The German Navy's seaborne refueling technology (a hundred years ago)

Most people are familiar with the concept in-fligh refueling, the process of transferring fuel from a tanker aircraft to another - often aircraft. But what is probably less known, is that the German Navy applied the same concept already over 100 years ago for refueling their steam powered fighting ships.

On the picture below you can see a small coal transport ship refueling the large German cruiser "Prinz Heinrich". A transport line connects the ships, allowing sacks of coal to be transferred to the "Prinz Heinrich", while both ships are moving. In 1906, when the photograph was taken, the German Navy was still practicing seaborne coal refueling, but it had high hopes of applying the new technology for its existing and future steam powered vessels. Whether these hopes were fulfilled, is more than I know. Later however, coal fired naval engines were largely replaced by oil fired engines, thus making the coal refueling technology outdated.

The German Navy cruiser "Prinz Heinrich" being refueled while steaming ahead.  The small  dots on the transport line are coal sacks.