Example B.2.1 – Bottom blocking and top-over lashings on a 16,600 DWT ship
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Statutory Documents - IMO Publications and Documents - International Codes - 2011 TDC Code – Code of Safe Practice for Ships Carrying Timber Deck Cargoes, 2011 – Resolution A.1048(27) - Annex B – Samples of Stowage and Securing Arrangements - B.2 Example calculation – Bottom Blocking and top-over lashings - Example B.2.1 – Bottom blocking and top-over lashings on a 16,600 DWT ship

Example B.2.1 – Bottom blocking and top-over lashings on a 16,600 DWT ship

Figure B.2. Midship section of 16,600 DWT ship with packages of sawn wood in two layers secured with bottom blocking devices and top-over lashings

 Ship particulars

Length between perpendiculars, LPP: 134 metres
Moulded breadth, BM: 22 metres
Service speed: 14.5 knots
Metacentric height, GM: 0.70 metres

 The deck cargo has the dimensions L x B x H = 80 x 19.7 x 2.4 metres. The total weight of the deck cargo is taken as 1,600 tons. Sliding between the layers is prevented by packages of different heights in the bottom layer.

 Dimensioning transverse acceleration

With ship particulars as above and considering a stowage position on deck low, Annex 13 of the CSS Code gives a transverse acceleration of at = 5.3 m/s2 , using the following basic acceleration and correction factors:

at basic = 6.5 m/s2 = Basic transverse acceleration
fR1 = 0.81 = Correction factor for length and speed
fR2 = 1.00 = Correction factor for BM/GM

 Cargo properties

m = 1,600 ton = Mass of the section to be secured in tons, including absorbed water and possible icing
μstatic = 0.45 = Coefficient of static friction between the timber deck cargo and the ship's deck/hatch cover
H = 2.4 m = Height of deck cargo in metres
B = 19.7 m = Width of deck cargo in metres
L = 80 m = Length of the deck cargo or section to be secured in metres
PW = 192 kN = Wind pressure in kN based on 1 kN per m2 wind exposed area, see CSS Code, Annex 13
PS = 160 kN = Pressure from unavoidable sea sloshing in kN based on 1 kN per m2 exposed area, see CSS Code, Annex 13
n = 26 pcs = Number of top-over lashings
PTV = 16 kN = Pretension in the vertical part of the lashings in kN
α = 85° = Angle between the horizontal plane and the lashings in degrees
np = 18 pcs = Number of stacks of packages abreast in each row
nb = 26 pcs = Number of bottom blocking devices per side of the deck cargo

 Required strength of the bottom blocking

The required strength, MSL, of the bottom blocking devices is given by the following equilibrium:

Parent topic: B.2 Example calculation – Bottom Blocking and top-over lashings
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