Q.what is meant by seaworthiness and when is a ship not seaworthy?

A big question is simply asked. When vessel's statutory certificates are not valid, she cannot be considered sea worthy. To make the certificates valid, she has to undergo thorough examination by Class Surveyors. On satisfactory completion of inspection, Class Surveyor may permit for sailing. Due to some accident, if shipside plate is breached, she becomes   unseworthy.

Under Common law, in every voyage charter party Seaworthiness is an implied term and is the Owner’s obligation to provide a seaworthy ship; this suggests that in the Owners has provided a ship with satisfactory physical condition, equipment, crew, cargoworthiness. Since it is an implied term, breach of seaworthiness means the Owner will be liable irrespective of fault.

Under Charter-Party there is an implied duty on the part of the Owner to provide a seaworthy ship making the Owner liable. Hong Kong Fir Shipping Ltd v Kawasaki Kisen Kaisha Ltd case on seaworthiness shows the complexity of the term.

Under Hague-Visby Rules Article III 1 (a)-(c) due diligence on behalf of the Owner/Carrier is stressed, calling for the need to make the ship seaworthy, properly man, equip and supply her as well as have the holds clean fit and ready to receive cargo before and at the beginning of the voyage. 

Under Rotterdam Rules the duty of maintaining a seaworthy ship makes it difficult for Owners/Carriers to avoid liability, as Carriers would be required to exercise due diligence to provide a seaworthy vessel before, at the commencement of, and during the sea voyage.