These surveys are usually carried out at the commencement and termination of a charter. The surveyor will be employed by either the charterer or the vessel's owners so it is not unusual to find two surveyors on board at the same time.
The purpose of the survey is to note every defect so that it can be verified later as being present prior to or occurring during the hire period. The on-hire survey is customarily carried out at the start of the hire period so that any additional damage found later at the off-hire survey can be charged to the correct party.
These types of surveys are time consuming and should be carried out in daylight with all hatches opened, clean and empty. On and off-hire surveys cover the vessel's structure, statutory documents and bunkers.