CAPACITY ESTIMATES AND GENERAL ARRANGEMENT

Transcription

1 CAPACITY ESTIMATES AND GENERAL ARRANGEMENT This will verify that sufficient space is available for the amount of cargo to be carried. For capacity ships, it is a primary factor and may be a starting point in the design. It also determines the distribution of weight and hence the LCG and KG. Before detailed capacity estimate 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 weight carrier, or as a starting point to estimate main dimensions on a capacity ship. PVC CARGO VOLUME L x Bx D x (CB 0.09) Assumes similar basis ship and also same stowage factor. The coefficient will vary with size and 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 room length. 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 ) 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/ + mean sheer The mean sheer is given by: Sa = sheer aft ; Sa 6 Sf 4.5 x 5.0 Sf = sheer forward and the last factor allows for sheer only between stations and 9 Mean shear = 0.35 (Sa + Sf) Week 7-

2 Corrected depth, Dc = D ddb + Camber (Sa + Sf) Length and breadth can be allowed for directly and a volume correction factor can be calculated as: Vol vactor = * * * L x B x Dc x( C L x B x D x( C c * B B 0.09) 0.09) This factor is applied to the basis ship gross volume to give an estimate of that for the proposed. From this, deduct all spaces, not available for cargo, i) Main machinery spaces ii) Shaft tunnel iii) Fuel tanks iv) Ballast only spaces v) Machinery casings vi) 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 the machinery space proper (between machinery bulkheads and under nd deck) so that the distance between machinery bulkheads for midship machinery will be approximately: LER = 0.7xCxSP B D d 0.77 DB ( m) Example: Basis ship: Carries 790 m 3 of general cargo storage factor.56 L = 0.0m B = 7.50m T = 7.4m Du = 0.50m CB = Vm 0.7 = LER x Bx(D ddb) and Vm 0.7 = 0.7 x C x SP 0.77 Week 7-

3 New ship: L = 6.3m B = 7.0m Du = 0.00m (depth to upper deck) Cb = Overall volume coeff. is given by :- Vc = C x L x B x D x [CB ] C = 790/(0 x 7.5 x 0.5 x 0.77) = *Vc = x 6.3 x 7.0 x 0.00 x (0.783) = 633 m 3 Additional information Basis New Length between peaks, LBP Shaft Power (kw) Engine room length, LER Depth of Double Bottom, ddb Sheer aft.6. Sheer ford.5.44 Camber at upper deck Second estimate: Vc = K x L x B x Dc x (CB ) Where: L is length of cargo spaces Dc is mean cargo depth L = Length LBP between peaks - LER Dc = D ddb (Sa + Sf) + (camber/) For basis, 790 = K x ( ) x 7.5 x ( (.6 +.5) / ) x 0.77 K =.378 For New Design, *Vc =.378 x (03.5.9) x 7.0 x (0.35(. +.44) )x0.783 = 664 m 3 Week 7-3

4 The Use of General Arrangement in Capacity Estimates The method of estimating cargo volume has already been given. Now an estimation of volume for each cargo compartment has to be found. To do so, an early GA has to be made available. The G.A. should show the following:- Main bulkheads Decks Machinery space Shear Extent of superstructure Etc. 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 adequate c) Allows estimated of KG d) Allows estimates of LCG can find LCB for powering The estimates should include a number of conditions:- a) Full load departure b) Full load arrival c) Ballast departure d) Ballast arrival e) 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, containers etc. 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 ship This is in terms of positioning hatches, cargo handling gears and hold capacity or shape. d) Bulkhead location define by classification society. Consideration for damage stability which depends on ship length. e) No. of decks determine by variety of cargoes or types and freeboard regulations. Week 7-4

5 f) Wing tanks for ballast and stability. g) Framing system transverse or longitudinal system of framing Affect cargo stowage. h) Accommodation depending on number of officers and crew members required. 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 length of the ship. b) Relate the positions on curve of cross section area of cargo sections and kg 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 is found by graphical manner [Linear]. AP,AP* Posn. Of bulkhead x Basis Ship FP X * New Ship FP* Relationship : L * x* x. length from AP L Week 7-5

6 b) Do numerical integrations Ord. Area sm f(v) kg f(mt) lever f(ma) a b c d Cargo space length = 5.40m Volume* = x7.86 x x73.58x x8.35 = 4.5m 3 kg* = x m LCG* = x 6.87m Week 7-6

7 Basis (m) New (m) Length Breadth D c d DB Week 7-7