There can be few instruments on a boat more important than that which indicates the exact amount of fresh water in the tanks. If there is one thing you need to know on a cruising yacht, it is an accurate indication of how much drinking water you have, especially if your boat doesn't have a water-maker. The accuracy has been a problem on every yacht I have ever owned.

tanks   My present 45’-foot schooner BRITANNIA has two stainless steel freshwater tanks amidships, one on each side. The outer shape follows the curve of the hull and the tanks are triangular shaped in cross-section, tapering to a point at the bottom.  This shape makes accurate calibration of water capacity difficult by most measuring devices, because when the water is measured halfway down the vertical side of the tank, the actual capacity is much less than half full—only about 1/3rd in Britannia's tanks. This physical divergence even applies to the simplest method of reading volume in odd-shaped tanks (and definitely the most reliable), a transparent sighting-tube up the outside of the tank.

   I considered installing sighting-tubes, based on the well-known KISS principle which applies to lots of things on boats, (keep it simple stupid). However, both tanks are fully encapsulated by bulkheads at either end, and it would be a major operation to drill a hole in the top and bottom of the heavy gauge steel tanks to install plumbing fittings and a clear sighting-tube. Even if I had managed to fit a tube on the outside of each tank, reading them would mean lifting the floorboards in the saloon every time I wanted to read the tanks.

   The original system was, (note the past tense here), pneumatic (air) operated, which works on air pressure differential as the water level in the tanks varies. It is a simple concept having only two components, a vertical pipe in the tank and a gauge, and no electrics other than illumination of the gauge. Just-the-job for a cruising yacht you might think.

original-tube-&-gage   A rigid plastic pipe mounts vertically inside the tanks from top to bottom, (at least, that's what I assumed), and is connected to a gauge by a long thin flexible nylon tube. As the water level varies in a tank, the air pressure changes in the tubes and is recorded on the gauge. However, my system never worked properly from the day I bought the boat. The gauge frequently dropped to zero, sometimes immediately after a tank was filled to the top, or sometimes slowly over a few days. The whole thing was erratic and unreliable.

   Since there are no electronics involved, there had to be an air leak somewhere in the connections between the tank pipe and the gauge, or even in the gauge itself. I installed new thin tubing and even sealed the connections with epoxy, but the thing still failed. I even dismantled the gauges and examined the delicate clock-like mechanism in minute detail, tightening the tiny diaphragm mounts, and inspecting the moving parts, all to no avail. I conducted water tests by removing the complete assembly and immersing everything in a bathtub, expecting to see air bubbles to identify a leak. Finally, I even submerged the gauge itself, but still no air leaks were visible.

   To make a diagnosis even more difficult, the original manufacturers had long-since gone out of business and I could find no information anywhere on the internet. The chances of getting help, or spare parts, was therefore slim. To cut a long, frustrating story short; I never did discover why the system kept failing. Finally, I decided to look for an alternative to replace the whole useless thing.

   The shape of the tanks meant that even a simple electrical swing-arm/float sender, (by far the cheapest device, available from any car-parts store), would not register accurately, because when the arm is halfway along its ark and the gauge registers half full, it will still not be accurate. There were also baffles in my tanks which obstructed a swing arms full travel.

   I found a product called "The Tank Tender", which works on the same pneumatic principal as my equipment. To read in various tank shapes the tank tender gauge is calibrated in inches of water, and it is left for the user to determine how many inches corresponds to a particular capacity. The manufacturers told me that most owners physically mark their gauges at the quarter, half and three-quarters point. This would indicate the capacity accurately, but from experience with my own air system I was concerned about leaks over time. I would also have had to have two gauges, one for each tank. The cost for two tanks would be about $570.00

Tank-top-fitting   I then found an electrically operated system, made by Wema/Kus USA. in Fort Lauderdale, Florida. The company also export to the United Kingdom.  www.wemausa.com/sensors/level-FuelWater.  This employs a vertical, stainless-steel tube inside the tanks, but instead of working on air pressure it has a float which travels up and down the tube. As the float rises and lowers, it activates electrical impulses in the tube which are then read by a gauge. Luckily, the tube's top flange fitting to the tank also matched the standard SAE (Society of American Engineers), five-hole pattern in the top of my tanks, so they should mount directly into the existing hole, and I would not need to drill and tap any new mounting holesor so I thought.

