According to the International Association of Classification Societies (IACS) rules, bulk carriers are longitudinally divided by fitting transverse watertight bulkheads detailed as below:

1. One collision bulkhead - fitted at a distance from the Forward Perpendicular (FP) of not less than 5% of the length (L) of the ship or 10 m, whichever is the lesser, and not more than 8% of L. The collision bulkhead must be watertight with no door, manhole ventilation duct or any other opening up to the freeboard deck
   
2. one aft peak bulkhead and one bulkhead fitted and made watertight up to the freeboard deck at the forward and aft boundary of the machinery space if located amidships · one aft peak bulkhead made watertight up to the freeboard deck and one bulkhead at the forward end of the machinery space if located aft
   
   
   
   
3. ships not required to comply with subdivision requirements should be fitted with transverse watertight bulkheads (in addition to the collision and the after peak bulkhead) which are extended up to the freeboard deck
   
   
4. the openings in watertight subdivisions are kept to a minimum to ensure proper operation of the ship. Any penetrations for access, piping, ventilation, electrical cables, etc must not reduce watertightness
   
   
5. bulkheads are of corrugated or plane steel construction.

Fig: Transverse section of a bulk carrier

Below figure explains number of bulkheads to be fitted for different ship lengths.

Ship Length : Ships machinery space aft : other ships

• 90 m or more but less than 105 m with ships machinery fitted aft no. of bulkheads 4 & other ship type no. of bulkhead 5
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• 105 m or more but less than 120 m with ships machinery fitted aft no. of bulkheads 5 & other ship type no. of bulkhead 6
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• 120 m or more but less than 145 m with ships machinery fitted aft no. of bulkheads 6 & other ship type no. of bulkhead 7
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• 145 m or more but less than 165 m with ships machinery fitted aft no. of bulkheads 7 & other ship type no. of bulkhead 8
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• 165 m or more but less than 190 m with ships machinery fitted aft no. of bulkheads 8 & other ship type no. of bulkhead 9
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• 190 m or more Determined for each ship individually
• 
  

While bulk carriers may appear similar to oil tankers, their structure is comparatively `weaker' due to the lack of strengthening members (beams, girders, stiffeners and deck plating) that would obstruct the large hatches. This results in enormous bending moments and a reduced ability to withstand torsional stresses.

Additionally, the loading/discharging patterns used for bulk carriers result in severe vertical shear and bending stresses. These can be reduced by careful loading and discharging operations and additional structural strengthening to compensate.

Many bulk carriers have a `ballast hold', which is an additional design consideration. Careful attention is necessary when loading ballast and deballasting if cargo is being worked at the same time. Some vessels are also built with extra ballast holds designed to be part filled in port only so that the vessel can maintain air draught, which may be required in some discharge ports. These holds must be discharged before sailing to avoid the effects of free surface.



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