Pointe Underhill (5°50'S., 13°26'E.) is located on the SE side of the river, about 1 mile W of Matadi. An overhead telephone cable, with a minimum vertical clearance of 40m, spans the river in the vicinity of this point. A road bridge spans the river close E of Pointe Underhill. It has a vertical clearance of 52.7m, which allows for a maximum rise of 8m in the river level, during the rainy season. The high hills standing on the NW bank of the river, opposite Pointe Underhill, fall 183 to 244m in sheer precipices to the dark and gloomy basin below, which is known as Chaudron d'Enfer (Devil's Cauldron). The river in this vicinity is very deep and the currents are violent. Numerous eddies and heavy whirlpools necessitate special care in steering and a fast speed. Although the current is not very formidable during the dry season, it generally attains rates of 10 to 13 knots, in places, during the wet season. The river pilots advise that steering for vessels of over 170m in length is extremely difficult within Chaudron d'Enfer and such vessels are almost unmanageable. Anchorage.Anchorage is reported to be possible in several places lying between Boma and Matadi. These places are known to the river pilots and local knowledge is necessary. The anchorages are, as follows: 1. Kinlele (5°52'S., 13°06'E.), lying on the N side of the river, 2.5 miles above Boma. 2. Iles des Princes (5°50'S., 13°26'E.), lying off the SE side of the island. 3. Bumbu (5°53'S., 13°09'E.), lying between Ponta Kimongoa and Ponta Bumbu. 4. Binda (5°51'S., 13°14'E.). 5. To the N of Ilot Oscar (5°53'S., 13°18'E.). 6. Muzuku (5°54'S., 13°21'E.), lying on the N side of the river, 1 mile ESE of Les Trois Soeurs. 7. Diamants (5°52'S., 13°23'E.), lying on the N side of the river, opposite Ponta Diamants. 8. Ikungulu (5°52'S., 13°25'E.), lying on the N side of the river, 1.5 miles W of Noqui. This anchorage is for vessels waiting to berth at Matadi. 9. Off Ango Ango (5°51'S., 13°26'E.), in a depth of 15m. Caution.Between Sango Bongo and Pointe Muzuku, exceptionally strong currents have been experienced. In the past, vessels generally encountered no whirlpools of sufficient size to render steering difficult below Les Trois Soeurs. However, severe whirlpools were often encountered between Les Trois Soeurs and Matadi. A vessel of 1,320 dwt and 86m in length reported (1947) that it was best to use full helm at once to counteract the slightest tendency to swing, as, if even a small sheer were taken, the current tended to turn the vessel rapidly broadside to the channel. A vessel of 25,000 dwt and 170m in length reported (1982) that while it was necessary to use the helm at once to counteract the slightest swing, full helm was neither necessary nor desirable, as this tended to overcorrect very quickly before the helm could be removed. The vessels also reported that the pilots preferred to use 10° or less helm in order to maintain a steady course.

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