Guide to Repairing Boat Shaft Packing

A stuffing box consists of a threaded sleeve and a hollow nut through which a propeller shaft passes out of the hull of a boat and into the water. This sleeve is typically filled with rings of flax rope sealed with lubricants and wax. Compressing this packing against the prop shaft--done by tightening the nut--forms a watertight seal that still allows the shaft to turn. Stuffing boxes are a critical ship component that can be very easy to repair.

  1. Leak Rates

    • Although a stuffing box is intended to keep the water outside of the boat, some water is needed to lubricate the packing material. When the shaft is stopped, the seal should be solid; however, some drips are necessary when the shaft is turning to avoid overheating and seal failure. Don Casey, a noted sailor and boat mechanic, suggests that two or three drips per minute is acceptable; nine or more drips per minute requires service--usually a simple tightening of the nut.

    Replacing the Packing

    • If the packing needs to be replaced, carefully open the stuffing box and remove all of the old packing. There are special tools for doing this, although a bent metal wire will work in a pinch--just be careful not to gouge the shaft. Casey recommends, in order to estimate the correct amount of replacement packing, that you "multiply the diameter of your shaft by 14 to get the approximate number of inches you need for four layers of new packing."

      Install the new packing as a series of stacked rings--do not just shove it in as one large piece. Four rings around the shaft, cut precisely to match the shaft's circumference, should be laid with the ring joints not overlapping. It may be necessary to tighten down the shaft nuts to fill all the layers.

    Adjusting the Hoses

    • A hose around the packing leads excess water away. Inspect the hoses regularly and replace them when they are damaged; leaking hoses can allow water to corrode delicate engine electronics.

    Considerations

    • Any repair done to a stuffing box will open the interior of the boat to the water, so it's preferable that repairs be done when the boat is on the hard. If this is not possible, then redirecting the water to the bilge and running the bilge pump should be adequate. Using a barrier on the outside of the shaft tube will also work, but be careful that this barrier (e.g., plumber's putty) is completely removed before allowing the shaft to work under power.