swath vs catamaran

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• ship motions
• small waterplane
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• small waterplane area twin hull

Figure 3-1: Control Fins on Bow of SWATH

Smooth Sailing: Pros and Cons of a SWATH Vessel

Welcome to luxury cruising.  Glide above the waves without any jerky motions.  Walk about your accommodation deck, unhampered by nasty rolling motions.  If this temps you, come realize the dream of the SWATH vessel.  But it comes at a price.  Discover if this unique vessel is right for you.

1.0 What is a SWATH?

SWATH stands for Small Waterplane Area Twin Hull.  Naval architects searched for a way to minimize the seakeeping motions of a catamaran.  They liked the large deck area, but those pesky waves were a problem, bouncing the ship around.  The designers noticed that the forces from those waves depended on the width of the hulls.  More specifically, the waterplane area. (Figure 1‑1)

The designers shrunk the waterplane area until it was a small strut, just wide enough to fit a crew member down.  All the buoyancy got concentrated into deep submerged hulls, which looked more like a submarine hull.  And the SWATH was born:  a vessel with excellent seakeeping because waves exert very little force on it. (Figure 1‑2)  The force of the waves depends mainly on the waterplane area.  Small waterplane meant small wave actions.

2.0 Advantages

SWATHS are specialized ships with one major goal:  excellent seakeeping capability.  SWATH ships have the same massive deck area of a catamaran, with far superior seakeeping capabilities.  In Figure 2‑1, compare the motions of the monohull in the foreground to the SWATH in the background.

Figure 2‑1:  Comparison Between SWATH and Conventional Ship

These reduced ship motions are a major benefit to the crew.  In the cases of research ships, the crew may not be seasoned seafarers.  They get seasick easily; so reduced ship motions help improve crew productivity.  Even experienced seafarers appreciate the smooth gliding motion of a SWATH vessel. No more rocking around.  Just gentle swells as the ship gradually rises and slides along the waves.

When comparing a SWATH to your current monohull, be sure to clearly identify the type of motion that bothers you.  If you feel the ship jerking from side to side and knocking you around, a SWATH may not be the best option.  The side to side jerking comes from roll accelerations, which is just one small part of the total ship motions.  We have retrofit options to reduce the roll accelerations, and these retrofits are far less expensive than a new SWATH.  On the other hand, if you are more concerned about total ship motions or see a lot of pitch motion, then a SWATH is probably the best way to go.

3.0 Disadvantages

The excellent seakeeping of a SWATH comes at a price.  First, a SWATH may be too insensitive to the waves.  Imagine that.  The wave crest swells up, rising higher and higher, but the SWATH does nothing.  That is, until the wave slams into the underside of your cross deck.  Then you get woken to a jarring bang followed by violet pitch motions.

To avoid waves hitting the cross deck, SWATH ships are often equipped with active or passive control fins.  These are small underwater versions of airplane wings. (Figure 3‑1)  They help the ship react to the oncoming waves and make sure the vessel still tracks along the larger swells.

Passive control fins are not a major cost.  They are the equivalent of adding a skeg to the vessel.  But active control fins require hydraulic machinery, motion sensors, and a control unit.  That makes a big price tag.  But all that machinery contributes to the magical smooth ride that a SWATH delivers.

SWATHS are also extremely weight sensitive.  With such slender hulls, SWATH ships sink down quickly as you add a few extra tonnes.  Looking at Figure 3‑1, you notice that the SWATH maintains a large air gap between the waterline and the cross deck.  The waves wash harmlessly in this air gap.  That is how it should work, unless you put too much weight on the ship.  Discipline over your deadweight is key.  The engineer can’t store 15 spare filters onboard.  Too much weight.  Any ship spares quickly reduce your mission weight capacity.  SWATH ships show minimal flexibility in their cargo capacity.

Speaking of weight, you will need to arrange the major ship machinery differently.  Those submerged hulls rarely have enough space for a full engine room.  The main engines typically get mounted on the main deck, which is great for maintenance.  But they require complex shafting or a diesel-electric arrangement to deliver that power to the propellers in the hull.  Not all of your main deck space goes to the mission.  Many of the spaces typically found in the lower decks now occupy your mission deck.  Arrangements on a SWATH get creative.

4.0 Applications

The seakeeping advantages of a SWATH make it valuable to many owners, despite the design challenges.  Common applications for SWATH include:

• Research vessels
• Pilot vessels / crew transport
• Semi-submersible drill ships

Research vessels are some of the most frequent SWATH subscribers.  A boat full of scientists and grad students who rarely frequent the sea.  They will thank you for the days without seasickness.  But even better, they love you when the weather gets bad and you can remain on station; continue the mission.  Due to their reduced motions, SWATH ships remain effective at higher sea states.

The stable ship and wide cross deck make SWATH ships perfect as a launching and support platform.  Plenty of deck space to mount new scientific equipment.  And a very reliable platform to deploy instruments into the sea.  SWATH ships are great for subsea operations and survey vessels.

Land lubbers aren’t the only ones who love a smooth ride.  Many pilot boats also enjoy a SWATH.  You find great reassurance in the safety of the stable platform before jumping over to the inbound freighter.  And the improved ride allows the SWATH to drive much faster.  Arrive at your freighter in short time, unfatigued from the ride.

Don’t assume that the SWATH hull only works for small ships.  Some of the largest SWATH vessels are used in the offshore oil industry, called semi-submersibles. (Figure 4‑2)  These huge ships can travel out to a drill site and ballast down with their lower hulls fully submerged.  Just four columns breach the water to connect with the cross deck.  The SWATH hullform creates a nearly motionless platform that allows excellent working conditions as they drill the wells.  Combined with dynamic positioning technology, the SWATH turns a semi-submersible into a movable piece of land.  These giants carry hundreds of tonnes in drill pipe, drilling mud, and related machinery.  They stand as testament that the SWATH ship is no child’s toy.

5.0 Conclusion

When you think about SWATH ships, remember seakeeping.  Imagine gliding gently over waves, placidly sipping your tea.  While the nearby monohull bounces around like a cork.  That serenity is what SWATH ships deliver.  It comes at the price of several new design challenges.  But for the right mission, a SWATH is worth it.

6.0 References

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What is a SWATH Ship?

A SWATH ship is the abbreviated form of the word ‘Small Waterplane Area Twin Hull’ ship. Swath ships are designed in such a way that they have two or dual hulls instead of the conventional single hull. Technically, a swath ship is a type of a catamaran.

The two hulls of the swath ship are built so as to offer the maximum amount of balance or buoyancy to the ship. The placement of the hull is such that it rests under the water surface, making it safer and easier for the ship to sail when high tides and fast currents hit with full force. Whereas in single hull ships or boats, the hull floats above the surface of the water which makes the sailing difficult especially during unpredictable and rough seas.

