stuffing box, shaft log ... terminology and questions

[Chuck K.]

I recently bought a 1982 25D (hull #15). One of the recomendations in the survey was that the stuffing box hose, clamps, and packing material be replaced, and after reassembly, the engine be realigned with the shaft.

I arranged for the yard to do the job, because I had no desire to cram myself in there to do it, even if it was physically possible. The yard service manager referred to the hose as the "shaft log," which confused me, because I thought the shaft log was where the shaft passed through the hull. From reading prior posts on this board, I now beleive that is called the cutlass bearing.

I'm still confused as to what or where the stuffing box is. I thought that was the point inside the hull where the shaft passed through the hull, and contained packing material to stop water from entering the boat around the shaft. Is the stuffing box located forward of that hose, or inside of it? If that is the job of the stuffing box, what is the purpose of that hose (approximately 4-5" long) that the shaft passes through? It is double clamped at the aft end where it attaches to the hull, and at the forward end, near the flange on the shaft.

If anyone can explain these terms, I would greatly appreciate it. My prior boats have all had outboards, this is my first experience with an inboard engine. I'm currently ignorant on these matters, but eager to learn.

[Cathy Monaghan]

The SHAFT LOG (also known as a STERN TUBE) is the tube (it may be bronze or fiberglass) that the shaft passes through to exit the boat.

The CUTLASS BEARING is long rubber or neoprene tube-like bearing that is housed within the SHAFT LOG and/or PROP STRUT. (Cape Dorys don't have prop struts.)

The STUFFING BOX (also knows as a PACKING GLAND) is the gizmo that prevents water from flowing into the boat where the shaft enters the SHAFT LOG. There's usually a rubber hose that's clamped to the tube at one end and to the STUFFING BOX at the other.

The STUFFING BOX, or gland, is packed with wax or Teflon coated flax packing material. The STUFFING BOX also has a nut that when tightened against the packing material controls the water flow through the gland (the part the packing material is in is called a SPUD). In most STUFFING BOXES, water is used to lubricate and cool the gland so you do want a slight drip -- every 10 or 15 seconds or so.

I think I explained that correctly. I know if it's wrong, somebody else will jump in with the correct info.

Fair winds,
Cathy
CD32 Realization, #3
Rahway, NJ
Raritan Bay

[Trawler Joe]

Sure looks good to me, very clear and precise!

One thing I've always been curious about is why a flexible (or semi-flexible, at least) hose is used to attach the stuffing box to the stern tube. Is it important that it be flexible? Is it just the simplest way to attach the two together? Is it flexible specifically to allow some movement (or wobble) of the shaft, if the shaft becomes misaligned (i.e., better to allow movement than have the shaft or stern tube break)?

[Lew Gresham]

Here is a 1" shaft log!


[img]http://i125.photobucket.com/albums/p52/ ... ems005.jpg[/img]

Sorry for the mistake! I know it's a stuffing box, just a senior citizen moment.

[Zeida]

The picture on the previous post is a 1" Stuffing Box or Packing Gland, not the shaft log. This piece is already inside the hull and is the one that connects via a hose and meets the shaft log, the one that holds the cutless bearing and traverses the hull. Running inside and through all of these gizmos is the prop shaft itself. On the picture below, you can see the difference between the pieces and what they are for.

[img]http://www.imagestation.com/picture/sra ... 818ee1.jpg[/img]

On the left, is the Stern Tube or Shaft Log... with a piece of the cutless bearing sticking out from the right side... on the right, is the stuffing box or packing gland. These two pieces are joined by the very thick hose, which traverses the hull. Below you can see how they all attach together. The prop shaft runs through all of them, and attaches to the black coupler, at the end.

[img]http://www.imagestation.com/picture/sra ... 818e29.jpg[/img]

[Parfait's Provider]

The hose is necessary to provide for the positioning of the stuffing box on the shaft while isolating it from the hull. Otherwise, there would be additional wear on the seal and it would require adjustment more often. Further, if there were no flexibility between the hull and the seal, the engine vibration, rolling, pitching and yawing would be working on the transmission and the shaftlog, trying to dislodge it from the hull. This is not desireable. Remember, the engine is mounted on flexible mounts, so it is going to move relative to the hull.

In your car there are universal joints; the closest you have in your CD to a U-joint is a flexible coupling, which has little capacity to provide flexibility in alignment; it is more for isolating rotational shock from the transmission.

I hope that helps.

[Trawler Joe]

It does help! Thanks.

[Chuck K.]

Thanks very much for all the replys. It is now much clearer in my mind. My stuffing box looks exactly like the one in the photos posted by Zeida.

Next question ... if I do this job myself in the future, the nuts look like they require a special wrench, as opposed to the standard hex nuts in the photo posted by Lew. Is that a readily available tool, and where might I find one.

Thanks again folks.

[Trawler Joe]

The wrenches are available from Spartan: http://www.spartanmarine.com/source/22.htm (see full catalog: http://www.spartanmarine.com ). They run about $50 for the pair, but they're very nice tools.

The first time I needed to make an adjustment, I didn't have the wrenches. You can break loose the stop nut by putting a screwdriver against a notch, and tapping it with a hammer. I managed to adjust them with giant channel locks after that.

[Chris Reinke]

Chuck - One additional point to consider when your evaluating if you want to replace your shaft log (stern tube) or hose. In a perfect world the flange on the stern tube that protrudes into the engine compartment would allow you to secure the hose with 3 stainless hose clamps. The same would hold true for the flange on the packing gland on the other end of the hose. Most owners would be happy with 2 clamps on either end. CD was notorious for installing a very short stern tube. On my CD330 the length of flange over which the hose attached was just long enough to secure only a single hose clamp. This was something that has always bothered me and so I replaced my stern tube as part of a major refit this past winter.

If your going to replace the hose then you will need to remove your shaft (the packing material can be easily changed without removing the shaft). I would suggest you consider replacing the cutlass bearing (located on the outboard side of the stern tube) while the shaft is removed. The additional cost is minimal since your already doing 75% of the labor just getting the shaft out and it would be money well spent now vs having to do it all again in a year or two should your bearing fail......just my thought.

[Bob Condon]

Cutless bearing is in the strut assembly on that boat!

Excellet replies.