Split dredgers and barges

dredgers : remarkable offshore units

by P. J. Latreille, Senior Principal Surveyor, Deputy Head of the Hull Department, New Buildings Division, Bureau Veritas

SYNOPSIS

From the beginning of the development of the idea, Bureau Veritas has been involved in the design of split barges and dredgers.

The basis of this rather original concept is that

spoil, carried in the well, is discharged by opening the hull of the vessel and partially rotating the two halves around a longitudinal axis. The vessel thus appears

as two floating bodies, connected by hinges and

hydraulic cylinders.

The main problems resulting from this operating mode are concerned with :

the longitudinal strength of the ship,

the power of the cylinders,

the behaviour of deck hinges,

the behaviour of deck-house hinges (deck-houses remain upright during opening and closing the well), structural details and continuity of main structural

elements.

The article describes the method used to check the longitudinal strength. Also, a description of the dyna-mic analysis (needed for the calculation of the dynadyna-mic reaction in hinges and cylinders) is made. The

deter-mination of static components is presented, together with approximate formulae.

(I) This article is after revision by the editorial staff of Bulletin Technique the text of a paper presented by the author at Marintec China' 81, also published by Schipen

Werf, N° 6, March 1982. It is published here with the kind authorization of Schip en Wert

SPLIT DREDGERS

and

BARGES

main aspects of their structural

_strength

(1)

Delft University of Technology

Ship Hydromechanics Laboratory

Library

Mekelweg 2, 2628 CD Delft

The Netherlands

Phone: +31 15 2786873 - Fax: +31 15 2781836

To _{conclude, a quick review of rudder and}

propul-sion is made and reference is made to stability.

NOMENCLATURE

The main symbols used are scantlings length

ship's breadth

C ship's depth

T ship's draught

I _{length of the hopper}

Q weight of spoil in the hopper kN

total displacement with the spoil kN total displacement without spoil kN a _{distance from the bottom to the sealing}

joint located

at the lower part of the

hopper rn

h _{level of the spoil above the bottom}

spoil specific gravity _If/m3

speed of the ship knots

A DESIGN WITH MARKED

PECULIARITIES

What is a split hopper barge/dredger?

It is a vessel built to carry spoil dredged by itself or by another dredger. Up to now, this is not original but let us describe the unloading of this vessel.

At the dumping ground, the ship opens, by partially rotating its two halves around a longitudinal axis.

This constitutes the originality of the

split barge

concept.

The equilibrium of each half is achieved by the hydrostatic pressure and the weight_{of the spoil, on the}

one hand, and by the mechanical and

_hydraulic connections located at each end of the hopper, on the other hand.

View of part of the hopper.

The rotation is made around_{the axis of the two} hin-ges fitted on deck, generally at each _{end of the hopper;} these are the mechanical connections.

The opening and the closing_{of the hopper is} achiev-ed by means of double _{acting hydraulic rams, fitted} below deck in the same transverse section as the

hin-ges.

The deck-houses remain _{upright by providing for} rotation around a longitudinal axis on one side and for sliding on the other side.

The analysis on the operational _{mode of these ships} shows the following peculiarities

concerning longitudinal bending, each half is 'inde-pendent of the other. _{Consequently, the floating} structure is asymmetrical : loads and boundary

conditions differ from those of _{a classical vessel.} Thus, a special investigation is to be made;

the main elements of these vessels are the hinges and

the cylinders. _{They are subjected to very high} dynamic and static forces _{which must be}

estima-ted. _{In the same way, the accelerations induced in}

the deck-houses must be known, in order to allow

for the study of the

_{scantlings of the rotating}

connections with the deck;

the continuity and the structural arrangement of hinges, supports of cylinders, hatchcoamings and

JULY 1982 _{BULLETIN TECHNIQUE DU BUREAU}

VERITAS

sloping plates of hoppers are to be carefully studied as they are subjected to a high stress level. More-over, the lack of space at the hopper ends makes it difficult to find simple solutions.

In what follows, these three main aspects of thesplit barge/dredger design are discussed.

LONGITUDINAL STRENGTH

Need for

_{simplification}

As far as the longitudinal strength is concerned, the main problem is the calculation of normal stresses

within the hopper area. _{This calculation is much}

more complicated than it appears_{at first. The} asymme-try of the structure causes high horizontal and vertical loads which must be estimated.

