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Ship repair: What goes on during underwater cutting and welding?

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Economic significance of underwater ship repairs In the normal course of operation, a ship is taken to dry dock once in 12 or 24 months. After thorough inspection, appropriate repair and maintenance work is initiated. But what if a ship develops a snag below the waterline during routine service? Emergency dry docking is not feasible by any reckoning; it is economically untenable to pull the vessel out of water abruptly. The costs are prohibitive, schedules go haywire and the shipping company’s reputation could be tarnished. Underwater repairs and maintenance is the pragmatic solution for this dilemma. It is both cost-effective and time-saving to initiate underwater repair to a ship. A closer look at underwater cutting Underwater cutting turns out to be the process of choice in the case of deformed propeller blades, plates or sections of plates that need to be replaced, among other tasks. It is also recommended in the case of ship wrecks, where the vessel is to be taken apar...
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Propeller polishing: Understanding roughness and the Rupert scale

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Propeller roughness - causes and concerns It is observed that after approximately 6 months out of dry-dock, a vessel’s fuel efficiency begins to decrease. There are several reasons attributed to this downslide, out of which propeller roughness is a prime factor. As the propeller spins and produces thrust to drive the vessel forward, it is continually exposed to all types of underwater attacks. The assault is multifaceted and on-going; biofouling (marine growth), rusting/corrosion, electrolytic action and cavitation erosion, among other types of damage. This constant exposure contributes to the propeller’s surface roughness, which increases every passing day. Unprofessional, shoddy maintenance can also add to the deterioration. An unmaintained, chafed propeller, clogged with incrustations or calcareous deposits, leads to several undesirable outcomes such as damaging the transmission axis, loss of thrust and diminished fuel efficiency. The end result is increased fuel cost, which d...
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Underwater Hull Cleaning: Avoiding the hidden costs lurking below the waterline

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What is ‘hull biofouling’? Once a ship is put out to sea, a lot from the water can latch on to the vessel’s underbelly: sea weed, light slime, tubeworm, hard barnacle growth and much more. This accumulation of marine algae and assorted microorganisms across the hull’s surface is collectively known as hull biofouling. Usually, we come across two types of biofouling. The first is hard biofouling, which is caused by barnacles and mollusks. Hard biofouling is also known as calcareous. The other is soft biofouling (non-calcareous), which is primarily formed due to algae. Affecting hydrodynamic performance Hull biofouling is undoubtedly undesirable. If left unattended, it can have a negative impact on the vessel’s hydrodynamic performance. It results in higher operating costs or decreased speed (lower max speed). Since fuel accounts for almost 50% of the costs in marine transportation, hull biofouling is detrimental from the viewpoint of economical vessel operations. Moreover, it ca...
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