Types:
- Stuffing box.
Without grease: constant slow drip of water.
With grease: no water drip ?
With dripless packing (Teflon or graphite).
Gives wet bilge; may score the shaft.
- Shaft seal: bearings or O-rings, with natural water or forced-water or oil lubrication.
PYI's PSS Shaft Seal ($240 for 1-1/4" shaft)
Lasdrop (forced-water)
Tides Marine (forced-water)
May be hard to inspect.
Forced-water usually tapped from engine raw water cooling hose,
adding another point for a catastrophic failure.
Dripless shaft seal review in 11/15/2000 issue of Practical Sailor.
- Lip seal.
Rota-Seal (press-fit rubber ring).
Tides Marine nitrile lip seal
Lip Seals:
From Mike Z on Cruising World message board:
|
I have had a stuffing box, shaft seal (bellows and clamp mechanism),
and lip seal (Tides Marine), each for several years with constant use.
There is no question that the lip seal is best.
Stuffing boxes need adjustment, damage the shaft, and, of course, drip.
... shaft seals can lead to disaster if there is even a minor failure,
and things do get loose / go bad on them.
[With a lip seal, keeping] an extra [spare] lip already on the shaft means it can be
inserted into the unit easily with the boat left in the water.
The lip can wear or even tear, but the result will likely be a drip no worse than a
badly adjusted stuffing box. Go with a lip. They are even cheap.
|
From Tides Marine 4/2004:
Our unit would replace the entire existing stuffing box. In the case of a
refit, shaft condition in the area where the lip seal itself would ride must
be good. This means that the shafting should be free of scratches,
toolmarks and scuffing from the old stuffing box. The lip seal in this
application would ride about 5.75" ahead of the end of the existing stern
tube. List price on the unit is $335, and if you have room the spare
seal carrier lists at $84. You would need to provide us with the OD of
the stern tube in addition to the shaft diameter.
...
All of our shaft seals must be [forced] water lubricated. The complete unit inclusive
of shaft seal, silicone mounting hoses and clamps is $335. The spare seal
carrier is a protective shell containing a single replacement lip seal. It
lists at $84. It is listed separately as some installs do not have room
available to fit it. If it is fitted you can change the lip seal without
hauling the boat, with common hand tools in about 15 minutes.
|
From Rota-Seal 4/2004:
|
Nitrile seal for 1.25" shaft about $11. Minimum order is $25.
You press the seal up against the flat surface, and rotation of the shaft
seats it in place. The seal is bi-directional and self-locating; it should not matter
which direction the shaft turns. The seal will need to run against a smooth
surface to extend seal life.
|
|
PYI's PSS Shaft Seal:
From Bob Taylor on the
WorldCruising mailing list:
|
Have had a PSS Seal on my boat about 5 years now. Love it.
No water has entered the boat through
the shaft log since. Get the one with a carbon wear ring, not plastic.
I have heard the plastic ones will melt and leak if run dry.
|
From Gary on Cruising World message board:
|
Installed a PSS shaft seal from PYI almost 6 years ago,
and have had flawless performance and a dry bilge since.
Word of caution - if you have a PSS, and you have your
boat hauled, you must release the air captured in the
shaft tube when your boat is relaunched. It is a simple
procedure. You simply pull back on the bellows tube when
the boat is in the water to release the air, and let the
water come all the way up the shaft. If you look at a
schematic, you'll understand this.
|
From Justin/PYI on Cruising World message board:
... Pro's - dry bilge (or easier to identify your other leaks!)
No adjustment necessary. No accidental scoring of the shaft.
A seal like the PSS seal will work even if you have a small
amount of shaft vibration.
Gary is right about "burping" the seal before launch.
If that doesn't tickle your fancy you can get a high-speed
option with a hose barb threaded into the graphite flange on
the seal. Run a hose from the nipple to your seawater cooling
system or vent way above the waterline and you eliminate
the pocket of air normally trapped during relaunch. Voila!
No more burping. Adds about $25 to the cost of the seal.
