tides, mine dip is at a maximum, which is the best time
to penetrate a minefield.
l Mine walking (horizontal movement of a mine)
— Movement of the mine anchor caused by currents.
In regions where the bottom slope is greater than 5° and
a strong current exists, moored mines can walk
downslope into deeper water. Walking is also
dependent on bottom sediment, bottom topography, and
wave action.
l Mine rolling — Rolling or tilting of a mine on
the bottom may result in magnetic or acoustic pressure
causing the mine to detonate. A delay-arming device is
used to eliminate this possibility.
l Acoustic mines — Strong currents can produce
enough turbulence to increase ambient noise at the
acoustic sensor to partially mask a ship’s acoustic
signature.
. Pressure mines— A ship drifting with the current
will have a reduced pressure signature as if the ship’s
speed was reduced.
. Explosive ordnance demolition (EOD)
operations — Current velocity for surface water may
not be the same as that below the surface. The layers of
water above and below the thermocline can move
independent y of one another, so divers may drift in
several directions while descending.
l Mine neutralization vehicle (MNV) operations
— Using an unmanned, tethered, remote-controlled
submersible known as an MNV, it provides mine
countermeasure (MCM) ships with mine neutralization
capabilities. MNV maneuverability can be drastically
reduced by currents because of the dragon the cable.
. Navigation errors — Currents can cause the
ship’s track to vary significantly from the intended
trackline.
Mine laying (spacing) and mine
countermeasures (sweep coverage) depend on an
accurate track
. Mine drift — By utilizing prevailing currents,
drift mines may be launched at safe distances to occupy
a minefield that would otherwise be inaccessible. A
change in current direction could present an inherent
danger to the mining forces or to other friendly forces
in the later stages of the campaign.
TIDES
Local topographic features, meteorological
conditions, currents, and the influences of the sun and
moon must be considered to establish the tidal
characteristics for a given area.
. Selection of mooring depth —Tides may cause
depth variations of a moored mine and can cause the
mine to surface during low tide and be too deep during
high tide.
l Mine sensitivity and damage width — In areas
where the tidal range is great, the position of a moored
mine relative to the sea surface may vary significantly.
As with the impact of water depth, increasing the depth
of a mine will cause a reduction in its sensitivity,
actuation width, and damage width.
l Submergence of reference buoys — Reference
buoys are used to mark the position of mines and as aids
to navigation. If these buoys are deployed at low tide,
they may become submerged during high tide.
BOTTOM CHARACTERISTICS
Bottom sediments vary in porosity, water content,
compactibility, and plasticity.
l Reverberation — Bottom reverberation depends
on frequency and grazing angle. Bottom scattering
depends on sediment type and bottom roughness.
. Acoustic contrast — Detecting and classifying
mines with high-frequency mine hunting sonars creates
a problem in acoustically distinguishing mines from the
background.
. Bottom sediments (hardness) — Initial
penetration in silt or clay will be greater than rock,
gravel, or a sandy bottom.
. Impact velocity — Softer bottom types affect
initial penetration more so than hard bottoms.
l Weight of the mine — This causes subsequent
penetration. This results from plastic flow (sediment
flow out from under the mine upon impact), and/or scour
and deposition.
. Angle of impact — The more perpendicular the
angle of impact, the greater the expected initial
penetration.
. Mine movement — A mine will not roll on a
bottom composed of various mixtures of fine-grained
sand, silt, and clay. Initial penetration into the bottom
will prevent subsequent rolling.
l Mine burial — Burial of a mine will have little
influence upon a magnetic-actuated mechanism, but an
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