44.1 DESCRIPTIONS
44.1.1 Mission
Advanced Marine Surface Craft are obviously not destined to only one type of mission, but their
Aerodynamic lift is used by Wing-In-Ground effect vehicles.
In some instances, the speed is high only relatively speaking if, for example, the goal is to maintain speed in a heavy sea. Small waterplane area vessels are designed to provide a high comfort and profile will typically include a need for higher speed and greater seakeeping than can be achieved by conventional means.
For military applications, missions of fast patrol boats are most commonly found to use advanced hullforms, while commercial applications encompass high speed ferries.
44.1.1.1 Military Missions
Patrol boats are often required to operate swiftly and present a significant and unpredictable threat to larger vessels by carrying missiles or torpedoes at high speed in coastal zones where detection is more difficult than in open oceans. To further these capabilities, patrol craft are increasingly required to make use of stealth technologies.
In order to remain operational in rough weather, these small craft are also required to offer good seakeeping while maintaining speed. These capabilities require the use of advanced hullform concepts such as hydrofoil or Surface Effect Ships.
Larger vessels such as corvettes, also capable of high speeds, have been considered for more significant military missions such as anti-submarine warfare, but have not been built yet for these missions.
44.1.1.2 Commercial Vessels
The common purpose of developing advanced hullforms for commercial use has consistently been to provide faster and/or more comfortable vessels to carry passengers and cars. It is notable, however, that with the growth in use of the generally more stable multihulls, combined with today’s more capable collision avoidance systems, there has been a significant improvement in the safety of operation of these vessels.
Most advanced hullforms are designed to have low resistance at high-speed compared to conventional
(e.g., displacement) monohulls. This is usually achieved by reducing wetted surface by lifting the hull entirely or partially out of the water. To achieve this, hydrodynamic lift is used by hydrofoils and planing hulls, while powered aerostatic lift is used by air cushion vehicles and surface effect ships. small added resistance in waves, but may not necessarily be intended for speeds higher than that of conventional vessels in calm water. Thus, their speed can be relatively high when compared to conventional craft in high sea states.
Passenger comfort on high-speed ferries is a critical issue and is addressed by most hullforms through the choice of vessel size and, in some instances, through active means of controlling the motions. Hydrofoils are the most extreme in this regard since the craft is supported entirely by the foils, which are actively controlled. Platforms such as
Surface Effect Ships have been fitted successfully with active vent valves to regulate the cushion pressure and, therefore, the motions. Trim tabs, T-foils and other active ride control systems are now utilized on many types of platforms to improve their seakeeping and ride comfort.
The growth of high-speed ferries has also been made possible by advances in propulsion plant technology, as lightweight diesel engines and waterjet propulsors have become more readily available in larger sizes. Meanwhile, the use of gas turbine propulsion for larger vessels has become acceptable to operators who realize the benefit of a lightweight propulsion plant in improving the deadweight capacity and, therefore, revenue on such vessels.
One benefit of advanced hullforms is their stability characteristics which are usually far superior to that of conventional monohull ferries. This is achieved with planing monohulls due their wide beam.
For multi-hulls and air cushion vehicles it is because of their wide beam and high amount of reserve buoyancy provided by the box structure.
Another characteristic found in most multihull car-ferries is that their car deck usually sits much higher above the water than in conventional monohull ferries, making flooding of this deck much less likely.
The few accidents in which advanced ferries were involved only reinforced the point that they are safer than conventional ferries. This, in the end, may be the most important aspect which convinces ferry operators to turn towards the advanced concepts addressed in this Bulletin.
44-1
44.1.2 Unique Features
44.1.2.1 Vessel Lift
There are essentially four practical ways of providing the fundamental lifting force for marine vessels. These are hydrostatic lift or buoyancy, hydrodynamic lift, aerodynamic lift and powered aerostatic lift. These means of lift can be simply represented through the use of the lift pyramid, Figure
44.1, which is usually shown as a simple triangle when the aerodynamically supported craft (which are still very few in the marine world) are excluded. Every marine vehicle hullform investigated can be located in the lift pyramid according to the type of lift by which it is supported.
At the four corners of the pyramid are the vessels which rely on a single mode of support. They are as shown in Table 44.I. Any combination of the four modes of support result in a hybrid vehicle. It is to be noted that most high performance craft are hybrids of some sort. Most high-speed vessels are designed to benefit from some hydrodynamic lift even if the vessel is not entirely supported by this means alone.
HYDROSTATIC
MONO AND MULTI-HULL
DISPLACEMENT CRAFT
SWATH
SEMI-SWATH
WIG
SURFACE EFFECT SHIP
AIR CUSHION VEHICLE
AERODYNAMIC
QUADRAMARAN
PLANING CRAFT
POWERED AEROSTATIC
HYDROFOIL
HYDRODYNAMIC
TABLE 44.1 - THE FOUR “PURE” TYPES OF
HULLFORMS
Figure 44.1 - Lift Pyramid
Monohull: Semi-planing and Planing
Multi-Hulls:
Water
Air
Static
Hydrostatic
Aerostatic
Dynamic
Hydrodynamic
Aerodynamic
Catamarans: Displacement, Planing, Low Wash,
Wave-Piercer
Trimarans
SWATH: And other small waterplane area 44.1.2.2 Hull Shape
The shape of the hull itself is often what characterizes a high-performance ferry. In the past decade, the emergence of multi-hulls, especially catamarans, has been significant. Such hullforms are still most often conventional in that they are supported by conventional displacement means and do not rely on advanced means of lifting themselves out of the water. In such case, the resistance may be reduced instead by the use of fine sidehulls which “cut effortlessly” through the water. Such fine hulls are not suitable for monohulls as they would not provide adequate stability in roll. This problem is alleviated when used in a multi-hull configuration.