The position of the hull under the surface of the water is also sometimes referred to being ‘submarine submerged’ as the technology looks similar to a submarine moving under the water. Along with the factor of buoyancy, a swath vessel is also known for its speed.  Another feature and advantage of a swath vessel over the traditional ships is that it offers a bigger and wider area than the conventional types of ships .

Swath ships are used as both – cruise as well as cargo ships and are also used as army and research vessels. The swath ship was first created by Fredrick G. Creed, a Canadian, in the year 1938. The patent for the same was obtained in the year 1946 in Great Britain. The vessel, however, was utilised for the first time in the shipping industry only in the 60s and 70s.The first swath ship was used as a research vehicle than as a transporting vessel across the water.

Some of the swath ships that are in operation today include the Cloud X which acts as a ferry between the Bahamas and Florida and the USNS Impeccable – a US marine surveillance vessel.

One of the main disadvantages of swath ships is that the two hull build of the ship makes it far more power and energy consuming than the single hull variety ships. Because of this, another disadvantage of the ship also appears regarding the overall expenditure involved in the construction and energy supply of the swath ships. The energy required to be spent on a swath vessel is eight times or 80% more than the energy spent on a ship with a single hull.

In their own way, swath ships have revolutionised water transport. In spite of their faults, they have been a very unique presence and will continue to do so in the days to come.

If you liked this you may also like Stealth ship & Expedition ship.

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SWATH, The Art Of Compromise

That truism has not changed, but it is clear that not all small ships in big waves are SWATHs today, and so how can that statement be true?

The truth of the statement is related to the disconnect between physics and design. Anything can be most efficient for any one condition, but that does not mean that it will be most efficient once it is turned into a real life object.

SWATHs are the poster child for this disconnect. While, for its size, a SWATH hull will have the best motion in waves, it does not necessary result in the most efficient overall vessel. The SWATH design is inherently expensive to build, has lots of wetted hull surface (which results in high drag at high speed), has limited payload capacity, tends to have deeper draft and is incredibly weight sensitive. Its inherent limited payload capacity limits SWATH applications to small vessels that do not carry high weight cargoes. That still leaves a large group of possible uses such as long duration slow speed patrol vessels, station vessels, crew delivery vessels, small offshore passenger excursion vessels and offshore helicopter support vessels. Still the number of successfully operating SWATHs is small. While the concept may be right, the execution often is left wanting. Almost invariably the problem starts with poor weight control during design and construction, and, once the design ends up on the overweight side, thing tend to fall apart. In addition, propulsion systems can be very complex, and the structural design and hydrodynamic design is often quite complex. Furthermore, once the vessel moves at speed it often requires additional ride control surfaces and technology.

Once in service, a SWATH tends to require more maintenance than less wave capable vessels of equal capacity and once the vessel makes any speed at all, fuel consumption becomes a problem.

Historically these design and operational problems could be a serious deterrent for SWATH vessel purchase, but there have been positive developments. Today there are propulsion solutions, such as electric propulsion, that can almost be described as off the shelf and that actually would be a joy to operate with generator engines placed in nice deck engine rooms, and the drive train (requiring very little maintenance) placed deep inside the submerged hulls. Ride control packages have become so much less expensive that these systems can almost become a trivial consideration. As a whole, despite the very limited successes in the past, today a clean sheet SWATH design should always be considered as an alternative when there is a need for a small low payload vessel in big waves.

As a young engineer I tested this concept and at the time there were serious issues that would be difficult to solve with the technologies of the day. (Mostly it would require very complex structure and control surfaces) Today there are viable solutions to the these problems, (composite struts, and cheap control systems) although it is not clear if a Monoform would make a good ship, mostly because the narrow below water hull, the angled struts and the wide deck are a berthing nightmare.

However, it is an intriguing concept and I particularly like the variation that I was toying with that has only three struts.

Regardless, while a Monoform may have advantages over a classic SWATH, at speed in modest waves, a catamaran will beat a SWATH anytime in overall efficiency. However, an all SWATH approach, or an all catamaran approach, may not be the answer.

At the last SNAME annual meeting, I attended a paper presentation by Dr. Stephano Brizzolara called “Comparative Performance of Optimum High Speed SWATH and semi-SWATH in Calm Water and Waves”. Here the SWATH concept is morphed into a very complex catamaran shape, which thereby trades wetted surface off against somewhat reduced performance in waves. Some pictures of this hull and a comparable SWATH shape as shown in the paper are provided below.

• Chris Law (7)
• David Del Corso (1)
• David Tantrum (15)
• Hannah van Hemmen (11)
• James Kline (1)
• Kyle Antonini (2)
• Marianne Herrick (2)
• Michael Raftery (8)
• Rik van Hemmen (255)
• Tomer Chen (9)
• Wayne Thomas (3)

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Are Swath platforms the ideal superyacht design?

The design of a SWATH is as extraordinary as its initials imply and may not mean much to you even when spelt out: Small Waterplane Area Twin Hull. But it could be the next design phenomenon to be taken up by clients who seek ever-increasing comfort and volume for their homes on the sea – a new style of expedition vessel, if you like.

The evidence comes from discussions with Till von Krause of Abeking & Rasmussen (A&R), which builds SWATHs for commercial applications, and Andrew Langton of Reymond Langton Design. Together they have been working on developing a 62m SWATH with interior volumes equivalent to that of an 80m monohull, for clients whose demands include travel in extreme comfort, staying at anchor on a stable platform in almost any weather conditions, use of an on-board helipad for guests and limousine tenders for ship-to-shore transfers.

To give you some idea of what a private SWATH looks like we take you back to an article on the 41m Silver Cloud (Boat International, April 2009) the first to be built at A&R for her American owners Alex and Renate Dreyfoos. They say it causes quite a stir wherever she goes. In just two years they have covered thousands of sea miles on board, encountering some nasty weather systems along the way that would normally have kept them in port – but such is the construction of these vessels that weather patterns are no longer a problem.

Extraordinarily, before the couple took delivery of Silver Cloud they were in danger of having to hang up their logbook and abort adventurous plans because of the oldest on-board affliction: seasickness. Even zero speed stabilisers on their previous yachts did not give enough stability in a swell and it soon became apparent that a monohull, however well-built, was not going to work. Alex Dreyfoos used his engineering skills alongside the expertise of A&R, and the result is a perfect cruising vessel for all weathers – and such is its stability that seasickness is no longer an issue.

What is a SWATH?

SWATH is an innovative hull concept for smooth service in rough seas. The idea was taken from the principle of semi-submersible offshore rigs, designed to provide a working platform with minimised motion in open sea.

