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Old 10-07-2010, 10:23 AM   #1
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Dripless Stuffing Boxes

If your*trawler has inboard engines, odds are it is fitted with a stuffing box to provide a watertight seal for the prop shafts. 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 yacht but yet keep the water out.* Today's stuffing boxes are made a bit differently than those of just a few years back, thus earning the name "drip less" seals. But this article is about the older boxes found on older trawlers.

The older stuffing boxes were just a compression fitting and sleeve filled with a flax material; they were intended to "leak" a little with the water providing essential 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 is made of Teflon thus permitting the packing to be compressed to a point where no water will leak from the stuffing box itself.* We have used it on the Patricia Ann for 2 years and have dry bilges.*

Replacing your packing is simple too.* Remove the four 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 force the old packing out.* You can do it while your*trawler 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 fast power vessels, the shaft packing should be replaced at least every 2 years.**Slow moving trawlers*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 you can remove the old packing in one piece, use it to learn what size packing you need. If it comes out as distorted 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 one new section of new packing back into the compression fitting and push the sleeve back into place by hand.* The easy 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.* Roll one of your cut lengths into a ring around the shaft and push it into the stuffing box.* Tamp it evenly with a little dowel or a square screwdriver to press 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 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 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 finish 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 alternatively 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.
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