A simplified method has been developed

_by Bureau Veritas to evaluate horizontal and vertical bending moments in

_{still water and in rough}

seas.

The main formulae are given below, after a brief description of the model used for the longitudinal strength calculation.

Model

- Beams and supports

The study of the longitudinal strength requires the study of this independant bending of_{each half, taken as} an idealized beam.

Flange of deck hinge, thickness 260 mm.

161

-The deck hinges and the hydraulic rams act as

sup-ports of_{the idealized beam.}

The span of the beam is thus equal to the

hopper length, corrected by the dis-tance of_{the hinges to these ends.}

Overall loads

_analysis

As the main inertia axes of _{each half are oblique}

with respect to the general axes, the loads_cause torsio-nal effects.

Fig. 1. _{Axes for the calculation} of bending moments.

In addition to the moments due to the vertical_forces usually considered, moments due to horizontal _forces are also to be taken into _account.

In still water, the moments are induced by_the diffe-rence of the action of the spoil inside the hopper and of the draught_{pressure outside.}

A variation of the outsi-de pressure due _{to waves is to be}

considered. As we assumed that the _{hopper beam s is simply} supported, the bending moment is maximum _{at mid} span, and thus the calculation is worked out in that sec-tion, assuming all moments are maximum_there.

The overall bending moments are first _calculated with respect to _{an horizontal axis GU}

and a vertical axis GV, then they _{are transfered to the main}

axes of

vertical loads

Vertical still water bending moment In general, a detailed _{analysis of the}

contemplated

loading cases allows us to pick out the maximum _still water bending _{moment, together with}

the associated

case. _{Often, this loading case corresponds to the} full load with maximum draught.

At the design stage, a good approximation _{of the}

vertical _{still bending}

moment may be reached _(in kN- m) using the following formula (for one half_{hull, in kN m):} of the

1 Q /

Mc, =T. ,-.-2A

-

_/)

with

C

P _{2.025 L-A}

where A is the wet area of the midship _{section, in m2.}

Vertical wave bending moment

The value of the vertical wave bending_{moment (for} one half, in kN m) may be calculated from_{the rule} for-mula: MB, = HL2B(C, + 0.7) 10-3-so with H

_{703 - 65 (3°°- L) 3/2}

L < 300 1 ₁₀₀ and where :

Cb is the block _coefficient, p is a coefficient relating

to dredging area.

The value of_{co is taken as follows}

1 . .

so _{within 8 miles from}

shore,

3

2 . .

9 =--within 15 miles from shore or 20 miles_{3 from port.} the transverse section. _{Figure 1 shows the}

reference

axes for the calculation _of

bending moments.

162

BULLETIN TECHNIQUE DU BUREAU VER1TAS_{JULY 1982}

-horizontal loads

Horizontal still water bending moment

The horizontal still water bending_{moment resulting} from the action _{of spoil and the}

external hydrostatic pressure may be computed from

p12( _{4 c)} MCH

=

k ₊

where c is the distance from each

end of the hopper to the deck hinges, in _metres

(fig. 2), and where_{p is the} load per metre, in kN/m, defined _by

P = Pi P2

where p, is the _{horizontal load due}

to the spoil

=-- 4.9 S(h _a)2

and p, is the horizontal external _{hydrostaticpressure} ---- 5.026 (T a)2

Figure 3 shows the geometry for the calculation _of the pressure loads.

Horizontal wave bending moment

The horizontal bending moment due to_{waves may} be obtained from the following

approximate formula : I +

=

₍

M

)

B with : 1)

a-16 kL

and H = go(Cb

_{+ 0.7) [ 1.38 O.128(3.}

3121

and where Mv _{is the vertical wave bending}

moment.

resulting loads

To calculate the

resulting bending moment, a sign convention is to be_{defined. This is done}

as follows.

For vertical loads

positive for_{a sagging moment,} negative for a hogging moment.

JULY 1982

BULLETIN TECHNIQUE DU BUREAU VERITAS

For horizontal _loads

positive moment if_{the shell plating}

is in tension, negative _{moment if the}

shell _{plating is in} compression.

Thus, according _{to this}

convention, the total

moments are given by algebraic _sums.

Fig. 2. _{Definition of}

distances.

Fig. 3.

Geometry for the calculation of the pressure loads.

