Tuesday, February 21, 2012

Volumes calculation in preliminary ship design

Volumes calculation
in preliminary cargo ship design


In following form, main dimensions of a cargo ship can be input in order to get  an approximate  calculation of her cargo spaces and ballast  tanks . User instructions are shown  at the end.





Volumes Calculation

Cargo ships



Length between pp (m)
Breadth B (m)
Depth to Upper deck (m)
Draft summer T (m)
Block Coefficient at T draft
Propulsion engine(s) power (Kw) 
Propulsion engine(s) RPM
Engine & Pump rooms length (m) *
Fore peak tank length (m) *
After peak tank length (m) *
Fore deep tank length (m) *
After deep tank length (m) *
Double bottom height (m) *
Double hull breadth (m) *
Hopper wing tank breadth (m) *(from double hull)
Hatch ways total length (m) *
Hatch ways average breadth (m) * *
Cargo volume experience coefficient *



Spaces     Volume(m3) 
Ship type
Cargo space
Fore peak  
After peak 
Fore deep tank 
After deep tank 
D. Bottom + D. Hull + H. & W. tanks







Spaces volume calculation

(At the preliminary cargo ship design)


Introduction

The calculation of cargo spaces volume is one of the basic tasks to be performed in the ship initial design stage as it usually is a ship feature specified in the contract. It is therefore advisable to be able to perform quick, approximate calculations at this stage, allowing to analyze several alternatives very soon. It should also be estimated the fuel, water and ballast tanks capacity owing to their impact on autonomy, drafts and stability in various loading conditions. In this blog I present a form to enter a cargo ship main dimensions from which the program roughly calculates cargo spaces and tanks volume.

Remarks

  • Engine room aft with a pump room in tankers and chemical carriers
  • A maximum of 320 m length b. perpendiculars is allowed
  • Ratios between dimensions should be normal
  • No cargo spaces above Upper deck are considered, except in reefer ships
  • Container and LPG carriers are not included

Definitions

The user is prompted to enter just ship type and following characteristics:
  • Length bet. perpendiculars
  • Breadth
  • Depth to Upper deck
  • Summer draft T
  • Block coefficient at T draft
  • Propulsion engine(s) power (Kw)
  • Propulsion engine(s) RPM
Optionally these other dimensions can be input, but, by defect, they shall be estimated by the program should the user omits them:
  • Engine & Pump rooms length: According to Ref.1
  • Fore peak tank length: According Ref.1
  • After peak tank length: According Ref.1
  • Fore deep tank length, next to Fore peak: 0
  • After deep tank length, next to Engine/Pump room: 0
  • Double bottom height: S/ Marpol, in tankers. Formula 3.8.6 in Ref.1 for other types
  • Double hull breadth: S/ Marpol, in tankers. Zero in other types
  • Hopper wing tank breadth (measured from double hull): 0
  • Hatch ways total length : 50% Lpp, except 0% in tank ships and 30% in Reefers
  • Hatch ways average breadth: 50% Breadth, except 0% in tank ships and 30% in Reefers
  • Cargo volume experience coefficient: 1
Optional data are * marked and in gray color cells.

Other less important features are just defined by the program, as follows:
  • Hopper wing tanks slope in oil-tankers and bulkcarriers: 45º
  • Top wing tanks horizontal slope in bulkcarriers: 30º
  • Top wing tanks in tankers does not exist; double hull goes vertically up to deck
  • Top wing tanks in bulkcarriers: From hatchways up to double hull (if any) or to outer shell
  • Upper deck with no sheer and with deck camber height of B/50 (m)
  • If vertical deep tanks (VDT) are fitted fore and/or aft, they will extend up to ship bottom
  • Top and hopper wing tanks do not protrude the VDTs
  • In ships with a length bigger than 100 m, a pipes tunnel in D. Bottom is assumed from fore to aft
  • No eventual fuel or water tanks are considered in engine room, double bottom or deep tanks
  • Reefer ships: Assumed to have a cargo tweendeck on Upper deck, of 20% Lpp length, spaces insulated for -30ºC, without lateral ventilation ducts, an elevated double bottom tank under No.1 hold

Results

Capacity estimates obtained in this form are made by approximate formulas, which were published in the following references. A sectional areas integration is not performed to calculate the volumes of each space, as is normal in the next phase of the design development. The final table presents results as shown.

References

Ref.1 El Proyecto Básico del Buque Mercante (Basic design of merchant ships). R. Alvariño, J.J. Azpiroz, M.Meizoso. FEIN 2007

Ref.2 Ship design for Efficiency and Economy. H. Schneelkuth. Butterworths
Ref.3 La determinación de las características principales en los buques de cabotaje (Getting main particulars of coaster ships). R. Alvariño. Ingeniería Naval 1977

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