Alaska. Simple, we just find some detail as it looked very familiar. So its original name was “Dragon” but it looked the same as the NZ tri “Timberwolf” so this should be easy. Opps.

Chris Cochrane, a NZ initially a home designer, designed a 26 foot very light trimaran that used extended Tornado floats, part of the hull of an inverted Flying 18 foot skiff for the cabin top and the Flying 18 rig and sails and a purpose built main hull. The main hull was a stressed tortured ply (4 mm) hull with glass on the outside and minimal internal framing. Chris made the rudders and foils from outdated helicopter blades. In this form the tri weighed 1,320 lbs and found he had assembled a trimaran that could equal wind speed upwind and go one and a half times wind speed on a reach - plus also having the expected magical trimaran high performance in light airs.

Chris sold Dragon in the early 2000’s to build Timberwolf. Now how did the 26 foot Dragon with Tornado floats end up being the 35 x 25 foot Dragon (Malolo)? The buyer of the 26 foot Dragon raced it twice and said I need to upgrade this tri. The new owner decided the floats were too small so he built new beams and new bigger floats, did another 2 races then decided it was underpowered now so he got a new taller rig and sails. Went racing again and decided Dragon needed curved float foils so he did that modification but then realized they were in the wrong position so removed them to a new position. He went racing again twice and decided the main hull was too draggy so pulled the boat out again and built a whole new bottom for the main hull. When he relaunched Dragon, the newly completed Timberwolf was racing and very competitive. So, both Dragon and Timberwolf owners built larger longer floats to beat the competition.

Dragon’s owner sold Dragon to a Canadian group in 2017 who wanted to win the Race to Alaska. Dragon has entered 2 times previously but has hit logs on course in 2 previous attempts. Now its leading the 2024 R2AK and hopefully will have a clear race to win.

Sorry I cannot give much construction detail here, as of the cabin top of the original 26 foot Dragon seems to be all that remains. Enthusiastic owners can achieve great things, but rebuilding the same boat several times takes a lot of skill, time and dedication. Well done to all involved.

The first jpeg is the original Dragon, next are jpegs of Dragon when sold to Canada, the final jpeg is Malolo racing.

 

Not sure why I thought it came from Australia. I beg forgiveness.
These guys really deserve to win this race and they are well in the lead. I've got my fingers crossed.

 

For those who thought the propellers on there multihulls were just an add on. This guy is doing some good research into propellers for larger RC models with electric motors. The research is on a small cat with an electric drive but the knowledge gained and explained give some very good insights larger vessels. EG some propellers are more suited to a high torque engines but not a low torque engine with the same HP. The propeller number of blades, pitch, diameter, blade thickness and shape etc can have large effects on the power required and the propellers efficiency. Even minor changes can cause an efficiency change.

The work is to partially advertise some 3-D printer technology and software he has done but as you will find in the 12 propeller Youtube he was also confirming the CFD projections of propellers can come very close to the actual performance results. Also, there are some very unusual propeller shapes and types tested with some interesting results compared to “conventional” propellers.

There are 3 Youtubes. The first is the rules of the competition and what is trying to be achieved, the second is the testing of 8 propellers then another testing 12 propellers. Each Youtube takes about 20 to 25 minutes.

The rules and purpose of the competition.



Initial testing of 8 efficient propellers



Testing of the next 12 propellers



The you tubes will tell the majority of the story.

 

Very interesting @oldmulti thanks.

 

MOD 70’s are very fast trimarans that go hunting for records to break. Jason Carroll and crew of his MOD70 trimaran Argo, took on the Honolulu to Yokohama passage record. The 3,370-mile course from Honolulu to Yokohama wasn’t straightforward and required relentless jibing to stay at pace. Argo’s average speed over the course was 18.08 knots. On page 174 of this thread is an article on MOD 70’s.

