In comparison to a car’s radiator ultimately using the air to cool to water which cools the engine, how do boats and ships cool the engines? Do small boats, for non-commercial use, air-cooling similar to a car’s radiator?
And, for larger vessels: Do large vessels take in cooling water from the ocean, or if too high in salt content, do they run it through a desalination process first?
The above systems I have described are known as “closed systems”, meaning the water does not follow a cycle - cooled by air, reheated by the engine, cooled by air…ad infinitum. But, there are also “open systems” which do not recycle. It only passes through once and is rejected.
Do any ships have, what would be called, an “open system” where cooling water is taken in, desalinized, and once heated, the hotter water is rejected out to sea? While this would would, is it environmentally permitted?
Any info onn how boats and ships cool their engines would be helpful!
Small engines (outboard L.T. 7hp) usually are air cooled. When the HP gets higher then they use a combo air and sea water cooling. when the HP gets 20 or higher then it’s mainly seawater.
For larger boats (moving into i/o and inboard engines) sea water is used for cooling. I don’t know if the sea water is used dieectly or passes through a heat exchanger to a coolent. As some have gotten more elaborate you can use a air cooled radiator.
Beyond that I would think - well I don’t know. It would seem to make sense to use cool seawater somehow. My wag would be a seawater to coolent heat exchanger.
I don’t think any boat uses desalination for cooling water - energy costs would be way too high.
My dad had a boat in the 1960s, a V-hulled 20-footer made of Philippine mahogany with an inboard, blue-printed Olds V-8 connected directly to the screw. High-sided, heavy – not at all like the sleek fiberglass ski boats at the time, but fast. My uncle wouldn’t sit down one time and wound up in the potato salad that was sitting on the engine cover.
I was way too young too know anything about engines, but I do remember seeing little scoops on the bottom of the hull. I realized later that they were there to take up water for cooling the engine.
On larger vessels, cooling is achieved by using heat exchangers.
In a direct system, the seawater is pumped around the engine jacket but there are many contaminants and there is a risk of water galleries becomoing blocked.
The more usual method is to have chemically treated water to circulate around the machinery cooling jackets, and that water is then fed to a large heat exchanger, on the hot side you have a positive pressure relative to the cool side.
The cool side of the exchanger is suppled by seawater.
There is usually an intermediate take off point on the hot side, this goes to another heat exchanger but the water on the ‘cool’ side is actually used either to pre-heat boiler feedwater in steam turbine ships, or to provide low pressure hot water for domestic use, or it can be used for general heating of the vessel.
A steamship will use waste steam heat exchangers for hot water supplies, but a gas turbine obviously cannot, although energy can be reclaimed from the exhaust gases.
Other more sophisticated systems use hot fluid to provide energy to run absorption coolers, for things like air-conditioning on large cruise liners.
The heat energy from engines can be used to run desalination plants on ships that do not have boilers.
Every cutter or small boat I’ve been on, was cooled in ways mentioned above. Either raw water (outboards), or internal heat exchangers using raw water. My last cutter, a small ice breaker, was cooled with keel coolers. Basically, large radiators were recessed into the exterior of the bottom of the hull, and fresh water/coolant was cooled that way.