Pulau Medang and Pulau Rupat are separated from the Sumatera coast to
the W and S by Selat Rupat, a deep passage with the petroleum port of
Dumai on its S side.
Supertankers can be accommodated alongside the berths at this port.
Between Pulau Medang and Pulau Bengkalis, about 25 miles SE, the coast is bordered by mudbanks which extend up to 23 miles offshore.
Selat Bengkalis passes through these banks and forms the E entrance channel leading W to the oil port of Dumai.
The other branch of the channel extends SE and E for about 100 miles and then about 32 miles NE to join the E end of the Strait of Malacca.
Pulau Bengkalis, Padang, Merbau, Rangsang and Tebing Tinggi are separated from the coast of Sumatera by Selat Bengkalis, Selat Lalang and Selat Pandjang and from each other by narrow channels.
The E end of Pulau Bengkalis and the N coast of Pulau Rangsang are fronted by several long, narrow ridges of mud and sand, which lie up to 19 miles offshore, N of Pulau Rangsang.
The coast between Tanjung Sinaboi and Tanjung Ketam, about 23 miles SE, is uniformly low and overgrown with mangroves.
Good anchorage can be taken in the channel off this coast.
Between the inshore channel off the coast between Tanjung Sinaboi and Tanjung Ketam and the fairway of the Strait of Malacca, there are many mud banks which are a continuation SE of South Sands, as far as and S of Pyramid Shoal.
Bakal Iba Bank lies parallel to and about 1 mile offshore close NW of Tanjung Ketam; it dries at its SE end, and has depths of 0.3 to 1.8m, hard sand, over the remainder. In the channel between the bank and the coast there is a least depth of 8.8m at its SE end.
Along the edge of the coastal bank W of Pulau Sinaboi and in the channel between Tanjung Sinaboi and Tanjung Ketam, the currents set generally fair with the channel, setting SE at a maximum rate of 2 knots, and NW at 3 knots. The currents turn about 3 hours after HW and LW along the shore. About 7 to 9 miles NW of Pulau Rupat, the currents set from E to ENE and from W to NW at a rate of 2 knots.
The irregular outline of the shoals, however, causes deflections of the current, so that caution is very necessary. The current turns about 3 hours after HW and LW along the shore.Near the banks off the N entrance of Selat Rupat, the currents set diagonally across, from and to Bakal Tua Bank.