Heat fresh water from a raw-water cooled engine?

[rad28]

Just wondering if it would be reasonable to run my salt water cooling through my hot water tank heat exchanger. My boats been in salt water for too long to add a fresh water cooling system, but if the salt wouldn't rot out the HW tank too quickly it would be nice to have engine heated water.

Any thoughts from the experts?

 

[littlebookworm]

Re: Heat fresh water from a raw-water cooled engine?

Our 2000 Chaparral came with a hot water heating tank. It uses shore power when I'm at the dock and engine cooling water when I'm underway to heat hot water. The water in the tank is heated high enough to take a shower and to require mixing with cold water to prevent scalding. Go the the "Seaward" web site for info on the connections. Hy

 

[rad28]

Re: Heat fresh water from a raw-water cooled engine?

Littlebookworm: Is your Chaparral raw water cooled? In other words, your engine does not have a glycol filled heat exchanger?

 

[seabob4]

Re: Heat fresh water from a raw-water cooled engine?

If you don't have FWC, that water heater will be eaten up in a heartbeat...

 

[foodfisher]

Re: Heat fresh water from a raw-water cooled engine?

Right on. IMHO

 

[JoLin]

Re: Heat fresh water from a raw-water cooled engine?

If you don't have FWC, that water heater will be eaten up in a heartbeat...

No it won't. An Attwood 6-gal. costs about $250. and he'll get at least 5 years out of it.

It's a perfectly doable upgrade and very handy if you spend nights and weekends on the hook. The heater does a good job of keeping water warm-hot, for 18-24 hours after shutting down the engine. 20 minutes at idle will heat it up again.

My .02

 

[DuckHunterJon]

Re: Heat fresh water from a raw-water cooled engine?

How about using a thin plate heat exchanger. They make them in stainless, and all that would be needed would be a small pump to circulate the secondary heating water. The raw (salt) water wouldn't come in contact with the storage tank/exchanger. Yes, there would be a small loss of efficiency, but there are plate exchangers that are 98% efficient. Just a thought.

 

[rad28]

Re: Heat fresh water from a raw-water cooled engine?

Thanks for the thoughts. If I could get 4 or 5 years out of the HW tank before it rusted out it would be well worth it. Of course the engine always gets a fresh water flush and Salt-Away on occasion.

We normally anchor somewhere in the San Juan Islands and heat the water with a Honda, but it takes 40 min. running full blast. Keeping the Admiral happy means more time on the hook.

 

[themaniam1]

Re: Heat fresh water from a raw-water cooled engine?

Our hot water heater uses raw water to heat when it is not connected to shore power. It does a great job even when the lake water is 40?F. The engines t-stat keeps the engine at 150? ish so that is the water temp being used to heat the fresh water. I think that is you do an occasional fresh water flush then you will get a long life out of your hot water heater. Heck, if you just anchor with the engine idling at the mouth of a river or large creek you can get your fresh water flush.

 

[seabob4]

Re: Heat fresh water from a raw-water cooled engine?

Sorry guys, I'm down here in one of the worst areas for salinity, Tampa Bay. You just get a boat or appliance NEAR the gulf and it starts to corrode...

 

[sasto]

Re: Heat fresh water from a raw-water cooled engine?

Beware of where you tap into your plumbing and the location of your water heater. Improperly plumbed and located above the engine manifolds may cause a problem when shutting down your engine and raw water flowing from the heater into exhaust manifolds and possibly into your engine. Depends on your setup and exhaust type.

 

[triman]

Re: Heat fresh water from a raw-water cooled engine?

I have a 1991 yamaha 5.7 sterndrive, raw water cooled, that runs through a small heat exchanger under the transom, giving me about 3 minutes of hot water at the end of a ski or snorkel.
The engine and heat exchanger are original, that is 20yo.
As for the plumbing, absolutely no idea how it was done, but I suspect someone here would be able to show a diagrammatic of a suggested system.