Stern Tube Integrity Test During Dry Dock: How Is It Done?

Blog | February 14th, 2019

Without making a habit of stating the obvious, let’s just say that a stern tube integrity test isn’t a job that’s done at sea. That tube is located way below the waterline. A boat’s propeller shaft passes through the shaft, so it’s about as near to the bottom of a vessel’s hull as you can get. Clearly, out of necessity, integrity tests must be carried out under drydock conditions.

When Drydock Calls a Boat Home

There are boat repairs that can be done while a ship is at sea. However, there are also tests and repairs that cannot be done unless a boat is pulled out of the water. A boat owner can’t paint a ship’s hull when it’s still wet, right? And that’s the case with stern tube integrity tests; the work has to be done with the boat securely held in drydock. The propeller shaft is exposed, the boat owner or repair engineer is in control of the test conditions, and the integrity inspection can commence.

Putting Into Drydock

Leaving the water behind, a boat enters a water lock. This structure is seen in rivers and canals. It’s actually a controllable little estuary. On canals, boats slot into locks, the water level rises or falls, and the boat moves onwards at a different level. For drydock procedures, locks are installed at boatyards and harbours. When a returning vessel enters its confines, the lock closes. This time, instead of lowering the water level, every litre of liquid is drained from the enclosed containment area. The boat settles onto a series of blocks. This procedure began when the ship entered the lock, with the drydock manager guiding its hull. It’s a tricky operation, with the ship skipper adjusting the ship’s trim from time-to-time so that it hits its mark.

Stern Tube Integrity Testing

Plain material seals and gaskets compete with water and oil-lubricated variants. A test connection couples to the seal housing. Pipe connections and valve fittings go in next, with an inflatable bladder completing the test equipment setup. Air and fluid pressures are recorded. If these measurements change without any apparent reason, the integrity test comes unstuck. Only when the pressures are maintained for a predetermined period, plus there are no visible signs of leakage, can the test be considered a success.

Again, there are procedures on boats that must be carried out in a drydock facility. There’s really no other option. Prime amongst these dry air examinations and repair scenarios, a stern tube integrity test is always conducted in a drydock, where the test fittings, including the air bladder and gauges, can be installed while a second engineer tours the stern tube in search of fluid leakage.

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