Fluid Momentum in Ship Hydrodynamics

Fluid momentum in ship

hydrodynamics

W. Beukelman

Report 1088-P

March 1997

Schip & Werf de Zee, 7e Jaargang

TU Deift

Faculty of Mechanical Engineering end Merme Teôhnology

Ship Hydromeohanica Laboretory

MAART 1997 SCHIP&WERFdeZEE

INHOUD

2 De Maritieme Markt Niches met perspectief 4 MaandMaritiem 6 Raad voor de Scheepvaart

De weggevallen schakel

10 Het ontstaan van de dieselmotor deel II

Van idee tot werkelilkheid; in twee dden vertelt ir. Ci: Verkleij over de ontwikkeling van de eerste dieselmotor.

Insert Inhoudsopgave "Schip en Weit de Zee" 1996. 16 Mars Reports

18 MRS Ptoneer

29 Cieatlefmadtlem

Een innovatieweek op de TU-Deift op maritiem gebied. 30 Fluid Momentum ¡n Ship Hydrodynamics

Ons gewaardeerd lid, de heer W. Beukelman heeft in juni van 1996 in St. Petersburg dit paper gepresenteerd als een van de Nederlandse bu-dragen aan de viering van het 300-jarig bestaan van de Russische vloot.

Zeif is hij oak onderscheiden. 39 Litersbjunwerzlcht

40 Markbo,g 43 Pmductinfomiatie 44 Eumpeesvevoembeleid

Europese beleidsvoomemens belicht vanuit havenperspectief. 46 Verenigingsnieuws

47 Agenda

48 Brancheregister

Bu de voorplaat De Schulpengar van de TESO in het Marsdiep tewerkgesteld als ijsbreker afstheid van de winter7 (Foto: Flying Focus)

Fluid Mömenturn ¡n Ship

Hydrodynamics

Unti! 1992 'W..Beukelmon was Associated Professor of Ship Hydromechanics atDelft University of Technology. He presented this paper dt the "ThinJlntèmational Conference in Commemoration of the.300th Anniversary of Creating the RüssionFleet by Peter the Great" (CRF-96), 39 June 1996 SL Petersburg, Russia.

Therateof change of fluid momentum is a very significant characteristic to determine important phenomena

In ship hydrodynamics such as motions in waves, slamming, iIft,forceson huiländ rudder, manoeuvrtng deri vatives, etc.

Three of these;phenomena wili'beconsidered'closer here, especially the calculation methods viz.:

-

slamming

-

liftproductlOnof the hull

-

manoeuvring

For slamming the.impact force is

deter-mined with aid of fluid momentum exchange and, strip theory including

forward speed influence.

To determine the lift forces and -mo-ments and alsothe hydrostatic- and

dy-hamic manoeuvng coefficients the

ship hull is considered-to bea low as-pect-ratio surface piercing wing. The determination is based upon potential

theory máking use of the variation of

the added mass impulse' or the rate of change of fluid momentum.

Transformation from seakeeping to manoeuvnng notation is used to amve at expressions for sway and yawderiva-tivesapplicabie for both deep.andshal-low water.

Reduction of waterdepth causes a

strong increase of liftandconsequently also of manoeuvring derivatives. The calculated results are rêlated to the

linear part of the coefficients, which

meansvalidity only at smalidrift angles or angles ofattack. As an example com-parisons with experiments are presen-ted for the cases considered.

SLAMMING

The impact pressureismainly determi-ned bythe velocity normal to the hull. In case of a ship with a flaUbottom, the impact pressures on thebottom can be determined if the velöcities normal to the bottom are known. This case will be considered here. [l]

'The hydrodynamic force. per unit length on. a strip of an oscillating ship will be

F' = F1'

+ F2' + F: = ₍₁₎

-2pgy,c -N'. --(m's)

in which, p = density'of water

g = acceleration of gravity = half width of the'

cross-Fig.?. Test points(;) and predicted results (--) of peak pressure as function of vertical velocity Vf?]

section

at the moment of

touchingthewater surface

m' =thesectiòaladded mass N =thesectionalidarnping

s = Sa cos COt = the vertical

dis-placement

Thefirst term F'1 is of minor importance because the vertical displacement s is

very small during the time that the

maximum slam pressureis built up. The contribution of the second term; F'2, is also negligible on account of thesmall

damping proportional to the first

po-wer of' the vertical velocity. What

re-mains is the third term, F'3, represen-ting the fluid momentum exchange of the section considered.

