Stuffing box maintenance
You are getting water in the bilge and you track it down to the propeller shafts stuffing box (also called stern gland). The stuffing box houses a seal which the prop shaft passes through. Some rudder stern glands work the same. Most stuffing boxes have an adjusting nut which compresses the packing material, controlling the rate of drip.
If adjusting the packing does not fix the leak you may have a damaged or worn shaft. If it’s in any way irregular, pitted, or damaged, the packing will be torn up each time the shaft rotates. If this is the case you can: Replace the shaft, or use a longer or shorter stuffing-box hose to move the location of the packing over to a smooth section of shaft.
1 This article looks at the stuffing box and its maintenance.
What does a stuffing box look like? The diagram courtesy of Catalina shows a typical propeller shaft installation with the shaft log and stuffing box. The shaft log is a tubular passage through the bottom of the boat where the shaft passes on its way from the engine to the strut and cutlass bearing. The stuffing box assembly attaches to the shaft log with a length of hose and a pair of hose clamps.
There are 2 types of stuffing box;
1 Traditional stuffing boxes
Water is required to lubricate conventional packing.
A properly adjusted stuffing box won’t drip when the shaft is idle, but 2-3 drops/minute when the shaft is turning.
2 Dripless Shaft Seals DSS
Dripless Shaft Seals don’t drip but still need cooling;
Most DSS units have a small barb fitting on the graphite flange where a hose can be connected to ensure that water is always present. From the fitting, the hose runs either to a place high above the waterline, or, in the case of higher speed vessels, into the engine’s raw-water cooling system.
2 Adjusting a conventional stuffing box
This fairly simple procedure can be done with boat in water.
This picture of a cross section of a shaft gland come to us thanks to the Alberg 30 class site.
Notice the “locking nut” and the “adjustable stuffing box nut” in the picture.
Conventional stuffing boxes require water to lubricate the packing. Often you will see water dripping from the box. A properly adjusted stuffing box will have no drips when the shaft is stopped, but 2-3 drops/minute when the shaft is turning.
When adjusting the stuffing box keep in mind that; if the adjustable stuffing box nut is too tight you will burn the packing which can end up with a damaged shaft. If your stuffing box leaks more than 8 drops a minute, it needs adjusting.
Two pipe wrenches are the tools needed for adjusting the stuffing box. Start by loosening the locking nut, this frees the adjustable stuffing box nut. As you tighten the Stuffing Box nut check for leaks while the props are idle. If you notice any dripping tighten the Packing Nut a bit more. Once you stop the dripping tighten the locking nut.
Now you are going to need to check the drip rate with the engine running. You can do this with the engine engaged in forward and the boat securely tied in the slip. If it is more than two drips per minute loosen the locking nut, then tighten the adjusting nut slightly. Access to the engine is critical and you should be aware of the shaft turning. It’s safer to take the engine out of gear, while you’re adjusting the nut. When the drip rate is one or two drops per minute, stop the engine then tighten the locknut.
Final check; As long as the box isn’t dripping too much and isn’t running too hot, you are in the correct range. While you’re at it give threads and nuts a coat of corrosion blocker.
Note; if you use a graphite packing like Gore’s GFTO, it can be tightened until the leaking stops completely but you will need to check the temperature of the stuffing box after running the boat for a while. The packing box should not be hot to the touch. “Since GFO fiber dripless packing is four times more thermally conductive than flax, it needs virtually no sea water for lubrication or cooling. And, because it doesn’t swell or shrink, leakage is controlled and kept to an absolute minimum.”
3 Replacing flax
Ideally to do this project you want the boat out of the water. It’s possible if you’re organized to do a short haul (boat hangs in slings) at lunchtime or overnight. If you don’t have the option the packing may be replaced with the boat in the water, but water coming in may be a bit disconcerting. If you’re organized the amount of water coming in can be handled by the bilge pump.
An excellent article; http://www.pbase.com/mainecruising/stuffing_box
To begin; Loosen the Lock Nut by placing one wrench on the Packing Nut and the other wrench on the Lock Nut. Using two wrenches helps prevent twisting and damaging the shaft log hose.
Removing The Old Flax; Once the Packing Nut is unscrewed from the Stuffing Box, use a pick and carefully remove all of the old packing. It can be difficult to see if all the old flax has been removed and so a dentist’s type mirror can be useful to inspect the Packing Nut. Careful not to score the Packing Nut or shaft.
Next installing the new Flax Packing. A common mistake is winding the new packing around the shaft as a continuous piece. This will not seal properly, instead It must be installed as a series of stacked rings. Usually 3 rings. This requires cutting the packing into lengths that just encircle the shaft with ends touching.
See section 4 materials for length and size.
Placing the new packing material in the nut is a delicate process and it
requires patience to get the packing right. Start by wrapping the first piece of flax around the shaft snug up against the stuffing box, ensure the 45 degree ends touch. Now slide the Packing Nut up against the flax carefully forcing the flax into the Packing Nut. Once the flax is as far as it will go into the Packing Nut, use a flat blunt object to carefully pressure the flax into the nut. Now install the next flax ring the same way and make sure the 45 degree joint does not sit in the same plane as the previous ring.
When all of the flax wraps are installed in the Packing Nut, begin to thread the Packing Nut onto the Stuffing Box. The Packing Nut will put pressure onto the packing and if it’s too full you may not be able to get the threads on, if you have it right it may take just a little pressure to get the threads. Nest apply more hand pressure to begin to tighten the Packing Nut. When you are max hand pressure, remove the nut and look to see if the flax is seating properly. If it’s OK re-install the Packing Nut and tighten snug using a wrench, back off slightly to ensure that it is not too tight when you first turn the propellers. Now thread the Lock Nut snug against the Packing Nut and tighten using your wrenches.
VIDEO; How To Replace Your Drive / Rudder Shaft Stuffing Box Packing With GFO packing
4 Materials and tools
The Stuffing Box Packing is woven flax or synthetic, squared-off rope like material.
There are two main types of material.
1 Traditional Flax packing; has been around a long time. This grease based packing is very reliable, however if the stuffing box gland nut is over tightened, the flax packing can heat up causing high temperatures and possibly damaging the shaft.
2 Modern Graphite packing; is an excellent a lubricant, reducing the chance of burning the shaft. It is very expensive however.
Sizing and finding the correct length of Flax Packing
Ensure you have the correct size flax packing for the stuffing box, if the old packing is relatively intact you can measure the thickness. The shaft diameter and type of stuffing box should reveal the correct size of the flax. Next you should plan on 3 full wraps of flax around the shaft to fill the Packing Nut.
Now you need to cut the flax to the proper length to fit completely around the diameter of the shaft. Lengths can be cut on the exposed shaft on the outside of the hull if possible. Cut the flax at 45 degree angles like a scarf joint. This will allow the ends to mesh together once the Packing Nut pressure is applied. If you can’t use the shaft you can use a piece of pipe the same diameter as your propeller shaft.
Suppliers; Stuffing-box manufacturer Buck Algonquin (www.buckalgonquin.com).
Packing; Graphite packing http://gfopacking.com/
Tools required; a pair of spanner wrenches or pipe wrenches. Razor knife or razor blades to cut the flax. You will also need a bent ice pick, or a stiff piece of wire bent 90 degrees to remove the flax.
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