Stuffing box packing

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How do I install the STUFF in the stuffing box? What is a stuffing box anyway? There are several different types of packing. What kind should I use and what are the differences between them? There are a range of different sizes of material from 1/8" to 5/8". What size do I use? How do I do this? Can I do it with the boat in the water, or do I need to haul her out?

We ALWAYS get questions that ask: "Can I do it with the boat in the water? Will it sink my boat? Answer: NO your boat won't sink. You CAN and actually SHOULD do it in the water, 'cuz if you do it on the hard, you still have to readjust it once the boat gets in the water, since the water affects the flax. Why do it twice?

Ultra X, discussed in Maine Sail's article, is very good stuff, new in 2012 or thereabouts.

Read on...

The stuffing box is actually the large nut on your propeller shaft between the stern tube where the shaft goes out of the boat underneath the aft cabin berth, and your transmission at the aft end of your engine. The stuffing box performs two major functions: it keeps that nasty water we float on OUT of the boat, and it lubricates the shaft as it spins inside the stuffing box itself.

Catalina's C34 manual that came with your boat has a very good illustration of the stuffing box. It is a section (engineering-speak: means a cutaway type drawing, like a slice right through the middle) showing the stern tube, the black hose, the shaft, the stuffing box gland assembly (the BIG nut forward) and the smaller Locking nut aft. See pages 39 and 40, drawing 4.4.2, Chapter 4.4.3, Auxiliary Power, Shaft Packing Gland (Stuffing Box).

Maine Sail has a very good photographic review on his website: [1] or

Ralph Johnstone has also developed some good ideas:

For most C34s you'll need 3/16 inch flax material, although that flax size has been reported to be 1/4" flax for hull # 713 (a 1988 model with a standard 1" shaft). Better check your manual. If you don't have one, just measure the distance between the edge of the shaft and the inside of the stuffing box after you have backed the stuffing box off. First loosen the locking nut (it will move aft), then loosen the stuffing box (it will move forward). If you're in the water, water will now make its appearance - don't worry, it's not much. There are five different types of "regular" packing material. "Regular" means the material that is inserted in your existing stuffing box, as compared to new equipment, like the PSS Shaft Seal, which requires removal of the existing stuffing box, and replacing it with a new piece of equipment.

The five types of "regular" or traditional materials are (2000 prices):

  1. Conventional flax @ $4.29 for a two foot length
  2. PTFE flax @ $4.19
  3. The "Drip-Less Moldable" packing kit
  4. The Goretex GFO from e-marine
  5. Ultra X new in 2012 or so

The size of the square flax material required is based on the clearance between the outside of the shaft and the inside of the stuffing box, where the flax goes in. Here's the differences between the flax material: both the conventional and Teflon impregnated flax need water for lubrication, hence the need to keep the stuffing box actually "dripping", one or two drops per minute when the shaft isn't turning, and four to five when it is moving.

There's been lots of discussion over the years on just how much "dripping" is required, covered in many old Mainsheet articles for Catalina 34s and others (the older C27 and C30 tech tips are also good sources). For traditional flax (NOT "dripless") the amount of water dripping is easily adjusted based on how much you tighten the stuffing box nut before you use the locking nut on the stuffing box assembly. The stuffing box nut is the bigger one that is forward on the shaft, tightening it moves it aft. Check the C34 Website, under Mainsheet Article Index, and search for packing gland and stuffing box to find those articles. The August 1990 Catalina 27 tech tips has a good article on how to install the material. Ron Hill covered it very well in May 1992 and Feb 1993. The search will detect those issues of Mainsheet that discussed the packing gland, assuming you have access to the old Mainsheets. Now that the website is up with the Tech Notes Online from Mainsheet articles (for C34IA members), you can read all of the C34 articles.

This next section describes the moldable packing process. If you are using traditional, Gore or Ultra X, please ignore this section although it does include how to get the old stuff out (this was originally written around 2000).

The "Drip-Less Moldable" packing kit works like this: First, you still need regular flax in addition to the green dripless goop that is the heart of the dripless package. It makes sense to use the Teflon, rather than conventional flax in any event, since it's both cheaper and has more inherent lubrication in the material itself. Second, there are three "rings" of flax in the stuffing box. The outer two rings are still the traditional Teflon flax, while the inner ring of normal flax is replaced with the new dripless green goop. What you do is warm up the green goop in your hand and roll it or knead it out into a thin square strand that matches the 3/16 inch square size of the regular flax. You make a piece long enough to fit around the shaft's circumference. That's easy to do by using the portion of the one inch diameter shaft forward of the stuffing box, so you end up with a piece about two inches long that'll fit around the shaft, same as the other two pieces. The magic tool to get out the old flax is a # 6 or # 8 drywall screw about 2" long. It has a very sharp point. Just push it in by hand into the old flax and screw it in with a hand screw driver. When it bottoms out, grab the head of the screw with a pair of pliers and pull it out. Other folks have reportedly found success with the use of a dental pick. The ones the hygienists use to scrape tartar. Nice sharp, but slender hook at the end. Reach in, grab the packing, yank it out.

