Third Symposium on Naval Hydrodynamics (English version)

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THIRD SV!POSIUM ON NAVAL RYDRODYNAMIC8 1960.

Ir. 3. GEE2ITSMA

1. Introduction,

The Third Symposium on Naval Hydrodynamics was organized

by the Office

of Naval Research (U.s.A.) in cooperation

with the Netherlands Ship Model Basin, and held at the

Zurbaus in Schéveningen froa the 19th to the 22nd of

September 1960.

The Symposium was dedicated to 31r Thomas Bavelock, the

well-known English scientist in recognition of his

valua-ble contributions to naval hydrodynamics.

The greater part of the Symposium was devoted to "high

performance craft": vessels which in one way or another

have outstanding qualities when compared with conventional

ships.

Hydrofoil craft, ground effect machines (usually

abbrevia-ted: GEM's) submarines, semi-submerged ehipa and

deep-divine oceanographic submarines were reviewed. Theoretical

investigations, economical aspects, actu&l and possible

applications of these craft were diecuesed as well as

ex-perimental research on models, prototypes and special

de-tails.

Also some aub1ecta connected with stiipmotione in waves,

resistance and power in smooth water were discussed.

The Symposium was opened with addresses of welcome by

Frot.Ir. L. Troost (Central Organisation of Industrial

Research TPN,O. Netherlands) and by Dr. Killian (Office

of Naval Research U.$.A.)

Dr. von flrmèri then dedicated the Symposium to Sir Thomas

Havelock and drew the attention to the valuable work in

the field of naval hydrodynamics carried out by this

scientist.

He expressed the general feeling of regret that $ir Thomas

was prevented to attend the Symposium.

The lis-t-o.t' participants mentioned 347 persons,

represen-tixig 21 nationalities.

die-

2-cussed.

The proram was as follows

Session 1: Chairman: Prof.DrIr W..A. van Iamrneren. (Netherlands Ship Model Basin)

1. O.H. Oakley (Bureau of Ships, United States Navy) "High performance ships - promises and problems". 3.0. van Mann (Netherlands Ship Model Basin) "Size, type and speed of ships in the future" Session

2: Chairman: Prof.J.K.

Lunde.

(Skipamodelitanken, Troridbeiiu)

3. J.A. Sparenberg (Netherlanda Ship Mod.el Basin)

"On the efficiency of a verticalaxia propeller11.

k. B. Timman and G. Vossers (Netherlands $bip Model Basin)

"A solution of the minimum wave resistance ,problem"

3. Zarp, 3. Kotik and J. Lurye.

(Technical Research Group Inc.,Syoaset, New York) 'On the problem of minimum wave resistance for strut and atrut-ifle dipole distributions'

Session 3: Chairman: P. Eisenber.

(Hydronautics Inc., Rookvtlle, raryland) M.P. Tulin (Hydronautos Inc., Rookville, Maryland')

"The bydrodynamios of hib speed bydrofoil craftt' 5, Schuster and H. Schwanecke

(Versuhaanstalt' fur

Waaserbau und. Schiffbau, Berlin)

"On bydrofoils running near a free surface"

A. Hadidakis (Aquavion Holland N.Y., The Hague)

"The effect of size on the seaworthiness of hydrofoil

craft".

G.J. Wenxxagel (Dynamic Development Inc., Babylon, New York)

"Design and inittal tests of our supercavitating

easion 4: Chairman J.A. Obermeyer..

(David. Taylor Model Basin, Washington)

H. von Schertel (Supramar A.G. Luzern)

Design and operatir

problems of commercial

hydro-foil boate'.

LB. Chaplin Jr. (David Taylor' Model Baein,Washingtoxi

"Ground effect machine research and development in

the United States"

12,

P. Mandel (Massachusetts

Institute of Technology)

"Hydrodynantic aspects of a deep.-diving oceanographic

submarine"

Session

5:

Chairman: Dr.

. Brard.

(Basein d'Essais

des Carènes, Lrance)

13.

F.Ji. Todd (National Physical Laboratory,Teddiiiton)

"Submarine cargo ships and tankers"

14,

A. Goodman (David

Taylor Model Basin, Washingto]1)

"experimental techniques and methods of

analysis

used in submerged body refearch"

F.W. Bogge

and N. Tokita.

(United States

Thibber

Company, Wayne, New Yersey)

"A theory of the stability of laminar flow along

compliant plates"

P.H, Wilirn (Service Technique do Construction et

Armee Navalee, Paris)

"The French bathysoaphe program"

Session 6: Chairman: Prof.d.r. GP. Weinbium.

(InBtitut fur Schiffbau der Universitt,Eamburg,

. Grim,

(Hamburgiache Scbiffbau Verausobeanstalt)

"A method for a more precise computation of beevizig

and. pitching motions, both in amooth water and in

E.V. Lewis and J.P. Breslind

(Stevens Institute of Technoio, Hoboken).

"Semi submerged ships for high speed

operation in

rough seas".

A.. 8ilver].eaf and W.J, Marwood.

(National Physical Laboratory, eddington)

"Design data :tor high speed displacement type hulls

and a comparison

with hydrofoil craft".

In the following pages, an attempt will be made to sun a-'

rize briefly the contents of the papers which were presen-'

ted.

2. Summary of the papers.

It will be clear that military demands conoernin speed,

manoeuvrability, limits of sbipmotions and accelerations etc., are a driving force for the development of high performance ships.

Oakley gave in his paper some particulars about the research work in this field which is carried out by the United States Navy.

An interesting part of this research concerns the develop mont of a high speed destroyer, It is known that in cer-tain circumstances the speed of a modern nuclear powered submarine can exceed that of the destroyer. In a heavy seaway the conventional destroyer cannot maintain full speed because

slamming and the

shipping of green water become too dangerous. The submarine however is not much affected by the seaway and a higher sustained speed can result. Therefore, new wye have to be ecplored to give the bunter a better chance to capture his prey.

One of the proposed solutions is a vessel Of which the mainhull travels under water, whereas a relatively small superstructure penetrates the surface,

-5-This combination is much less affected. by surface waves

and probably such a vessel is able to maintain higher

speeds in a seaway than the conventional type. Several

modifications of this idea are

considered., an eztreine case

betng the "spar ship": a vessel with its largest dimension

in the vertical direction and only a small part piercing

the surface.

Another posSibility je the use of hydrofoil boats where

hydrostatic buoyancy is replaced by the lift force of

relatively small wings' attached to the bull, The bull

itself does not touch the water surface when the veasel

is at speed and. in this way the wave resistance, which

forms an important

part of the total resistance of Last

diap,lacemant

type vessels

is practically eliminated.

Therefore hydrofoil craft are particulaily well aui.ted

for high speeds. Many problems however arise when these

vessels are operating in waves.

These problems are diacuased in detail in some *f the

other papers.

Van Manen drew the attention to the fact that generally

owners and builders of merchant ships are too well aware

of the expenses and. Linanc&al risks associated with the

development and. applications of vessels which differ

radically from

conventional types. Therefore £t is not

surprtaing that research work on progressive ship types

is mai.nly stimulated and supported by military

organisa-.

tions. Obviously the need for a htgb performance balances

the financial. consequences.

It is made clear that untill now, naval architecture

always had, a more or less ernpirióal character. In the

future however more ecientifc and. tuud.amental metboda

have to be employed in the research and design methods

for new sbp types.

Ãìóó the

!àrói

iior

eOntcntl

1tip

aid.the

increase of power per ahaft are sometimes a source of

-6-The high power per shaft and the £uU, form of supertankers

for instance can result in severe cavitation.- and vibra

tion phenomena, Van Manen proposed. in this respect the

use of the cigarshaped. Hognex' afterbody in connection

with a complete ring nozzle propeller system. A somewhat

better propulsive efficiency, a 25% smaller propeller

diameter and. notably better vibration and cavitation

charaoteristioa may be obtained.

In general it is expected that the speed of normal

nor-chantshipB will not inorease beyond 20 to 2 knots.

Perhaps in the future the nuclear powered submarine WiU

offer a djstinet advantage for speeds exceeding 25 knots.

The dimensions of this type of vessels are restricted.

because of the limited harbour depths and. the available

dry-docking facilities, At this moment the maximum draught

seems to be limited to approximately 35 feet.

A study carried. out by the Electric Boat Division of the

General Dynamics Corporation showed. that the largest

nuclear propelled submarine merohantehip wich could be

built with the present state of powerplant technology

would have the following dimensions:

cargo deadweight

41565

tone

speed

37

knots

circular cross-section

maximum diameter

80

feet

surface displacement

91903

tons

submerged displacement

101000

tons

loaded draught

6?

feet.

length

936

feet

power

240000

sbp

number of screws

4

The "most conservatIve" of the 27 designs carried out,

-7-cargo deadweight

21189 'tons

speed

20 knota

surface displacement

38791 tone

submerged displacement

42671 tone

loaded draught

35 feet

length

583

feet

beam

80 feet

dptb

40 feet

rectangular cross section

power

50O0 sh,p

number of screws

I

Neither military nor economic considerations were

consider-ed in thi

otudy.

With the aid of some reasonable and realistic estimations

concerning power and weight coefficients, Van Manen oon

eludes that the displacement of hydrofoil boats and G]M's

will be restricted to about 100 tons and the speed will

probably not exceed 100 knots,

A mathematical st*dy on the efficiency of a vertical-axis

propeUer (Voith-Schneid.er type) was given by parenberg.

The blades of such a propeller are forced to oscillate by

a system of rods and hinges. The angle of incidence of

each blade is prescribed by this system and varies in

such a way that the propeller as a whole can deliver a

tb.rus1 in any 'direction perpendicular to the vertical axis

In this study a number of simplifying assumptions are made:

the blades axe infinitely thin, top effects are ignored

and the chord of the blades is assumed to be small with

respect to the aallest xadius of curvature of the orbits

of' the blades (these orbits are oycloide)'.

The optimum angle of incidence as a function of the poi.

tion of the blade along the circumference of the propeller

is found with the conitton that the kinetic energy left

-behind---jn-the -wake--of th

ropefler-is

tn1y1 mum., Phi

-

'kinetic energy i-e-- expzessei -in terms

f the-bound vortiea

-8-Also the case of avertical-axis propeller witbma

blades

or a high rotational velocity is considered. Here the bound

vortioity and. the vortex layers in the wake are approximated

by continuous vortex densities.

In this case the angle of incidence with respect to the

tangent at the cycloid can be expreased explicitly as a

function of the position of the blade alou

the

circumferen-Ce.

In the future numerical calculations based upon this theory

will be compared with experimental results.

The determination of ship builforms with minimum wave

resis-tance has been the eubjeot of the paper given by T1.rnman and

Voseers.

As is known the wave resistance of relatively slow ships

amounts to 20 to kO percent of the total resistance tn

smooth water. The problem of the determination of optimal

hull forms in view of minimum wave resistance can be

con-sidered as solved for this type o

ship as a result of the

experimental research carried out by the towing tanks

througho4t the years.

For fast ships much remains to be done; here theoretical

work can give valuable indications for experimental research

even if the theory is based upon a number of simplifying

assumptions

such as the linearization of the problem.

8eaides the condition that the wave resistance should be a

minimum, an additional condition is necessary, because

otherwise a hull with zero beam would result. A natural

additional condition is the requirement that the

displace-ment should have a given value4

Timman and. Vossers use this condition and give a method to

minimize the wave resistance resulting from Michell's inte-.

gral. By considering a certain class of hull forms for

which the additional condition can be expressed as a quadra-.

tic functional the problem is reduced to i

tion of the second kind. In order to obtain a simple

inte-gral equation the influenoG of the bottom in the evaluation

Numerical results were not yet available, but will be

given in the near future.

Kari, Kotk and. Lure treated a

similar problem; the

minimizing of the wave resistance of a strut of

fixed

length and volume per unit depth at a given

Proude number.

(by length is meant; the dimension of the strut in the

direction of travel).

They formulated the problem by using the dipole die tn-bution rather than the form as the unknown function. The

optimizing dipole d,istnibv.tiona have been found. Although the dipole densities turn out to be infinite at the ends,

the corresponding shapes can be found for large depths. These optimum shapes have rounded enda with

a relatively

large radius and make one think of the lower waterlines of a ship having a bulbuous bow.

The authora

remark that three-dimensional etecte and

other corrections on the linearized theory are

not COnr

sdered in their paper.

me following five lectures were devoted to

hydrofoil ortt

and investigations on the behaviour of hydrofotle.

Tulin summarized the hydrodynamical probleriaasootated with the de8ign of hydrofoil

bots.In general there are

also problems in the design of power plants transmissions,

structures etc. but these are not considered

in the paper.

Wing loadings are very large. A hydrofoil boat

hAvingTa

speed of 60 knots experiences a static wing loading

which

is 20 to 50 times as large as that of supersonic aircraft

travelling at 600 knots. At the same time the demands

con-certiing resistance and cavitation characteristics result

in toils as thin as those of the supersonic aircraft. For high speede a aupercavitating propeller can be used.

with advantage (efficiency 65-72%), because serious

-10-Por speeds beyond 70 knots the supporting foiTh will expe-rienee serious cavitation accompanied. by drag rise and buffeting.

The only way to overcome these difficulties seems to be

the use of supercavitating foils. The first hydrofoil

craft designed with this prineiple in mind io being tested this year. The cavities behind the foils are not filled with water vapor but are ventilated by air paths to the atmosphere.

In addition to the static wing loading the hydrofoil c'aft experiences severe variable loads caused by the sea waves. A comparison of the vertical velocity components in the North Atlantic (5 ft.beneath the swfaoe) and. the vertical velocities in the atmosphere at low altitutes (0-10000 ft)

and moderate altitudes (30 to 50.000 ft)Is made,

It

iB

shown that a root mean

square

value of one foot per

second Is cxceeded only 17%

of the time at moderate alt±

tudes in the atmosphere 53% at low altitudes and. 89% of the

time at the depth QZ 5 feet in the North Atlantic.

In general it is

desired that hy&rcf oil craft maintain their distance from the sea surface and. follow the wave

contours when the wave length equals or exceeds the length of the boat. With increasing frequency of encounter (high speeda) however the experienced accelerations will become to severe. In that case a foil with variable angle of incidence has to be used, which is controlled in ouch a way, that the seacraft ploughes through the waves. The fully submerged wing seems to be the most suitable in contrast with the surfaee-piercing foil.

The use of controllable flaps in order to adjust the lift is discussed and some results 0± calculations on the be-haviour of two-dimensional flaps for both subcavitatIng and supercavitating foils, operating at high speeds are

given.

In- pra ha e1iessiiou1d.. b&inodi1ied. t& take into

- 11

magnitude of the influence of the surface proxiiity

however is clearly demonstrated..

For speeds exceeding kO knots the danger' of cavitation bn toils, vertical strLlte and propulsion macsilas in-..

creases rapidly.

because of its erosive effects1

local cavitation BbQUld.

be suppressed and also more extensive

cavitation (short

of superoavitation) should be avoided,f or this type of flow is often not stable and may be accompanied by buff e

ting.

The designer must thus strive to suppresecavitation, a

process which leads to very thin underwater structures.

For speeds exceeding 70 knots eupercavitating toils mu3t

be used as mentioned earlier.

Finally lift-drag ratios of eupercavitating hdroZoils

and the influence of the free surface on these ratios

are discussed.

Schuster and Scbwanecke presented the results of theore.

tical and experimental research on two types of

hydro-foils: a fully submerged

wing

and a dihedral toil.

For the steady state flow the pressure distribution

along the chord of the foils was measured as a function

of speed, depth of submergence, anglO of incidence and

roll angle.

For two dihedral foils the total forces and moments are

also given. For speeds below

7/R

(b means waterdepth)

the pressure distribution is influenced. by shallow water

effects as was already known from the work of Laitone

Plesset

nd Parkin.

Above this critical velocity no dependency on speed

exists, Here the pressure distribution ii influenced -only

by the distance of the bydrotoil

to

the surface in

rela-tion to the chord length. For this situarela-tion which is

- o

dorOrlWfttthd'er serviceondiUons ,

12

-mic forces are given.

'inally the relations for the vertical and lateral stability

of the two types of kzydrofoila are derived as well as the

influence of side slip motion,

Had3jidaki discussed the effect of size on the seaworthiness

of hydrofoil craft.

The behaviour of the hydrofoil craft in waves was compared

with a simple linear maas.aprixig system, excited with forces

and moments in the frequency of encounter of the waves. Assuming that wave length and wave heigth are propQrtional

to the length of the boat the author draws the following conclusions:

In a following sea the maximum pitching angle is the criti. cal factor. The danger exists that the combined effect of

a large negative pitch angle and the moment

caused by the

orbital motion of the waterpa.rticles can make the bow touch

the water with the

result that the craft is slowed down. It is shown that the seaworthiness of the hydrofoil craft in a following sea is nearly unaffected by size. Actually

the seaworthiness improvee slightly with decreasing E'roude number.

In a head.sea the vertical accelerations are critical.

They decrease more than proportionally with the Froude

number.

From these considerations the author concludes that the 8eaworthineee and comfort of hydrofoil boats increase with

increasing dimensions,

Wennagel mentioned the research. and development programs

concerning the improvement of hydrofoil craft in which

dynamic Developments Inc.

nd Grumman Aircraft Enginee.

xtng Corp. are engaged.. Three of the testprograms were consIdered of special

interest to the symposium. !ew

çPl7ed. to teat bydofot1s. The first was

13

-the mnnerside is open. The centrifugal force caused by

the high speed of rotation forces the water against the

outer boundaries and. the free surface becomes nearly

vertical. In this way a model hydrofoil attached to a

strut and placed in the flow1 can be tested at speeds

up to 100 knots. Froes and moments

experienced by the

model can be measured electronically.

The second program utilizes a pendulum apparatus, in

which model foils attached to the end of a pendulum

swing through

watertank of variable water temperature

and. variable vapor pressure. Instantaneous measurements

of speed, forces and moments can be done.

The third teatprogram utilizes a research and test craft

the XCR6 with a gasturbine powerpiant aud. a

supercavi-tating propeller.

The propeller has a diameter of 10 inches and develops

a thrust of 77. lbs at a speed of 62 knots and

6000 r.p.m.

With this number of revolutions of the propeller, the

engine runs at 19500 r.p.m. and has a continuous normal

output of 765 bp, which is greatly in excess of the

required power.

Forward of the center of graitity the boat is sup:ported

by two surface piercing dihedral foil systems (one at

each side) and aft of the transom by a fully submerged

foil.

Each of the forward foilsystemo eonsists of a vertical

strut attached to the hull, a cruise foil pointing

out-ward and up attached. to the bottom of the s'brut and a

diagonal foil element connecting the upper end of the

cruise foil with the upper region of the strut. The

cruise foil is designed with a supercavitating cross

section. The diagvnal foil, which is only used during

low speeds, has a ubcavitating cross section with a

blimttraiiing edge.

The tail foil einploys a subeavitatiñg eross étin

The cavity regions of foils and struts are ventilated..

'or intermediate speeds forced ventilation is provided.

When operating at a speed of 62 knots the lift-drag ratio

of the forward bydrofoils is estimated to be approximate

Ly 10.

Initial tests have a].ready been performed.

An extensive paper about the different aspects of the

design and. operation of hydrofoil boats was read by

Von Schertel. He compared this type of vessel with other

fast water craft and aircraft.

A calculation of the specific power requirements for planing

craft and hydrofoil boats in the speed range of 40 to 60

knots showed that for the same length of 160 ft. and the

same displacement of

0O ta the hydrofoil boats need only

55% of the power of planing vessels. Por this epeed range

comparablö with the Epeeds of trains and. automob1.les,

hydrofoil craft can be expected to operate economically.

The airplane attains much higher speeds with lower specific

power and therefore represents an economical means of

trans-portation. However the extensive and expensive ground

organisation makes the airp]ane far lees suitable for relative short distances, This does not hold in the case

of helicopters; these require a high specific power and

the operating and

maintenance costs are several times as high as for

hydrofoil boats.

Planing vessels do not provide the necessary comfort when

travelling in waves, because of high vertical accelerations (actually accelerations of 6g have been measured). It can be stated that hydrofoil craft can maintain higher speeds with less vertical and. transverse motions than any other type of seacraft of comparable size.

Then Vos Schertel discussed the characteristics of the two basic foil systems: the surface-piercing 3ysteni,

eon-gjtin either of aaingle dihedral foji or of several

emll f 01. ls arrange on top of each other and the fully

15

-The first system is automatically stable because any deviation from the position of equilibrium of the craft Causes a change of the lift producing wetted area and

this creates restoring forces.

The fully submerged foil does not have natural stability. The depth of submergence must be controlled by mechanical or electronical devices which measure for instance the distance between the water surface and the bull. These sensing elements are used to command a mechanism which changes the angle of incidence of the foil or of a flap.

Therefore this last type can offer better seariding

qualities and. conz.tort.

However the complicated controlling devices form a serious drawback. A new self-controlling system has been developed by the author and a teetboat equiped with this device is

already being tested.

At cruising speed both foilsyatems have

approximately

the

same lift-drag ratio of

1L.

3eyond this speed the condi-tions change in favour of the surface-piercing foil because of the decreasing wetted area.

In general the fully submerged foil will offer in the

future some advantages for long distances and ieee

protec-ted sea areas.

Experience with commercial

passenger services baa shown that the hydrofoil lxat can be operated entirely success-ful and profitable if there is a sufficient high passenger

frequency.

With PT 20 and PT 50 hydrofoil boats approximately ten, mainly coastal, services are established.

One of the

most prosperous services

exists between Maracal-bo and Cabimas; annually.over 6O00OO passengers are

car-ried. over a distance of 20 miles.

The str.ngth, reliability and seaworthiness of these ves-sels proved to be entirely satisfactory.

he author concludes with the statement that-

under-the-present circumstances hydrofoil boats can compete economi-cally with aircraft over distances not exceeding 300 to

-. 16

OO miles.

Ohaplin read a paper about ground effect machines (GiM's)

and the development of these vehicles in the United atates.

At present some forty commercial firms are engaged in

ground effect investigations. The diversity of the

count-lees variations in approach makes a comprehensive review

impractical. Therefore only the more significant concepts

are discussed. With 'he aid of the elementary principles

of fluid mechanics the performance of the various GEM eye.

teme are estimated and the outstanding advantages and pro

bl.ems are revealed.. With our present knowledge of ground

cushion effects however, it is as yet not poeible to say

which of thasystema will prevail.

Seven concepts to maintain the air cushion pressure are die-.

cussed. The first system, the air curtain or "annula' jet"

has received by far the most attention. The ground cushiOn

is generated and contained by a jet of air exhausted

down-ward and indown-ward from a nozzle at the periphery of the base.

The eeoond concept is only auttable when the GEM operates

exclusively over water. In that case a part o

the air

curtain can be replaced by sideplates or skegs, which extend

into the water. Compared with the complete air curtain

oon-cept a substantial reduction in power can be obtained at

moderate speeds

The third system: the integrated air curtain is related to

the first concept. Here the integrated air curtaXn provides

for propulsion by directing the peripheral jet at a rear

ward inclined angle by means of vanes.

In principle the air cushion can be contained by a per$.pbe

ral jet of water as is done in the fourth system.

In theory a large reduction in power compared with the

irst concept is effected

but it is not clear at present

bow much of this advantage is left in practice.

The most simple system is the "plenum cbambex'. The

under-rsoesne

aa -adorns and air

i-aimpl-pumped jnto the recess; the ar is allowed toleak out

17

along the ground.

Probably the "ramwing" is the oldest system, having

been

inbx'oduced in Finland by Kaario in 1935. The vehicle has

the form of a box with the bottom and the frontside removed. At a speed V

the

ram pressure +,

Vzis built up beneath the base, giving a lift force L

Finally there is the academic possibility to sustain a

GM at a finite height above the

ground without

dissipa-ting energy. This concept is called the "diffuser-recircu-lation" system. It consists of a recirculating flow, rather like a standing vortex ring which is maiutsined within and under the vehicle. The average static pressure under the base can exceed the atmoaperic pressure and so a net lift Zrce is created. Under the assu*ption of an inviscid flow

this system has no energy dissipation. Practical appl±ca-tion will meet large difficulties.

The author offered the following

conclusions. The

perf

or-mance of a GM depends directly on the ratio size-height, in which height means the distance between the base of the GM and the ground or the water surface.

Since laud. areas are

in general insuitable for the

opera-tion of large, high speed vehicles at low heights,

one is

inclined to think of the large ocean going GEM as. a

possi-bility in the future.

In the meantime however, moderate-sized GEM's could be attractive for special purposes. There seem to be two

fields of application:

Passenger- and cargo ferries, emergency craft, sports

craft, etc. on flat inland areas and protected waters,

where extremely low operating heights guarantee good

performance.

Limited militarr applications where requirements for

speed, amphibious capability and load-carrying ability

outweigh the conventional economic performance criteria.

Mèitid the

ódic iáti fdedfvii

This vesoel is designed for operation at depths down to

15.000 ft.

The Aluminaut differs in basic concept from the

bat1yeoaphes

RT8 and

rieste, which were developed by Auguste Piocard..

It will be recalled that it was the Trieate

which made the

record.breaking dive on January 22 1960, to a depth of

3?.800 ft.

The buoyancy of the pressure bull of the

Aluminaut supports

over 80% of the total weight, whereas the buoyancy

of the

small pressure cabins of the batbyscaphas support

only 5%

of the weight. The remainder of the batbysoaphe's

weight

is carried b' a non pressure hull filled with a buoyant

liq4d..

With a total submerged. displacement of slightly more than

half that of the Trieste, the Alurninaut baa about 9

times

the

aeful volume and possesses a superior mobility

and

enduranoe.

The ballast intended for routine ascent consists

of 1,8 ta

of iron shot contained in two amidebip external

saddle

tanks. The tanks can be emptied through hollow solenoids.

When the solenoids are eriergizàd they magnetically solidi-.

ty the iron shot; when the current to thesolenoids

is cut

the iron shot flows out at.ay depth of

operation.

In addition there are tanks for 1,35 ta. of water

ballast

ar4 provision is made for jettisoning 3,18 to. Of

a3.uxniniuin

wrapped lead, in oases of emergency.

The remaining ballast of over 3 ta. is fixed. This ballast

io partly needed for stabiItr pux'poees and.

partly forma

a margin available for design, construction or suture

growth.

Special attention has been given to the motions of

the

vessel when rising vertically. In order to avoid violent

oscillations the natural rolling period was chosen so that

the probability of resonance with the psriód of

the shedding

ofvorticeawould remain very smalid In addition

large

19

-Modeltests were carried out In order to

be certain

that the

expeimental

data confirmed the computed values.

The submarine is equiped. with two screw propellers of which one, mounted on top of a email superstructure, has

to

provide thrust in vertical direction, the other Is a swivel-ling propeller which can deliver a

thrust in

the horizontal

plane.

With the two propellers working Bimultaneous].y it is

possi-ble to descend. to 15.000

ft.

in 40 minutes (without propul-sion it would take about 4+ hours).

An emergency ascent from a depth of 15.000 ft. takes 22 minutes. With no power available

it

would take 44 mInutes.

Todd. discussed extensively the possibilities of submarine cargoships.

In order to have some figures s a basis for

comparison

between surface ships end submarines, calculations have been made of

the horsepower required for

displacements ranging from 25.000 tons to 150.000

tone.

The comparison is made on the base of equal deadweight, For the lower speeds (10-15 kn.) there appears to be no difference In the power requirements between the surface

tanker and. the submarine tanker

with circular cross

section

At higher speeds the submarine with circular section

re-quires less power.

For large dead.weighte the draught of this type of ship becomes excessive. When the

section La made elliptical

with a beam equal to four times the draught, the gain in power is lost.

For all shiptypee nuclear propulsion is

assumed.

For speeds up to 25 to 50 knots, the limit to

which surface

ships can be built and operated economically the advantage

of the submarine tanker is not sufficiently large to

justi-fy its use.

In addition it would require expensive new

building facilitieB, now dry docking fai1ities

andnew

20

-Por speeds beyond 30 knots the gain in power would be

sub-stantial. The weight

and the required volume of the power plant however increase considerably and thiB would result in a deadweight-displacement ratio which will be rather

small.

It depends on. a number of economic factors whether it would be justifiable to build submarine cargoahips. It is possi-ble that in the future the coat of nuclear fuel will

de.-crease, at present the conventional fuel is considerably less expensive.

The author mentions an interesting comparison made by

Teasdale. With

the assumption that a small aumbarine tanker of 26.000 tons deadweight because of its higher speed could deliver yearly the same quantity of oil as a surface tanker

of 7.000 tons deadweight, Teasdale estimated that

the fuel

consumption of the submarine tanker would be about four times as large as

that of its

surface counterpart. Both

ships were supposed

to be nuclear powered.

There is no doubt that for military use the submarine is of great value for the transport of valuable cargoes in

wartime, with little

chance of detection. It is possible that some government will build a craft

of this type

very soon, both for its military potential and national prestige

The paper of Goodman

dealt with the various experimental techniques and methods of analysis which are either preaenb-ly being ued or are contemplated in the near future at

the David

Taylor Model Basin in

the field of dynamic

stabi-lity and. control of submerged

bodies.

The D.T.M.B. has

in

operation

the

"Planar Motion Meohaniam' system, a device which allows the experimental determina-tion of the coefficients of the linearized equadetermina-tions of motion for a submerged body with six degrees of freedom. Brief deacriptions of the new

Rotating

Arm

Facility

21

-The paper of Bogga and. Tokita contained a contribution

to the theory of boundary layer flow, namely: a treatise

on the stability of laminair flow along compliant plates.

It seems that the use of a flexible skin (for instance a

skin Of rubber with liquid backing) may have a favourable

effect on the stability o± laminar flow, because the onset

of turbulence is damped out and transition is prevented.

The paper of Bogge and Tokita unde±takes the development

of a theory which will predict the stability conditions

of the boundary layer

in contact with a flexible wail.

One

the cono.usions of the authors is that the

condi-tionsof stabtliztn

a flow are rather critical and that

all flexeb3.e coatings do not necessarily have a favourable

effect on the flow.

Wilim presented a paper concerning the history of the

batbyscaphes, the principles of their destgn and the

contribution of trance in the development of each craft.

The pressure bull of the batbyscapho is a sphere because

this is the beet shape to wttbatand high external

pres-sures. The shell of this sphere has a certain thickness

which is so large that the weight of the sphere is far

in excess Of its

buoyaoy.

This pressure hull is suspended underneath a float filled

with extra light petrol directly exposed to the external

pressure to proide the necessary buoyancy. This system

is comparable with the principle

of the free balloon.

Vertical movement is effected. by jettisoning ballast:

ateelehot for rising and petrel for sinking. The steel

shot is bld magnetically and the petrol can be replaced

by seawater.

The use of petrol has a serious drawback: its

compressibi-lity is substantaily rnore than that of seawater. Thiring

the descent the loss of buoyancy due to øompresion of

Vtirol-iB morehant1ie gain due to t

nceafli

22

Once the bathyacaphe has started to sink, it descends

quicker and quicker. On the other band., once the

batbyscaphe starts going up, its speed will increase

progressively and it is impossible to stop it.

The maximum speed under these conditions is approximately

one meter per second..

Short descriptions were given of the bathysoaphes 'IB8 III

and 11.000. The last one is designed for a depth of 11.000

metres.

The FNI8 III baa been used for five years and during this

period more than 80 dives were made. Biologists,

geolo-giats, oceanographers and other scientists have had the

opportunity of carrying out their respective

investiga-tions.

Wilim concluded with a plea for international cooperation

of all the research workers who are interested in

oceano-grapby.

Grim discussed the computation of the hydrodynatnic forces

associated with the pitching and. heaving motions of a

ship. In general the methods which have been applied to

the theoretical treatment of this problem may be

sub-divided crudely into two groups.

The first group employs the representation Of the moving

s

hull form by perodioal singularities.

The disadvantage of these methods is that the boundary

condition on. the surface of the body is insufficiently

satisfied. Therefore only qualitative information

concer-nine the influence of the main parameters may be expected.

The methods used in the second group assume solutions

to be known for two-dmensionslbodtes of which the

seetions correspond with the cross sections of the ship,

The results for the three-dimensional body can be

obtatned

by integraUng the two-dimensional solutions over the

23

influence of three-dimensional floW can scarcely be taken into account and that the influence of the speed of the

shi:p caxmot exactly be established.

Grim combines the two methods: a strip method will be applied for the distribution of the singularities, i.e. fOr each

eecton of the ship the similarity will first

be chosen to satisfy the condttion on the cuiface of a two dimensional body of the section in

question. An

im-proved distribution of singularities to allow for three

dimensional flow is

then obtained with the help of an

integral euatiou.

The following problems

re treated.

The heaving motion, the pitching motion and the forces

generated by the waves in a vertical direction. In the

paper only the case

of zero speed is considered. however it is possible to carry out the calculations for a ship with forward speed. Numerical results for this case were not yet available.

Lewis and Breslin discussed the possibilities of obtating high speed in a seaway with ships of normal displacement. As is mentioned earlier, the submarine which is not

affec-ted by the seaway, baa a poet&ve advantae over th

destroyer. The speed of the submarine is in principle only limited by the weight and volume of the rower plant.

The resistance oZ this type of vessel is directly

proper.-tional to the square of the speed, whereas the resistance of the destroyer is proportional to a much higher power of the speed.

Research has been carried out to arrive at ship types having reasonable dimensions and a higher sustained speed

in waves than the present destroyers in order to meet the challenge of the submarine.

To this enda number of possible eolutiirns of the problem

is reviewed. bydrof oil cra1,planing vessels, long slender

shipa and semi-stthmerged craft, which are neither pure

-21l-.

These craft potentially

ean exceed submarine speeds becaus

of their low resistance, good sea performance and. relative.

ly low power.

An interesting conoept is a ship which operates at the

surface in fair weather; in bad weather large peak

bal-last tanks can be filled to enlarge the natural pitching period by increasing the displacement and the radiue of gyration. In addition the waterplane area is reduced as a consequence of the hull form. In this way it is possible to avoid synchronism at high speeda and head seas.

Another interesting type is a long slender hull, with large bow and. etern bulbs. The radius of gyration i large and consequently the natural pitching period is large, where-.

as the resistance is not excessive. In comparison with the semi-submerged design it has the advantage of leas

uU.-volume limitatione.. Sufficient freeboard and flare can be provided forward to keep the water ol't the foredeck

The last group discussed consisted of semi-submarines,

which oan be considered as the next step in the transition

from surface ship to submarine.

The main hull of the semi-submarines is fully or nearly submerged, while a fin or strut pierces the surface. The

advantage of thIs type when compared with the true sub-.

iarine lies in the fact that conventional air-breathing power plants can be used. The weight of a nuclear

power-plant is at present still far- in excess of that of a

con-ventioxial plant.

The behaviour of the semi-submarine as regards depth sta-bility is interesting, for it cannot be expected to rwi at a constant depth below the surface without controlling

devices because of surface interaction effects and. lack

of natural vertical stability. Simplified lineair equa-tions of motion have been set up and solved with the aid of an analog computer. The influence of the distribution

aud area of the stabtitsation fins

as

iveetiated.

PiiverleaI and Marwood presented .eaign data for small high speed displacement type hulls (Froude number betweoi