Sinking situation

Just before reaching Kaub, Sep slowed his ship to a crawl. The forward thrust generated by a propeller drives a ship deeper, so a slower ship is slightly higher in water. The reduced speed would also make pulling the boat off rocks easier, if the worst were to happen. The number on the Rex-Rheni’s digital depth meter dropped, and dropped some more, eventually showing only about 25 centimetres, or 10 inches, of water below the ship.

It passed the Pfalzgrafenstein Castle, which resembles a large, stationary boat in the river. Built in the 14th century to collect tolls, it has a windowless foundation to withstand the Rhine’s high water levels. Today, the foot of the building is at least 5 feet above water.

“Low water events will be more frequent,” said Douglas of the Federal Environment Agency, “and at the same time the Rhine fleet is becoming bigger and heavier.”

When the Rex-Rheni was built in 1966, it would have been considered a big ship. Today, at least under normal conditions, it would be one of the smaller ones on the Rhine, where it is not unusual to see a 600-foot freighter capable of hauling 6,000 tonnes — when there is at least 12 feet of water.

A clause in German shipping contracts that allows ships to set their own prices when the water level is below about 32 inches at Kaub makes such trips worthwhile for smaller boats, even if their holds aren’t full. But the clause cannot make the river deeper.

“We need the level in the Bodensee to rise,” said Martin Deymann, using the German name for Lake Constance. His 35 ships stopped transporting goods along the middle section of the Rhine last month. “We need rain, and hopefully it will come before it becomes cold and it comes down as snow.”