The next wave: Navy maps make for safer sailing

By ELLEN READ

For centuries, mariners have placed their trust in maps of the seabed that are patchy at best and sometimes downright dangerous.

The problem was locally demonstrated in 1960 by the submarine Anchorite. While exercising in the Hauraki Gulf at a depth of about 30m, Anchorite hit an uncharted pinnacle. She damaged her bow but was able to surface safely.

The rock is now marked on charts as Anchorite Rock.

Disaster can strike closer to the surface. In 1992, the cruise liner Queen Elizabeth 2 struck rocks off Martha's Vineyard, off Massachusetts, tearing her hull. Although the depth in the area was charted at 39 feet (11.88m), the sounding was based on a 1939 survey that used sextants and an echo sounder, which was new at the time.

Such accidents occur because charted depths are based on individual soundings that give the depth at a single point on the seabed but not the area around it.

Rock spikes and shallows falling between soundings may be missing from charts.

The Royal New Zealand Navy has a solution. During the past year, its hydrographic unit in Takapuna on the North Shore has expanded from producing traditional printed charts to a range of computer-based digital products.

Using a combination of multibeam surveying and Canadian software, the Navy can now produce charts showing 100 per cent of the sea floor.

Caris, the company behind the software used to produce the digital charts, is so impressed with the Navy's work that it plans to recommend its service. It is also interested in testing future products here.

There are two sides to the Navy's success: the technology used to survey the seabed and the software then used to manipulate data and produce the charts.

The Navy began using multibeam surveying in 1998, when the ship Resolution came into service.

Multibeam technology transmits a pulse of sound in a wide arch, the echoes of which are then recorded.

An extremely large volume of data is collected, making it possible to map and reveal all hazards to navigation with high confidence and allowing surveying under wharves and ships.

Multibeam means a survey ship can cover the entire seabed.

After the data is collected at sea, it is sent to the Takapuna office for production. This is where the Caris systems come into play.

The software allows the hydrographic unit to manipulate the data collected by the survey ships into a range of charts.

These include 3D digital terrain models, customised digital and paper charts, and seabed analysis.

The coast off Oamaru is the first area to which the new surveying and production techniques have been applied. It was chosen because the area's chart was the last in New Zealand still measured in fathoms.

Two hundred charts cover New Zealand's sea territory and new international rules state that multibeam must be used to do the surveys for them.

From here, the country's shipping lanes are the priority areas.

Mapping these will hopefully attract more shipping business and reduce insurance premiums for ships, because it will eliminate the risk of hidden obstacles below the surface.

As cargo ships increase in size, they often navigate channels with only a few feet of clearance from the seabed.

A single uncharted rock or piece of wreckage can puncture a ship's hull, causing potentially hundreds of millions of dollars of damage.

Other uses for the new process range from pre- and post-dredging surveys to resource consent applications to surveys for oil pipe placement and telecommunications cables.

The Navy's director of hydrography, civilian Mark Hambrey, said the aim one day was to transmit data and customised charts to hand-held global positioning systems.

About a third of the unit's work is carried out for the Navy, half is for Land information New Zealand and the remainder is for commercial contracts.

Mr Hambrey would like to double the proportion that is undertaken for the defence forces.

He said this would make sense because the unit was a Navy operation. "The driver must be defence work," he said.

At present, the unit produces only sea charts but could move into land and air charts.

Mr Hambrey said software development could be New Zealand's way of contributing to world defence - a non-provocative, non-confrontational contribution.

www.nzherald.co.nz/marine