The origins of a SWATH concept date back to the early 20th century but it was 1946 before a Canadian, Frederick Creed, was able to take out a British patent on his version. The US Navy became interested and carried out extensive design and test work in Hawaii, from which Dr Tom Lang obtained a patent for a Swath with additional stabilising fins. Just as importantly, the navy put a massive effort into design software, which later became available to purchase.

‘Without computer-aided design, a practical SWATH would hardly be possible,’ explains A&R’s technical director, Dr Klaas Spethmann.

The buoyancy of a SWATH ship is provided by its submerged torpedo-like bodies, connected by single or twin struts to the upper platform. The cross-section at sea surface level is minimised so very little of the vessel is exposed to the lifting forces of the waves. Abeking & Rasmussen has developed SWATH technology over the past 15 years, on the back of its long-standing experience in hydrodynamics, lightweight construction, special materials and leading-edge ship design.

With the know-how gained from full-scale service data of reference ships and special software tools A&R is now in a position to design and deliver SWATH ships under the brand name Swath@A&R.

The new generation

With the demands from potential clients for designers to provide ever-increasing volumes for guests, technical spaces and crew aboard superyachts it made sense to look at how these vessels can be adapted even further to deliver unsurpassed luxury living to include the integration of such items as a helicopter, submarine and toys carried on board, instead of using a mothership.

Some sceptics will disagree, of course: the design of the commercial SWATH is less than pretty, with a cumbersome Lego-like structure atop a flat base, mounted on what looks like a submarine-type structure to each side of a very prominent girth. It spans almost the same width as the length, with struts to hold the ship above the waves.

So why go for a SWATH? The keys are volume and stability, and for those that get seasick, it’s a revelation. We went aboard a 50m SWATH vessel at Cuxhaven in Germany that is used as a floating hotel for pilots working out at sea; she stays offshore 365 days a year. The technical spaces are incredible, cavernous even. The torpedo-style bulbs attached to the platform can swallow up to four engines (diesel electric propulsion gives the choice of operating at a greater range of speeds), generators, complete crew areas, storage spaces with incredible headroom, and because they are separate from the living quarters, vibration can be significantly reduced compared to a monohull.

The motionless ride is due to the fact that the vessel has almost no waterplane area that can be lifted by a wave. It gives the vessel horizontal stability in some of the worst weather, keeping it riding the seas with near zero roll and a very slow pitching motion over large waves.

Andrew Langton has been fascinated by alternative watercraft such as hydrofoils, cats, trimarans, and SWATHs since his university days, so when von Krause asked him to develop a SWATH superyacht, he jumped at the chance.

‘The SWATH concept is a huge platform that enables us to create just about any form of superstructure we like; the only limits are the overall weight of the vessel and the distribution of that weight,’ he says. ‘A&R gave us freedom to come up with a new concept. The buoyancy of the SWATH is set out in such a way that we need to have the superstructure much further forward than on a monohull. Our concept for the SWATH was to create the volume of an 80m-plus yacht inside a 62m vessel; the layout of the interior spaces had to be considered at the same time we were creating the exterior look.

‘As this vessel is radically different from a monohull superyacht, a different look was more appropriate than to make it look like a conventional yacht. The front of the superstructure is almost vertical and almost entirely glass, giving the accommodation panoramic, unobstructed views of the ocean, with floor to ceiling windows and access to private terraces for the owner and guests. From this very strong design aesthetic the superstructure tapers dramatically aft, which eliminates the boxy look of the commercial vessels and helps limit the weight distribution.

‘As the SWATH has effectively four hulls – a pair of submerged torpedo tubes and the struts penetrating the water surface – this gives you the feeling of flying above the water.

‘We integrated the huge platform into the superstructure to make the vessel look like one form, whereas the commercial Swath looks like a platform with a house on top.’

The volume Langton has created is so much more than on a large yacht, so had to be approached differently. Considering the rooms in a large monohull, Langton arranged them over four decks, keeping the stairways and lifts in the centre. One important area is the private owner’s deck with panoramic views and terraces all around.

The guest accommodation is designed looking forward with views to the sea, with the living spaces toward the aft decks. The huge windowless void underneath a commercial SWATH has been turned into a cinema, gym and spa area with sections of glass flooring .

‘The design connotations are endless,’ continues Langton, ‘with the only limit being weight. You can think out of the box with a SWATH and get creative.

‘We were already thinking about an observation room in the front of the torpedo hull, glass floor sections between the hulls, a helicopter pad , and we have planned a beach platform that drops from the main deck aft to the sea with a connecting staircase. It is even possible to integrate a paddle tennis court on main deck…

‘The most challenging part of the design is that the platform of the SWATH is a huge ungainly rectangle and we had to work around this to create a form that would pass as a superyacht and not look like a box.

‘The incredible beam also means that a fully certified helipad is easily achieved. Landing a helicopter is safer as the SWATH will not be rolling around like a monohull can do.

‘The main tenders are located on a lower section of the main deck aft. They are launched overboard to the stern by an overhead ‘A’ frame davit/crane integrated into the styling of the superstructure. The tenders can be launched and retrieved very quickly and safely even on the move – even with guests on board if they are feeling brave!’

The superstructure is radically different from Silver Cloud’s clean and simple lines. Langton felt he could more radical in his design of Abeking and Rasmussen’s private SWATH because there are no real limits. With his creativity, a blank canvas and ideas of what prospective clients want, he concludes, ‘You have to recognise this vessel as a superyacht, whilst appearing refreshingly different to conventional yachts.’

The one burning question is how much it costs to build a SWATH compared to a monohull superyacht. Till von Krause has an answer: ‘If you look at the comparable volume, it is about 10 per cent more than a monohull, but the interior is very similar.’

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Small waterplane area twin hull (SWATH)

In 1999, the German pilots started to work with two 25m SWATH pilot tenders, followed by a 50m SWATH pilot station ship ELBE built in 2000 by the German shipyard Abeking & Rasmussen. Both the station ship and the pilot tenders have excellent seakeeping performance and manoeuvring capabilities. During adverse weather conditions, the pilot transfer service can continue even at a waveheight of 3.5m (wind force 10-11). See also SWATH research vessel PLANET .  Useful website:  www.abeking.com

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Advantages of swath hull.

Article about the SWATH Hull

SWATH hulls, or Small Waterplane Area Twin Hulls, are a type of catamaran design that aims to reduce the hull cross section area at the sea surface, where most of the wave energy is located. By minimizing the ship's volume near the waterline, SWATH hulls can achieve lower wave resistance and higher stability than conventional monohulls or catamarans, especially in high seas and at high speeds. The main features of SWATH hulls are two submerged hulls connected by thin struts to a platform above the water. The submerged hulls have a large displacement and a small waterplane area, which means they have a low vertical center of gravity and a high metacentric height. The platform provides a large deck area and a high freeboard, which means it has a high vertical center of buoyancy and a low metacentric radius. The combination of these factors results in a low natural frequency of heave and pitch motions, which reduces the ship's response to waves and improves the comfort and safety of passengers and crew.

