Multihull Structure Thoughts

This is a short one about an aluminium power cat by Chris Tucker Marine Design, an Australian designer who has a wide range of design work from dinghies to personal and commercial craft in both monohulls and catamarans. His latest design launch is a 100 foot paddle steamer for charter work on the Murray River in Australia.

The power catamaran is 32.5 x 12.5 foot with a weight of 12,678 lbs. The length to beam on the hulls is 8.25 to 1. The draft is 1.3 foot over the hull. The underwing tunnel clearance is 1.1 foot. The power is 2 inboard diesels.

The accommodation is a forward double berth with a small cabin then the main saloon with 3 seats and helming position followed by either a small galley and toilet area or storage cabinets. There is a large cockpit area for EG fishing work, charter work etc.

The construction is aluminum and as you can see from the jpegs there is extensive stringers, chines and steps to add to the panel stiffness. There are no details beyond the diagrams.

A good practical design. The jpegs give the idea.

 

As I indicated yesterday, Chris Tucker Marine Design has a range of design work from dinghies to personal and commercial craft in both monohulls and catamarans. I will show the other end of his skills. A fiberglass dingy that is capable of meeting local survey rules (Survey 4E, waters within 200 meters of shore). I am not suggesting this would be an easy build but the overall concept and structure is interesting.

For a homebuilder a simple plywood chine dingy would be satisfactory but if you required something more substantial, I suggest contacting Chris Tucker about this design.

The dingy is 11.5 x 4.9 foot and can carry up to 5 passengers implying a displacement of about 1100 lbs. The power can be a small outboard but the rowlocks show a preference for human oar power.

The build is single skin fiberglass with some foam blocks adding stiffness and seating. The hull laminate from the outside is a gelcoat, 225 gsm CSM, 600 gsm biaxial e-glass, 600 gsm double bias e-glass, 600 gsm biaxial e-glass and a flow coat inside. Any internal fitouts are covered with a gelcoat, 225 gsm CSM, 600 gsm double bias e-glass and a flow coat (if required). The resins can be polyester or vinylester. The foam seat blocks are for buoyancy as well as a structural element.

A nice little dingy. The jpegs give the idea.

 

The final Chris Tucker Marine Design for now. You have a favourite spot on a river or a coast line in a secluded bay and you want to start a business, have a school camp or a remote hotel for those who like fishing business etc here is a good solution. This floating hotel will accommodate 14 double berth cabins with ensuites, 14 back packer modules (upper and lower single bunks) with 4 toilet shower areas plus in the starboard hull have 5 crew cabins with amenities. The total guest complement is 42 with 5 crew available. There is a roof top area that is partially covered for lounging and entertaining.

The hotel is 83.6 x 49.2 foot with a displacement of about 200,000 lbs. The draft is approximately 3 foot. The cat is basically a barge that can get towed into position and is anchored for the long term.

The build is an aluminum structure with a lot of internal fit out in hardwearing materials.

The jpegs give the idea. Back to reality tomorrow.

 

Spirited Designs created by Craig and Marina Schionning (one of Geoff Schionning sons) have an entry level cruising cat design called Seascape. This is a trailable cruising catamaran with realistic accommodation for a couple for a week or so.

The Seascape is 19.5 x 8.7 foot that weighs 1870 lbs and can carry 770 lbs for a total displacement of 2640 lbs. The beam of the boat can be modified to an 8.2 foot to allow for local trailing rules. The 26.5 foot aluminium fixed or rotating mast carries 253 square foot of sail area. A Hobie 16 or 18 rig could be substituted. The hull length to beam is about 10 to 1. The draft is 1 foot over the hull with a dagger board in the port hull drawing about 4 foot. The underwing clearance is 1.2 foot. The design according to the designer has “underwater hull design is aimed at efficiency with a reasonable payload capacity enabling extended cruising with coastal open water capabilities”. The auxiliary power is a 10 HP outboard.

This is basically an open boat with some hull accommodation suited to warmer waters and outdoor living. The open cockpit design is spacious enough for groups of up to 6 to 8 people with comfortable seating around the table for 5 adults. There is an optional cockpit roof over the seating area. There are 2 berths below along with seating and a spot for a portable toilet. There is plenty of locker space and an internal area for a mini galley etc. but there is an outdoor BBQ for cooking if required. Please understand you are dealing with a 19.5 foot long boat with headroom below of a maximum of 5.25 foot. This cat is practical without being luxurious.

