One of the later changes that H.sie made to his famous patch for SH3.exe (the executable file for Silent Hunter III) was complex code to manage the carbon-dioxide (CO2) production of the crew, with its effect on lowering oxygen in the air of the U-boat. The original (stock) SH3 code apparently allowed underwater travel for three days, which was far too long for realism.
As a result, on the basis of calculations of U-boat volumes of air carried, crew numbers and rates of breathing and CO2 production, H.sie’s hard-code patch allowed about 5 hours of underwater cruising (all U-boat types), and then replenishment oxygen from a coded ‘tank’ of spare oxygen for another 60 hours or so. The ‘tank’ could not be topped up again, even on the surface. H.sie did an excellent job on this – I’ve have a copy of his assembly code and it covers such variables as numbers of crew aboard (affects rate of breathing) and whether silent-running or not, as well as the code needed to operate the reserve tank and the tank meter displayed on screen. He provided algorithms for rate of oxygen consumption and for CO2 production, and the correct maximums of CO2 permitted in the boat.
Owing to disputes as to the time that each oxygen supply should last, the Options Selector (supplied with the H.sie patch) provides two sliders at the bottom which the user can adjust. The original values were 1.0 for each slider, but longer quantities of oxygen-supply can be set with the slider. The recommendation for the NYGM supermod was renewable oxygen = 2.5 and oxygen-tank = 2.0.
However, this basic model is over-simplified. In real life, the U-boat contained compressed air reserves to restore the air in the U-boat while potash cartridges removed carbon dioxide. The same compressed air was used to surface the boat, and the tanks were refilled whenever the U-boat was on the surface. Thus we have a model where air in the U-boat was essentially replenished seamlessly underwater. Cylinders of compressed pure oxygen were used to eke out oxygen supplies during long periods underwater. These cylinders could not be recharged.
From June 1943 U-boats had orders to cross the Bay of Biscay almost completely submerged to avoid air attack. The U-boats were to come to the surface only once at night, for long enough to recharge their batteries (2-4 hours). NOT to recharge their air – I checked this with real U-boat survivors. Thus the U-boats were cruising underwater for up to 22 hours without replenishing their air.
I’ve carried out further tests with SH3, and I consider that values of 3.5 (renewable supply) and 1.0 (non-renewable supply, bottled oxygen) should now be recommended. Maximum permitted underwater times (before use of oxygen tank) with these values (full crew, not silent-running) measured in SH3 thus:
Type II: 21 hours; Type VII 23.5 hours; Type IX 28.5 hours; Type XXI 29.75 hours.
Big problem: the original Options Selector did not allow slider values greater than 3.0 for the air supply (assumed at the time to be the oxygen supply).
Therefore I have created a new version of the Options Selector (version 1.6C) that allows values to be set from 1.0 to 4.5 in steps of 0.5. This new version can be downloaded here:
http://www.subsim.com/mods1/nygm/Hsi...lector_V16C.7z
(Or item 13 after clicking on the NYGM web-page at Subsim, below my signature.)
Stiebler