Danish underwater robot polishes propellers

17. januar kl. 10:31

By Søren Rosenberg Pedersen, Journalist at the danish news site Ingeniøren.

Read the articel online Here: https://ing.dk/artikel/danish-underwater-robot-polishes-propellers

In mid-December 2023, SubBlue Robotics carried out an important test at the Port of Aarhus. The picture here is from a test carried out on 17 January 2024. Illustration: SubBlue Robotics.

SubBlue Robotics has carried out important tests of an underwater robot that can polish ship propellers. The robot should provide a safe and sustainable service to ships, while saving shipping companies money on fuel.

On a cold and stormy day at the end of December, Odense-based company SubBlue Robotics tested a new prototype of a remote-controlled underwater robot. The robot, which is the first of its kind, can polish the propellers of large ships and remove fouling such as barnacles. Here in the December cold, it will be put to the test.

Engineer Don Fischer, CEO of SubBlue Robotics, has arrived with the robot, a diesel generator, and some colleagues at the Port of Aarhus. Already the day before the big test, the wind has picked up, and there are gale force winds in some parts of the country. It is nine o’clock in the morning when Don Fischer and his team begin setting up.

“We enter the port, get set up, and start doing some diving tests with the robot. However, we do not manage to polish the propeller before we are asked to move, as some cranes have to be moved around. We use the time to inspect the propeller we are planning to polish,” Don Fischer says.

Twenty hours of testing

It is 2 p.m. before the robot can get back into the water, and an hour later it can start polishing the propeller. The test continues for the rest of the evening and night. Tired, after twenty hours of testing, the team can conclude that the operation has been a success.

“This is the first time we have let the robot operate for twenty hours without it breaking down. This is completely new for us. It was finished a fortnight ago, and yesterday was the second time we were out to test it,” Don Fischer says.

“The old robot we had broke down all the time, so we spent more time going to the port and screwing things together than we spent polishing ship propellers. The new robot here is built like a tank. Right down to the detail with what kind of connectors we use to connect wires.”

Clean propellers save fuel

Today, the polishing of ship propellers is carried out by divers. It can be both a time-consuming and dangerous process, requiring a diver to spend many hours underwater, which has caused accidents and fatalities over the years. In general, several ports have over time made diving prohibited in the port area—for example in Singapore.

In some ports, however, diving is permitted, but not while unloading and loading. This means that ships must extend their stay in ports to have their propellers polished, Don Fischer explains. Therefore, some ships also wait to have their propeller cleaned until it is absolutely necessary.

“We know that there is a need to clean propellers more often than is done today. So, if we can ensure that a ship’s propeller can stay clean for a longer period of time, fuel is saved. A robot like ours can be sent down and polish the propeller while loading and unloading. And no one gets upset if a robot is lost—apart from us, of course,” Don Fischer says.

“Our vision, hope, dream is actually to make it so easy and accessible that every time a ship comes into port, the propeller is polished with the robot. And the buffing itself is done with a super fine polishing disc, so that the geometry of the propeller does not change, and it does not wear out too quickly. If it wears too quickly, or changes are made to the propeller during grinding, the ship again uses more fuel.”

The underwater robot, or ROV (remotely operated vehicle) is electric and on today’s occasion gets its power from a diesel generator that has been brought along. But in the long term, the hope is that the power can come from the port. Built into the side of the robot are electric thrusters that steer the ROV underwater.

Robot arm too heavy for land

A three-metre long waterproof robot arm, which SubBlue Robotics has developed itself, is also attached to the robot. The robot arm only works underwater as it is too heavy to operate on land. A strategic buoyancy is placed on it, which means that it is not completely weight neutral, but with small motors it can be controlled underwater.

“The degree of invention in the robot arm is relatively high. The fact that it must be waterproof makes it somewhat complex. While some robot arms are designed to operate super precisely, for example, if they need an accuracy of ten millimetres, we have created an enormously large and robust robot arm with an accuracy of half a centimetre. This means that it works under water,” Don Fischer says.

“At the end of the robot arm is the polishing disc itself, which is an ordinary 3M Scotch-Brite disc, the same that divers use today. On the other hand, we have a water-powered unit with 200 bar pressure that makes the polishing disc rotate. At the same time, it produces a suction that picks up all the material that we polish off, so that it does not contaminate the marine environment with metals and fouling. All in all, we can carry out uniform and precise polishing on the entire propeller surface.”

The robot is controlled from a control room in a van at the port, where an operator manoeuvres the ROV with a joystick. From the van, a series of hoses and cables are connected to the robot to provide power, signal and buoyancy as well as lead dirty water up to a cleaning filter.

The operator can follow the robot’s movements on a screen that shows angles from four cameras on the ROV, such as four cameras at the end of the robot arm. The propeller itself is illuminated by eight powerful LEDs, so that the entire sea lights up. Don Fischer puts it as using what they consider indirect light.

The ROV attaches to the propeller, the robot arm unfolds, and the polishing can begin. The robot arm is semi-automatic, so it has a feedback loop that calculates the orientation in relation to the polishing disc.

No problem areas

“We are very happy with the test we have carried out. It’s only been a fortnight since we completed this prototype, and to our great amazement, it works. The thoughts and ideas we’ve had have turned out to be right. We’ve confirmed that we can now polish the entire propeller. There are no problem areas. We were also nervous about whether we could get the hub. That succeeded too,” Don Fischer explains.

The SubBlue Robotics team will now continue their tests, going out once a week to see what else the ROV can handle and for how long. Don Fischer expects that a fully operational version of the underwater robot will be ready within the next six months. At the time of writing, negotiations are underway with several shipping companies.

“Right now, we’re focusing on finishing the final robot, and then getting a business up and running. In the future, we would like to have more things automated, so that the robot can eventually dive down and polish the surface on its own. In the long term, we dream of sonar, computer vision, and all those buzzwords. We’re actually working on that a bit already,” Don Fischer concludes.