The following list delineates the hullforms discussed in this chapter:
vessels (including Semi-SWATH)
Hydrofoil: Fully submerged or surface piercing foils (Monohulls and Catamarans) and HYSWAS (hybrid of hydrofoil and small waterplane area singe hull)
Air Cushion Vehicle and SES
Wing-in-Ground-Effect Vehicles (WIGs)
44-2
SPECIFIC
ISSUES
ATTRIBUTES AND
The following sections present a qualitative discussion of the principal strengths and weaknesses of each concept. The text provides an examination of each type of platform and identifies the most suitable types prior to examining vessels available on the market. Only those aspects which are particularly important to a given concept are discussed. Attributes or issues that are not mentioned can be assumed to be minor for the platform or comparable to others.
44.2.1 Monohulls
There are numerous types of monohulls; displacement, semi-planing and planing, but this bulletin looks only at the last two categories. The technology associated with planing and semi-planing monohulls is generally mature. Recent efforts in the development of semi-planing monohulls, however, have led to larger length-to-beam ratios, pushing highspeed designs toward long slender ships. These monohulls can be considered advanced in that they are pushing the limit of the state-of-the-art.
44.2.1.1 Planing Monohulls
A planing hull has the majority of its weight supported by dynamic lift with the small remaining part of the weight supported by buoyancy or hydrostatic lift. These hullforms are typically of the hard chine type with a Froude Number
F n
V gL
> 0.9 or a Volumetric Froude Number
F v
V g
> 3.0. Another characteristic of planing hulls is the occurrence of complete flow separation at the transom and the sides. There are many variations of planing and semi-planing monohulls which include; round bilge, hard chine, double chine and stepped hulls. Cross sections of some of these are illustrated by Figure 44-2.
State-of-the-Art Examples. Small combatant ships and high-speed patrol craft of light displacement, and round bilge have been used by the world’s navies since the early 20th Century. For the most part, these designs finally gave way to hard chine hullforms and then to double chine hullforms. Most of today’s planing craft are of the hard chine type.
Recent developments have pushed the fast ferry monohulls beyond the 100 meter mark due to the trend towards larger capacity vessels. The principal characteristics of a number of operating vessel’s are shown in Table 44.II. Figure 44.3 shows the
Aquastrada “Guizzo” in operation.
ROUND BILGE HARD CHINE
Figure 44.2 - Types of Planing Monohulls
DOUBLE CHINE
Characteristics
Length, m
Beam, m
Draft, m
Hull Depth, m
Power, MW
Displacement, t
Speed, kts
Passengers
Cars (or Buses + Cars)
TABLE 44.II - PLANING MONOHULLS
Guizzo
(Aquastrada)
101.8
14.5
2.12
9.5
27.93
1034
41
450
126
Albayzin
(Mestral)
96.2
14.6
2.1
8.9
21.6
946
35
450
84
NVG Asco
(Corsaire)
102
15.4
2.4
5.2
24
1100
37
500
148 (4 + 108)
MDV 1200
Pegasus
100
17.1
2.75
10.7
27.5
1200 est.
38
800
175 (6 + 106)
44-2
Figure 44.3 - Aquastrada
Specific Attributes. Planing and semi-planing monohull technology is mature. Many designers round-bilge types). Typical hull cross sections are illustrated by Figure 44.4. The use of multi-hulls in and shipyards have experience designing and building these vessels.
Construction of these hullforms is relatively simple.
Large useable volume in the transom area available for machinery plant and propulsor integration and access.
Large deadweight capacity combined with relatively high speeds. marine transport has rapidly increased in the last ten years mainly due to the large gain in arrangeable deck area and advantages in powering and seakeeping over a monohull of the same displacement The multi-hull concept is usually retained in order to allow the use of slender hulls while maintaining adequate stability. The concept is now being extended to an ever increasing number of hulls (up to the pentamaran concept, for
Due to their maturity, there are numerous operating vessels from which a wealth of operational statistics are available.
Specific Issues. Roll stability is usually an issue for displacement monohulls, but not for typical planing monohulls due to their wide beam. The trend toward high length-to-beam ratios brings to light concerns about static and dynamic roll stability in turns.
Typically, power plants and propulsors of example).
44.2.2.1 Conventional Catamaran
A catamaran is a twin hulled vessel which uses the separation of slender hulls to gain low drag with acceptable transverse stability. The twin hulls are typically symmetric, but can be asymmetric.
The hull shape can be of a round bilge type or with hard chines depending upon the design speed. high output are necessary to achieve high speeds.
Growth in size of such vessels is limited by the need to operate at high enough speed to be in the planing or semi-planing regime.
Heave and pitch motions and vertical accelerations of planing and semi-planing vessels may be severe at high speed in rough water. Thus, size may need to be larger than necessary for the ridership, lowering the deadweight to displacement ratio. However, active ride control has been shown to help in this regard.
Hull bottom slamming is also an issue for planing monohulls, both from a passenger comfort and from a structural design point of view.
