Don.
The German alarm dive is a typical wartime manoeuvre and required a highly trained crew to perform, it is not a matter of divingangle alone. There are several ways to carry out crashdives, some potentially dangerous like preflooding the ballasttanks and excessive diving angles. Generally you may say a crashdive required a combination of speed (hydroplanes lifts) and flooding. Crash dives are performed under roughly 3 major circumstances 1. Dieselcruising on the surface, when you have the speed ( hydroplane efficiency), as well as the Q filled and the submarine is prepared for diving. 2. After surfacing and during exhaustblowing of ballast tanks, that`s why some COs preferred to use one of the diesels for propulsion to have a surfacespeed rather than an e- motor having much lower output. 3. At the surface, charging the batteries, some CO preferred to have a dieselpropulsion as well. Under all conditions the submarine is prepared for crashdives in hostile waters and possibilities of suprise attacks. The schnorchelling made these crashdives a bit easier.
Basically the first stage, from a divingangle point of view, is the normal 7-8 degrees as you want to have sufficient water above your propellers and hydroplanes all the time. As soon as you are below the surface and you want to go deep, you start blowing Q at 10 meters as previously described. At approximately 20 meters controlroom reading you turn the bow down between 8 and max. 30 degrees depending upon circumstances, watching the bow depth carefully, at 25 degrees bow down it is some 30 meters wc pressure difference between bow and stern, before eventually flatten out. See my sketch below.
Tore
