miles
away but a hydrofoil is a measure of
progress
that has come at last to stay.”
-Dr. Leopoldo Rodriquez
M.D.,
Cantiere Naval-Technical
Shipyard
[Italy]
1.
The word unconventional conjures up in ones mind various things, from
long hair and a bohemian lifestyle to avant-grade architecture. But what, if anything, does it imply when applied to the maritime
scene? The conventional in this environment
may be construed as merchant vessels plying serenely for trade, warships going
about their business, submarines, perhaps, engaged in their mysterious tasks
and aircraft flying about in execution of their chores. Conversely, the unconventional would can note
the family of surface skimmers like hovercraft, hydrofoils, SWATH ships, ram
wing craft and the like or by a stretch of imagination; mammoth submarine
bulk tankers [if these could become a reality].
2.
In the same way that the super tankers, at their inception, may have
been thought of as unconventional, but are now quite commonplace, similarly,
a number of innovations like the helicopter, have gone the same way. In the case of surface skimmers, however, the
state of the art is still sufficiently novel and exclusive, to a few, for
these craft to be called unconventional, within the meaning of the term as
specified in the Oxford English Dictionary.
3.
The hydrofoil has been conceived through a marriage of the aerospace
and marine technologies [1]At
the present moment this craft as well as the other such innovation – the hovercraft
– have a bright future in numerous applications in the military and civilian
fields.[2]
4.
The maritime environment today is fraught with a high threat factor
where large warships are a definite liability.
Aircraft carriers, for instance, require protective screens of escort
ships, which are out of proportion to the cost effectiveness of the Task Force.
Even so, some justification for carrier task forces can be found if
one is to argue, for the preservation of a global stake, like the USA and
more recently the USSR are doing. For smaller developing nations with a regional
stake this argument is a fallacy. What
is required by them are small ships and craft with a sufficient punch, that
brooks no mischief. It is for this
reason that today, small fast craft, armed with immense firepower, are cheaper
by the dozen.
5.
A stage has been reached, when an edge in this high threat environment,
can be obtained only by him who exploits the one capability which gives a
significant advantage – speed. For
conventional displacement craft the speed barrier of 35 knots or so cannot
be economically crossed. This barrier
needs to be crossed, however, for the advantage, to accrue. The rapidly blooming skimmer technology has not only enabled this
speed barrier to be broken, but sights are now set, on the attainment of a
hitherto inconceivable speed at sea – 100 knots.
6. It is the aim of this paper to examine the feasibility of adapting the hydrofoil craft to the Indian environment. The aspects studied would be the need for such a craft and the capability of a nation like ours to imbibe the emerging technology and put it to practical use. The associated effectiveness of the craft, cost and otherwise, as against conventional displacement vessels like frigates, for the roles envisaged, would also be examined.
7.
India is a nation, as yet, developing, which can ill afford the exorbitant
cost of defence in general, and warship production in particular, but which
nonetheless has an important role to play in the region.
To give credibility to this status it is imperative, that the Indian
Navy has a credibility at sea. With
our Research and Development [R & D] and industrial infrastructure it
is more than possible for us to adapt to the basic skimmer technology required
for hydrofoil craft, and use its advantages to achieve, in some measure, this
credibility. Additionally, hydrofoil technology is sufficiently widely dispersed
for its acquisition, to be possible, from more than one source.
8.
Through the application of this technology it is possible to convert
the fast patrol boats [FPB], in the inventory from merely fast craft to craft
with immensely improved capabilities. The
OSAs, for instance, if given a shot in the arm with this technology, could
be transformed, into well-nigh unbeatable adversaries, at sea.
9. For the study, accurate figures of the cost or time required to design a modified diesel, for the hydrofoil craft; have not been readily available. However, the annual costs for running such craft, the cost for modifying existing assembly lines and developing designs, have been extrapolated from information, regarding similar projects, carried out elsewhere, allowing for factors such as inflation, existing know-how and the possibility of collaboration with foreign firms in the field.
10.
Understanding the principles of hydrofoil operation requires knowledge
of some specialized terms. These have
been placed in the glossary at Appendix
A.
11.
The
study will examine the hydrofoil craft under the following headings:
[a] History of Military Hydrofoils.
[b] Principle of Operation.
[c] Military hydrofoils – their roles and advantages over other
craft.
[d] Current state of the Art and Futuristic Projections.
[e] Do we need the hydrofoil.
[f] The possible options.
[g] The Financial Burden.
