Multihull Structure Thoughts

Michael Schacht whose design featured yesterday also did a follow up design called “Camel of the Sea”. Beside Michael being an excellent Graphic Artist and he has an innate understanding of proa designs, he is the major driver of the Proafile.com so he also does some very interesting conceptual design work. The “Camel of the Sea” is a 54 x 29 foot with a displacement range between 11,000 and 35,000 lbs depending on the cargo load being carried. Sail area is 886 square foot split between two standing lugs. The masts are 30.5 foot above deck and free-standing. The lugs have the advantage of balancing the sail area forward of the mast, reducing sheet loads. This is a benefit for a vessel that must shunt to change direction, and reverse the rig for every tack.

The waterline beam is 4 foot waterline beam on the main hull provides a length to beam 13.5 to 1 ratio. However, the main hull flares above the waterline out to 9 foot. Draft is 1.25 light to 3.25 foot fully laden. The rudders are quadrant-style that retract into cases like centerboards. Only the aft rudder is employed, which also shifts the CLR aft to balance out the aft position of the schooner rig’s CE. The pivoting leeboard on the ama is actually to windward of the hull, so call it what you will. The board is adjustable to fine-tune the CLR as well.

The main space between the beams is in this concept devoted to a cargo space but the overall design could be a pure cruiser with a large amount of space (24 x 9 foot) available between the beams for accommodation. Additional storage space would also be available in the ends.

Michaels words from here “All hull surfaces are “developable”, meaning the boat can be built of flat sheet material like plywood, aluminum or KISS®-style foam composite panels. Materials will be specified as necessary by local availability. Taking a page from Phil Bolger’s playbook, sections are as square as possible: vertical hull sides with no flare, a dead flat sheer and chine, and a flat bottom. The hull is a 5-panel design to provide a smoother ride and reduced wetted surface - compared to a true sharpie-style flat bottom.

The ama has a sharp V-shape bottom to provide a well-modulated ride at varying angles of heel, immersion and wave states. The ama deck is also V’d to shed water when immersed. One design aspect borrowed from ships and jets is a constant mid-section between the beams. This permits the build to be easily modified to suit. The mid-section may be lengthened or shortened depending upon requirements with no changes required to beams, masts, foils, etc. The constant section also speeds up construction of internal furniture or fittings.

Even though The Camel is a working vessel, when lightly laden the boat would still be capable of showing the speed that made proas famous. This will make for fast return passages, as well as spirited racing.”

This would be a simple design that could be a fun boat. It would be a large building task but you would end up with a 54 foot waterline for a 40 foot cat build type effort. Michael has not done a full design or build plans for this design. As I said Michael is a Graphic Artist.

 

The thing about Phil Bolger's playbook is that they are buildable and built designs with the construction and weights worked out. Posters have their place on a wall but designing involves more than a picture usually. These boats would be more interesting if there was evidence they could float on their lines, balance with the drawn rigs and rudders, tack, shunt.... actually sail... Perhaps borrowing Phil's book instead of a page?

 

François Perus, multihull designer from Pérus Yacht Design and the Yacht Design Collective has designed several trimarans for Corsair. His latest is the Corsair 880. The Corsair 880 is 28.7 x 22.25 foot and can be folded to 8.2 foot for trailering. The weight is 3659 lbs. The sail area on the standard 40 foot carbon mast is 554 square foot and on the sports version, the 44 foot carbon mast carries 677 square foot. The “Sport” version has the taller carbon rig, laminate sails with high-aspect square-top main and sprit. The length to beam on the main hull at the waterline is 9.5 to 1. The float length to beam is 15 to 1 to 13 to 1 depending on how hard you are sailing. The draft is 5.25 foot with the daggerboard down and 1.25 foot with the board up. The rudder is a transom hung kickup.

The float and stern shapes are of real interest and continues the trend toward very full ends with almost hard chines aft on floats and main hull aft. The advantage of the wide sterns is the ability to carry more weight aft (crew etc) and reduce pitching whilst helping to promote “planning”. The reverse rake bows may be visual trend or required to add buoyancy forward, but I suspect vertical bows would achieve the same outcome. The floats are full buoyancy but have a minimum cross section shape which helps both in trailering when folded and allowing the widest possible main hull waterline for internal accommodation. This float trend has developed over the last decade as the older style of floats had less buoyancy, were taller and or wider and were shorter. Result was a slower float shape less able to minimise pitching and tripping either fore or aft when driven hard or in a big seaway.

