Hydrofoil craft of today and tomorrow

Hysroo.i boats

are vessels, the hulls

of

which are lifted out of the water, as speed in-creases, by so-called underwater wings and

mo-sad fumed in din position.

In thus way. both the drag and the cffcct of the waves are to a large extent neutralized, always provided that the sane of the waves does not esmed the dimensions of the bust. The wings, profiled slim-larlyto those of an aircraft, arc joined to the hull by supporting Struts. Underlying the shape of the wings see aerodynamic and hydrodyflamic laws with special reference to the conditions which arise whets tilled flaps and proftles move in the boundary betwecn two media, namely air and waler. Since however, additional compli-cations are introduced by the wavcs, the hydro-dynamics of the free water surface arc basically more difficult to deal with than the theors of air-craft or of fully submerged submarines, both of which move in a single medium.

The fact that water is about 800 times denser than air enables underwater wings to be of sub-staniiafly smaller dimensions than aircraft wings. this despite the lower speed. Disregarding for the

A' D4i1. lag. K. Bülier. Lawrnse

moment the effects of the free water surface, wings and profiles can be treated in accordance with the principles of aerodynamics. This leads mainly to thin foil surfaces, capable of carrying high static beds and requiring a correspondingly high number of supports, which in turn means in-creased drag and a reduction in thc lift-drag ratio. In the higher speed range-for foil ships this mean, around 60-80 m.p.h.the dimensions and shape of the foil must also take account of ca-vitation.

Cavitation is

roughly similar to

the p1-ic-nosnena occumng with aircraft wings in the sonic speed ranges. The cavitation of propellers and wings can be explained by the fact that static low pressure arising at the top surface of the profile drops to vapour pressure and leads to the lorina-Lion of bubbles. These bubbles wander in the higher pressure zone, i.e. in the arcs of the rear wing edge, where they coliapsc. and damage is caused by the water.

Until a short time ago, it was thought that this cavitation limit would not be exceeded, but now so-called supercavitating profiles for water

v.

Schcsbouwkunde

';

fCraft of

Today and Tomorrow

propellers and wings have been developed in the USA which, at good degrees of mechanical efficiency, are capable of use beyond the speed limits which have existed until now. Further problems do. however, arise in this connection. If excessive drag is to hc avoided, wings intend-ed for high speintend-eds must have very small di-mensions and extremely thin profiles, in sonic cir-cumstances making a essential so use expensive methods of construction and to build in expen-sive materials e.g. titanium. In

the cue of

military hydrofoil ships the cost factor is unim-portant, and the difficulties can accordingly be overcome: as far as civil hydrofoil boats are concerned, however, each case has to be consid-ered ass its merits and other solutions found.

In determining the cavitation limit and the permissible lift coefficients in connection with it, attention must 1-c paid to so-called orbital velo-city in thc water particles of the wave, which is equivalent to a rotating inosetnent of the water and thus leads to changes in the angle of inci-dence of the wing.

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Fig.S. lpsadc po lot osdoes sels (sJs.p. tomes) maw iesed. IA - mabcasuatu.g lo.l boat

II -

s.muaa lod boat; 2 - Y-chnie spesdbo.i. 3 - corsentional desp)accsnnst sane)

4- me.oia bmt; 3-

- hind-wing astreafl.

In (he ierty stagmof its deeelopmsent. the hydro'

boat gsse ewe to a large number of dient

vction nsuhode and patented idosa. which the esunom shapes of the feat aireraft. This m coewisuction arose from the osrly diet

to

''

of

stability in pitch, roll and

ry of depth, and can be czpl.ined by the

say

doi wase of knowledge at the time

con-rnng the by*odynan

of the wii

at the

flee and asused easer surface.

The hy*uioil boat sywase which arc here

under disesiun and of which diagram. appear

rnFict. 1-4, are aa follows:

I) The boat ilhustratcd is diaracterizrd by its

surfacr-pisrcing V-lode which may vary aceording to tl

shape and azrangst at the bow or the

acre. Adequate pitch and roll stability and

ole-satior stability are acbicvcd by wing parts which

penetrate the waler surface. When the boat

eaccuies a banking mosement, staLiilizing forom arwe at the submerging and emerging wing tips.