For the vertical _moment

Mu = MHV4 MCV For the horizontal _moment

Mv =Matt _MCH

check of

_stresses

To verify the behaviour of the_{structure, the} longitu-dinal stresses are .to be calculated _{in the most}

loaded 163 Pon9t1 hopper well 4

L)

-:

areas. _{For this purpose, the moments are transferred}

to the main axes. _{This leads to} cos a + My sin a Mu sin a + M, cos a.

The stress, a, in Nimm2 at each point (x, y) is given

by :

a ( _{myI4 1O-3}

where _{and ly are the moments of inertia of the}

trans-verse section with respect to axes Gx and Gy.

The calculated stresses are to comply with the

follow-ing condition at any point of the transverse section (construction assumed to be in ordinary steel), the nor-mal stress is not to exceed 137 Nimm2 except for the hatchcoaming where it can reach 147 Nimml.

rion+

WIS111..

POUTRES PR ISMAT I DUES

9

11204 CIX1P,

DC MINCE TIN LW .041111..i

Fig. 4. - Geometrical plot produced by the programme.

conclusion

In spite of the simplification resulting fromthe use of

approximate formulae, the calculation is rather long

because the stresses must be calculated at a number of locations.

In order to make the check easier, Bureau Veritas

has developed a programme to perform this longitudi-nal strength calculation. _{Figure 4 shows a typical} geometrical plot produced in the course of using the programme. In addition, this programme calculates the rule values of plating thickness and of stiffeners

moduli.

HINGES AND CYLINDERS

Assumptions

These main elements of split barges and dredgersare

subjected to static and dynamic reactions. _These for-ces are induced by the spoil inside the hopper and the hydrostatic pressure outside. In what follows, we

des-cribe the method used to calculate these loads.

The restrictive assumptions are

the total number of hydraulic _{rams connecting the} two halves is even,

there is

_{only one hydraulic ram in}

_{any given} transverse section,

the fore and aft cylinders are assumed to carry equal

loads.

Evaluation of the static components

The equilibrium of weight against pressure results in

a zero static vertical reaction in hinges.

The horizontal equilibrium is expressed by stating that the static moment, with respect to hinge axis, is nil and that the resultant of horizontal forces,on one

half-hull, is equal to the algebraic _{sum of the horizontal} reactions in hinges and cylinders.

From the two resulting equations, we may calculate Fc.), and F (see fig. 5).

164

BULLETIN TECHNIQUE DU BUREAU VERITAS JULY 1952

14.11 0.11,1 11 WPM. .211=11 LE. ILIMMIA Ms. ..11.-11 ..11.-1107.. a..V.M1. =

=

:

-The horizontal static reaction in each cylinder, in kN, is given by 1 Fha, + Fda,

F"

n,a3 + F,a1 + Fiha, + 0.5 (h, Q/33)1

where n, is the total number of cylinders and F, = 5.026 (T a)2

F, = 4.9 (h a)2 16

3

Fig. 5. - Definitions for the calculation of the forces on hinges and cylinders.

The horizontal static reaction, in each hinge, in kN, is given by

F = 0.5 IF,

n,Fcy

(F, + Fiv

Fj,)]

The symbols used in the previous formulae are

defined as :

F,, horizontal hydrostatic buoyancy on the full length of the well, in kN. This force takes account of the hydrostatic counter buoyancy due to the water located between the two half-hulls below the seal-ing joint situated at the lower part of the hopper

well;

horizontal pressure of the spoil, in kN; force in each hydraulic press, in kN; force in each hinge, in kN,'

reaction of the vertical sealing joints located at ends of the hopper well, in kN;

Fp, reaction of the horizontal sealing joint located at the lower part of the hopper well, in kN.

JULY 1982 - BULLETIN TECHNIQUE DU BUREAU VER1TAS

Sealing joints.

Evaluation of the dynamic

components

computer programmes

Dynamic loads are induced by waves. It is an

intri-cate problem, solved by programmes developed in Bureau Veritas.

behaviour at sea and strip theory

The calculation of dynamic forces in the hinges ofa split ship is based on strip theory, which appliesto the

motions and dynamic loadings of slender ships. One

considers the split ship as a catamaran andone

calcu-lates hydrodynamic and other forces acting on one

Strip theory predicts the behaviour of a ship advan-cing at constant speed in regular waves rather accurate-ly and fairaccurate-ly easiaccurate-ly. _{It essentially consists of}

replac-ing a

_{tri-dimensional problem by a sum of}

bi-dimensional problems easier to solve. It assumes that a slender body can be considered as the sum of adjoi-ning elements perpendicular to the longitudinal axis (strips). The forces applied on each of these elements

165

:.

Fch

Fp

-are calculated as if it were part of an infinite

cylin-der. _{The solution of the}

global motion problem _is transformed into a succession of solutions_of

bidimen-sional problems

independent from each other, and so a

sum of partial results, from a linearity _assumption regarding the motion components.

ship motions

In its six displacements

(motion components), a ship can be located in space by the following _coordinates (fig. 6) :

Surge; rh heave; _pitch

772 sway ; _{--= roll ;}

7/6= Yaw

Fig. 6. - Coordinates for the motions.

with the assumptions that the_{responses are linear and} harmonic, the six linear coupled differential _equations can be written in the _{following abbreviated}

form

6

l(Mik Alk) k Bikrik _CJklik}

Fjeicdt; I, 2,..., 6 where the symbols have the following meaning :

Mik components of the generalized mass matrix, Ajk added-mass coefficients,

damping coefficients,

Cik _{restoring coefficients.}

In the strip theory, the surge _{component cannot be} calculed and we have _{five equations.}

They can be separated in two _{groups of two and three}

equations (heave and pitch _{sway, roll and yaw).}

Added-mass coefficients, damping coefficients and exciting _forces are first determined as functions of frequency.

bi-dimensional problems

The calculation of the added-mass and damping coef-ficients represents the _{most delicate part of}

the whole problem. _{The results are integrated}

in the first mem-bers of the equations _{of motion after}

having been added

strip by strip. _{Calculation of these}

sectional

parame-ters is based upon a development of the Frank _close-fit method, using a source/doublet distribution_{and a} cor-rection for elimination of irregular frequencies.

The second members of equations _{express the} exci-ting forces and moments. There are two_{types of} exci-ting forces : the incident_{forces and the diffraction}

for-ces. _{The first ones are calculated directly}

from the expression of the incident wave potential. _{The second} ones are calculated pretty _{much like the added}

mass coefficients. _{In fact, the two}

problems of diffraction (hull kept at rest in the incident wave) and of radiation (added mass oscillating hull in calm water)_{only differ}

in the boundary condition on the hull.

calculation of

_{forces on hinges}

_and

cylinders

After having found the motions of the_{ship, it is} pos-sible, by partial integration from aft to one particular section, to obtain the loads on this section. _However for a catamaran, we need a more complex _{way to} obtain the loads on a half-section. _{We consider for} the whole calculation only one half-hull. _{Each term} of the motion equations is separated_{into two parts, one} symmetric and one skew-symmetric with_{respect to the} ship's transverse coordinate.

For motions, one uses only symmetric_{terms and we} have the same problem as for the complete ship. On-ce the motions are obtained,

one has the forces in each strip of the ship in two parts : a symmetric_{one which}

does not give_{any force in the interconnecting}

structure,

and a skew-symmetric

one, which gives reactions _in this interconnecting _structure.

We obtain by this

method the distribution _{along the ship of}

vertical and horizontal forces and _{the moments of}

forces around a longitudinal axis drawn by the centre of gravity. _{It is} necessary to have a structural _{model of ship and}

her

interconnecting structure to calculate the reactions. In the vertical plane, for split ships with_{two hinges,} the system is isostatic and vertical reactions _{are solely}

166

BULLETIN TECHNIQUE DU BUREAU VERITAS _{JULY 1982}

Assembly of deck hinges, thickness 260 mm and 150 mm.

determinated from the distribution of vertical forces along the ship.

In the horizontal plant, we have, for the same type of split ships, four unknowns and only three equations (sum and moment of horizontal forces and sum of tor-sional moments). We need another equation and, to this end, we assume that the two cylinders give the same contribution to torsional effects.

We adopt the following notations (see fig. 7) : general force component along Gy (real and imaginary part),

R2 _{general force component along, G, (teal and}

imaginary part),

M.

general moment component around G,

(real and imaginary part);

general moment component around Gy (real and imaginary part),

general moment component around Gz (real and imaginary part),

horizontal force on the section, of the aft hinge located at X

A

R2A2 horizontal force on the section of the fore

hinge located at x42.