However, SWATH hulls also have some disadvantages and challenges compared to other hull forms. First, they have higher surface drag than conventional catamarans due to the increased wetted surface area of the submerged hulls. This means they require more power to achieve the same speed and have lower fuel efficiency. Second, they have a deeper draft than conventional catamarans due to the length of the struts. This limits their operability in shallow waters and increases their vulnerability to underwater hazards. Third, they have a complex structural design due to the bending and torsional stresses on the struts and the platform. This increases the construction and maintenance costs and requires sophisticated control systems to ensure stability and maneuverability. Fourth, they are sensitive to changes in payload and trim, which affect their draught and waterplane area. This means they need to adjust their ballast or speed to maintain optimal performance. One of the main challenges of controlling a SWATH ship is to avoid excessive pitch motions that can affect its performance and safety. To achieve this, SWATH ships are often equipped with control fins that are mounted on the inner sides of both hulls near the bow. These fins are small underwater wings that can generate lift forces by changing their angle of attack according to the oncoming waves. By adjusting the fins in a coordinated way, the ship can counteract the wave-induced pitch moments and maintain a level trim. The control of the fins can be done by using feedback sensors that measure the ship's motion and wave characteristics, and applying a suitable control algorithm that determines the optimal fin angles. There are two types of control fins: active and passive. Active fins are powered by hydraulic or electric actuators that can move them in response to a control signal from a computer or a human operator. Passive fins are not powered but rely on hydrodynamic forces or springs to move them in response to the ship's motion or wave pressure. The difference between active and passive control fins is that active fins can provide more precise and effective control of the ship's pitch, but they also require more energy, maintenance, and complexity than passive fins. Passive fins can provide some degree of pitch stabilization without any external power source, but they also have limited control authority, performance, and reliability than active fins. The choice between active and passive control fins depends on factors such as the ship's size, speed, mission, cost, and availability. SWATH hulls are an innovative hull form that offers superior seakeeping and deck space for certain applications, such as oceanographic research vessels, pilot tenders, yachts, and cruise ships. However, they also have some drawbacks and limitations that need to be considered and addressed in their design and operation. SWATH hulls are not suitable for all types of ships or sea conditions, but they are an interesting alternative for those who seek a smooth ride on rough waters.

Small-waterplane-area twin hull

A small waterplane area twin hull , better known by the acronym SWATH , is a catamaran design that minimizes hull cross section area at the sea's surface. Minimizing the ship's volume near the surface area of the sea , where wave energy is located, minimizes a vessel's response to sea state, even in high seas and at high speeds. The bulk of the displacement necessary to keep the ship afloat is located beneath the waves, where it is less affected by wave action. Wave excitation drops exponentially as depth increases, so wave action normally does not affect a submerged submarine at all. Placing the majority of a ship's displacement under the waves is similar in concept to creating a ship that rides atop twin submarines.

The twin-hull design provides a stable platform and large, broad decks. Compared with conventional catamarans, SWATH vessels have more surface drag, but less wave drag. They are less susceptible to wave motion but more sensitive to payload, which affects draught. Additionally, SWATH vessels cannot operate in planing or semi-planing modes and thus gain no drag reduction when operating at speeds normally associated with such modes. They require a complex control system, have a deeper draft , and have higher maintenance requirements. The design of SWATH vessels is also considerably more complex due to the structural complexities inherent to the design.

The SWATH form was invented by Canadian Frederick G. Creed , who presented his idea in 1938, and was later awarded a British patent for it in 1946. The first full-scale SWATH vessel to be built and put into service was MV Duplus , a diving support vessel built in the Netherlands in 1968. In the 1970s, several units were built in different countries (including the RV Kaimalino by the US Navy, and an 80 ft (24 m) ferry in Japan). Since the 1980s, oceanographic research vessels , pilot tenders, yachts and other craft are more routinely being built with the SWATH hull type.

Specific examples

• Duplus (1969): oil industry support ship, the first SWATH ship built
• Sea Shadow (1984): US Navy experimental stealth ship
• CCGS  Frederick G. Creed (1988): Canadian Coast Guard survey ship
• USNS  Victorious  (T-AGOS-19) (1988): lead ship of class of four US Navy surveillance ships that use a SURTASS
• RV Kaiyo  [ jp ] (1985):research vessel operated by the Japan Agency for Marine-Earth Science and Technology
• Hibiki -class ocean surveillance ships , (1991): three patrol vessels operated by the Japan Maritime Self-Defense Force
• MV  China Star (ex- Radisson Diamond ) (1992): cruise ship , largest SWATH when built, displaces 20,000 t (20,000 long tons; 22,000 short tons)
• RV  Western Flyer (1996): Monterey Bay Aquarium Research Institute mothership for the research ROV Doc Ricketts
• HSS 1500 (1996): class of three Finnish high speed ferries withdrawn after a decade due to high fuel consumption
• USNS  Impeccable  (T-AGOS-23) (2001): US Navy ocean surveillance ship that uses a SURTASS, additional ships cancelled
• RV  Kilo Moana  (T-AGOR-26) (2001), University of Hawaii oceanographic research vessel
• Planet (2005): German Navy weapons and sonar research ship
• Sea Fighter (2005): US Navy experimental littoral combat ship
• Silver Cloud (2008): 41 m (135 ft) private yacht
• NOAAS Ferdinand R. Hassler (2009), a NOAA hydrographic survey vessel
• Type 639 oceanographic surveillance ship (2009): class of six vessels for the Chinese Navy
• M/V Susitna (2010): ice-capable convertible SWATH/barge
• Ghost (2011): experimental super-cavitating stealth ship
• Skrunda-class patrol boat (2011): class of five 26 m (85 ft) patrol vessels
• Iranian high-aspect-ratio twin-hull vessels
• Multihull  – Ship or boat with more than one hull
• M80 Stiletto  – Prototype naval stealth vessel
• Catamaran  – Watercraft with two parallel hulls of equal size
• Sea Slice  – Experimental SWATH vessel, an experimental US Navy ship with multiple SWATH hulls.
• Semi-submersible  – type of vessel which can partially submerge Pages displaying wikidata descriptions as a fallback
• Trimaran  – Multihull boat
• Wave-piercing hull  – Hull with fine bow with reduced reserve buoyancy
• ^ Misra, Suresh Chandra (2015). Design Principles of Ships and Marine Structures . CRC Press. p. 474. ISBN   9781482254471 .
• ^ Busch, Ian Richard (1990), On the Cost Effectivelness of Large Commercial SWATH Vessels , Cambridge: Massachusetts Institute of Technology, Department of Ocean Engineering, p. 418
• ^ "Boele-Bolnes launch twin-hull craft for offshore work". Holland Shipbuilding . 17 (9): 58. 1968.
• ^ LaPuzza, Tom (March 2005). "SSC San Diego Command History Calendar Year 2004" (PDF) . United States Navy SSC SAN DIEGO. Archived (PDF) from the original on February 28, 2017.
• ^ Arps, Jan L. (May 1973). "The Role of the Semi-Submersible Work Vessel In Offshore Production Operations". Fifth Annual Offshore Technology Conference . Offshore Technology Conference. doi : 10.4043/1867-MS . ISBN   978-1-55563-659-3 .
• ^ "AOS Hibiki Class" . GlobalSecurity.org . Archived from the original on September 5, 2009.