The Supsamar boats, built on the so-called

Scheriel-Sach.enbcrg system, belong to this group. In this system the boats have fully submerged foils at the stern. Stability is achieved with the aid of additional wings or bodies which glide on the waters surface. V. Grunberg experimented with similar boats to France in the twenties, and lately this system has been used by .Aquavion.

In this group, the foils are arranged in the form of ladders, stability being maintained by the

sub-merging and esub-merging of individual foils, as in

the case of I above. In 1911 Graham Bell was

concerned with development of boats of this kind. as was the Royal Canadian Nas', a Few ynars ago. 41 These are boats with fulls submerged foils, the

load, shape and arrangement of vhi,.h can sirs,

but which in any case are without inherent

sta-bility. This stability must be ahievcd

automata-calls or bs ckctrons,sgnctic sensors which regulate

the angk of incidence in response to the surface

of the water A further improvement in the

per-fornunce of hydrofoil boats is to be expected from

this tpe of cvirisruclion, since the

mm np arc

Tha meat lpottaM bydsefati syate

Sad

Fe.,. Boat wsth parity siutace-p.ercuig inherently stable V-foils under the bow aad 15sfn (Sch.rtel-Sachtsnberg

Systemi.

Fig. 2. Boil with fully mbnwrped (nib under the seen

and stabdiaing lost, under the bow.

Fig. 6. Seapsing qualityofa lost boat vs. length of hull. I -Inoit of

w.s height at full engine powe1'2 - limitof wuse height at vedwsd speed but with hull still emerged. 3 - wage of wave heights at which the boatcon onintravel submerged.

Fe. .1. Roil with inhcrcnilv stulukfoils

urr.nrd

aJdr-wise underbooand stern.

bill length (it)

removed from the influence of the water surface and subject to orbital movement on a imall scale

only, which diminishes as the wing gets further

from the water surface.

As the wing is no longer exposed to aeration, the serious aeration problesm facing the constructor

of wings which penetrate the water's surface do

not arise. However, deeply submerged wings

generally require rather long supports, which,

besides causing constructional difficulties, increase the drag. The stabilization devices so far developed

are on the lines of the automatic flight control

systems used in aircraft, but such installations are both costly and subject to disturbance. Supramar

is therefore developing a new wing with

quasi-inherent stability for boats of this type.

As already mentioned, in the case of the foils

which penetrate the water surface or approach it, there exists the danger of aeration. This phenonie-non is produced by the pressure on the top side of the foil and may result in instability in the wing. To meet this danger, those parts of the foil lying near the water surface are provided with "aeration' proof" profiles.

Fig. S shows the specific power requIrement of a foil boat of some 300 tons displacement versus speed, the same relationships being likewise shown

for consentional vessels, in order to facilitate

comparison. From this, it can be seen that at a

certain speed range hydrofoil boats must be more

economical than other equally large and fast

means of transport.

As compared isith other fast ships. hydrofoils

cthibit lower power requirement, still higher

speed. particularl good seagoing quality (hg. 6)

and less wase formation. They reach a speed

about threc times that of conscrition.tl vessels

and can accordingly carr

three tImes is many

passengers over the sante route during the same

period of time with lhc result that ..is evperience

to dair h.rs shown, they are comprtltise with ill

eon'v'ntional coastal sesscls Their dis_idmantages

art considered to be their greater draught when

moming in thc water and th

bulkiness 01 their

flon.intierrnti, mtabk

I

Fig. 4 Bout mitt liaiI submerged

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In the second world war the VS $ tank tramporic.

was built at a shipyard in Hamburg- Harbors.

Length l0 II masintum speed 45 knots.

The P.T 20 Standard type

transpost foil boat is m rS ice in the Mediter-raisean. in Japsisese waters. off the VoaeusIsa coast and ott the North Weal Coast of the USA.

The Sos-set Meje.,, fast boat foe 150 psa.enershas fcp mote nsooths burn ulaily plying the Volga between Gotti .nd

Ubats-ossk and attains cruising

weeds of 40 knots.

H

_______a'-.-.-,.-Hydrofoil.

Apart from the I SSR. it v,as onis in the ISA that shipping authorities and nasal circles sup-ported the use of hydrofoil boats and accordingly passed the word to the aircraft industry to took foe a new field of application in this sphere. In Soviet Russia, besides the hydrofoil passenger vessels already in use, boats of the Rtzkera class carsying about 70 persons) and of the Sputnik class (ISO persons), as well as still larger vessels, are expected to come into operation in the next few years over the whole river and lake traffic system. As for the USA. the Maritime Adminis-tration has recently placed an order with the Grumman Aircraft Engineering Corporation foe the development and construction of a vessel with a displacement of 80 Ions and a speed of 70 knots.

The American aircraft industry in the foil

boat a welcome addition to its building

pro-giamme, especially considering the decline in military aircraft construction. Super-fast and super-large craft are under development, which will probably have more significance as military vessels than for civil purposes. A first US naval hydrofoil ship, the joint creation of the Bureau of Ships and Boeing, will shortly be completed. and this vessel, intended lo anti-submarine work, should herald the era of military use of hydrofoil craft. This first ship will have a displacement of about 110 toes and a speed of 50 knots, but the U.S. Navy is said to be alecad, plannIng the con-struction of larger and substantially laster ships of this type.

When an American 10-year plan, which fore-sees the building of even ocean-going vessels of

this kind (1,000 tons displacmern. 100 knots, nuckar propulsion of 52.500 h.p.) was under dis-cussion, it was the shipbuilding industry, with its conservative altitude, which was held responsible for the lagging development of the Iwi boat.

In looking at this talc of woe, one cannot help being reminded of the principle of Archimedes. initiated in the 3rd Century B.C. hut not put to use until 1800 years later, when i'i about 600. shipbuilder first applied this lan in his calcula-lions.

rhrre.c to draw,ng of a ron boat developed shorti' after

the war for the Ss,'yt \nt and equipped with a

piston-engine driven waler erection turbtne. Thus vessel was the project of a (,rrm,Ln design eftice at rise Ro,aiatacl-Sachsenberg Shipsard.

Meanwhile there

hsc been

considerable changes in shipbuilding Although at launchings

and or sutular occasions it is customary to speak of an "esemplary development in shipbuilding." in fact it is clear that decades have passed since the seasel of conventional construction reached a state of perfection which, for physical, technical and commercial reaSons, can hardly he further iisipeosed on The conventional ct-aft a dl

there-fore probubly in future also follow the curreni dale of technical development, and a ill no longer be marked by any Increase in speed. but by the completion and modernoution of the propulsion units and internal installations, as well as by the

application of the laies rcflnwi,ts in

hydro-dynansics. As is well known, this stagnation in the development of slispa is inc to the fact that eSci) further increase In nsu.izum speed must be paid fee b

an oneesnous u5c'e in motive p...cr.

no

proposnion.Thehydro-loll boat, bused on the utilization o(hydrodynamic

lll

lemma. oas the only pouthility for

ship-iding to liecak the stalemate. l'he fact that in bye years the hydrofoil boat has given proof that it is a practical propoatton

saul undoubtedly have far reaching effects on shipping, especially coastal and island traffic.

In addition to mosenisents of passengers in coastal and inland waters, in which hydrofoil boats base shown themselves far supenor to the convential vessels, such boats also lend them-selves to use by' police, customs and pilot services Furthermore, they can be used profitably in

industry in conditions where workers and materials have to he moved quickly. e.g for oil production in the coastal waters of Venezuela. The valuable assistance which hydrofoil boats can render in the transport of perishable goods. especially in tropical waters. ShOUld also be mentioned.

On the strength of its experiences to date. Suprama is in a position to draw a fairly clear picture of the present applications for hydrofoil boats. As regards the future, special endeavours will have to be made towards a further increase in speed, an improvement in seagoing quality and an increase in the useful load.

What sue hydrofoil boats will reach is. for the tune being. still an open question. II one forgets military uses and confines oneself to conanercial

Stern foib. suppoetn5

suits. niddin and

propsi-let shafts of ihcPT,O

P1 'ii)

(,eneisl sot UI

Ssprafliar S nm ionttantt 'mSSd for 4O passengers. '4asumum SPCtd: 33 knots.

Bow toils and suppoeting strati a(ihe P130. The bound-ary enema ma. the upper side o( the foil sea ,o'called as bamens(Ofptt'Cfliiflg aerationinth unasay.

'onsidcrstions, it seems that, in the present state of technical knowledge and research, the hydro-foil boat will for the presen. hardly reach, let alone exceed, a displacement of L000 tons. The largest hydrofoil boat so far built was produced during the war and had a displacement of some SO tons. A boat at present under construction in the I.SA will haves displacement of SO tons and is expected to attain 70 knots. The vessels cur-rently in development at Supramar. with a dis-placement of some 120 tons, are designed for a maximum speed of 53 knots. In the coming years, Supramar will lay down a still larger type foe 550 passengers with a displacement of 250 ions. Equipped with 2 ps turbines of altogether 35.000 h.p.. this boat will attain ama,umumspeedof70 knots. As regards boats already mentioned and those of the future, one should be able to count on a payload amounting to 25-35' of the full displacement. Ocean crossings with a boat of this type are, however, ruled out by the Large fuel con-sumption, but this obstacle will perhaps bc over-come later on b' a nuclear propulsion system.

From the hydrodynamic, technical transport and construction points of view, the hydrofoil boai occupies a position midway between aircraft and ship. The question as to whether as a general rule only shipyards should build hydrofoil boats or whether, as seems the case in the USA ioslas, the aircraft industry should take them up. .anoot yet be answered, depending as it does on lines the further development of thcse new sesscls will proceed. As long as it is only a question of building normal bo,its in relatively small quanti-ties, isv have been alread built by shipsards of various sizes, the aircraft factories should not be competitse in price This position ni,iy of cstur,e

- SW,'

tss. XcN4 Ø

-

d

Hyórooii

ships ate now being .ucee(uIly

oçaated to many parts of the world. So far, their

_

iaiil

f

purposes on

mutes where ed is desirable, but recently the United States Navy has become keenly and actively intcrested in them as a result of modern developments in the submarme. which can now operate

buwul1 for prolonged periods at

remarkable speeds. Again, it is because of the desire foe higher speeds in a surface ship, this The author adev to make deal that the statements sad enpruweJ ,n thIn an.de do so. ascamanly

coin-ride *u,h threw or tiw as Department or Burasu ot

These doi.ms of .00w yp.cat fod

boats of the line 20 yean. wbálst coo-fined to boats both inrface-psercmg

fo.I n,_-- st

m mampuss. Thin a spsasfly true of

the mime.. The .s.aea smad the IS 6 (6.3 ions

.---) and the

lar*, the VS.$ (tome $0 Ions). The

(ugliest - is

aduevsi* by the XCH4 boat dross. by sucrafl engine. sad by propellers (2 630 h.p.).

Whereas the boats shows. hise at,

without esorpeto.. equipped with

piston espies, the fod boat of

fatton should be pt,domrnsatty .

turbine drerea.

change later on, should there bean increase in the demand for hydrofoil boats, especially for military purposes.

Orders for high speed "see aircraft" as anti-submarine ships, landing craft, minclayesi. tor pedo boats, rocket boats and so on. could opea up mass production possibilities for the aircraft industry, as happened at the tinte with the build-ing of large flybuild-ing boats.