R3A3R3A2 'vertical forces on the aft and fore sections. The vertical reactions are obtained directly

R3A1 = (MY -+- RZ XA2)/(xA2 XA.I)

R3A2 = (My + R2 XA11)/(XA2 XA 1)

JULY 1982 BULLETIN TECHNIQUE DU BUREAU VERITAS

For the horizontal' forces the equations are t R2, + R,,,, _R2A

+ _{= R2A 2}

R2H I x (HAH ZG) R2Bl x (HAS ZG) + R2H2 X

(HAN - ZG) x (H ZG) =

where R1, and R2172 are the reactions on the fore and

aft hinges and R2.1, R,n, the reactions in the fore and aft cylinders.

The supplementary hypothesis is (same value of for-ces in cylinders)

R2B = R282 = R28

Fig. 7. Notations for 'the 'calculation of forces on hinges and cylinders.

Then, modifying, the, last equation, We obtain

R2B

2 (HAB HAH )".

We' then obtain :

R2A,1 = (7- Mz 'Ry IA2)/(XA2 1

R2A2 = M, Ry

an

R2H1 = R1, R25 R2H 2 = R2A2 R211

Numerical calculations are carried out with Bureau Veritas'programme M 1208.

The first step' of calculation is to obtain the transfer functions of the loads in regular waves.

167 Mx -R2.411. =

-R252

-ZG)

(-

*XA1)/(xA2

-Generally, the procedure _{used is as follows} two loading cases are analyzed

the _{case called working condition}

s, _which

corresponds to the dredging operation,

the case called _{sailing condition .;}

5 wave-encounter angles are chosen : 0, 45, 90, 135 and 180 degrees from the bow (0° = heads seas) and

30 wave-lengths for each angle. _{Wave amplitude}

is taken equal to 1 m (2 m crest to crest).

The second step of calculation consists in obtaining

the statistical values of _{the loads.}

The method may be _{summarized as follows. It is}

assumed that a monodirectional _{confused sea is}

repre-sented by a spectral _{power density function, or}

spec-trum. _{This sea generally propagates in direction 0}

with respect to the ship's route and, in nature, actual

seas are composed of a number of such

monodirectio-nal seas. _{We then define this}

pluri-directional confused sea by a series of spectra S(w) such as, for

each of them

Kco) =

S.(co) Aco

whereKo. is « the _{wave amplitude in direction 0,}

for

an angular frequency in Zito around _cp.

The response spectrum for an effect represented by

its transfer function K(w) on the sea represented bySe,

is defined by

12.(w)=

_1404-

So(co)

Rico) represents the _{square of the amplitude of the}

components in Ls,co about co of the response spectrum (spectral density).

Sea spectra and response spectra are assumed to be narrow enough to be used in connection with Rayleigh

statistics, i.e., the phases _{of the wave}

components of a

complex sea are assumed_{to be randomly distributed.}

The Rayleigh distribution _{law for a variable x with} average square value R is

P(x, x _{dx,) = exp(}

)

From this, we obtain the probability that x be equal

to or larger than x'

2

P(x x') = exp(

Two types of statistical calculations_{may be made}

short term and long term estimates. Short term

calcu-lations give statistical values _{of parameters on a given}

sea state. Long term statistical calculations _are

per-formed with a selected _{distribution, over the life of the}

ship, of sea states and angles_{of sea encounter.}

The two types of calculations _{can be made using}

limited sea state conditions.

These calculations allow us to obtain the values of

the accelerations _{necessary to calculate the reactions}

on the deck-house hinges.

exploitation of the calculations

of forces

The evaluation of static and dynamic components of

forces allows us to study_{the hinges and the cylinders.}

These components are denoted as shown in table I.

Table I. _{Symbols for components} of forces on hinges and cylinders.

The cylinders are to withstand a total force equal to

FTI = FHSI + Ftsini

This force has to counteract the opening of the

hop-per.

Moreover, this force is transmitted to the ship structure where the hydraulic_{rams are connected. It}

leads to an heavy _{and complicated}

structure, because

the loads are high. _{The deck hinges are to withstand}

the two total forces

Frv2 -= FvD2

FTH2 = FH52 FH02

Again, these high forces require a complex structure

to withstand them.

force

item static dynamic

hinge FHS2 FHD2 FVD2 cylinder FRS] FHDI 168

BULLETIN TECHNIQUE DU _{BUREAU VERITAS JULY 1982} :

:

+

: a

simplified formulae

The previous discussion shows that if the calcula-tion of the static components is simple, the calculacalcula-tion of the dynamic components is complex, long and

expensive.

Bureau Veritas, using its experience, is developing approximate formulae to evaluate thedynamic

compo-nents, in the case of medium size split ships _{(that is,} 500-3 000 cubic metre ships).

Flanges of hydraulic rams.

DECK-HOUSE HINGES

Calculation parameters

As indicated above, the dynamic calculation_yields the accelerations in the deck-house.

The results may be used to design the hinges and the corresponding connection of the deck-house with the

deck structure.

JULY 1982 _{BULLETIN TECHNIQUE DU BUREAU VERITAS}

However, after having made several _{calculations,} Bureau Veritas has adoptedmean values, in connection

with stress levels incorporating safety _factors. These values correspond to a rolling angle _{of 20°}

and a roll period of 6

s, for an admissible stress of

100N/mtn2.

The check of the scantlings of hinge plates and pins is specified in Bureau Veritas' Rules.

Structural

details

The calculated forces being large, 100to 200

tonnes-force for a split ship within the

_{range of 1,500 to}

3,500 rn', the structural details are to be carefully design-ed.

The hinge plates are to be continuous _{through the} ship's deck and the deck-house floor. _{The welds are to} be carefully checked by X-rays.

Any discontinuity is to be eliminated; _{hard points} are to be avoided; efficient overlappings are to be pro-vided and smooth shapes using a nose for brackets are

recommended.

Deck structure and deck-house floor structure arc to be reinforced by heavy beams and girdersto withstand

the imposed forces

STRUCTURAL ARRANGEMENTS

RELATING TO HINGES,

CYLINDERS,

HOPPER AND HATCHCOAMINGS

Limited space versus good continuity

Generally, cylinders are located _inside compart-ments fitted at the fore and aft ends of the hopper. These compartments are bounded by two transverse bulkheads, by the side and bottom shell and by the upper deck, on which hinges are installed.

These spaces _{are only used to house}

the hydraulic rams. _{Consequently, shipyards}

tend to limit

_this space to the strict minimum.

This restricts the _space available for extending _{the structures of}

hinges and cylinder supports. _{At the same time,}

it reduces the space necessary to ensure a good continuity_{of the} hop-per sloping bulkhead.

However, using an adequate

structural arrangement, the continuity may be ensured.

Continuity of

_longitudinal

_elements

The hatchcoamings are to be continuous_{and safely} overlapped at the ends. _{Brackets as large}

as possible

are to be fitted at each

_{end. No deck}

opening or other

discontinuity is to be fitted in the neighbourhood _{of the} connection between _{these brackets and the deck, to} allow stresses to spread through the deck plating.

The recommended_{slope of brackets is}

1/2.5.

Figu-re 8 shows typical bracket

arrangements.

Fig. 8. - Typical _{bracket arrangements.}

The sloping sides of the hopper are to be efficiently overlapped at the hopper ends, using large _brackets welded to the deck_{and the bottom.}

These brackets are to be in the_{same plane as the structure}

welded to

the deck or the _{bottom (fig. 9).}

170

si, he same

P41,..l

Fig. 9. - Brackets _{coplanar with}

structures.

Continuity of deck hinges

The deck hinges,

being subjected to tensile loads and reversing secondary moments, are to have_{their plates} continuous through the deck.

The deck is to be _{full penetration welded to these}

plates.

Under deck, inside the cylinder _{compartments, the}

hinges are to be_{connected to strong}

girders and beams,

allowing the _{transmission of loads}

to bulkheads and

platings.

On deck, the hinge plates are to be fitted_with longi-tudinal tripping brackets, avoiding _{any longitudinal} bending due to clearance.

In addition, _{to avoid longitudinal}

clearance, it is recommended to provide

for small and medium size split ships_{(capacity less}

BULLETIN TECHNIQUE DU BUREAU VERITAS _{JULY 1982}

than 3 000 ay?),

one longitudinal reacting _{plate at} bottom level;

- for large size split ships,

two longitudinal reacting plates, one at deck _{and one at bottom.}

WIDE EXPERIENCE

AND INNOVATION

A large number

_of

_split

_ships

classed

_{with Bureau}

_Veritas

This article has touched _{on the main problems} relating to the split barge/dredger concept

longitudinal strength, deck hinge design, hydraulic press choice, deck-house hinge design, structural details.

