Adopting Appropriate Specification

Hydrographic surveys may be specified to meet many different requirements. For example, a survey may be for nautical charting to re-survey a shipping channel where under-keel clearance is critical, or it may be for the general survey of a coastal area. Examples of surveys for non-nautical charting applications include geophysical site surveys, pipeline route or environmental surveys for the oil and gas industry, or inshore surveys for coastal zone management projects. Different hydrographic surveys require different end products, which influence how that survey is planned, what equipment is used and how it is operated.<P>

The International Hydrographic Organ­isation (IHO) has developed Standards for Hydrographic Surveys , where the primary requirement of the survey is nautical charting. These standards are published as Special Publication (SP) 44 – the first edition was in 1968 and the latest, fourth edition was published in April 1998. Minimum standards are described for four orders of survey, depending on requirement. They are Special Order for harbours, berthing areas and critical channels with minimum under-keel clearances, Order 1 where under-keel clearance is less critical, Order 2 where a general ­description of the bathymetry is required, and Order 3 for offshore areas. The S-44 standards have been updated as technologies and procedures have changed. They have been adopted widely and are referenced in a number of hydrographic authorities’ standards and specifications. The S-44 standards have also influenced developments by hydrographic equipment manufacturers.

It is important that any specification adopted for a survey is appropriate for the requirement. While the risk of under-specifying a survey may be self-evident, the risk of over-specifying a survey may be less obvious but may lead to inappropriate resources or inefficient procedures being applied. For example, S-44 Order 1 and 2 surveys require full bottom search in selected areas, where the bottom characteristics and risk of obstructions are potentially hazardous to vessels. Over the last few years, a number of authorities have specified surveys with a requirement for full bottom search everywhere, without regard to the characteristics of the seabed, the risk of obstructions or the potential use of the area. It is considered that this practice results in smaller areas being surveyed at higher costs, while vast areas are left poorly surveyed for longer periods. It is acknowledged, however, that some surveys are specified with secondary purposes, in which case the specification should consider the wider range of requirements and end products.

The fifth edition of S-44 is currently in the hands of the IHO Working Group. It is understood that Order 1 surveys will be partitioned into sub-orders to better differentiate between areas where full bottom search is required and where under-keel clearance is not considered to be as important. The emphasis of this distinction is very important – the challenge will remain for authorities to specify surveys correctly. This author applauds the efforts of past and current IHO Working Group members and looks forward to the development of the fifth edition.

Mark Sinclair, Program Manager, Tenix LADS, Australia