BRIEFING OF METOC EFFECTS ON MIW OPERATIONS

LEARNING OBJECTIVES: Brief the effects that water depth, currents, tides, and bottom characteristics have on MIW operations. Understand the impact of the magnetic, acoustic, pressure, and biological environments on MIW operations.

There are environmental considerations unique to the planning of MIW operations and this section will beComposite Warfare Oceanographic Support Modules (CWOSM), Part 1, TM 04-92.

Water depth is a factor to be considered in the spacing of mines, sensitivity setting, mine type, and mine impact velocity (air-laid mines).

. Bottom mines In deep water (180 ft or greater), detonation will not cause much of a disturbance in the upper layers of the ocean.

. Moored mines Depth may exceed the mooring range required for the mine to be effective.

. Sensitivity and actuation width Important for bottom mines since an increase in depth will result in a decrease of the sensitivity and actuation width of a bottom mine.

. Damage width Water depth affects the damage width in the same way as in actuation width. Increasing water depth causes a reduction in the damage width of a mine.

. Mine burial upon impact The depth at which terminal velocity is reached depends on the initial velocity when launched and the depth of the water.

Subsurface currents may set in different direction as mines descend, and current velocity may also vary during descent. These factors must be considered during planning of MIW operations.

. Burial Burial on the sea floor can result from scour (water velocity increases around the mine, setting sand and sediments in motion, burying the mine). Once the mine is completely buried, scouring stops.

. Sand ridge migration Currents may cause large sand dunes to migrate along the bottom in the direction of the current. The dunes can be as high as 12 to 20 ft.

. Mine dip (vertical movement of mines) An increase in mine depth from the normal vertical position above the mooring point. Current action creates forces against the mine, increasing the depth, Dip is directly proportional to current speed; therefore, dip will increase with faster currents. During flood and ebb tides, mine dip is at a maximum, which is the best time to penetrate a minefield.

. 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.

. 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.

. Acoustic mines Strong currents can produce enough turbulence to increase ambient noise at the acoustic sensor to partially mask a ships acoustic signature.

. Pressure mines A ship drifting with the current will have a reduced pressure signature as if the ships 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.

. 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 ships 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.

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