External links

• Small waterplane area twin hull vessels

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The Small Waterplane Area Twin Hull (SWATH) is a hull form used for vessels that require a ship of a certain size to handle in rough seas as well as a much larger vessel. An added benefit is a high proportion of deck area for their displacement — in other words, large without being heavy. The SWATH form was invented by Canadian Frederick G. Creed, who presented his idea in 1938 and was later awarded a British patent for it in 1946. It was first used in the 1960s and 1970s as an evolution of catamaran design for use as oceanographic research vessels or submarine rescue ships.

Catamarans provide large, broad decks, but have much higher water resistance than monohulls of comparable size. To reduce some of that resistance (the part that generates waves), as much displacement volume as possible is moved to the lower hull and the waterline cross-section is narrowed sharply, creating the distinctive pair of bulbous hulls below the waterline and the narrow struts supporting the upper hull. This design means that the ship's floatation runs mostly under the waves, like a submarine (the smooth ride of a sub was the inspiration for the design). The result is that a fairly small ship can run very steady in rough seas. A 50-meter ship can operate at near full power in nearly any direction in waves as high as 12 meters

The S.W.A.T.H. theory was further developed by Dr Thomas G. Lang, inventor of improvements to the semi-submerged ship (S3) in about 1968.  Basically, a SWATH vessel consists of two parallel torpedo like hulls attached to which are two or more streamlined struts which pierce the water surface and support an above water platform.  The US Navy commissioned the construction of a SWATH ship called the 'Kaimalino' to prove the theory as part of their ship research programme.  The Kaimalino has been operating successfully in the rough seas off the Hawaiian islands since 1975.

'Chubasco' - built in 1986 by Ocean Systems Research Ltd - marine grade aluminium

Swath designs are more expensive to produce than conventional twin hulled vessels.  The advantage to such a design is that a significant proportion of the hull remains below the surface of the sea.  For this reason wave contact is reduced where it may only act on the thin leg areas.  Wave drag is a major component of the total drag on a vessels hull.  For this reason the hull is more stable, being less prone to pitching and rolling and requires less power for propulsion than conventional designs.    

A Swath design wastes proportionally less energy climbing wave peaks and accelerating down troughs.  The passage is smoother.  The below surface hull (in normal operating conditions) is subject to laminar (or pipe) friction, which is more predictable.  The SSC Radisson Diamond is an example of a commercial ocean liner claiming to offer unrivaled cruise comfort.  Click here for more information SWATH hull design   Deck plans .

SWATH TECHNOLOGY FOR DIVING PLATFORM

The Nekton Pilot shown below, utilizes Small Waterplane Area Twin Hull technology to provide the smoothest ride for a small vessel. Why is a SWATH vessel so stable? The key is the two submarine pontoons that can ride completely submerged beneath the surface of the water (unlike a catamaran where the pontoons only ride on the surface of the water.) If you are a diver, you would recognise that even on a rough day, the water is calmer just a few feet below the choppy surface.  That is precisely where the pontoons which provide the buoyancy for a SWATH  are located, hence the submerged pontoons act as stabilizers giving you the feeling you're on a vessel up to eight times its size!

The Nekton Pilot is the 32nd SWATH in the world and the only SWATH designed and engineered from the ground up specifically for scuba divers. The Nekton Pilot measures 78 feet (25 meters) long and 40 feet (12 meters) wide. Propulsion is provided by two large diesel engines located down aft in the pontoons thus isolating the guest area from noise and vibration and providing for more space. Electrical power is provided by redundant diesel auxiliary engines.

Nekton Pilot SWATH diving boat

The pontoons contain ballast tanks which can be flooded with seawater and pumped out by huge pumps in very short notice.  Ballasting up (catamaran mode) allows for shallow water harborage (6 feet / 1.8 meters) and maximum speed. Ballasting down ( SWATH mode) provides for maximum stability.  The entire dive platform raises and lowers via hydraulic lifts. The Nekton Pilot has modern instrumentation and communications including an Inmarsat gyro-stabilized satellite station with voice, fax and Internet access; dual GPS navigation; RADAR; real-time weather data; EPIRB; high-seas SSB short-wave and VHF radios; and cellular telephone. The Nekton Pilot also has an onboard Pentium class PC with USB, SCSI Zip Drive, Nikon Super Coolscan 2000 hi-res 35mm slide scanner, and Color printer.  Internet Email connectivity is possible via satellite.  This PC is also capable of uploading dive computer logs via RS-232 interfaces.

Telephone via calls via satellite can be placed anytime while onboard via pre-paid satellite calling cards which can be purchased onboard.

http://www.global-travel.co.uk/swath.htm

The SWATH (Small Waterplane Area Twin Hull) design is not a new concept in naval engineering, but it is relatively untested. It resolves or reduces many issues that plague other surface hull designs such as monohulls and catamarans, which suffer from uncontrolled pitch, roll, and or heaving.

The submerged hull design, small waterplane area, and high mass to dampening ratio leads to stability in theory. These characteristics make SWATH a candidate for autonomous scientific development platforms and an investigation into the feasibility of utilizing this technology. For example, bathymetry data is important because it allows scientists of many different fields to analyze ecosystems, habitats, and geological compositions and anomalies. It is currently difficult to collect this data in shallow regions which are prone to tides, high currents, and wave motion. 

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Six Amazing Boat Hull Designs

• By Dean Travis Clarke
• Updated: October 25, 2016

The American boating consumer bears a remarkable psychological profile when it comes to wants and needs.

A cursory glance at the lines of most boats proves that profiles haven’t changed dramatically over the past 60 or so years. Certainly, construction methods such as resin infusion and injection molding have altered business as usual, and ingredients have also changed to include all manner of space-age composites, epoxies, paints, computer mapping for engines that produces vastly greater horsepower from smaller blocks, and so on. Even propulsion has changed with the advent of pod drives and big outboards. But here’s the weird part: Any time a designer or builder introduces a model that looks significantly different, whether it is Euro-styled or functionally clunky, it fails. It doesn’t matter how well the boat performs, the typical boater rejects it because it doesn’t look like what he knows. We, as an enthusiast niche involving boats, are horribly set in our aesthetic ways.

