Blowing ballasttanksquestion

[momo55]

How was it in those 40's when they blowed there mainballasttanks or emergency surfaced ? Wasn't there any air escaping the sub at all like in SHIV ? No airbubbles at the surface etc. ?

Sinds i play with TM 1.4 i take it easy with the WARPSPEEDbuttons and started looking at the details and beauty of the game and not the x 1000's of tons i can sink (thanks Ducimus;)) and this question popt up :hmm:

[Webster]

as i understand it, blowing the tanks means to blow highly pressurized cylinders or tanks of air into the water filled balast tanks to force the water out and refill them with air to raise the sub. when doing this some air bubbles inevitably escaped but i suspect it was not much since losing any air would be avoided because air was so precious to a subs survival for breathing or the ability of surfacing.

[nattydread]

I believe (I could be wrong), that the ballast tanks were vented to the outside world from the bottom. The air was pumped in from the top, so you have to completely blow all the water out before any air escaped.

From what i seem to get from my readinsg, is that the American subs used big, honkin' blowers for the ballast tanks. You'd likly give yourself away with those monster things before the bubbles gave you away. All this is just my impression though, it may be totally off...maybe a more informed poster can clarify.

[Webster]

i think the general concensus would be that although BLOWING THE TANKS sounds like you would see action outside the sub, in reality the visual result would not be noticable outside the sub.

as natty stated it would be mainly all noise but not visual bubbles or just a few if any.

[momo55]

I thank you , WEBSTER and nattydread for those explenations . Couldn't find anything about that specific aspect of "blowing ballasttanks " on the web.
It sounds all logical what you 2 are saying .

Thanks again :up:

momo55

[Shirkon]

Being an ex-bubblehead I can answer this one. First, as someone else stated the MBT's do have permanently open flood grates on the bottom of the tanks. In the top of the tanks are placed valves (MBT vents) which when opened allow the air in the tanks to escape while water enters through the open flood grates. Once submerged the MBT vents are shut so that in an emergency air can be blown into the tanks immediately. When you are going to surface, the MBT vents on the top of the tanks are checked SHUT and then once the ship is forced high enough so that the top of the Air Induction/Snorkel Mast is out of the water the Low Pressure Blower is started forcing a large volume of air at low pressure though air lines into the top of the MBT's which forces the water back out through the open flood grates. It is normal when doing the LP Blow that air will spill out of the flood grates which is about the only real way you can tell that the MBT's are actually empty. It is the diving planes and the propellers that force the boat high enough to start the blower. Only in an Emergency Surface would High Pressure air from air flasks (normally at 4500 psi) be emptied into the MBT's since refilling those flask is a long time consuming process for the equipment available on the WW II boats.

To get an idea of how the MBT's work, take a styrofoam cup and cut a small hole on the bottom, turn it upside down and place one finger over the hole, then lower it into a sink full of water. The air trapped in the cup cannot escape until you lift your finger off the hole and then the air in the cup will bubble out and water will enter the cup from below.

[switch.dota]

Judging from the above, a ship sitting still in the water (no movement) should only be able to perform emergency surface manuvers. No other depth change should be possible. Am I correct?

[momo55]

ahoi Shirkon ...welcome skipper ;)

When i'm 120 ft deep and want to surface i only use diving planes and propellers (speed) to go up and when i'm almost at the surface and the air induction/snorkel mast is out the water ...then only i blow ballast if i understand well wat you are saying ?

If that is the case ...then there is something wrong in the game ....they blow mainballasttanks when i'm at 120 ft to surface ....:hmm:

[nattydread]

Submerged? If so, only depth changes due to ballast. But they are loud and/or resource intensive. You gotta have water travelling over the planes to maneuver and thrust from the engine to climb or descend without ballast changes.

As mentioned above, its also the same for airplanes, "climbing" is all done with the thrust(assuming no use fo ballasts)

[nattydread]

ahoi Shirkon ...welcome skipper ;)

When i'm 120 ft deep and want to surface i only use diving planes and propellers (speed) to go up and when i'm almost at the surface and the air induction/snorkel mast is out the water ...then only i blow ballast if i understand well wat you are saying ?

If that is the case ...then there is something wrong in the game ....they blow mainballasttanks when i'm at 120 ft to surface ....:hmm:

You have air stored at compressed gas that you can vent out instead of using a blower drawing air from above the surface.

Thats compressed air also fires your fish and maybe flushes the toilet. But if you use it up you cant get anymore until you surface. You can expect 1 good blow, or a series of smaller blows. but when you blow it...you blow it. You better hope your heading skyward

[Shirkon]

Under normal circumstances you would never blow your Main Ballast tanks as it simulates in the game until your Main Induction/Snorkel Mast was clear of the water. The planes and ship's speed were used to drive the boat to the surface. There is one other large use those air flasks are put to as well, there is a special ballast tank that is only used for submerging and once submerged is used to assist in surfacing. That is what they called the Negative tank. It is called that because when full and the MBT vents were opened it gave the boat a negative bouyancy allowing it to submerge faster. Once fully submerged, this tank was blown until the boat had a neutral or a slight positive bouyancy. There were other variable ballast tanks forward and aft on the ship that were used to TRIM the boat. By pumping water forward or aft into and out of these tanks the boat could be balanced over it's center of bouyancy.

