Our modern propeller design operating in a high efficiency nozzle gave the trawler MV Trygvason improved performance and lower running costs. |
Built in 1988, MV Trygvason is a single-screw trawler originally equipped with an opentype, 2600 mm-diameter CPP. The vessel is powered by a Wärtsilä Nohab F38A with an output of 1580 kW, running on marine diesel oil. To save fuel, the owner was seeking a propulsion retrofit with an attractive Return On Investment (ROI).
Our proposal was a modern propeller design of diameter 2400 mm operating in a high efficiency (HR) nozzle. Calculations indicated a bollard pull increase of 29% and a 13% improvement in free-running efficiency. Operating parameters in both sailing and fishing conditions were optimized. The ROI for this rebuilding was calculated as being less than two years.
Reverse engineering
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A MUCH QUIETER RIDE
MV Trygvason’s owner is very pleased with the overall result. "It’s much quieter onboard now,” says Captain Støle Lønning, a regular visitor to North Sea fishing grounds. “In the first year, we used the boat just as it was when we bought it, but it became very expensive to run. Even though it wasn’t the cheapest option, Wärtsilä’s nozzle solution was the most effective. We can now use more efficient trawling equipment, and we haven’t suffered any loss in sailing speed, something which has happened to others.”
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As the original propulsion unit was not a Wärtsilä design, measurements were made on a spare propeller blade to establish the blade geometry. Both hydrodynamic and mechanical calculations were performed to define the maximum hub loading. Cavitation calculations provided reference values for noise and vibration.
Using this data and a technical specification, new geometry for the propeller blades was produced. Our state-of-the-art computer techniques make it possible to not only improve bollard pull and efficiency, but also to reduce hub loading. In this case, the nozzle effect meant that the new design’s cavitation and pressure-pulse performance offered a considerable improvement over the vessel’s original equipment. Both noise and vibration levels remained well within reference limits.
Better than expected - Bollard pull: 30 tons; fuel reduction 30%
The retrofit was carried out in Norway and the trawler was out of operation for about two weeks. Trials showed a bollard pull close to 30 tons - calculations had indicated 27 tons. Before the retrofit, the bollard pull had been 21 tons. The owner also reported a reduction in fuel consumption of approximately 30%. The trawler now uses less fuel when pulling a specific net, or can trawl using a larger net.
Propulsion improvement
We offer propulsion improvement for both Wärtsilä and third-party installations. Following an initial assessment, deliverables are a budget price, an indication of the resulting efficiency improvement and the estimated ROI. The entire conversion process from initial discussions to sea trials of a new installation takes 6-12 months.
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After: |
Originally built non-Wärtsilä propeller (2600 mm) |
After conversion new Wärtsilä design propeller blades in HR nozzle (2400 mm) |
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