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Dripless Shaft Seal versus Stuffing Box

57K views 73 replies 41 participants last post by  Don L 
#1 ·
I took a tour of the Catalina facility last week. Really enjoyed meeting the folks and was shocked at the systems they have in place there. For those that have not see it (catalina lover or not), it is interesting - especially when compared to something like Valiant which only put out 8-12 boats/year.

Anyways, Catalina has moved away from the dripless shaft seals. My previous boats (320 and 380) had a traditional stuffing box but my C400 has a dripless. all the new vessels out of Catalina are back to a traditional stuffing box.

I inquired with them about this and they responded that effectively they changed because a stuffing box gives some warnings before going out and is not necessarily a big deal when it does. However, the dripless may fail with little notice and can become a, "water hose" down below.

I thought about that, and I tend to agree with them. I saw another Catalina 400 when I had my boat pulled and the yard owner told me the 400 had an emergency pull becuase their dripless failed and threatened the boat.

On the flip side, keeping a dry boat sure has its advantages too. Sure makes tracking down any potential leaks easier.

I am curious what others think about this? Opinions?

Brian
 
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#2 ·
I use the wonder packing :) and it gets wet BUT it does not really drip faster than it can evaporate from all the motor heat

BUT even a small drip would go to the small deep part of my bilge that has a big capacity BUT with the pump i installed there is never even a gallon of water in the boat

The REAL issues i see are boats like a C&C 35 Mark I that literally do not have ANY bilge
 
#3 ·
I cannot imagine why anyone would install a Dripless Shaft seal. Why install somthing on your boat that could fail at any moment and sink your boat? I thought about installing one until a friend whom has one tells me how rapidly they can fail. Dripless not for me.
 
#4 ·
Think about it it like this.
It is probably cheaper for Catalina to go with the traditional stuffing box then a dripless shaft seal. The traditional stuffing box gradually exhibits failure mode as more water gets in as packing wears away. (New packing is < $20) If the Dripless Shaft Seal rubber bellows ever cracks, rips or otherwise fails you may need a haul out and a new bellows.
I'm with Catalina on this one. The traditional stuffing box is a tried and true, hundred+ year old technology. Using this method saves them money and makes their boats a little bit safer. It is a no brainer.
 
#7 ·
Are there any statistics supporting the assertion that a traditional stuffing box is safer than a dripless shaft seal (DSS)?

I would think the insurance companies would consider a DSS an additional risk factor and increase the premium if this were true, especially if its failure results in a total loss.

I have read and heard merely anecdotal evidence of DSSs failing, including an article in Boat/US magazine. A DSS is a moving part, which needs periodic inspection and replacement in due time (10 years?).

I am not surprised that a production builder would use a less expensive traditional part based on an unsubstantiated belief among buyers.
 
#8 · (Edited)
I am not sure on the statistics. But I hear a lot of bad things:
Emergency advise needed on a leaking pss dripless shaft seal ! [Archive] - Boat Repair Forum, Classifieds & Photo Gallery

I do not think insurace companies get that involved with how you boat is made, although maybe they should. Insuranace companies do not care if you use plastic through hulls or chinese carbon steel chain for you anchor rode. Like your car they do not raise your rates because your SUV has tires on it that have been recalled and are known to blow out at highway speeds. Buyer beware.
 
#9 ·
I've had both. From my perspective I can't see a lot of difference as far as risk to the boat goes. The stuffing box uses a piece of heavy duty hose to hold the packing gland and there is arguably more torque on that hose from the friction of the packing than from the carbon block sliding on the stainless ring of a dripless type. Which is more likely to rip or tear and create a large leak? How often do you change that hose, I'm guessing most people have never changed it or even thought about the torque put on it. Dripless types recommend that the bellows (which is very thick and heavy duty) be changed every 8-10 years IIRC and that includes the hose clamps, and I just can't see one failing in that short amount of time. Another aspect is shaft wear, not a safety issue, but an expense over time from wear at the packing. There is no wear on the shaft of the dripless type. I'm not convinced that there is a big difference either way from a safety perspective but if there were any statistics that compared failures of the two types I'd be interested to see them.
 
#10 ·
I believe that jrd22 hit the nails on the head. Less wear & tear on the shaft is a major positive attribute of a dripless system.

I swapped my stuffing box over to a PSS dripless last year. I was impressed by the quality of the components, and the statement that most PWCs use them (anything that can survive a PWC is a good thing). I was, however shocked at the price, and the fact that the recommended replacement interval is 6 years, although I believe that they could run for 10.

As with any rubber hose below waterline, the PSS bellows must be inspected on a regular basis for any sign of wear, aging or chemical deterioration. PYI suggests preventative maintenance. The PSS bellow should be replaced in six year intervals. During bellows replacement it is recommended the o-rings & set screws in the stainless steel rotor also be replaced.

Bellows may need to be more frequently inspected in an environment where non-sealed batteries emit sulfuric acid. Sulfuric acid vapor will accelerate rubber deterioration, as will an ozonater.
Ever since replacement I have had NOT A DROP of water in the bilge.
 
