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SMK 3522 SHIP DESIGN I Dr Koh Kho King 2013

Week 7-1

CAPACITY ESTIMATES AND GENERAL ARRANGEMENT

This will verify that sufficient space is available for the amount of cargo to be carried. Forcapacity ships, it is a primary factor and may be a starting point in the design. It alsodetermines the distribution of weight and hence the LCG and KG. Before detailed capacityestimate can be performed, a preliminary general arrangement (G.A) must be prepared.

Preliminary Volume Coefficient

This coefficient could be used to check volume, given main dimensions of a dead weightcarrier, or as a starting point to estimate main dimensions on a capacity ship.

)09.0C(xDxBxLVOLUMECARGO

PVCB

Assumes similar basis ship and also same stowage factor. The coefficient will vary with sizeand speed in a similar way to the DWT/ ratio.

A slightly improved estimate can be made if the gross volume of the basis is known, measured between the peak bulkheads and from inner bottom to uppermost continuous deck. This can be adjusted for differences in fullness, sheer, camber, double bottom depth, engine roomlength.

Fullness should be compared at 0.8D to relate it to depth rather than draught. This can be

estimated from CB as will be described later, or a figure of (CB + 0.09) can be used.

Double bottom depth, sheer and camber are allowed for by calculating a mean cargo depth,which is:

Moulded depth to upper deck, D- depth of double bottom, d DB + half maximum deck camber, camber/2+ mean sheer

The mean sheer is given by:

2

f a 0.55.4

xSS61

Sa = sheer aft ; S f = sheer forward

and the last factor allows for sheer only between stations2

1 and

2

19

Mean shear = 0.135 (S a + Sf)

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Week 7-2

Corrected depth, Dc = D dDB +2

Camber + 0.135(Sa + Sf)

Length and breadth can be allowed for directly and a volume correction factor can becalculated as:

Vol vactor =)09.0()09.0( ****

Bc

Bc

C x D x B x L

C x D x B x L

This factor is applied to the basis ship gross volume to give an estimate of that for theproposed. From this, deduct all spaces, not available for cargo,

i) Main machinery spacesii) Shaft tunnel

iii)

Fuel tanksiv) Ballast only spacesv) Machinery casingsvi) Store rooms etc.

An approximation to the total volume of machinery spaces (engine room, tunnel,casings, fuel tanks) is given by:-

Vm = CxSP 0.77

Where C is obtained from basis ship. From the total, about 70% will represent themachinery space proper (between machinery bulkheads and under 2 nd deck) so thatthe distance between machinery bulkheads for midship machinery will beapproximately:

LER = )(xx7.0

2

77.0

md D B

SP C

DB

Example:

Basis ship: Carries 17920 m 3 of general cargo storage factor 2.56

L = 120.0mB = 17.50mT = 7.41mDu = 10.50mCB = 0.6800

Vm 0.7 = LER x Bx(D2 d DB)

and Vm 0.7 = 0.7 x C x SP 0.77

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Week 7-3

New ship:L = 116.3mB = 17.02mDu = 10.00m (depth to upper deck)Cb = 0.6913

Overall volume coeff. is given by :-

Vc = C x L x B x D x [C B + 0.09]C = 17920/(120 x 17.5 x 10.5 x 0.77)

= 1.05545

*Vc = 1.05545 x 116.3 x 17.02 x 10.00 x (0.7813)= 16323 m3

Additional information

Basis NewLength between peaks, L BP 106.5 103.5Shaft Power (kW) 2165 1860Engine room length, L ER 12.35 11.90Depth of Double Bottom, d DB 1.05 1.025Sheer aft 1.26 1.22Sheer ford 2.52 2.44Camber at upper deck 0.58 0.56

Second estimate:

Vc = K x L x B x D c x (CB + 0.09)

Where:L is length of cargo spaces Dc is mean cargo depth

L = Length LBP between peaks - LER

Dc = D dDB + 0.135(Sa + Sf) + (camber/2)

For basis,17920 = K x (106.5 12.35) x 17.5 x

(10.5 1.05 + 0.135(1.26 + 2.52) + 0.58 / 2) x 0.77K = 1.378

For New Design,

*Vc = 1.378 x (103.5 11.9) x 17.02 x (10 1.35(1.22 + 2.44) + 0.5612)x0.7813= 16264 m3

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Week 7-4

The Use of General Arrangement in Capacity Estimates

The method of estimating cargo volume has already been given. Now an estimation ofvolume for each cargo compartment has to be found. To do so, an early GA has to be madeavailable.

The G.A. should show the following:-Main bulkheadsDecksMachinery spaceShearExtent of superstructureEtc.

The G.A is important for the following purposes:-a) First graphical description for discussion

b) Allows estimates of all volumes to ensure they are adequatec) Allows estimated of KGd) Allows estimates of LCG can find LCB for powering

The estimates should include a number of conditions:-a) Full load departureb) Full load arrivalc) Ballast departured) Ballast arrivale) Special conditions [eg. At half load]

For each condition trim, stability and strength has to be estimated.

Considerations in determining the G.A:

a) Position of machinery usually either aft or amidships.Aft machinery allows efficient cargo stowage for cargo ships, containersetc.

b) Height of double bottom Determines by classification society regulations and

requirement of greater storage of water ballast and fuel.

c) Cargo accesses Depends on type of shipThis is in terms of positioning hatches, cargo handling gears and holdcapacity or shape.

d) Bulkhead location define by classification society. Consideration fordamage stability which depends on ship length.

e) No. of decks determine by variety of cargoes or types and freeboard

regulations.

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Week 7-5

f) Wing tanks for ballast and stability.

g) Framing system transverse or longitudinal system of framing Affectcargo stowage.

h) Accommodation depending on number of officers and crew membersrequired.

Estimating Cargo Hold Capacities and Centres

If a basis ship G.A. is available, an estimate of cargo hold capacities and centres can be found provided the G.A. is similar to basis ship G.A.

The following procedure can be adopted:

a) Identify the positions of bulkheads, cargo holds with respect to lengthof the ship.

b) Relate the positions on curve of cross section area of cargo sections andkg of cargo sections.

For G.A. of new ship:-

a) Transform values read from curve to appropriate positions on new

ship.The positions of bulkheads and cargo holds between basis and new ship isfound by graphical manner [Linear].

Relationship :L*L

.x*x length from AP

AP,AP*Posn. Ofbulkhead

x

Basis Ship

FP

X*

New Ship FP*

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Week 7-6

b) Do numerical integrations

Ord. Area sm f(v) kg f(Mt) lever f(Ma)

abcd

111.48104.5185.4751.09

1331

111.48

732.51

5.185.495.916.49

577.466

4149.70

0123

0

979.62

Cargo space length = 15.40m

Volume* =35.8x70.1386.7x85.12

x58.732x83

x340.15

= 124.5m3

kg* = m28.584.035.886.7

x94.051.73270.4145

LCG* = m87.6340.15

x51.73262.979

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Week 7-7

Basis (m) New (m)Length 94.5 85.3Breadth 13.70 12.85Dc 8.35 7.86

dDB 0.94 0.84

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SMK3522_Wk07