Sources of Data
12.
The source matter available in the College Library, on which this study
is primarily based are the monthly editions of Hovercraft and Hydrofoils,
the annual publications of Jane’s Surface Skimmers and data available on ship
building in India. The Bibliography
has been placed at Appendix B.
13.
No discussion on the pioneering design and development efforts, in
the field of hydrofoils, can begin without a mention of Baron Hans Von Schertel. In the period, from 1927 to 1936, he designed
eight experimental boats, despite the negative attitude and discouraging prejudice,
against the concept, of the conservative ship owners of the old school, in
the Germany of that day. He was however,
convinced of the feasibility of the idea, of flying on foils in the water,
to reduce drag and thus attain extremely high speeds, whilst improving sea
worthiness. This steadfastness and
some financial help from the pragmatic management of the Rhine Shipping Company
enabled him to demonstrate his seventh experimental boat to Professor Kampf
of the Hamburg Experimental Institute.
14.
Professor Kampf was so taken up by the concept, that with help from
the Institute, Baron Von Schertel, proved the utility of this craft, when
he did a trip, in his eighth boat, on the Rhine, from Mainz to Koln and back,
a total distance of 370 kilometer in unfavorable weather conditions.
This first success induced Herr Gothard Sachsenberg to form with him
the Schertel-Sachsenberg Syndicate, in October, 1936, which granted a license
to the Gebrunder-Schsenberg Shipyard, in Germany.
This Shipyard subsequently produced a 17-ton minelayer [VS-6] and other
hydrofoil craft for the German Navy.
15.
In the meanwhile Professor Tietjens, in the United States had tested
a one-seater hydrofoil craft using a monoplane configuration, for which he
filed a patent in 1934. The Vertens
Shipyard in Germany obtained a license from him, in 1940, and also constructed
a 17-ton minelayer. The problem of maintaining flight in a seaway
was not sufficiently solved, however, and the craft crashed several times
due to foil broaching. Although the
boat was considerably faster than the Gebsuder-Sachsenberg VS-6, its turning
ability and longitudinal stability were not satisfactory. The Tietjens concept never came into prominence
and development was eventually stopped.
16.
Two other personalities who bear mention as pioneers, in the field
of hydrofoil technology, were Grunberg who had migrated from Paris to USA
in 1939 and Christopher Hook, an American.
Both of them were instrumental in developing the fully submerged foil
system and the associated control system.
17.
Construction of the first vessel for the German Navy was started in
June 1940 and completed in 1941 at the Gebruder-Sachsemberg Shipyard at Dessau-Rosslau. This hydrofoil craft, called the VS-6, was
equipped with a vee-foil system in a tandem configuration. The craft attained a speed of 47 knots on two
1,500 h.p. diesel engines, each running its own propeller.
18.
A month after starting construction of the VS-6, a series of six smaller
craft was started. The propulsion
system of the last of these is interesting as an attempt was made to avoid
the use of long propeller shafts and their brackets by employing a double
bevel gear or a “Z” drive, for the first time.
This craft was less thoroughly tested than the VS-6, as the Russian
Army occupied Dessau-Rossiau just after completion of the craft.
19.
The wartime hydrofoil craft which deserves the most attention was the
80-ton VS-8. Just as the speed of
the VS-6 was unchallenged for a number of years the VS-8 remained the largest
craft for over two decades. It was
initially designed as a 70-ton fast transporter working on two super charged
2,500 h.p. Mercedes-Benz diesels. The
craft was designed to carry tanks from Sicily to North Africa. For this purpose, the after quarter of the VS-8 could be flooded,
so that a pontoon raft with a 20-ton Army tank could float in. After unloading the tank and withdrawal of
the raft, the ballast water was pumped out and the craft could take off. Due to the supply of normal 1,830 h.p. diesels
and weight additions during construction, the craft could attain only 37 knots
in six-foot waves as against the designed 45 knots. The dimensions and performance of the VS-8
were as follows:
[a] Length overall 105 ft.
[b] Beam over deck 25 ft. 6 ins.
[c] Width over front foil 33 ft.
8 ins.
[d] Draught hull borne 14 ft.
[e] Draught foil borne 6 ft.
6¾ ins.
[f] Displacement 80 tons.
[g] Relative Payload 33%
[h] Power 2
x 1,830 h.p. diesels
[i] Max speed 40 knots
[j] Material hull: aluminum
20.
