Multihull Structure Thoughts

There is something similar here in Pender Harbour. When it leaves the dock, which is rare, if I'm on the water, I actually have to look the other way.

 

The following is a cat being built in Australia of which I know little about beyond the length of 52 foot and the jpegs. The following is a guess but a cat like this would be about 52 x 27 foot with a weight of about 35,000 lbs. The rig is unknown but would have about 1500 square foot of sail. The fix keels would have a draft of 4 foot. power would be EG two 50 hp diesel engines.

To the jpegs. This is an aluminium cruising catamaran that has been built by a guy who wanted a strong cat that would take him far. He understands aluminium and has skills in the material. I do not know if he had assistance or a if he is helping a builder. The source for this was a Facebook post that I cannot find again but there were few written words and a lot of jpegs.

The structure is “classic” aluminium. T section frames about every 3 foot, stringers every 300 to 400 mm, probably 4 mm shell, aluminium bulkheads with rib reinforcements and round bilge construction. Who ever did the welding are skilled. The big advantage of aluminium is that material can be cut like wood and can be tack welded into position before being finally fully welded. This allows you to set up an area check it is al fair and correct before finally locking it into position. With foam glass you have to commit and if there is a mistake, rebuild the area.

The down side of aluminium is electrolysis. You need to plan from the start of construction where there are going to be dissimilar metals, electronics, engines, propellers, winches and even carbon fibre masts etc that have to be isolated or have electrolysis protection. If protection is done correctly you will have a long lasting boat, if not you will be surprised as to how fast problems can arise.

The jpegs tell you more than the words.

 

If your Newick went by, I'd crash into something because I couldn't take my eyes off. There's a big gulf between a beautiful boat and some of the modern boats and some modern boats can just ruin a landscape for me.

 

An old mate of mine works for a bareboat company that has several French condomarans.
Four/five doubles with en suite heads, huge picture windows in the hull topsides, windage like a block of flats.
Customers love them. He hates them.
Main problems are blocked heads, aircon complaints, and occasionally having to unzip the mainsail cover to clean out the dust. They don't get used often.
None of the big hull windows have leaked......yet...

 

The Tricat 30 is a production trimaran designed by J.Michal / A.Houdet from CN Tricat France. The Tricat 30 is a sport cruiser, swing wing transportable (to wide to be trailable) trimaran. The Tricat 30 is 30.2 x 23.3 foot and can be folded by swing wings o 12.5 foot/ The weight claims range from 4000 lbs (original brochure) to 5000 lbs (several test reports) with a displacement of 6500 lbs. The 36 foot aluminium mast carries a 430 square foot mainsail, 215 square foot jib and a 485 square foot gennaker. The main hull length to beam is about 8 to 1. The hull draft is 1.6 foot and 5 foot over the float based daggerboards. The floats are 29.5 foot long and have very full square sterns. The outboard is 10 HP.

The accommodation is a forward and aft double berth with a separate toilet area. The main saloon has a 7 foot galley with a dinette opposite. There is also a fold down chart table with seating. This is a practical cruising layout with 6 foot headroom in the main saloon. A couple could cruise this tri for a month in comfort. The cockpit will handle 6 people with all sail handling available.

The performance stories vary as do the test reports but this tri can sail at near wind speed, tacks well, points high and has peaked at 20 knots. Then Martin Fisher assisted in the design of a Tricat 30 PERFORMANCE with a new lighter rigging and asymmetrical daggerboards. The upwind performance was improved and the Tricat won a few local races. In short it can sail well on all points.

When this tri was being developed by Tricat, they did a 3D CAD design then built a full size plywood model of the tri to sort out the ergonomics and any sail handling issues, winch locations sheets leads etc. It is far cheaper to change things on a cheap plywood structure than modify a production mould.

The structure is mainly foam glass. It is a polyester foam glass vacuum infused structure but the second tri, at the request of a customer, had the hulls vinylester foam glass vacuum infused. There are solid glass areas but any flat panel has foam cores. The crossbeams are carbon fibre structures with stainless steel pivot pins.

This is tri is a practical fast cruiser that can sail far if required, at least 10 have been launched. The jpegs give the idea.

 

Hi John, thanks for post further info about your design. Obviously a lot of work has gone into the concept which looks very practical. The restrained approach to accomodation is refreshing.
In comparison with some of the amateur design propositions discussed here from time to time, yours looks like it could work well.

