Multihull Structure Thoughts

Here is where life gets confusing. Do you believe the designers (Eric Jean) 2013 specifications or the Catamaran Companies second hand sales advertising. Not only is the length and beam being different but also the build material. I am going to take a combination of both. The basic custom tri was built to be a dive cruise charter catamaran with cabins for 12 guests.

Victoria cruise tri was 54 foot when launched but had bulb bows added to extend the length to 59 foot. The beam from the designer is 23.4 foot but the later advertisement says 26 foot. I accept the 23.4 foot option. The rig is a masthead sloop rig with roller furling headsails. Engine power is unknown but the engines would be powerful enough to allow this design to be a motor sailor.

The floats are for sleeping cabin accommodation for 12 guests and have 4 shower toilets. The main hull below bridgedeck level have the engines, dive compressors, “dive shop”, generators etc. At bridgedeck level aft is the master cabin with direct access to the internal helming and navigation station. Forward is the galley and seating area for about 14 people. Life is comfortable for those who are guests on this tri. The boom acts as a crane for the large RIB on the aft deck used for some of the diving tours.

The construction of this tri is mainly aluminum. The used advertisement says glass fibre, which may be the case above the gunnel line but below the gunnel the sharp edges and bulb bow says aluminum to me, also the designs claim it’s an aluminum build.

Performance moderate. The jpegs give the idea.

 

This is purely a commercial catamaran designed by Frenchman Eric Jean. The cat is of interest due to the windows below the waterline to view the coral reefs of Djeddah, Saudi Arabia. The cat was also built in Saudi Arabia.

The cat is 72.1 x 26.3 foot. Little else is known.

The interior of the cat is broken into 2 levels. The hulls are deep with viewing windows below the waterline for guests to sit and observe the reef from the in-hull seating. On the next level, the bridgedeck, there is a galley and bar setup for up to 200 guests to enjoy the onboard viewing and entertainment. There is also external seating and viewing available.

The build of the cat is basically aluminum with some very thick and strong glass in hull ports below the waterline. The structure around the glass ports needs to be very rigid and have excellent sealing compounds as glass and aluminum expand and contract at different rates and have different flexibility. Result as the cat moves through a seaway the design of the windows and sealing becomes very important.

Performance is not relevant here as the cat will slowly motor over the coral areas to allow good viewing.

An interesting design, the limited jpegs give the idea.

 

Solgato please look at Crazy Ideas thread, you may be able to help.

 

Qingdao boat company in China produces several types of boats. The Grandsea catamaran Model AL-1500B is a 78 seat charter catamaran that is produced in Shandong, China. The cat can be used as a leisure, entertaining, chartering or cruising.

The Grandsea cat is 49.2 x 17.5 foot with a weight of 65,000 lbs. The hulls length to beam is about 10 to 1. The draft is 1.6 foot to 4.6 foot depending on propulsion type. The 2 x 500 hp Weichai diesel engines which can provide a peak speed of 25 knots.

The accommodation is the bridge deck and flybridge which can provide 78 seats in a charter sightseeing format. There is sufficient room for a roomy cruiser if you choose.

The structure is basically welded 5083 aluminium. Being built in China the price for the shell with engines and standard shaft drives is under $500,000 US in China. Cheap.

The jpegs give the idea of 1 of the 2 built so far.

 

The following is about an electric powered passive foiling catamaran used initially as a chase boat for the Alinghi AC team. The design is a production boat that can be used as a personal pleasure cat or limited range commercial craft. The driving force, is Javier Ibanez from the De Antonio group. Javier worked for the KER yacht design group prior to working at De Antonio and used KER for the design work.

The De Antonio E23 is 23.5 x 7.6 foot and displaces 3,196 lbs. The draft is 1.3 foot (without engine lowered). The engine is a Torqeedo Deep Blue 50 that produces 80 hp electric motor powered by a 40 kWh battery. The cat has a peak speed of 30 knots. The range at 5 knots is 50 nautical miles. The range at 20 knots is 24 nautical miles. Charge time is 8 hours with a standard charger or 1.5 hours with a fast charger.

