Multihull Structure Thoughts

In reference to the ama post regarding Dick Newick's designs I'm guessing "pot bellied" refers to the keel rocker? The "pinched in" ends is also unclear. These boats have a very smooth, even progression in their shape as the photos show. The rocker of a keel profile does add lift as well. I talked with Dick regarding his alternative New Moon ama shapes which were designed for leeway resistance and he was reducing the amount of asymmetry because they found a smaller amount was effective. You can see the original shapes on Echo1, Limmershin and Tremolino etc ..
A neat test for designers is to tank test just the ama shapes, I towed a set of Jim Brown's Searunner 31 amas and was quite surprised by their tendency to vault when encountering wake. The shape gave lots of lift and contributes to the whole boat's lively motion. A rounded V is a more gentle ride, good for cruising. Amas don't really have a one size fits all design as intended use will call for different shapes.
In other observations in regards to dynamic hull lift planing is customarily spelled with one n. Using 2 results in displacement speed from the effort of lifting the unneeded letter.

 

Cavalier mk2. To put this is numeric terms. The prismatic coefficient of "pot bellied fine ended" hulls is in 0.55 region, modern full ended flat keeled floats have prismatic coefficients of 0.62 plus. Harryproa hulls have prismatic coefficients (PC) of 0.7. Big generalization. The higher the prismatic coefficient the faster the shape (there are models that match PC's to specific speed length ratio's). The reality is, hull shape, displacement length, stability and sail area is more of a factor but having a good PC helps.

Pot bellied means a lot of the displacement is in the middle of the hull with very little displacement in the ends. Pinched in ends mean fine or little displacement in the ends.

 

A short one on why professional designers go mad. This is what some people want and will build it because they cannot find a production boat to match there wants. Tiger is designed and built by shipwright Mal Hone in 2004. The cat is 28 x 16.3 foot. The displacement would be about 10,000 lbs. The rig is unknown beyond it being a masthead with a roller furling headsail. The draft is 1.4 foot. The rudders are kickup. It is powered by two 20 HP outboards resulting in 7 knots maximum and 5 knots cruise. This cat is more a motor sailor I expect.

The rational for this cat is 6 foot headroom. It has a dinette in the main cabin with a fridge, some bunks forward and a galley and toilet area in the hulls. The cockpit is large with an aft deck. In short accommodation overcame sailing performance.

The boat was built with ply and timber with the exterior covered with fiberglass and epoxy. The work looks good and the exterior finish has been done well.

I have no idea of performance, underwing clearance etc. The jpegs give the idea of the cat

 

Actually there are quite a few production cats like that around. Low bridgedeck clearance, narrow beam for marinas. Fortunately most are also underrigged. Awful sailboats but for charter or owners who mostly want the accommodations and shallow draft but motor most of the time I guess they fit a niche.

I was looking at a couple for sale a month or 2 ago. They sold surprisingly quickly. It astounds me that a boat like that (in glass) got similar money to a somewhat tired Chamberlin parralax 9, but horses for courses I suppose...

Nice to see another article on a smaller boat. I struggle to get interested in 40' plus monsters ..

 

Totally tubular man.
Good to have definitions for your descriptive terminology.

 

Re Tiger:
The idea behind this boat was an affordable comfortable local Whitsunday cruiser.
A roller headsail for when the wind was aft of the beam. Slow powerboat the rest of the time, not intended for long distance work.
Exactly what Mal Hone wanted for himself.
I used to see Tiger a lot, she was used and enjoyed. Mal made a habit of drying out at low tide off Catseye beach in front of the swanky Hamilton Island resort. When they tried to tell him to bugger off, he quoted the relevant law and stayed put.

Mal built his previous boat, Chica, not far from my place. A Seawind 24 extended to 26, with a little aerodynamic bridgedeck cabin containing an athwartship double. The additions were foam sandwich and very light and stiff.
The fellow who bought Chica years later sailed her home to Darwin in a reported 9 days with no problems.

 

The second 6 foot headroom, 25 foot catamaran, this one is designed to be a sailing cruiser of which at last 2 were built. “Cygnet” is 25 x 25 foot with a weight of 10,080 lbs. The aluminium mast is a 140 x 80 mm with 5 mm stainless steel rigging, but the mast head rig height and sail area are unknown but the rig has a mainsail and roller furler headsail. The draft is 1.5 foot with “centreboards” (no evidence of them or what depth they go) and retractable daggerboards rudders. The underwing clearance is about 1.4 foot. The power is a Yamaha 9.9 High Thrust four stroke, maximum speed is 6 knots and a cruise speed of 5.5 knots.

