Contra-rotating propellers (CRP) in a push-pull configuration take icebreaking capability, manoeuvrability and performance to an entirely new level. The harsh conditions of ice-covered waters demand reliable propulsors that can provide your vessel with that extra thrust when the going gets tough. “In addition to higher free running efficiency, Steerprop’s Arctic azimuth propulsors with contra-rotating propellers also offer higher thrust in bollard and icebreaking conditions”, says Hannu Jukola, Senior Sales Manager at Steerprop Ltd.
Contra-rotating propellers provide superior efficiency and fuel economy
Managing a vessel through thick ice can be a challenging task even for a skilled captain. Any misjudgement or lack of propulsion power can cause a ship to become stuck, which might result in serious damage to the vessel. Ice class requirements often force shipowners to make a compromise between bollard pull/icebreaking thrust and free running efficiency.
The propulsive performance of an ice-class propeller is inferior to that of a non-ice class propeller. This is because an ice-class propeller requires high propeller loading, which is enabled by large blade areas and high hub ratios. On the other hand, nozzled propeller configurations, which are required for high bollard pulls, present challenges with ice-clogging. “Shipowners do not need to make these compromises anymore. Our CRP solutions provide superior performance, thus eliminating these challenges”, says Mr Jukola.
Proven technology with valuable customer benefits
Azimuth propulsors are the tool of choice for ice management operations. In fact, they have now become the industry standard for ice-going vessels. One of the reasons for this, is their ability to direct the vectored thrust from the propeller (slipstream) in a full 360 degrees, which allows the vessel to use the thrust itself not only to open and widen fairways, but also to blow ice ridges and free Arctic offshore installations from ice pressure.
Steerprop’s continuous commitment to R&D has led, among other things, to the contra-rotating propulsor. However, being simply good enough is not enough for this company. That is why Steerprop conducted a series of ice model tests at Aker Arctic Technology’s ice laboratory. The ice basin tests were compared against traditional single-propeller propulsors that are currently used in ice-going applications. “The results revealed several benefits that CRP propulsors offer. In particular, the slipstream of the CRP propellers provided entirely new opportunities in ice-management operations”, says Mr Jukola.
The unique propeller slipstream from CRP has proven to be highly effective when clearing ice formations and widening fairways.
Net thrust 10-17% higher than single pulling propellers
In a CRP unit, the power is split between two contra-rotating propellers. This means a much lower propeller loading, with the second propeller recovering the rotational energy from the forward propeller. Therefore, the propellers are much more efficient without the constraints caused by the high loading of a single propeller. Steerprop’s Arctic azimuthing propulsors achieve this through lower blade area ratios, more favourable pitch and RPM settings, as well as a reduction of rotational losses that are not possible with single propellers.
“We found that in bollard configurations, CRP provides about a 10% higher thrust with the same power, or the same thrust using 15% lower power when compared to a single propeller of the same diameter. The free-running efficiency is 5-10% better depending on the vessel speed. Test results show that the CRP can bring benefits to several different applications – ranging from dedicated ice management vessels and Arctic cargo ships to tankers and ice-going offshore support vessels. The net thrust of the CRP was 10-17% higher than a single pulling propeller with the same power”, says Hannu Jukola, adding that “Ridge penetration times were also significantly reduced because of the unique effectiveness of the slipstream from the CRP-propellers.”
Mr Jukola mentions LNG carriers (Liquefied Natural Gas) as an example of an application type that could benefit from Steerprop’s CRP solution. “The ice resistance was reduced by approximately 10% in level ice, and the speed in brash ice was increased by 50%. Even the ridge penetration time was reduced by about 50%.”
A reliable partner to support you all the way
Steerprop has a strong track record, having delivered more than 90 units for ice-classed vessels, including icebreakers. Among these deliveries we include the world’s most powerful and highest ice-class mechanical azimuth propulsors. These two SP 110 PULL ARC units with total power of 18 000 kW were installed on the icebreaker Vladivostok in 2014.
“We want our solutions to resolve our customers’ challenges in such a way that they add critical value to their businesses. The best result is achieved when we can support and advise our customers already from the ship design phase. Our support ranges from needs analysis and proposing the best solution to maintenance and service throughout the lifecycle of the solution”, says Mr Jukola.
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