Skip to main content

Fitting a New Holding Tank Sensor

If your boat has a holding tank, chances are it doesn’t have a level gauge. This is odd, as you’d think they would be standard on all new boats, but in fact, just the opposite is true.

If your boat has a holding tank, chances are it doesn’t have a level gauge. This is odd, as you’d think they would be standard on all new boats, but in fact, just the opposite is true. After experiencing firsthand what happens when a holding tank is overfilled last summer—not at all a pleasant experience—we decided to fit a gauge to the holding tank on Poppy, our 60-foot canal barge, and set about researching the options. 

Sensors for tank gauges are positioned either inside or outside the tank. If you opt for sensors inside the tank, it clearly will be a more complex job than fitting sensors on the outside. However, inside sensors are less expensive. For example a simple “almost full” alarm that fits into the top of a tank costs relatively little, while a system that measures the waste actual level will cost a bit more. The downside in either case is that you have to drill into the tank to fit the sensor and presumably have to clean it periodically if it gets gummed up—a maintenance task I would not relish, for sure.

For simplicity’s sake—both in terms of fitting and future servicing—we opted for a system that senses the level of a tank’s contents from outside the tank. The initial cost is higher, but the savings in time and effort made this approach worth it.

The Gobius tank gauge, from Sweden, comes with three sensors, which reportedly work with almost any tank material, including steel, stainless steel, polyethylene and fiberglass. Poppy’s holding tank is a 60-gallon polyethylene type, so we didn’t envision any problems. 

The Gobius sensors work on the “knock and listen” principle, tapping on the side of the tank and listening for the echo, which tells the sensors whether there is liquid inside the tank and at what level. The face of each sensor is covered in 3M self-adhesive tape, so you literally just stick it onto the side of a tank. The three sensors plug into a control box connected to a separate display unit that can be fitted where it can easily be monitored—in our case next to the electric toilet control panel in Poppy’s head. The display features a series of LED lights to illustrate tank level. The control box is connected to the display with a Cat 5 computer cable, so the installation is “plug-and-play.” 

The Gobius system draws 40mA, and we wired ours to the toilet circuit, so it would be switched off when the toilet was off. Overall, we found the system was simple to fit, with clear instructions. One thing we learned the hard way was that you need to heed the warning that the sensors won’t stick to a tank if applied when the temperature is below 68F. The cabin on Poppy was just 64F when we started work, and the first sensor wouldn’t stick, so I turned on a heater and left the boat to warm up for a couple of hours. Later we fitted all three sensors without a problem. It really does pay to read–and follow–the instructions when doing jobs like this.

Photos by James Turner; Illustration courtesy of Gobius

CONTACTS

AB Marine (Gobius)

BEP marine

Centroid Products

Fireboy-Xintex

Groco

Hart Systems

Montour Marine Systems

Raritan Engineering

Sealand/Dometic Sanitation

Wema USA

Related

01-LEAD-IMG_2056

South Pacific Storm Prep

Having set ourselves the task of transforming our recently purchased Open 66 ex-Vendée Globe racer, NV, into a performance family cruiser, my partner, Timo, and I found ourselves (extremely) high and dry as cyclone season approached. The favorite cyclone strategy in Fiji is to ...read more

00-Alexe-1---GUaGKDY4-single-boat-sailing-away-from-skyline,-Hill-Holiday

Cruising: Find Your Own Adventure

Whether they’re at the end of their collegiate career or after aging out of a summer sailing program, a lot of young sailors have a hard time finding a way to continue sailing as adults. Some of the barriers to sailing, including location, finances and time, can be hard to ...read more

00LEAD-IMG_2183

Heavy Hitters on Heavy Weather

“What’s the joke about heavy weather? You know it when you see it.” Figure 8 singlehander Randall Reeves drew laughs from the Cruising Club of America (CCA) sailors attending the forum “Heavy Weather Sailing: Bluewater Perspectives” as part of the CCA’s centennial celebration in ...read more

Nominne-Promo-2048x1149

Best Boat Nominees 2023

The more things change, the more they seem to stay the same. Some of it is timing. Some of it is just the way of the world. Either way, it can be fascinating to see the evolution of the boatbuilding industry over the years, as has been evident in SAIL magazine’s annual Best Boats ...read more

NOAA-1280x

Notice to Mariners: 2023 Hurricane Season in Full Force

There’s so much going on in the news that you would be in good company if you didn’t realize the first major storm to hit the Caribbean was in full force. Hurricane Fiona is currently raging over the Turks and Caicos and is projected to make its way north in the coming three ...read more

StarWorlds2 Photo by Matias Capizzano

Star Worlds Celebrates 100 Years

The 2022 Star Worlds featured six days of intense racing where the final and deciding gold medal win went to Diego Negri and Sergio Lambertenghi of Italy. During some of the toughest sailing conditions in the race’s recent history, sailors and race management overcame daily ...read more

Screen Shot 2022-09-16 at 9.16.00 AM

Dockside Chat on 3D Sonar Technology

Over the years, these products have become simpler to use, smaller, and lower cost. This technology is both more advanced and more accessible than ever before. Bob has much to share with his extensive knowledge of seamanship, safety systems, and vessel operation. Matt is the CEO ...read more

01-LEAD-Caribbean-600---Feb-21th---Start(All)---High-Res-115

Offshore Racing with Brian Thompson

Brian Thompson could have become just another financial type on Wall Street, which would have been surprising enough in itself for a Brit who grew up in the London suburbs, reading Science Fiction books on smoke-filled commuter trains. From an early age, though, Thomson wanted ...read more