2007 310 DA -- Why am I getting hot water?

[mobocracy]

I've owned this boat for 4 years, and the admiral handles the galley clean up duties after a day on the water as we head back to the marina.

One day a couple of summers ago, I asked her how she cleaned up that day without hot water. She said, "I just turned on the hot water heater and we had plenty." While we do have a hot water heater, as far as I know, it's AC only and while she "turned it on" on the main control panel, the generator wasn't running so the hot water heater shouldn't have been providing hot water. I just assumed she had "warm-ish" water from the water tank which had gained some trivial warm up by the general heating of mechanical spaces due to engine run, etc. As long as she wasn't griping about clean up I wasn't going to lecture her on how it really worked.

I never thought about this until yesterday when I was doing cleanup without the admiral on board. Sure as shit, we had actual HOT water. The hot water heater was never turned on, although we did cruise for about 90 minutes before anchoring and did run the genny for about an hour during meal prep.

I'm sure there's a practical explanation, but since this boat is raw water cooled and stern drive, I'm kind of baffled at where the heat for hot water came from. Is there some fresh water heat exchanger someplace on the genny or engines? I haven't been into the engine spaces to track lines to see if this is the case, but its the only thing I can think of, as there's no DC side switch for water heating. The genny makes the most sense since it is physically closest to the hot water heater and has an intercooler.

 

[sbw1]

You have a hot water heat exchanger that routes your hot water line through the water heater when the engine with the heat exchanger is running. If you look in the engine room you will be able to trace the water line and locate it.

 

[dwna1a]

Very true. Your water heater acts like a heat exchanger. Look for two lines running from the motor to the heater.

 

[stephenm27]

It should be plumbed to/from your port engine using 5/8” heater hose.

Also, note that if you boat in salt water, do not flush afterwards and have raw water cooing, this raw water heat exchanger will typically fail from corrosion before the heater fails otherwise.

 

[JimG]

Yep, what they said... tell the Admiral that she doesn't have to turn on the hot water heater switch... she will still have hot water.

 

[stephenm27]

Yep, what they said... tell the Admiral that she doesn't have to turn on the hot water heater switch... she will still have hot water.

And a last safety note: there is *no* thermostat on the heating of the water in the tank using the heat exchanger.

In other words, the potable water will eventually get nearly as hot as the engine raw water (+/- 160F) as there is no thermostatic bypass. This can and will scald.

When using the electric element to heat the water, it's thermostat is typically set much lower for safety.

 

[mobocracy]

Thanks for the info. This is kind of humbling for me, because honestly, I thought it was just another example of the admiral's dubious technology mastery, but it turns out that I'm the one who didn't know how it worked.

I'm actually kind of surprised this was an included feature on this boat, it feels like a "big yacht" feature.

It makes me wonder if a companion heat exchanger on the starboard engine could be used for cockpit heat or run through an absorption chiller for air conditioning.

 

[wyrman]

My 06 260 had it.

 

[stephenm27]

I'm actually kind of surprised this was an included feature on this boat, it feels like a "big yacht" feature.

It makes me wonder if a companion heat exchanger on the starboard engine could be used for cockpit heat or run through an absorption chiller for air conditioning.

The engine block has a few "normally plugged" threaded holes into the water jacket and 2 of these plugs are simply replaced with a barbed host fitting to enable the loop to the water heater.

When my heat exchanger loop was still connected, I noticed that my port engine ran a bit cooler than the starboard, presumably due to the extra thermal dump that the 6 gal water heater provided (at least until the 6 gal reached thermal equilibrium).

I'm sure someone has done the cockpit heater on a similar principle. Not sure of the absorption chiller...

 

[techmitch]

Thanks for the info. This is kind of humbling for me, because honestly, I thought it was just another example of the admiral's dubious technology mastery, but it turns out that I'm the one who didn't know how it worked.

I'm actually kind of surprised this was an included feature on this boat, it feels like a "big yacht" feature.

It makes me wonder if a companion heat exchanger on the starboard engine could be used for cockpit heat or run through an absorption chiller for air conditioning.

Yep. A member here, Todd/Nehelenia (I think it was) from the PNW did the cockpit heater thing.

 

[Soulshine]

Same thing happened to me when I first got my current boat. I thought she was crazy.

The heat exchanger lines were well hidden behind a stringer and with all the plumbing going in and out of that thermostat housing I hadn’t noticed yet.

The water heater itself is tucked away in the far reaches of the ER and was no fun to change last summer.

 

[mobocracy]

The water heater itself is tucked away in the far reaches of the ER and was no fun to change last summer.

I feel like the major selling point of stern drives vs. v-drives on my model year 310 is that it pushes the engines back enough that most things are pretty easy to get to. I would not want to mess with the trim tabs or much else on the back "shelf" (basically under the swim deck) past the engines, though.

When I was having trouble with my vacuflush and was worried about maybe replumbing the waste line from the head, that gave me an ill feeling, too, I have no idea how you'd replace that in the original path. Maybe its easier if you open up more access panels or something, but I started thinking about McGyver solutions, like scrubbing and relining the hose with flexseal.

 

[Soulshine]

I see your point, but in my case with inlines and a wide beam there are only a few things that are tricky to work on. Anything drive related is cake.

I’m off the outdrive thing for a slipped boat myself after having twin IOs in a smaller boat for years. Literally everything was a PITA to work on and the maintenance was a hassle.

Of course your 310 is roomier I’m sure.

 

[mobocracy]

I see your point, but in my case with inlines and a wide beam there are only a few things that are tricky to work on. Anything drive related is cake.

I’m off the outdrive thing for a slipped boat myself after having twin IOs in a smaller boat for years. Literally everything was a PITA to work on and the maintenance was a hassle.

Of course your 310 is roomier I’m sure.

Heh, the added space with I/Os *in this specific hull* is about the only selling point for outdrives, IMHO. But I couldn't work on these outdrives even if I knew how (marina, access, etc), so having the space in the engine room to do what I can do kind of makes up for it.

 

[Soulshine]

Yep. Every time I’m working on my boat with the hatches off and someone walks up they comment on the roominess. I could lift my engines straight up and out with the transmissions still attached with clearance to spare.

If my generator wasn’t right in the middle and aft, everything would have similarly easy access.