Selat Riau (Riouw Strait) Indonesia)

The route from Selat Bangka to Singapore, E of Pulau Lingga and through Selat Riau is the one commonly used by vessels proceeding either way between Selat Sunda (Soenda Strait) and Singapore.

The route is safe, sheltered, and easily navigable, with lights and beacons on many of the dangers. The route E of Pulau Bintan is exposed in both monsoons, and the fairway is encumbered with many dangers, which renders it necessary for vessels to keep off a considerable distance from land.

Selat Riau is available for all classes of vessels, both by day and by night.

Selat Riau, the S limit of which is between Pulau Mesanak and Pulau Telan (Telang), is bounded on the E by Pulau Bintan and on the W by the chain of islands, of which Galang Rempang, and Batam are the main ones.

Numerous smaller islands and shoals front the main shores on each side of the strait. The  strait is about 50 miles in length, in a NW and SE direction, and has depths ranging from 10 to 55m in the fairway, with the least depths being in the S portion of the strait.

The S entrance of the strait is about 17 miles wide for a distance of 11 to 12 miles and then contracts to a width of 3.5 miles between Pulau Karas-kecil (Karas-ketjil) and the shoals to the S of Pulau Tapai.

About the middle of the strait, and 3.5 miles N of Pulau Karas-besar is Pulau Pangkil with dangers extending 5 miles SE; between these and the dangers N of Pulau Karas-besar is the principal channel, about 2 miles wide, with fairway depths of 18.3 to 37m bounded on the W by Pulau Mubut Laut, and the islets and dangers within it, off the NE end of Pulau Galang.

The principal dangers are marked by buoys or beacons. The shores of the strait are, for the most part, sparsely populated, the greater portion of the population consisting of Malays, with the remainder being Chinese.

At Pulau Lobam, about 10 miles NW of Pulau Pangkil, the strait is about 2 miles wide between Johannes Shoal and Orion Rock this is the narrowest part of the strait.
North of Tanjunguban, the W extremity of Pulau Bintan, the strait rapidly widens to its N entrance, where it is about 10 miles in breadth.

Less water than charted was reported (2001) in an area approximately 2 miles E of Pulau Tundjuk.

The tide in the China Sea comes from the N; and being divided by Pulau Bintan, sweeps around its shores and flows into Selat Riau at both entrances, the current from Singapore Strait at the N end meeting that from the S, NE of Terumbu Soreh.

The tidal currents in the S approaches to Selat Riau E of Pulau Lingga and the other islands has the flood current running NNW more or less parallel to the islands, with indrafts into the several straits, and the ebb in the opposite direction.

In the N entrance, on the W side, a portion of the flood current entering the strait is deflected between Malang Orang and Karang Galang and runs as an eddy to the NW, with the flood to Singapore, or in the reverse direction to the flood current entering the main passage of Selat Riau.

The ebb takes the reverse direction, circling S of Karang Galang, where it joins the main current ebbing NE. This must be guarded against when near Karang Galang.

The main body of the S current follows the trend of the W shore past the Karas Islands and turns gradually to the W into Selat Dempo, much of it diverging to the S through the channels dividing the several groups of islands lying between Pulau Mesanak and Selat Dempo, and a portion turning off to the NW in the direction of the Karas Islands.

This is joined by the currents flowing through Selat Telan and adjacent channels.

To the E of Pulau Pangkil, between it and the Pulau Tapai, the flood current from the N entrance is met by the flood current coming around the E side of Pulau Bintan and through Selat Telan and adjacent channels, which curves around Pulau Mantang, and thence taking a NW direction.

The direction of the flood current at Tanjung Pinang and N into Teluk Bintan is N. The flood current at Pulau Terkulai runs SE, toward Tanjung Pinang. The current sets W through Selat Bulan and Selat Tiung, on the W shore of Selat Riau.

The monsoons and currents of the China Sea very much affects the regularity of the currents, which are strong, and at springs rush with considerable velocity through the channels among the islands, forming numerous eddies and stirring up the mud.

In the narrow N part of Selat Riau, abreast Tanjung Uban, this is particularly the case, the current running from 3 to 4 knots, and sometimes even 4.5 and 5 knots.