Minesweeper

Overview

A minesweeper, more precisely a mine countermeasures vessel, exists to find and clear sea mines so that other ships can pass safely. The job splits into two methods that this ship carries at once. Minehunting locates individual mines with sonar and then sends a vehicle to destroy each one. Minesweeping tows gear through the water to cut moored mines free or to fake the magnetic and acoustic signature of a target ship so that influence mines fire harmlessly behind the sweep. The hull, the propulsion and the sensors are all shaped by one hard constraint: the ship has to work directly above live mines without setting them off.

The vessel is built around eight major systems. The Hull & Superstructure keeps the structural signature low and survives nearby detonations. The Propulsion System gives quiet, precise low-speed control. The Minehunting Sonar Suite suite finds and classifies contacts on the seabed. The Mine Disposal System system neutralises mines one by one. The Sweep Gear gear clears wide areas by mechanical or influence means. The Degaussing System system cancels the ship's own magnetism. The Combat Management System ties every sensor and effector into one tactical picture, and the Auxiliary Systems systems keep the ship and crew running.

Hull and signature management

The hull is moulded as single-skin glass-reinforced plastic rather than steel, because a steel hull carries a strong magnetic field that magnetic influence mines are designed to detect. The GRP Hull Shell is stiffened by bonded top-hat Hull Frame members and divided by GRP Watertight Bulkhead panels into watertight compartments. Almost everything fitted inside, from fasteners to brackets, is chosen for low magnetic content, and heavy equipment sits on Shock Mount units so that the shock wave from a near miss does not wreck the sonar and machinery. GRP also flexes under blast loads better than welded steel, which raises the chance of surviving a detonation close aboard.

Cancelling the residual field is the job of the Degaussing System system. Loops of Coil Cable run through the hull on three axes, and the Degaussing Control Unit unit drives current through them so the field they make opposes the hull's own magnetisation. Fluxgate sensors measure the leftover field and feed the control loop, so the cancellation follows the ship as it changes heading.

Minehunting sonar

The ship searches with sonar before it commits a disposal vehicle. The Hull-Mounted Sonar sits in a retractable keel dome and uses a high-frequency Transducer Array to sweep the seabed ahead, with a Sonar Hoist that lowers it clear of hull noise and raises it in shallow water. Where the water layers and bends sound, the Variable Depth Sonar lowers a Towed Sonar Body on an armoured Tow Cable to put the array at the depth that gives the best view, which also helps against mines moored up in the water column rather than lying on the bottom. A Side-Scan Sonar sonar builds high-resolution imagery of the bottom to separate real mines from rocks and wrecks. The Sonar Processor beamforms the returns and presents classified contacts to the operators.

Mine disposal

Once a contact looks like a mine, the ship sends a vehicle rather than risk a diver. The Mine Disposal ROV is a tethered remotely operated vehicle on the PAP pattern: it flies down the ROV Umbilical under thruster control, identifies the mine on its ROV Camera, and places a Disposal Charge alongside before the ship backs off and fires it. For faster work the ship also carries the Expendable Disposal Vehicle, an expendable SeaFox-type vehicle that homes on the mine over a guidance fibre and detonates its own Shaped Warhead against the target in a single run. Both are launched and recovered over the side by the Launch & Recovery Crane and flown from the ROV Control Console.

Sweep systems

Sweeping clears areas without locating every mine. The Mechanical Sweep tows a serrated Sweep Wire held out to the side by an Otter Board board and down to depth by a Depressor, so the wire catches mooring cables and a Wire Cutter severs them, letting the mine float up to be destroyed. The Acoustic Sweep tows a noise source that reproduces ship sound to trigger acoustic influence mines, and the Magnetic Sweep runs current through a buoyant Magnetic Sweep Loop to fake a ship's magnetic signature for magnetic mines. The towed bodies pay out and recover on the Sweep Winch.

Propulsion

Hunting demands that the ship hold position over a contact in current and wind, so propulsion favours control over speed. Diesel Diesel Generator Set units generate power that an electric Electric Propulsion Motor turns into thrust, which keeps engine vibration off the hull. Each Voith Schneider Propeller is a Voith Schneider cycloidal unit whose vertical Cycloidal Blade elements change pitch through the rotation to point thrust in any direction, and a Bow Thruster adds bow control. Top speed is modest at about 14 kn, with a slow 6 kn search speed that keeps the radiated noise and the magnetic and pressure signature low enough to work safely over influence mines.

Combat system

The Combat Management System is where the ship is fought. Redundant tactical servers fuse sonar contacts, vehicle positions and sweep tracks onto the operator consoles, and the Navigation System system, built on an inertial unit, GNSS and a gyrocompass, fixes each mine to within metres so cleared and uncleared contacts stay separate as the route is opened.