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The steel plates that form a ship's Hull take a lot of punishment. Berth contact, grounding, corrosion and fatigue can all leave them dented, cracked or thinned. Underwater steel plate repair in Nagoya aims to restore strength or watertightness without waiting for a dry dock.
Before any repair, the Diver inspects the plate. He records the size and shape of the damage, takes photographs and measures the thickness around it with an ultrasonic gauge. Thin plating or a long crack can change the whole plan. The measurements go to the surveyor, who decides what repair is acceptable.
The most common repair is a doubler, a steel plate fitted over the damaged area and welded around the edges. It gives the damaged plate extra strength and covers small holes or cracks. The doubler is cut to shape and bent to fit the curve of the Hull. Its size and thickness are chosen by calculation and approved by the class society. Welding is done wet or dry, depending on the plan.
For small holes, a bolted or welded patch can be used to stop the leak. A rubber gasket and a steel plate pulled tight with bolts can work as a temporary measure. The patch is later replaced by a welded repair when time and conditions allow. We use patches mostly in emergencies and when the ship must sail.
Where a plate is badly damaged, a section can be cut out and a new piece inserted and welded in. This is a larger job and is best done dry, in a cofferdam, or in dry dock. In-water insert plates are done in some cases with class approval.
Class societies often accept underwater plate repairs as temporary, with a permanent repair at the next docking. In some cases a repair can be accepted as permanent. The surveyor decides. We prepare a clear plan so the repair is acceptable and the surveyor is not asked to take anything on trust.
We inspect each weld on video and, where possible, check it by other means. The report includes before-and-after photographs, welding details and thickness readings. If a repair needs to be rechecked later, the report is the starting point.
Send us the ship's particulars, photographs and the description of the damage. We inspect, produce a plan and arrange class attendance. A doubler repair can be done in a day or two once the plan is approved.
The plate used for repair must match the grade and thickness of the original, or be approved by the surveyor as an alternative. We cut the doubler to size on the surface, bend it to the Hull shape using a template made by the Diver, and check the fit before welding begins. A tight fit reduces gaps and gives a better weld. If the Hull curve is complex, a clay or wax impression may be taken.
The surveyor may ask for a follow-up inspection after a few weeks or at the next port. We can return to the same plate, film it and report on its condition, which also helps the owner plan the permanent repair.
Q1. What is a doubler plate?
A steel plate fitted over damaged shell plating and welded around the edges to restore strength or cover cracks and small holes.
Q2. Are underwater plate repairs permanent?
Class societies often accept them as temporary, with permanent repair at the next dry-docking. In some cases they can be accepted as permanent. The surveyor decides.
Q3. How long does a doubler repair take?
Once the plan is approved, a doubler repair can often be completed in 1 to 2 days, depending on size and conditions.
Q4. What measurements are taken before repair?
The size and shape of the damage and ultrasonic Thickness Measurement around it, so the surveyor can decide on the repair.
