There are custom solutions for measuring the contents of odd-shaped storage compartments.

The shape of water tanks that are situated against the hull makes it difficult to get an accurate reading of the water levels. Gauges that use a float sensor (above) need to be calibrated for the specific tank.

Cruising World

One of the instruments I find most useful on a boat is the gauge that indicates the amount of fresh water in the tanks. If there is one thing you need to know when out cruising, especially if you don’t have a watermaker, it is an accurate indication of how much drinking water you have.

Over the six years I have owned my Down East 45 brigantine schooner, Britannia, I have expended endless hours messing about trying to get the twin water-tank gauges to register correctly.

Britannia has two stainless-steel water tanks amidships, one on each side. The shape follows the curve of the hull and is therefore somewhat triangular in cross section, tapering to a point at the base. This makes accurate calibration of any type of measuring system difficult because when the water is halfway down the vertical side of the tank, the actual capacity is much less than half full — only about one-third full in my tanks.

I considered installing a transparent sighting tube up the outside of the tank, but since my tanks are enclosed by bulkheads on all sides, I couldn’t easily drill a hole in the bottom of them to install plumbing fittings and a clear plastic tube. Even if I had managed to fit a sighting tube in each tank, I still would’ve had to physically mark the tube at various capacity levels. To read it would also have required lifting the floorboards on each side every time.

The original system was pneumatic (air) operated. It was supposed to read the air pressure differential in a thin pipe as the water level in the tanks varied and register on the gauge. Basically, it is a simple concept, having only two components and no electrical circuits. Just the device for a cruising boat, you might think.

But the system never worked properly from the day I bought the boat. The gauge would frequently drop 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.

To cut a long, frustrating story short, I never did find out why the system didn’t work properly. Finally, I decided to look for a reliable alternative.

 
old fresh water gauge

The old gauge used air pressure to measure the water level. Unfortunately, it never worked correctly. Roger Hughes

The shape of the tanks meant that a simple electrical swing-arm float sender would not register accurately, because when the arm is halfway on its arc and the gauge registers half full, it will not be correct. There is also a baffle in my tank, which would obstruct a swing-arm system.

There is a product called the Tank Tender that works on the same pneumatic principle as my original equipment. To overcome tank-shape problems, its gauge is calibrated in inches of water. It is for the buyer to determine how many inches corresponds to any particular capacity. The manufacturers told me that most owners mark their gauges with an ink marker at the quarter, half and three-quarters point. This would be accurate, but from my experience, I was concerned about pressure leaks in any air system, and I would have had to have two gauges, one for each tank. The cost for two tanks would be about $570.

There is a product called the Tank Tender that works on the same pneumatic principle as my original equipment. To overcome tank-shape problems, its gauge is calibrated in inches of water. It is for the buyer to determine how many inches corresponds to any particular capacity. The manufacturers told me that most owners mark their gauges with an ink marker at the quarter, half and three-quarters point. This would be accurate, but from my experience, I was concerned about pressure leaks in any air system, and I would have had to have two gauges, one for each tank. The cost for two tanks would be about $570.

 
sender units and gauge

The new custom device includes two sender units and a gauge. Roger Hughes

I then found an electrically operated device, made by KUS USA in Fort Lauderdale, Florida. This product also uses a vertical stainless-steel tube inside the tanks, but instead of working on air pressure it has a float that travels up and down the tube, activating electrical signals inside the tube, which are read by the gauge. The sender tube’s top flange fitting also matched the standard SAE five-hole pattern in the top of my tanks, so I would not have to drill and tap any new mounting holes — or so I thought.

 

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Source: www.cruisingworld.com

 


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How to Install a Custom Tank Gauge
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