Science of Silence

Overheating the Exhaust

System Protection

A wet exhaust system for a marine diesel engine is heavily dependent upon a working and efficient flow of raw cooling water. The causes of a breakdown in the raw water system are numerous. Some are accidental, like sucking up a clump of weed or plastic bag into the sea water intake or some can be mechanical like a worn pump or a burst pipe. Even human error can play its part as we forget sometimes to open the sea cock. Either way the effects are serious if not disastrous as the engine is starved of cooling water, the pump dries up, then the engine overheats and the exhaust system starts to melt.

Placing reliance on the engine temperature alarm is not sufficient since by the time the alarm is raised, the damage will already be done. What's needed is a protection system that will react immediately. There are two good vital spots to monitor, one is located between the sea strainer and the raw water pump and is covered by Halyard's Sea Strainer Alarm and the other is at the engine raw water exhaust injector cover by Halyard's Exhaust Alert. Each can operate as a separate unit or they can be installed and used in tandem for double protection.

HMI Exhaust Alert

Marine diesel exhaust systems are designed to take temperatures of only 120°C. The exhaust gasses, however, may reach more than 500°C. To cool the gasses, the exhaust depends on a free flow of cooling water from the engine. This flow can be cut off, by a plastic bag or seaweed being sucked into the intake, or by a problem with the water pump. The exhaust temperature will rise immediately to around 450°C, the exhaust will overheat and may be seriously damaged. In most situations Exhaust Alert will warn you before serious damage occurs.

Sea Strainer Alarm

This system buys you precious seconds to deal with the problem before any damage occurs. Impede the flow of water through the strainer, or start the engine with the sea-cocks turned off, and the Sea Strainer Alarm tells you instantly. The Sea Strainer Alarm spots the restricted water flow in the hose between the strainer and the pump. Too great a restriction and the sensor loses current. The control box instantly picks this up, and the alarm system is set in train. Halyard has taken three years to research the Sea Strainer Alarm, studying the flow between sea strainer and pumps for engines of over a hundred different sizes and types. With the aid of a significant EC grant, we’ve plotted these to ensure we can specify a sensor which alarms immediately the water flow is seriously impeded – but doesn’t alarm unnecessarily. All you need tell us are the engine size and the inside diameter of the pipe from the sea strainer to the engine pump.

System Control

The components of the control system for both the Sea Strainer alarm and the Exhaust Alert are remarkably simple. There's just the probe(s), a control box, a display unit and an optional siren.

The control box can receive up to three probes in any combination and send out to two display units. This means for example we can monitor the raw water cooling flow, and the exhaust injection temperatures of the main engine and a generator set, whilst watching over the system with display units in the wheel house and the fly bridge.

The 12V 24V power supply to the control box must pass through the engine's ignition circuit to ensure that the Sea Strainer Alarm and the Exhaust Alert are guarding the system at all times when the engines are running.

The Display Unit is usually located by the helm position, and rather like an engines 'Oil Pressure Alarm' the Display unit self-tests when the engine is first turned on. If the Display Unit isn't to one's liking then it is possible to build the display warning lights into the existing engine dash board, making one's helm console less cluttered. For this, one needs the special 'OEM Junction Box' and the customer supplies their own lights for the engine dash board.

To view the Halyard Exhaust Alert Systems, then please click here.