Why do marine generators (and A/C) require seawater?

[bstreep]

As I recall, water transfers heat about 25 times better than air. Makes for a much more efficient transfer.


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[Lepke]

Years ago when water was plentiful, larger land ac units were cooled by water that dumped into drains. Now they are illegal. Others covered the advantages of sea water cooling, but air cooled engines in an enclosed space are unbearable.
Marine anything is generally better built and longer lasting than land units. Diesel engines greatly outlast gas engines and the fuel doesn't explode. I have a Perkins driven generator that is 46 years old and can be rebuilt indefinitely. My mains are about 65 years old and only rebuilt twice in that time. Try that with a gas engine.
Not to mention fuel savings. Cheap equipment will also effect your resale value.

[transmitterdan]

The main reason marine engines and air-conditioners use seawater cooling is because the alternative is massive amounts of air flow. This air has to come from somewhere and go somewhere. The inlet and outlet openings in the deck would be huge and a much greater risk of flooding than the comparatively tiny holes required for water cooling. The inlet and outlet water penetrations can be easily closed with a small valve whereas the air openings would be many times larger and thus much more difficult to seal.

It is possible to use air cooling but it isn't clear that it is safer. I think it would be significantly less safe for small craft.

[valhalla360]

Originally Posted by bstreep

As I recall, water transfers heat about 25 times better than air. Makes for a much more efficient transfer.


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No it makes the heat transfer unit smaller.

In my RV I have the same BTU as the old marine unit in the boat. They both use the same amperage.

[valhalla360]

Originally Posted by Lepke

Years ago when water was plentiful, larger land ac units were cooled by water that dumped into drains. Now they are illegal. Others covered the advantages of sea water cooling, but air cooled engines in an enclosed space are unbearable.
Marine anything is generally better built and longer lasting than land units. Diesel engines greatly outlast gas engines and the fuel doesn't explode. I have a Perkins driven generator that is 46 years old and can be rebuilt indefinitely. My mains are about 65 years old and only rebuilt twice in that time. Try that with a gas engine.
Not to mention fuel savings. Cheap equipment will also effect your resale value.

I think you are confusing geothermal units which are a different animal taking advantage of the fact that well water used for cooling typically comes at around 50deg rather using air which may be at 80-100 degrees. They are still legal but you can't dump the water into the sanitary sewer, you need to pump it back into the ground via a secondary well.

The durability of older diesels had nothing to do with being marine. The higher compression ratios forced them to be built more heavily and truckers (the vast majority of purchasers) needed long term durability. Modern engines particularly small diesels used in cruising boats don't shows the same increased lifespan as it's nothing to get 250k miles out of a gas car engine. I had a 30yr old V8 powered boat with the original engines. They ran fine when we sold it and to the best of my knowledge they had never been rebuilt...so I tried it with gas engines. The vast majority of boat engines fail due to abuse and neglect. They very rarely wear out.

I will agree a window unit doesn't boost resale value but a window unit is easily removed when it comes time to sell and when you compare a couple hundred to a couple thousand for a "marine" unit, you are unlikely to get the extra cost back on resale.

[DotDun]

Originally Posted by valhalla360

No it makes the heat transfer unit smaller.

In my RV I have the same BTU as the old marine unit in the boat. They both use the same amperage.

Efficiency isn't in power usage, it's the square feet of heat transfer required for each method. As mentioned, a water based unit is 25 times smaller.

[valhalla360]

Originally Posted by DotDun

Efficiency isn't in power usage, it's the square feet of heat transfer required for each method. As mentioned, a water based unit is 25 times smaller.

There are multiple types of efficiency.

Power usage is the more typical efficiency consideration and there is typically negligible difference in two well designed systems.

As I stated before, the main reason for a sea water system is the size can be reduced.