Crawl
Creep speed is an operating condition of submerged military submarines . The aim is to reduce the likelihood of detection through acoustic reconnaissance by the enemy ( passive sonar ). During crawl speed, all noises on board are avoided as far as possible, e.g. B. by shutting down systems whose operation is not absolutely necessary. The crew is made to rest. The cruising speed is also greatly reduced in order to minimize the propeller noise.
The propellers have a characteristic speed / rotational speed band in which no cavitation noises occur due to the inflow . Since this rotation speed is usually relatively low, the first electric submarines had special crawl speed motors, which had a better efficiency at a correspondingly reduced speed, required less active cooling and with sliding bearings (no "ball bearing crackling"; but a lot lower durability at too low a speed). These motors were also acoustically decoupled from the fuselage due to their suspension, which of course also included their power transmission: V-belts or toothed belts transmitted the engine power to the propeller shaft.
In modern nuclear submarines , such as those of the Ohio class , the pumps of the reactor cooling system can be switched off when crawling in order to drive even more quietly. The reactor is then only cooled by the natural convection of the water. However, this is only possible at very low speeds.