   Another advantage of the Wema/Kus system is that the signals from the tank sender can be calibrated up the height of the tube and register on the gauge. This would overcome the main objection to any gauge reading system and all the manufacturers needed from me was a sketch, showing where the three water levels I wanted were on the tube in the tank. This would ensure the gauge would read the correct volume of water in the tank, throughout the whole range. Info@kus-usa.com

 Tank-gage  Kus also supply a twin tank gauge on a facia panel with a switch. When this is switched to one side the gauge reads from one tank, and when switched to the other it reads from the other tank. In the middle, the switch is off and no electric current is being used. However, for this gauge to register accurately on twin tanks, both must be the same shape and capacity, which my tanks are. The gauge also lights up when reading a tank, with a choice between red and yellow illumination.

water-flow-meter   The first test I therefore needed to conduct, was to find out exactly how much water the tanks actually held. I drained both tanks by running them dry through the boats sinks, then refilling them one at a time using a flow meter fitted to the water hose. I bought this from Amazon.com for $14.96 (part # P3-P0550). The actual capacity is 160 Imperial gallons on each side, a total of 320 gallons, (1455 Litres), eight more than the boat builder’s specification.

   To find exactly how long the new tank sender tubes needed to be I measured the depth with a length of 1/4" inch diameter wooden dowel. This measured 31" inches to the bottom of the port side tank. The tube would not go to the exact bottom of the tank due to the curvature, so I settled for 29" inches. This was when I realized the original tubes, which were only 21" inches long, could never have registered accurately even when they worked properly, because they were 8" inches too short and never reached anywhere near the bottom of the tank. I calculated this produced an error of about 25 gallons on eachTank-kit side.

   Having determined the exact tank volume, I took the opportunity to sanitize them with two gallons of swimming pool chlorination liquid, then I drained the tanks once more. I then ran 42 gallons into the tanks, this being one-quarter of the total capacity, then measured the water level with my wooden dipstick. Then I poured in another 42 gallons and measured were half full actually was, then another 42 to bring the capacity to three quarters. I added these physical measurements on my sketch, which I e-mailed to the Kus engineers. I received my kit within two weeks.

                                                            INSTALLING THE NEW SYSTEM

   I drained the tanks once more, then lowered the port side tank tube through the hole in the top of the tank. This was when I discovered that the standard SAE five-hole plate does not have symmetrical holes around the top of the plate, even though it looks like they are equally spaced. There is in fact only one position the plate can be fitted and to find this I had to rotate the plate and gasket, until the holes all lined up with the screw holes in the tank. I kept losing the location of the gasket and plate until I actually glued the gasket to the top of the tank, then rotated it to mate with the holes. I screwed five machine screws in the top and tightened in on the gasket.

   As I inserted the starboard side sender tube an unforeseen problem arose. As I lowered it into the tank the end of the tube bottomed against the tapered side of the tank, and would not go fully into the tank, and the top plate would not sit flat. I took some measurements with my dipstick and discovered the hole in the top of this tank was 6" inches nearer the outboard curve of the tank, causing the tube to catch against the side. There was nothing to be done, except to cut a new mounting hole in the same place as the port side tank.

  This meant first cutting out a square piece of the saloon floor boarding to gain access to the top of the tank. I did this with my oscillating multi-cutting tool fitted with a plunge cutter. Drilling into the tank top presented another problem, because fillings from the drill would certainly fall into the water tank. I positioned my vacuum nozzle close to the drill bit, and this captured most of the swarf. The float on the tube needed a 1" inch diameter hole in the top, but a hole-cutter would not even scratch the top of the 1/16" thick (16 SWG) stainless tank. I therefore drilled a series of 1/8" inch holes very close to each other in a 1" inch circle then enlarged them with a " inch drill, which joined the holes together. I was then able to lift the centre piece out of the top of the tank. The resulting hole isn't pretty, but it is covered-up by the sender top plate.

   I lowered the sender tube into the tank, where it went all the way to the bottom of the tank. I still had to drill and tap five new holes for the top plate. I drilled only one of the five securing holes and tapped a thread, then screwed the plate tightly in place. This prevented it moving while I drilled the other four holes and tapped them, thus securing the top plate. I used the original top plate and a home-made blank gasket to seal the old hole in the tank.

wiring-diagram   The gauge was easier to fit, but it did need more than a normal 2" inch round hole to mount it. It is more like a square hole, and a paper template is supplied to stick in place with tape, then the corners can be drilled, and the spaces between them cut out with a keyhole saw. I wired the gauges through a spare contract breaker on the master distribution panel.

   It was then just a matter of refilling the tanks with the flow-meter, in one-quarter increments, and checking the gauge registered correctly in both tanks. It was gratifying to see it stop at each incremental level.

   Of course, it is important always to be aware that the reading from any tank system, including even a simple sighting tube, will be slightly incorrect when a yacht is under sail and even slightly heeled. I suppose the only remedy for that would be gimbaled tanks…??

   Kus make a similar system for fuel tanks, because the same problem exists on any yacht when diesel tanks are also formed to the shape of the hull. At least, when running an engine, the approximate consumption can be estimated by knowing the hours/fuel ratio—unlike freshwater consumption.

   It is now a relief knowing I have reliable water gauges showing the capacity for each tank. This enables me to maximize and enjoy the usage, according to whatever length of passage we are making.

Articles by Roger appear regularly in these boating magazines, about improvements to Britannia and other nautical matters

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