MOD 70’s were developed as the OMRA 60 class as it became too expensive. The intention of the MOD 70 was to produce cheaper more reliable one design tris that had a 10 year life. In 2006/8 the majority of the design was done by VPLP Design with several builders (CDK Technologies /Multiplast /Décision Suisse) doing the construction of 7 tris from 2009 to 2012. The MOD 70 is 70 x 55 foot with a weight of 14,220 lbs. The 90 foot carbon fibre rotating and canting wing (4 degrees either side) mast carries 3200 square foot upwind and 4,300 square foot with a screecher. Spinnakers optional for the brave. The length to beam of the main hull is 17 to 1. The floats length to beam is 21 to 1. The draft ranges from 5.6 foot to 14.8 foot with the boards down. The engine is a 50 HP diesel.

The construction of MOD 70’s is carbon fibre with all panels with a chance of slamming, have a foam core, while the rest is Nomex cores. EG. the floats outboard sides are in foam, while the inboard side have Nomex cores. Also, the type and density of the foam and Nomex varies according to the location, flexing and slamming loads that may effect that panel. The carbon fibre is high strength and mainly pre preg with epoxy resins. The builds are post cured to ensure strength and consistency.

Back to the record attempt. The sailing master, Brian Thompson, was aboard Lakota (think ex WaterWorld tri) when they beat the Honolulu-to-Yokohama record in 1995. The rest of the crew are star sailors who cross the start line off Diamond Head just after dark, at 8:30 p.m. on August 20.

Argo covered 500 miles off the trip in the first 24 hours in strong easterly winds, which was great for morale. But then the Pacific served up a 1,600-nautical-mile oblong area of high pressure directly on the rhumb line—time to head south, way south, to stay in the trades. The jibe fest began. Sailing on starboard brought us up to the light winds on the southern edge of the high, and jibing to the south brought us into more wind but yielded very little VMG. We jibed endlessly and on the slightest shifts, anxious to spend as little time sailing to the south as possible. The jibing and our southern routing would add more than 1,200 miles to the trip, which didn’t necessarily help with morale.

The living conditions were harsh on board in the unrelenting heat. Down below was an oven during the day, easily exceeding 100 degrees F, making sleep impossible. The crew withered away with little appetite and pined for the nights, which were just cool enough to sleep and be comfortable on deck.

The idyllic conditions ended followed by a robust low-pressure system toward the end of the trip. It became more of a mixed blessing as the low deepened and showed signs of rotation. Eventually, it developed into Typhoon Damrey, with sustained winds of 75 knots and gusts to 95. Very warm water made for rapid development and intensification. The crew had a very unpleasant 24 hours, with winds up to 40 knots. The sea state was disorganized, with the storm waves on the beam and the prevailing swell coming from behind. We were still sailing downwind and trying hard to slow down. We kept in reasonable control most of the time. The sea state was the biggest issue with storm waves and swell would merge and then break; at the bottom of many of these, the boat would almost completely disappear beneath us. A unique head space was required to helm the boat in these conditions. An hourlong stint at the helm seemed like an eternity. The MODs are famously tough boats; ours passed this stern test with flying colours. The sailors had a more challenging time; the stress and physicality of the sailing drained relatively low energy reserves to near zero.

For example, the wailing of Argo’s T-foil rudders cuts right through crew earplugs, and you become familiar with how the underside of the deck feels as the boat falls off wave after wave. Suddenly, it’s quiet as the central hull lifts entirely out of the water. I know what’s next—a violent deceleration as the boat touches down and noses into the wave in front. The resting crew do a reflexive deep knee bend as the boat stops, and your body keeps going. Without a word, the off watch piles out and heads on deck. It’s clearly time for the second reef. It’s a battle scene on deck as off-axis waves merge and explode around us; the rain stings like needles. OK, Reef 2 in, staysail furled; let’s hope that is the worst of it.

The last challenge was negotiating the Kuroshiro Current, similar to the Gulf Stream. Approached the coast, the shoaling water produced spectacularly sized waves around 6 meters high. These were benign because they were well-spaced, but being in the trough gave us one last sensation of the indifferent power of the ocean. A smudge on the horizon soon revealed itself to be Mount Fuji, with the coast following. Up Yokohama Bay the crew stopped the clock at 7 days, 18 hours, 25 minutes. This shaved six days off the 13 day benchmark.

