Topic - 19 Ballast and Deep Tank Bulkheads

1.                  Plating

Plating of Ballast and Deep tank bulkheads is to be of thickness obtained from the following equation:

t = [sk√qh/254] + 2.5 mm           t = [sk√qh/460] + 0.10 in. (3-2-7/3.1)

                     =  mm

But not less than 6.5 mm (0.25 in.) or s/150 + 2.5 mm (s/150 + 0.10 in.), whichever is greater,

In addition to the above, the top strake of effective longitudinal bulkheads is not to be less in thickness than given by the following

t = 0.0521L + 4.8 mm            t = 0.000625L + 0.19 in.

                              = mm

Finalized ballast and deep tank bulkhead thickness = 8 mm

And the second top strake is not to be less in thickness than given by the following:

t = 0.0347L + 5.3 mm             t = 0.000417L + 0.21 in.

                             = mm

Finalized ballast and ballast tank bulkhead thickness =  mm

2.                   Stiffeners

Bulkhead stiffeners are to have their ends attached. Each stiffener, in association with the plating to which it is attached, is to have a section modulus SM not less than that obtained from the following equation:

SM = 7.8chsl²Q cm³                   SM = 0.0041chsl²Q in³      (3-2-7/3.3)

For horizontal or vertical stiffeners on transverse bulkheads and vertical stiffeners on longitudinal bulkheads, SM=cm³

     Depth considered = in.

     Web thickness = in.

     Flange thickness = in.

     Flange width =  in.

                                         SM_obtained =  cm³

3.                   Stringers and Webs

Ø    Strength Requirements

Stringers and webs which support bulkhead stiffeners are to have section moduli SM as obtained from the following equation. Where the expanse of the bulkhead is relatively large, consideration is to be given to fitting of deep girders in line with webs and stringers so as to obtain complete planes of stiffness.

                         SM = 4.74chsl²Q cm³             SM = 0.0025chsl²Q in³          (3-2-7/3.5.1)

                               =  cm³

     Depth considered =  in.

     Web thickness =  in.

     Flange thickness =  in.

     Flange width =  in.

                                         SM_obtained =  cm³

Ø    Proportions

The stringers and webs are to have a depth of 125 mm per meter (1.5 in. per foot) of unsupported length and the thickness is to be not less than 1 mm per 100 mm (0.01 in. per inch) of depth plus 3 mm (0.12 in.). See also 3-2-4/3.11. In general, the depth of the girder is to be not less than 2.5 times the depth of the cutouts. See also 3-2-4/3.9iv).

Stringers and webs are to have a depth =  mm

Thickness is to be not less than =  mm

Finalized thickness =  mm

Finalized Depth =  mm

BALLAST FW TANKS

Certain bulk carriers may be provided with ballast tanks on port and starboard side which do not extend up to the tank top, such tanks are termed as wing or top side tanks.

All ballast tanks must be fitted with filling lines arrangements, pumping out or decanting arrangements, air pipes, sounding pipes and man entry access way arrangements.

FRESH WATER TANKS

Every ship must be provided with Potable water tanks additionally wash water tanks may be provided.

These tanks location will vary with the size and type of ship.

OTHER FUEL OIL TANKS

Separate tanks for various grades of fuel oil 'i.e. Heavy oil, Diesel oil storage tanks, fuel oil settling tanks, day tank and lubrication oil tanks are provided on board. The location of these tanks on board will vary from ship to ship.

CARGO TANKS & BALLAST TANKS

CARGO TANKS

Cargo Tanks, generally speaking are referred to cargo compartments on board tanker or Gas Carrier.

The volume enclosed between the weather deck, inner bottom (Tank top) and between inner skin (Hull) of a tanker is transversely and longitudinally divided into several compartment termed as cargo tanks.

This type of arrangement is generally found on board product carriers, where various grades of liquid cargoes have to be carried on board.

Transverse and longitudinal bulkheads are extra strengthened by webs, deep frames, stringers etc., so is the tanks bottom and hull plating strengthened, this strengthening enables the bulkheads to

with stand the head pressure exerted by the liquid.

BALLAST TANKS

These are compartments on board all ships, dedicated for carrying Sea water as ballast for the purpose of stability & trim of the vessel. during the vessels unladen voyage.

Ballast tanks are located between the ship’s bottom plating and tank top, these tanks are termed as double bottom tanks. The volume forward of the collision bulkhead and abaft the aft bulk head are

termed as fore and aft peak tanks respectively.

In addition to the afore said tanks, certain modern ships such as container ships, bulk carriers and tankers vessels & OBO’s, side ballast tanks may be provided on the port and starboard side through the length of the vessel. These tanks are independent of the double bottom and peak tanks.