The resulting slam pressure may be

written as

I ,

din'

. ,

p = -(i-- r + ms )

(2) From eq. (2)rit appears that;

the slam pressure.is inversely pro-portional to the wetted width, 2y

the second term is proportional

to the squared vertical velocity and

showing also that the increaseof added mass with depth isvery important

-30 .

Fig.2. Forces acting on the wing section

3. the third term may become very significant if the vertical acceleration is high. Thismay be the case if a compo-nent anses due to the forward velocity of the ship.

In case of forward speed U with a trim angle CL (bow up) the vertical impact speed will be

V=-Usm

(3)

An extension of this method takinginto account more significant forward speed influence and 3-D effects is presented in part U of [I]. An example of measured and calculated impact pressures depen-dent on the vertical speed V is

presen--ted in Figure 1 from [I] (part Il) for a dead rise angle f3 = 0.46 and a trim

angle OE = 0.50'. Most existing calcula-tion methods show too high pressure predictions. A strong ncrease of peak pressures with dead rise angles could

be established up to 1.15' dead rise

angle.

TRANSVSEFORCES

The-calculation of the transverse forceis

also based on the exchange of fluid momentum according to method as

proposed by Jones [21 to determine the

lift forces on a wing profile. For zero

drift angle the'transverse force is equal to the lift force (Figure 2). The

hydrosta-tic and hydrodynamic manoeuvnng

-coefficiénts are derived from the trans-verse forces and moments. In this way a ship is considered to be a wing profile with-a low aspect ratio.

The derivative of the local normal or

transverse force N may be set equal to the time-derivative of the local added mass impulse in transverse direction or

the fluid momentum exchange and

can be written as

dx = -

d

(mI'v) ₍₄₎

with: m' = the added mass per unit

length

Equation (4) may be developed into

dW

din'dx

,dvdx

-=

- V +

m

-dr

dx dt

dxdr

Keeping in mind that dv/dx = O and

dx/dt = - U (being the fluid flow speed on the- wing which is opposite to the wing-model speed U the expression be-comes:

dm'

₍₆₎

dx and

dN =

-U2ßdm'

(7)

The total normal force on the

wing-mo-del will be obtained by integration of

dN over the length/chord of the wing (5)

as:

N=j

=_U2ßJthn'=

(8)

[NF-NA]=

-U2ß[m'F-m'A1

(9)

If m' = m'A = O which is generally the case, the total transverse force will be zero. This phenomenon is quite in

ac-cordance with D'Alembert's paradox

on the assumption that the flow is irrd--tational in-an ideal fluid without viscosi-ty, vortex sheets and separation. Only for a body with a tail fin -at the end, so mA # 0, the situation is fündamentally différent as stated by Newman in [3]. lt is well known, however, that viscosity is

required to start the potential lift

pro-duction. Jones [2]pUt forward that with

the aid of the Kutta-condition it may easily be shown that sections of the

wing behind the-section of the greatest width develop no lift. Katz and Plotkin

even showed in [4] that there will beno lift if b(x) is constant with x. Integration

up to the section with the maximum

width shOuld then be sufficient. If the integration ineq. (8)iis carried out from the forward point (F) -to the

sec-tion with the maximum beam (mb) and if m'F = 0, it then holds that the

transverse force may be writtenas

N _U2pmxF (10)

The sectional added thass m' was de-termined using a method based upon potential theory only as presented by Keil in[5] including the influence-of res-tricted waterdepth. The sectional ad-ded mass m' may also be obtained by-a diffraction method i.e. Delfrac of Pink-ster as presented by Dmitrieva in [6]. The advantage of this method is that wall influence or influence of other ob-stacles in the neighbourhood may be taken into account.

UFT PRODUC11ON

Here the lift production at zero drift

angle 13 will be considered for which case holds-that the lift force L is equal to the transverse force N. For other drift angles the longitudinal lorce T should be accounted for to find the lift force L and drag D as denoted in Figure 2. If the lift force coefficient is presented as

CL=

L

!

U2LWT

(11)

the slope of the lift curve-at = O may be writtén as

m'

(12)

.pLj

inwhich L.« = the.length of the wing or ship and T = draught.

The moment of the-local transverse for-ce with respect tothe origin of a body-fixed right hand coordinate system xyz (x longitudinal, positive in forward speed direction at f3 = o', y transverse, positive to the right or starboard side SB, z positive downwards) may be ex-pressed as fol!öws:

dM=xdx

(13)

With the origin of the coordinate sys-tem situatedat D(Figúre 2).añd

substi-tuting eq. (6) into (13) the total

mo-ment of the transverse force on thé

wing modelwith respect to D will be:

M =

= -U2ß x dm' F F (14) M = -U2g'3{xm" I

-1 in'dr}

Db

-MAART 1997 SCHIP&WEAFdeZEE 31

y =+

as- the transverse

component of

the flow

speed - U

13 = drt angle or angle of

1,2 Cccn A 1 Ql

0.8 "

32I

o _0,6

Fl5

H 8 12 20 3 (deg)

Square Tips, H = 0.48 rn, T = 0.30 rn

16

Rg. 3. Lift and drag coefficients.

Fig.4. Measured and calculated.y as hinction of fo,ward speed lt follows with /

mF

-(15) M = U2flmD

'Following the reasoningas use&for the transverse/lift force Dshould be chosen as located at Xmb. (Figure 2)

F

is the added mass from F to Xmb. This moment with respect to LCG delivers

'the well known destabilizing.

Munk-moment for a body with a drift angle at a steady translation. The distance fxmb from xmb to'CN (See Figure 2) is found as follows: z

upm

m

f

-

X,,,b 16

JXNU2ßm/

_m1 X,,.b b

The-distance e from CN to the forward wingipoint will be:

40 oJ 30 + o 20 0

e = L

-(17-) L

d

-and (L

- d

-e (-18)

The moment of the transverse force or

lift force at

= O with respect to

F is:

M = Ne =

m (19)

U2)9mÇ _(L

_{- d}

_-

_4±)

and the moment coefficient

CM

!pu2L,T

±pir L

2 2 ₍₂₀₎

M

mÇß

_e

The slope of the moment curve at 13=0 is fou ndto be as follows:

aCM m'

* e

(21)

äCL

e-&i L

[7] show that lift and drag increase

strongly ifthe-waterdepth reduces. See

as an example Figure 3. Calculated values confirm this very well. 'Using

faired tipsat the bilge in-stead ofsquare tips decreases drag and lift considera-bly. Experimenthlresults with faired -tips approach .for both lift and moment the calculated linear values in case of zero angle of attack43.

MANOEUVRINC

General

The manoeuvring coefficients -will be calculated with aid of the seakeeping coefficients. See for .a description [8]. These coefficients generally are built up from terms with sectional fluid added mass (m')and damping coefficient(N' --U dm'/dx) For manoeùvring it is as-sumed that the oscillation frequency is zero (static measurements) or very-low at oscillation so that the damping

N' . o. The term U dm'/dx of the

damping coefficient will deliver the

transverse- forces as shown before 'For this reason terms with U dm'/dx wilIbe integrated from the forward, point (F) to the section with the maximum beam (mb). This holds also for terms-with m' following from U;dm'idx by partial in-tegration. Terms with pure added mass,

m' will be integrated over the whole

model length L as shown exper

men-Table!: Ove,view of Sway coefficients.

'PP

dr FPP-

-Yb,'-

_f

m'dx APP FPP

N,.Uf

FPP

U[-x.4m,'- f

m'dl

X-4 FPP

N4-- f

m'xdr=Y, APP -Y,-

-pLU

!pL 2 N,,

LPLU

14

pL,,

APP FPP =

x4m,- f

m'dxj N4 FPP

'PP

1

f m'xdx=Y

APP

Co,*tJo,, a E.,t,(m,n,. Scua,. IIfl "T - Oie 'T .020 -oso,,

c.aw.,1,.;v,, r_o,,,,

- - T 020 u, - T -- 0,30 m 1,2 0,8 0.2 o CicitcnA UI UI 114 UI - (21 - '141.

, r

CL C.M.0 Co 0.4 02 I

(fl..

I

(i

---- cAic

o UI,

.. ---I

32 SCHIP&WERFde/EE MART 1997 4 a 12 16 20 al 015 0.2 Fn 0 25 03 m = m" dx L) =X,th - F

-tally in the past. The relation between seakeeping and manoeuvnng has to be considered to find expressions for the manoeuvring coefficients. The mostre-markable difference is thechoiceof the vertical axis z, positive upwards in sea-keeping; and downwards for manoeu-vring. Hence the transverse axis is álso

different in direction, positive to BB

for seakeeping and to SB for manoeu-vring.

Sway

Theequation of motionforthe swaying motion related to seakeeping may be

written as

( m,,

a» )

j + b»

=

(22)

Y0 sin( ot

*

e )

Substituting y= ya sinWt delivers for the

qudrature component of the

side-force:

b)7 0 Ya = Ya Sifl E (23)

The sway oscillation for manoeuvring

(

Y - m )v + l'y

=

sin(

W

+ E )

maybepresentedas from whichfollows

0

_{Ya =} Sfl

e

(25)

The sign for thisforce is opposite to that found for manoeuvring due to the dif-ference inthe directionof they-axis. Pn the above equations are:

m = mass of the wing

a»,, b»,= seakeeping coefficients for resp. added mass and damping

''

manoeuvring coefficients for

resp. added mass and damping With aid of theexpressions for the sea-keeping coefficients aspresented n[8]

it follows with(22), (23)and(25) that

F

f±!

= -Um',, dx Amb ₍₂₆₎ Y,

-

-pLU

In the same way is found:

F

Yv =

_{= -}

_{f m"dx}

(28) A m_X=b

¡

2

-pL

(24)

In non-dimensional form the

expres-sions becomes

(27)

which becomes in non-dimensional form:

-

_pL,,,

f

m'dx (29)

A

The other coefficients may be

deter-minedlin the same way. An overviewof thesway coefflcientsis presented in

Ta-blei

As an examplé:

Figure 4 shows the measured and cal-culated valuesof -Y', as functionof for-ward speed Fn for HIT = 1 .2 H =

Wa-terdepth, T = draught

Yaw

Yaw in manoeuvnng may be divided in sway and yawwith a mutual phase dif-ference of 90 degrees.

The velocity vector of LCG istangent to

the swaying path of LCG which is

achieved by adjusting a phase angle (p betweena fore and aft leg in caseof an oscillatior_[8],so that

2 2U (30)

with I =the distance between oscillator

legs.

The force equation for sway/yaw may be written as:

The force here is taken in phase with

the yawing angle i]! and negative in

sign in view of the manoeuvring nota-tion. Substitutionof y = Ya sinUlt and

cos W

= -

srn - cos w,

2

(32) in (31 ).and using the pure yawing mo-tion equamo-tion Y1 +

_{(Y, - mfJ)r}

₌ (33) l'acos(ot + e) yields which resultsinto Y,

= -

e,

- Ua»

(35)

Using the seakeeping expressions for ey. and a'», as presented in [8]

andta-kingN' -0 forO) -'0 yields

F

/

F

Y.=U[ f

-xdxfm'dx]

A (36)

In non-dimensional form after partial

integration;is found Y' _¡

pLU

-pL

F

F

-

x,,1, m

_-

_{f m1 dx +fm}

Xmb A

The in-phase relation of equation (31) and (33) gives in the same way:

Y,

= -

d,,

+

(38)

and after taking N' ' O for a-p O there remains

Non-dimensional presentation gives:

F

I

m'xdx

(40)

The other coefficients maybe determi-ned inthesameway.

Intheaboveequations are

= seakeeping moment coeffi-cients for resp. added mass and dam-ping

Y, Y, = yaw moment coefficients for

resp. addedimass anddamping If foryawing thevelocity vector of LCG

(

Y, - mU )

Y0 sin -w2i m +

a».) Y0

-(a0

o(m,,,+a )l

_»

2 sin

-2

O- Othén sin -

1g -.

--2 2 2 2U or 'pa (34) MAART1997 SCHIP&WERFdeZEE ₃₃

F

Y, =

-f in'xx

= N, (39) A

Table Il: Ove,view of Yaw coefficients.

LCG the yaw coefficients may change rather strongly. In [8] a counter phase of i 80' has been considered showing these very strong alterations in value. An overview of the yaw coefficienti is presented in TablelL

Semi..empiricaFmethods

In the past several attempts have been made to find empirical expressions for the

rnanoeuvring coefflcientsat ships based on measured values from planar mo-tion and rotatingarmexperiments.

Gemtsrna e.a. (1974) [10], lnoue e.a. (1981)[11]. Clarkee.a. (1982) [12] corn-pared several empirical' formUlas against scatter plots of velocity derivatives. CIake used multiple linear regression analysis to develop empirical formulas to explain the variation in theavailable data for the velocity derivatives and 'álso the acceleration derivatives.

His resultingfourequationsfor velocity

derivatives were obtained from the

pooled data andare, together with the remaining equations for acceleration derivatives, also presentedin [13].

the manoeuvnng derivatives for the

shiplike condition T= 0.1 0' m, H 2.50 rn (deep water) arecomparedwith the presentcalculatioh results and the semi-empiricalmethods mentioned above. Fig 5 presents the yaw coefficient -Y' as function of forward speed Fn, H/T = 2.0. In this case, condition B, there is a counter phase of 180'.

FPP

_FPP

U [-x

rn- f

m'dx +

f

n'dx]

XaIb

M'P

FPP

Y,,,,-

_f

m'xdx=N,,

APP

FPP

=

U [-xm- 2 f m'xdx

FPP

N,,=-

_f

m"x2dx APP

FPP

fm'xdx]

APP = Y,,

FPP

i

/

f

/

- ¡

[-xm-

j

,ndx*

Xmb pL

FPP

_FPP

N,

(4

_f

x2dx *

_f

m"xdx] N =

N,

APP

-pLU

N'=

FPP

fm'xdx=N,,'

APP

¡

_*

14

FPP

f

m'dr]

APP

FPP

FPP

[-x m

- 2

_f

m'xdx

_f

in'xd]

APP

FPP

15

f

m'x2dx -PLW APP 34 SCHIP&WERFdZEE MAART 1997

FPP

_FPP

Y. =

U (

¿ .

xdx

_f

m'L]

U

FPP

¡

-xm-2 f

m"xd,] -Y;

pL

figS. Measured and calculated Y,"'as function of fo,ward speed

0

0.1

Fn

Willem Beukelman onderscheiden

Ons lid de heer W. Beukeiman uit Pljnacker heeft opi Juni 1996 te St. Petersburg, Rusland, de "Peter de Grote me-daille" ontvangen. Een en ander vond plaats op de

plenai-re siotzitting van de "Derde Internationale Confeplenai-rentle ter herdenldng van het 300-fang bestaan van de Russische vloot opgerkht door Peter de Grote" (CRF-96), georgani-seerd door de Staats Marine Technische Universiteit van

St. Petersburg.

Totaal werden ongeveer 15 medailles uitgereikt, waarvan 2 aan bui-tenlanders en de overigen aan hooggeplaatst burger personeel en officieren van de Russische vloot.

De andere bultenlander die ook een medaille ontving, was mevr: M. Coleman (USA) van de historische afdeling.

ACC0WAL1I411 flETPOHAYI(A

OcHosat.. rOCYß,fl.,NUM UOPCKHM TtxHRqeclolu ynaaepc.cyeyoM

CAHKT.flETEpSypr pta1.

Harpa,caanc, o6wa,Seioá naaRrnoÑ M,naAb,o .flETP BEAHKHSh,

yupeac,s,.n,oA a cOq,,, C300,ier,,eaPoccug,oro 4cm,., ,a auarn,rescI.WÑ BKA5A 3 pasaN?,,, a nosnepocy aayaa, TunaN.

u flOaroTOaay nOpcKI4xCnesaanwcroa

--___ t99

roso

flpaaaean YqeowA ceupeeaps

Bijgaand een afbeelding van de oorkonde in het Russisch en een vertaling:

De Associatie "Peterwetenschap" opgeñcht door de Staats Manne Technische Universiteit van St. Petersburg heeft

Prof. Willem Beukelman

op 7juni1996 in St. Petersburg onderscheiden met de Jubileum Her-denkingsmedaille

"Peter de Grate"

ingesteld in verband met de 300 -jarige Russische I/loot vooropmerke-ulke bijdrage in de ontWikkeling en ondersteuning van de wetenschap,

techniek en opleiding von manne specialisten.