There’s standing headroom in the main hull with a well-configured galley, seating space that can covert to berths, a double berth forward and an under cockpit double berth which is spacious for this type of tri. You can sleep up to 5 inside. The Corsair is a legitimate pocket cruiser and in the standard version there is options from comfy seat backs in the cockpit to a full marine head, a generator and air conditioning.

The hull, deck and amas are also all vacuum infused with E-glass, a PVC closed-cell core and carbon-fiber reinforcements for added strength where it makes sense.

The are interesting details in the beam design. The beams of the 880 are under extremely high loads. Often under loaded conditions on the beams will be 3 to 5 times the total boat weight. On the 880 the calculated max load on the beams is around 20,000 lbs. During the early design stages of the 880, composite strut attachments were investigated as it was Corsairs initial intend to go in this direction. Extensive weight analysis identified little to no weight gains by using composite attachments. Also the methods typically used for a composite attachment point actually hindered the folding geometry. Finally, given the results of our design testing and the extensive successful history of aluminum bracket attachments Corsair choose to use aluminium brackets and folding components.

The attachment of the beams to floats method was also reviewed. Corsair had used beams bolted to float decks and beams permentaly attached to float bulkheads. Both had there good and bad points. The solution on the 880 incorporates a composite socket built into the float to accommodate each of the beams. The beams will be bolted in place however once underway the composite socket will actually do all the work of transferring the float loads onto the beams.

The beams themselves are designed with a centrally infused stringer. Using a technology found in the rear targa bar of Seawind Catamarans 1190 model, this stringer is infused in one hit as part of the infusion process of the upper and lower shells. For the male moulds Corsair followed the traditional process of framing and planking which was the fastest way to produce the general shape however in critical areas, such as the beam and strut landings, large scale 3D printed components have been produced and grafted into the hull male mould surface producing pinpoint accuracy for this critical areas of the 880 design.

An interesting and very successful design that literally took thousands of hours to design and bring to manufacture. It performance from all reports is very good EG. A sailing magazine report “The helm was easy, almost neutral, even as the speedo touched 16.8 knots on a reach with the screecher up. Better still, this is the kind of boat that “talks” to you, giving you plenty of warning before it starts playing any kinds of dirty tricks. Every now and then as the true wind speed drifted up to 15 knots or more.” This design can sail at or exceed wind speed when conditions are good.

 

Michael Schact is a good guy, But this is a silly design. Cargo does not need to travel fast, it is cargo. Passengers are willing to pay a premium for speed, cargo occasionally yes, generally no.

The hull in the water has a high length it waterline beam ratio, possibly approaching 20 to 1.

This gives a fast hull, but has less volume, thus less carrying capacity. The cargo of 12 tonnes or so, is ridiculously low for a large vessel of this high capital cost.

There are some very substantial cargo carrying multihulls in Mozambique,, that can easily carry 5 tonnes, at a capital cost of 1 or 2 percent of this craft, thus they operate without a subsidy. An example of saving costs is simply to use a trunk from a small tree, remove the bark, let it dry a little, and then use ropes from the top to keep the mast in place

Another example of multihulls used to carry cargo is the Sailau of south east Papua New Guinea. they go up to 12 meters in length, travel up to 300km and can carry a couple tonnes easily. from memory they comes in many sizes and the larger ones can be had for around $5000 USD,,, possibly a little more. Hulls of a Sailau last 20 years, they are reasonably seaworthy, not as safe as the cargo proa. They have the advantage of being built with traditional materials and can be beached.

Maybe old multi can do a post on the Sailau of PNG, he would be able to point out the plusses and minuses far better than me

capital cost for a boat like this is getting close to a million,,, a lot of money to carry 12 metric tonnes or so

 

On Wayne Barrett’s “trimarankits” web site is an interesting 10 metre catamaran drawn in 2020. I do not know if the design was finalised but there were quite a few jpegs and some information available. You will have to look at recent news items around 2020 on the site to find any detail.

The design is a sailing cruising catamaran of 32,5 x 21.8 foot beam. The displacement is 13,300 lbs. The 49 foot mast above deck carries a 540 square foot mainsail and a 210 square foot self tacking jib. Other sail and mast options would be possible. The hull length to beam is 11.5 to 1. The draft over fixe low aspect ratio keels is 4 foot. The underwing clearance is 2 foot. The power is two 10 HP outboards located under the cockpit seats.

The accommodation has full headroom through out. There is 1 double bunk 2100 x 1250 mm in each hull with shower & separate head. In the main saloon is a 6 place dining table, separate navigation station and cooking and refrigeration as per standard configuration. There is ample storage capacity for fuel and water. This is a very practical cruising layout for a couple for long term crising.

