Answer
A – SOLAS Chapter 1 Regulation 10.
DD is done as per Admin’s requirement. In India, DGS requires vessels to undergo drydocking.
Requirements are stated in IACS UR Z3- twice in 5 years, interval between the two shall not exceed 36 months. One of these inspections can be IWS.
it is a class requirement (URZ3) as well as statutory requirement to drydock. The rules of the class are further influenced by statutory requirements. In case of India, D/G requires the vessel to be drydocked for inspection of the outside of the ships bottom atleast once in 5 years.