As for installation, if you've got at least 5" between the front
of your stern tube and the back of your shaft coupling the
PSS seal will fit. ...
|
From Al Miegel on Cruising World message board:
|
Have PSS from PYI, love it, no water at all in the bilge.
Only note to add is to expect a small amount of graphite dust
the first season until it "seats in". Inspect the
clamps annually as you would any below-waterline through-hull
and otherwise forget about drips, water in the bilge
and all the attendant ills it brings.
|
From Al Schober on Cruising World message board:
|
The [high-speed version of the] seal will have a 'vent' fitting on top.
Hook this up to the output from your engine seawater
pump through a filter. This will keep the seal faces
running in nice clean water. A 50-micron filter should
do the job nicely. If the filter is any coarser than
that, don't bother.
|
From Howell Cooper on SailNet's Gulfstar mailing list:
|
Regarding the PSS dripless, I have asked many professionals about it and
not one to date trust it. I know it is standard on many new boats and
many of our sailing friends swear by it. We also know of several who
have removed it due to chatter, no help from the makers, leaks and
downright failure. As one old-timer put it, at least the old packing
gland is predictable.
|
From Bob on SailNet's Gulfstar mailing list:
|
I guess as in all things, some swear by them, others swear at them. I myself
have had the PSS for five years ... no problems. As a rigger, I recommend
them, as do several yards in the area. I guess problems can always
occur with any product.
|
From John Viera on "Tyche":
|
I installed the PSS Shaft-Seal, which is one of the best designs on the market according to
Practical Sailor. I like it because there is no maintenance required, but you do need to protect
it from oil getting onto the rubber seals, as this will cause then to deteriorate.
|
|
Tom Neale says stuffing can be replaced/renewed without hauling;
other types can't be.
SailNet - Tom Wood's "The Stuffing Box And Stern Tube"
Small "Dope for Stuffing" article in issue 2000 #3 of DIY Boat Owner magazine.
Article by Bill Sandifer in March/April 2002 issue of Good Old Boat magazine
Propeller/shaft/stuffing inspection article by Steve D'Antonio in Sept 1996 issue of Cruising World magazine
Replacing cutless bearing with a waterproof bearing:
Seems to me that the main problem is the cutless bearing, and its need to
have water run through it for lubrication. But no one seems
to replace that with a greased bearing. Why not ?
[Actually, I'm told
there just has to be water present in the cutless bearing, not
running through it. The drip is needed to keep the stuffing
from heating and/or scoring the shaft.]
Large ships are going the other direction: replacing an oiled
bearing with a water-lubricated one, partly to reduce pollution
caused by escaping oil.
Evolution Marine's EMSS has an
oiled bearing through the stern tube, but they require buying a complete
system which also replaces shaft and absorbs prop thrust in a "thrust bearing"
at the end of the keel
instead of on the engine mounts. About $4800 for my Gulfstar 44
(1.25" diameter shaft, about 4 feet from gearbox to stern tube)
plus $100 each for motor mounts.
From Evolution Marine:
... The shaft system
includes the engine adapter, internal connecting shaft utilizing
universal joints at each end and with splined slip joint to further
allow the engine to 'free float' on truly soft motor mounts rated just
for the engine's static, vertical weight. Also included is the 'oil
lubricated' section which is a alloy 22 s.s. shaft 1.25 inches in
diameter enclosed in a 316L s.s. shaft log tube. Inside of the vessel
this tube and shaft mate up to a larger steel diameter housing tapered
thrusts bearings for forward and reverse. Outside of the vessel the
same shaft and tube mate up to a bronze bearing assembly that contains
needle bearings, seals and races. Within the shaft log tube there's
another bearing.
Once the system is installed, the prop thrust will have been transferred
to the hull ... the cutless bearings and packing glands will have been
eliminated.
