What is a ship’s IMO Number and Official Number?

Navsregs>Ship Certification>IMO and Official Numbers

Uniquely identifying ships

This post explores two of the terms used in the last post, two numbers assigned to all foreign going ships.

The IMO Number

A permanent number that remains with the ship throughout its life; a number that identifies a ship regardless of what name, flag, and ownership changes it goes through, from build to scrapping.

What is it?

It is number made up of the three letters ‘IMO’, followed by seven digits. The digits are the numbers used in Lloyds Registe against the ship.
Why is it needed?
It is required by SOLAS Chapter XI, regulation 3- Ship identification number

The number is to be clearly legible on all plans, manuals and other documents required by IMO conventions to be carried on board ships.

Which ships must have the number?

Passenger ships of 100gt  and above and Cargo ships of  300Gt and above.

How is it obtained? 

It is issued by HIS maritime and Trade on behalf of the IMO.

Where can the number be found?

On the Certificate of Registry.

Permanently marked in a visible space on stern, side hull, or superstructure, in an easily accessible pace on a transverse bulkhead of machinery space, end of hatchway, pumproom, or transverse bulkhead in a RO/RO space.

A useful link

IMO number website

The official number

What is it?

A  number issued by a flag state when a ship enters its register.

How is it obtained?

The number is assigned by the Registry with a carving note, and will remain with the ship unless it changes flag.

The number will be stated in the official log book.

SI 1981 No. 0569 – The Merchant Shipping (Official Log Books) Regulations


IMO number = Issued by IMO for life of ship

Official Number = Issued by flag state for period ship is on their registry

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