Boatnerd Discussion Forum

Tugboats, especially smaller ones involved in dredging in shallow waters will have keel coolers that keeps the cooling system a closed system and it works just like a radiator on a car. They also are used on towboats on the Mississippi and Ohio rivers.

Ocean ships use a combination of Fresh Water and Sea Water for all cooling. Different approaches are used, but most common is the Main Engine using a separate cooling water system for jacket water, often called HT (High Temperature). Another loop called LT (Low Temperature) is used for lub. oil cooling, air coolers, as well as all other machinery cooling needs in the machinery spaces.

In essence, the sea water cools the LT water, generally in plate coolers. The sea water enters the ship by sea chests, though large pipes and into strainers, through pumps that move the sea water to coolers, and then overboard. The LT water is also circulated by pumps.

A 3-way valve is fitted at the LT coolers which regulates how much water is passed through the coolers. This allows the LT water to maintain the correct temperature (for example 34-38 C is normal). LT water is generally cooled to a set temperature, where HT water is constantly adjusted to keep engine outlet temperatures constant. For example, a running engine requires more cooling, so the inlet temperature will be lower than on a stopped engine.

An expansion tank is located in the engine room spaces, often up high in the funnel casing. This keeps positive head pressure on the HT and LT systems as well as providing a means for air to vent from the system.

LT and HT water is treated with inhibitors as mentioned by Guest. This is not antifreeze, but is specific to corrosion prevention.

US Flag lake ships are not concerned with sea water and the dangerous effects, since few ships rarely venture out of the Seaway.

Some ocean ships are also still designed with pure sea water cooling. Only the main and auxiliary (generator) engines will have fresh water cooling loops (HT water). Sea water is used for everything else. The upside of this is less equipment and piping, but the downside is more pipe and equipment repairs due to the corrosive effects of sea water.

the cooling water comes from the lakes and rivers the boat is traveling in. comes in through the water chest through the eng over board. very little change in temp

some of the newer boats have a pipe system that in 'ice' they can run water through the aft blast tanks

the older one do not have this unless it was added later

if you look at Cort, AM ship built boats you see a stream of water of the aft end thats cooling water going back in the lake [the chest is under the haul

charlie

Engines use treated cooling (jacket) water to cool the engine components. This water is then usually, cooled by seawater. The treated water is more resistant to corrosion than plain water.
Smaller engines like the one in your car operate the same way. The coolant fluid is cooled by air via radiator.

Now, sometimes ships may use water stored in either afterpeak or ballast tanks. This is especially common during the winter when ice and slush can foul our strainers.

For ships with large diesel engines, where does the cooling water come from? Are there onboard tanks with filter systems that are being continuously being filled with lake water or large thru-hull fittings in the bottom of the hull that are connected to the engines or some other system?