The build is not specified beyond a lot of foam glass flat panel construction. If this design follows the build options of his trimaran designs it will be a relatively fast simple build. Also I am sure a kit version could be done for a builder.

The umbers indicate the cat will be a good performer under sail. Call it a fast cruiser more than a racer. 7 to 10 knot averages sort of cat when st up for cruising.

The jpegs tell more of the story. I hope the design was finalised as this is the type of cat many are looking for with full headroom and reasonable performance.

 

Quite a nice video from this year's R2AK:
I don't always agree with the approach of the organizers, but they came up with a truly great race. Not so great for multihulls this year, but good that it happened after two years of Covid.
I like that no-one sprays champagne all over themselves at the finish and proud that my town came up something so out-of-the-ordinary.

 

The Donzi 44 power catamaran is fast, seriously ridiculously fast. It has a minimum cruise speed of 60 knots and with appropriate power will travel at 100 knots (115 miles per hour) at top speed. Why am I doing this item. The cat has an interesting build material. The Donzi 44 is 44 x 12 foot with a weight of 8,300 lbs. The draft is 1.5 foot. The power can be four 250 HP outboards but for peak performance you should have quad Mercury 400R 400 HP supercharged “race breed” outboards. With 1600 HP on the back Donzi is in the process of “tuning” the cat to top 110 knots. You could own a good Farrier trimaran for the cost of just 1 of these engines. The 2020 price for the cat was over $1 million US. Fuel economy is measured by $1000 bills.

The cat V shaped hulls are stepped aft and the centre of gravity is about 80% aft. The technology, design requirements and intuitive skills required to develop a boat like this owes a lot to offshore racing catamaran.

The cockpit has 6 bucket seats and a large walking space behind with rear steps leading to the water between the 2 pairs of engines. Not specified but there is probably a portable toilet space but not much more. This boat is about speed. The helmsperson better be very aware of what they are doing as this cat speed will get you in trouble very quickly. Even wakes of other boats could cause problems at speed.

The Donzi 44 cat is constructed with advanced composites including carbon, infused epoxy resin and a new foam coring that forms a honeycomb pattern. According to Craig Wilson of Wilson Custom Composites of Fort Pierce, Florida the core is 10 percent stronger and 40 percent lighter than the cores most manufacturers are currently using. Wilson was responsible for the development and build of the Donzi 44. The honeycomb foam filled core is shown in the last 2 jpegs.

The jpegs give the idea. Good luck to those who can afford to pay the fuel bills and live in a relatively calm world with minimum ripples to use the Donzi 44. It would be fun for about 30 minutes for me.

 

Perttu Korhonen of Kaamos Boats is an amateur design who is very creative and does good quality plans. He focusses on smaller boats but each is unique. The vessel we will focus on is the “Toucanoe” a canoe that can be converted to a trimaran. The 2 person canoe is 15.7 x 2.5 foot and with the trimaran conversion the “tri” version is 15.7 x 8.5 foot and the floats can be folded to 6.1 foot. The tri’s maximum displacement is 440 lbs including crew. The sail area is either a 47 or 82 square foot lug sail from a Michael Storer Oz Racer as well as Oz Racer foils. The hull draft is 100 mm. The rudder is a kickup on the stern.

The canoe version is designed to carry 2 people but when converted to a trimaran, that version is best sailed as a single handed. The trimaran is not designed for big open waters. Maximum speed reached is 7.4 knots in quite strong wind. There was some water inside due to wave action, but it was still comfortable to sail.

Canoe takes three sheets of 4mm plywood. Trimaran needs four sheets of 4mm plywood and one sheet of 12mm plywood. The hulls are mainly 4 mm plywood with stich and glue seams and timber gunnels. The 12 mm plywood is used in some bulkheads and cross beams. Plans come in both A4 and letter formats. Be sure to select the right file to match your paper size. Please look at Free Kayak Plans https://duckworks.com/free-kayak-plans/ or free http://www.kaamosboats.com/free.htm to be able to download a free set of plans for a performance kayak to give an idea of Perttu plans and style of building he suggests. The Toucanoe plans cost $40 US.

The jpegs give the idea with some sailing shots.

 

El Toro trimaran is a fast racer trimaran from Queensland Australia. The design was done by co-owner and boat builder, Aaron Carle and Ben Kelly a sail maker. These guys along with 2 other co-owners spent 6 years of part time work to design and build the tri. El Toro is 29.5 x 24 foot and weighs 2700 lbs with a 47 foot carbon fibre wing mast with a 280 mm long section and a C-Tech carbon boom and bowspirit. The mainsail is 419 square foot, the genoa is 231 square foot, screecher of 408 square foot and a spinnaker of 903 square foot. The sails are North Sails 3Di Raw will be used for her working sails, and then NPL panelled materials, along with Helix luffs, will give her a formidable, furling downhill selection to play with. The OMR rating is 1.017 (anything over 1 is very fast). The daggerboards are in the floats with rudders on the float sterns.

