salt water and hot water heaters

[woodster]

i am looking at new water heaters and am wondering if not haveing a fresh water cooling system on my 2QM15 (raw water cooled) is going to be a problem in that it may not work well or have a short lived service life...i am planning on useing a water heater that is 110 volt ac along with a engine heat exchanger for heating water when not on shore power ....

any comments are welcome

thanks
woody

 

[Ed Schenck]

My 2QM20 was NOT sea-water cooled so not much experience. But there was a thread once that stated that the sea-water never gets hot enough to really heat the tank water. And a its a guess but I think that salt water would definitely shorten the tank life.

My own 2QM had an owner installed heat exchanger and pump to convert to internal cooling. That might be an option. Otherwise I think that I would stay with shore power or a generator for 110 heated water.

 

[rickmorel]

i am looking at new water heaters and am wondering if not haveing a fresh water cooling system on my 2QM15 (raw water cooled) is going to be a problem in that it may not work well or have a short lived service life...i am planning on useing a water heater that is 110 volt ac along with a engine heat exchanger for heating water when not on shore power ....

any comments are welcome

thanks
woody

We had a 3 cylinder Yanmar (don't remember the model number) with raw water cooling. I wound up bypassing the water heater line because it never got more than slightly warm and would quickly cool down any hot water in there from the AC heater.

We spent a couple years cruising and wound up finding a very small generator to get hot water. 1,000 to 1,500 Watts will do it. I think ours was a Coleman 1,200 Watt we got at a bargain price. Or we used the solar shower, sometimes just heating water on the stove when overcast.

A couple times, when the solar was really kicking, I used the inverter. 10 to 15 minutes would give hot enough for a shower and took about 25 Amp Hours.

If you're going to run the engine for hot water anyway, the inverter route might be the way to go. It'll take about 100 Amps so the alternator probably won't keep up, but should shortly catch up.

Rick

 

[Moody Buccaneer]

i am looking at new water heaters and am wondering if not haveing a fresh water cooling system on my 2QM15 (raw water cooled) is going to be a problem in that it may not work well or have a short lived service life...i am planning on useing a water heater that is 110 volt ac along with a engine heat exchanger for heating water when not on shore power ....

any comments are welcome

thanks
woody

Service life on a raw water system is not a concern, figure 15 years +.

The trick to getting good hot water out of it is how you plumb it into the system. If you plumb it into the hot side of the engine cooling system before the t-stat you get good hot water. If you use the outlet hose that cools the exhaust, you won't get water as hot as it could be.

When my old heater gave up, it was the tank that leaked, not the engine cooling side. When I upgraded to a closed cooling system the problem became water that is too hot! I might add a Scanvik type mixer to limit how hot the water going into the heater is.

I don't have personal experience with the propane fired "on demand" water heaters, but some of my friends in Canada swear by them. They eliminate the need for shore power or an inverter to heat water and they save the weight of having 6+ gallons of water sitting in the tank.

 

[Hermit Scott]

Service life on a raw water system is not a concern, figure 15 years +.

The trick to getting good hot water out of it is how you plumb it into the system. If you plumb it into the hot side of the engine cooling system before the t-stat you get good hot water. If you use the outlet hose that cools the exhaust, you won't get water as hot as it could be.

When my old heater gave up, it was the tank that leaked, not the engine cooling side. When I upgraded to a closed cooling system the problem became water that is too hot! I might add a Scanvik type mixer to limit how hot the water going into the heater is.

I don't have personal experience with the propane fired "on demand" water heaters, but some of my friends in Canada swear by them. They eliminate the need for shore power or an inverter to heat water and they save the weight of having 6+ gallons of water sitting in the tank.

How do you plumb the water that is in the block and head to circulate into the water heater? Do you need a circulating pump? Because while that water is heating in the head, it is not moving.

 

[Stu Jackson]

Heater connection

How do you plumb the water that is in the block and head to circulate into the water heater? Do you need a circulating pump?

With a freshwater cooled engine (i.e., with a heat exchanger), there is a hose between the freshwater (engine) circulating pump and the thermostat. Interrupt that line and run it to the hot water heater. The circulating pump is already there: it's the one on the engine that moves the freshwater (i.e., antifreeze/coolant) around. It's usually called the freshwater circulating pump, as opposed to the raw water circulating pump. Many folks with freshwater cooled engines who don't sail in salt water often get confused.

 

[rardiH36]

To elaborate more on Ed Schenck's comment that sea water 'coolant" doesn't get hot enough to heat a water tank:-

My Seloc Yanmar repair manual cites that salt water forms salt crystals at water temps above about 160F -- temps that are normally exceeded in the hottest parts of the coolant system around the cylender walls and in the cylinder head. Unless saltwater circulating through the engine is kept safely below the 160F, the coolant channels in the engine become blocked and impossible to unclog again. To prevent this, raw water cooled engines are fitted with thermostats that open at about 140 F as compared to the +/- 160F or so for closed anti-freeze coolant systems.

The Yanmar 2QM20 installed on my boat was originally sea-water cooled. But either at commissioning or by the original owner, it was converted to a closed system by the addition of an external bulkhead mounted heat exchanger, reconfiguration of the various hoses, and installation of a second pump (one for the seawater which cools the heat exchanger and the other to circulate the anti-freeze coolant through the engine and heat exchanger). Yanmar made different housings for the raw water and closed cooling systems. To prevent someone from ruining their raw water cooled engine by installing a 160-170F thermostat, only a 140F themostat will fit in engines with the raw water housing. So even though I now have a closed system, the coolant never gets very hot. Actually even after running the engine for a while, it's just very warm. Certainly not hot enough to convey much heating energy to a hot water tank!

 

[Maine Sail]

140 degree engine water temp will certainly heat a hot water heater to close to 140 if you run the engine long enough. A 160f or 180f t-stat will heat the water faster but should not be used on a raw water cooled engine. The problem is that many of these engines have only crude measures, or none at all, to tap into the 140 F cooling water..

With a high quality water heater like the Isotemp it will have a mixing valve built in as standard equipment. A tempering or mixing valve will mix the internal tank water with the cold supply. You will get more volume of 120 degree water by mixing the 140 degree tank water with the 70f domestic water.. You can do the same with a single lever faucet. Salt water through a quality SS tank should not shorten the life by all that much considering your engine is iron and lasts for many years..

My own indirect fired domestic hot water heater is being fed by 142 degree water today, as controlled by my outdoor temperature control. Because it is 45 F here today, and I don't need nor want my boiler running at 180 F on a warm day, the control drops the boilers hi-limit to closer match the outdoor temp and avoid needless stack loss.

The difference is that on a home system I have a priority setting for domestic water. In the event that we need lots of hot water it will drive the hi-limit of the boiler to 180 degrees if necessary despite it being in the 40's or 50's outside. On a boat with a raw water cooled system you are stuck with 140 F.. It will get hot but will also take longer to do so..

 

[kloudie1]

The problem with the raw water cooled systems is that the engine is at 140 but the water accessable to the water heater is a good bit cooler because the thermostat bypasses cold water around the block to keep it cool. this gets mixed back in usually before the water heater .. kinda like trying to use the heat exchanger outlet water on a fresh water cooled motor to warm the water heater.. it will warm the water, but it will take a while. The 140 F water in a typical raw water cooled system is usually not plumbed in a useful way for heating domestic water.

 

[rickmorel]

The problem with the raw water cooled systems is that the engine is at 140 but the water accessable to the water heater is a good bit cooler because the thermostat bypasses cold water around the block to keep it cool. this gets mixed back in usually before the water heater .. kinda like trying to use the heat exchanger outlet water on a fresh water cooled motor to warm the water heater.. it will warm the water, but it will take a while. The 140 F water in a typical raw water cooled system is usually not plumbed in a useful way for heating domestic water.

Yep. Except the bypass is to keep the block warm. My raw water cooled engine had a bypass. As I recall, the thermostat controlled which way the water went. When closed, it routed the water from a bypass pipe. As it opened it allowed more and more water to flow through the engine and allowed less and less water from the bypass pipe to flow. Still always a good amount from the bypass though.

Sort of like a tee coming into two ports of a 3-port valve. The same amount of water flows out the third port, but depending on the position of the valve the source was one or the other inputs or some combination of both.

In 70 degree water, the output was maybe 90 degrees. As I mentioned before, it never heated the water to more than slightly warm and quickly cooled it down if the water was already hot from shore power.

Rick

 

[Hermit Scott]

After thinking about it, there is no way to use the hot water in the enigne to heat a water heater with out some serious plumbing and modification to the engine it's self.
The 140 degree water sits in the block nd head and only leaves when it gets too hot and opens the thermostat. There is no circulation circuit for this water. To use the water before it goes into the exaust wouldn't even be close enough to the temperature needed. As it is msotly bypassed seawater.
The plumbing would be so extensive that it would be simpler to install a heat exchanger and use that in the conventional way.
If any one has any other way I am open to suggestions. But I just don't see it.