WW II sbumarines had a total of 7 Main Ballast tanks, of these MBT 1, MBT 2A, 2b, 2c, 2d, MBT 6A, 6b, 6c, 6d and MBT 7 were strictly used for diving and surfacing and were permanently open at the bottom. MBT's 3A, 3B, 4A, 4B, 5A, 5B were also fuel tanks and at the start of a patrol were full of diesel fuel. As fuel was used from these tanks a valve at the bottom of the tanks could be opened to allow sea water to enter the bottom of the tank. This is safe to do since diesel fuel is lighter than sea water and will float on top where the piping is to draw off fuel as it is needed.

[Sailor Steve]

The bow planes are placed on ten degrees dive and rigged in automatically unless the conning officer gives other instructions. A report, "Bow planes rigged in," is made to the conning officer. Speed is increased to about 6 knots to give maximum lift. Due to the up-angle on the ship, the increased speed makes the inclined surface of the hull effective and the resultant lift raises the ship. The stern planes are used to limit the up-angle to about 5 degrees. The up-angle may be increased by blowing the bow buoyancy tank. Blowing the safety tank increases the positive buoyancy. However, this is not usually done.

The main ballast tanks are partially blown to surface normally. After surfacing, the high-pressure air is secured and the blow is completed with the low-pressure blowers.
http://www.maritime.org/fleetsub/chap18.htm#18C

[DS]

MBT's 3A, 3B, 4A, 4B, 5A, 5B were also fuel tanks and at the start of a patrol were full of diesel fuel. As fuel was used from these tanks a valve at the bottom of the tanks could be opened to allow sea water to enter the bottom of the tank. This is safe to do since diesel fuel is lighter than sea water and will float on top where the piping is to draw off fuel as it is needed.

I've heard of this, though I did not realize they would allow sea water into these tanks while still drawing diesel from them. The light than water coupled with drawing from the top of the tank makes sense, but I wonder if this was risky in rough seas when the water and fuel was more apt to mix. Also, was there any issues with foreign floating bodies (flotsam, etc) getting into the fuel? Just curious

[Frederf]

In game I know (at least from SH3) that pressing "Emergency surface" once would activate the compressed air reserve to shoot you upward. Pressing the command twice actually increased the effectiveness/speed (3rd time? Think 2nd press was the maximum rate).

As far as gameplay goes even from 400' and double-emergency surface there was always 70% or so compressed air left in the tanks and thus there was never any real concern of running out.

For real WWII subs wasn't boyancy changes at depth cause to use some of this compressed air. Was running out of compressed air ever a real concern?

It seems weird to give us this guage when 99.999999% of the time it's of no concern.

[Shirkon]

There were additional fuel tanks between the fuel/ballast tanks and the diesel itself. First there are the Normal Fuel Oil tanks (NFO), 4 of them. Then there is the Fuel Oil Collecting tank (FOC) which acts as a settling tank which ensures that the fuel oil and water are separated. Lastly there is the Clean Fuel Oil tank (CFO). Fuel is pumped from the ballast tanks, through a filter and into the NFO tanks, from there it goes to the FOC tank and finally to the CFO tank before going to the engines.

[momo55]

Way this man is turning those buttons when you ask 1/3...2/3..etc. is clair to me.
Buth ...he's turning those same buttons when you change dept in both way's even when 1/3 on the scale stay's 1/3 ?

http://img513.imageshack.us/img513/5895/odometeruu7.png

He's the one that reacts to the command from the guy behind the maptable .
Shouldn't those 2 at the diveplanes react instead ? They turn those big wheels ..ok ..buth stay speechless to .

Thanks for all the intresting replies here guy's

greetz:up:

[Shirkon]

Way this man is turning those buttons when you ask 1/3...2/3..etc. is clair to me.
Buth ...he's turning those same buttons when you change dept in both way's even when 1/3 on the scale stay's 1/3 ?

http://img513.imageshack.us/img513/5895/odometeruu7.png

He's the one that reacts to the command from the guy behind the maptable .
Shouldn't those 2 at the diveplanes react instead ? They turn those big wheels ..ok ..buth stay speechless to .

Thanks for all the intresting replies here guy's

greetz:up:

This is the helmsman, part of his job is to change the engine order telegraph (the one with 1/3, 2/3, etc.) which sends the order back to the engine room itself. Both of the instruments you are pointing out are engine order telegraphs. There are 2 for the port and starboard engines since on the old boats it was common practice to also use the engines for steering. The two sitting at the big wheels are the planesmen. The forward one is for the bow planes and the one aft for the stern planes. Using a combination of the planes and ships speed they use the big depth guage near them to control the depth of the ship. Normally it would be the helmsman that would reply to speed and course orders and then planesmen only to depth orders.

Added information about the man standing forward of the bow planesman, he is what was/is known as the Chief of the Watch, he's responsible for ensuring all opening in the boat are closed (the board with the red and green lights, a pair of red and green for each hull opening, red for open and green for closed) and for blowing/pumping water from the variable ballast tanks. He was also responsible if not done from the bridge of sounding the diving alarm.

[Torpex752]

WWII Diesel boats had a "Normal Blow" system which used 700 psi air to help them surface. They didnt have to use their High pressure air bank (3000psi) for this purpose. They also had a hard tank all the way in the bow which was kept ready to flood when surfaced in enemy air cover territory. its sole purpose was to weigh the bow down and help the sub submerge faster. This tank is why US submariners didnt have to run forward like U-Boats. ;)

Submarines do not use air in the ballast tanks to help them change depth. Air in the ballast tanks is a VERY BAD thing when submerged....VERY BAD. Injesting seawater into the 'negative" tank would be one way of trimming the boat heavy and aid in making it going deeper. However keeping the boat at a neutral bouyancy and changing depth with the planes angle & speed was the norm even in WWII.

Frabk "Torpex" Kulick
Subsim Staff :cool: