Multihull Structure Thoughts

I thought the ECO 7.5 sailing cat was a variation of the ECO 75 power cat and did a little research. Although the structure is similar there are variations which make the design different. The sailing cat has similar looks to the power cat, the ECO 7.5 sailing cat is wider with slightly different hull shapes although it has similar displacement.

The ECO 7.5 sail is 24.6 x 14.75 foot with a weight of 1,680 lbs and a displacement of 3,100 lbs. The aluminum or carbon mast is 26.3 foot high and carries a 189 square foot mainsail, a 69 square foot jib and a 120 square foot genoa in a fractional sloop rig. The second rig option is a slightly smaller wishbone gaff rig. The hull length to beam ratio is 9 to 1 as the hulls have a slightly different hull shape to the ECO 75 power cat. The draft is 1 foot over the hull and 4.25 foot over the daggerboard in the port hull. The underwing clearance is 1.5 foot. The power is either two 5 HP outboards or two 1.5 KW electric drive outboards.

The internal layout has a single berth aft in each hull, a galley in the starboard hull and a toilet forward in the port hull. The main saloon has a dinette convertible to a double berth. There is standing headroom in the hulls and 4.5 foot in the main saloon. There are 2 doors from the cockpit into the saloon on either side of the cockpit to allow easier entrance to the hulls. The cockpit is large and comfortable.

The structure again is plywood, timber, epoxy and a layer of glass externally. The hulls are 6 mm ply on the sides and 2 layers of 6 mm ply on the hull bottoms with biaxial 340 gr/m2 and one layer 200 gr/m2 glass fabric. The underwing is 12 mm plywood with the forward part of the wing 3 layers of 4 mm plywood. The cabin roof may be 2 layers of 4 mm plywood. Beyond that I suggest buy the plans as it maybe similar to the ECO 6 sailing cat but I suspect with a wider beam and more displacement the main cross beam structures will be stronger. The rudders will be ply skins with some timber in the core and carbon fibre strengthening. The jpegs will give an idea but the structure looks similar to the ECO 75 power cat.

Performance is interesting. A chart provided by Bernd say a potential of 19 knots if driven hard in 25 knots of wind but more realistically about 15 knots if sailed in 20 knots of wind. This is a cat capable of 8 to 10 averages on coastal voyages under favorable conditions. This cat was not designed to be an ocean crosser but is capable of sailing offshore.

The jpegs give the idea.

 

The following pacific proa was done as a student design (in design and Naval Architecture) by Victor Laurent in about 2008. This is a very minimalist proa that is of very simple design and construction.

The Proa 10 is 32.8 x 15.7 foot with a weight of 2400 lbs. The sail area is 300 square foot lanteen with 30 foot yards and a 14.5 foot mast that is supported by a spar going out to the crossbeam. Shunting the lanteen spars and sail end to end will be interesting but possible. Length to beam main hull 14 to 1. Float length is 13 foot and has a length to beam of 13 to 1. The float can have 335 lbs of water ballast. The hull draft is 0.7 foot and over the rudder boards 2.85 foot.

The stability of this pacific proa is relatively high with the water ballast. The righting moment is about 11,000 ft/lbs with 300 square foot of sail with a centre of effort of about 12.7 foot. That equals 2.9 lbs/sq ft or about 23.4 knots of wind speed over the sail. (don’t use this number as an absolute, as it assumes a steady wind and does not take account of sea conditions)

The accommodation of this proa is 2 single berths, some storage and little else. The cockpit can fit 2 at best.

The construction is plywood, timber and epoxy mainly with some aluminum tubing. The hull bottoms are 8 mm plywood, frames are 10 mm plywood, hull sides are 3 mm plywood 8 mm airex with an internal glass layer in epoxy. The decks are 6 mm plywood. Cross beams are 80 x 60 mm box with 20 mm walls with aluminum support tubes 50 x 4 mm from mid cross arms to hull sides. There are a lot of wires to help maintain fore and aft rigidity of the float in place.

Performance is unknown but I suggest even with a simple hull shape this will be a 20 knot peak sort of boat. The only area of weakness may be close to the wind but reaching should be very good.

The jpegs give the idea.

 

The NAOS 800 is designed to allow smaller engines than similar-sized boats while still being faster than its competitors. The goal was to create a high-performance, low-maintenance power catamaran with good comfort. The design and production were/is done in Turkey.