Look at how well multihulls handle heavy seas. When it comes to seakeeping ability, efficiency and performance, the catamaran has a lot going for it, as anyone who happened to catch some of the most recent America’s Cup racing can attest. And yet, to date, production multihulls have enjoyed only moderate acceptance by boaters.

Here are six of the latest hull-design innovations and technologies being used elsewhere in the maritime world that we will likely never accept for our recreational boats — even though they all work well.

Wave-Piercing Hulls Most accounts cite wave-piercing technology as coming on the scene around the start of the 20th century. However, it has been employed as far back as the times of the Phoenicians and ancient Romans. The design concept consists of a bow with little buoyancy, a hull that slopes inward from the waterline and, ergo, a large reduction in wave-making resistance. While it works well in heavy seas, the drawbacks include reduced interior volume forward and a very wet ride because the waves come up and over the bow as a matter of course. Wave piercers fell out of favor for a period of time due to these same drawbacks but have recently enjoyed a resurgence of popularity because of their dramatic fuel-efficiency gains.

Stepped Hulls OK, this hull form has achieved a certain level of acceptance in our recreational boats, mostly in performance boats or offshore center consoles. But why isn’t it more popular? The stepped bottom has been around as a V-bottom refinement since at least 1912. Steps are grooves in the hull stretching outward from the keel to the chines. Most hulls sport one or two steps per side. And a vessel should really be capable of cruising in excess of about 30 knots for a stepped hull to be worthwhile. Steps work by allowing air to be “injected” against the running surface, breaking contact between part of the hull and the water, which in effect turns the running surface into numerous short, wide planes, rather than one long, narrow one.

How much the hull surface contacts the water directly determines the amount of drag a hull suffers. Steps (also called vents) decrease the amount of hull contacting the water (called the wetted surface), thereby decreasing drag, increasing speed for the same horsepower, and increasing fuel efficiency. It all sounds good. But steps also come with potential drawbacks. Though modern deep-V designs have enough deadrise to counteract the problem in most cases, stepped hulls have been known to suffer from transom slide in sharp turns at speed. They also require attention to loading and trim because the steps need the proper angle of attack to function correctly; they don’t offer an advantage in flat, calm water; and they require a special trailer.

Most owners of stepped-hull vessels are experienced and want to travel at high speeds in moderate to heavy seas, and/or achieve good economy and range. Yet to date, performance and center console builders aside, only Regal Boats, with its FasTrac hulls, and Formula have committed to using steps in production cruisers and sport boats.

Asymmetrical Twin Hulls This unique design concept comes from the drawing board of Larry Graf, the pioneer who put power catamarans on the map here in the U.S. when he founded Glacier Bay Boats in 1987. His new company, Aspen Powerboats, employs a cat design where one hull is narrower (35 percent) than the other. His patent calls it a Power Proa, and it relies on a single engine in only the wider of the two hulls. The hull shapes, alignment and placement compensate for the offset propulsion thrust, allowing the vessel to run straight and true. With only one set of running gear in the water, inherent appendage drag is reduced by 20 percent. Combined with the efficiency of the hull designs, overall fuel efficiency of the Aspen rises to an impressive 70 percent over monohulls of comparable size. Aspen won an award for the best 30- to 39-foot catamaran in the world in 2014.

SWATH A quick glance might lead you to believe that a SWATH (small waterplane area twin hull) vessel is a catamaran. And it is but only to the extent that it has two hulls in the water with a bridge across the top. But that’s where the hulls’ similarities end.

Consider a submarine. Once under the surface, it runs stable, with no roll or pitching from wave action. All that wave energy remains on the sea surface. That basically explains how a SWATH design functions.

If you’ve ever dived under a wave at the beach to avoid being smacked by it, you know that the water beneath the wave is calmer. SWATH minimizes a vessel’s volume where the water meets the air (which is where all the wave energy is at its peak). The bulk of the vessel’s displacement and buoyancy runs beneath the waves, affording amazing stability, even in big seas and at high speeds. Please think of high speeds as a relative term here, as this is not a planing hull. What SWATH does provide, however, are a wide, stable deck and unsurpassed ride quality, especially in rough seas.

Drawbacks to SWATH designs include the fact that each hull must be custom designed. Draft runs deeper than standard hulls (especially planing hulls). The underwater “torpedoes” providing buoyancy must run parallel to the water’s surface, which requires a fairly complex trim-control system. And the underside of the deck must be far enough above the sea surface to avoid waves slamming up into it. Finally, SWATH vessels cost more to design and build than conventional hulls.

Hydrofoils Once the strict province of commercial ferries and a few high-speed military vessels, the most recent America’s Cup has spurred hydrofoil acceptance to new heights. Will it catch on with powerboats?

The hydrofoil design acts exactly like an airplane wing, providing more lift than the drag coefficient the vessel produces, thereby lifting the entire hull out of the water. Only the hydrofoils remain in the water, unaffected by surface wave action. In fact, hydrofoils cut inherent resistance to zero while the hull is out of the water. In the case of power-driven boats, you still suffer drag from the propulsion system (prop, shaft or the like).

The most significant disadvantage to this system on recreational boats is definitely the deployment of the foils. Unless you want the added draft of these struts sticking down below your hull all the time, you must be able to extend and withdraw them — a complex engineering feat. There is at least one recreational powerboat employing hydrofoils: Twin Vee builds a catamaran with foils that don’t actually lift the hulls completely out of the water. It does improve fuel economy and ride stability nonetheless. Still, boats ride more smoothly in a sea and go much faster with hydrofoils. With the dramatic acceptance of this technology in sailing, is it only a matter of time before recreational powerboats incorporate foils into their designs?

Ulstein X-Bow The Norwegian Ulstein Group has been designing offshore vessels since 1917. Presently, it has the notoriety of creating the most advanced bow design in history. The Ulstein X-Bow looks like it might be upside down, but it’s proven itself in more than 100 offshore support vessels to date. The X-Bow allows higher speeds and smoother rides in even the worst seas. Gone are the slamming and vibration that occur when the bow of a ship drops off a wave. It functions better on all points of sea, and its lower hydrodynamic drag substantially decreases fuel consumption. The X-Bow has proven so successful that Ulstein is in the process of creating an X-Stern design now.

You won’t ever see this on small recreational boats, but you can nod knowingly when someone points one out on a mega-yacht in the near future.

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Catamaran vs. Trimaran: The Differences Explained

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Most boat lovers know the differences between a catamaran and a monohull. But when it comes to differentiating between a catamaran and a trimaran, things can get tricky because it’s not always clear how much difference the extra hull of a trimaran makes in performance, safety, comfort, and handling. If you’re trying to choose between the two, this is a post you’ll want to read before making a decision.