El Toro is completely demountable, with the structural beams running through channels in the main hull and plugging into the floats. Her mast is located at exactly halfway along, and sits on the main beam, with the traveller then mounted on the aft beam. The “accommodation” space can handle a few bunks and has some storage space. This tri is about racing not cruising.

El Toro is primarily e-glass and epoxy, with carbon reinforcing where needed, which has allowed them to keep the cost down. The OMR rule is not kind to super lightweight boats, so she is solid (by multi standards) to rate well, which means she be competitive now, and for some time to come. Her mast, boom, foils and beams are all 100% carbon epoxy.

El Toro has performed very well in local racing and was being considered as a semi production boat. This is a serious fun boat. The jpegs give an idea.

 

This is about a cross-harbour ferry in Wellington NZ. The ferry is all electric power and is 62 foot long. Other details unknown. The ferry can transport 135 passengers, while the company’s current ferries can only carry 99. The ferry companies existing two diesel ferries use around 250,000 litres of diesel between them each year. As a result the ferry company owner wanted a more environmentally friendly solution that would be financially viable.

SSC Marine was chosen to design the vessel who then worked with the Wellington Electric Boat Building Company – headed by boat builder, Fraser Foote, manufactured the vessel in its premises in Hutt City. Construction is all-carbon, epoxy, foam construction engineered by Gurit in Auckland, assembled from CNC-cut infused panels, with only the lower hulls being moulded with a materials pack from Gurit Asia Pacific. The flat panel topsides construction minimised tooling costs and assembly time. The structural weight is reduced to enable the electrical propulsion system to be viable. The build technology when combined with the highly efficient canoe-stern hull form reduces the resistance and so allows the weight (and therefore cost) of batteries to be minimised. The life-time costs of the vessel’s energy consumption and maintenance costs are reduced to the extent that the higher initial construction costs are paid back well within the operational contract time-frame, and a higher profit per passenger per trip is returned.

So what was the cost for the design, build and initial introduction of the first electric cat ferry? Try $8.5 million compared to compared to $3m for a new diesel-powered aluminium ferry. But the increased electric cat investment will pay for itself after seven to eight years of operation.

So what about the electric cats power, performance and recharging? Compared to the conventional fuel ferries, with a maximum speed of 14 knots (16 mph/26 kph), the electric ferry on the water does 22.5 knots (26 mph/41.6 kph), thanks to its 350 kW motors. The ferry “cruise” at 20 knots. “Ika Rere’s” (the electric ferries name) battery is charged up at a station on Wellington’s Wharf that resembles an oversized diesel bowser. The charger supplies 325 kilowatt hours of charging capacity, which can fully recharge the battery in 1.5 hours. Upgrading it to 1.25 megawatts will allow Ika Rere to be fast-charged in just 15 minutes – about how long it takes to turn around the ferry between sailings.

When compared to a diesel-powered alternative, Ika Rere is expected to save about 640 tons of CO2 per year. The result is reduced operational costs – up to 80% increase in passenger miles per kilowatt. Total cost of ownership reduced by up to 35%. Outstanding on-water performance in terms of kW/tonne of displacement.

The jpegs are of the build and on water performance. Most ferry runs done by Ika Rere are 25 minutes long.

 

That really is a very impressive ferry!
More info about her on her Builder's webpage -
WEBBCo https://www.electricboatbuilders.co.nz/

And on her Operators website (East by West Ferries) -
Electric Ferry | East by West Ferries https://eastbywest.co.nz/electric-ferry

And on the website of the folk who built the propulsion machinery -
Electric Ferry partnership | Meridian Energy https://www.meridianenergy.co.nz/community-support/electric-ferry

 

The Aventura 44 cat has been around for 10 years has recently been upgraded to the Aventura 44 S. The S makes the difference. This new cat is designed by Samer Lasta of Lasta Studio and takes the lines the younger Aventura 37. The Aventura 44 S is 43.3 x 24.5 foot with a weight of 21,000 lbs. The aluminium fixed mast carries a 740 square foot mainsail and a gennaker of 860 square foot. Upwind sail area is 1,238 square foot. The draft over the fixed low aspect ratio keels is 4.3 foot. The motive power is two 38 HP inboards.

