Packing Boat Stuffing Boxes
by
Marinetrader
If your yacht is equipped with inboards, chances are it is equipped with a stuffing box to allow a watertight seal for the prop shafts. Stuffing boxes are also used to seal off rudder posts that penetrate the hull below the waterline too.
Stuffing boxes are really the seals that permit prop shafts and rudder posts to come into the yacht but yet keep the water 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, motor yachts and sailboats.
The older stuffing boxes were simply a compression fitting and sleeve filled with a flax material; they were intended to “leak” a little with the water allowing 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 substituting your present flax packing with a new material called GFO Packing, made by Gore-Tex. The new packing has a Teflon impregnation permitting the packing to be constricted to a point where no water will leak from the stuffing box itself. We have used it on the Patricia Ann for two years and have dry bilges.
Replacing your packing is easy too. Remove the 4 nuts that holds the stuffing box together and work the fitting apart. You may need to strike it with a mallet to loosen it. You will also need a packing removal tool available at any boat yard.
Remove the existing packing by using the extraction 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 propshaft — a condition you want to avoid. On power vessels, 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 needing frequent adjustment, it leaks too much or if it begins to feel hot, it’s time.
If the old packing comes out relatively intact, use it to learn what size packing you need. If it comes out as shapeless wads of gunk, then measure the space between the shaft and the inside of the packing nut to define the correct packing size.
When all of the old packing has been removed, place one new segment 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. Pack it evenly with a little dowel pin 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 push the other rings deeper, then loosen 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 push the compression fitting into place as much as you can by hand. Next screw on the two compression nuts and tighten with a wrench to continue to apply pressure to the packing. Not to much however, 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. Finally, install the remaining 2 lock nuts to complete the job.
A common mistake is winding the new packing around the shaft as a continuous piece. Packing installed this way will not seal correctly. It must alternatively be installed as a series of stacked rings. This requires cutting the packing into lengths that just circle the shaft with ends meeting preferably with cuts on an angle.
Now you can brag to all of your buddies that you have drip less seal on your yacht too.
Mike Dickens, the author, is a live aboard boat owner and owner/Broker of Paradise Yachts in Florida USA.
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Packing Boat Stuffing Boxes