Blame it on the longitude

1628 map (National Library of Australia)

It’s an interesting fact that of the four Dutch sailing ships known to have been wrecked off the coast of Western Australia, two of them – the Batavia and the Zeewijk – struck the reefs of the Abrolhos Islands and there has long been speculation that a third ship, the Aagtekerk , lies in the deep water off North Island. The question is why? Why didn’t the Dutch navigators avoid these islands?

The basic answer is longitude. In the seventeenth and eighteenth centuries there was no reliable way of calculating longitude because there was no sufficiently accurate means of calculating either time or distance travelled. Sailors used what means they had plus a lot of educated guess work to estimate where they were in the world. Latitude was not an issue; they had the means to find that value with precision but longitude could be off by many, many degrees and many miles.

On their journey from Amsterdam to Batavia, capital of what we now call Indonesia, the Dutch mariners sailed their ships south from the Cape of Good Hope and used the winds of the Roaring Forties to speed them on their way. When they estimated they were far enough east, they turned north, heading for the Sunda Strait and the gateway to Batavia. Remember, at that time they had very little knowledge of the coast of Australia. They knew something lay out there and had glimpses of its hostile shores but that was all. These seas were uncharted. Houtman had encountered the Abrolhos in 1619 – fortunately for him, in daylight – but even if the islands’ existence had been communicated to the skippers of the VOC’s fleet, the extent of the island chain was not known and they could not be accurately charted. The Abrolhos islands comprises no less than one hundred and twenty-two islands in four groups over a distance of about fifty miles, and they lie about fifty miles off the Australian coast – well out to sea.

So in 1629 Adriaen Jacobsz turned the Batavia north well off shore from the coast of the Unknown South Land. Little was he to know that out there in the depths of the Indian Ocean, the weathered remains of a coral reef still poked above the waves of high tide. Even after the events of the Batavia had been concluded and the islands marked on a map, the route was not safe. Nearly one hundred years later the Zeewijk ploughed into a different part of the island group, now known as the Pelsart group because it was assumed that these were the same islands the Batavia had struck.

Both ships ran aground at night, both lookouts reported ‘moonlight on the waves’ instead of the tell-tale surf on the reefs. I wonder how many ships actually sighted the islands as they sailed safely past in the full light of day?