#11 ·
I've just bought a PSS dripless also. Not tested it yet but the rubber is quite thick and feels sturdy. I believe that with regular inspections and changing as eherlihy said it should be fine. I plan to reinforce the stainless steel ring that keeps the compression on with perhaps a spare anode to prevent any possible slip.
Despite that I must admit the fact that the sea would come rushing in with a failure and little could probably be done to stem it is somewhat disconcerting.
 
#14 ·
My current boat has a drip-less. It was on when I purchased it, otherwise I would keep to the old stuffing box technology.

I'm pretty far out on my own mooring so I rely on neighbors in the mooring field to keep an eye on things.

If/when the time comes, I'll probably go back to a traditional stuffing box with the high tech stuffing material.

My mast is keel stepped so my bilge is rarely completely dry so what's the point in pretending :D
 
#15 ·
My mast is keel stepped too, and the bilge is completely dry with the PSS Shaft Seal.
 
#16 ·
Who cares if you have a dry bilge. Any time you do some serious ocean sailing your bilge will get water in it. So what, boats are made to get wet inside and out. If your boat cannot handle a little water, somthing is wrong.
 
#18 ·
You may not care, but I, and several others, do. I do not want stagnant water to collect in the bilge. For more on why see this thread. It can also lead to that "boaty smell."

If you don't mind water in your bilge, that's your business...
 
#20 ·
Interesting article Casey. He makes some good observations about what can go wrong and that maintenance is required. Bottom line: the author has a dripless shaft seal on his boat.
I put a shaft zinc on forward of the stainless ring on the seal instead of a hose clamp.
 
#23 · (Edited)
I had a "failure" of a PSS seal. First hand! Still sweat thinking about it.

In the PSS design, a carbon bushing on the bellows rubs against the rotor, a steel ring, to provide the watertight seal. The rotor is held in place on the propshaft with two grub screws - each with a second grub screw behind the first to prevent backing out,

In my case, the grub screws loosened over time, and while moving into my slip the rotor slipped about 1". I am guessing the engine moved on the engine mounts when I put her into reverse, putting pressure on the loose rotor. Luckily I heard the rushing of water before I left her, or she could have sunk at the dock. Within 5 minutes the water level was within 1/2 of the cabin sole. Think 3-4 hosepipes fully on.

People have alluded to this in this thread, but just in case anybody here has a PSS seal I want to be perfectly clear: ENSURE THAT THE ROTOR IS LOCKED IN PLACE. Check next time you are in the boat; a hose clamp, zinc, or stainless steel collet will work. http://ct4.pbase.com/g1/84/622984/3/131607031.5lrRHrj9.jpg (from MaineSails excellent PSS Shaft Seal Installation Photo Gallery by Compass Marine at pbase.com)

The two grub screws are not enough. it's like driving without airbag, seatbelt - or doors. Beats me why PSS doesn't recommend this - reputable yards add a backup as a matter of course - they seem like nice folk, and set me free grub screws to re-attach my rotor to the shaft. CHECK YOURS. Sorry to rant, but that was a lot of water.....
 
#25 · (Edited)
I would suspect Catalina moved back to a traditional stuffing box because they are about 1/3 the cost of a PSS (based on wholesale pricing and Catalina pays less than I do I am sure).

The installation is also less costly for Catalina with a traditional gland not having to run an extra hose for the vent.

The PSS seals are extremely reliable and are used by the USCG and the world best builders. I know of some in commercial used with over 10k hours on them.

All the failures of PSS I have read of have been due to installer or owner error. The stainless rotors do not slip if properly & competently installed. I have seen 20 year old PSS seals still working perfectly. I have one customer who still has the old cloth covered bellows, this despite my very strong suggestion he replace it. I don't think PYI has made those bellows for about 15-20 years.

The term "properly installed" means the grub/set screws that contact the shaft are only ever tightened once. ONCE!!!! Tightened and used are two different things. They also need to be tightened to the proper torque with the proper Allen key.. PSS ships the proper Allen key but I still see grub screws molested by using the wrong Allen key.

Often times installers mess up the adjustment or compression of the bellows. Sadly they think nothing of loosening the set screws and simply moving or re-adjusting the rotor and snugging up the set screws. PLEASE DO NOT DO THIS! If this is done it is no longer a proper installation and you have just increased the risk of the rotor slipping and a leak. If you need to adjust the bellows you need to use brand new set screws.

These set screws can only be tightened once because the shaft, usually Aqualoy or Nitronic, is harder than the grub screw. These volcano head screws rely on the initial "cut" or bite into the shaft for the grip. Loosen the screw and move the rotor, even 1/8" and you need new screws.

PYI Says this right in the installation instructions:

"Do not re-use the supplied cupped pointed sets screws."

What is a one time use? If you tighten the set screws onto the shaft even once, that is your use. For example if you are installing the PSS and adjust it, tighten the set screw then realize the adjustment was wrong you now need to use new set screws. This is installer error numero-uno with PSS seals....