President Studie-Secretons,

CONCLUSIONS AND RECOMMENDAÌ1ONS

The presented calculation methods ba-sed ori the rate of change of fluid mo-mentum are suitable to determine phe-nomena as

- slamming pressures

-

lift production of the hull - manoeuvring derivatives

Reduction of the waterdepth causes a strong increase of lift and consequently also of manoeuvnng derivatives.

The influence of external oscillatiors

such as a rudder and propeller on the hull coefficients needs further investiga-tion. Research into viscous influence due to the curvature of the bilge and/or

Table Il!. Camporison of measured. calculated and semi-empirical values far the coefficients

C A T.O.IO.. H2.5O

the influence of bilge keel, is also need-ed.

REFERENCES

Radev, D. and W. Beukelman, 'Slamming on forced oscillating wedges at forward speed', Part I - Test Results, Part II - Slamming simula-tion on Penetrating Wedges at Forward speed, Intematlonal Shipbuilding Progress. Volume 39, No.420. 1992 and Volume 40, No.421, 1993.

jones, R.T. (1945), 'PropertIes of Low-As-pect-ratio Pointed Wings at Speeds Below and Above the Speed of Sound', NACA-Report 835 Newman, j.N. (1977), 'Marine Hydrodyna-mics", Book, MIF Press, cambridge, Massachu-sekts.

Katz, J. and Plotldn, A. (1991), 'Low Speed

Co,,olt$o.. 8 500,ie,..ne. Sq.00r. n0.

- 0.20 ,.. - 0.30 ',a F,,.d lløe T

-C,loml.non. vii r sia ,.

- - r - 0.20

'. r

-. r - a.o

.

irr

-- O io 030 u' -H.T. 53 Co,ftIaluoa Fa

-.

Sque F.Iod - Nuobin 0u,flo,.

Tip. Ti9. (1902) (1901) (1911) 0u.p 11910

1.' .12 0.92 0.51 0.59 0.71 0.90 0.92 0.90 05 1.04 005 I0 .21 1.2$ 0.62 4' IS 2,15 (.39 0.91 1)7 0.96 1.90 0.96 .39 2.13 (Ia (0' .23 2.02 (.20 .9,' lS nit .009 005 002 009 005 .00) .39 .0.15 .009 1O' .20 011 .0.17 .N' IS 0.46 0.26 0.50 037 0.39 035 0.68 .39 0.46 0.23 ¡O' .25 0.51 035 4,' II 005 0.03 0.0) 034 005 0.05 003 .39 016 0.12 IO' .23 0.12 0.21 .3' 1$ 0.47 0,5) 0.50 0.21 0.31 0.24 sSo .39 038 0.21 I0' .25 066 030 '97' IS 00) 0.10 0.07 0.04 3.07 0.07 007 .39 005 0.10 IO' .25 007 0.16 .9,' .15 0.24 0.14 0.22 0.18 0.21 0.2) 0.13 05 027 0.16 IO' .2.) 0.21 0.15 '.1ART 1997 SCHP&WtRFdoZEE 35 ("I

- 100

o

50-0.15

0.2

0.25

0.3

D i ve r se n

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Added to this, interpretation of the

in-36

thods',Book, McGraw - Hill, International Edi-tions

[S) Keil, H. (1974), 'Die Ñydrodynarnische

Krafte bei der periodische Bewegung zwei-di. mensionaler Körper an der Oberi lache flacher Gewasser', Institut ftir SchIffbau der Universität Hamburg, Bericht No. 305

16] Dmltrieva, Dr. I. 'Numerical Investigations

of Motions and Drift Forces on Different Bodies Using the DELFRAC Program', Report 1016, Ship Hydromechanics Laboratory, Detft Univer-sity of Technology, The Netherlands

[7] Beukelman, W. (1993), 'Lift and Drag for a

Low Aspect-ratio Surface Piercing Wing-Model in Deep and Shallow Water', Deift UniversIty of Technology, Ship Hydromechanics Laboratory, ISBN 90-370-0095-9

temational Convention on Salvage which entered into force on 14 July 1996 is causing some problems. Its provision for an enhanced salvage

award taking into account the skill and efforts of the salvors in preventing or

minimizing damage to the

environ-ment has led to the LOF speciâl com-pensation award - Article 14.