The jpegs give the idea.

 

Wonder if he has done, or plans to do anything on dual counter-rotating props?
older posting of mine....

 

Amphfoil marries Air Propellers and Hydrofoils together with ground effects to produce a ground (or maybe a sea) effects “catamaran” that claims to require up to 75% less energy to achieve a given speed range.

Amphfoil is an idea of longtime builder of quality cruising sailboats Shannon Boat Company of Bristol, Rhode Island, announced the rollout of the Amphfoil Offshore Foil Boat, a foil-borne multihull available in a range of shapes and sizes, from 28‘ to 160‘ (8.5m to 18m). The press release says: “The Amphfoil introduces tilting air propellers for dual-purpose propulsion and lift, complemented by custom-designed quad hydrofoils for enhanced maneuverability and comfort, thus combining catamaran stability, surface effect and hydrofoil lift, and electric tilting air propellers that are tasked with producing most of the lift and all propulsive power to create a totally new type of efficient offshore foil boat [that] eliminates the common sea travel nuisances like bouncing, fatigue, and seasickness.”

The press release also says: “Speeds of 70 mph/60.8 kts/112.6 kmh and a range of 350 nm (648 km) for a boat powered by a hybrid-electric drivetrain. The company claims that this technology overcomes shortfalls of traditional hydrofoils, such as inadequate lift in waves and limited adaptability, and “represents a paradigm shift in maritime travel, seamlessly integrating hydrodynamic and aerodynamic technologies to redefine the hydrofoil experience.” The patented design “enhances maneuverability without complex electronics.”

Shannon Boats have patents on the technology and will build a 16‘ (5m) prototype for bollard testing and gathering dragline information, and data for energy requirements. Next will come a 28 foot [8.5m] Amphfoil prototype, which is an eight-passenger plus two-crew boat. There is no size limitation on our patents, but everything depends on the hybrid-electric propulsion systems. Shannon Boats hope is hydrogen-fuel-cell technology will be a game changer someday in the future for all marine craft.”

Explaining the hydrofoils (which he calls “Seafoils”), he said they account for only 30% of total lift, with surface effect and the tilting air propellers of the propulsion system providing the rest. On the 28‘ model, two small, submerged propellers on [electric] 7.5-kW pods mounted on the rear foils will assist docking and in-port maneuvering. Below the first jpeg is a rendering of Shannon Boat Company’s Amphfoil 28′ (8.5m), a foil-borne commuter that uses a 400-hp (295-kw) hybrid-electric propulsion system with air propellers.

The other jpegs give an idea of the possible options for Amphfoils.

 

The strength of modern tested ropes is impressive but the stated strength of a rope can be degraded significantly if you put a knot or splice in the rope. The amount of strength loss surprised me and is very dependant on the type of knot or splice. The testing was done by Marlow Ropes.

If you’re taking lines ashore while anchored, extending a towline or running out a kedge, you’ll probably need to bend at least two lines together. But which knot is strongest and most reliable? Is a reef knot stronger than a sheet bend? Marlow Ropes at its Hailsham UK tested ropes and knots on its 30 ton testing equipment.

A knot is the weakest point of any line, but exactly how much weaker? We tied overhand knots in the Dyneema and Marlowbraid to see how it affected their known strength, and found that the break load of both lines was reduced by as much as 65 per cent of their ISO2307 specifications (proof-loaded up to 50 per cent of their theoretical break load before testing).

12mm Marlowbraid, the cruising yachtsman’s favourite; 10mm Dyneema the future of knot-making; and 14mm three-strand was used to find out the best solution for mooring. Using Marlow Ropes’ 30-tonne strain facility, 7 loops and 5 bend knots were tested to destruction to find out which knots could bear the most load for each of our three cordage types. First a simple overhand knot in Marlowbraid and Dyneema to see what difference a knot makes to the break load of any line. Then loop knots were tested. For three-strand we looked at a round turn and two half-hitches, a bowline and a spliced loop, all popular mooring options. For the Dyneema and Marlowbraid polyester we tested a bowline, splice, figure-of-eight, anchor bend, double fisherman’s loop and a splicing nut. (some jpegs will show the knots but reference a knot thread to understand them.

