It’s my first time installing packing in the stuffing box. My nonsuch 324 is on the hard. I was able to get 3 wraps and have the nut about 2 and a half full turns. I just read in my manual that it requires 2 wraps of packing. Should I remove the third piece? Thanks
Having flown and maintained military aircraft for many years, it has always been very important to follow the designer’s instructions. When you deviate from those things that have been tried and tested, you venture into the experimental category. The reason that the designer made the specification in the manual may not be obvious and your slight deviation may seem harmless. I always tend to think about risk mitigation and management as well as, what opinion my insurance company may have on the matter. These are just my thoughts on these sorts of things in maintaining my vessel.
I’d make the same recommendation but, with all due respect to Stephan, want to present different reasoning behind it.
The following is a bit long. It’s only worth reading if you’re interested not just in the answer, but in the process of arriving at it.
My approach is that it always pays to weigh the tradeoffs. What’s the risk, the cost of being wrong, and the effort of taking an action? Also, what’s the quality of the information you’re working with?
Frankly, mistakes in aviation and nuclear safety have higher costs than boats, so a higher standard of caution applies to them. Boat operation can be unsafe, but most things won’t get you killed (until your partner asks, “You spent how much on that?”).
My guess is that the factory recommendation on wraps is based on the reasoning that two wraps is sufficient. Since a stuffing box works by compressing low friction packing against the shaft, I’d be surprised if a single additional wrap could harm the shaft, transmission, engine or performance. In fact, I’d be very concerned about the quality of the mechanical system if that alone could do harm.
Replacing the packing is based on it having worn to the point where compression no longer works. My guess is that extra packing will make the irritating job of removal that much harder when it comes time to do the job again. After all, it’s prying out tightly packed gunk, and you’d have more to pry out. I’d also guess that it won’t last longer – since different parts of the shaft wear on different parts of the packing, I’d expect three wraps to reach end of life just about the same time as two.
Noting my point about quality of information, if former boat mechanic Joe Valinoti speaks up and says I’m wrong, listen to him rather than me. He’s trained. My only qualification is that I’m still alive after 43+ years of sailing on boats where I did most of the work myself.
Anyway, I don’t regard think it’s a big risk to leave it be.
So, why am I still agreeing with Stephan to re-do it according to the factory recommendations? Because, with the boat still on the hard, the cost of re-doing it is pretty low.
I.e., I’m weighing small risk of bad things happening and the moderate risk of P.I.T.A. effort at your next re-do, vs. the small cost of re-doing it now. Since the re-do now is easy, why not?
Now, key to this whole thing is being fairly confident I understand how this particular system works. There are lots of other things where I know that I’m ignorant, and in those cases, I always follow recommendations to the best of my ability.
All this said, you’ll never go wrong if you operate at Stephan’s level of care.
-- Bob
And yet another perspective. The packing under pressure and pressing against the shaft is similar to a brake pad being applied to the brake disk or drum. If two wraps is sufficient to keep the water out, why add 50% more braking (drag) to your shaft?
3 is fine. Just make sore that you are getting about 3 drips per minute after taking it on a sea trial. DO NOT OVERTIGHTEN!