For all these, Bureau Veritas has developed calcu-lation methods and laid down Rules and

recommenda-tions.

Table II.-_{Main split ships classed with}

Bureau Veritas. JULY 1982 - BULLETIN

TECHNIQUE DU BUREAU_VEFIITAS

This is the result of a wide experience_{in the field of}

split ships, which_{is exhibited in table} II.

One must note that _{Bureau Veritas has}

published

rules relating to _{split-ships in Amendment}

N° 3 to

its Rules and Regulations.

A Guidance

_{Note on}

_stability

For completeness, _{we add a few lines}

on rudders, machinery and stability.

Rudders and machinery are classical and each half-hull possesses its own installation.

Concerning stability, _{one has to note that Bureau} Veritas is the first _{classification society to have}

publish-ed recommendations _{on dredger stability.}

A Gui-dance Note _{was published in 1971 (NI}

144 BM 1

-January, 1971). _{Nowadays, this document}

is used as

a reference and _{as such, several national}

authorities

have completely adopted the recommendations_{of the}

Note.

_{Practically all the}

hopper and split hopper dredgers classed with Bureau Veritas comply _{with this} Guidance Note.

Fitting of one ofthe hydraulic _rams.

171 I name _remarks L M B M C )71 T M hopper capacity /713 BZ 1 . more than 10 ships 59 _{9.5 3.35 3.25} 660 5 ships 51.3 10.7 3.6 2.8 500 .Sea Splitter. 8 ships 57.5

to 59 11 3.7 abt. 3.5 ₇₅₀ . Stapel 135 . _59.3 11.24.25 3.7 900 . Anow 6 . _{7 ships 65} 13 4.9 4.3 _1,000 WD Medway. 2 ships 70.5 15 6.3 5.1 _1,500 Krankeloon . _{3 ships 89.33 17.36 7.3} 6.25 2,700 . Gamma Bay, _82.5 16,6 7 5.05 2,700 Alpha Bay . _{104 21.4 8} 6.25 _4,300 building 101 21.5 7.55 6.65 _4,900 : -a

A mendement N° 3 to the 1980 Rules_{of Bureau}

Veri-las.

Nguyen Ket, J.-P. Jaunet and Mrs._{Henry -} Corn-portement du navire stir houle : quelques _domaines d'application des calculs sur ordinateur ,, Nouveau-tes Techniques Maritimes, 1981.

P. Guevel and J.-M. Kobus - _Flotteurs

cylindri-ques horizontaux soumis a des oscillations_forcees de tres faible amplitude _{ATMA 1975.}

N. Salvesen, E. 0. Tuck and 0. Faltisen - i Ship motions and sea loads _{,, SNAME 1970.}

This conference will take place in Sydney, Australia, in September 5-8, 1982, sponsored by the_Australian chamber of shipping.

The proposed major subject _{areas will be :} the projected developments : mineral and energy

exports, liquefied natural gas;

the user view : production and_performance;

172

false identity

CORRIGENDUM TO OUR ARTICLE ON

* OSTREA *

April, 1982, p.91

Nostra culpa! We failed to correct a misspelling in the name _{as transmitted to us of}

Ostrea )p's designer particularly well known in Bureau Veritas

BUREAU VOOR SCHEEPSBOLTW Ir. P. H. de Groot b.v.

Bloemendal, Holland.

REFERENCES

COMMUNIQUÉ

RESOURCE DEVELOPMENT AND SHIPPING

J.-M. Planeix - _{Wave-loads. A correlation}

bet-ween calculations and measurements at sea ,, Inter-national Shipbuilding Progress, August 1972.

J.-M. Planeix - _{Mouvements de pilonnement et de} tangage du navire sur houle simple oblique ,, Bulle-tin Technique du Bureau Veritas, November 1969. J.-M. Planeix and F. Tournan - _{Efforts tranchants,}

moments flechissants, acceleration verticale et mou-vement relatif par rapport a la surface en houle sim-ple, debout ou oblique 0, Bulletin _{Technique du} Bureau Veritas, January 1970.

the industrial scene;

the capabilities of transport _{infrastructure;} the shipping experience;

the bulk carriers of the future.

The conference secretariat, Resource _development and shipping, G.P.O. Box 2609, Sydney, _Australia N.S.W. 2001, Tel.: (02)241_1478.

BULLETIN TECHNIQUE DU BUREAU VERITAS JULY 1982