This will be a 2 part entry with some knots and results being shown tomorrow.

Round turn and two half-hitches (starting 1 in jpegs)

The RYA says it is ‘one of the safest, secure and reliable knots you will ever use’, a general purpose knot used for fastening a line to a fixed loop, hoop, bar or bollard. Used especially for moorings. The 14mm three-strand stretched but held well, right up to 2.6 tonnes when two of the three strands parted at the knot. The load represented 67 per cent of the line’s specified break load.

Bowline (starting 2 in jpegs)

It’s the go-to knot for bending sheets to sails and attaching lines to harnesses, but it can’t be tied or untied under load. It’s not one for bearing serious loads, though. The Dyneema line’s jacket broke just behind the knot and the core pulled through at 1.9 tonnes, a mere 35% of its rated break load. The Marlowbraid snapped in the same place, at 2.1 tonnes, 47% of rated break load, and the three-strand failed at 2.4 tonnes, or 62%.

Eye Splice (starting 3 in jpegs)

Many of us can splice three-strand, but splicing an eye into Marlowbraid cores is a lot harder. But it’s a handy skill to have – our test shows that spliced loops, with good long splices, are the strongest option. The Dyneema splice withstood 4.4 tonnes, 81 per cent of rated break load, before the core snapped at the base of the splice. The Marlowbraid snapped, again at the base of the splice, under 3.7 tonnes or 82 per cent of its break load. There was a much shorter splice on the three-strand but it also endured 3.7 tonnes, 95 per cent of its rated break load, before two strands snapped at the eye.

Reef Knot (starting 4 in jpegs)

The reef knot is useful for joining two lines together but it’s not secure. Pull one bitter end perpendicular to the line and the knot capsizes. Nor is it a particularly strong knot. The Dyneema jacket snapped at just 0.9 tonnes, 17% of its rated break load, and the Marlowbraid managed only 1.2 tonnes, 27%, before the knot pulled through. It’s useful as a binding knot, if you ensure both bitter ends are on the same side of the knot, but as a bend it’s hopeless.

Sheet Bend (starting 5 in jpegs)

This is more useful than the reef knot, particularly for tying two lines of differing diameters. Also known as the weaver’s knot, as it’s used to make fishing nets, its main drawback is that it can fall apart if there is no tension in the standing parts. Make sure both working ends emerge from the same side of the knot, otherwise you have a ‘left-handed’ knot, which is less secure.
Again, Dyneema seems to buck convention as the knot just slipped through. The pull was stopped before the two lines slipped free, but there was only 0.9 tonnes of strain on the gauge, just 17% of its rated strength and the same as the reef knot. Marlowbraid fared much better, with 1.8 tonnes, 40% of its strength, before it exploded.

Tomorrow other knots that were tested will be discussed. But the general trend is most knots will cause a line or knot failure at below 50% of the “strength” of Marlowbraid and Dyneema. A splice is the most effective way of maintaining line strength. Also, 3 strand rope with a knot can handle higher loads (as a % of ultimate strain) than Marlowbraid and Dyneema. But 3 strand is not as easy to handle or as light as Dyneema.

Real message here, don’t buy a Dyneema line the same strength as a rigging wire then tie a knot in the end as you use it as a substitute for a shroud. An expensive bang may follow.

 

Part 2 of the strength of ropes when knots are introduced. He previous part was about commonly known knots, this part will be about the fisherman’s knot, double fisherman’s knot, double fisherman’s loop and a summary.

The Fisherman’s knot (6 in jpegs) is popular with anglers and it’s called a ‘knot’ to distinguish it from the fisherman’s bend (anchor bend). Simply, it is two lines, overhand-knotted to each other, and used for bending together two similar lines. The Dyneema held briefly until the jacket once again snapped and the core pulled through. The jacket failed with 1.1 tonnes of strain, just under 20% of its strength, while the Marlowbraid snapped completely at the pinch point where the standing end meets the knots. There was a creditable 1.8 tonnes on the gauge, 41% of its theoretical strength.