Another major wartime construction was the 46 ton, VS-10, torpedo boat
which was designed to use four 1,500 h.p. diesel engines and be capable of
60 knots. The outcome of this venture was unknown as
a day before the scheduled launching of the boat, it was completely destroyed
in an air raid. Another fast hydrofoil
to be tested was a single seat 30-ton torpedo boat. During tests in the lakes of Berlin this craft had attained 52 knots.
Tests stopped at the end of the war and were not completed.
21.
Concluding the line of wartime boats one particularly unusual craft
was the four-ton Pioneer workboat built for the German army’s Pioneer Corporations. The requirement was for the boat to be able
to beach. This was achieved by providing
the forward hull of the craft with floats with the forward foil between the
floats. The rear, foil was attached
to the transom by struts. As the craft
approached the beach the foils were retracted and the craft settled onto the
floats maintaining a constant draught of two feet six inches. With the foils fully retracted the craft could
run ashore bow on and remain steady on the floats for unloading or loading.
22.
Switzerland: Baron Von Schertel moved for good to Switzerland
in 1952, for the foundation of Supramer AG,[3]a
concern which today produces one of the widest range of hydrofoil craft. He took with him all the scientific works;
results of tests and trials carried out before and during the war, as well
as construction plans of various hydrofoil craft built during the war, in
other words the technical know-how of two decades.
These form the basis on which Supramer craft are built today. Baron Schertel is presently one of the directors
of Supramar AG.
23.
Soviet Union: The Soviets received their first knowledge
of hydrofoil technology from studying the craft which fell into their hands,
when the Russian army occupied Dessau-Rosslau.[4]
This was a 6.3-ton coastal surveillance hydrofoil in which
the Z-drive had been used for the first time.
This Schertel-Sachsemberg vessel formed the basis, for the Soviet passenger
craft Myr and Strela and the military version of the Strela, called the Pchela,
which are in widespread use today, in the USSR.
The Russians subsequently developed their own semi-submerged foil system,
for their boats operating in relatively calm shallow rivers.
24.
Italy: In 1953 one of the principals of the Leopold Rodriquez Shipyard,
in Italy, obtained a construction license from Supramar AG. The Rodriquez Yard which had earlier been a
repair yard for locomotives and railway carriages was transformed into a
25.
United States: Apart from an examination of the possibility
of constructing foil borne landing craft interest in naval hydrofoils, generally,
was not displayed in the United States, till after the Second World War.
After some preliminary comparative tests, the Department of the Navy,
decided to abandon the surface piercing foil system and employ fully submerged
foils. This was, possibly, due to
the influence of Grunberg and Christopher Hook in this field.
The fully submerged foil was, however, found to be inherently unstable. To achieve stability an automatic control system was necessary to
vary the lift of the foils according to their submergence. Grunberg did toy with the idea of developing
an autopilot based on sensing accelerometers on the principle, enunciated
by Nicolai Miniovsky. This principle
is the foundation, on which all modern autopilots used in aircraft, inertial
platforms and spacecraft, are based[5]. The practical application of
this principle was hampered, however, by the lack of precision engineering
and complex electronic control mechanisms in those days.
He thereafter, devised the Grunberg system, which though of simple
design and a high drag and gave a rough uncomfortable performance in waves.
Subsequently the Gibbs and Cox design and an autopilot developed at
the Massachusetts Institute of Technology were tested.
In 1959, test runs were carried out on a DUKN amphibian when the vehicle
was also to attain 35 knots when equipped with fully submerged controlled
foils and a gas turbine. In 1961 the programme was expanded to include
a design of a LVHX-2 [Landing Vehicle Hydrofoil] which also attained 35 Knots
with a 1,000 h.p. gas turbine and fully submerged foils. In 1960 super caviating foils were tested for
the first time, on a 50 feet amphibious experimental craft, constructed by
Grumann, called Sea Wings.
26.
Canada: In early 1961 De Havilland Aircraft of Canada, was contracted by
the Department of Defence, to construct the FHE 400, to establish the feasibility
of an ocean going ASW hydrofoil. The
first foil borne trails took place in April 1969. The craft was a super caviating steerable bow
foil and sub caviating main foil in a canard configuration. The main foil is a combination of the fully submerged and surface piercing foil types
and has a unique design made for excellent sea keeping qualities. The FHE 400 has been commissioned into the
Canadian Navy as the Bras d’ Or.
27.