To sum up, in the lower speed range the hydro-foil boat is inferior to all other types of vouch as regards power required. Its advantages do not emerge until speeds of over 30 knots, wilds is equivalent to three tunes the speed usual in cosini traffic. As long as the foil boat is used only as a short-haul vemel, it win hardly feel any coinpeti. lion from aircraft, and it is not easy to me where the line should be drawn This is bemuse, as in the our of road and railway vehicles, the cal-culation depends on geographical and technical uansport factor,., which vary in each

Generally sp.aing the

sue of

hydrofoil boats appears to be tied to a certain speed range, which at present lies between 30 and 60 knots. As regards military wasels, which are pwarnrd by different considerations. this limit wifl be extended, especially as the seagoing quality of hydrofoil boats ii being atsutantly The ranpes,mentioned may of omree dess as a mush of new physical knowledge and o(fasthar asdueleal developments. A worth of warnmg is however needed here, sime it I all too easy to pma from prophecies of this kind into the realm of qiseulatioss of $ most or less fantastic nature. On die other hand, it is a fact thee hydrofoil boats are already in service on and around many omen. Where they ate once in an-vice, it is bard to imagine doing without thesis. The future of modens shipping, it may be b'uly tald, has now bnpm.

The U.S. Navy's Hydrofoil Projects

lv Lleweamiz Convnonr Pews W. NeIma. LI. S. Navy

time to combst a submarine threat, that the hydro-foil principle is being exploited.

Over the past twelve years., the United Statcs Navy has been pursuing an active programme of investigation into the use of the hydrofoil pnn-ciple for various Navy tasks. In this connection, theoretical studies as well as an extensive model and full scale test programme have been under-taken. These studies havt covered practically all the arrays of foil configurations and arrangements, including surface piercing foils and fully sub-merged foils tvaides the various longitudinal area distributions of the toil, i.e. canard, tandem, or

- type.

Sea Legs, the US Navy's most succeatful tsi

craft, which is illus*ratcd overleaf. is 29 ft is

length, 8 ft in beans and has a displacement of 11000 lb. Powered by a 210 h.p. engine, the maximum tpeed attained by this craft is 31 knots.

It utilizes a fully submerged foil system with a canard area distribution, and its most singularly successful feature is the autopilot system. Excellent seakeeping qualities have been demonstrated by Sea Legs, which has been run through four or five loot waves, both in following and head seas, with) no loss in stability or control.

Based on the successful evaluation of this test craft, an operational mu!itary hydrofoil ship.

designated P(IH). is bring built for the L.S.Nass bs Boeing Its mission will be to carry out anti-submarine patrols in h,arbours. harbour ap-proachcs. and coastal waters, and it should gist the U.S Navy a small. relatisely inespensive surfate ship capable of attacking high speed subnsanncs, The ship under construction will be ItO It an

length and 31 (eel an beam. with .i displacement of 110 ions. Two propulsion systems will tie pro.

sided. namely a diesel engine for huliborne

operation, giving a cruising speed of 12 knots, and two gas turbines (or toilborne operation. givmg a speed of 40 to 50 knots. The toil system on the P0 H) is fully submerged and controlled by an autopilot system.

From the point of view cf simplicity and ceo-nixny. surface piercing foals.. staid seem to be the logici cliosee. Thei'e are, however, two basic reasons why a submerged Foil system was in fact selected. FUnth. with surface piercing foils, each change in the watcr surface is transmitted as a hft Force to the hull because of the change in wetted foil area, which results in a rather rough ride as catuirared to the submerged foal system. Secondly. in a head sea the performance of a ship equipped with surface piercmg foils is noticeably different front that an a following sea, this difference being a direct result of the oct',tal velocity of the water in the wave crest of a following sea. The two effects of thu orbital velocity are to reduce the effective angle of attack and also the relative velocity of the water oser the toil, and both effects Send to reduce the lift of the foil, at tames to such a degree as to cause an accidental landing on the water. Such a performance characteristic would clearly be undesirable in an operational military craft.

The hydrofoil ship ass means of transportation now a rcahty. and in the neat future the prin-ciple will be utilized in a mtlitary craft. How much larger and (aster hydrofoil ships may be sus-full built and operated &pends upon the ability of the scientist and engineer to noise the many problems that stand an the way of further pro-grew. Additional research and development are still

naary in the fields of hydromechanics.

pro-pulsion systems, structures and control.

