The extent of the survey, with delays caused by adverse weather, kept the Norfolk in the Tamar estuary for a full month. On December 3rd her westward course was resumed. From this time forth Bass and Flinders were in constant expectancy of passing through the strait into the open ocean. The northern trend of the coast for a time aroused apprehensions that there was no strait after all, and that the northern shore of Van Diemen's Land might be connected with the coast beyond Westernport. The water was also discoloured, and this led Flinders to think that they might be approaching the head of a bay or gulf. But on December 7th the vigilant commander made an observation of the set of the tide, from which he drew an "interesting deduction." "The tide had been running from the eastward all the afternoon," wrote Flinders, "and, contrary to expectation, we found it to be near low water by the shore; the flood therefore came from the west, and not from the eastward, as at Furneaux' Isles. This we considered to be a strong proof, not only of the real existence of a passage betwixt this land and New South Wales, but also that the entrance into the southern Indian Ocean could not be far distant." On the following day the deduction was confirmed. After the Norfolk had rounded a headland, a long swell was observed to come from the south-west, breaking heavily upon a reef a mile and a half away. This was a new phenomenon; and both Bass and Flinders "hailed it with joy and mutual congratulation, as announcing the completion of our long-wished-for discovery of a passage into the southern Indian Ocean." They were now through the strait. What Bass months before had believed to be the case was at length demonstrated to a certainty. "The direction of the coast, the set of the tides, and the great swell from the south-west, did now completely satisfy us that a very wide strait did really exist betwixt Van Diemen's Land and New South Wales, and also now that we had certainly passed it." No time was lost in completing the voyage. The Norfolk sped rapidly past Cape Grim and down the western coast of Van Diemen's Land. Amateur-built as she was, and very small for her work in these seas, she was proving a useful boat, and one can enjoy the sailors' pride in a snug craft in Flinders' remark concerning her, that "upon the whole she performed wonderfully; seas that were apparently determined to swallow her up she rode over with all the ease and majesty of an old experienced petrel."