Mud box

A mud box is the coarse sea-water strainer fitted at a ship’s sea suction, just downstream of the sea chest and seacock, to trap mud, sand, weed, and debris before they reach the cooling and service pumps. It is a perforated basket inside a bolted or quick-opening housing that can be cleaned without securing the sea chest when a duplex arrangement is fitted, with one strainer in service while the other is cleaned. It protects the salt water service pumps, heat exchangers, and oil coolers from blockage and impeller damage. Differential-pressure or visual checks tell the watchkeeper when to clean it; a fouled mud box starves cooling and trips the main engine.