Ships Safety-Preventing Water Ingress

Watertight Integrity Testing – The advantages and disadvantages of the various methods

Watertight integrity is paramount to ship safety and the protection of cargo. The International Association of Classification Societies comment on three methods for ensuring the watertight integrity.

Ultrasound testing:

Ultrasound testing is where a transmitter emitting ultrasound at around 40 KHz is placed one side of a seal and a receiver on the other side of the seal. If there is no signal received when the seal is closed, then the seal is watertight.

·???????Ultrasound testing is accurate and able to find exactly where the leak in the seal is.

·???????Ultrasound testing can be used for internal seals as well as the more common hatch-cover testing.

·???????Ultrasonic testing only requires one person and can be used in all weathers.

·???????Ultrasound testing has a number of advantages over the other methods and is the preferred method of watertight integrity testing of all the major P and I Clubs.

Careful consideration needs to be given when choosing an ultrasound watertight integrity tester.

For hatch-cover leak testing, filling the hold with ultrasound with the same intensity is vital to obtain exact and repeatable readings.

Contrary to what is sometimes written ultrasound does not swirl around and fill a hold with the ultrasound signal. Ultrasound travels in straight lines expanding into a cone the further the signal is from the emitter. It therefore follows that for reliable results the transmitter will need a dome with each emitter positioned so that the signal reaches all parts of a hatch cover seal evenly. There should therefore be a minimum of thirteen emitters in a dome configuration and the emitters to have sufficient ultrasound levels to fill the largest of holds. A total of over 150dB is recommended.

Transmitters that have a fewer number of emitters will not “illuminate” a hatch cover seal evenly. Transmitters that have emitters pointing horizontally are not effective.

Classification Societies require that the unit of measurement be in decibels.

It is especially important that an instrument is provided with an emitter tester so that emitters can be checked prior to and after a survey to show that they have been functioning correctly throughout a survey.

When the transmitter is on the tank top it is extremely helpful if it can be turned on and off remotely using the receiver. This conserves battery power and saves time,

• It is important to consider the manufacturers recommended recalibration period. The cost of recalibration is around GBP200. An instrument with a manufacturers recalibration period of five years can save an operator GBP800 plus the cost of annual shipping and the instrument is available for surveys throughout the five-year calibration period, compared with the extended down time when an instruments manufacturer requires a recalibration every year.

Instruments with the transmitter and receiver encased in military grade water resistant leather give added protection and a much longer life.

It is exceedingly difficult to climb on and off hatch covers with one hand holding the receiver and the other hand holding the microphone, and so instruments provided with neck straps allow the surveyor one free hand and improves personal safety.

Ultrasonic testing is highly recommended by the P&I clubs.

Chalk testing:

Chalk testing is where the compression bar is coated with chalk and then the door or hatch cover is closed transferring the chalk to the seal. If the seal is fully coated with chalk, then the seal is considered waster tight.

Disadvantages are:

§?This method gives no sign of the compression of the seal. If the two surfaces kiss the seal may appear to be watertight.

§?This method is not able to evaluate deck glands or transits.

Hose testing:

Hose testing is where water under pressure is sprayed on the closed seal. It requires two persons, one spraying the water at the seal on one on the other side seeing if water is leaking. In this test a water spray from a nozzle of 12mm diameter is sprayed over the joint of hold and cover from 1m to 1.5 m with a pressure of 0.5 m/ second water jet.

Disadvantages are:

§?It is difficult to ensure that the mandated requirements are being met.

§?This method does not show leaks accurately.

§?It cannot be used when holds are part loaded.

§?Is not suitable for temperatures below freezing.

§?Is not suitable for evaluating the integrity of internal seals.

§?Time-consuming method.

§?Excessive water draining from decks when vessel may be alongside wharf, pier or jetty.

§?Two surveyors must undertake the testing.

Captain Christopher Loat.

L&L Maritime Corporation

Distributor of Quality Ultrasonic Instruments

For Class Instrumentation Limited - the Leading Manufacturer of Ultrasonic Instruments

T: 604 922 8342

E: [email protected]