The Salvage Convention now forms part of English law, and the special compensation provisions are

embo-died in the salvage contracts of LOF9O and L0F95.

But the Conventionevokesvery

diffe-rent views; and 13M reports on the

opinions of various salvage contractors and theIntemational Salvage Union as

to the future of LOF. And their opi-nions on the growing involvement of

governments, and the increasing role of P&I Clubs, in salvage.

Two other major features in the Janu-ary issue of Uoyds Ship Manager look at European ship management, where officer shortage is making an impact; and at Gibraltar, where the change in government has led to a greater em-phasis on boosting Gibraltar's maritime earnings and activities, but the;Catego-ry 1 register Status saga continues.

Moving the second tension leg

pbffomi ÇILP)

For the second time Dockwise has

been awarded the sea transportation of a 113-metre wide tension leg

plat-form for Shell from the construction

yard in Taranto to the Aker Gulf

Mari-rivatives for a Low Aspect-Ratio Surface Piercing WungModel in Deep and Shallow Water', DeIft University of Technology, Ship Hydromechanics Lab., (MEMT, ISSN 0925-6555, 35) ISBN 90-370-0127-0

(9] Norrbin, N.H.(1971), Theory andObser-vations on the Use ola Mathematical Model for Ship Manoeuvnng in Deep and Confined Wa-ters' Swedish State ShipbuIlding Experimental Towing Tank, PubI 68, 1971

110] Gerritsma, J., Beukelman, W. and Glans, dorp, C.C., (1974), The Effect of Beam on the Hydrodynamic Characteristics of Ship Hulls', 10th Office of Naval Research Symp. Boston, USA or Report No. 403P, Ship Hydromechanics Lab., DeIft University of Techn., The Nether-lands

ne yard, wherecornpletion and

outfit-ting of the TIP will take place. The load-out operation was carried out in four steps. Firstly, the hull was

skid-ded from the construction quay onto

two barges, rnooredstem to the quay. The.barges were towedto Mar Grande bay, off Taranto, where the floating hull was discharged by means of the

float-off method. Subsequently, the TLP again was loaded by a float-on opera-tion onto the "Mighty Servant 2".

The diagonal setting of the 14,500 tons 'Ram Powell' TIP on the 40 me-tres breadth "Mighty Servant 2" in-creased the width of the transport to

an astonishing 113 metres. This

resul-ted in a protrusion of 36,5 metres on

each side of the heavy-lilt vessel. Atthis moment the Atlantic crossing of

the 'Rarn Powell' tension leg platform

is carried out by the "Mighty Servant 2", one of the largest vessels in the

'Hydrodynamic Derivatives on ShipManoeu, vring', Int. Shipbuilding Progress, Vol.28,

No.321. May1981, The Netherlands

112) Clarke, D., Gedllng, P. andHine, G. (1982), The Application of manoeuvres9 Criteria in Hull Design Using Linear Theory', Trans. RINA, 1982 [13] Book: "Principles of Naval Architecture', Volume llI:Motions in Waves and ControllabIli-ty, The Soc. of Naval Arch. andMarine Eng., New York,

Dockwise fleet. She is expected to am-ve in:Corpus Christiby rnidNoam-vernber 1996.

Dockwise NV. is operating a fleet of

fifteen semi-submersible heavy-lift ves-sels. Nine vesselsfocus on the oil, gas

and petrochemical industry; three in

the fully erectedcontainer cranes and dredging material markets; two in the subseacable layingmarket; and one in luxury yachttransportation.

For more information please contacL Mr. Bas A. de Jong or Mrs. Jeanny C.M.

de Leeuw; Dockwise N\'., Luxem.

burgstraat 2 2321 Meer (Hoogstraten) 1 Belgium

Tel: +32.3.31 70200, fax: +32.3.31 58553.