Double fisherman’s knot (7 in jpegs) serves a similar purpose to the fisherman’s knot but the working ends are tied over the opposing standing parts in a double overhand knot. This makes it more suitable for slippier line, like new cordage with a shiny jacket or slime-covered lines.

The double fisherman’s knot proved to be the best bend for Dyneema, withstanding 1.6 tonnes of load or 30% of its rated break load, before the jacket broke and the core pulled through. It was also the strongest bend for the Marlowbraid, withstanding 2.6 tonnes, 58%, before failing in the same way as the single fisherman’s knot.

Double fisherman’s loop (8 in jpegs) is strong and easy to tie, but once it’s under heavy load, you’ll have no chance of sliding it back again or untying it. You’ll need to cut it off. The Dyneema jacket failed again and the slippery core pulled through, but it withstood 2.1 tonnes of load. That’s only 39% of rated break load, but it’s the second best performer after the splice. Incredibly, for the Marlowbraid, this loop equalled the load borne by the splice, 3.7 tonnes and 82% of its break load.

Conclusions

For all three types of cordage, the eye splice was the strongest loop, provided the splice is very long and tapered, because splices tend to fail at its end. A spliced loop is fine for mooring lines and it’s the best solution for fastening shackles to halyards, provided the splice is served with whipping twine.

Of the other loops, the double fisherman’s loop is the strongest. If you can’t splice Marlowbraid or find a rigger to do it for you, that’s the knot to choose. The bowline, the ‘king of knots’, fared marginally worse than the figure of eight, suggesting a shackle spliced onto your jib sheets and taped round with Velcro for protection is the best option.

Of the bends, the double fisherman’s knot was the pick of the bunch for both Dyneema and Marlowbraid, with the double sheet bend a fairly distant second. The single version of both performed better than the reef knot.

In general, it’s clear that a knot in any load-bearing line weakens it significantly so anything but a long line with a splice at the end is seriously compromising the line’s strength.

 

This is an update on page 248 about the Dual Flyer 400 cruising catamaran was partially designed by design by Simonis Voogd Yacht Design and upgraded by the builder Greg Davis from Western Cape, South Africa. The tested hull shape remains as the original design by Simonis Voogd Yacht Design and Greg Davis added the upper chine and the two coach roof options. The Dual Flyer 400 featured here has a fixed main cabin top for serious cruising.

The Dual Flyer 400 is 39.5 x 21 foot with a weight of 9,260 lbs. The 54 foot aluminium mast carries 656 square foot mainsail, a 387 square foot jib and a 968 square foot screecher on a roller furling drum. Spinnakers are optional. The draft ranges from 2.6 foot to 6.7 foot with curved semi foiling asymmetric dagger boards or there can be optional fixed keels. The engines are 2 x 19 HP inboard Yanmar Diesels or 2 x 4 stroke outboards.

This versions accommodation is interesting, there is a double berth cabin and associated toilet in each hull with a single berth in the crossbeam forward in the starboard hull.

On the bridge deck there is a U shaped saloon unit and table. There is a large galley with fridge, freezer, Induction stove and sink. Forward access to the foredeck and drop down window and 2 doors opening onto the aft cockpit with helming on the starboard side with instrument panel and engine controls.

The construction uses the latest technologies and build methods such as resin-infused core construction with epoxy resin and carbon reinforced bulkheads and cross beams. Hulls are epoxy infused with 20mm PVC foam core. Aft, forward cross beams and major bulk heads are carbon fibre epoxy sandwich. The boat is light and strong built according to CE Certified Standards.

Performance is an interesting question. The builder claims the Dual Flyer 400 can top 25 knots in good conditions. It is possible with the sail area and the low displacement but the choice of foils would affect the peak speeds.

The jpegs give the idea.