After removing the old flax, you install the first ring of normal flax (the forward piece), then the ring of green goop dripless material in the middle ring, then the last (aft) ring of normal flax. The regular flax should be cut at 45 degree angles. See the C34 manual's description of how to cut the flax and stagger the joints.

Instead of needing to have water dripping for lubrication of the flax, you can hand tighten up the stuffing box so it doesn't drip at all, but not too tight. The final adjustment part is trial and error, covered in one of Ron Hill's Mainsheet articles. The trick is to tighten the stuffing box until water stops, but don't tighten too much. Don't tighten and then back off. Always tighten up the locking nut to the stuffing box with a wrench.

The advantage with the dripless stuffing material is you don't have to think about constantly checking the drips and keeping water out of the bilge anymore, except for checking the box once in a while to make sure you didn't originally over tighten it (too much heat is the giveaway). The film can of stuff that comes with the kit is Syn-Tef lubrication which you should use anyway with any kind of flax stuffing. Install the Syn-Tef with Qtips. It's called "Dripless" because the middle ring of green goop provides the internal lubrication for the flax that the water used to provide. When you install the flax (of any kind) be sure to cut the edges at a 45 degree angle, not butted, and stagger the joints of all three rows so they do not line up. The manual shows this very clearly on the drawing. Clean the shaft with fine wet/dry sandpaper and then lightly oil it prior to tightening the packing gland. At first tighten the packing gland big nut by hand only, and be sure to tighten up the locking nut to the gland with a wrench. This locking nut keeps the gland itself from loosening. If you've used dripless packing, it should NOT drip, either at rest or with the shaft turning with the gears engaged. A tight locking nut is critical for being seaworthy.

The cost of the dripless seems high at $50 instead of $4.19 plus tax, because you only use a little bit of the whole package. You could either look at it as a good long term investment that'll last 20 years (!), or share it with a dockmate or two (since the material isn't size specific like the size specific 3/16 inch traditional flax, because you knead it by hand, it'll work for anybody with a stuffing box) and reduce your investment by asking them to chip in. The natural progression seems to be from traditional (either conventional OR Teflon) stuffing material in the stuffing box, to adding the dripless green goop in the center of the three rings, and then it seems that the gang moves on to the PSS mechanical seal, which is $200. Regarding the PSS replacement solution, Ron Hill recently wrote: "There are a number of solutions out there. With a 1" shaft most of the "bellows" units like PSS will fit. You might also consider "drip free packing" which I wrote up in the May 1992 Mainsheet . I've used it since the spring of 1991 and still have it installed today (with a dry bilge). I saw it's still available at West Marine.

[Added Oct. 2009 by Stu] The e-marine Goretex GFO packing is a popular alternative to the green goop. It was invented well after I originally wrote this material.

[Added June 2012 by Stu] I've switched to Ultra X, I ran out of the green goop, 13 years, not too bad!!!:)

Any advantage of the packing over the bellows unit? If the bellows were to break - for whatever the reason - you have a real EMERGENCY and had better find a travel lift fast. If the normal flax/dripless packing leaks all you need to do is stuff more flax /dripless packing or even stuff pieces of shoe lace/rag in the packing gland to temporally stop the leak." The swap from traditional flax to dripless can be done with the boat in the water, gets a little water in the bilge and is great fun to work around. If you're unsure about this, do it when it's out. Have the new rings cut and ready to go in if you are in the water. Actually the hardest part is getting the old packing out. Ron made a special tool, but he got it out easily and stuffed the new material in with a blunted pencil I think. I used a wire coat hanger to get the old material out. The drywall screw idea seems the best, and I've used it and a small flat screwdriver, too. The flax pullers sold in stores DO NOT work because they are too big for the opening on our boats, so don't bother buying one. Also, you'll probably notice green crud on the outside of the stuffing box. That's the equivalent of rust on the bronze material. Recently learned from an article somewhere that anhydrous lanolin will work to keep it clean, so once you clean off the "rust" apply some lanolin and it should keep the box and locking nut clean as a baby's bottom.

Orig: 1999; Edited 2009