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.
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 each 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 1½" 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 1½" inch circle then enlarged them with a ¼" 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.
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.