The NAOS 800 is 27.5 x 10 foot with a waterline length 22.5 foot, so the actual cat part of the boat is 22.5 x 10 foot. The aft overhang around the engine is a walking space more than a hull extension. The weight of 2,550 lbs and a displacement of 3,990 lbs. The standard power is 2 x 60hp 4 stroke outboards to 2 x 115hp outboards. The maximum speed is 45 knots. The cruise speed is 14 knots with a fuel consumption of 1.5 litres/hour which allows a maximum cruise range of 300 nautical miles. Fuel consumption at maximum speed is 8 litres/hour.

The accommodation has either a single or 2 single berths forward under a raised fore deck or 2 seats in an open forward cockpit. An enclosed shower toilet is next in the port hull. On the bridge deck forward is a galley with 2 dinette/berths available in the covered cockpit with the possibility of side curtains to form an enclosed cockpit area. Aft is an extended bridge deck around the outboard engines. The accommodation is practical for 2 or 3 people to cruise for a week or so. Again, the limitation of this design is the need to stop frequently to pick up fuel, water and food as the payload is limited. EG 600 lbs of people and gear, 440 lbs of water, some food and 330 lbs of fuel already equals the available payload.

The build is by the vacuum infusion process using foam sandwich composite in production. This method helps build a homogenous body without any weak points. Dual body design (outer hull with internal liner) helps improve the structural strength and maintain rigidity.

This is an interesting design. The jpegs give the idea.

 

The following comes from a young Italian designer Christian Grande who teamed up with award-winning Italian actor, Pierfrancesco Favino to conceive this cat. The Picchio (picchio is woodpecker in Italian) The external shell of this power cat was not the important part for the team, the interior was the highlight. I will not use the description of the interior as I get bored with very artistic descriptions but basically this cat can motor well but the owners will be in the lap of artistic luxury.

The Picchio is a displacement catamaran that is 71 x 31.5 foot and displaces 112,000 lbs (50 tons). It is powered by 2 x Volvo Penta 1PS 1200 diesels which will give a 12 knot cruise with a range of 2500 miles. There are 10,000 litres of fuel. The maximum speed is 19 knots.

The accommodation is spread over the hulls, a bridgedeck and a large flybridge. There are 2 doble berth cabins, a childrens playroom and a galley area in the hulls. On the bridgedeck there is the master cabin forward with a glass floor, a partially raised helming/navigation cabin and a main saloon with a partial glass floor to view the water in the cats tunnel. The aft cockpit and flybridge have a large amount of seating, bars and space for toys like windsurfers, tenders, bikes etc.

The build is unknown but I suspect foam glass with quote “sustainable, environmentally friendly interior and exterior”. The garden growing on parts of the aft deck may give a hint along with the statement of “flowing timber arches” in the interior and timber decking (teak).

The jpegs will give the idea of what $8 to $10 million will buy.

 

Designed for slow, comfortable cruising the Tortue (means “turtle” in French) 147 is an environmentally friendly catamaran. This cat is very much orientated for long distance cruising in a cat designed to take you comfortably anywhere you like. The design is built in Tuinisa and Jean SOMMEREUX, Julien BERNILLON (naval engineer) and a team of qualified craftsmen hand build each catamaran.

The Tortue 147 is 48.2 x 25.7 foot with a half load displacement of 38,000 lbs. There are 2,500 lbs of optional water ballast tanks to increase stability and provide improved balance under different load conditions. The design has bulb bows to minimize pitching. The 75 foot aluminum mast carries between 990 square foot upwind and 1,930 square foot downwind. The draft over the fixed keels is 5.4 foot. The engine power can be Hybrid Propulsion using two 57 HP diesel engines and two 10 kW electric motors that give an all-electric range of 12 nautical miles at 6 knots. The electric power is boosted by main cabin top 5.5 kW of solar panel array, lithium and AGM battery banks, and Victron 2 x 8 kVA converter inverters. The solar panels can generate up to generate over 20 kWh daily, exceeding onboard electrical needs. The Lithium Batteries have 65 kWh storage capacity. Also, there is a 6 kVA generator.

The accommodation has 3 double berth full cabins and a double berth “pilot berth”. There are 2 bathrooms in the hulls. The main saloon has a large galley, internal helming/navigation cabin and table/seating which are attached to fore and aft cockpits. The flybridge is for an external helming and sail control position with additional seating. You can really get away from people in this design.

The build is mainly 8 to 10 mm thick aluminum with a lot of Paulownia timber internally which is a fast growing light weight timber that consumes a lot of CO2 in its growing process. The build jpegs give an idea of the complexity of the build.

Performance is not the aim of this design; long distance comfortable cruising is the main aim. Translation 8 to 9 knot averages with 15 to16 knot peaks.

The jpegs give the idea of a very individualistic design.