The real difference between the 44 and the 44 S is the accommodation and the deck layout. The 44 in standard format had either 3 or 4 cabins and a simple navigation control position in a raised position in the front corner of the cockpit. The 44 S can have up to 6 cabins and the helming position is separated from the rope control position (both on a raised floor position) with a seating cockpit on the cockpit roof beside. The jpegs give more detail. The accommodation has 4 double berth cabins and 2 single berth cabins in the hulls with 4 toilets. The main saloon and cockpit have 2 seating areas, galley and navigation/entertainment area. There is a large glass door between the main saloon and lower cockpit.

Aventura is Tunisian built and is an economy priced cat. Result is a polyester foam glass structure with minimum of exotic materials. This is not implying poor quality, just using minimum cost materials effectively used to produce a relatively light effective structure.

The performance of the new model is unknown but if it follows the performance of the 44 it will sail about half of wind speed with peaks of 16 to 18 knots.

The jpegs give the idea. The first jpeg is the older 44 model after that is the drawings of the 44 S.

 

Hey Russell,
Great video, in Australia ringing the bell means your buying your competitors a drink, Same ?
Some scary looking tides and currents going on there, and those log rafts, they just strike fear. Warning Will Robinson !

 

Mark Gumprecht had a 22 foot cruising cat that he needed a dingy for to carry his wife, dog, supplies and himself from ship to shore--and back again. He disliked his monohull dinghy so he designed and built the Lil Nip instead. The Lil Nip (cat skiff) is a 7.9 x 3.9 foot dingy (there is a 10 foot version in a second PDF). This is a light to slightly heavier dinghy depending on the type of plywood used in its construction. It can be rowed or powered by a small outboard.

L’il Nip is a small dory-hulled catamaran skiff built out of sheet plywood, and is a very easy boat to build. It takes 3 sheets of 1/4” mahogany plywood and 1/2 sheet of 1/8" mahogany plywood to build. Many grades of plywood will work. Okume plywood would be the best, but is also the most expensive. Luan mahogany door skin available at many building supplies will work just fine if epoxy coated and painted.

The jpegs show the 7.9 foot version. The first PDF is 13 pages of full plans for the 7.9 foot version, the second PDF is 1 page of the 10 foot version.

 

One of the designers for Pure Design & Engineering NZ decided after doing work on AC boats to do his own thing. So he decided to start his own business to produce a relatively affordable, more stable and safer alternative to the ‘tinny’ (small aluminium boat). He designed and ultimately produced the Fatcat in several sizes. We will focus on the Fatcat 4500. The 4500 is 15 x 6.5 foot. The bare cat weighs 630 lbs an weighs under 1100 lbs with outboard fuel etc. The draft of the hull is 200 mm. The 4500 when fitted with a the Parsun 60hp 4 Stroke, will peak at 26 knots while the 40hp 2 Stroke pushed the 4500 along at 22 knots.

The FatCat has asymmetric hulls with a 15 degree deadrise and a central ‘sponson’ (stability pod) under the wing deck that gets lower, wider and flatter towards the transom. The pod helps smooth the water flow over the propeller to avoid cavitation, which can be an issue for catamarans with only one engine. The pod is also part of the single hull mould and adds extra rigidity overall.

The 4500 is built by Rotomoulded Polyethylene in special moulds that are rotated to spread a predetermined amount of polyethylene over the surface of the moulds to form a boat shape. This is a very fast effective way to produce a boat shell but it requires excellent production design tools, computer modelling to place the right amount of material in the right position etc. Translation expensive to setup, low costs to produce each unit. A lot of canoe’s, Hobie tri’s etc are produced this way.

The advantage of Rotomoulding is you can have hulls with complex shapes and compound curves. Polyethylene is extremely impact-resistant and Polyethylene is quiet in the water, resilient to scratches, low maintenance, easy to repair & recyclable.

The disadvantage of Rotomoulding is moulding tolerances are not as exact as they are with fiberglass, so items like hatches may not fit as perfectly as they would on a fiberglass boat. Rotomoulded PE boats are not as "fair" as fibreglass boats. Meaning when you look along the panels of a PE boat, they will be more wavey. This waviness occurs in the cooling process during manufacture.

There is also limitations to the size of full catamaran type Rotomoulding. Cats of about 17 to 18 foot are the maximum length using existing technology. HDPE (high density polyethylene) panel boats have been built up to 50 foot but they are piece by piece builds plastic welding panels together.

The Fatcat is an interesting cat that is well priced and according to tests handles well, is very stable and can be towed behind an average family car. The cat can also be knocked around with minimum effect. Good design. The jpegs give the idea.