19 minutes

Nortek brings scientific accuracy to commercial vessels with IMO-approved speed log

Nortek’s engineering team has carried out three pilot projects to test the reliability and accuracy of Nortek’s speed log in everyday practical situations on ships. The results from the pilot projects are uplifting!
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Installation of Nortek’s speed log, the NSL500, on board the three pilot vessels was completed within hours, and Nortek worked with the owners to provide easy retrofit solutions.

The first pilot, initiated in 2017, involved installing the speed log on a ro-ro cargo ship that sails along the Norwegian coast. As the vessel’s route took it past weather buoys fitted with ocean current meters (including a Nortek Aquadopp current meter), it was possible to make an accurate comparison of the data from these buoys, speed over ground data from GPS, and the NSL500 speed log on the ship. The results showed a close correlation between the readings. Nortek’s NSL500 also impressed with its ability to accurately read a current speed of just 8 cm/s, when the vessel was travelling at 13–14 knots.

Nortek’s speed log provides accurate readings in rough conditions

In the second pilot project, an NSL500 speed log was installed on another Norwegian cargo ship in summer 2018. This project was carried out with the Norwegian Research Council, Rolls-Royce (now a part of Kongsberg), the Norwegian University of Science and Technology (NTNU) and the Norwegian Meteorological Institute. This time the vessel had a very pointed hull, which meant the NSL500 had to contend with greater vessel motion. That motion became extreme when the ship encountered the worst sea conditions in our tests during a major storm at Christmas 2018, providing a stiff test for the speed log.

Read why Nortek has developed a speed log that has much better accuracy than its competitors.

The vessel sailed out of Kristiansund in Norway, before returning safely to port in waters that can be difficult to navigate at the best of times – they are in the same area where the Viking Sky passenger liner ran aground, just three months later.

The on-board instruments showed wind speeds of 20 m/s and a rudder angle of 25 degrees, so the vessel was struggling to move forward and avoid drifting.

Noise in the data intensified as the storm worsened, but it was possible to apply standard deviation to the figures to assess accuracy. This varied in a narrow range, between 0.01 m/s and 0.2 m/s, showing that the NSL500 was still able to provide accurate readings even in the roughest of conditions.

The high-end transducer and sensor technology found in the Nortek Speed Log ensures reliable and accurate speed through water measurements.

Testing the speed log’s abilities on the open ocean

The third pilot project tested the speed log’s abilities on the open ocean. In December 2018, the NSL500 speed log was fitted on a bulk carrier sailing long distances around the globe. The log provided stable readings consistently over multiple voyages and performed favorably when compared to the vessel’s existing EM log. Assessing data recorded over three days in the Strait of Malacca and the Indian Ocean, the NSL500’s standard error mean value was 0.074 knots at a mean speed through water of 13.3 knots – which is an error of just 0.55%. By contrast, the vessel’s existing EM log has an offset error of 1.5–2 knots when measuring speed through water at similar speeds.

The NSL500’s current measuring capacity meant the carrier’s crew could also accurately assess the strength of variable currents, such as the Agulhas current off South Africa.

Accurate and reliable

Nortek’s speed log is now IMO-approved. This comes after DNV GL has issued the «MED B» approval certificate for this groundbreaking, new speed log for the maritime market.

The NSL500 provides reliable readings over time and is self-calibrating, meaning that installation and commissioning are simplified and there is no need for further adjustment at sea. Nortek provides installation solutions for newbuilds and retrofits and can provide installation assistance. Pitch and roll and the vessel’s draft are all accounted for in Nortek’s algorithms.

In addition, the log can measure speed over ground in water depths up to 200 m and measure both the strength and direction of ocean currents. It also functions independently of water salinity, avoiding a major calibration problem for EM logs and other Doppler logs.

Users also benefit from the NSL500’s state-of-the-art data logging and user interface.

Nortek has listened to vessel owners and operators and has provided the improved speed log they were seeking – capable of accurate, reliable performance anywhere.


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