Vibration from the engine to the hull is reduced significantly. Also,
vibration from the prop to the hull is also reduced significantly. With
less vibration, we have seen noise levels reduced by 17 decibels. Also
with less prop vibration, we have seen increases in speed and fuel
utilization since typical propeller slippage is reduced. This is
accomplished by the extremely close clearances between mechanical
bearings as compared to rubber cutless bearings. ...
> I'm curious about the "prop thrust will
> have been transferred to the hull" angle of it.
> I'm sure the hull designers put in strong
> engine beds, expecting the thrust to be on them.
> With EMSS, the thrust will be on the shaft tube
> area of the keel, right ? Any concerns about
> that area not being strong enough ?
Since both assemblies (thrust bearing and aft bearing) are attached to
the s.s. shaft log tube plus the shaft is captured within the thrust
bearing assembly ... the oil lubricated section is ONE PIECE. Where one
would grap it initially is where the thrust is ... even though the prop
thrust dead heads inside the vessel at the thrust bearing assembly.
For example: We tell people with a strut configuration that the
internal bulkhead to which the thrust bearing assembly is bolted
to ... must be strong enough to accept 100% of the propeller thrust for
forward and reverse gears. If the vessel has a full keel or sternpost
with an existing two or four bolt external cutless bearing assembly, we
can produce a duplicate flange to which our aft bronze bearing assembly
mates up to. If this is the arrangement, then the prop thrust is
captured outside right at this flange. If the sternpost were to be weak
and wiggle, one would see the corresponding movement inside at the
internal bulkhead. However, this simply doesn't happen since this tends
to be the strongest point of the hull.
Another arrangement for installation of the EMSS is to allow us to
attach a fiberglass stern tube (typically used for cutless bearings,
etc). We machine the aft face, drill and tap for six 3/8 s.s. bolts.
The circular bronze flange has a pilot that goes into the fiberglass
tube. Before bolting together, we seal with marine sealant. The
boatbuilder or boatyard takes the unit into the vessel and slides the
entire 'oil lubricated' section from inside the vessel outward. Outside
the vessel, the yard then fiberglasses the hull to the fiberglass stern
tube and they are done outside. Inside of the vessel they lay the
forward part of the s.s. shaft log tube into a U-shaped bulkhead to
maintain the shaft angle desired.
> And I guess you've answered my other question:
> since the oil-lubricated section is one piece
> all the way to the thrust bearing, I can't
> buy just the stern-tube bearing from you,
> right ? I'd really like to replace just
> the stuffing box and cutless bearing, with
> an oil-lubricated bearing through the stern
> tube, and leave everything else unchanged
> (old shaft, thrust onto engine mounts, etc).
> But you don't sell just an oil-lubed bearing
> for the stern tube, do you ?
... we manufacture and sell the complete system.
At one point, we wanted to be the "Sears Roebuck" of shaft
components ... in that, we wanted to have price alternatives to our 'Rolls
Royce' EMSS ... so we developed a unit comparable to Aqua-Drive. By the
time we priced it out with expected margins, we were selling it at 60%
of our complete EMSS. For the additional 40%, and the very significant
benefits ... we stopped building the abbreviated version. ...
|
|
Replacing stuffing in stuffing box, from Rick Kennerly on
Yacht-L mailing list:
... get one of those little flax picks (has a
really wicked looking corkscrew on the end of a flexible wire). It
will make getting that last piece out much easier.
I've used the teflon grease and the harder flax that goes with it on
our Westsail 32 with a 50 hp Perkins 4-108 in it. It's a bit slimy and
messy, but works great. This is our 3rd season with it. The only
drawback to the teflon grease is that makes the flax so slippery that
you can't put two or three rings on the shaft and slide them in
together (like you can with grease because the grease makes them stick
to the shaft).
If you try to do this in the water, figure what you're going to do if
you can't get it back right. 8 pm on a Friday evening is not the time
to be looking for a travellift operator. Once you've done it a couple
of times you get the hang of it, but it is a bit nerve wracking the
first time in the water.
