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Concerning the generally held opinion that traditional packing glands require a minimal
continual drip past the packing material, ostensibly to cool any frictional heat generated by the shaft and packing material. It is my opinion that the purpose of this drip is generally misunderstood, It appears to me that the drip at the suggested rate
could remove only an insignificant amount of heat. The real contribution of the drip is
to also allow any air trapped in the stern tube to escape, so that the upper end of the stern tube is always filled with cooling water. It appears normal for some bubbles to
be continually introduced into the outside end of stern tubes.
I believe that I have solved this problem by drilling and tapping a vent into the top of my gland assembly just aft of the packing, and routing this vent to well above the waterline. There are occasional bubbles traveling up this vent, and the assembly is running cool, and entirely drip free. I used gore-tex and teflon packing, and the nuts against the compression bushing are tightened to less than finger pressure.
A friend recently had a serious problem with one of the 'no-drip' seal type assemblys
when he put his boat in gear after a months inactivity. The carbon/stainless seal face
had become frozen, causing the lightweight rubber hose/bellows to twist to destruction, allowing a very fast rate of flooding. Fortunately, he was at the dock, and
had help finding rubber strips and tape to stop the flooding. The Manufacturer did pay
for hauling the boat and replacing damaged parts. Previous similar accounts, and now
this incident, reinforces my distrust of these lightly constructed seals. I noticed that
this installation also incorporates a vent similar to that described above, and I expect
for the same reason.
Regards, ED
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