The structure is based on simple surfaces and shapes in this design. Flat panels are used in the construction with minimal complex shapes to contend with. Material options include all Gaboon plywood and timber, plain PVC foam glass or Duflex (choice of balsa or foam core) glass. If a kit system is chosen this boat is very quick and easy to assemble with all parts cut to size. Cats of this size generally 6 mm ply shells with 200gsm cloth covering in epoxy. The underwing can be 9 or 12 mm ply. In foam glass you would probably be building in 10 mm PVC foam with 400 gsm e glass either side.

This is a relatively simple cat to put together that does not depend on complicated folding systems to be trailable. It lowers the cost and build time. The downside is the need to handle these cats with care in stronger winds and bigger waves as they do not have the stability of folding designs.

Performance is in the 8 to 12 knot region. The jpegs give the idea.

 

This cat is a concept of what one person would like to have. He started with a few sketches of a 60 x 28 foot cruising cat with a biplane rig. The design changed as he discussed it with web members and he remodelled into this design. His next move was to sell his house and employ a professional design to turn his concept into a real buildable biplane fast cruising design which he was going to do.

The general concept was a fast cruising cat of 75 x 33.5 foot with a weight of 31,400 lbs. Great if he can achieve this weight but I suspect it may be more after the professional designer gets to work. The biplane rig has 2 free standing masts that are 90 foot above deck with about 2,000 square foot of sail per mast for a total of 4,000 square foot. We are talking serious carbon fibre masts here and a lot of sail for a light boat. The central underwing centreboard will be an engineering challenge but possible. The power is intended to be solar electric feeding into 72 KWH batteries from a 13 KWH solar array.

The best comparison I have is the 70 x 28 foot Chris White 2017 designed Saphira biplane catamaran weighs 34,000 lbs and carries 1,360 square foot of sail on each mast. Saphira is a 300 mile/day boat with 2 crew in moderate conditions. It has sailed thousands of miles and can validate its speed credentials. Its average speed on her several trips to Bermuda is 246 miles/day. Saphira was recently for sale at $3.6 million. Check Chris Whites website.

Back to the conceptual design. The layout is a minimalist boat for its size. The hulls contain berth cabins and toilets. A relatively short bridge deck cabin containing a galley, seating, table and internal helming position. There is a forward external sailing cockpit at the base of the mast and an aft cockpit. There is a solar array on the main cabin roof.

No mention of the structure but the engineering team and proposed designer are specialists in carbon fibre and foam glass construction.

I hope this gentleman understands the size of the task and the amount of money he will need to complete this cat. The jpegs give the idea.

 

"One item of your thought processes caught my attention in particular; your desire for a single centerboard, and real shallow draft capabilities. I'll certainly second that motion, that shallow draft idea. One of the greatest attributes of multihulls is their capability to really go exploring ALL the water areas including those tributaries, lagoons, reefs, etc. That's why I had kick-up CB's in each hull of my design.

BUT, what you may not have noticed was my alternative to the CB's in each hull. Look at the attached drawing, (or the very bottom profile drwg that denotes "asymmetrical CB's, nacelle mounted". First, imagine a flat plate, on edge, mounted down the centerline on the underside of the bridge deck. This flat plate will act as a rib to strengthen the fore-to-aft rigidity of the vessel, a somewhat weaker characteristic in a catamaran structure vs. a keeled monohull. If a tow bundle (rope, etc) of carbon fiber (kevlar, PBO, etc) was laid along the bottom edge of this flat plate, the rigidity could be even greater (sort of akin to a bottom truss structure, or a flange of an 'I' beam). Now on either side of this flat plate I propose to mount a centerboard, not a single, symmetrical one, but rather two asymmetrical ones; sort of like a single board split in half. The flat sides of these asymmetric boards would fit up against the flat plate nacelle, and rotate on oversize (possibly 1-foot) diameter bearings. The flat fit & big bearings would together supply a great big surface for the large bending moments to bear against. Only one board at a time would be lowered. In fact the two could be linked together such that the act of lifting one automatically lowers (& powers) the other down. And they both could be rigged to 'kick up' upon hitting any solid object and/or for shallow cruising. The control lines (cables) could be routed right up to the cabin top and back to the cockpit.

There are several advantages to an asymmetrical shaped centerboard. First, it requires less total board area to develop a leeway reducing force....so the board size is reduced. Secondly, since it is asymmetrical, it does not require an angle of attack (does not require the boat itself to be sailed at a skewed angle) to develop the 'board's lift' (leeway reducing force). This actually
may result in the vessel making less leeway. Plus the drag forces associated with the CB lift forces are on the centerline of the vessel, rather than off in one hull that produces turning moments about the center of the vessel.