The accommodation is partially what this cat is about. There are 3 cabins and 3 fixed berths and a queen size fold down table in the main saloon. There is a toilet cabin. The galley is in a hull. This is a practical layout for a couple for an extended period.

The construction is foam glass hulls. Part of the decks are foam glass. The upper decks/cabins are ply timber covered with fiberglass. The underwing also appears to be ply covered with fiberglass. The main bulkheads are plywood. T Bowen (Australian) appears to be the designer and builder, at least a second one was built.

There is no performance indicated but this cat can really sail although I suspect windward performance may not be its best point. Again, a cat intended to provide good accommodation and reduced sailing performance but sufficient for an owner to have a good coastal cruise.

The jpegs give the idea.

 

The final on short full headroom cruising cats. Guzzi3 there are some production cats so I thought I would remind us of a few of them. The cats are examples of what is possible. The Heavenly Twins, not quite 6 foot headroom but vast accommodation for 26 foot. Summer Twins (original version) that is 25 foot and has big accommodation. Catalac 8 meter with a smaller 6 foot headroom but still with good accommodation. The 28 foot Smartcat S280 and finally Craig Schoinning Take Away 8.5 meter motor sailor.

Each of these cats have similar characteristics. Small underwing clearance, virtually full length bridgedecks, 6 foot headroom over part of the bridgedeck, mainly mast head rigs and narrower beams for there length except Summer Twins. The construction of the Catalac and Heavenly Twins in the majority of there production run had solid glass hulls with limited balsa coring above gunnel level. Low aspect ratio or no keels were on the Heavenly Twins, Catalac, Summer Twins, Smart Cat.

What does this all mean. Excellent accommodation for there lengths, heavy displacements for there length, not as good upwind for there lengths. Each one of these cats can sail and average 5 – 6 knots but their peaks are 15 knots down a good wave. Heavenly Twins have gone global, Catalac’s have crossed oceans, Summer Twins are ocean capable as is the Smartcat S280.

BUT all of these cats are not comfortable upwind in stronger wind and wave conditions. The Heavenly Twins has a short waterline and pitched a lot, the Summer Twins was an upgrade of the Heavely Twins by the same designer with longer waterline, more beam, better length to beam on the hulls and a bigger rig. The Summer Twins was meant to be faster and more comfortable. It pitched less but weighed virtually the same and pounded on its underwing just as much. The improved hull shape was offset by more weight than expected and aerodynamic drag from a bigger topside and more beam.

The Catalac had a unique hull shape with a very V forward section that worked to a degree but was not outstanding up wind and had relatively fat hulls. The Smartcat and Take Away have better hull shapes but the windage on both is relatively large. All these cats will sail OK downwind or reaching and do 50 degrees plus upwind in moderate conditions but it would be best to use engines or a sea anchor if your destination is directly upwind in strong conditions. If you are on a serious cruise, just wait until you have a good weather forecast. You have the accommodation to relax in and watch the scenery go by.

Translation. These cats prove Dick Newicks words. You can have any 2 of the following: speed, accommodation, cheap cost. Most of the above cats can be brought relatively cheaply and have good accommodation. But unfortunately, they will not have good all round sailing speed.

 

And just like magic here is one for sale;
Custom Built GRP Sailing Catamaran | Sail Boats | Gumtree Australia Moyne Area - Port Fairy | 1313551953 https://www.gumtree.com.au/s-ad/port-fairy/sail-boats/custom-built-grp-sailing-catamaran/1313551953

 

Described as a boat for the cruiser that enjoys sailing and intends to travel. Jim Antrim and associates designed a 46 foot cat initially for BAADS, a disabled sailing association group, then modified the design for long term cruisers. As there are no published figures except the length, most numbers are scaled from diagrams and calculated.

The cat Is 46 x 27.5 foot and weighs about 24,000 lbs. The fractional cutter rig carries a 57 foot standard mast or wing mast with a 600 square foot mainsail, a 390 square foot fore triangle with a 600 square foot genoa. The length to beam is 11.3 to 1. The draft varies from 3.8 foot over the rudders to 6.8 foot when the daggerboard is fully down. The underwing clearance is 2.7 foot. The engines are outboards but could be inboards.

