Stuffing box (packing gland)

What it is

A stuffing box is the classic shaft seal, with packing and a controlled drip. Many Scandinavian shaft-drive cruisers are still on packing; a dripless seal is more often fitted at a refit. A dry bilge with the packing pulled too tight does not prove that the seal is healthy: an extra drip, scoring on the shaft and a seized nut are survey points, not one drip rate for every brand.

West Marine's adviser writes: a correctly set classic stuffing box lets through two or three drops a minute when the engine is running and the shaft is turning. That water lubricates the shaft. Tightening the packing to zero means heating and cutting the shaft. A completely dry bilge on packing is not a survey medal. It can be over-tightening. Classic packing usually drips a little under way; zero can mean the packing is too tight and the shaft is heating.

Graphite packing under ABYC P-6, as Steve D'Antonio quotes it in a Task Sheet for Professional BoatBuilder, is forbidden because of galvanic action with the shaft material. There, temperature matters more than the drop count: no part of the box should be hotter than about 30 to 40 degrees Fahrenheit (about 17 to 22 degrees Celsius) above the seawater temperature at any speed. That sheet's policy is to change the packing and the hose clamps to the shaft log every four to five years or 1,000 engine hours, whichever comes first. Marine How To writes separately: even synthetic GFO should drip a little on a turning shaft; air in the log with no drip gives a sudden jump in temperature.

A dripless seal does not cancel the calendar, and it does not exist without maintenance: the bellows and the water feed are in the survey too. On the PSS FAQ, a Type A bellows is changed every 6 years; PSS PRO and Type B every 8 to 10 years, even if the outside still looks new. At the same change: the O-rings, the rotor set screws and the clamps. The bellows are inspected at least every six months. The West Marine dealer table writes 3 to 5 years for the bellows. That is not the maker's page. One "forever" number is not taken from here.

A speed under power of about 12 knots and above, on a PSS, needs a forced water feed to the friction faces. Slow boats with no bearing in the log can vent: a hose at least 2 to 3 feet above the waterline, closer to the centreline. Low-Speed Type A with no fitting is for vessels that will not exceed 10 knots. After the boat is lifted, the seal face has to be burped: the air is let out of the bellows once the boat is afloat again, before the first start. A thin mist and black dust in the first hour of bedding-in are called normal on the PSS FAQ.

Tides SureSeal is a different scheme, a lip seal, not a PSS carbon disc. The catalogue: inspect at least once a year, the blue hose, the clamps, the water-feed fittings. The FAQ: if it does not leak, do not change the lip; if the unit is more than two years old and the shaft is being split on the slip anyway, it is then reasonable to change the lip. PSS bellows years are not carried onto Tides. Water in the bilge is traced to its source: the stuffing box, a seacock, or rain. This page does not announce one drip rate for every packing and one year for every dripless seal. Nearby on the site: propeller shaft, Cutless bearing, bilge pump and survey checklist are other pages, not this drip rate.