44.2.2 Multi-Hulls
Four different types of multi-hulled vessels are described in this bulletin. The two general categories from which the four types were derived are catamarans and trimarans. Further dividing the catamaran category into three subcategories yields the following; conventional (round bilge or hard chine), wave-piercing and low wash (usually with
State-of-the-Art Examples. mainly due to the improvements in propulsion packages. Figure 44-5 shows a recent example of the state-of-the-art,
DELPHIN, an Auto Express 82 in operation.
Specific Attributes . Due to the twin hulls and the separation between them, the catamaran has good inherent intact and damage stability as demonstrated in recent accidents including the “St. Malo” incident, April 17, 1995.
Large arrangeable deck area due to separation of hulls (allows, in particular, to turn cars around for car ferries).
Hulls are large enough aft to allow integration of waterjet propulsion and suitable for in-hull machinery arrangements.
Numerous catamarans are in commercial operation. The characteristics of four representative vessels are shown in Table 44-3.
The top speed and size of these catamarans have continued to increase
44-2
Characteristics
Length, m
Beam, m
Draft, m
Hull Depth, m
Power, mW
Displacement, t
Speed, kts
Passengers
Cars (or Buses + Cars)
ROUND BILGE
WAVE-PIERCER
Figure 44.4 - Typical Multi-Hulled Vessels
HARD CHINE
Table 44.III - Conventional Catamarans
Hai Chang
(Austal)
40
11.5
1.4
N/A
4
N/A
32
338
None
Juan Patrico
(INCAT K55)
70.4
19.5
2.15
5.65
21.24
383 est.
45
294
53
Westmaran
4200S
42.23
10
1.6
N/A
4
N/A
35
230
None
Delphin
(Auto Express 82 m
82.3
23
2.5
6.5
24.0
1100 est.
37.5
600
175 (10 + 50)
Figure 44.5 - DELPHIN, Auto Express 82
44-1
Due to the slenderness ratio of the hulls, they are of low drag, therefore, a catamaran has high performance capabilities. There are numerous vessels operating from which good operational statistics can be developed.
Specific Issues The wide beam of catamarans (or any multi-hull) may cause difficulty in accessing some port facilities for which they have not been designed.
Structural weight fraction is high due to cross-structure and connections to the hulls.
Catamarans may experience high vertical accelerations and pitch motions in head seas.
Catamarans also are very stable in roll, but because of this they may produce high lateral accelerations in beam seas.
Performance is sensitive to hull separation, therefore, the wave interaction between hulls needs to be investigated.
Slamming of wet-deck could occur if its height over the waterline is not sufficient for the seas encountered on the route.
44.2.2.2 Wave Piercing Catamarans
The increasing need for high-speed marine transport coupled with the fact that passengers often experience discomfort on open ocean or exposed routes on conventional catamarans, created a void which the wave-piercer was developed to fill. Again, this hull form has twin hulls, but they are long and slender with minimal freeboard and little buoyancy in the bow section. This configuration allows the bows to cut or pierce the waves reducing the tendency of the vessel to contour or ride over the waves, thus providing lower pitch motions and accelerations, while carrying similar deadweight. It should be noted that some wave-piercers have a third half hull or bow forward. The hull does not provide buoyancy to allow increased deadweight, but does help mitigate wave slap and slam loads on the cross-structure while operating in a sea state.
State-of-the-Art Examples Wave-piercing catamarans were introduced in the early 1980’s with the INCAT
28 m as the first to operate on a commercial route.
Since then, several companies have developed their own approach to this type of design, the characteristics of three of which are shown in Table 44-4. A photo of the INCAT 78-m CONDOR 11 wave-piercers is shown in Figure 44.6.
TABLE 44.IV -WAVE-PIERCING CATAMARANS
Characteristics
Length, m
Beam, m
Draft, m
Hull Depth, m
Power, mW
Displacement, t
Speed, kts
Passengers
Cars (Buses + Cars)
Condor 11
(INCAT 78 m)
77.5
26
3.4
7.2
17.28
785
35
600
150 (6 + 90)
Hayabusa
(AMD 1500)
99.78
20
3.10
12.6
18.96
2200
30
460
94 (24)
Surf Express
(Gold Coast)
31.7
9.8
1.35
N/A
2.6
61.1
35
128
--
Figure 44.6 - CONDOR 11, INCAT 78 m Wave-piercer
44-2
Specific Attributes Heave and pitch motions and accelerations are reduced while in head seas due to wave-piercing action of sidehulls. Due to the twin hulls and the separation between them, the vessel has good inherent intact and damage stability. They have large useable deck area due to separation of hulls.
Hulls remain large enough aft to allow integration of waterjets and propulsion machinery.
Due to slenderness of the hulls, they are efficient, therefore, have high performance capability.
Due to their recent success, there are numerous operating vessels from which good operational statistics can be developed.
Specific Issues Construction is more difficult than with conventional catamarans due to the structural complexity of the forward hulls. The transition area from wave-piercing bow to the more typical crosssection in way of the cross-deck starting point is very structurally complex. Although the structure is more complex, the structural weight fraction is similar to that of a conventional catamaran.
The wide beam of wave-piercer catamarans is also an issue where ports are not designed to harbor such vessels.
High roll or lateral accelerations or “lateral jerky motions” in beam seas can also be experienced by wave-piercer catamarans due to their inherently
Beam, m
Draft, m
Power, MW
Speed, kts
Passengers
Cars
5.7
0.75
0.506
25
62
None
44.2.2.3 Low-Wash Catamaran
Due to increasing global environmental awareness, the low-wash or low-wake catamaran hullform is becoming increasingly popular for inland or sheltered routes, e.g., rivers or estuaries. The hulls are generally symmetric with rounded sections and a high length-tobeam ratio providing lower wake profiles.
State-of-the-Art Examples Low-wash vessels are typically in a size range that is smaller than the conventional and wave-piercing catamarans since they are typically designed to operate in restricted waters.
Due to the relative newness of these designs there are only a few operating vessels, the leading particulars of some of which are shown in Table 44.V. Two of the
NQEA low wash catamarans are shown in Figure 44.7.
Specific Advantages Although top speed is limited due to the need to maintain the wave-making properties of the hull, these vessels can operate at a higher speed in low wake areas than most conventional or advanced marine vehicles.
Hull forms are designed for a low-wake profile, therefore, they are very energy efficient and have low resistance properties.
Typically, operating on congested inland waters, these vessels are designed to have good control and maneuverability. high lateral stability. Active ride control has proven to be effective in controlling such effects.
TABLE 44.V - LOW-WASH CATAMARANS
Characteristics
Length, m
Thames Class (FBM)
23
Castelo (FBM TransCat)
44
11.8
1.4
1.896
25
496
None
Low-Wash (NQEA)
35
10.5
1.35
0.746
24
200
None
Figure 44.7 - NQEA Low-Wash Catamarans
44-2
Due to the twin hulls and the separation between them, the vessel has good inherent intact and damage stability.
Again they have large useable deck area due to separation of hulls.
Hulls remain large enough aft to allow integration of waterjets and propulsion machinery.
Specific Issues Since these vessels are designed to operate in restricted water, they typically have a low wet-deck clearance and would be subject to slamming as well as deck wetness and high accelerations, if operated in open waters.
They are of relatively light density and may prove difficult, therefore, to apply tgo car carrying ferries.
Higher speeds than those demonstrated (e.g.,
44.2.2.4 Trimarans
Trimarans are basically very slender monohulls fitted with small sidehulls or outriggers to provide them with sufficient lateral stability. The more recently proposed pentamaran concept operates on the same principle. A proper balance between the slenderness ratio of the main hull and the size and separation of the sidehulls is needed to ensure a net benefit from a speed powering viewpoint. Note that some vessels like the wave-piercing catamarans and the tricat may look like trimarans, but really are catamarans as the third central hull is normally not in contact with the water. (Their third hull only provides additional buoyancy when encountering large waves.)
State-of-the-Art Examples While trimarans have been around for centuries, only recently has there been about 25 to 30 kts) may be difficult to achieve while maintaining their low wake capabilities. interest in pursuing trimarans as viable options for ferry hullforms. The appearance in 1988, of the Ilan
Voyager aroused interest in the trimaran concept.
There has also been interest shown by the UK and U.S. navies including several prominent shipyards, in investigating the use of a displacement trimaran hullform for frigates and corvette size warships. This has also lead to designs for larger (~100 m) trimaran passenger/car ferries. Some of the few operating trimarans are shown in Table 44.VI. Figure 44.8 shows the Thames River Ferry in operation.
TABLE 44.VI - TRIMARAN PASSENGER VESSELS
Characteristics
Length, m
Beam, m
Draft, m
Power, MW
Displacement, t
Speed, kts
Passengers
Cars (Buses + Cars)
Ilan Voyager
21.3
10
1.1
0.18
4.5
24
12
None
Lay Consultants,
Thames River Ferry
17.5
5.5
0.8
0.35
15
20
60
None
Figure 44.8 - Thames River Ferry
44-2
Specific Attributes Highly efficient hullform allowing higher speed or lower installed power. Sidehulls can easily provide adequate intact and damage stability characteristics.
They also have large useable deck area due to separation of hulls.
Good seakeeping qualities in all but quartering seas. Good directional stability.
Specific Issues Interest in this concept for large vessels, such as ferries, is recent and there is, as of yet, very little design and operational experience.
Structurally complex due to cross structures and outer hulls (lack of design experience entails some risk).
Maneuvering is poor unless outer hulls are large enough for propulsion units to be located within them.
Quartering seas cause problems for both seakeeping and directional stability. There is a tendency for the vessels to corkscrew.
Depending on the vessel, the utility of the outer hulls is generally limited.
44.2.3 Small Waterplane Area Vessels
Three types of small waterplane area vessels can be defined. The SWATH (twin hulls) was the first concept using reduced waterplane area, which is aimed at decoupling the vessel’s motions from surface waves.
Two recent developments in the small waterplane area hullform include the recently introduced semi-
SWATH which is derived from a SWATH and conventional catamaran hulls and the developmental/prototype HYSWAS which is a combination of a small waterplane single hull and hydrofoils, see Figure
44.9. The HYSWAS is discussed in more detail under the subject of “Hydrofoil Craft” later in Section 3.5.
French and German companies have also developed low water-plane concepts using three hulls, while
Lockheed in the USA has developed a similar concept using four hulls that they refer to as the “SLICE” concept.
44.2.3.1 SWATH (Small Waterplane Area Twin
Hull)
As mentioned above, the basic idea of the
SWATH concept is to reduce the action of the waves on the vessel by reducing the waterplane area to the minimum. Waves act on a ship primarily through their intersection with the waterplane. As depth below the surface of the water increases, the motions of the water due to surface waves decreases sharply. The buoyancy of a SWATH is concentrated in two large underwater bodies which, because of their depth below the water surface, are much less subject to the action of waves while the accommodations are concentrated in a platform high above the water. Narrow (knife-like) struts link the underwater body(ies) to the platform.