For years I have installed PSS seals with "clamp collars" from McMaster Carr as added insurance. Hose clamps and zincs are really not the ideal solution but a clamp collar is designed for this:


Here's a better view:


PYI saw me using these and they now offer their own "clamp collars". IMHO all PSS seals should come standard with a clamp collar, and a bag of extra set screws, but I digress. It would virtually eliminate installer error and slipping rotors and help eliminate the "I had a PSS failure" threads, which were really "installer error".

Both standard glands and PSS seals are reliable. I have however seen and know of plenty of sinkings related to traditional boxes. They are also highly prone to installer or user error. Hoses on traditional boxes also need to be changed so a traditional gland is not immune from hose replacement maintenance.


Despite misleading marketing messages by packing manufacturers traditional boxes should not be run "dry" or "dripless" but they can be "drips-less" than older plant based packings.. They, all PSS type or traditional glands, need to pass some water (traditional) or vent air (PSS type), or they can overheat. Trapped air or not passing of water can also lead to stagnation and corrosion of the shafting up inside the log.

This is what stagnant water on a traditional box set to not drip can do:


Some boats are more prone to trapped air in the log hence PYI's move to all vented/plumbed seals even on slow moving craft. "Burping" on some boats was more than just at launch time so vents make a lot of sense on all sailboats.

Newer packings can be pretty darn drips-less but should not be 100% dripless. it can be so minimal that engine warmth evaporates any drips before it accumulates.

Unfortunately I can't count the number of times an owner or yard mechanic has said to me "Yeah when I adjusted the PSS." and I ask "Did you replace the set screws?" and am treated with a blank stare? Scary stuff!

If a failure were to occur with a slipping rotor, in this scenario, it is installer error not the fault of PYI or the PSS seal.

I also very often see the vent holes plugged with brass or ss plugs. The vents should always be plumbed (power) or vented/used on sailboats. Metallic plugs should never, ever be used in the carbon rotor. There is a reason PYI uses a nylon hose barb and that is because the carbon is the most noble element in the galvanic scale and the differing expansion contraction characteristics between brass or SS and the carbon...

PYI says this in the instructions but many people choose not to read or heed them:

"Do not tighten or replace the installed nylon hose barb fitting with a metallic fitting (bronze or stainless steel). Metal hose barbs will damage the carbon and destroy the PSS."

Again, this type of failure, overheating of the seal, dissimilar metals corrosion or a split carbon would clearly get blamed on the PSS seal. Sadly on the "net" PSS takes the hit not the dolt who caused the failure by not following the installation instructions. These are examples of installer error not a failure on the part of the seal. I see the metallic plugs and set screw errors frequently.
 
#26 · (Edited)
Adding to Maine Sail's excellent post above;

When I purchased my PSS seal in April of 2012, it included 6 set screws. I believe that the reason there were so many is; 1 set (2 screws) were intended to hold the rotor in position, 1 set are meant to be snugged against the first set (thus locking the first set in position [See Maine's "better view" pic above], and allowing them to be used as spares) and the third set as spares. All of the set screws had thread locking compound pre-applied. Also included was the proper size allen wrench, and two sets of O rings.

The only part that PSS did not include was the Clamp Collar, which I have since purchased from McMaster-Carr.
 
#30 ·
I was so excited to hear from the broker(friend of the owner) when we bought the boat last Spring, "and hey, you've got a dripless shaft seal to go along with that fancy feathering prop". Now I'm not so sure.. I guess I gotta add it to fall maintenance.
 
#33 ·
I never felt safe leaving my boat with the PSS type sea, as anything falling on it would quickly sink the boat. The most a stuffing box will do is drip slowly. So I went back to my stuffing box and regained much peace of mind.
 
#34 ·
I use the orthodox stuffing box on my Polaris 36, and have for the last 20 years.
Last time I changed the packing on it was 15 years ago.
It is reliable, orthodox and cheap to maintain. It really has never given trouble. It drips a bit, but I live with that, as other owners have since the beginning of steam power.
 
#37 ·
I installed a "Lasdrop" dripless systel about two years ago and haven't had an issue yet....nor a drop od water!

The manufacturer reccomended installing a spare seal on the shaft in the event the operational seal fails. This would eliminate the need for a haul out and is a good safety measure for a failure while underway.
 
#38 ·
my boat came with a stuffing box. a couple of years ago i pulled out the flax packing and put in the gore type packing . it runs cool, drips very little when running & not at all when the shaft is not turning. it is not supposed to wear the shaft either so i am well satisfied with it.
 
#39 ·
I've installed several lasdrops and like them. They use heavy hose, exactly like a traditional stuffing box, and no set screws, they clamp like the collar in Maine sails photo instead. The carbon is not directly threaded, the housing for it is instead allowing metal fittings to be used.

However I think the replacement seal on the shaft is a bit funny. More useful in that you have the spare available, but considering how hard it is to swap the seal out while held vertically on a nicely lit dry work bench...
Not bloody likely especially on the first try. You'd need to have excellent bilge pumps, all the tools including a hacksaw and heavy duty cutters etc, and a lot of luck.




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