 

This is about several blue water aluminum catamarans designed and built by Australian, Tim Mumby. The cat is claimed to have: “Narrow hulls, high bridgedeck clearance, flexible sail plans and light weight means averaging more than 200nm a day is the normal. You’ll be sailing in 5 knots of wind, or trying to slow it down above 15 knots of wind. This is one of those rare designs a sailors cat and a fast passage maker.” OK. The Mumby 48 (Harwood marine Cyber 48) is 48 x 24.4 foot with a shell weight of 13,670 lbs, a cruising displacement of 16,600 lbs with a maximum displacement of 19,500 lbs. If the numbers are real, this is a light aluminum cat. The 61 foot aluminum mast carries a 817 square foot mainsail, a 516 square foot genoa, a 107 square foot staysail, a 968 square foot screecher and a 1,560 square foot spinnaker. The length to beam on the hulls is 12.2 to 1. The draft over the rudders is 2.4 foot and over the daggerboards is 5.9 foot. The bridgedeck clearance is 2.9 foot. The engine power is 2 x 35 HP diesels which give 8 knots or at 6 knots 1800 mile range with 1300 litres of fuel. An interesting number is the total drag at 9 knots is 622 lbs. The hulls have a total of 413 square foot hull wetted surface area including rudders.

What does all the above mean? To quote Tim Mumby *Our average day run on "Trim" after the last 32,000 nautical miles {circumnavigation via south Africa} was 238 miles / 24 hours. Top speed reached a few times was 22 knots”. Other people on Mumby 48 cats have had similar stories. This is a genuine 8 to 10 knot average cat over long distances. Peaks of over 20 knots make sense with the sail area versus the loaded displacement. This is a good design that matches the publicity of a performance cruiser.

The accommodation varies according to the owners preference but it has either 3 or 4 doubles with attached toilets in the hulls. The galley can either be in a hull or on the bridgedeck. The bridgedeck has seating and navigation areas. The cockpit is where the sail handling and steering is done. A practical cruiser.

The build has been done in Australia or in Cebu, Philippines and takes about 2 years on a semi custom basis. The structure is in the hulls are 4mm 5083 aluminum. Cabin top and decks are 3mm 5083 aluminum. The hulls and decks are supported by T section frames and stringers. This cat is well designed and will take knocks better than fiberglass but like all builds they are not rock proof, just more rock resistant than most.

The jpegs give the idea of the cats. These are good serious performance cruisers.

 

This trimaran was designed by Laurie McGowan and Michael Schacht as a long-distance coastal cruising and adventure racing trimaran for one or two. Eureka is 20 x 13.4 foot with a weight of 500 lbs and a sailing displacement of 800 lbs and a maximum displacement of 1100 lbs. The 26.5 foot Hobie 16 mast carries a working sail area of 220 square foot and a spinnaker of 180 square foot. The length to beam of the main hull is 12 to 1 with a gunnel width is 3.1 foot. The floats length to beam is 17 to 1 with a buoyancy is 120% of displacement. The draft ranges from 0.75 to 4.9 foot. Both the centreboard and rudder are kickup.

The accommodation is basically a single bunk on top of the centreboard case and some limited storage. There is also an internal seat for protected sailing with a “joystick” for steering from inside. There is a hatch that has a viewing plexiglass viewing dome. The cockpit is a sit down at the rear where the helmsperson steers by foot pedals. Also, there is a pedal powered Seacycle unit that provides a minimum of power for light airs etc. If you are sailing solo in the cabin you can be protected in heavy weather but sail handling will need a self furling jib and a reefing system for the mainsail. Sailing 2 up will require a lot of cooperation if you are sailing for more than a day.

The structure is plywood timber. The hulls are developed tortured 6 mm plywood with stitch and glue joints. The decks and bulkheads are 6 mm plywood again stitch and glue to the hulls. All exterior surfaces are covered with 200 gsm fiberglass cloth and epoxy with a double layer below the waterline. The crossarms are box section of spruce and plywood and are tied on by Dyeema rope lashings. The tri is demountable.

Performance unknown but I suspect it would give a Hobie 16 a run for its money.

The original request to the design team was to have a fast solo cruiser for coastal sailing. This tri would also be suitable for EG the Race to Alaska etc. Just a good fun boat for one or 2. The tri equivalent of Matt Leydens Paradox monohull.

The limited jpegs give the idea.

 

oldmulti, this thread is EPIC!!! Best ever anywhere!
(did I overlook it or you haven't divulged your identity? Very curios to know...!)

 

Tane, Oldmulti just wants a quite life, I do this for fun not anything else. And yes, I have done a lot of sailing on different multihulls and been involved in building quite a few (that was less fun).

