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 TM 55-1905-223-SDC
Section II. BELOW WATERLINE DAMAGE
2-3.
BELOW WATERLINE DAMAGE - GENERAL. Underwater damage may be from battle damage or
from collision damage caused by contact with another ship or by underwater obstacles, fixed or floating.
Below waterline damage to a hull resulting from collision, explosive device, or grounding might not
cause a ship to immediately sink or require abandonment but the following can occur:
a. List.
b. Flooding with sea water and/or fuel oil.
c.
Impairment of vital operating systems in damaged area.
d. Fire.
The list of the ship can be presumed to be due to off-center weight. If the ship is underway when
damaged and the probability of receiving further underwater damage is possible, prompt removal of list is
the prime consideration. List has many undesirable effects:
a. Impaired speed due to increased propulsion resistance, increased difficulty in operating the main
propulsion plant, and possible improper immersion of screws.
b. Impaired maneuverability.
c.
Impaired overall stability due to list and improper trim.
d. Increased difficulty in servicing and operating deck equipment.
e. Ultimate swamping or sinking.
A combat hit which strikes the ship's side below the waterline can cause all the effects outlined
above and, in addition, may seriously decrease hull strength. A hit near the stern may damage or carry
away one or both propellers and can render inoperative or destroy the rudders and steering gear.
Damage causing total flooding of tanks or void spaces below the water-line, although reducing
the reserve buoyancy, may have a beneficial effect on stability if there is no list and sufficient freeboard
distribution before the damage occurs. New ballasting figures must be calculated using the methods
described in the Trim and Stability Booklet to ensure that a safe amount of reserve buoyancy remains.
If an underwater weapon (mine or torpedo) is fuzed to explode on contact with the ship's hull, a hole
is torn in the shell and the interior of the ship is subjected to blast and fragment attack, followed by
a violent inrush of water. Surrounded by a liquid medium, underwater weapons do not depend upon their
casing for fragment attack, but instead, tear loose large chunks of the ship's structure and hurl them into the
ship with projectile-like violence.
2-2
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