Southern Boating

Shaft Seal Maintenance

Shaft seal maintenance should be part of your boat’s regular check-up.

Ever since the first prop was connected to the first shaft being turned by the first internal combustion engine, there has always been the dilemma of how to keep water from entering a boat through that all-important hole in the hull while also protecting the rapidly spinning shaft from the ravages of friction.

If your boating years go back as long as mine, you are familiar with the steady dripping of the practical, always carefully attended-to stuffing box. This most important piece of gear housed a series of packing rings—numbering three to five and often made of braided flax rope—coated with a waterproof material, and allowed the shaft to pass through the hull and keep turning while under power. It also prevented the water from getting in and flooding the bilges. Once properly tightened down by a collar, the rings were compressed enough to allow a few drops of water every minute or so to “leak” in, permitting the shaft and the packing to be cooled enough to prevent scoring the metal surface or “burning” the packing.

But as with all things in the marine industry, a change was due. Enter the dripless shaft system. Utilizing highly machine-polished, mechanical mating surfaces held together by pressurized tension on a rubber bellows surrounding them and a hose connection between the intake side of the engine’s raw water pump and the device, they have become the familiar norm in most applications.

One of the big downstream concerns associated with the old stuffing boxes was one created when there was a more than acceptable raw water flow. Sprayed outward by the spinning shaft, the ensuing salty mist would, of course, hasten corrosion to any metal it landed on. With a fully encased design, shaft seals alleviate this problem.