Quote:
Originally Posted by Bubblehead Nuke
You experienced a situation that we called a 'snap roll'. It is more prominent in teardrop hulls that have a sail set farther back on the hull than more forward. The Permit and Sturgeon class had it but it was not too bad. The 688 class on the other hand almost lost boats due to it. I know of two incidents where control was regained only when they blew the tanks and went to the roof.
This is what happens:
(ramble mode on)
When you throw a hard rudder on the stern (back of the boat) swings out opposite direction of the turn. That is, if turning to port the stern swings to starboard.
Now this is the interesting part. If you look at sub from a side view what do you notice. You have a sail on TOP of the hull and nothing below. So the stern swings out there is more resistance to the turn on top due to the side of the sail having more dynamic pressure on the side of the sail opposite the turn. This causing a twisting of the hull around its center of rotation.
This has the effect of rolling the boat into the turn. Now the rudder that was straight up and down now has a tilt and functions as a rudder AND a stern plane. This will cause the bow to pitch down and your stern planes now act partially as a rudder when used. The causes even more forced to act on the sail and cause FURTHER rotation INTO the turn. At about 30 degrees or so roll things start to get scary, This is because your bow/fairwater planes ALSO have this tilt to them and they no longer have a up/down force but a diagonal/lateral force making recovery even more problematic.
Oh.. and this happens FAST, as in SECONDS. You will go from a nice bank and turn to 45+ down with a 60+ roll rapidly if the Vernier rudder fails. At flank speed you have VERY little time to recover.
We had premade speed/depth operation charts. Basically it was an operating envelope. At this depth go no faster than this speed without reason. It took into account the ability to recover from certain casualties.
You CAN use it to your advantage. Torpedo evasion is the best ride in the world when you have someone who knows how to use it to get the most out of maneuvers.
When you rig for high speed the planesmen , dive and COOW put on seatbelts and they activate the vernier rudder.
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Also remember, vernier and the stick/divestops are NOT used during battlestations. Only during normal steaming. Its safer that way.
I did not want to get into any of the theory and whys from the above post. Just saying that in the game the boat does not turn as fast as the real thing.
Says a former Diving Officer of the Watch...