HomeProjectsChallengesThe AccountingThe NameMusingsOn-Water Photos
Hot Water On the Cheap


One of the reasons we decided to spruce up this boat so much, rather than trade up to a larger boat, is that I am reluctant to cross the line past which the number of boat systems and their levels of complexity increases dramatically.  More electronics, complicated electrical systems and the accompanying monitoring equipment, fancy galleys with large electric and water needs, hot water, refrigeration and air conditioning – all nice, but are consumers of space, energy, and especially money.  For the one or two two-week cruises, the few overnighters, and the mostly day-sails that we use our boat for, I, well, just don’t want to cross that line.  However, I have to admit that human bodies confined to any boat for days at a time could greatly benefit from at least one of those luxuries – hot water.

This had been in the back of my mind for some years and I had been wondering if there was some way to get hot water without giving up much storage space or adding an energy source such as a large battery bank or shore power.  This far along in the renovation of Ayacucho almost all unused space had been turned to some use, so locating a tank or heating unit would require something draconian, I thought. 

I did, however, run across an idea that another Tartan-30 owner came up with that really struck me as a clever way to go.  It was a vertically mounted, long and narrow tank/heat-exchanger made of 6-inch PVC pipe and copper tubing that stood in the aft inside corner of the head on his boat.  He plumbed it to the engine cooling system, and with manual controls he claimed he had a workable, satisfactory system.  Good, there’s an idea I could steal.  It wouldn’t be the first.

But I had a bit of a problem since earlier I had moved the head door back 5 or 6 inches and reversed the hinges.  The space in that corner could now only accommodate maybe a 2-inch pipe – and the forward inner corner wasn’t any better because of the toilet platform.  Dang!  Now what?  This was like trying to solve a riddle.  The space I needed had to be long.  It had to be close to the engine.  It had to be close to the water system. It couldn’t displace something else unless I realistically could relocate that something else.  I’d rather not be able to see it. If you have been following this site you know that sooner or later I’d figure something out (No vanity here).  I did, and it’s even better!  Determination, as much as necessity, is the mother of invention.

There is some space behind the settee back where we store some bulk stuff like paper towels, water jugs, and of course, wine when we cruise.  But all that sat on the settee bottom cushion.  A cabinet running the length of the settee forms the top of this space.  Aha!  The underside of the cabinet!  It’s nearly perfect since the stuff stored under it does not go so near the top. A pipe can be completely hidden there and yet be very accessible.  The space can accommodate 6 ½ feet of 4-inch PVC.  That gives me 4 ½ gallons of additional water capacity, bringing the total to just shy of 40 gallons.  The outlet to the engine coolant is about 3 feet away.  Access to the water pressure system is 18 inches away.  And as a bonus the head faucet is just 12 or so inches away (or would be after moving the faucet so that the hose to it is always above the head counter).  This is too good.  I must have missed some obvious obstacle, but it wasn’t so.  As the idea progressed even more advantages surfaced.


The design is very simple.  Inside the length of PVC pipe common ½-inch household copper tubing runs from the forward end of the pipe to the aft end, turns 180 degrees and returns to the front of the pipe.  Basically I soldered together what looks like a long narrow trombone slide.  The ends have hose barbs; one hose connects to a diverter valve fitted to the coolant outlet at the back of the engine’s exhaust manifold, and the other connects to a tee at the intake at the bottom of the regular heat exchanger that sits just forward of the engine.  The diverter valve’s normal position (hot water system not in use) directs hot coolant to the regular heat exchanger inlet.  Turning the valve so that it points toward the hot water pipe (easy to remember) redirects the hot coolant to the tubing that loops inside of the PVC pipe and then on to the inlet of the regular heat exchanger.


Pipes offset so hot water exits at top



Water from the outlet of the ship’s water pressure pump is directed into the PVC pipe through a hose barb located on the bottom side of the pipe at the midpoint between the ends.  Water fills the pipe and is heated by the hot coolant inside the copper tubing.  It then exits either at the top edge of the forward end of the pipe where it supplies the head faucet, or at the bottom edge of the aft end of the pipe where it supplies a line to the galley sink and to a rinse hose at the transom.  Having one end exit high and the other low allows for purging of both air and water.

After giving it some thought I decided to let all faucets be for hot water.  This is not a full-time or really ”hot” water system; so heated water is all you need for showers, dishes and swim rinses.  Drinking water comes from jugs and the heated water is likely cool enough for brushing teeth by bedtime.  A manual pump at the galley sink still provides cool water all the time, but we rarely use it.



Here’s where the system shines.  After pulling into an anchorage and while the engine is running at or near idle, I turn the diverter valve to engage the hot water system.  While at idle I watch the engine temperature gauge rise to about 180 degrees.  I then switch the valve back to normal and return to the cockpit and shut down the engine.  All this takes about 2-3 minutes with a warm engine, about 7 minutes with a stone cold engine. The reason for the quick heat-up is that the small volume of water in the PVC pipe heats quickly and actually cannot cool the engine for very long.   I found that after switching the valve while at cruising speed the engine temperature heads up sharply after a less than a minute.  The diverter valve can be partially turned to proportion the coolant between both exchangers; however, I have not played with that since heating at idle works so well.

The temperature of the water is then about right for a shower or an after-swim rinse.  But for some reason, long routing I suspect, water to the galley loses some of its heat and comes out tepid.  We’ve gotten into the habit of pouring off some hot water from the head into one of those insulated coffee dispensers, and saving it for dishes later.  That works OK.  Of course, as hot water exits the pipe the water pressure is pumping cool water into the pipe, which cools it.  But that is why the pipe inlet is in the middle.  Water tapped from the ends should stay mostly warm until cool water ventures from the middle.  In practice, a couple of good and surprisingly long showers in addition to the dishwashing reserve are what we’ve experienced.

Total cost: about 160 bucks.  My kind of system.