This centerline mounting may also improve the tacking capabilities of the vessel as it allows the 'clean' hulls to slip a little while pivoting about the central board.

The front of this nacelle/plate could be configured to act as a wave splitter to actually attack, up front, the formation of those peaky waves under the tramp areas that eventually slap at our bridge deck underside. We kind of slice those waves down a bit. A lightweight fairing might also be added to this 'flat plate nacelle' so it appears outwardly much more esthetically pleasing, as well as more curvature to shed those peaky waves.

And how about the maintenance factor, particularly in remote cruising areas. No need to haul-out the vessel to repair kick-up CB problems, or even bottom painting problems. Everything, including the cables, bearings, and boards is all above the load waterline. The initial building cost should be less by eliminating the trunks in two hulls, and the watertight integrity is much
better. The twin boards might have to be made a little bit longer as they operate with a 'free-surface' end, but then they are asymmetric so they can be correspondingly shorter. I would further suggest that surplus helicopter blades are prime candidate sources for both CB blades and rudder blades....high tech, extremely strong carbon fiber fabrications that have a
prescribed limited life span aboard aircraft, but are perfectly happy for our use.

 

This is a plate alloy power catamaran that can be obtained in a kit form from Platealloy catamarans, an Australian company that provides a range of alloy monohull and catamaran kits. The design was done by Chris Tucker. The power cat has some accommodation for cruising but is more aimed at the fishing charter market.

The cat is 26.4 x 9.2 foot over the hull and 29.1 foot overall including the outboards. The “displacement” is 6,940 lbs. The V hull have an 11 degree deadrise at the sterns and a more V bow section for a softer ride. The draft over the hulls is 1.3 foot. The 2 outboard engines can be from 150 HP to 250 HP. The design complies to structural and charter rules in Australia.

The accommodation has a double berth forward with a toilet shower beside in one hull and cabin space in the other hull. Aft is the main saloon with a forward inside helming position then a galley to starboard and a dinette to port. The aft cockpit is roomy for fishing etc. There is 6 foot headroom throughout.

The structure is aluminum. The bottoms, chine, transom and stringers are 4 mm 5083 aluminum. The sides, deck and gunwales are also 4 mm 5083 aluminum. There are aluminum bulkheads sub frames and deck stringers etc. If you have the welding skills this would be a relatively easy boat to assemble.

The boat was designed to work in rougher coastal waters and can achieve 20 knot plus speeds with appropriate engines.

A good solid design that could make a nice cruiser. The jpegs give the idea.

 

The following is a 7.5 meter power cat that can be built from a kit done by Platealloy boats. The designer is Chris Tucker. This is a power catamaran with a large cockpit and a smaller helming cabin with some cooking/galley facilities. Forward is a small cabin with a toilet area and a double berth on the wing deck. The bridge deck cabin has 6 foot headroom. This is a boat for coastal work with the occasional overnight stay capability. The boat is trailable if you have a large SUV (3.5 tons or better) but this is a very large boat to tow.

The 7.5 is 24.6 x 8.2 foot (length over all including motors is 26.8 foot) with a weight of 6,272 lbs. The draft is 1.2 foot over the hull and 2.2 foot over the outboards. The power is two 100 to 200 HP outboards. There are two 250 litre fuel tanks with 150 litres of water.

The structure is aluminum. The bottoms, chine, transom and stringers are 5 mm 5083 aluminum. The sides, deck and gunwales are also 4 mm 5083 aluminum. There are aluminum bulkheads sub frames and deck stringers etc. Notice yesterdays8 meter power cat is larger and slightly heavier but had a 4 mm plate thickness in the bottoms, chines and stringers. Because this cat can be trailed the hull bottoms are slightly thicker to handle the additional road knocks.

No performance figures but again with appropriate power this could be a 20 knot boat. A 200 HP outboard can use 15 litres per hour so at a reasonably fast rate you have about 8 hours of fast cruising. The jpegs give an idea of the boat.

 

Pangeos is a proposed $8 billion terayacht designed to be the largest floating structure ever built, capable of accommodating up to 60,000 guests. Pangeos is an ambitious project designed by the Italian firm Lazzarini Design Studio, inspired by the ancient supercontinent Pangaea. The turtle shape is conceived to allow a maximum of apartments with excellent views.