Before you open the gland up, prepare everything first. Cut your flax
this way: Wrap the flax around the shaft in a spiral. Take a sharp
knife (a razor knife works well) and cut through two of the rings at a
45 degree angle This will give you one complete ring that has
overlapping ends. Don't try to cut 90 degree angles as butt joints
will leak. Cut as many rings as you need and when you pull the gland
back arrange them on the shaft with the cuts staggered at different
"o'clocks" around the shaft. Use the packing nut to run them into the
gland evenly, each new flax piece pushing the ones ahead of it into
the body.
Don't forget the locking nut when you're finished. Too loose is better
than too tight. Remember that a slight drip when running cools the
shaft and prevents scoring of the shaft. Watch it for a day or two
until it settles down. I've had new flax that wouldn't seal at all
for the first day no matter how many lines I put in or how tight I
cranked down on the packing gland nut and some that would never leak,
even with the packing nut almost off and the prop turning over.
|
"The Zen of stuffing boxes",
from Roy Miles on Cruising World message board:
A conventional stuffing box acts exactly like the faucet valve on your sink.
It has to turn in an environment where water under pressure wants to
leak along the shaft. The packing nut on both a stuffing box and a
valve stem cranks down on a base, squishing the packing material inside
against the shaft. When either begin to drip excessively, you tighten
down some more. Eventually, you need to change the packing because
it's all "squished" tight.
Stuffing box packing is pretty robust stuff, made of waxed teflon
or flax, generally woven in a square section. You buy it at marine
stores in packages sufficient to seal one stuffing box.
When you arrive at the point where tightening no longer works to
stop the drip, it's time to change the packing. It's not rocket science,
it doesn't cost much, and you can do the job without hauling the boat.
You will need a minimum of tools: good lighting, a pair of large wrenches,
some needle-nose pliers (preferably right-angle), a piece of stiff wire,
a razor knife, and a measuring device (tape, ruler, or calipers).
You will be working on your knees, possibly in an uncomfortable
position, so make the necessary accommodations.
Expose the stuffing box, and get your tools arranged nearby.
The packing nut is directly held tight by a locking nut,
located aft of the packing nut. If the stuffing box is dirty,
it may appear to be one big nut. Place a large wrench on each,
and loosen the lock nut from the packing nut, then back the lock
nut off as far as you can (thereby cleaning the threads on the base).
Next, back the packing nut towards the engine, away from the locking nut.
WHOA!!! Look at all that water rushing into the bilge!
Don't worry, you have a bilge pump, and it takes a lot of water
to sink the boat. Slide the packing nut back along the prop shaft
so that you can look at its interior. You will see a space between
the shaft and the threaded portion of the packing nut. Measure this,
if you can. If you can't, estimate it. Then tighten the packing nut
back on the base until the flood tapers down to a less terrifying stream.
Go to the store and purchase a package of packing of the size you
measured (or buy the most reasonable sizes
according to your estimate). You can even do this ahead of time
by telling the salesperson your prop shaft diameter and (if you
know it) stuffing box manufacturer.
You're back now, on your knees, admiring the stream of water
entering the boat. Wrap the length of packing material around the
prop shaft. You will probably have at least three full wraps,
plus some extra. Keeping the wrap as tight as possible, run the
razor knife along the length of the shaft, cutting all the strands.
Remove the pieces, keeping the three best ones nearby. Once more,
remove the packing nut, admire the pressure of the cold seawater
flowing in, and begin to remove the old packing from the inside
of the packing nut.
This is the most difficult part now, but it gets much easier in
a couple of minutes. Using wire, needle-nose pliers, or, if you have
access to one, a cork-screw looking tool mounted on a spring with
a tee-handle [or a cheap dental pick, or a large fish-hook straightened out],
remove the pieces of old, squished packing.
Get it all out, then scrape around inside the packing nut to confirm
everything is clean inside. Place the three new rings of packing
around the shaft between the base and the packing nut.
Gently ease each ring into the packing nut space between the shaft
and the thread. Be sure that the cut section of the packing material
is staggered with respect to its adjoining piece (much like piston
rings in an engine. When it's all inside the packing nut,
gently slide the packing nut onto the threads of the base and
begin to screw down until the leak stops.
Stuffing boxes are dynamic, meaning that they require regular adjustment.
This means that the thing is going to start leaking as soon as the
shaft begins to turn. It's supposed to, thereby keeping the shaft
lubricated with seawater and cool when turning. So, the dynamic is this:
Stop tightening JUST as the drip stops. Don't crank down as hard as
you can. Fire up the engine, make sure the spring lines to the dock
are secured, and put the boat in forward gear, slowly. Water will
begin to drip through the packing nut. Gently tighten the packing nut
until the drip rate is about one drip per second. Increase the RPM to
cruising speed, and if necessary, tighten again to the one-drip rate.
Now, shut the engine down and watch the shaft. If you have adjusted it
sufficiently, the friction of the shaft against the packing material
will now be cooled by the leaking seawater to the point where the
wax congeals, STOPPING THE DRIPS! It's a dynamic because you sometimes
need to play with the tightening a few times to get to this
point. Voila! The shaft drips underway and seals when it stops ...
until, one day, you notice that the drips don't stop at the end of use.
That just means that you need to tighten down the packing nut once again,
gently, as before. Oh, lest you forget, after you get the adjustment
correct, then tighten the lock nut against the packing nut to keep
that level of tension.
Stuffing boxes are simple to use and to maintain.
Lots of folks get intimidated by them and switch to more expensive
packing-free stuffing boxes. Or, sometimes, naughty builders install
them in places that normal humans can't work on them.
There is a special place in Hell for these builders.
Then you might consider the other form of stuffing box.
Keep a spare length of packing in the tool box for an eventual change,
but it shouldn't be necessary for several years.
|
From Larry Dill on the Morgan mailing list:
Stuffing Box Packing:
I replaced my shaft and bearing last spring. I used the stuff West has that
has PTFE in it. I applied the PTFE lube they sell along with the packing.
I also gave everything a final soaking before closing it up with the Super
Lube from K-Mart (Silver spray can -- has PTFE in it as well). I have the
gland running only hand tight, and no dripping. I figured that it would
commence dripping once it was broken in a bit. I motored for approximately
600 miles with this set up last summer -- no dripping (I frequently wrapped
my hand around gland and shaft after shutting down to see if it had
warmed -- found nothing unusual). Recently, I backed off the packing nut,
expecting that maybe I had scored my new shaft. It was as smooth as new.
I do have a few more layers of packing than one might normally put in. As a
result, the nut is not as far onto the gland as one would normally expect (I
left it rather loose, and ensured that the lock nut was snug). My theory
is that if you use extra packing (there is a limit to how much you can
reasonably use), then limit the compression, the packing will be placing
very little pressure on the shaft, thus minimizing scoring. I would add
that several times I tried to get my packing to drip, but to do so, I'd have
had to remove packing or back the nut out until it was hanging by only a few
threads. I was lucky -- had I found scoring, I'd have been pretty unhappy
with myself for not going ahead and pulling out some of the packing to make
the thing leak.
I am not suggesting that you try this, but it worked for me.
|
From Bob Clinkenbeard on The Live-Aboard List, 7/2001:
With new flax packing in place ... the proper way to tighten the packing
gland nut is to slowly tighten the nut when the boat is in the water and at
rest, until the drip ceases. When you run the boat, shaft is turning,
there should be a drip every few seconds to keep the shaft cool and the
packing from burning. When you stop ... the drip should also stop.
The shaft/stuffing box should not be so hot that you can't hold your hand on
it. Warm is from friction and ok. Hot is going to score. You should be
able to turn your shaft by hand when it is disengaged.
Old packing will not adjust this way. It will be hard and dry and will
probably leak all of the time no matter what you do. If you tighten old
packing too tight it will burn the shaft = score the shaft.
There are many types of packing ... some claim dripless, teflon, and greased,
etc.
Packing should be replaced when you can't adjust it as I have described
above ... it has become hard and dry.
|
|
