Bulbous bow optimization

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BULBOUS BOW OPTMIZATION for multipurpose/heavy lift vessel

CUSTOMER: —

RELATED SERVICES: HULL FORM OPTIMIZATION, SHIP RESISTANCE & POWERING PREDICTION

SCOPE OF WORK:

  • Multi objective Bulbous bow optimisation by means of CFD
  • 3D model of the selected bulbous bow for production
  • Assistance in stability calculations of the new shape for Class. Requirements
  • Design, Scantling and Production drawings for a Bulb in the original rudder

RESULTS:

After conducting an Energy Audit for a series of several MPP sister vessels, one of the results was that the performance of the original bulbous bow could be highly improved. The Ship Owner finally decided to go for the bow retrofitting and a specific project for its optimisation was started.

The original bow was designed/optimised for high speed condition (High Froude number). Hydro dynamically, the behaviour of such bow was quite critical performing well in the top speed range but inducing a bad wave pattern (very energy demanding) when reducing speed.

It is usual that ship owners make use of slow steaming as a fuel saving measure for their fleets. This customer was not an exception and the vessels are operating in the range of 12-14 knots which is much lower than the design speed.

Twelve conditions (in terms of speed, trim and draft) were defined along with the ship owner as the most probable for the actual ships operation in order to being able to obtain a representative overall saving figure after the analysis.

With these conditions as target, a bunch of parametrically modified bulbous bows were designed and generated in 3D.

Every single geometry was analysed with viscous CFD performing Resistance tests for each condition. After this set of simulations Propulsive efficiency was also calculated for each of the conditions and bows.

Once all results were post processed, energy demanded in each condition for every bow modification was calculated in order to assess the best geometry in terms of energy instead of power. This allows to take into consideration the amount of time spent in each condition.

Finally, results showed a huge improvement for all conditions below design speed. This means an overall energy saving above 10% compared to original bow configuration. In the most probable condition for the ship to sail in, the power savings were up to 15%.

Additionally to this retrofit, a Costa Bulb for the rudder was designed and installed for an extra saving achievement. The figure was 2% for the propulsive power. This would be a very small investment to make an ultra-efficient whole package.

Along with the energy and power savings, a simple ROI study was provided to the Ship owner in order to make the GO/NO GO decision for the project.

It must be mentioned that this was a very special case where the bow was very sensitive to speed. But it is also true that if the operational speed is far from design speed, savings can be noticeable for every ship.

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