Prop Shaft, Stuffing Box & Cutless Bearing

Most sailors treat the running gear (stuffing box, cutless bearing and shaft) as low- or no-maintenance items, but they deserve attention. A leaky stuffing box can allow a truly irritating amount of water into the boat, while over-tightening of the packing gland will cause excessive wear, necessitating the replacement of a $500 shaft.

Stuffing box
Stuffing box opened
Scored shaft
Removing bearing
P-bracket with bearing

Running gear pictorials

This site covers a wide range of running gear issues, including

generally in greater detail than we do on this site.

Stuffing box maintenance

Traditional packing for a stuffing box is wax- or grease-impregnated flax that looks somewhat like squared sash cord. The correct size is 1/4". Earlier it was suggested here that 5/16" was also an option, but the consensus on the Forum is that while this is possible, 1/4" is better. Two rings go on easily, one person reported that he would put a third on once the first two had compressed a bit.

As built, 27's had several rows of flax packing in a stuffing box like the one above. A stuffing box should be just tight enough that it does not drip when the shaft is motionless, and drips two or three drops per minute when the shaft is turning (necessary because the water lubricates the packing). With packing in good condition, this is firmly hand-tight. You do need two large wrenches, though, to set the lock-nut, without which the compression nut will loosen and perhaps come off, which will sink your boat.

In the time since our boats were built, alternatives have appeared that are drier, probably more durable and less likely to cause the damage visible on the scored shaft above. These are:

Which to choose?

  • The owner of 27 Iris used the first option in 1997 and eight years later, was still very happy with it. He reported that the kit is widely available, costs about $50 and will do two boats.
  • The author of this very thorough tutorial on cleaning and repacking a stuffing box prefers Gore-tex packing and has nothing but scorn for mouldable packing. As they say, "different ships, different long splices", or more recently, "your mileage may vary". A kit of Gore-Tex is about $20; a kit of Teflon packing is about $8 (Gore-Tex and Teflon are trade names for the material PTFE but the Gore-tex packing appears to include additional materials). This tutorial is worth looking at if you are doing anything with your stuffing box as it goes into considerable detail about every aspect.
  • Towser acquired a PSS Shaft seal with a new shaft in the spring of 2006 on the recommendation of other Association members and it has remained virtually unnoticeable since, which is ideal. Forum discussions of the device have included criticism of its cost (about $200), but not its performance (Towser's bilge is so dry an occasional bucket of water is needed to flush out the spiders). Potential buyers in Canada should note that 1) the price in Canada is significantly and unjustifiably higher than in the US and 2) Canadian buyers should never allow a US seller to ship UPS, as they charge a $50 brokerage fee – use plain old mail. If you install one of these, you will have to remove the shaft from the engine coupling, which can be difficult. This tutorial shows how.
  • If you fit a PSS Shaft Seal, never leave the shaft uncoupled or unsupported when the boat is in the water. If the sealing faces become misaligned, a boat-sinking-size gap can open between them.

According to a post on another sailing site, it is possible (though probably still not fun) to replace the packing in your stuffing box on the water. Undo the lock-nut and release the compression nut from the body. Tie a length of bicycle inner tube tightly around the stuffing box body and shaft. This should at least keep the water from gushing in while you replace the packing.

Another source suggests that you should loosen (one at a time), rotate and inspect the hose clamps every few years as drips may collect on the unseen underside and cause corrosion. Given the reliance on a single clamp at the packing gland end, this seems a reasonable precaution.