Foiling, in which the hull of the boat is lifted out of the water reduces the water friction and drag of a design. KYD and Javier have extensive experience with catamarans and foils, they came up with an innovative proposal for the E23. KYD developed a catamaran hull that integrates ‘passive’ hydrofoiling design – a foiling assist – with no advanced electronics involved. A stationary foil situated in the optimal position under the hull connects the pontoons, and a pair of aft foils connected to the trim tabs stabilise and allow the trim angle of the boat to be adjusted. (see the jpeg). This allows an easy to control and fly hydrofoiling power catamaran. Ker design of a combined hull and foil, that has been submitted for a patent application.

A stationary foil situated in the optimal position under the hull connects the pontoons, and a pair of aft foils connected to the trim tabs stabilise and allow the trim angle of the boat to be adjusted. When the E23 hits a speed of about 16 knots, the water flow above and below the foil lifts both pontoons out of the water enough to reduce drag…and increase both range and speed capabilities.

The build is a composite fiberglass infusion structure with vinylester resin. The foils are 6061 aluminum castings.

An interesting concept that with a more modern battery higher capacity battery (the initial design work started several years ago and final build was done in 2024) would be a great fun machine. The jpegs give the idea.

 

Bajansailor "Here is a thread on the YBW Forum in England, looking for advice re what cat to buy.
In it, a question is asked as to what make of cat the one in the photo below is - @oldmulti do you recognise her?"
What catamaran should we buy? https://forums.ybw.com/threads/what-catamaran-should-we-buy.617071/page-2#post-8619085

Eric Jean naval architect France, designed “Image” which has many similarities to the mystery design. It is epoxy composite 17 x 8.2 meter.

 

This is an update on the Silent Yacht 62 3 deck option. To quote Steve Bell chairman of Silent Yachts: “The SY62 3-Deck Open has proven that long-range solar-electric cruising is a reality today. We crossed an ocean quietly, efficiently, and dependably, demonstrating what clean propulsion can achieve.”

The Silent 62 3-Deck Open “100%” successfully completed its transatlantic crossing, reaching Antigua on December 12 after departing from Gibraltar on November 14. Following a route via Morocco, the Canary Islands and Cape Verde, the 18.9-metre solar-electric catamaran covered approximately 3,800 nautical miles over four weeks at sea. The crossing was carried out with minimal fuel consumption, operating primarily on solar energy, battery storage and electric propulsion. The journey offered a full-scale test of all onboard systems under offshore conditions, confirming the yacht’s ability to cruise long distances with a high degree of autonomy. With daily energy needs of between 350 and 600 kWh depending on the speed, the yacht operated with exceptional efficiency.

The Silent Yacht 62 is 61.9 x 29.5 foot displacing 85,980 lbs. the draft is 4 foot. The yacht runs two electric motors. Total usable battery capacity sits at 340kW with 350 kilowatt hours of storage. At 6 knots with no solar gain you see close to a 100 nautical mile range. At 7-7.5 knots, the range drops to around 60 nautical miles. The solar gain runs at about 9 kilowatts an hour. At 6 knots the motors draw roughly 14kW a side, so 28 kilowatts an hour. The solar feed offsets some draw though not all, and the hotel load adds 1-2kW per hour without air conditioning.

Silent added a second auxiliary generator since the last model. This ties into the shore power charger and gives redundancy for extended runs. The yacht carries 2,000 litres of diesel. With one generator supplying constant charge, the range rises enough for transatlantic passages if you choose. Silent built in an auto start system for the generator. You set a state of charge for the batteries and a time window so the generator never fires at three in the morning and upsets the neighbours. Set it to run only between 10 am and 6pm and it behaves itself. The system covers marinas with weak shore power or weeks of cloud cover with no solar feed.

Translation if all works well the cat can run about 12 hours on a good day but will need to run the auxiliary generators for overnight travel. If you have strong winds against you or rough weather you may be continuously running the generator for those times. The issue is the solar panel feed in rate of 9 kilowatts and hour versus the 28 kilowatts an hour output required for the motors at 6 knots.

The jpegs provide the layout etc with the house load on electricity of 1-2 kW an hour.

The structure is foam glass composite.

An interesting chart is jpeg 1, which suggests the solar gain per day (not usage just the solar input per day). This cat uses a minimum of 350 kW a day. The maximum gain was 54 kW from solar. Result, you will need a very power cord or you will be running a generator.

The jpegs give the idea.

 

I wonder how many millions that Silent Yacht will cost?
This power cat 'Electric Philosophy' designed by Sam Devlin is much more affordable, and it runs 100% on solar power.
A Solar-Electric Catamaran, The Ultimate Low Maintenance Cruiser - ELECTRIC PHILOSOPHY - OffCenterHarbor.com https://www.offcenterharbor.com/videos/solar-electric-catamaran-ultimate-low-maintenance-cruiser-electric-philosophy/?prev=devlin

Electric Philosophy 40 Downloadable Study Plans https://devlinboat.com/product/electric-philosophy-40-downloadable-study-plans/

Here is another interesting hybrid electric boat - it seems to have derived inspiration from the 78' Dashew FPB. A catamaran version would be the next logical development.
Passagemaker Magazine https://www.facebook.com/passagemakermag/posts/pfbid033v2A7ubknusCoKBMwMdGD3b3oWB4sPtJi4tFuPjpmkpWx8DwGTWLfJxbMvcNJyihl

 

Bajansailor. About $US 4 million depending on options etc for the Silent Yacht 3-Deck Open “100%”.

 

Thanks for this @oldmulti
Our Ministry of Fisheries here (Barbados) recently enquired about a 22 metre hybrid electric longliner built by Damen in Holland, and the price of this vessel is around US$ 5 million. I will attach a specification sheet for her which they sent on to me. Again this is a monohull - but I think that a hybrid electric catamaran fishing vessel would work well.

 

This 24m zero emission electric river catamaran ferry concept from Global Marine Design Australia. GMD is mainly and aluminum kit boat manufacturer that ships aluminum kits to builders for final fabrication. This is one of their larger designs built for a specific purpose of ferrying 100 to 150 passengers on sheltered short water routes. The duration depends on the on land charging facilities, size of batteries and speed required. There are two versions a High Tunnel Clearance for rougher waters and a low air draft version for bridges.


The electric catamaran is 78.7 x 23.6 foot The length to beam on the hulls is 12 to 1. The draft is 3 foot. The underwing clearance in the low height version is 2 foot. In the rough water full height version has underwing clearance of 3.2 foot. This is a pure electric cat depending on its batteries and onshore charging facilities. Now each cat needs to specify its speed requirements, duration of each ferry journey and water conditions expected. The engine and battery requirements are then specified to suit the cat. The peak speeds can be as high as 20 knots but the “normal” cruise speed is around 9 knots. 9 knots is just over a speed length ratio of 1 meaning minimal power will be required to achieve 9 knots.

The final accommodation arrangement can be flexible, the ferry can be single or double deck, with room for 100 seated passengers in the main cabin and 50 seating or standing passengers externally. Electric range will be customized to suit your operation and charging facilities, with genset backup charging also possible.

The structure is basically aluminum in a kit form. The interior fit out can be any material that is hard wearing and very maintainable.

The jpegs give the idea.

 

This is a British home designed and built day sailing trimaran that can be sat in, not sat on. The owner wanted to be comfortable whilst sailing in British waters and weather. The owner studied many other trimaran designs before he did the design work and was initially inspired by Wharram work but wanted more comfort. He found the tri concept would work better for him especially for trialability.

The tri is 18 x 12.4 foot with a beam able to be reduced to 6.5 foot with sliding cross beams. Main hull bottom is 1.9 foot. This implies a loaded displacement of about 800 to 1000 lbs. The lateral resistance is a leeboard on the main hull which proved a good choice as the balance of the boat was not correct when first sailed and moving the leeboard aft was easily done which balance the tri under sail. The sloop rig sails and mast are from a Firebird dinghy. Main hull length to beam at deck level 5.9 to 1 and at waterline a length to beam of 9 to 1. Float length to beam at deck level 8.7 to 1.

The construction is ply with some timber for gunnels and stringers. The ply is likely to be 6 mm throughout with an internal sub floor of 18 mm in the cockpit area. The exterior is covered with a light glass and epoxy covering. The aluminum sliding 70 mm cross beam tubes are attached to the floats. The main hull permanent tubes externally are 80 mm implying 4.5 mm walls.

