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The missing link in vessel performance

The shipping industry has stepped up its investment in digital tools and technologies to optimise ship performance, cut costs, and tackle shipping’s contribution to global climate change, but CEO of Norwegian technology company Miros believes some companies are missing an important trick.

“We see a lot of investment in equipment like propellers and coatings, better drive trains, propulsion systems, even kites and sails,” Andreas Brekke, CEO of Miros, told delegates attending VPO Global’s forum held late last year in Copenhagen. “Companies are also spending a lot of money on sensors to monitor equipment they have invested in to improve performance.”

Speaking at the forum, Mr Brekke explained that while he believes this demonstrates a widespread commitment to improving vessel performance and efficiency, there is a missing ingredient when it comes to optimising and assessing new technologies. “How do we assess the effect of new technologies?” he asked.

An important parameter in order to be able to compare new equipment is to establish baselines, or comparable situations. This includes removing a major influence on vessel performance – the weather. “Everything that you are trying optimise will be influenced by weather,” he said, “You always need to take weather out of the equation to really understand how and why something is working in terms of performance optimisation.”

One way of understanding the impact weather has on vessel performance and gaining insight into the true effect a technology or method has on this performance is by creating an accurate speed through water (STW) measurement. “This can be difficult as STW will constantly vary thanks to local environmental conditions and will make a lot of the optimisation that you are trying to achieve even more difficult,” Mr Brekke explained.

Using hull performance as one example, greater accuracy can be determined by eliminating the weather factor. Measuring hull degradation requires measuring fouling over time, but the weather needs to be removed from the equation to get a true view of performance.

“We always see chartering contracts being quite weather orientated in their structure, but without really having the tools in place to monitor or follow up on the parameters stipulated in those very contracts. With onboard weather instrumentation, coupled with accurate STW measurements and fuel metres, the parties can efficiently monitor the performance of the contract.

“The more relevant and accurate data you have, the more confidently you can go into any type of charter party negotiation and talk about how your ship has performed and will perform.”

Optimising the speed-fuel curve

A new functionality from Miros designed to provide accurate STW measurements can be used to help optimise the speed fuel curve in real time. “When we measure STW on a moving vessel, we use the X-band navigation radar as our sensor, measuring the ocean surface in front of the vessel – the body of water being moved into, which is yet undisturbed by the vessel itself.

“We measure current speed, direction and course, and with specific algorithms we calculate STW very accurately. Wave and other sea state parameters can also be determined. This is all based on real-time measurements viewed from the ship in the ocean, with data pushed to the Cloud.”

One of the key challenges Miros observes in the maritime industry is the lack of understanding around which problem a company is trying to solve. “This is very important for digitalisation efforts, as the problem you are trying to solve needs to be clearly defined. You need a platform to aggregate all data and you need access to the right data which will help solve the problem at hand.

“We believe that some of the platforms available in the maritime industry today gather and display too many data points. If you’re trying to fix the speed-fuel curve, what you need is a flow metre, a torque metre and draught, and then you need accurate weather data. The combination of these three or four parameters gives you the first step towards truly optimising fuel consumption.”

The problems with current STW measurement

While there are a number of traditional methods to measure STW, according to Mr Brekke, there are some issues:

Speed logs – these can be acoustic or electromagnetic and can work well for certain purposes. However, the data is influenced by noise and systematic errors caused by air bubbles, turbulence, inhomogeneous hydrodynamics, fouling, and inadequate calibration. There are many operational issues, beyond maintenance, due to the nature of putting a sensor on the hull and trying to measure STW acoustically.

Models – model data generally suffers from a lack of local accuracy. Model data is best suited to explaining tidal parameters and periods of stable conditions. They deliver insufficient granularity in time and space.

How Miros solves the STW measurement issue

Over the last 6 months, Miros has tested and compared the effects of the company’s own STW technology, Miros Speed Through Water – a functionality of Miros’ Wavex Virtual Sensor – against a traditional speed log, as well as against model data (see figure 1.) As shown below, the longitudinal current components in metres per second varies between the Wavex data, the speed log data, and the model data.

Figure 2 illustrates the variations between different measurement principles further. The offset between Wavex and the speed log indicates that it would be difficult to adjust for the differences

“For this project that we conducted over a period of 6 months, we saw a variable offset of between 0.3 and 0.8 metres/s. That is a lot when this speed log is certified to measure at 0.1 metres/second.”

“The weather data from weather forecast providers is directionally in line with the Wavex data and shows that on a less granular level it coincides very well with both sensors.”

Figure 2 also illustrates that the offset is decreasing over time and then suddenly increasing again, which indicates some of the challenges with the offset of the speed log.

“Weather forecast providers do a great job with their models and can deliver the bigger picture, but one of the challenges is that the distance from the centre of the grid to certain measurement points in a weather model can be up to 25km, which is great on a weather routing application, but trying to provide a current measurement at the right time and the right place for it to be relevant for the exact location of your ship is by nature difficult for these kinds of data sets.”

According to the above data, Miros’ radar-based STW solution provides significantly less noise and more accuracy when it comes to measuring STW compared with traditional speed logs. Accurate STW data enables vessel owners and operators to make better decisions, specifically related to hull and propeller performance, weather claims, and speed optimisation.

For three years, Miros has been piloting its STW technology with several shipping companies including Höegh LNG and BW Dry Cargo providing verification of the accuracy of the Miros technology.

Miros CEO, Andreas Brekke, presented during VPO Global’s forum on ship performance and optimisation held in Copenhagen on October 22. 2019. Download his presentation here.

Source: VPO Global