Besides the number of hulls catamarans(two) and trimarans(three) differ in speed, safety, accommodation, helming, and anchoring. Generally, catamarans are more manageable in a marina and provide better accommodation and comfort. Trimarans, on the other hand, are faster and more fun to helm.

In this post, we’ll cover these differences in greater detail to make it easier for you to choose between a catamaran and a trimaran. First, let’s quickly review each multihull type.

Table of Contents

The Lowdown on Catamarans

Informally dubbed a “cat,” a catamaran is a type of multi-hulled sailing craft with two equal-sized parallel hulls. Cats are typically geometry-stabilized, leveraging their wide beams for stability. That’s unlike monohull boats, which use ballasted keels for stability. Catamarans also have a smaller displacement, lower hull volume, and a much shallower draught ( draft ) than similarly sized monohulls.

The earliest forms of catamarans can be traced way back to the 17th century. They were primarily used for fishing by the Pavaras community in Tamil Nadu, who preferred them over other fishing vessels due to the extra balance and stability provided by the twin hulls. Later on, the British adopted the concept of twin-hulled boats and popularized it worldwide.

Modern catamarans are much more sophisticated than their ancestors. They’ve evolved in terms of the usage versatility, construction, and design, giving rise to two primary configurations:

• Small-Waterplane-Area Twin Hull (SWATH)
• Wave-piercing catamarans

The hulls in a catamaran with a SWATH configuration are typically submerged. That means they’re less affected by ocean waves , which is great for stability when sailing in rough waters. In the recent past, SWATH configurations have been used on research vessels and rescue ships. 

Their wave-piercing counterparts, on the other hand, have low-buoyancy bows fitted on the twin hulls. The bows allow the hulls to puncture ocean waves instead of riding over them, making catamarans with such a design faster on rough waters than SWATH cats. In the recent past, wave-piercing cat designs have been used on passenger ferries, military vessels, and yachts.

The Lowdown on Trimarans

Also known as a double-outrigger, a trimaran is a type of multihull boat with one main hull flanked by two smaller “floats” (technically known as outrigger hulls) connected to the larger hull by lateral beams. Such a design makes trimarans incredibly stable, meaning they’re hard to capsize even in the roughest of waters. 

The earliest forms of trimarans can be traced to the Austronesian people and are still the most common hull design you’ll find on traditional fishing boats in Maritime Southeast Asia. The majority of today’s double outriggers are yachts meant for racing and recreation, but some warships and ferries have this design.

The Differences Between Catamarans and Trimarans 

The most apparent physical distinction between a catamaran and a trimaran is that it has three hulls instead of two. 

But other than that, are there other differences between the two vessel types you need to know? Do those differences make one type better than the other?

To find out, let’s compare the two types of multihulls based on the following merits:

Comfort and Accommodation

A Cat’s geometry is ideal for comfort and accommodation. The two load-bearing hulls provide additional habitable space, and you can always create a sizable nacelle between them. Connected to this central living space is a large cockpit, and there are cabins on either end of the hulls. This arrangement is perfect when you’re looking to relax a bit as the party rages on in the saloon because it gives you a bit of privacy. 

And with flybridges virtually standard on modern catamarans, you have extra space for entertainment and lounging. The deck area is safe for kids, and the fact that catamarans don’t heel much means that you can do things like cooking at ease. Also worth mentioning is that cats can carry a decent load, meaning you can stock up on food and gear when going away for an extended period.

While trimarans do provide a decent degree of livability, they fall short of catamarans in two regards. First, they heel more than cats, making it difficult to do things like cooking on board. Second, they support much less load than catamarans. To put things into perspective, some 45 feet (14 meters). Cats can carry nearly three tons of payloads, whereas similarly sized trimarans can barely support half that load.

Overall, catamarans provide better, more comfortable accommodation than trimarans.

One of the main concerns when choosing any water vessel is how easy it’ll capsize in the event of a storm. If you’re looking to spend more than just a couple of hours on the water, you want to sail on something that won’t capsize/sink easily because sea conditions can sometimes fluctuate within a short period.

When it comes to safety, three hulls are better than two. Having one main hull and two overhangs on each side makes a trimaran more stable because of two reasons. First, the side overhangs widen the beam of the vessel, which minimizes the chances of the boat flipping over when hit by a large breaking wave from the side. Second, trimarans are typically designed with the weight centered on the main hull, further enhancing stability. 

Multihull stability is a complex topic and should be understood in detail if you want to stay safe at sea!

• Why do catamarans capsize?

On the rare occasion that a trimaran flips over, it’ll stay afloat. That means if the worst happens, a capsized trimaran will turn into a potential life-saving raft that’s easier to spot from a helicopter. That’s because almost all trimarans designed in the last decade or so come with closed-cell foam distributed throughout the various parts of the boat to provide reserve buoyancy. 

Thanks to this kind of construction, you could cut most trimarans into pieces, and each would still stay afloat.

While catamarans are typically more stable than monohulls, they’re no match for a trimaran in this regard. Hypothetically speaking, it would be easier to tip over a catamaran than a trimaran if both boat types were subjected to equal magnitude storms. That, however, doesn’t mean that catamarans aren’t safe. They’re still harder to flip over than monohulls and will stay afloat when that happens because they come with the same closed-cell foam found in a trimaran.

While on the subject of safety, it’s worth mentioning that trimarans require less vigilance as far as reefing is concerned . Since catamarans heel less, most of the extra wind force translates to more “push” on the rig, increasing speed. But because the pressure exerted on the sail nearly quadruples when the wind speed doubles, you need to be extremely careful when timing your reef to keep a cat sailing flat. 

The same goes for reefing a trimaran, except that the slight heel gives you more room for error in terms of the timing.

Most people who’ve ever steered both a trimaran and catamaran will agree that the former is more fun to sail. Most light trimarans, especially tiller-steered ones, have a terrific response to the helm. They have a slight heel that somewhat feels like a monohull, but the angle is a bit limited.

A catamaran is stable, but it doesn’t heel. While heeling may be frowned upon by people who prioritize comfort and accommodation in a boat, it’s one of the most exciting parts of sailing. With three hulls to ensure stability, trimarans combine the heel of a monohull with a catamaran’s stability to deliver the best sailing elements of monohulls and multihulls in a single package.  

Considering that trimarans are more stable, you may be better off with one if you’re looking to have some fun as you perfect your helming skills.

Speed is another area where trimarans outperform their twin-hulled counterparts. Typically lighter than catamarans, trimarans need less sail distance to hit double-digit speed averages. A trimaran can maintain a formidable course up-wind when fitted with centerboards/daggerboards (as is often the case for modern models).