Because waves impart energy to a ship via the area of the hull which intersects the water surface (waterplane area), the reaction of a vessel to waves is directly proportional to the size of its waterplane area.
Therefore, reducing the waterplane area minimizes motions due to waves.
State-of-the-Art Examples Some fairly large SWATH vessels (3000 to 5000 ton displacement) are in operation for military and oceanographic missions.
The largest SWATH, the 11,000 ton cruise vessel “Radisson Diamond” shows that there are essentially no limits to the size of the concept.
However, all of these larger vessels have relatively low speed capability (e.g., less than 15 kts).
A number of high-speed passenger vessels are in operation. The characteristics of these are shown in
Table 44-7. Figure 44-10 shows the CLOUD X ready for launching.
SWATH
FWD
AFT
SEMI-SWATH
HYSWAS
Figure 44.9 - Typical Small Waterplane Area Vessels
44-2
Characteristics
Length, m
Beam, m
Draft, m
Power, MW
Displacement, t
Speed, kts
Passengers
Cars (Buses + Cars)
TABLE 44.VII - SWATH PASSENGER VESSELS
SSC 40 FBM Atlantic Class Navatek 1
44
16
3.5
8
N/A
30.6
410
None
37
13
2.7
4.1
180
31.7
400
None
44
16
2.5
2
N/A
18
440
None
Cloud X
37
18
3.4
5.7
340
30
365
None
Figure 44.10 - CLOUD X, SWATH
Specific Attributes Seakeeping is the number one attribute for SWATH. These vessels can maintain speed in heavy seas where most vessels would have
The operating draft, heel and trim of SWATH vessels are more sensitive to overloading than is the case with conventional catamarans due to the low reduced speed or could not operate at all.
The useable deck space is usually greater than monohulls of comparable displacement as the motions are low essentially anywhere on the ship. Some of the most successful applications have been for dinnercruise ferries.
Specific Issues The narrow struts sometimes make waterplane area of the struts. Control of fixed weight is very important to ensure that the vessel is continuously operated close to its design draft and trim.
SWATH vessels have a large draft when compared with other vessels of similar displacement.
SWATH vessels, as a result of the sensitivities mentioned above, usually require active access to and integration of the machinery plant difficult.
The top speed achievable by SWATH vessels remains limited as the wetted surface, unlike most advanced hullforms, is increased rather than reduced.
Also, the narrow transom makes it unsuitable for waterjet propulsion in most cases.
Damaged stability may become an issue for
SWATH ships as their reserve buoyancy is located high in the ship. control of trim and heel.
44 2.3.2 Semi-SWATH
A semi-SWATH is a hybrid of the forward half of a SWATH and the aft end of a conventional catamaran. The combination results in vessels with nearly equal seakeeping to that of regular SWATH vessels, but with far superior speed/powering performance.
As a result of the catamaran type stern, the semi-SWATH concept also allows the integration of
44-2
waterjet propulsion, which is usually the preferred choice for high-speed ferries.
State-of-the-Art Examples The first and largest semi-
SWATH in operation is the Stena HSS 1500 with a displacement of about 4000 ton and a deadweight of
1500 tons. This vessel is shown in Figure 44-11.
The leading particulars of a number of vessels which are in the construction stage, or have recently been delivered, are shown in Table 44.VIII.
Specific Attributes The principal attribute of a semi-
SWATH vessel is its seakeeping combined with a relatively low resistance even to fairly high speeds
(40+ knots).
The catamaran-like aft sections are more suitable for machinery arrangement and especially for integrating waterjet propulsion.
Like a SWATH, semi-SWATH vessels offer a great deal of arrangeable deck space.
Specific Issues Although not quite as sensitive as
SWATH vessels, semi-SWATH vessels are somewhat sensitive to overloading and trim. The small waterplane of the forward section makes it more sensitive, in particular, to forward trim. However, this concept is fairly new and more operational experience is needed to assess its future.
44.2.4 Hydrofoil Craft
44.2.4.1 Conventional Hydrofoil Craft
Hydrofoil craft have been around since the late 1800’s with major advancements only occurring in the last half century mirroring that of the aerospace industry. These advances have allowed the development of reliable and efficient hydrofoils to be built and put into profitable service. Recent advancements have allowed for a departure from the typical monohull hydrofoil to catamaran hydrofoils, both of which are discussed in this chapter.
The hulls of hydrofoil craft are lifted out of the water by either surface-piercing or fully submerged foil systems. These systems are illustrated in Figure 44-12. Both types of foil systems are prevalent in military and commercial operations throughout the world. The surface-piercing foil system is self-stabilizing with regard to hull height and attitude above the water. Thus, they will cause the vessel to respond to surface waves in pitch, heave and roll and require more limited sea-state operational restrictions. The fully submerged hydrofoil,
Characteristics
Length, m
Beam, m
Draft, m
Hull Depth, m
Power, MW
Displacement, t
Speed, kts
Passengers
Cars (Cars + Buses)
Figure 44.11 - Stena HSS 1500, Semi-SWATH
Table 44.8 - Semi-SWATH Passenger Vessels
Stena HSS 1500
124
40
4.5
13
70
4000 est.
44
1500
375 (50 + 100)
Stena HS 900
88
28
3.7
12.6
34
1650 est.
40
900
212 (10 + 154)
44-2
Seajet 250
76
23
3.4
8.05
30
890 est.