The cockpit is 8 foot long allowing 3 crew members to sail in comfort or if you want have an overnight camping experience for 2.

The jpegs give an idea.

 

The following is about a person who wanted to sail in a reasonable time and had a 17 foot Wenonah Jenson canoe available to him. The canoe had a rudder option but in a sailing, format was pretty unstable. He did some research work and did a similar float arrangement to Micheal Storer float plan option available for many canoes that can make them into trimarans. A bit of construction work and you have the basis of a day sailing trimaran. The tri can be disassembled for trailering.

The trimaran version is 17 x 12 foot of unknown displacement. The mainhull width is about 2.6 foot and the mainhull as a canoe weighs about 30 lbs. The sail is a Sunfish rig (about 75 square foot) adapted to a crab claw configuration on a short aluminium mast. The lateral resistance is a lee board attached to gunnels. The floats are deep V plywood about 8 foot long.

The structure of the main hull is fiberglass with additional reinforcement for the lee board, cross arms and mast base. The floats are 3 or 4.8 mm plywood. The cross arms are laminated using nine layers of 1/4″ x 1 1/2″ x 12′ yellow pine. Translation 6 mm strips vertically to form 60 mm wide by a minimum of 38 mm high cross arms that are 12 foot long. The cross arms are bolted to the floats and roped onto deck beams in the main hull. The mast base has a wide timber deck support and a base plate on the keel.

The canoe can accommodate 2 but is mainly sailed single handed.

The tri sails well and has been sailed in drifting condition thru to the low twenties mph and sailed well in every wind range. It accelerates very quickly with the slightest puff and sails like a dinghy only requires hiking in heavy winds. The amas bury only for a second or two in puffs.

A nice way to get a reasonable day sailing trimaran. The jpegs give the idea.

 

Thanks, Oldmulti
Nice building ! Vertical layers for the crossbeams is very unconventional ! As bending is impossible in this direction, huge wood losses to cut the shapes ?

 

Here is a German guy whose aim was a small trimaran that was very light so he could tow the sliding beam tri on a trailer behind his bike. OK The good part was he designed and built 2 tri’s. The first worked but the second tri “Watermouse” was to be the improved version.

The “Watermouse is about 14 x 10 foot expanded and can be reduced to about 6.5 foot using the sliding beam cross arms. The tri is about 250 lbs all up weight. Each float weighs 16 lbs and is 12.1 foot long and has about 112 lbs of buoyancy each. The sloop rig is from an A class boat of some description and had to be modified to suit the tri. The float based foils were developed to allow the rig to be used in stronger winds.

Now we start on the fun part. First, you go around the corner and find a rubbish bin with strips of Styrofoam XPS strips the right length for your floats and a seat shelf. You cut and shape them into a float shape. Cover the floats with 2 layers of glass and epoxy inside and out. Then go on to Craigs list and get a second hand kayak. Next get some aluminum tubes from a friend for the cross beams. He then used aluminum road sign mounting hardware to connect the tubes to the floats. The odd bit of timber was used for the float to cross beam connection. The cross beam tubes look about 50 mm and are likely to be 1.6 or 2 mm walls. This is about the minimum size of unsupported cross arms you can use is a sheltered water small tri. The bike trailer is light and looks effective.

Now sailing has proved informative. The skipper weighs 220 lbs and the tri lacks freeboard when he is sailing it. To quote the skipper “The boat feels a bit clumsy. So small ensures that the mainsail and jib halyard line and the furling jib line are very close together with little space to store it next to other equipment. The mainsheet line comes from behind my back when I’m in the canoe.” But when sailing the skipper said (slightly edited due to translation issues): “The boat reacts well to its rudder and tacks well not losing too much height sailing upwind. The foiling daggerboards in combination with the hull shape seem sufficient. I cannot yet see whether the foils provide sufficient stability with more wind. I think waves are more likely to become a problem due to insufficient freeboard.”

Result of this is the tri requires more buoyancy built or he was going to sell “Watermouse” to a smaller person. The owner skipper returned to sailing on his first tri “Breeze” (also known as Tripple B) which was more able to carry his weight.

Sorry I do not more details about “Watermouse” but the jpegs give the idea.