While a catamaran is still faster than a monohull of identical size, it falls short of the trimaran in terms of sheer speed. Understand that this doesn’t make catamarans slow boats; it’s just that tris are typically designed with more emphasis on performance.

Why are Trimarans Faster Than Catamarans?

Trimarans are easier to anchor than catamarans because they allow you to keep the ground tackle in and deploy it from the main hull. 

However, catamarans are more maneuverable and manageable in a marina. They also handle docking lines more conveniently.

Catamarans vs. Trimaran: The Verdict

In summary, here’s what the differences between a cat and tri mean for anyone trying to choose between the two: A catamaran is a better choice if you’re looking to accommodate many people on board for something like a party because it’s more spacious and comfortable than a trimaran. On the other hand, a trimaran is an ideal choice for speed junkies and individuals looking to push their sailing skills to the next level on every stable platform.

Hopefully, that has cleared the air and made it easier for you to pick a more suitable option for your sailing needs.

• ResearchGate: A comparison of the motions of trimarans, catamarans and monohulls | Request PDF
• Why are trimarans faster than catamarans?

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SWATH vs Catamaran question

Discussion in ' Boat Design ' started by Red Dwarf , Feb 13, 2013 .

Red Dwarf Senior Member

Please critique this idea. Start with a SWATH type hull but have it ballasted so at rest in smooth water the hull is only 95% submerged. This provides normal stability at rest so you don't have to worry about where people on the boat are standing. Then when in motion, for example 10 knots, use the control planes to pull the hull down to a true SWATH mode. The control planes are just small wings so I expect they have decent L/D. If the L/D is 20:1 5000 lbs of down force may increase drag 250 lbs. Of course the other option is to pump in water to lower the hulls to SWATH mode draft. In this video the control planes clearly have more than enough authority to vary the ride height, look at the 2:05 minute mark. http://www.youtube.com/watch?list=PL0BD4D97C5818A05F&v=c13IrmOF4eE&feature=player_detailpage#t=121s  

BMcF Senior Member

The SWATH (A&R) that you provided the video for certainly does not have the control authority in the appendages to vary the draft.. Otherwise..you have it backwards in your first hypothetical and correct as an aside at the end of that. What has been done in practice by Swath Ocean International, JMS, and MAPC, and others, is to take very inherently unstable extreme SWATH designs and ballast them down with water when docked or manuevering slowly..and/or include larger appendages and rely on those for lift and to increase cross-structure clearance underway. Then the ballast is pumped out and the appendages used to provide support for some of the vessel displacement as the speed increases. The MAPC HYSWAS is probably the most extreme example of that in an applied sense, but A&R are building one like that at this very moment, and there are other examples.  

Ad Hoc Naval Architect

BMcF said: ↑ The SWATH (A&R) that you provided the video for certainly does not have the control authority in the appendages to vary the draft.. Click to expand...

Submarine Tom Previous Member

Ad Hoc said: ↑ We did the same sea trial tests on the SLICE....its like a roller coaster ride, in flat calm sea at the push of a button. Click to expand...

FAST FRED Senior Member

When I look at most Swath style boats , wonder why did they not just modernize the decades old Box Keel concept. Many claims were made for modern style box keels that take the majority of the displacement about their Superior Sea Keeping ability. In GRP the box keel can be as shapley as modern hydrodynamics require with little building hassles.  

BMcF said: ↑ Otherwise..you have it backwards Click to expand...

yipster designer

FAST FRED said: ↑ When I look at most Swath style boats Click to expand...

Abeking is building an interesting "SWASH"... http://www.maritimejournal.com/news...ing/a-and-r-makes-waves-with-new-swash-design  

BMcF said: ↑ Abeking is building an interesting "SWASH"... Click to expand...

as we all like pic's TSL-F TSL-F looks good for her 20 year i had this demonstator in mind, stuffed with electronics still interesting i find this swath foil stevenson build a small bulb swa, as former forum member Rick Willoughby did a bulb with 3 floads and pointed out that for a small swa the bulb should be at least 3 diameters below the surface Tony Graiger drew a swath with nose foil others imagine wig swaths as this recently winning design of witch i think it fly's backward saw also some jets and supercavitation pics with Bolgers boxkeel hardly yet mentiont wiki answers original posters question probably shorter  

Leo Lazauskas Senior Member

Ad Hoc said: ↑ Yeah…I saw this recently. It’s a variation on a theme, been done before. The Japanese TSL-F back in the early 90s, the other which I’m sure you know more about the HYSWAS way back and also more recently at UCL and their Tri-SWACH Frigate. Click to expand...

Leo Lazauskas said: ↑ Would you regard them as successful vessels?, i.e. fulfilling their SOR at a reasonable price? Click to expand...

yipster said: ↑ [ still interesting i find this swath foil Click to expand...

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Here are a couple shots of the hybrid we built and tested a decade ago. Super-slender monohull supported by foils and twin lifting bodies. The 3D rendered view shows a typical flying configuration relative to still water surface. Of interest, perhaps, was that we proved we could operate quite well with those "bulbs" very close to, even touching, the mean water surface (the undisdurbed surface).  

Attached Files:

1stguess.jpg, bwb 002.jpg, bwb 019.jpg.

SWATH design ideas

Waller 1480 vs Dix 470 vs some other ideas / semi swath

Why Are SWATH Tubes So Long?

Early US SWATH vessel name ???

SWATH speed and stability opinions

Compartmentation of a SWATH vessel

Swath wind farm vessel.

SWATH concept design - Feedback wanted

SWATH hull trimaran

1 man homemade swath for flyfishing

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(Small Waterplane Area Twin Hull),

a catamaran ship—though the technology is equally applicable to a trimaran hull—which is shorter than a monohull or conventional catamaran of equal displacement tonnage. The basis of the design is twin underwater torpedo-shaped hulls to which are attached two or more streamlined struts. These pierce the water surface and are connected to a platform deck designed for cargo or passengers by means of what is known as the haunch. It is usual for each submersed hull to have independent machinery. The advantage of this design is that a large proportion of the hull stays below the surface which reduces wave drag and increases stability, giving smaller vessels the steadiness associated with much larger ones. It is also more economical as less power is needed to climb the waves, and it can sustain higher speed in rough weather than a conventional vessel. The theory of SWATH was developed by Dr Thomas G. L. Lang in the late 1960s, and the US Navy commissioned a SWATH ship in the 1970s which has proved successful. The technology is now being employed to build ferries and small cruise ships. SLICE (not an acronym) technology is now being developed, using underwater propulsion pods (see propeller), which allows SWATH ships higher speed through the water without sacrificing stability.

SWATH International's Super-4000 Class Ferry

From:   SWATH ship   in  The Oxford Companion to Ships and the Sea »

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