Condition of the Hull and Main Engine Power for Ships
Dry docking and Speed
The speed of the vessel and consequently the engine power and fuel consumption are affected by the condition of the hull bottom. The smoothness of shell plate is reduced over a period of time due to damage to the paint, corrosion of plates, growth of shells and barnacles etc. contribute to the roughness of the hull and increase in power/fuel consumption and decrease in speed of the vessel.
Due to the above, the timing of dry docking of the vessel may not only be based on Survey Requirements but also economic considerations. Thus the owner has to compare the cost of dry docking with the extra money spent on maintaining the vessels speed by way of additional fuel cost and take a decision.
Apart from additional fuel costs, hull roughness may result in over-loading the engine due to shifting of propeller curve and hence the engine speed may have to be maintained as before or even reduced to avoid machinery problems.
Restoring the hull smoothness at the time of dry-docking requires hull cleaning by grit blasting/water jet blasting and painting with modern SPC paints which prevent growth of organisms like shells and barnacles. The painting itself has to be done carefully in order to achieve the required paint thickness as well as surface smoothness.