I received a call from a
concerned customer yesterday with a harrowing tale. I asked him
to e-mail me the details and include a photograph that I might
share with other Catalina sailors. Lessons learned from his
experience with his 1988 Catalina 30 could be relevant whether
you own a Catalina 22 or a Catalina 36.
Raimund's harrowing tale:
Last Sunday we sailed with a
reefed main in about 15+ Knot winds when all of a sudden the
windward (starboard) chain plate for the upper shroud broke.
We managed to get the sails
down and saved the Mast. I ordered new chain plates from
Catalina Direct but I am concerned that this might reoccur in
future... There is some surface rust on the part but the
breakage almost looks like a result of electrolysis. To my
knowledge, the boat was never hit by lightning and as you know
the mast is grounded via the starboard side upper shroud.
I am attaching a picture. I
did not clean the chain plate up so you can see the condition
(the port side is ok), Please note how shredded the breakage is.
Any comment you have would be appreciated. At this point I don’t
know if I should warn the other owners of Catalina 30’ in my
club (one was hit by lightning) or is this just an isolated
case.
Thank you
Raimund Haunholter
Cape Coral, Florida
Classic crevice corrosion.
The failure of the upper
shroud chainplate is a classic case of crevice corrosion. The
"crevice" in this case is the small space between the stainless
plate and the sealant that was intended to protect the boat from
water intrusion.
Platinum, palladium, and gold
do not corrode. Every other metal known to man does. Stainless
steel becomes rust resistant with the addition of chromium. When
chromium in the alloy is exposed to oxygen, a thin layer of
chromium oxide forms. This ultra thin oxide layer is what
protects the stainless. More chromium in the stainless protects
better. This is why Catalina Direct uses higher chromium content
type 316 stainless in all of our standing rigging.
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A typical
case of crevice corrosion on a Catalina 30
chainplate. |
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The
corrosion at "A" will not be visible when
the part is installed. However, upon close
inspection, signs of corrosion are visible
at "B". The entire part should be bright
silver like at "C". |
But, under the wrong
conditions, any stainless steel will corrode. Airborne
pollutants as well as chlorides in salt water attack the oxide
layer. When stainless steel is kept clean, the oxide layer forms
faster than the chlorides can attack it. But, if dirt and
pollutants from the air and/or salt is left on the stainless, or
if the surface of the stainless is deprived of oxygen, the oxide
layer degrades faster than it can re-form. Once it breaks
through the oxide layer, the chlorine attacks the metal itself.
It quickly begins to damage the integrity of the hardware or
fasteners as you can see in the photo.
The upper shroud chainplate
can be an ideal environment for crevice corrosion where it
passes through the deck. Often the chainplate is attached to a
bulkhead and passes through the deck. When loaded and unloaded
each time you tack the chainplate moves ever so slightly
relative to the deck it is passing through. This small motion
breaks down the bond between the sealant and the chainplate.
Now, salt water, with it's chloride content, not only enters the
crevice between the plate and the sealant, but it is held there
in an oxygen starved environment.
Crevice corrosion is also a problem on early Catalinas that used
a simple, single eyebolt through the deck for the lower shroud
chainplates. There was no provision made to prevent them from
rotating in the hole. When adjusting the turnbuckle or, on
trailerable boats, stepping or unstepping the mast, it was easy
to accidentally rotate the eyebolt. Any slight rotation broke
the seal and provided an ideal location for crevice corrosion to
take place.
Bad for your deck too!
In addition to rigging degradation, your deck structure is also
effected. Every Catalina deck has a marine plywood core to add
stiffness to the structure. Water intrusion at any point where
hardware penetrates the deck is introducing water into the
plywood core. This creates an ideal environment where the spores
that cause dry rot can thrive. In just a season or two dry rot
can destroy the plywood layer and create a void in the deck
structure.
What can you do to prevent crevice corrosion?
1) Wash down your boat thoroughly with fresh water every time
you sail even if sailing in fresh water. If you don't sail as
often as you would like, make a pact with an adjoining slip
renter to hose down the other's boat every time you visit yours.
In the photo, the rust at the top of the chainplate, under the
turnbuckle is just from contaminates sitting between the toggle
and the chainplate. A regular washdowns after each sail will
help prevent this.
2) Check chainplates often both on deck and inside the cabin for
any sign the seal has been compromised. Be sure to use a
flashlight inside the boat to check for the slightest sign of a
leak. Is there anything but shiny stainless? Is there the
slightest patina of rust on any of the hardware? Is there any
indication of water having been on the adjacent wood? You can
see in the photo the patina of rust on the top of the horizontal
plate. This is a clear indication that the chainplate had been
leaking. There is no small leak. Any leak at all is dangerous to
your rig and the integrity of your deck!
Is it time for action?
If there is any indication water has gotten through the seal at
deck level, then the answer is an emphatic yes! Remove the
entire chainplate and check for crevice corrosion that might be
hidden within the thickness of the deck. Undetected it could
cause the loss of your entire rig. Carefully clean the metal
thoroughly. Re-bed both the chainplate and cover plate and
you're good for another season. