Cut Away Diagram of a Stuffing Box and Packing

The stuffing box is located on the inboard end of the stern tube in the vessel machinery space. The job of the stuffing box is to allow the propeller to rotate freely inside the stuffing box and at the same time, keep any water from entering the vessel from inside the stern tube.

The sealing surface in a stuffing box is between the stuffing box packing rings and the propeller shaft liner or for smaller shafts the propeller shaft itself.

The rotation of the propeller shaft against the stuffing box packing creates friction and heat and over time grooves are worn into the propeller shaft. Because of this friction your stuffing box must be lubricated with grease or water or both.

Stuffing boxes, generally above approximately 5 inch shaft size, can also have an emergency inflatable tube that can be inflated in case of shaft damage preventing water from flowing into the machinery spaces. The shaft must be stopped prior to inflation of the inflatable tube.

Choosing the correct packing for your stuffing box is also important. As mentioned, the packing is compressed by the packing gland until it pushes up against the rotating propeller shaft thus causing friction. Using the correct packing is important, we recommend our Ultra X packing made specifically for stuffing box applications, as a good packing will allow the following:

- Reduce wear of the shaft or shaft liner

- Allow heat to be transferred into the stuffing box frame

- Allow for less water dripping into the engine space

Things You'll Need To Install A Stuffing Box

Stuffing Box

Ultra X Packing

Utility Knife

Wrenches and Non Ferrous (Non Corrosive) Fasteners

Water Hose and Fittings (If Water Lubricated)

Grease / Grease Gun (if Grease Lubricated)

Installation of the Stuffing Box

Stuffing boxes are typically bolted to the flange that is on the inboard end of the stern tube. In the above cut away image the flange and pre drilled bolt holes can be seen on the left side of the image. It is important that the mounting flange on the stern tube is as perpendicular to the propeller shaft as possible. In addition, the propeller shaft should be centered in the stern tube. This will assist in proper sealing of the propeller shaft.

If needed, your new stuffing box flange can be provided 'blank flanged' meaning that there are no holes pre drilled in the flange. This is desirable when non standard hole patterns are used in the stern tube flange. The other option is to have a mating flange fabricated.

When you order your stuffing box you need to specify male pilot or female recess. If your stern tube flange is male, then order a stuffing box that has female recess flange and vice versa.

When bolting your stuffing box to the stern tube flange be sure to use non corroding (non ferrous) fasteners. In addition, use a reinforced neoprene gasket that is 1/16' to 1/8' thick between the flanges to prevent leakage.

Installation of Stuffing Box Packing

Remove old packing from stuffing box (if replacing packing). Clean the stuffing box and shaft thoroughly. Be sure to remove any silt, sand, metal filings and other grit that may cause shaft wear and scoring. If your existing shaft or shaft liner is badly worn or damaged it should be replaced.

IMPORTANT: MAKE SURE PACKING IS THE PROPER SIZE

To determine correct size, first measure the diameter of the shaft (at position where packing will operate). Then measure the internal diameter of the stuffing box. Subtract the ID measurement from the OD measurement and divide by 2. The result is the required packing size. Our Ultra-X packing is available in any size from 1/4' to 1-1/2'.

ALWAYS CUT THE PACKING INTO SEPARATE RINGS PRIOR TO INSTALLING

Never wind packing into the stuffing box. Rings can be cut with butt (square) or skive (diagonal) joints. IMPORTANT: IF POSSIBLE CUT EACH RING ON A MANDREL (CYLINDER) with the same diameter of the shaft in the stuffing box area, to keep proper joint angle. If there is no shaft wear, rings can be cut using the shaft outside the stuffing box area. Rings should be cut to correct size - or service life could be reduced. When cutting rings, hold packing tightly on the mandrel, but don’t stretch the packing excessively. Ultra-X can easily be cut with a sharp utility knife.

INSTALL ONE RING AT A TIME

Make sure packing is clean of any dirt or grit from handling. Joints of successive rings should be staggered – at least 90 degrees apart. Each ring should be seated firmly using a tamping tool. When the packing rings can be reached by the nose of the packing gland, tamping should be supplemented by the gland.

BREAK-IN PROCEDURE IS CRITICAL TO INSURE LONG PACKING LIFE. After the last ring is installed, take up the bolts until they are finger tight. Do not jam the packing into place by excessive packing gland loading. Make sure gland bolts are taken up evenly. Stopping leakage at this point will cause the packing to burn up. For proper break-in Ultra-X must be packed loosely for the first 5-10 hours of operation.

AFTER THE INITIAL BREAK-IN PERIOD THE PACKING GLAND MAY BE TIGHTENED TO THE DESIRED LEAKAGE RATE. (Stuffing boxes are designed to always have some leakage)

Because of the superior thermal conductivity of Ultra-X, the stuffing box surface may run hotter when compared to traditional flax packing. This is normal. Ultra-X packing minimizes shaft wear and scoring by transferring frictional heat to the stuffing box which acts as a heat sink. Flax packing acts as an insulator keeping harmful heat on the shaft. Ultra-X does not require grease in stern tube applications where water is present. In bulkhead stuffing box applications it is recommended that grease is added to aid in lubricating the packing. Grease will not harm Ultra-X packing.