44
450
120
ROUND BILGE HARD CHINE DOUBLE CHINE
SURFACE P IERCING FULLY SUBMERGED HYDROFOIL CAT AMARAN
Figure 44.12 - Surface Piercing and Fully Submerged Hydrofoils
Table 44.IX - Hydrofoil Passenger Vessels
Characteristics Boeing Jetfoil 929-100 RHS-160F Kometa-MT
Length, m
Beam, m*
Draft, m**
ROUND BILGE
Hull Depth, m
Power, MW
Displacement, t
Speed, kts
27.4
9.5
5 (-)
--
5.534
110
42
31.2
6.7(12.6)
3.76 (1.7)
--
2.8
91.5
34.5
35.1
3.6 (1.7)
--
1.64
58.9
31
Passengers 190 238 102
(*) The number in parenthesis is the foil width for surface-piercing hydrofoils.
Foilcat
35
12
4.7 (2.55)
4.2
8.95
150 est.
45
403
Figure 44.13 - Jetfoil at Speed in a Seaway
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is not self-stabilizing and requires an active control system. Since, in this situation, the hull is nearly decoupled from the water surface, craft with fully submerged foils are not as limited by sea-state and provide a very comfortable ride. The hullform used is usually a monohull or a catamaran. Since the hull lifts out of the water, the hull shape has only a second order importance. However, the hull needs to be designed to minimize resistance while accelerating through the take-off hump and a hard-chine planing hull is usually preferred. Also, the hull needs to be able to structurally withstand wave impact in heavy seas and an emergency landing without damage due to slamming.State-of-the-Art Examples
There are numerous military and commercial craft in operation throughout the world. The leading particulars of some of these are shown in Table 44-9.
One of the most famous hydrofoils, the Boeing Jetfoil, is shown in Figure 44-13.
Specific Attributes
High speed is possible once foilborne due to low wetted areas and high lift-to-drag ratio achieved.
Good seakeeping and low motions for the fully submerged hydrofoils with almost no degradation of speed with respect to sea state. These craft are also highly maneuverable at speed.
Surface-piercing hydrofoils can use a more conventional hull and propulsion system similar to those on planing monohulls.
Specific Issues
Deadweight is limited because foils support the entire weight of the vessel. Thus, these vessels may only be used effectively in passenger ferry service. It should be noted that there are numerous naval applications for these hullforms, but, in all cases, the concept is not efficient in very large size applications.
Since the hull is lifted a significant distance out of the water with the fully-submerged hydrofoil concept, the integration of the propulsion system is complex.
Waterjets or propellers may be used, but, in the foilborne mode of operation, propellers are generally more efficient. Additionally, a second propulsion system for hullborne operations is often required.
These are high cost platforms due to these complexities combined with the automatic flight-control system required for the foils.
Construction is difficult due to structural complexities of attaching the foils to the hull and designing a hull of minimum weight, to take the applicable environmental loads especially slamming loads during emergency landing.
Surface-piercing hydrofoil craft are much less expensive, but operation is limited to coastal or partially protected routes. They sometimes employ active ride control systems to ameliorate motions due to the wave-foil interaction. b) HYSWAS
Description
The Hydrofoil Small Waterplane Area Ship
(HYSWAS) concept is a hybrid between the SWATH and Hydrofoil concepts. A single hull with a small waterplane area and a large underwater body is fitted with a fully-submerged foil system to provide partial lift as well as active control (especially in roll).
This concept is intended to improve speed/powering characteristics compared to conventional SWATH vessels as wetted area is reduced, while keeping the positive attributes of small waterplane area.
State-of-the-Art
There are no operational HYSWAS yet, but some prototypes show great promise and are delineated in
Table 44-10. Plans for large vessels capable of carrying 1000 tons deadweight are being considered as part of Japan’s Techno-Superliner program The prototype TSL-F for this program is shown in Figure
44-14.
Table 44-10
HYSWAS Vessels
Characteristics TSL-F Prototype Sea Quest
Length, m
Beam, m
Draft, m
Hull Depth, m
Power, mW
Displacement, t
Speed, kts
17.1
6.2
3.1/1.6
Unknown
2.8
38
41
8.2
3.7
3.0/?
4.0
0.6
12
35
Specific Attributes
HYSWAS offers a good combination of high-speed and excellent seakeeping.
The foils act to unwet the underside of the platform and a significant part of the strut linking the platform to the underwater body. They also provide the means of actively controlling the vessel’s motions, especially in roll.
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Small wake when foilborne.
Specific Issues
HYSWAS machinery installation poses the same challenges as with SWATH vessels; the narrow struts make the installation and access to the machinery difficult.
Craft stability at speed is entirely dependent upon the control of the foils, as for hydrofoil craft having fullysubmerged foils. Control at low speed is more of a challenge.
Foilborne speeds are relatively high, thus extrapolation to large vessels would require targeting very high speeds (60+ kts) and large propulsion plants.
The vessels have relatively deep draft, while off foils.
44.2.5 Hovercraft a) Air Cushion Vehicles (ACVs)
Description
Figure 44-14. TSL-F HYSWAS the vehicle, is usually provided by dedicated lift fans.
Propulsion is usually provided by air propellers.
The platforms reduced contact with the water results in low resistance at high speed.
State-of-the-Art Examples
Air Cushion Vehicles are essentially hovercraft with rectangular platforms supported by a cushion of pressurized air, the escape of which is impeded by flexible skirts attached around the whole periphery of the platform, as illustrated in Figure 44-15. The pressurized air, which supports 100% of the weight of
Most air cushion vehicles being built today are for military use, but the SRN.4 has been a very successful car ferry for more than 28 years. This vehicle is shown in Figure 44-16. Smaller passenger ferries are also available on the market (see Table 44-11).
