subject: Servicing Stuffing Boxes [print this page] If your boat has inboard engines, odds are it is fitted 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 beneath the waterline too.
Stuffing boxes are really the seals that permit prop shafts and rudder posts to come into the boat but yet keep the water out. Stuffing boxes built today 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.
Keep in mind that the older stuffing boxes were merely a compression fitting and sleeve filled with a flax material; they were intended to "leak" a little with the water allowing essential lubrication. A drip or two a minute is about right. But if want dry bilges, you can make the older stuffing boxes drip less too. How? By substituting your current flax packing with a new material called GFO Packing, made by Gore-Tex. The new packing is made of Teflon thus allowing the packing to be constricted to a point where no water will leak from the stuffing box itself. We have used it on our trawler, the Patricia Ann for 2 years and have dry bilges.
Substituting 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.
Take out the existing packing by using the extraction tool like a corkscrew and force the old packing out. You can do it while your yacht is in the water as you will only take on about half gallon of water. Over time, packing has been tightened some the packing gets so compressed that it becomes hard enough to actually wear a groove in the shaft -- 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 5 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 you can remove the old packing in one piece, use it to determine what size packing you need. If it comes out as lumpy wads of gunk, then measure the distance between the shaft and the inside of the packing nut to determine the correct packing size.
When all of the old packing has been removed, place 1 new segment of new packing back into the compression fitting and push the sleeve back into place by hand. The simple way to do this is to wind the packing around the shaft in some accessible location and cut across the overlap with a razor knife on an angle making 4 individual rings of packing. Wrap one of your cut lengths into a ring around the shaft and force it into the stuffing box. Tamp it evenly with a small dowel pin or a blunt screwdriver to press it all the way to the bottom of the box. Press 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 remove it again to see if this made room for an additional ring of flax.
By the time you have the 4th section in place, all water leakage should have 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 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. Finally, install the remaining 2 lock nuts to complete the job.
An everyday error is winding the new packing around the shaft as a continuous piece. Packing installed this way will not seal correctly. It must instead be installed as a series of stacked rings. This necessitates cutting the packing into lengths that just circle the shaft with ends touching preferably with cuts on an angle.
Now you can brag to all of your buddies that you have drip less seal on your boat too.
