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What's a cable gland?
It is a sealing piece that prevents water from entering through the propeller shaft. There are several models, and while some provide a perfect seal, for others it is normal that they let a few drops of water pass through.
What's with the oakum?
Tow is the fibrous component produced, among other things, during the combing of flax or hemp.
In the old navy, tow was mainly made from hemp and the lint of old rope and was used for smothering (filling the gaps in a hull between planks with tow for sealing) and caulking (filling the gaps in a hull between planks with tarred tow to make it watertight).
With the advent of shaft-line motor vessels, a problem of water ingress arose and the gland, previously soaked, was the only known seal.
How about today?
Many boats are equipped with a shaft line motorization and the stuffing box is a must. This is the case for some inboard motorboats, but also for most sailboats also equipped with inboard. The propeller shaft line is composed of :
a cake for connecting the propeller shaft to the inverter and thus to the motor
a gland packing for the sealing
a stern tube for guiding and holding the propeller shaft
a hydrolube ring which will limit the vibrations of the propeller in rotation and cool the shaft by letting the water pass through the stern tube.
There are two main families of cable glands:
- The rubber seal gland is a popular product for sailing boats. Water circulation lubricates the seal. Sealing on the propeller shaft is achieved by a lip seal. On some installations it is necessary to provide a water inlet for better operation.
- The classic cable gland, which actually presses cable gland. On these models, sealing is ensured by the friction of the stuffing box (previously sucked braid) on the shaft and, on more advanced models, by the grease or the water inlet.
A little maintenance and vigilance
- On a gasketed model, make sure that the rubber bellows is filled with water. This can be checked by slightly spreading the bellows slightly apart to allow water to pass through. For boats that fail or just after launching, it is very important to press the seal so that the water replaces the air in it. Rotating joints are well suited for boats with few hours of engine operation. Replacement is necessary after 500 hours of use, which leaves a little time ..
- On a model with a cable gland, it is normal for it to let some water pass through when sailing with the engine. But just a few drops! When stationary, there should be no leakage. Imagine that at standstill your gland lets one drop per second pass through, if you leave the boat for a month without sailing, 540 litres of water will have entered the boat... It must also be tightened regularly, but moderately to avoid overheating the gland braid.