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Figure 44-15. Air Cushion Vehicle (ACV)
Figure 44-16. The Venerable SRN.4
Table 44-11 - Air Cushion Vehicles
SRN.4 Mk3 AP.1-88 Characteristics
Length, m
Beam, m
Draft, m
Cushion Depth, m
Power, MW
Displacement, t
Speed, kts
Passengers
56.4
23.2
0
1.5
11.3
300
65
418
24.4
11.0
0
1.37
1.4
40.8
50
101
Cars (Buses + Cars) 60 0
* Note the Landing Craft, Air Cushion (LCAC) is a U.S. Navy Amphibious Assault Landing Craft.
LCAC*
26.8
14.3
0
1.5
11.8
154
50
*
*
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Specific Attributes
The principal specific attribute of the ACV is its amphibious capability which enables it to operate from a variety of unprepared beaches and with minimal terminal facilities.
The amphibious capability also enables them to operate in shallow waters, even over sand banks, and over marsh land or various types of terrain inaccessible by conventional means. This, in some instances, can significantly reduce the time in transit by reducing the length of a route.
The air cushion allows these craft to operate efficiently at high-speed (50+ kts) as it considerably reduces frictional resistance.
Specific Issues
To maintain its amphibious capability, air propellers are used for propulsion. The high cost and low efficiency of air propellers compared to marine propulsors in this application is an issue. There is also a high noise level generated by such propellers which could cause problems for operating on certain routes.
Since the lift power is dictated by the overall weight of the vehicle, lightweight (aerospace) technology is usually required, thus making the price of ACVs high compared to other types of advanced marine vehicles.
The inflatable skirts used to contain the cushion of used at high speed and, particularly, when operating over land. Their maintenance is, therefore, a specific issue that must be adequately planned and addressed by an operator.
Directional stability can be a problem.
Specific Attributes
The concept has low frictional resistance due to the air cushion, as for conventional ACVs although this is tempered by the presence of the skegs. Compared to an ACV, the ACVAS benefits from its “foot in the water” as it can be fitted with marine propellers or waterjets for propulsion, with a far greater propulsive efficiency than air propellers and reduced noise as a result.
Another benefit of the access to the water is the use of water-cooled engines instead of air-cooled engines for propulsion power.
Air-cooled engines are most often required as there is no connection with the water.
The low length-to-beam ratio required for stability reasons results in high hump drag, thus ACVs are suitable mostly for high-speed operations or posthump operations.
Long exposure to the “cobblestone” like motions of
ACVs can generate fatigue for their riders although they do not result as much in sea sickness as do the lower frequency motions of a conventional vessel. b) ACV With Aft Skegs (ACVAS)
Description
The ACVAS is a hovercraft that is very similar to a conventional ACV, but is fitted with skegs at the aft end of each side skirt in order to give it a “foothold” in the water for (more efficient) marine propulsion.
State-of-the-Art Examples
This concept is still in the development stage. There are no production craft on the market, but some developmental prototypes and designs exist. The characteristics of one of these is shown in Table 44-12.
A photo of this same craft is shown in Figure 44-17.
Table 44.12 -ACVAS Vessel
Sumidagawa
20.0 Length, m
Beam, m
Draft, m
Hull Depth, m
Power, mW
Speed, kts
Passenger
7.9
0.5
3.7
0.8
30
80
Specific Concerns
The ACVAS looses the amphibious capability of the pure ACV although it can still operate in shallow water, particularly, if waterjets are used.
The concept is still at a developmental stage, but shows great promise.
Other comments applicable to ACVs also apply here.
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c)
Figure 44-17. Sumidagawa ACVAS During Operations
Surface Effect Ship As with ACVs, the SES concept aims at reducing friction drag by reducing the wetted surface of the hull.
Description
A Surface Effect Ship (SES) is a hovercraft that combines the twin rigid sidehulls of a catamaran with the flexible seals of an ACV fore and aft to contain, beneath the platform, a cushion of pressurized air.
This cushion supports typically 80% or more of the weight of the craft and results in a significant reduction in resistance at high speeds. A sketch of the concept is shown in Figure 44-18.
State-of-the-Art Examples
The first SESs appeared some 35 years ago and a fairly large number of SES passenger ferries are now in
Table 44.13 - SES Vessels
Characteristics UT928 HM 527 TSLA-70
Length, m
Beam, m
Draft, m
Power, mW
Displacement, t
Speed, kts
Passengers
38
12
2.6/1.0
5.1
150
48
350
27
10
2.6/1.7
2.7
87
36
200
70
19
3.5/1.1
30
Unknown
54
None*
* Prototype, designed to carry 200 t deadweight.
Like the ACVAS, the contact with the water allows the operation around the world. The principal characteristics of three of these are shown in Table 44-
13.
The largest SES built to-date is a 70-m prototype built by Mitsubishi and Mitsui for the Techno-Superliner program, shown in Figure 44-19.
Plans for large cargo/container vessels up to 5000 tons of deadweight are also being considered.
Specific Attributes use of marine propellers or waterjets as well as water cooled engines.
The sidehulls also provide the SES with lateral stability. This allows higher length-to-beam configurations than ACVs which result in a greater flexibility for operating efficiently at medium speeds
(lower hump drag).
SES are, therefore, suitable for a wide range of speeds, but particular so for high speeds (>40 kts).
