Engine cooling

[clay1diver]

I have a question concerning engine cooling systems. I have found a boat that I am considering purchasing. She is a 45' Ketch built by Columbia Yachts in 1974. She has an 85 hp Perkins 4236. The survey I was sent says the cooling system is fresh water. The boat I worked on in the Bahamas was salt water. If I remember correctly. Is it normal to have fresh water cooling on a boat? (She has 2 tanks at 120 gallons each) Is it possible or advisable to change from fresh to salt water cooling?

[Nausikaa]

Hi,

Fresh water cooling systems are fairly common in certain areas where boats are working in ice or polluted waters or in waters containing lots of silt or mud.

On a normal boat it would seem like a waste of space to carry so much cooling water arround.

Cheers

Stephen

Yachr NAUSIKAA

[JeanneP]

You don't use your tankage for cooling in a fresh water system.

The fresh water runs through the engine in a closed loop, passing through a heat exchanger where salt water is used to cool the fresh water. Is that clear? In other words, the fresh water in the cooling system is continually recirculated between engine and heat exchanger - you just need to inspect it periodically in order to be sure there is sufficient fresh water in the system. It is a better system. Your engine will run better, and you won't have to worry about the terrible corrosive effects of hot salt water on your engine.

[Nausikaa]

Hi Jeanne,

Sorry to contradict you but I spent a winter an an engineer on an ice breaking tug in Sweden. We had a huge tank for cooling water as the intakes (which were used in ice free conditions) would be blocked by ice slurrey.

The tank was just under the main deck, which was kept ice and snow free by the heat of the cooling water. The only drawback with the system was that we had to empty the tank if the engines were not going to be run for over a day as the whole thing would freeze.

On the other hand, I have never seen this system on a yacht.

All the best

Stephen

Yacht NAUSIKAA

Clay without being to technical, fresh water cooling is one of the better systems for boats in salt water. Stephen on Niausikaa, is talking about a specialized system used for Artic Type waters. I was on a boat in the Canadian Artic which also used this system but we could switch to keel cooling in warmer waters (also a specialized cooling system)

Think of the cooling system in a car. The engine is usually cooled by water which is connected to the radiator which is then cooled by the outside air.

In a boat you usually use water (raw water)from outside the hull to cool the engine water through what is called a heat exchanger (think of it as a type of radiator). In freshwater you can forget the heat exchanger and just use the raw water to cool the engine directly but in saltwater this causes several problems which I will not go into here (Joanne mentioned one above).

Joanne is correct, your water tanks on board are not to cool you engine.

I had a friend who sailed around the world in the 80's in a Columbia 45. He had a 20 meter ham beam antenna on his mizzen mast.

Cheers, John

[Auzzee]

Many fishing boats operating in Australia's tropical waters use fresh water cooling, yet do not keep a large reserve of water. The water circulates through the engine's water jacket, then through pipes which are attached externally to either side of the keel. These pipes act as the heat exchange as sea water flows across them. I have seen the systen on long keeled steel yachts where there is a sharp angle between the keel and the hull, and it is clean and highly efficient. It would not be so easy to fit to a composite hull where the moulded section of hull to keel is flared. A short, modern keel would probably not offer enough area in the appropriate places to make the 'keel' cooling option worthwhile.

[KaptainKen]

Clay1diver;

I have a 50 HP Perkins engine on my sailboat. It is "freshwater cooled" in that the engine block contains fresh water (or coolant). Mine is as JeanneP described. The coolant is "cooled" by a heat exchanger containing seawater. This was (is) the conventional set-up for ordinary production sailboats ... there is no reason to believe the one on the Columbia is any different.

Ice breakers, fishing boats and tug boats may have special engine cooling arrangements. But ordinary, production, recreational use, fiberglass sailboats made in the last few years have the seperate coolant/seawater system described.

[clay1diver]

I appreciate all the input. Now, I feel a little... not so much stupid since the only experience I had was salt water cooling... but green. (Not seasick green.)