 

Caracat 66 has an intelligent layout providing everything you would expect in a caravan or tiny house, from a wardrobe to a balcony. The Caracat 66 is a mobile home being trailable that can cruise on water for extended periods. The Caracat has a CE certification class (C) and can navigate along the coastline, on rivers and canals.

The Caracat 660 is 21.65 x 8 foot expandable to 12 foot by hulls sliding sideway under the main cabin area. The draft is 1.6 foot. The total height on the trailer is 12 foot. Engine power can be 15 to 15 HP outboards, a 25 HP inboard diesel or electric trolling motors for more sheltered quieter waters. Speeds depend on motor options but can range from 4 knots to about 8 knots for the 660 model option.

Cabin space is good and has 6.2 foot headroom throughout. You can transform 2 seating areas into double beds. There is a large galley and dinette seating aft, a toilet and separate shower mid cabin and a seating area forward as well as an internal helming position. This is literally a floating caravan that with its expanding hulls and fore and aft extension plates can provide a useful external deck area for lounging and EG fishing etc.

The CaraCat 66 is a 6.60 meter houseboat has a fiberglass / grp hull with 4 mm to 4.8 mm tempered glass windows. This is not a rough water boat. Stay in quiet waters or have very good weather information available. The scenic windows are great for views bad for rough weather.

The jpegs give the idea. There is also a 760 and 860 model in the Caracat range which are basically lengthen versions of the Caracat 660 model.

 

For people who like trailable catamarans the following is one persons idea of a way to trail them. The problem with trailable cats is they are either narrow (a beam of less than 8.5 foot) or they have to fold in some fashion EG Woods Skootas or Wizard cats. Sliding beam cats have been tried but if they have aluminium beams tend bind during the folding or unfolding process. To build a folding cat also takes longer than to build a completely solid cat.

What this guy wanted was a solid cat that had a reasonable internal accommodation with 6 foot headroom over part of the internal space. He also wanted to be able to trail and launch/retrieve the cat in a reasonable fashion to save on mooring fees etc.

This is an Australian guy who had to meet certain restrictions, maximum width without permits is 8.2 foot, maximum height is most of Australia is 16 foot but in QLD it is 14.1 foot, anything over that requires permits.

The resulting sailing catamaran design he came up with was a 24.6 x 11.8 foot catamaran that weighed 3,000 lbs ready for trailering. The trailer/rotary frame was completely costed/weighed and comes in at 3,340 lbs. This brings the total trailering weight to 6,340 lbs which is in the range of lager SUV’s 3.5 ton towing limits.

Good so far and the design/trailer is in the jpeg below. Now we start on a few thoughts. The problem with this concept is strong side winds. You have over 200 square foot of hull deck area subject to side winds. On a 25 knot wind day 5 ft/lbs of pressure is landing on 200 square foot at an average height of 8 foot. That equals 8000 ft/lbs of overturning moment (if you are not going around a corner) versus the trailer “righting” moment of 12,000 lbs. Stronger winds or going fast through a curve could cause problems.

Next is the structural issues of the trailer. Boat trailers are not inherently strong, they act a support for a strong stiff boat that has its trailer wheels generally under the centre of gravity of the boat, so what conventional boat trailers do is have a frame that weakly supports the ends and has axles to support the real load in the centre.

This trailer concept has the majority of its loads at each end of the trailer with the rotating arm pivots supporting the boat whilst trailering and launching/retrieving. In short, the trailer has to be a lot stronger over its entire length and the engineering of the lifting rotational pivot arms has to be good as do the bearings etc. This is the reason that this trailer is twice the weight of a conventional trailer and would cost (guess) 3 times as much.

Finally, when you have completed your days sailing you would have to repack your boat as things stored in cupboards would fall out, your toilet would slop water, your bedding would fall on the hull side, your fuel tank would possibly leak etc as the entire boat is rotated through 90 degrees.

I am not saying the idea would not work, it would need to be thought through a lot more. The jpeg gives the idea.

 

This is about Island Spirit catamarans. From 2011 Island Spirit Charters manufactured cruising catamarans in Chonburi in Thailand. The cats are mainly designed for charter fleets but can also be built on a semi custom basis for private individuals. The initial production was of a 38 and 41 foot design but now they have added the Island Spirit 525 has been added to the range.

The Island Spirit 525 is 51.7 x 26.9 foot with a weight of 36,376 lbs. The 65 foot fixed aluminium mast carries a 1,313 square foot mainsail and a 592 square foot roller furling jib. This is the standard charter catamaran rig, for personnel use there can be many optional sail extras that can be carried. The length to beam on the hulls is 8.5 to 1. The draft over the fixed keels is 5.05 foot. The engine power can be diesel sail drives 45 or 57 horsepower or an electric drive train (see the jpeg below). The electric drive has a range extender (generator) that will charge the system at 55kW, the drive motors are 65kW (88 hp) rated power and the E-drive system storage is 210kWh. There are supplemental solar panels charging up to 4.8 kW per hour. The cat only requires 37kW to power the boat at 8 knots giving up to 6 hours run time and unlimited range while running the range extender.

The accommodation comes in either a 4, 5 or 6 cabin option. In the 4 cabin option each hull has 2 double bunk cabins with an attached ensuite as well as a single berth crew cabin forward. The bridge deck cabin has a large galley and pantry bar area with seating and a table. But the main seating is available in the forward and aft cockpits that are connected by doors to the main saloon. The main helming and sailing controls are on the flybridge that is very comfortable.

The build is foam e-glass through out and is designed to cost effective and very maintainable. This is not to imply any build quality issues but the original design is for charter work which requires structurally tough, if slightly heavy build specifications. There is little need for exotic materials etc.

There is no performance report but I would suggest averages of 9 to 10 knots with peaks around 18 knots. The basic design indicates the Island Spirit will sail well on all points.

The jpegs give the idea.

 

The Island Spirit 380 cruising catamaran is aimed at eco-friendly sailing. The design was done in 2011 and the first cat was delivered in 2012. The designer is Albert Nazarov of AMD (over 140 designs) and the builder is Island Spirit Catamarans of Thailand. The cat is a production design aimed at the charter market but has some private owner options available. We will look at is the 4 cabin option.

The Island Spirit 380 is 37.4 x 22.7 foot with a weight of 15,000 lbs. The fixed aluminium mast 51.5 foot mast carries a 624 square foot mainsail and a 334 square foot jib. The draft is 4 foot over fixed keels. Engines can either be two 20 or 30 HP diesels or with an Oceanvolt SEA electric drive system (Oceanvolt Drives output 8kw each (15-25 hp)) paired with an 11kva diesel generator, offering a sustainable alternative to traditional diesel engines.

In very light winds, the screecher and electric engines will generate apparent wind, reducing diesel consumption to just 25% of what twin diesel engines would typically use. The generator operates at peak performance to charge the batteries, resulting in exceptional fuel efficiency and significantly lower maintenance costs. This allows quiet motor sailing at just 500 watts per engine and with just 1-2 hours of the generator provides up to 10 hours of motor sailing at 5-6 knots, even in light winds. The LiFePO4 48V 200AH batteries, provide over 40Kwh. There is up to 2 Kwh of solar panels available for additional electrical support. The diesel fuel consumption in this mode is 1-3 lt/per hour (while the generator is operating) and provides a maximum speed of 12 knots and a cruise speed of 6 knots.

The accommodation is in each hull is a double berth cabin aft and a toilet shower forward. On the bridge deck forward are 2 double berths accessible from the main cabin. Followed by a large galley down one side of the main cabin with a large dinette on the other side. The main cabin and cockpit have no bulkhead between them and depend upon a curtain screening. The roof carries through over the cockpit. Helming and sail handling happen either side of the cockpit.

The build of the hulls and decks are resin vacuum infused foam (DIAB Divinycell) e-glass which results in a 35% lighter build than hand glass layups. This is due to a better glass to resin ratio, virtually no voids and compressed surfaces removing any excess resins. Result a stiffer, lighter and stronger structure. Again, the concept of a charter cat is a strong reliable structure that requires a minimum of maintenance.

No performance numbers but probably an 8 to 9 knot average with 16 to 17 knot peaks.

The jpegs give the idea.

 

Expandacraft is a modular boat system that allows you to quickly reconfigure it from one type of watercraft to another. It can be a ready-made craft or buy the hull sections separately to build or add to your own craft. The Expandacraft segments can be used as a float(s) for a proa or trimaran. Using 2 float kits you can create a rowing or sailing catamaran. The length can be from 8 foot to 20 foot by using multiple 4 foot segments. The popular size is 12 or 16 foot kits.

The hull segments are 4 foot long with midship sections being 1 foot in cross section. The bow (and by default stern) sections are 1 foot cross section to join the midship section tapering to a bow. There is no specification of the buoyancy available in each segment but a midship segment should support about 200 lbs and a bow segment about 100 lbs if submerged. Translation, a 12 foot catamaran kit should support about 400 lbs leaving 50% freeboard.

The hulls are rotation molded plastic. Hulls like this if correctly designed are strong, virtually scratch proof and resist damage. If the design is done really well the components will fit together in minutes with large pins to attach cross beams etc. The components are manufactured and assembled in Florida. The standard cross beams are 1.5 inch (37 mm) square aluminum tubes for up to 8 foot beam but for 10 foot (3.1 meter) beam or heavy service boat requires 2 inch (50 mm) square tubes. Each of these components can be purchased as a kit or separately.

The jpegs below give you an idea of the configurations that are possible with the system.

 

The Trika 540.2 is a “kit” or plan day sailing folding trimaran designed by Dudley Dix for a German friend who wanted a fun tri for the family. The original Trika 540 had smaller floats and in some builds had a fixed beam. There is a Trika 560 done by Fyne boats which was the original “kit” manufacture following by CLC boats who do a kit of the Trika 540.

The Trika 540 is 17.75 x 10.75 foot that with swing arm cross beams can fold to 4.25 foot. The main hull is 2.25 foot wide and the floats are 11 x 0.8 foot. The weight is 154 lbs with a 15.7 foot aluminum or carbon mast that carries a 59 square foot mainsail and a 25 square foot jib. The length to beam is 9.2 to 1 on the main hull and 13.75 to 1 on the floats. The Trika 540.2 has an upgraded float design which now 225 lbs of buoyancy. One builder upgraded the floats to 330 lbs buoyancy.

The designer commented about floats “The Trika 540 it is not especially designed for high waves and – as many small boats – it likes longer waves better than the short choppy waves, but if reefed in time and combined with the new 100 liter amas (225 lbs displacement) I think it needs not fear comparison with its competitors.” This tri is a bay or lake sailing fun machine suitable for light to moderate winds and smaller waves.

The construction is basically plywood. The hulls are mainly 4 mm plywood. The bulkheads and frames are 9 mm plywood. 12 mm plywood is used in the crossarms. The hulls have taped glass seams. The gunnels are timber. The folding cross beams central component are aluminum channels which the folding wooden cross beams sit in.

The jpegs show the details of the cross arms and the ‘post’ slot in the floats. A fun design which the jpegs give a good idea about.

 

Part 2 Trika 540.2

 

The VIZIBILE 105 is a transportable fast sport catamaran which has accommodation for up to 7 people. The cat has some interesting features that allows you to do an open wing deck or a solid wing deck with or without a cabin top. As the VIZIBLE105 was designed for homebuilding or for production for large or small start-up builders. This is the ultimate modular small cruiser. The design is done by Florin Isvoranu is an architect with practical experience in the marine industry using his technology skills.

The Vizible 105 is 34.4 x 20.5 foot with a weight of 5,600 lbs and a displacement of 7,000 lbs. The 38 foot wing mast carries 754 square foot in a cutter rig (main and fore triangle). The hull length to beam is about 11 to 1. The prismatic coefficient is 0.645. The draft ranges from 1.15 foot over the hull to 6.2 foot over the underwing central centreboard and kickup rudders. The underwing clearance is 2.4 foot. The power can be a 20 HP outboard or an electric drive system.

The accommodation in the hulls provide standing headroom in the entry, galley, head and nav station area. A 3.25 foot wide berth is aft in each hull with a single forward tapered bunk in the starboard hull. A folding table and seats transform the galley into a cozy dining area for two. An enclosed bridge deck area can provide 2 dinette areas that convert into 2 double berths. The headroom in this area is only about 5 foot. The cockpit provides seating on the mast beam with good site lines over the low cabin roof.

The construction can be home built in foam glass with some plywood. The majority is vacuum infused flat table construction but this design looks “simple” to build but has a lot of curves in it which will require some skill to execute. The cross beam structure looks like simple, but being capable of transport, requires another layer of complexity and additional weight.

The performance is not mentioned but I suspect a 10 knot average, 20 knot peak sort of boat.

The jpegs give the idea of the concept.

 

What do you think of the rig? I like the idea of short rigs that are dependent on a screecher for lower wind speeds, especially with the articulating bowsprit.

 

Russell. I like the rig for several reasons, the screecher can be lowered and by default the center of effort of the rig moves aft. This helps in heavier airs to get a better balance cat especially upwind. It helps that this design has a centerboard that can be moved slightly fore and aft to help balance the rig. I am a fan of fat head mainsails as you can have a "shorter" mast for the same sail area reducing weight aloft which helps reduce pitching. The articulating bowsprit is a very useful addition which allows a more efficient cutter rig upwind and gives more options when deep reaching. The only issue is the design of the bowsprit to handle the loads which in this design should be relatively limited if it is only flying a screecher or code zero. I hope painting the new tri is not too time consuming.