U-Boat Stability

[trongey]

To those with knowledge of RL u-boat performance, I'm curious how real subs behaved in rough water. Specifically:
1) Is the in-game pitching and rolling at periscope depth realistic? I've always understood that at that depth the surface conditions would have very little effect. Of course in heavy seas the scope head would be repeatedly submerged by the waves, but without stabilization it really seems to move around a lot.
2) How did u-boats behave on the surface compared to surface ships of similar displacement? Would they rise and fall on waves similar to a DD for example, or would they have more of a tendency to punch through the waves?

Tony

[Sailor Steve]

Underwater action on the u-boat is pretty realistic, in my opinion. Waves actually exist mostly underwater. This should help:
http://hyperphysics.phy-astr.gsu.edu/hbase/waves/watwav2.html
http://en.wikipedia.org/wiki/Ocean_surface_wave

As for question #2, the answer varies. Part of the problem is that besides its height, a wave also has length, or period. A long period will have even larger ships 'riding' the waves, while a short period will have everything 'punching through' except maybe a lifeboat.

In general, destroyers, due to their long slender shape, will almost never ride the waves. This makes smaller escorts, like the Flower class, superior for extended work in storms. On the one hand, Nicholas Monsarrat noted that corvette sailors like to say that their ships would "roll on wet grass", but the same tendency that made them uncomfortable in calmer seas also made them safer when the going got heavy.

Submarines have most of their displacement underwater, even while surfaced, so they are more likely to roll with the waves, but their shape is also relatively long and narrow, so they should have the same tendency to plow through the waves as destroyers would. I'm guessing that this also means that the smaller, rounder Type IIs would ride the waves better.

But going deep is still the best way to ride out a storm.

[MarkShot]

Until the nuke boats, hull design was primarily for surface performance as opposed to submerged performance.

Subs unlike surface ships even when surfaced have a lot less reserve buoyancy. Thus, taking on some water in rough seas would impact a sub more than a surface ship.

Stability depends on moment arms and location of the CB and CG (center of buoyancy and center of gravity). USN fleet boats had lead weights in the keel to further improve stability and lower the CG. This would also be the reason for the batteries being located low in the design. Things like upgrades to the con like radar or new and heavier deck guns could have a dramatic impact on handling characteristics.

Balast tanks were generally all flooded or all blown to promote stability. Much smaller trim tanks and pumping were used to adjust trim and buoyancy. However, at the point of surfacing and blowing the balast, there was a potential for temporary instability with large amounts of water sloshing in the tanks based on angles. This was in part addressed by having baffles in the balast tanks to restrict the flow of water.

Above comments are the result of reading declassified USN fleet boat docs and not anything related to U-boats.

[MarkShot]

Fascinating reading if you really want to get inside this amazing creations:

http://www.maritime.org/fleetsub/index.htm