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:

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

02-'17-Trans-Atlantic_Downwind-Schralpin

At The Helm: Man Overboard!

Imagine this simple scenario: the boat’s powered up, sailing close-hauled in a building breeze under full sail. I come on deck as the skipper during the watch change to make sure the new crew is comfortable and the boat is properly set up for both the current conditions and ...read more

Promo-01-LEAD-MGR00321

Contrasting X-Yachts & Moody Cruisers

One of the most fascinating things about sailboats is the different ways that sailors, naval architects and builders will approach a single design problem. The result has been a bewildering array of rigs and hull forms over the years, and in the case of the two boats we’ll be ...read more

04-Yacht-anchored-in-front-of-one-of-Lastovo's-gunboat-tunnels-(3)

Cruising Charter to Croatia

As is the case with so much of the Mediterranean, to sail in Croatia is to take a journey through time. Centuries before the birth of Christ, Greeks traded amphoras of oil, wine and grain across these waters. During the first millennium, the Romans built lavish palaces and ...read more

m123728_13_01_171012_PMA_02901_9999

Alicante Announced as an Ocean Race Europe Stop

The Ocean Race Europe, a new event in offshore sailing, will include Alicante as one of four stopover cities. This European offshoot of the former Volvo Ocean Race will include the biggest change to the racing rules under the new title—fully crewed IMOCA 60s will join the ...read more

01-LEAD-doublehanded2

Preparing for a Doublehanded Race

A few months ago we took a look at the development and attraction of doublehanded racing (Two to Tango, June/July 2020). Hopefully, that served to whet your appetite. If so, the question becomes: “How do I get started? The good news, as we explained in Part 1, is that if you are ...read more

01-LEAD-Day-three---dolphins.-300-dpi

A Key Approach to Passagemaking

How you approach offshore sailing is key to the success of each passage. In addition, some of the most valuable, even crucial attitudes and skills may not be either learned or valued in everyday life on shore and may even fly in the face of talents that are greatly admired and ...read more

OceanVoyagesInstitute-2048

Point of SAIL: Mary Crowley of the Ocean Voyages Institute

In this episode of Point of SAIL, Principal Editor Adam Cort talks with Mary Crowley, founder and executive director of the Ocean Voyages Institute, a not-for-profit based in California that has been both educating sailors and working to preserve the health of the world’s ocean ...read more

01-Ocean-Voyages-Institute_PHOTO-READY_1_pg

Tracking and Catching Plastic Waste

Plastic waste—in the form of everything from plastic soda bottles to abandoned fishing nets—constitutes a major threat to the health of the world’s oceans. Giving the immense size of an ocean, though, actually finding all the plastic floating around out there in a time-efficient ...read more