The advantages of the hovercraft principle high speed and low footprint pressure have been exploited in a number of applications, particularly in marginal and difficult terrains. Since the later 1960s, hovercraft have been employed for both hydrographic and seismographic surveying. Initially, medium-sized hovercraft have involved smaller, more cost-effective craft. Techniques and equipment have been developed that enable hydrographic surveying to be completed at up to three times the speed achievable with more traditional methods. Similar benefits accrue in seismographic operations. It is conjectured that, as the advantages become more widely known, the demand for hovercraft in surveying is likely to increase significantly.

INTRODUCTION

Recent years have seen increasing pressures to exploit oil or other resources, no matter where they exist. This has resulted in the extraction of oil and natural gas from the North Sea and the exploration of the Irish Sea and other areas.

Although the depth of water and severity of the environment crated difficulties, objectives have been and are being satisfactorily have presented no major obstacles.

However, there are other areas where surveying needs to be carried out, which present their own particular problems. Shallow-water areas, surf zones, tidal areas-particularly those that dry out- and "tender areas" such as the Arctic tundra, are typical example. Surveying by traditional means is either difficult, or impossible, so alternative methods were needed. An alternative method becoming increasingly popular is to use medium-sized hovercraft, both for seismographic and hydrographic surveying.

In fact, the first usage took place in the later 1960s, with later developments leading to more efficient surveying. Surveys have taken place in a large number of locations, scattered around the globe. More recent applications have seen the use of smaller hovercraft, which have proved capable of completing a worthwhile job both efficiently and cost-effectively, often with the employment of ethnic personnel.

Wide ranging though pass and current uses are, the employment of hovercraft for surveying has only begun to scratch the surface of potential applications. The object of this chapter is to bring the advantages to the notice of wider audience than has previously been attempted.

Hydrographic Surveying
Background and Early Operations

Hovercraft confer two major advantages to hydrographic surveying: the ability to carry out surveys in shallow or tidal areas, and an increases in surveying speed from around 8 knots to nearly 30 knots.

The first major entry to this field occurred in October 1968, when Hovermarine (Now Vosper Hovermarine) and the Decca Navigator Company (now Racal), signed an agreement with the East Pakistan Inland Water Authority (EPIWA) to produce a high-speed survey system. The resulting Surveymarine craft was launched in January 1969, and is based on the HM2 side-wall hovercraft, but having a much larger bridge to accommodate the surveying equipment. Additional fuel stowage increased the range from 140 to 400 nautical miles and, with the fitting of air conditioning and domestic facilities, the craft can operate away from base for up to five days.

Seafix, Hifix or Decca Main Chain were used to fix the craft position.

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