But I would practice on a boat out of the water before doing it in the water. besides the rubber hose connecting your stuffing box to the shaft log most likely is due for a replacement. I would use Gore GFO when you do it.
Measure your shaft with a set of calipers. If it's 1 inch, 1 1/8, 1 1/4, 1 1/2 go to a local canvas
shop and ask for a scrap pice of stainless tubing the same OD diameter of your shaft and use it to make your rings on. Or if the boat is out of the water go outside the boat and clean a portion of the prop shaft with scotchbrite and cut the rings on it.
Cutting the rings:
Wrap some packing around the shaft or piece of scrap so the ends over lap each other by about 2 cm or so but are side by side on the shaft tightly. Then take a new razor blade and make a 45 degree slice through both ends, where they meet, in center of the area where the ends overlap. Now remove the flax and you have a ring that will fit perfectly on your shaft and the ends butt together with a perfect 45 degree scarf joint. Make three, or two depending on your stuffing box, rings and insert them into the nut, after cleaning
out the old flax with a dentist pick or similar, with the 45 degree cuts offset from each other. You don't want the 45 degree cuts all in a line they need to be off set from each other! Tighten packing nut by hand and allow it to drip for a few hours of engine
run time with the shaft spinning. Then re-tighten & adjust it to a point where the stuffing box is slightly warm to the touch and you're done. Use GFO packing and no grease it will drip much less than standard packing but you should still get a couple of drops per minute... I find it's a lot easier to pre-cut the flax rings before you start the job and maybe even have a couple of extra rings if you're not so good at it!
Be very careful with the Teflon grease mentioned in an above post. I used teflon flax, non GFO, and the grease for two seasons on one of my boats. Towards the end of the second season my stuffing box was running very, very hot. When I took her out of the water, and took apart the stuffing box I noticed a mass of teflon grease and teflon flax residue clogging my stuffing box between the shaft and the inside of the bronze stuffing box! The spinning of the shaft & tightening of the gland nut had squeezed & spun a coating of the teflon grease onto the inside of the stuffing box log until it built up enough to slow the cooling
water flow to next to nothing! The water that did drip out was boiling hot because not enough cool water could flow around the shaft. Stuffing boxes were never designed to have grease in them and the cheap
teflon flax (imitation Gore GFO) with the grease is a band aid approach at minimizing water ingress. I learned the hard way on this one as I had to pull my shaft to fully clean out the stuffing box. I actually figured while I had the shaft out to put in a PSS and love it!! No water, simple and easy!
If you want a good flax for a traditional stufing box buy the Gore GFO packing it does not require a grease like the cheap
Gore knock off flaxes do and when adjusted properly it drips very minimally compared to other flaxes.
In contrast to what others have said about GFO it is NOT deisgned to be entirely drip free. Even the GFO instructions do not say it's drip free. You can however adjust it to get less dripping than you can with the imitation GFO packings. GFO takes considerably less water to cool it than the West marine
Teflon flaxes do but it IS designed to drip slightly when the shaft is spinning. Mine was dry when the shaft was stopped but dripped a little when spinning and did not get to hot.
Installing the PSS: