Back / Company & product news / 25.02.2020

Introducing a highly accurate speed log for large ships

Intelligent data processing is central to the performance of the new Doppler speed log created by oceanographic instrumentation specialist Nortek, which makes sure that accurate measurements of vessel speeds are available even in challenging conditions at sea.

Providing accurate and reliable measurements of speed through water is key to monitoring vessel performance. But it is a constant complaint in the industry that existing speed logs are generally neither reliable nor accurate enough to meet today’s performance requirements – and these issues have been confirmed by research. 

210b-goa_part2__8-01.jpg#asset:13748The Nortek Speed Log applies the Doppler principle to measure speed through water with the help of its four beams.

Many speed logs on the market advertise high accuracy. They achieve this in ideal conditions, with calm water, no wind and no strong currents. But a speed log needs to be accurate in non-ideal conditions as well. 

Nortek has therefore developed a speed log that has been shown to have much better accuracy than its competitors under real-life, challenging operational conditions. It has achieved accuracy to within around 0.5% consistently, even while sailing on the open ocean with varying wave and weather conditions. 

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.

Why measuring speed through water matters

Accurate measurement of speed through water matters because it is this speed that helps determine a vessel’s operational efficiency and rate of fuel consumption.

Furthermore, the maritime industry is focusing on the EU’s new monitoring, reporting and verification (MRV) regulation as well as the International Maritime Organization’s data collection system (DCS) rules governing emissions reporting. These regulations and rules mean there is an increasing focus on performance monitoring on board vessels – and that requires accurate measurement of speed through water. 

Nortek_speedlog-with-tube_sideview.jpg#asset:13749Nortek’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.

Measuring a vessel’s speed correctly has always been challenging, not least because there are two types of speed measurement on ships – speed through water (STW) and speed over ground (SOG). To take a simplified example, a vessel with a speed through water of 15 knots sailing directly against a current of 5 knots would only be making progress across the earth – its speed over ground – at 10 knots. Speed over ground can be measured fairly easily, for example by using GPS. But speed through water is more complicated to calculate accurately, requiring knowledge of currents and other forces acting on the vessel.       

Measuring speed through water is a challenging task

Measuring speed through water can be done using a speed log, which calculates the speed from a sensor mounted on the hull underwater, but it is not straightforward. There are a lot of variables to be considered. 

Read case study on Nortek's speed log pilot projects here!

One of the most challenging issues is that the vessel itself creates a flow field around the hull. If speed through water is measured within this field, you can end up measuring the wrong speed. This field will vary dynamically with changes in vessel, speed, draft and trim.

Nortek_speedlog_screen_sideview_illustation-01.jpg#asset:13750The touchscreen of the Nortek Speed Log display allows for easy user interface and operation.

A moving vessel also experiences pitch and roll – another factor that affects the readings. On top of this, flow patterns in the boundary layer around the hull created by the vessel’s movements need to be distinguished from ocean currents to ensure accurate speed measurement. 

Speed logs – especially widely used electromagnetic (EM) logs – often have poor reliability and become less accurate over time. They are also difficult to recalibrate, and often provide poor data quality, logging and data transfer.

Adjusting log data to compensate for the resulting errors is both time-consuming and complex, using valuable resources that the industry could better employ elsewhere.  

Providing real-time, reliable and accurate measurements 

With that in mind, Nortek’s engineers decided to develop what the maritime industry needs: a speed log that works! One that meets the needs of a digital world by providing real-time, reliable and accurate measurements.       

The Doppler-based Nortek Speed Log NSL500 has been developed in close collaboration with the maritime industry, taking advantage of Nortek’s experience gained over more than 20 years developing instruments to measure movement in water using the Doppler principle.

The NSL500 carries integrated sensors to correct for temperature, draft, pitch and roll. Advanced algorithms then adjust measurements based on these input parameters to ensure accuracy. Not only does it measure speed through water, speed over ground and distance, it also provides temperature and current profiles too, enabling owners to plan routes for better fuel efficiency.

Contact us to learn more.

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