Saturday, June 25, 2011

Replacing the Packing

Several friends have asked me about replacing the shaft packing, so here's a quick post about it.  It's not hard to do and I figure it is important that you know how in case of an emergency.  I replace the packing each time I haul out whether it needs it or not.  I have replaced the packing on the MV Independence every time I've hauled out for the last 20 years except for once when I had a boatyard do it - and they did it wrong.

On all boats there's a "packing gland" or "stuffing box" where the shaft comes through the hull and into the boat.  There's a great deal of variety on stuffing box designs.  Some have a single large nut, some like the MV Independence have a collar with with two nuts.  Typically flax packing is a square cross-sectioned rope impregnated with greased flax.  The flax packing is wrapped around the propeller shaft and squeezed tight to prevent water from leaking in.

The Independence uses 1/4" flax packing.  There's two types of flax packing - plain and Teflon.  I try to use Teflon flax packing.  It costs a bit more because of the Teflon and supposedly it reduces some wear and tear.  When you remove your old packing you can determine the size.  It is important to use the right size - too big and it will not fit, and too small it will leak.

I've heard of some folks replacing the packing while the boat is in the water, but I don't want to risk it.  I prefer to replace the packing while the boat is out of the water ensuring that you can take your time and do the job right.  For me the job takes about an hour or so.  It's tight cramped work accessing the stuffing box but if you have the tools and the time the job is not too bad.

Here's the steps to replacing the shaft packing:
The stuffing box of the MV Independence
  1. Clean the shaft just beyond the collar of any dirt, and smear with just a bit of water proof grease.
  2. Undo the stuffing box nut or nuts - there's two on the Independence and slide the packing collar well up the shaft giving you room to work and remove the old packing.
  3. Remove the old packing with an old dental pic or a packing removal tool.  Make sure you have removed all the old packing.  I make sure all old packing has been removed by ensuring I hear a metal scratching sound at the end of the stuffing box.
  4. Cut your new packing with a very sharp knife to exactly make a ring around your shaft.  There should not be a gap of anything more than 1-2 mm of distance from the ends as it is wrapped around the shaft.  I typically cut four lengths of packing and ensure they are all the same length. Tip: I always cut one extra ring of packing and keep it ready by the stuffing box in case of an emergency.  You can always add a wrap of packing later if needed.
  5. Make sure the shaft is clean of any dirt.
  6. Smear some packing grease on the flax packing and wrap a single ring around the shaft.  Using a screwdriver gently push the packing into the stuffing box making sure not to twist the packing.  Make a mental note of where the two ends of the packing meet.  You do not want to simply wrap the full length of packing corkscrew style around your shaft.  It will be uneven and wear rapidly and leak.
  7. Repeat step #6 above but make sure to not have the gap on subsequent rings of the packing line up.  I generally rotate the packing to ensure the gap on each subsequent ring is rotated a quarter distance from the previous ring.
  8. Once all your packing rings are wrapped around the shaft, gently slide the collar down and lightly tap it with a rubber hammer down on the newly replaced packing.  Then start to tighten the screws down on the packing.  I try to ensure an even tightening by one turn on the port nut followed by one turn on the starboard nut and I count each turn until there's some resistance, but not too tight.  Note the number of turns in your log book.
Make sure to tell the boat lift operator that you have replaced the packing.  They will permit you to board the boat just after it gets in the water and before they slide the slings off to see if it is leaking too badly.  If it is leaking more than a drip every 2-3 seconds then gently tighten each nut until the drip slows to one drip or less every 4-5 seconds.  Signal to them it is okay and you are off.  Again, note the number of turns in your log book. 

Once you start the engine and put it in gear continue to monitor the stuffing box for leaks and drips.  Adjust the nut or nuts to tighten to stop any drips.  Note the number of bolt turns in your log book.  This will tell you how well your packing is wearing.  Old wisdom is that a drip every so often is okay.  The dripping water will "cool" the stuffing box.  I don't fully agree.  I have my packing tight so that it does not drip, but at the same time not so tight that it gets hot or even warm.  Occasionally while running I check the stuffing box for drips, tighten as needed and touch it.  The stuffing box on the Independence is cool to the touch and does not drip more than once every 30 seconds to a minute.  About after every 15-20 hours of running I give the stuffing box a check and adjust if necessary.

Hope the above helps.  If you have questions, let me know.

1 comment:

Alfex said...

Thanks for all the great info. I never thought of entering the turns in my log book.