French Pass Tides Now Predictable

Press, Volume CII, Issue 30210, 15 August 1963, Page 6

French Pass Tides Now Predictable

The discovery that the sea is higher on one side of Nelson’s famous French pass than the other has made it possible to predict favourable tides for ships to traverse the pass. The discovery was made during an examination made by the New Zealand navy’s hydrographic surveying service. The pass is the gap between D’Urville Island and the mainland, and lies on the main Wellington-Nelson shipping route. Although it is 2000 ft wide, the navigable channel is only 200 ft and subject to strong tidal flows. For years mariners have timed their arrival at French Pass to take advantage of a favourable tide flow. However, the prediction of these was not always accurate, nor was the extent fully known. In March two survey motor launches, the Takapu and the Tarapunga, commanded by Lieutenant Commander G. L. Haskins, began work on a more accurate prediction of the tides both at French Pass and in Tory Channel. The results of their examinations have now been analysed. The analysis shows that the sea level is 6 in higher on the Nelson side of French Pass than the ocean side. This is

caused by sea from Tasman Bay building up behind D’Urville Island and pouring out through the pass. The examination showed the value of traversing the pass on the tide which reaches maximum speed of 8J to nine knots. It also fixed with greater accuracy the times When this could be expected.

The launches had less success in establishing a pattern in Tory Channel. They found that the flow there was almost entirely affected by the weather in Cook Strait, both at the time and for some time before.