If your boat has inboard engines, chances are it is fitted with a stuffing box to provide a watertight seal for the propeller shaft. Stuffing boxes are also used to seal rudder posts that penetrate the hull below the waterline too.
Stuffing boxes are actually the seals that allow prop shafts and rudder posts to come into the boat but yet keep the sea out. Today’s stuffing boxes are built a bit differently than those of just a few years back, thus earning the name “drip less” seals. But this post is about the older boxes found on older trawlers and motor yachts.
Keep in mind that the older stuffing boxes were merely a compression fitting filled with a flax material; they were intended to “leak” a little with the water providing necessary lubrication. A drip or two a minute is about right. But if want dry bilges, you can make them drip less too. How? By replacing your current flax packing with a new material called GFO Packing, made by Gore-Tex. The new packing has a Teflon impregnation allowing the packing to be compressed to a point where no water will leak. We have used it on the Patricia Ann for two years and have dry bilges.
How do you repack a stuffing box? Replacing your packing is simple too. Remove the two nuts that hold the compression fitting together and work the fitting apart. You may need to tap it with a hammer to loosen it. You will also need a packing removal tool available at any boat yard.
Begin to repack a stuffing box by remove the existing packing by using the tool like a corkscrew and pull the old packing out. You can do it while your boat is in the water as you will only take on about 1/2 gallon of water. Over time, after the packing nut has been tightened a few times, the packing gets so compressed that it becomes hard enough to actually wear a groove in the shaft–a condition you want to avoid. In a powerboat used regularly, the shaft packing should be replaced at least every other year. Sailboats may not need to have the packing replaced for five years or more, but when the stuffing box starts requiring frequent adjustment, it leaks too much or if it begins to feel warm, it’s time.
If the old packing comes out relatively intact, use it to determine what size packing you need. If it comes out as shapeless wads of gunk, then measure the distance between the shaft and the inside of the packing nut to determine the correct packing size.
When you have all of the old packing out, place one new section of new packing back into the compression fitting and press the sleeve back into place by hand. The easy way to do this is to wrap the packing around the shaft in some accessible location and cut across the overlap with a razor knife on an angle making 4 separate rings of packing. Wrap one of your cut lengths into a ring around the shaft and push it into the stuffing box. Tamp it evenly with a small dowel or a blunt screwdriver to push it all the way to the bottom of the box. Push a second ring into the stuffing box on top of the first one, staggering the joint about 90 degrees. Add a third layer, then the fourth, each time staggering the joint. If you don’t seem to have room for the fourth layer, hand tighten the adjusting nut to force the other rings deeper, then remove it again to see if this made room for an additional ring of flax.
By the 4th section, any water flow will have about stopped. Now press the fitting into place as much as you can by hand. Next screw on the two nuts and continue to apply pressure to the packing. Not too tight mind you, just a firm application until the leak stops. You will need to probably adjust it a bit after you run the boat the next time.
A common mistake is winding the new packing around the shaft as a continuous piece. Packing installed this way will not seal properly. It must instead be installed as a series of stacked circles. This requires cutting the packing into lengths that just encircle the shaft with ends touching preferably with cuts on an angle.
Now you can tell all of your buddies that you have drip less seal on your boat too; you can tell them you know how to repack a stuffing box.