The 1.5. hass test r.1t Sea L,gt ibtialt b Git't.s and

Con lnc.i with her hen and stern bus baii siaf'mengeat.

Coinparuson of the drag of. irudrorout situp and of sentionat drspiacrmcni ,n.ci misuse io speed. A us the r'hsw at hwtt the hsdro(oui situp is hecoutsing (ottbomite and B is its top speed.

To increase the speed of the hydrofoil, a new type of Foil shape. known as supercavitatang foil. will have to be used. Whereas, up to now, the results of the aircraft industry's careful testing and evaluation of airfoil section and wing con-figurations have. for the most part, been

apph-cable to the design of the "wings" for

sub-cssitatmg hydrofotls, in the case ofsupercavitating hydrofoils little is known about their behaviour, and consequently a whole new theory must be developed and tested Early investigations have already shown that the problcms to be overcome are manifold, as the esamplcs in the following

paragraph show.

Firn, tests have shown that the supercavitating craft have a lower lift drag ratio. Furthermore. the foal operates just undcr the surf-ce of the water, and there is a posaibility that the cavity Formed at the vapour pressure of water will be vented to the higher atmosphenc pressure either through a strut or through the trailing 'omen. Should this happen, the foil is no longer super-cavitating but superventalating, and a considerable drop in lift will occur. Third, nupercavurating foils are quite unlike subcavitating foils in that a major change in the angle of attack will give only moder-ate changes in lift. These then are three enampks of the problems confronting the designers of high speed hydrofoil craft.

Another worry facing the designer of the larger. faster hydrofoil ship into provide it with adequate power. Again, recourse has been had to the tech-niques in use in the aircraft industry where the necessary high performance engines. characterized by a low weight h.p. ratio, a low specific fuel rate and high power output are to be found. Although the aircraft industry's gas turbines can be used. and do an fact meet most of the stipulations for hydrofoil ships, such engines must first of all he adapted for operation ins salt wales' ensironment. This ins olves the solution of probkrns of corro-sion. life espectancs and reliability

(.)nux the designer has an engine which he feels will do the oh, he must still find a way of con-serting the power to thrust, whether ittse air

screw, water screw u.sr jet. If wate. screw is chosen. the problem then becomes one of pros iding a s.atiniactor. high performance drive

Hydrofoila

Just as in the products of the aircraft industrs. the weight going into the structure of the hdro-foil ship must be kept to a minimum, since each pound saved means an additional pound of pay-load. Since the hull of the ship represents a major portion of the weight, special care must be taken in its design the production of a minimum weight high strength hull can be ach,escd only by com-bining the best of marine and aircraft technoloi

The design and construction of the foils them-selves must take account of the fact that the foils and struts must be relatively thin in order to reduce their resistance to a minimum and at the same time strong enough to support the full weight of the ship when in flight. In addition, they must be capable of withstanding the dynamic loads due to manoeuvring and heavy seas.

Resistance to elastic deformation, corrosion and erosion, as well as to fatigue, are cssenttal yet dufilcult characteristics to provide.

The PC(H) dana fast btdroboil imp, developed its Boeing boo the U.S. Nass. n lIght Stuo has Lienjuost a high sprod homing torpedo against an enrns submarine. which was detecied its a laster sluip using sonar nquupnwni.

Finally, there is the question of proper auto. pilot control. The submerged foil system is not inherently stable in either heave or pitch and must therefore fly under constant supervision of the autopilot system, which accordingly must ohs' ously be reliable at all times during take-off, in llighl. and while landing. As speeds increase. thc basic problems of control are intensified, since sery high dsnjmic loads will present any oser. control.

From this brief discussion of hydrofoil craft. it can tic seen that it has some set's distinct adsan. t,ages and showi promise of prosisling the long awaited high speed surface ship On the other hand, it will be realized that there arc many problems to solse before large high spced hydro-foil ships become a re,alit%

It is very encouragtng to see that two great industries, aircraft and shipbuilding with all their outstanding equipment and ingenuits. are making a joint effort to meet this challenge