Venting and Blowing
Yes C., There is a Difference
To the layperson, the operation of a submarine is just as mysterious as the waters in which it lives. Fortunately, the submariner community is very generous with their time and the explanations of what’s going on in an image help resolve the problem.
| This image appeared as photo of the day on Friday, October 12, 2012 with a caption that indicated that Ojibwa was ‘blowing’ her tanks. Retired submariner Lucky Gordon, explains what is really going on. Note: Ojibwa was sporting her pennant number (72) at this date. |
Open Main Vents
Although it looks like air “blowing” from the main ballast tanks (MBTs), it is in fact “venting” from them as they are being filled with sea water through free flood holes in the bottom of the tanks.
There are many other factors regarding the state of other tanks, order to the “Planes” and speed of descent desired, in essence, the order from the CO in the control would be “Open Main Vents” at which time the first panel Watchkeeper would switch # s 1, 2, 4, 6 and 7 main vents to open (in that order). This allows sea water to rush in through the free flood holes in the bottom of the main ballast tanks (MBTs) replacing the air in them and forcing it out of the top through the open vents. Think about a paper cup forced upside down into water capturing the air inside, then; poke a hole in the bottom of the cup.
There are many other factors regarding the state of other tanks, order to the “Planes” and speed of descent desired, in essence, the order from the CO in the control would be “Open Main Vents” at which time the first panel Watchkeeper would switch # s 1, 2, 4, 6 and 7 main vents to open (in that order). This allows sea water to rush in through the free flood holes in the bottom of the main ballast tanks (MBTs) replacing the air in them and forcing it out of the top through the open vents. Think about a paper cup forced upside down into water capturing the air inside, then; poke a hole in the bottom of the cup.
Removing the last bit of air
Once the submarine is submerged, normally achieving about 100 feet of depth with a down angle, the CO will order a brief up angle to allow all remaining air that may still be trapped in the MBTs to be released. Then he will order “shut main vents”.
‘Stand by to blow the mail ballast’
| To surface the submarine, the CO will order “Blow” main ballast tanks. Under normal circumstances he would order “Stand by to blow main ballast tanks, Blow 1,.... Blow 2,... Blow 4, 5 and 6 main ballast tanks,” the exact timing & sequence pause and grouping of tanks would be determined by the angle of ascent that he wants and/or the speed |  |
at which he wants to gain the surface. In response, the first panel Watchkeeper will repeat the order and open the appropriate HP air valves, allowing high pressured air to blow into the MBT forcing water out of the same free flood holes in the bottom of the tanks.
‘Stand by emergency surface…’
In an emergency he might order “Stand by emergency surface, full rise on the planes, blow main ballast tanks” or some semblance of that order, depending upon the depth of the submarine at the time the emergency arises, that will achieve the same results, i.e. to get the submarine on the surface as quickly as possible. That is when she would be “blowing her tanks.”
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