Shaft Packings and PSS

The Stuffing Box

To keep the water out, most inboard drive boats have a prop shaft stuffing box that contains flax or Teflon packing rings in a compression nut called the packing gland. The stuffing box (packing gland) is generally constructed out of bronze. We recommend that plastic packing glands (usually white in color) be replaced with bronze. We have seen the plastic packing glands melt and become brittle due to overheating and age.

The most popular type of packing material is a synthetic fiber treated with P.T.F.E. (Teflon) such as Tefpack shaft packings. When properly installed, this type of shaft packing material will outperform most conventional shaft packings such as wax impregnated flax. The flax shaft packing should be replaced every 1 to 2 years depending on use, while the Teflon shaft packing can last as long as 4 years depending on use. The best time to renew the shaft packing is when the boat is out of the water

Both flax and Teflon packings are adjusted in the same way. The traditional stuffing box (packing gland) is made to be lubricated and cooled by water and should drip a few drops per minute during operation. Ideally, the shaft packing should not leak at all while the shaft is at rest. As the shaft packing material wears down, the packing nut will have to be adjusted.

A shaft packing that is adjusted too tightly may overheat and destroy itself. This over tightening and overheating could also score the shaft making it impossible for the shaft to hold a proper seal even if new shaft packings are installed at a later time.

If the packing is adjusted too loose or it is worn out, excessive water intrusion will result. While the boat is at rest, water could drip into the boat at an ever increasing rate and if the bilge pump fails to operate properly, the boat could sink at the slip.

When the boat is in operation, a loose and/or leaking shaft packing can cause a salt water mist to fill the engine room rusting any carbon steel it comes in contact with, including the engine. It can also cause corrosion and a failure of the electrical systems within the engine room.

New shaft packings can be installed (after the old ones are removed) with the boat in or out of the water but, the final adjustment is always done with the boat in the water.

When the boat is out of the water, there are more options available to repair or upgrade the shaft sealing system. Sometimes it is advisable to remove the prop shaft so that all the components of the shaft sealing system can be inspected and cleaned or replaced, if needed.

While the shaft is out of the boat, it should be sent to the machine shop to be checked for trueness and any evidence of roughness, galling, or scoring. Most of the time it can be dressed back to the proper surface smoothness before it is reinstalled.

If the proper smoothness cannot be achieved, the pedro hose (the water tight hose between the shaft log and the stuffing box) can be replaced and lengthened so that the shaft seal is on a more inboard and smoother section of the shaft. Often it is advised that the pedro hose and all four hose clamps be replaced before the shaft is reinstalled.

If the stuffing box shows signs of corrosion, it should be cleaned, bead blasted, and then inspected. If the threads are damaged, replacement of the stuffing box may be required. While this area of the boat is accessible, the shaft log should be checked for cracks or looseness and should be repaired or tightened if necessary.

The PSS

Analternative to the traditional stuffing box is the PSS (Packless SealingSystem). With the PSS, a mechanical seal is created by the contact ofa turning surface against a stationary surface. In the case of the PSS ShaftSeal, the stationary surface is a carbon flange held in contact against astainless steel rotor which turns with the shaft. The carbon flange is attachedto the boat by a nitrile bellow which, with the help of water pressure,produces a constant contact between the carbon and the stainless steel ring.These type of seals are unaffected by engine motion or vibrations. The resultis a 100% watertight and totally maintenance-free seal.

1. Propeller Shaft 2. Shaft Log (Stern Tube) 3. Stainless Steel Hose Clamps (4) 4. Reinforced Bellow (1)
5. Carbon Graphite Flange (1) 6. Stainless Steel Rotor (1) 7. Stainless Steel Screws (5 total/4 for Rotor, 1 spare) 8. Nitrile O-Rings (2 in Rotor/2 spare) 9. Nylon Hose Barb Fitting