no need to blow tanks?

Originally Posted by codmander

how come we dont have to blow tanks when surfacing ? at least no compressed air gets used unless you blow em under emergancy than you pop like a ballon to the surface,,, down 200 meters or so the tanks are filled with water and should have to be blown to rise thoughts?

Compressed air was normally NOT used to surface a boat! Propulsion and hydroplanes were used to bring the boat to nearly surfaced and exhaust fumes from the diesel engines removed all remaining water from the diving tanks.

From chapter 4, page 51 of U-boat Commanders and Crews 1935 - 1945 by Jac P Mallmann Showell (isbn 1861261926)

"Many science books suggest that air was blown into the diving tanks to bring a submerged submarine to the surface, which is not quite correct. Diving tanks need to be open to the sea, and water pressure decreases as the boat rises. Therefore, the volumn of air in the diving tanks expands as the boat rises, which will produce an uncontrollable upward motion.

To prevent the boat from coming to the surface in a mass of bubbles like a champagne cork released under water, a careful surfacing procedure had to be maintained, and this usually did NOT involve the pumping of air into the diving tanks. In fact the oposite usually happens: water is pumped out of the tanks as the boat rises to allow for the expanding hull.

Before surfacing it was necessary to determine whether it was safe to do so.......... The next step was to engage the hydroplanes to steer the boat to periscope depth, and then to the surface. The trim would have allowed the upper deck of the casing to come roughly level with the surface of the water, but the boat would have been too heavy to get much higher. At this stage the conning tower, with the ends of the ventilation shafts on the top, was clear of the sea, making it possible to start the diesel engines and to use the exhaust fumes for blowing water out of the diving tanks. This had the advantage of saving compressed air."

[Penelope_Grey]

Usually I always surface with one press of the E key.. its quicker.

Originally Posted by Penelope_Grey

Usually I always surface with one press of the E key.. its quicker.

You are surfacing like a cork. Besides, BdU requires you to stop at periscope depth and check the surface and sky for contacts before surfacing. Suggest you read your U-boat Commanders Handbook. Otherwise, they may send you to the Eastern Front.<g>

[Jimbuna]

Originally Posted by Penelope_Grey

Usually I always surface with one press of the E key.. its quicker.

I thought that was the emergency eject button

[codmander]

hmm intresting I would think tho... for realizm that a touch more air would be used from compressed air when sumerged to the extreme.. if more is used at slower speeds It must be adjustable somewhere in game file maybe the modders could toy with it :hmm: I like the -s- key myself sounds are cooler with a little das boot in there as well

[Sailor Steve]

Originally Posted by codmander

...down 200 meters or so the tanks are filled with water and should have to be blown to rise thoughts?:hmm:

When you perform a crash (emergency) dive the tanks are full, and must be partially blown to achieve neutral bouyancy. In a normal dive, and when operating submerged, the tanks are only half (or so) full. Rising and sinking are controlled with the dive planes; this includes surfacing. Either when surfacing or shortly after the tanks are emptied, giving positive bouyancy. If done just before surfacing, this does require compressed air. If done after breaking surface, engine-powered blowers are used.
http://www.maritime.org/fleetsub/chap18.htm#18C

When the torpedoes are fired, some compressed air is used, but compensating for the lost weight of the torpedoes requires taking on water, not expelling it. Here is the straight dope:
http://www.maritime.org/fleetsub/chap19.htm#19A

Originally Posted by Sailor Steve

When you perform a crash (emergency) dive the tanks are full, and must be partially blown to achieve neutral bouyancy. In a normal dive, and when operating submerged, the tanks are only half (or so) full. Rising and sinking are controlled with the dive planes; this includes surfacing. Either when surfacing or shortly after the tanks are emptied, giving positive bouyancy. If done just before surfacing, this does require compressed air. If done after breaking surface, engine-powered blowers are used.
http://www.maritime.org/fleetsub/chap18.htm#18C

Sailor Steve, with all due respect, your article appears to be on US Fleet Submarine technolgy.

One must understand that German U-boat technology, contruction and engineering was some what different than US technology. According to Jac P. Malmann Showell (a noted U-boat and Kriegsmarine historian) under normal conditions U-boats did not inject compressed air into their diving tanks to surface but rather sea water was pumped out of the diving tanks to compensate for the expanding air within the diving tanks as the boat's depth was reduced by props and hydroplanes. Once the conning tower and diesel motor air intakes were above the surface, the diesels were started and their exhaust gases were first vented into the diving tanks to blow out all remaining sea water thus raising the boat to a normal surfaced depth.

One reason this might have differed from US subs is that many of the U-boat diving, fuel and ballast tanks were open to sea water and they had valves to allow for the release of air pressure within the tank and thus the flooding of the tank.

[Sailor Steve]

I don't see where we disagree; my point was that compressed air was not used or needed as much as some people seem to think. Your point seems to be the same, except with (possibly) slightly different technology and procedure.

Originally Posted by Sailor Steve

I don't see where we disagree; my point was that compressed air was not used or needed as much as some people seem to think. Your point seems to be the same, except with (possibly) slightly different technology and procedure.

I misunderstood your post, so we are in agreement. Thanks.