The concept of the hydrofoil craft was born from the need to break
the speed barrier, caused in the case of displacement vessels, due to the
drag caused by wave resistance. Sheer
increase in power did not provide the answer as it was realized that after
a certain stage, normally reached at speeds of approximately 22 to 24 knots,
an inordinately high increase of power was required to generate even a marginal
increase in speed. Thus the speed
of displacement vessels is restricted to about 30 knots for larger vessels
and about 35 knots for small patrol craft.
28.
The use of a foil section to gain lift had been demonstrated, by the
Wright brothers, at the turn of the century.
It was not long before the aerofoil spawned the hydrofoil concept,
designed to overcome the speed barrier. A
significant aspect of this -concept is that since water has a density 815
times that of air the same lift as an aeroplane wing, is obtained for only
1/815 of the corresponding wing or foil area; for a given speed.
29.
Construction: The hydrofoil craft is essentially a lightweight
hull similar to that developed for FPBs i.e., it is a hard chine hull section.
The hull is supported on foils which are mounted on struts forward
and aft. With the increase in speed the foils generate lift until at the
take-off speed the entire hull rises out of the water. The percentage of hull weight supported by
the forward or aft foil, when the craft is flying, depends on the configuration.
There are three types of foils employed currently namely the surface
piercing or vee foil, the fully submerged foils and the shallow draught submerged
foil invented by the Russians, for their craft plying in calm shallow river. All the foils can be made retractable, to decrease
the hull borne draught. Among these
the fully submerged foils being inherently unstable require an automatic control
system and is the most expensive to install.
30.
Propulsion System: There are two methods by which hydrofoil craft
are propelled. Firstly by propellers
which are mounted on shafts inclined between 10° to 15° to ensure submergence
of the propellers when the craft is flying and secondly by water jets.
In some craft there are separate propulsion system for hull borne and
foil borne operation to increase the endurance of the craft and provide an
emergency “get home” capability. In either case, whichever method of propulsion
is used the main engines can be either gas turbines or diesel. Examples of the various types of propulsion
systems are available in craft currently in operation such as:
[a] High Point: This
is a hydrofoil craft built by Boeing Aerospace Company for the US Navy.
The foil borne propulsion is provided by two gas turbines coupled to
a pair of contra-rotating super caviating five bladed propellers whilst the
hull borne propulsion is provided by a single diesel driving a propeller.
[b] Flagstaff: This
hydrofoil gun boat built by Grumann Aerospace Corporation is an example where
a single gas turbine with a controllable pitch propeller provides foil borne
propulsion and two diesels driving one feet four and half inch wide water
jets, equipped with + 35 degree steering and reversing nozzles, provide
hull borne propulsion.
[c] Swordfish: This
is a missile equipped hydrofoil craft built for the Italian Navy, which uses
a single gas turbine driven water jet for foil borne and single diesel with
propeller or hill borne propulsion.
[d] Soviet Hydrofoils: These
craft seem to favour diesel engines for both foil borne and hull borne propulsion
possibly due to the economy of operation.
31.
Comparative Study: Despite the major drawback of low efficiency
of water jet propulsion it has specific advantages over conventional propellers
namely:
[a] It allows speeds in excess of 50 knots as beyond this speed the drag of appendages like propellers hubs and brackets is too high.
[b] Besides the ship auxiliary and lubricating
machinery, it does not require any additional units as everything is already
integrated in the system. Water jet
propulsion systems normally require a bow thruster to enable control at slow
speeds.
32.
Operation: For take off the foil depth is set [in case
of fully submerged foils only] and the throttles are advanced. As speed increases the hull clears the water.
Landing is accomplished by reducing the throttle setting.
Speed diminishes from 45 knots to 15 knots in as little as 30 seconds. There is a height command lever provided in
some craft to make emergency landings. In
this case since the foils are not retracted a minimum depth of five fathoms
is required.
THE ROLES AND ADVANTAGES OF NAVEL HYDROFOILS OVER CONVENTIONAL WARSHIPS
33.
Although military hydrofoils had been built during World War II, it
is only recently that they have found acceptance, among NATO nations, as instruments
of naval warfare – some 30 years after they had first proved their feasibility. Unlike the NATO nations, the Warsaw Pact countries
were quick to recognize the suitability of hydrofoils for military roles and
have been employing them on surveillance and other roles for many years [6][6].
34.
If the world fuel shortage is taken into consideration, as well as,
the pollution problems which strangle today’s economy and life, the hydrofoil
is tailor made to overcome these difficulties.
A hydrofoil files clean and requires only 50 per cent of the power
of a displacement vessel of comparable size, for a given speed. The advanced military hydrofoil is superior
to conventional warships, due to its superior speed, which can be maintained
even in a seaway and due to better sea keeping ability. In fact, hydrofoils do not need to be large
[multi-thousand ton size] to provide an all weather capability, which is in
stark contrast to conventional warships.
35.
Various comparative studies have been undertaken to ascertain the validity
of better sea keeping qualities in a hydrofoil as follows:
[a] A study conducted by Boeing, for the Royal
Navy and presented before the Royal Institute of Naval Architects, showed
that the Boeing Jet foil [a 110 ton craft with fully submerged foils controlled
by a sonic control system] was capable of operation in the North Sea 96 per
cent of the year [at speeds greater than 38 knots] [7][7]. This corresponds to wave heights
of four meters [see state 6].
[b] In November 1977, a study undertaken by
the Cantiere Naval Technica [Italy] showed a far lesser roll and pitch in
a surface piercing foil craft in sea state 6 compared to a conventional ship
at 20 knots in sea state 5.
[c] An all weather; high speed, smooth ride capability is illustrated in the graph opposite which was obtained as a result of a study, conducted by another leading Italian hydrofoil manufacturer; the Cantiere Navli Riunitis [CNR]; the makers of the “Sparviero Swordfish” missile hydrofoil, for the Italian Navy.
36. It is doubtless that larger warships due to their greater size and lesser maneuverability, are targets rather more vulnerable to tactical offensive weapons, like missiles. They are also more attractive both in terms of value and prestige. Therefore, employment of even a modern frigate, like the Leander, in a high threat environment is too hazardous, to be cost effective. Another consideration is the crew size of larger ships. This is quite a remarkable factor because of the high level of specific and qualified training required, for personnel to run the complex and sophisticated modern equipment.
37. All these considerations, of course to the advantage of the small ship, normally find compensation, in the employment limitations, which they have to face in rough sea conditions. The hydrofoil craft has overcome this handicap, and guarantees to a small craft the ability to put to sea in safety, have good platform stability, high speed and maneuverability and an all weather capability. It has been conclusively proved that the speed advantage passes from a hovercraft to a hydrofoil craft beyond sea state 3 and to conventional craft beyond sea state 6.[8]
38. When considering hydrofoil craft in general, and naval hydrofoils in particular, it is easy to get an impression that these are highly specialized vessels. This idea promotes the belief that they need to be supported by highly specialized workshops, specially trained and highly skilled technicians and extensive logistics. As a result, the idea develops that exceptional costs are involved, not to mention the high technical risk.
39. Any modern equipped FPB yard, however, would also be able to construct and support naval hydrofoils if a certain design philosophy is respected. When operational and maintenance requirements of a modern FPB are compared with those of a naval hydrofoil, it will be seen that the problems involved are identical Garden Reach Shipbuilders and Engineers [GRSE], Calcutta which has hitherto constructed FPBs for the Indian Navy could therefore be ideally suited for the purpose.
40. The lightweight form of construction, developed for hydrofoils, is in demand, increasingly, for a modern FPB’s. However, as the weight of marine engines is reduced,
so the need for this lightweight construction for naval hydrofoils is decreased. This enables the project engineer to specify heavier materials and use less expensive approaches, with lesser demands for a high level of metallurgical engineering. The marked similarity between well proven FPBs and hydrofoils currently operational is evident from the table below. Another thing brought out vividly in the table, is the power required, for the same speed, for a FPB [MT 250] and as hydrofoil [MZ 50G] of comparable displacement.
|
|
|
FPBs |
|
|
Hydrofoils |
|
|
|
|
SA'AR |
OSA |
MT 250 |
MT 504 |
FHE
400 |
TURYA |
PEGASUS |
|
|
|
|
|
|
|
|
|
|
Max
Displacement |
240 |
210 |
250 |
250 |
212 |
190 |
235 |
|
|
|
|
|
|
|
|
|
|
Max
Power [h.p] |
13,500 |
12,000 |
25,000 |
14,000 |
22,000 |
13,000 |
-- |
|
|
|
|
|
|
|
|
|
|
Max
continuous |
30 |
27 |
53 |
53 |
50 |
40 |
40 |
|
Speed
[knots] |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Max
dash |
40 |
35 |
60 |
60 |
60 |
-- |
45 |
|
Speed
[knots] |
|
|
|
|
|
|
|
|
|
|
|
|
| |||