12-71TI rebuilds-dripless stuffing boxes/shaft seals

[Tawney1]

Covington Diesel in Wilmington begins the tear-down and rebuild of our 12-71TIs next Tuesday. After negotiations (and an increase in price) they have agreed to build A-frames to raise and turn the blocks, etc. This is as close as we can get to an out-of-frame rebuild. Estimated time is 2 weeks per engine, assuming all the parts arrive as expected.

One of the "while in you're in there" things we are considering is the installation of dripless stuffing boxes/shaft seals. I have never seen these installed on a boat and I know little about them--but the concept is very appealing.

I would appreciate any advice anyone has to offer about whether or not these are a good idea and what kind or type is the best or better. Also, any suggestions about improvements or "must dos" to the engine room or systems during the process would also be appreciated.

Thanks,
Paul

 

[Genesis]

I do not like dripless seals.

They keep the small amount of water out of the boat. However, if they fail, they can (and occasionally do) sink boats.

 

[Jackman]

I asked this same question about 2 weeks ago. I think genesis is the one who convinced me most, not to go with the dripless shafts...for valid reasons. So while going through the repower process I cleaned up the old shaft logs and stuffing boxes and put them back in. Once cleaned up they looked as good as new...nothing, absolutely nothing wrong with them except I replaced the bolts that hold the stuffing box together with a new set of SiBr bolts because after years of tightening they just needed it. New these things are well over $450 each because they are solid bronze. They lasted 25yrs (They were obviously never removed). That is testement enough for me.

 

[Finalee]

If the prudent Captain visually inspects the dripless shafts the same way he did the dripping shaft there should be very litttle chance of a problem. Has anyone installed them while in the water?

 

[MikeP]

You can't install dripless shafts in the water because the shafts have to be disconnected/moved back sufficiently to remove the old box/install the new one. When you do that, more water will be coming in the boat than you will be able to deal with. You may have to remove the prop as well to get sufficient rearward movement of the shaft.

I think the concern with dripless is that they can fail catastrophically if the seal is torn whereas a stuffing box/packing cannot. I was considering them a few years ago but Karl brought up the use of goretex packing which, once properly adjusted, is essentially dripless. I tried that - screwed it up the first time because I didn't follow the instructions; got it right when I re-did it - and it works as advertised.

It really is essentially dripless thus combining the best of both methods - no water and no scary failure mode. Plus it costs nearly nothing compared with putting in a dripless system.

 

[Tawney1]

I never considered installation while the boat was still in the water. I considered the dripless installation, since the boat will be hauled out for part of the time during the rebuild. The shafts were repacked last July but even with tightening, I think they still drip too much. We have put about 90 hours on the boat since then.

It's pretty frightening to consider the possibility of a catastrophic failure. That is a big concern. I admit that I did not even think of that.

Replacing the bolts is a good idea and I should have done that last year. What was the total cost to do that?

 

[thoward]

I researched this with the Egg and found the GORTEX is the way to go. There is no advantage to the dripless seals and they cost more.

 

[Pascal]

finalee... there is not much to inspect on a dripless shaft except for sign of wear. i had dripless on my previous boat, vee drives, and had no issues with them. They rarely fail however when they do, it tends to be catastrophic... as in massive leaks, with no warning. Worth it with Vee drives since the stuffing box is under the engine with bad access and leaks sprayed on the pan... no worth it on a straight shaft boat with good access.

i discussed this with my surveyor when i got the 53, that was is opinion too.

goretex packing is "virtually" drip free and the best compromise

 

[Tawney1]

Thanks very much guys for the advice and the information. I will stick with the dripping stuffing boxes but go with the Gortex!

That stuff sounds great and it should give a couple years of practically drip free performance.

Thanks,
Paul

 

[captddis]

I have replaced the PSS systems in the water. Not really a big deal as long as you have everything ready to go. I guess it is what you are comfortable with.

 

[Boatsb]

I used the standard flax last year on my shafts and ran about 150 hours with little if any change to the 6 drops a minute. The shafts don't get hot and I have neoprene clamped in a half collar over the stuffing boxes so spray is caught and put back down instead of spraying in the bilge.

 

[Captned]

I have had my boat for over six years and have never adjusted my packing glands because they have never dripped a drop or got hot! I'm dying to pull them apart and install new packing but why??? This has always been somewhat of a puzzle to me. Any suggestions?

Captned
46 78 Con

 

[MikeP]

Dang, you need to get in their right away and pull that old packing out and put in new stuff! Otherwise, you risk belonging to the "If it ain't broke, don't fix it" crowd!

Seriously...I'd leave it alone!

 

[captddis]

I use the white teflon packing and have used it since the mid 80's. It goes about 5 years without adjustment. I service a Trojan that was repacked with the teflon in 1994, still going strong and never been adjusted! I wonder how long it will go?

 

[jim rosenthal]

Good article recently in Passagemaker about the dripless packing glands...which also states that most things work well if they're maintained. If not...well, you know the rest of the story.

I bought my PSS seals when Blue Note was repowered in 1998. I have had no trouble with them. I have kept an eye on them. One thing I asked Tom Slane's techs to do this go around was check the bellows and see if they need to be replaced. This would be the time to do it.

Dripless seals have one other advantage over standard shaft logs, which hasn't been discussed here- they tolerate misalignment better than the old-fashioned shaft logs do. No one intentionally runs their boat when the shaft alignment is out, or they shouldn't, but alignments do drift, and the dripless seals are not bothered by that the way the bronze shaft logs are.

I have to say that when I bought them, I don't think the Gore-Tex/Teflon alternative was available. Had it been, I might have done something different. But, so far, I have been happy with the dripless seals. Mine are PSS, incidentally- I can't comment on any of the others.