The accommodation for the disabled version is basically designed to be a flat wingdeck with a large bridgedeck cabin with wide side doors for wheel chair access. The forward area “cockpit” is focussed on sail control and handling and the aft area is where the galley and a large disabled toilet is located. There is some additional space in the hulls but is not fully accessible to the disabled. The Blue Water Cruiser version which was designed later in 1997 with 2 double berth cabins and a single berth cabin in the hulls with a large toilet area. The main saloon has a large practical galley, a U shaped seating area and an internal helming navigation area. The cockpit is a practical size for sailing. This design is intended for sailing with accommodation, not an accommodation machine with some sailing ability. It is in Jim Artrim’s DNA to design excellent sailing yachts with useful accommodation.

The build is not specified but Jim does good foam glass designs mainly in his multihulls. The base design is good and could be adapted to any fast cruising concept that an owner may require. The hull perspective give an idea of a forward chine to provide additional buoyancy in the bows and a flat wide stern to helps minimise pitching. This is a relatively high prismatic coefficient hull that will provide a good combination of performance and sea keeping capability whilst carrying a cruising load.

An excellent design for a variety of roles by a very good designer. The jpegs give the idea, BAADS first.

 

Today we talk about ambition and versus environmental impact. The current Transatlantic powerboat record is held by a Danish flagged catamaran called "Cat-Link V" and in July 1998 covered the distance in two days, 20 hours and 9 minutes, at an average speed of 41.28 knots. This hull is 91.3m (300 foot) long, was propelled by four 34,000 hp diesels that propelled water jets. It is a big aluminium ferry that can carry a payload of 500 tons (800 passengers plus 200 cars).

A proposal has been put up for another cat designed by the Design Studio Levi ltd corporation to do a "100 metres-100 knots" catamaran that could try the record. The technical implications of this design are large. For the design they turned to Renato "Sonny" Levi and son developed a "ram wing" catamaran shape and structure. He did not bother to do the internal layout of 3000 square meters (about 30,000 square foot) and left that to others.

An Initial design study was done with a length of 82.5 meters x 29.7 meters and the internal volume of around 2,000 square meters. The power of 25,000 HP was enough to reach 50 knots and with 71,000 HP you can exceed 90 knots. After the initial design study they decided to to go for the 100 meter 100 knot concept.

The Levi 100 Ramwing dimensions are 100 x 35 meters (328 x 115 foot) with fully loaded displacement of 2000 tons (4,480,000 lbs yes 4 plus million lbs). The engines are 2 by 42MW (56,300 HP each gas turbines motor) and 2 by 4MW (each 1340 HP diesel engines). Result at 100 knots with all engines working 115,200 HP is pushing it along. Result of using the 400 tons of fuel required is at 100 knots you will go less than 2000 miles, at 50 knots you will go 2800 miles and using the diesels only in displacement mode at 12.5 knots your range is 4000 miles.

No details on the accommodation beyond the jpegs and the comment of three floors, with more than three thousand square meters of internal space Please notice the racing style seats in the cabins which would be required at 100 knots. Seatbelts may be an asset.

The build material is aluminum and a little foam glass. Again, a real problem in the structure is the interface between the rigid windows and the “flexible” aluminum hull structure. I suspect this is but one of the many design/build issues. Driving any boat at 100 knots into a seaway puts enormous point loadings on the forward sections even if there is a ram wing effect. Also, a unique problem is you cannot leave anything laying around on deck like EG a spare helicopter at 100 knots as it will probably be blown away.

All I can say if this is ever built Greta Tunberg will never cross the Atlantic on it. The jpegs give an idea.

 

One has to ask 'why'? The obscenity of humanity knows no bounds. I will stay at home and make do with my bicycle.

 

Today will be a short one from me but a long read for you. I was reading the Farrier group mail out’s and a tri named Thriller was mentioned. I followed up and found the following building blog F32R(s-) Thriller multi page boat building blog. The build started in 2011 and was completed but upgrades were still happening in 2023 to correct things like a hum in the daggerboard at 14 knots, but when you have a tri that can do a speed of 17.7 knots in a maximum of 20 knots wind speed with only a jib and main there is always a few issues.

So what is Thriller an all carbon fiber foam epoxy Farrier F32R. These could only be “home built” and had an 8.2 foot wide main hull. The F32R is 32.3 x 23 foot with a weight of 2800 lbs (f built in carbon) and a displacement of 5500 lbs. (this depends on specific model and build, the F32R has a short main cabin and larger cockpit). The 46 foot rotating carbon mast carries a sail area of 682 square foot in its main and jib (later models went to 48.8 foot masts and 775 square foot main and jibs). The draft over the hull is 1.5 foot and over the daggerboard is 5.9 foot. The outboard power can range from 10 HP to 20 HP. The main hull shape on the F32R is almost a flat bottom with a soft chine and the floats are full ended. This design is a performance orientated boat.

