The Tonnage survey includes a set of measurements that approximately determine the weight of grain that can be carried by the vessel. Traditionally this was a very useful means of determining the worth of a commercial trading ship, and the authorities have seen no good cause to change the process since. The survey also includes a record of identifying marks on the vessel, such as the engine type and serial number, and the hull identification number.
The survey is provided to a notified body who are authorised to issue a Tonnage Certificate. This certificate is required by the MCA when registering the vessel.