The Pangeos is 1800 foot long x 2000 foot wide (yes, 1800 x 2000 foot) which will make it the largest floating structure in the world. Powered by nine 16,800 horsepower HTS engines, the Pangeos is expected to have a top speed of just five knots (5.7 miles per hour/9.2 kilometers per hour). This vessel will be very stable allowing the permanent and temporary guests enjoy the world at a leisurely pace with the ability to see new views every few days.

The accommodation includes on each side wing of Pangeos would be space for nineteen villas and sixty-nine apartments. Seventy-two terraces will be available on the rooftop shell. Some will have sea views whereas others will overlook the vessel’s central port area. This allows 60,000 guest and an unknown amount of crew to live. There are endless amounts water toys etc for fun. There is also several helicopter pads for people who need to get to an airport to get to places. There are all facilities aboard such as a hospital, dental facilities, shops, hair dressing etc to allow you to live a normal (if expensive) life.

The build will be unique. You need a square mile of land that is beside a water source. Then you build a dam wall and dig down to a greater depth than the draft of the vessel. Start your build in steel and many other materials and after spending $8 billion see if the vessel will float. First you open up one floodway to fill the dam see hope the vessel floats then proceed to open up a 2000 foot hole in the dam to allow the vessel to go to sea. The build is expected to start in 2025 and take 8 years to complete. Saudi Arabia is likely to provide the land for the build of Pangeos.

You want to get a part of this floating adventure all you have to do is be part of an NFT crowdfunding initiative that exists as part of a strategy to acquire funding. Backers can pay with cryptocurrency for virtual space on Pangeos within the metaverse. Hmm.

The jpegs give an idea.

 

Re Pangeos, I am very skeptical - it sounds like a very elaborate scam to me.

Even if they can find the land space to build it, how are they going to launch it - and then dry dock it, when routine maintenance is required?
I wonder if anybody has done any strength calculations re the longitudinal and transverse bending moments in a worst case scenario? I doubt it.

I am reminded of the Freedom Ship concept - I wonder how many punters lost money by investing in this?

 

Spirit design has a range of “Ripple” tenders ranging from 6.5 to 13.8 foot built in ply or composite. There is a production design that is very similar to the Ripple 4.2 being built in Russia in aluminum. The design was called the Raptor 4.2. A tender or a power catamaran for day use and EG fishing.

Designed specifically to suit aluminum construction, this is a planning hull with an expansive self-draining fishing deck. Commissioned for a client with a preference for aluminum. The recommended engine size is 30hp with estimated cruise speeds of 25 knots and a top of 30 knots. The design is based on the successful Ripple range with customisation to suit alloy.

The Raptor can be supplied as a laser-cut kit which includes folded hull sections. The folded aft hull sections are supplied ready to install and are cut with some of the forward hull panels as part of this section. This build system reduces the amount of build time and welding required.

This design was followed by the Viper 5, a 16.5 foot aluminum cat that was to be a plate alloy production power cats by a Queensland builder. The kit was refined to suit this medium with a high level of detail. Every detail has been CNC cut including hull drains, service routing, access hatches and all stiffeners. This centre console 16.5 foot cat is fully engineered to Iso standards and is rated for a 115hp single engine in a central engine pod.

Interesting power cats but I have not seen any tests of the cats. Spirit only show the composite construction cats on their web site but direct inquires may gain access to the kits or plans.

The first set of jpegs is the Russian Raptor. The white power cat is the Viper.

 

Someone read lots of Terry Prachet .

 

I like the looks of that bi-masted/ biplane cat design at posting # 4745 above,...
Multihull Structure Thoughts https://www.boatdesign.net/threads/multihull-structure-thoughts.62361/page-317#post-980414

 

Hi. I am having computer issues will be back soon.

 

I knew Lock, and on one occasion he visited the Annapolis Sailboat Show. I had him over to the house, and we discussed several multihull ideas. I was particularly enamored with his Tara Vana design. Here is an article I saved from Marlin Magazine,..
RunningTideYachts, Ltd. - Archives https://runningtideyachts.com/archives/TaraTour1.php

These discussion prompted me to design my version,...
Gamefishing Design - a 65' mast-aft sailing catamaran. https://runningtideyachts.com/gamefishing/

It was my thoughts that I make it extremely easy for any powerboat/gamefishing guy to understand HOW to use a sailing rig, and HOW to make it extremely easy and quick to rig and unrig this sailing rig,...my mainless, all-3-sails-furling was the answer. I'm still quite amazed I never found that adventurous client for this vessel?

I've been thinking about the virtues of such a vessel quite a bit lately, and I have some new ideas,...both for the rig, and.....??