The following trimaran was known as Sea Flash, designed by Mauro Sculli of Studio Sculli and built by Atelier Alfabravo. Then the design reappeared as the Stress 14. The Stress 14 is 14.3 x 9.2 foot and can be disassembled into parts for cartopping. The weight of the tri is 157 lbs. The 23 foot, 2 part mast carries a 118 square foot mainsail. The beam of the mainhull is 2.7 foot with a length to beam of 5.6 to 1, which indicates a planning type mainhull. The 8.8 foot long float length to beam is 11 to 1. The draft over the kickup centerboard is 2.5 foot.

This is a fast daysailor for 1 or 2 crew with class racing available.

As you can see in the plan diagram this tri has solid fiberglass hulls and decks. There is foam glass stringers and a vertical plywood spine in the main hull to add stiffness fore and aft The plywood spine also acts as a support for the mast base. The cross beams are aluminum tubes that slot into support tubes on the mainhull and are bolted to the outriggers.

No performance numbers but I think it would match a Hobie 14 in light to moderate airs.

The jpegs give the idea.

 

This is about 2 charter cats. “Flow” and “Crystal Dancer”. They are aluminium charter cats used in Thailand. Crystal Dancer is 60 x 25 foot and weighs 26,900 lbs with a displacement of about 44,000 lbs with its 70 charter guests and 6 crew. Crystal Dancer is a power cat that has 2 x 125 HP diesels and can cruise at 10 knots. The builders next built a sailing version of the charter catamaran called “Flow”. Flow is 65 x 25 foot with a weight of 30,000 lbs and a displacement of about 49,000 lbs with up to 90 passengers and 6 crew. The 77 foot mast carries and unknown amount of sail (guess about 1600 square foot). Flow has 2 Nanni 154HP diesels fitted with 52 mm shafts and 560 mm 4 blade bronze propellers. The top speed is 17 – 18 knots constantly at 2400RPM. When she is fully loaded, the speed is 15 knots. The draft over the low aspect keels is about 4 foot.

These cats are pure charter machines and have wide open deck space with a large Bimini roof tops for shade. There is a large bar area on the bridgedecks of both cats with toilets down in the hulls.

The builds of both cats are all aluminium. They have 4 mm 5083 aluminium shells with aluminium bulkheads, T frames and T stringers. The hull forms a simple flat bottom sections for ease of build. This is probably the fasted way to build a big cat that can optionally be painted. It is the one huge advantage of aluminium, you don’t have to paint it if you have finished the build well. Only problem with charter cats is they have to look painted “pretty” to attract the customers.

The jpegs give the idea. The first set of jpegs are of the sailing “Flow” in build. The white cat is the power “Crystal Dancer”.

 

A lot of interesting big aluminum Multis covered in the last few posts.

It’s neat to see the builds in the raw at the fabrication stage as a fabricator who will soon be shaping my own car body for a Cycle Car project I’ve been building (think Bugatti Boat tail roadster).

The one posted a little while back standing on end looks like it would be right at home as a modern art sculpture in the front yard of someone’s house.

Joking aside, it’s interesting to see how they deal with creating the shapes and are able to achieve pleasing lines from a flat material, and the varying levels of execution requiring more or less finish work down the line.

Stuff like the square flat transom on the charter cat above are pretty interesting to study.

With regard to painting aluminum and charter flash, I imagine vinyl wraps might be an option, although I’ve always wondered how they would hold up in a marine environment.

I followed the wrap job the installers who did the Shockwave Tri on social media a while back and wonder how it has held up in the years since.

 

I am taking a few days off (see you next Tuesday) but I thought I would leave you with some reading for those who would like to learn more. A few random items.

An old publication on boat building timbers and various types of glue. The PDF below about 2.5 meg in size.

The next is from Professional Boatbuilder magazine about environmentally friendly boat building materials: The Quest for Eco Composites - Professional BoatBuilder Magazine https://www.proboat.com/2020/12/eco-composites-quest/

Next an Epoxyworks article about butt joints in plywood: Joining Plywood - Epoxyworks https://www.epoxyworks.com/index.php/joining-plywood/#more-4197

A final item was removed at the request of the author.

 

Some great links, Old Multi. I'll read the timber article, but liked the JR Watson article about butt-joints and scarfs. All the testing those guys did has been very helpful to me. I just finished scarfing my plywood topside panels together and will post a photo here when it looks like a hull.

 

Thanks for the links. Will be great to read through the Easter.
Enjoy your weekend!