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Figure 44-18. Surface Effect Ship (SES)
Figure 44-19. TSLA 70 Surface Effect Ship
Specific Issues
The added complexity and maintenance of lift fans, lift engines and end seals is often viewed as a penalty
Very long exposure to the “cobblestone” like motions of an SES may generate fatigue for the rider although they are not quite as prone to generate seasickness as the lower frequency motions usually encountered on compared to what can be achieved with simpler catamarans, but those need to be traded against the much higher speed/power performance offered by
SES.
Although the flexible skirts used at both ends of the cushion are much smaller than on fully skirted ACVs, their maintenance is still an important consideration for an operator. conventional vessels.
44.2.6 Wing-in-Ground Effect (WIG) Craft
A WIG, wingship or ekranoplan is an aircraft which takes advantage of the fact that a wing, operating in close proximity to the ground or water surface, will experience a reduction in lift-induced drag. However, during one cycle of operation, a WIG encompasses three corners of the lift pyramid. At taxi it is a displacement vessel, at take-off and landing it is a
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planing craft and then a power augmented ram wing and, finally, during cruise it is an aircraft in ground effect, a purely aerodynamic vehicle. A WIG may also operate at higher altitudes to circumvent traffic or small land masses for short periods of time. The ram wing and channel flow wing craft are hybrid vehicles which use aerodynamic lift to achieve high speeds. It is essentially a low-aspect ratio wing with the trailing edge virtually touching the surface and endplates sealing the wing tips to the surface. Both the WIG and ram wing types are described in this bulletin. a) WIGs
Description
WIGS are generally a mix between a seaplane hull and low aspect ratio wings which have been shown to obtain efficient speeds up to 400 kts within ground effect. When in the cruise mode, no part of the vessel is in contact with the water as illustrated in Figure 44-
20. Although the beneficial effects of ground effect on the lift-to-drag ratio of aircraft have been observed since the Wright Brothers, WIG specific research and development has only really occurred within the last
30 years. Most of this research was done in Russia and has only recently been released.
State-of-the-Art Examples
Following the opening of the iron curtain, a flood of information about Russian ekranoplans hit the western world. This information has shown that it is physically possible to build and operate a large WIG such as the
Caspian Sea Monster. One of the more notable achievements in the use of ground effect was the 1929 flight of the German DoX Flying Boat across the
Atlantic within ground effect. Some commercial applications of WIGs are presently being considered in
Germany, Japan, France and the United States. The characteristics of some examples of WIGs are shown in Table 44-14. It should be noted that, except for the
Ekranoplan shown in Figure 44-21, none of these craft have been operated commercially.
Specific Attributes
The ability of the WIG to fully leave the surface of the water allows it to operate in the aircraft speed regime which is, at a minimum, twice that of the typical highspeed marine craft.
Specific Issues
There are no commercially operated WIGs. They are basically still in the demonstration stage, although the western world has greatly benefited from the research and development accomplished in the former Soviet
Union.
Because WIGs are very similar to aircraft, their structure and mechanical systems are of higher complexity than the structure of a typical marine craft.
WIGS are operationally limited by sea states and winds for take-off and landing.
Numerous regulatory issues would need to be addressed prior to implementation of these craft as passenger carrying vehicles.
Figure 44-20. Wing-in-Ground Effect Craft
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Figure 44-21. A.90.150 Ekranoplan in “Flight”
Table 44-14 - WIG Vehicles
Characteristics
Length, m
Beam, m*
Power, mW**
Displacement, t
Speed, kts
TAF VIII-5
19.8
8.5
1.2
9.2
95
Passengers 15
(*) The beam indicated designates the wing span of the WIG.
(**) The power indicated is the cruise power only.
A.90.150 Ekranoplan
58
31.5
11.0
125
216
150 b) Ram and Channel Flow Wing Craft
Description
Operating Ram wing or Channel Flow wing craft are not truly aerodynamic craft, but are supported by a combination of hydrostatic, hydrodynamic and aerodynamic forces. These craft also tend to by multihulled vessels using the cross deck structure as the wing and the hulls to cap the wings. A ram wing operates by creating dynamic overpressure on the bottom side of the wing to increase the lift-to-drag ratio when at operational speed. The channel flow wing operates similar to a WIG in that the trailing end of the wing is open.
XTW-2
18.5
12.72
0.448
3.6
100
14
State-of-the-Art Examples
The theory behind ram and channel flow wing craft is not new. Applications have included very high-speed catamarans (>100 kts) used in offshore power boat racing. Only recently has there been any commercial applications of these designs albeit at much lower speeds. The particulars for two of these designs are summarized in Table 44-15. One of these is the
Quadrimaran shown in Figure 44-22.
Specific Attributes
The ability of the ram or channel wing craft to utilize both aero and hydrodynamic lift allows them to operate in the upper end of the speed regime.
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Specific Issues
There are only a few commercially operated craft and these have not been operating for a long period of time.
Ram and channel flow wings may be structurally and mechanically complex when compared to typical multi-hull hullforms.
Table 44-15 - Ram Wing Vessels
Characteristics Wild Thing Quadrimaran
Length, m
Beam, m
Draft, m
Hull Depth, m
Power, mW
Displacement, t
Speed, kts
Passengers
30
11
Unknown
1.2
2.25
80
45
149
25
10.4
0.4
Unknown
1.25
216
40+
150
Figure 44-22. Quadrimaran, Channel Flow Wing Craft
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