An effective bulbous bow can reduce ship resistance by between 3% and 7%.

Can this be Retrofitted to Existing Ships?: Yes

Image used with kind permission from Ebbe Holsting (menkent.dk)

How does it work?

Traditionally, a bulb’s primary aim is to generate a wave forward of the waves being generated by the hull in order to cancel out the waves generated by the hull.

The performance of a bulbous bow depends on the Froude number and draught in which the ship is being operated. A bulbous bow is not always appropriate and may cause an increase in resistance away from its design condition.

The bulbous bow also has impacts on seakeeping and structure as well as the hull’s hydrodynamic profile, as explained in Grech La Rosa et al. [2015].

Feedback from Lloyds Register/Alejandro Caldas Callazo

It is dependent on the Froude number; the higher the Froude number the higher the potential improvements due to a bulbous bow. It is quite dependent on the draught. The bulbous bow can even be a penalty to the efficiency for certain conditions. For example, if the bulb was designed for 15 knots at design draught it can be a bad design for 15 knots in ballast or for a different speed.

How this is was modelled in the Whole Ship Model

The bulbous bow correction in Holtrop and Mennen [1982] was used. The calculated change in resistance was checked by comparing to the model test data for a ship that was tested at Marintek [Nervik, 2000].

Kracht [1978] did develop specific geometric coefficients in order to distinguish different bulbous bow designs.

References

A. Grech La Rosa, G. Thomas E. Muk-Pavic and T. Dinham-Peren, Bulbous Bows for Energy Efficient Ships: Towards A Novel Design Approach, 2015.

Holtrop, J. and Mennen, G., “An Approximate Power Prediction Method” International Shipbuilding Progress, 29, pages 166-170, 1982.

Kracht, A.M. ‘Design of Bulbous Bows’, SNAME Trans. SNAME Transactions, 1978.

Nervik, A. Chemical Tanker Performance Tests (Report No. 601736.00.01). Internal Marintek Report, 2000.