Question

You have been appointed as 2/E on a crude carrier, recently purchased by your shipping company. The company supdt. Requests that you examine the vessel with a view to increase its dead weight capacity without altering the ship's length. Outline the suggestions that you would make justifying your proposals.

Answer.

The deadweight of a ship is directly related to its length, breadth, draught, and block coefficient (i.e. form of the vessel) so to increase the deadweight, either of the above four parameters required to be increased of which the question rules out an increase in length. Of the remaining three parameters it would seem to be totally impractical to convert the ship by increasing the breadth or block coefficient.

The only solution left is to increase the draught by reduction of freeboard taking due consideration of LOAD LINE REGULATIONS, there may be scope for a free board reduction. The following modifications can increase the draught by reduction of freeboard.

1) The vessel is a dry cargo ship, hence type ' B' , therefore attracts the maximum freeboard.

If the vessel had wooden hatch covers fitted , then the replacement with steel, gasket covers would reduce the freeboard.

2) In the design/build stage the Assigned freeboard is increased if the design is deficient in sheer, extent of superstructures and bow height. Thus, if any of these deficiencies existed, there is capacity for structural alteration adding superstructure - increasing deck sheer adding a forecastle, (although the first two of these options would be very demanding) The ship could also be deficient in depth and this could be increased (there have been conversions of this type carried out) which would raise the freeboard deck and for the same freeboard, increase the draught.

The ship may be an open shelter deck type which could be converted by ensuring all the openings had permanent means of watertight closing, thus raising the freeboard deck, effectively increasing draught.

It may be possible to modify the structure to a bulk carrier and have Type B-60 assigned which would allow a reduced freeboard.

Although an increased draught by increasing freeboard would seem to be the only option , there are some modifications that can be made.

Sponsons have been fitted to some vessels (notably RO-RO vessels) to improve stability.

However, the extra buoyancy provided could be used to increase dead weight. Other hull protuberances could be fitted for some other reason than extra buoyancy and allow an increase in deadweight.

For instance, a bulbous bow may be fitted to reduce wave making resistance, and it does add extra buoyancy.