Bio-Fouling in the North Sea…things can get…well…pretty slimy.

        (keeping optical sensors clean: How Hydro-Wipers are helping researchers)

“What you are looking at is the recovery of our Dowsing SmartBuoy, (located at 53.531N, 1.053E) after 3 months in the North Sea”.

Tom Hull, Marine Observation Scientist, took the time to share with Zebra-Tech about a recent annual nutrient baseline survey and SmartBuoy maintenance trip and his use of Hydro-Wipers. Tom works for CEFAS – the Centre for Environment, Fisheries and Aquaculture Science in the UK.

keeping optical sensors clean - Cefas Smart Buoy after 3 months deployed in the North Sea
figure 1: The Dowsing Buoy after 3 months.
CEFAS Smart buoy uses Hydro-Wipers for anti-fouling - keeping optical sensors clean
Figure 2: The Buoy as it looked prior to deployment.

The problem: Bio-fouling.

Not very clean is it? Bio-fouling, especially among the buoys deployed closest to the shoreline, can interfere with data gathering within a fortnight. Hardly ideal when trying to run an extensive long term Eutrophication monitoring program.


As the UK’s “most diverse applied marine science centre”, CEFAS helps to shape and implement policy through their “internationally renowned science and collaborative relationships that span the EU, UK government, non-governmental organisations, research centres and industry”.

They achieve this through collecting, managing and interpreting environmental, biodiversity and fisheries data including through their annual nutrient baseline survey in the North Sea using SmartBuoys.

Hydro Wipers

What is a Hydro-Wiper?

Hydro-Wipers are a rugged mechanical wiper designed to gently remove sand, grit, mud and biofouling from underwater sensor windows and camera lenses. Keeping optical sensors clean.

Ensure data quality, deploy sensors and cameras longer, save money!

Hydro-Wipers are designed and manufactured at Zebra-Tech. A New Zealand based underwater equipment manufacturer.

keeping optical sensors clean - Cefas Smart Buoy after 3 months deployed in the North Sea
Figure 3: A Seapoint turbidity sensor after a 3 month deployment in the North Sea. The sensor is still free from biofouling.

Time, money and data:

Real savings with Hydro-Wipers.

This SmartBuoy forms part of a network of water quality buoys placed at key locations around the UK shelf.

As you might expect, the maintenance program required to keep this network going is costly and labour intensive. The CEFAS Endeavour, a research ship is used to swap out each SmartBuoy with a replacement on a pre-planned schedule.

Despite this maintenance program, data quality can be compromised by bio-fouling in a very short time. As it is prohibitively costly to constantly check and clean instruments, a viable bio-fouling solution is needed to extend deployment times without risking data loss.

Hydro-Wipers provide real cost saving benefits

The Hydro-Wipers role – keeping optical sensors clean.

Tom explains that “The Dowsing SmartBuoy is equipped with our CEFAS built and designed ESM2 data logger, which is fitted with a range of sensors including the Aanderaa optode and Seapoint chlorophyll fluorometer and optical backscatter sensors which are coupled with the Zebra-Tech Hydro Wipers”.

The buoys (most of which are funded by DEFRA, The UK’s Department for Environment, Food & Rural Affairs) deployed on this trip have been fitted with Hydro-Wipers. Together with some “strategically placed copper tape to discourage growth in key areas”.  He hopes that the time each buoy will now be able to spend on deployment, gathering good data, should be more than doubled.

The Results:

“Biofouling is the primary cause of data loss at our coastal sites and the use of the Zebra-Tech wipers has enabled us to extend the length of our deployments, significantly reducing the amount of ship time the program requires”.

A Hydro-Wiper gently cleans
Figure 4: A Seapoint Fluorometer with a bright shiny sensor good data.

“The sensors have not been damaged by the wiping action. This is particularly important for the Oxygen sensors which have a thin permeable membrane rather than a hard quartz glass”.

These results are very typical of  Hydro-Wiper assisted deployments. The wiper is designed not to fail in front of a sensor window, defaulting back to a “home” position if the arm is bumped or battery power becomes low.

The unit is robust and is engineered to exacting standards in Zebra-Tech’s New Zealand workshop. Customised options are also possible.

Contact Zebra-Tech

Ask us about our Hydro-Wipers for a wide variety of optical sensors.

More about the SmartBuoy:

“SmartBuoy has been developed to provide a reliable, cost effective platform that can collect physical, biological and chemical data over extended periods (> 1 yr.). Its introduction into the UK marine monitoring programme is important for the development of an effective monitoring strategy for improved assessment of nutrient status and ecosystem responses against a background of increased concern over the health of European coastal seas”. (

While primarily targeted at eutrophication monitoring, they also serve as valuable R&D platforms and provide essential observations for climate, biogeochemical and ecosystem models.

Near real-time data from the SmartBuoys is publicly available and can be found here

Examples of some of the science done with the CEFAS SmartBuoy data can be found here and here.


More about Zebra-Tech’s Hydro-Wiper:

Built to last, mechanical Hydro-Wipers gently wipe the surface of sensor windows and lenses. Keeping optical sensors clean – without damaging delicate membranes, allows longer deployments. Designed to be deployed in harsh environments for months at a time, the wipers incorporate “failsafe” features to ensure that data quality is not compromised. For example, if the unit is bumped, or moved, it automatically senses its position and readjusts so that the wiper brushes do not stop over the sensor.

The Hydro-Wiper is customizable and available for a wide range of sensors and cameras. Zebra-Tech engineers can work closely with the customer to develop customised solutions if needed.

The CEFAS Endevour

“CEFAS Endeavour 242” by RHaworth – Own work. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons