School of the Boat - Emergencies (1 November 2008)

[Mark Sarsfield]

Any of the No. 6 MBTs filled with air, since they hold a lot of air (and water) compared to other tanks aft of the ship's center point.  I guess aft trim tanks in the ATR  that have too much air could also cause forward listing.  The further back from the center point that you travel along the length of the boat, the less air that is required to cause a list.  Large moment arms need less force to accomplish the same work as a short moment arm with a lot of force.  The worst case scenario in my mind, though, would be No. 6C and/or 6D having vents stuck closed with air trapped inside the tanks.

[Darrin]

Mark,
you got the correct tank earlier, sorry I made you dig farther then you had to dig. Was trying to answer your post at work while I was WAY too busy to read all of the post that you had made about getting the #6 MBT vents open.. GREAT job all who participated in this part of school of the boat, looks like I will be in the Scullery this week after that mixup

[JTheotonio]

Sitting here still in Atlanta early am waiting to start my meeting (half day then head home)

Good job on identify the problem.  Stuck vents are allways a pain and it did happen on occasion. This problem would need to have been solved rather quickly as you can see the boat was going deeper - that was being driven by the steep down angle and the fact that the Captain ordered all ahead full on the dive. 

Certainly the diving officer would have quickly asked that the vents be cycled, upon that failing, each compartment aft of the control room would have been looking for a problem.  So in the mean time the Captain may have order all back full.  There is a reason that he would not have ordered all stop - the propellers would still be turning so this would not have helped. 

Other actions to be taken while the stuck vent was found and opened, would have been as you guys stated earlier, start pumping from aft trim, blow bow bouyancy, maybe blow negative, bow and stern planes to full up angle. 

Well done everyone.  I need to find the accident that occurred when such a problem almost caused an Argentine boat to sink - since it was one of our old fleet-type boats the problem was relative to this SOB on emergencies.

Now - I need to get focued on my meating

[Mark Sarsfield]

I got the idea of stuck vents from watching Periscope Down.  The first time that they dove the boat they had a list to port because one of the vents was stuck closed. 

[Brian Flynn]

It sounds like the answer was a stuck vent.  I'm not 100% convinced that more air in an MBT would make you go down faster...I'd need to have that explained in more detail why.

The big picture as I saw it - you don't want to go up (enemy plane) or down (briny deep).  Question - are you sinking or driving yourself down?

Slow down - backing bell for...10 seconds? then ahead at slow speed.  Monitor depth as you do, if the depth change accelerates, blow tanks and go faster ahead because you're heavy and sinking.  If the depth change slows down, you're driving yourself down due to something with the planes not being right.

If you're heavy, why?
tanks not at expected levels or have changed since last trim dive.
flooding in the FTR
I can't think of another source of weight that would cause that much heaviness forward.

If you're driving yourself down, why?
bow planes not actually rigged correctly.
Something else?

Remember that at this point you're on batteries and you don't have nuke style reaction ability on answering bells.  If you ring up all back emergency on the batteries for too long, you're going to be surfacing again because your batteries are going to run down real fast.

[Darrin]

The excessive down angle was caused by the stuck shut vent on MBT #6 and with the captain ordering the fwd bell that he had ordered at the time, yes pumping water from fwd to aft will correct that problem while cycling all of the vents to make sure that there is no more air trapped in any of the tanks. Also using a backing bell will slow down if not stop the depth change assuming that there is no flooding,

[JTheotonio]

I'm going to try this -

Slow down - backing bell for...10 seconds? then ahead at slow speed.  Monitor depth as you do, if the depth change accelerates, blow tanks and go faster ahead because you're heavy and sinking.  If the depth change slows down, you're driving yourself down due to something with the planes not being right.

If you're heavy, why? You are diving, therefore the boat does have negative buoyancy, also remember that the boat is being driven down by the angle of the bow and stern planes, plus the turns for all ahead full.  As long as the boat has a negative buoyancy it will go down.  By filling the MBT's your boat should be in a neutral buoyancy (maybe a bit heavier).

tanks not at expected levels or have changed since last trim dive.
flooding in the FTR There was no flooding
I can't think of another source of weight that would cause that much heaviness forward.There was not additional weight

If you're driving yourself down, why? Typically the boat dives at ahead 2/3rd or less.  Because of the urgency of getting under before the planes spotted the boat, the Captain did an emergency dive.  Negative can be flooded to a mark (as blown), but in this case, negative was flooded, bow buoyancy was flooded, which is normal. To dive a boat you can stop dead in the water and do a control dive that would settle the boat without an angle, or you can dive with a down angle under power. Under power, with a down angle, will drive the boat under faster.  In this emergency when the down angle rapidly increased, the boat would be driven down faster

bow planes not actually rigged correctly. Not a problem, if the planes could not be rigged properly it would have helped
Something else? nope

Remember that at this point you're on batteries and you don't have nuke style reaction ability on answering bells.  If you ring up all back emergency on the batteries for too long, you're going to be surfacing again because your batteries are going to run down real fast. I did not throw this into the problem, but after a certain angle, your battery water would start coming out and this would cause a few other problems. Fires, toxic fumes, shorting of batteries, etc

[Brian Flynn]

You are diving, therefore the boat does have negative buoyancy, also remember that the boat is being driven down by the angle of the bow and stern planes, plus the turns for all ahead full.  As long as the boat has a negative buoyancy it will go down.  By filling the MBT's your boat should be in a neutral buoyancy (maybe a bit heavier).

That's where I don't get it.  If a vent was stuck causing a list, the list would not become apparent at deep depth, it should have been throughout the dive.  The boat would be light aft and take a deeper angle, but if properly trimmed, it should be positively boyant with an a stuck vent and become nearly neutral when the #6 MBT is vented.  I don't have the math on it, but my gut feeling is that if the bouyancy from the tank is stronger than the plane's ability to control the angle, then it won't be overcome by the screws.  I could be wrong on that, its just a gut feeling.

The angle should happen right away, the dive is slower and the boat is harder to get down.

Brian