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.
Author:
Updated:
Original:
TankSensor
 Everything you need, clockwise from upper right: control unit, cables, three sensors, display head

Everything you need, clockwise from upper right: control unit, cables, three sensors, display head

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. 

TankSensor4

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.” 

 We mounted our display next to the electric toilet control in our head

We mounted our display next to the electric toilet control in our head

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

Pico-Michael

Cruising: Less (LOA) is More

The breeze kicks up. The boat digs in, and I tighten my grip on the mainsheet. It’s overcast but warm. The slate-blue water around me is patterned with whitecaps. Ahead, the low, tumbling hills of Old Mission Peninsula, a 17-mile long finger of land separating the east and west ...read more

2020-06-01_13-53-06

A New Era for Sailing Program Safety

As states begin to lift restrictions on gathering and marinas open back up, many sailing programs are still wary, especially since sailors from different households will necessarily be in close quarters, whether on their boat, in a launch or at a yacht club. Most will not be ...read more

MTcyNTIwMzc1NDYzMTkyNDkw

Zipwake

Zipwake Series S, the world's first inexpensive dynamic trim-control system, incorporates a state-of-the-art family of durable, fast-acting interceptors. The system is fully automatic, and is designed to significantly enhance performance, fuel economy, comfort and safety when ...read more

CCA-story-2048x

Safety Culture Starts with the Skipper

Sailing might not be the first pastime that comes to mind when you think of extreme sports, but that’s not to say risks don’t abound. The Cruising Club of America tackles many of them head-on in their newly released guide for skippers, Creating a Culture of Safety: The Skipper’s ...read more

GMR19_F53_0539

Boat Review: Beneteau First Yacht 53

Luxury performance-cruising isn’t entirely new. You can go fast and still be comfortable. You can even race if you make the right tradeoffs—or so says Beneteau, which recently launched its First Yacht 53, in the process also reinventing the company’s “First” brand. Design & ...read more

BirdonBoard

Cruising: Birds of a Feather

One of the neatest things about sailing offshore is the other lifeforms we encounter. We smile when we see flying fish skimming over the surface of the sea. We cheer when dolphins leap and dance in our bow waves. We are duly reverent when mighty whales sound and spout, and ...read more

pirate-marlin-logo

Pirate’s Cove Billfish Tournament

This Spring has felt a bit like a slow day of fishing but it’s almost time to time to Bait…and Switch. The Pirate’s Cove Billfish Tournaments offer something for every member of your crew. Exceptional fishing, fun times with family, old friends and new. Our run is short, our ...read more