I will not go through the full blog but one feature will show you the intention of the builder. The marine toilet on this tri was full carbon fibre, yes he brought a standard marine head and then used it as mold for the carbon fibre version of a marine head. He was serious about reducing weight.

The blog is at: F32R(s;-) Thriller: 2023 http://f32thriller.blogspot.com/2023/

The head story is at: F32R(s;-) Thriller: March 2015 http://f32thriller.blogspot.com/2015/03/

This is a nice informative blog that will give a good insite into the issues of building a 30 foot plus tri. The jpegs are of the “standard” design and Thriller sailing.

 

I saw that when it listed the other day. I understand the rational behind the Heavenly Twins and Catalacs. They were built some time back before designs for cats were as well understood as they are now.

As I've said before for a given build method every kg of hull build costs the same, so instead of putting time and money into a huge bridgedeck cabin I'd invest that into bigger well designed hulls. Such a boat will be more expensive to berth in a marina but if you are actually going to sail the thing it will be better. More load capacity, good access forward, deck space for guests and you have about the same space in teh bigger hulls, and good seperation.

I would buy a heavenly twins at the right price, but every one I've ever seen for sale has been massively overpriced. Same with most of the old glass overseas cats. The older Australian/NZ designs are similar money and usually better sail boats.

Anyway...

 

Today is about a Transatlantic unmanned trimaran designed for research. The Mayflower Autonomous Research Ship (MARS) will use state-of-the-art wind and solar technology for its propulsion enabling an unlimited range. The revolutionary trimaran vessel will carry on board a variety of drones through which it will conduct experiments during its voyage. The project is being developed by a partnership of Plymouth University, autonomous craft specialists MSubs and Shuttleworth Design who did the Naval Architecture and engineering.

The trimaran is 106.6 x 55.1 foot of an unknown displacement (guess about 60,000 lbs) with a sail area of 1710 square foot in 2 mainsails in a schooner rig. The length to beam on the main hull is approximately 16.5 to 1. The draft is 3 foot over the keels and 6 foot over the rudder. The maximum speed under Electric Motoring is 12.5 knot. At 5 knots the range is unlimited. Maximum speed under sail is 20 knots.

The hull construction is Composite (Glass/Aramid/Foam) and the deck construction is Composite (Carbon/Nomex). The rig is free standing carbon fibre masts.

From here I will quote JSYD "A trimaran was chosen because it provides the most efficient hull form for low speed motoring. The hull configuration developed from a requirement to reduce windage, while keeping the solar array sufficiently high above the water to reduce wave impact. Without the need for accommodation, the centre hull has been kept low to the water and the wings and deck are separated and raised above on struts. This allows waves to break through the vessel and significantly reduces roll induced by wave impact. The outer hulls are designed to skim the water reducing resistance by 8%."

"The two masted soft sail rig will enable a top speed of around 20 knots. Each sail is simply controlled by a single sheet, and can furl into the boom and allow multiple reefing configurations for varying wind speeds. Stowing the sails while motoring reduces windage and eliminates shadows cast over the solar cells on the deck, while allowing the masts to stay standing to carry navigation lights."

"MARS will be a genuine world-first, and will operate as a research platform, conducting numerous scientific experiments during the course of its voyage. And it will be a test bed for new navigation software and alternative forms of power, incorporating huge advancements in solar, wave and sail technology. As the eyes of the world follow its progress, it will provide a live educational resource to students, a chance to watch, and maybe participate in history in the making."

"An Atlantic crossing could take as little as 7-10 days with optimal wind conditions but what's important is that it could take 7 - 10 months if we so choose, so that the ship could collect voluminous data for ongoing analysis by shore based teams of scientists and not worry about refuelling, or re-provisioning, or illness.....or loneliness. It is optimized to be AT-SEA supporting science, not racing across the Atlantic, however speed will be useful when the MARS needs to head to remote areas of the globe and again, collecting data all along the way!”

An interesting design, of which initial funding of the multi million British pound project has been provided by Plymouth University, MSubs, and the ProMare Foundation, and corporate and private sponsorship will be sought for ongoing support. Lets hope it gets up as we will learn a lot.