by Chris Collins
Pic showing the location of the grease fitting in the stuffing box
Modern dripless propeller shaft seals work great, but they can be expensive. If they fail, they cannot be serviced without a haul-out. Some ocean cruisers report this to be a disadvantage, preferring the ability to replace the packing in their stuffing boxes while at sea. I suggest that none of us like having seawater leak into our bilge.
Judikay and I have two sailboats, and I have modified the stuffing box on each to accept marine grease on the seawater side of the packing. Seawater pressure keeps the grease against the packing. The shaft seal in each boat is now dripless and well lubricated.
The cost of the modification was near zero! In my research, I learned this method is common in the UK and nearly unheard of in the US. Note, most automotive grease is soap based and should not be used where it might contact seawater.
The shaft log on our Catalina 30 is fiberglass. Since fiberglass made with polyester resin will absorb moisture, I was concerned about grease being absorbed and weakening the structure. I sanded the inside of the shaft log and then applied multiple coats of epoxy as a barrier coat.
Our ketch has a stainless steel shaft log with the cutless bearing pressed into the outer end of the tube. Greasing the stuffing box also greases the cutless bearing and fills the clearance between the shaft and the bearing. The cutless bearing is normally lubricated with seawater. That works great until the critters plug the intake ports, blocking the seawater. Then both the shaft and cutlass bearing suffer wear from extra friction.
On each boat, I replaced the connecting hose with the extra strong “Buck Algonquin” connecting hose. My jury is still out on how the marine grease will affect the hose. I used stainless steel grease fittings (Zerks) that are threaded with 1/8 NPT. A tap can be obtained at most hardware stores.
I installed the grease fitting as far aft as possible leaving just enough room for a wrench. I keep a spare fitting and a wrench on board. If the adjusting nut should reach the fitting when tightened, I will add more packing.
See the photo above for the location of the grease fitting in the stuffing box.
Our ketch had sat, and does sit for months without the engine running. The previous owner had replaced the propeller shaft, and yet I found it corroded under the packing. This was a classic case of being wet with saltwater and lacking oxygen.
I have learned this is very common when the propeller shaft does not rotate regularly. Our local propeller shop was kind enough to smooth the corroded area so I was able to postpone the expense of replacing the shaft until the next haul out. The resulting recess in the shaft makes it very difficult to install the packing. I don’t recommend the smoothing process if it will create a recess.
My next question was how would greasing the stuffing box cause or prevent shaft corrosion? I contacted Steve D'Antonio of Steve D'Antonio Marine Consulting Inc with just that question. Steve is an expert on stainless steel corrosion. Steve replied back with wonderful and lengthy information including the statement...
"Grease will not promote corrosion on a stainless steel alloy shaft as it excludes both air and water, the latter is needed for crevice corrosion to occur."
If you elect to install a grease fitting in your stuffing box, my suggestions are as follows:
Install a new heavy duty connecting hose, apply epoxy barrier coat to any fiberglass that might come in contact with the grease, and grease the packing as you install it to insure it will be well lubricated when the shaft first rotates.
Use a grease gun to pump as much grease into the shaft log as possible prior to launching - i.e. make an effort to keep saltwater in the sea by filling the shaft log with grease.
For the adjustment process, begin with a pretty loose adjusting nut. Tighten after seeing grease leak from seal. Ultimately, snug the nut so grease is not slung about as the shaft rotates, but not so tight that much heat is created.
The thick grease will create some heat, so expect warm. Too hot to touch would not be acceptable. Use your hand or an infrared thermometer to monitor closely and confirm the stuffing box does not get hot.
Use a grease gun to add marine grease frequently as needed to keep seawater in the sea and out of the shaft log. If this method does not work well for you, simply loosen the adjusting nut and let her drip normal.
Chris Collins owns, sails, and maintains a Catalina 30 on El Dorado Lake in Kansas and a 45 foot ketch in Rockport, Texas.
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