Monday 23 May 2022 | 18:07 | SYDNEY
Monday 23 May 2022 | 18:07 | SYDNEY

Reader riposte: Mapping Sandy Island

30 November 2012 11:37

Mike Prince, Director of Charting Services at the Australian Hydrographic Service, responds to Olivia Wilson's piece on Sandy Island, which appeared on numerous maps but which the Australian research vessel Southern Surveyor recently (re)discovered did not actually exist:

Congratulations on an interesting and well informed article. If you would like to know a little more about how 'Sandy Island' appeared on charts in the late 1800s, and was removed around 100 years later, you may find this article in Hydro-International of interest.

The editor of Hydro International has faithfully repeated all my input on behalf of the Australian Hydrographic Service. The extract from the nautical chart is from the current edition of INT chart 602 (AUS 4602) for which, by international agreement, Australia is responsible. The article explains a little history of how the feature first got onto the charts, long before there was any concept of any 'database', and how it was definitively disproved (the first time) in 1985. For ships of the Australian Hydrographic Service, correcting, improving upon or occasionally disproving old information and reports is part of routine business.

Our conclusions were that the Master of the whaling ship Velocity most probably saw a series of patches of floating pumice prior to the first report in 1876. This is based on sightings of similar patches by the survey team in 1985. However, it is also possible that the sighting was actually of the eastern side of Bampton Reef around 45 nautical miles further west. This has a very similar orientation and extent to the original report. For this to have occurred, it would have taken no more than a ship's chronometer being out by two or three minutes, affecting celestial navigation, or the effects of the prevailing west-bound current over as little as two days, which was also unknown at the time. Welcome to the world of unravelling old and mysterious reports in remote areas.

Finally, to answer the question of why was the island charted in the first place.

Safe navigation at sea is very different to on land. Most hazards are hidden, either just below the surface, or by the darkness of night. This is quite unlike a land map, where you can look up from the map and see a hazard for yourself, and most places are well lit. So, for those at sea, reports of potential hazards are taken very seriously. This means that, until they can be positively disproved, many old reported dangers can still be found on nautical charts. While satellite imagery makes relocating confirmed ones easier, it often still takes a survey ship, or aircraft, to undertake a definitive search to disprove those that are not.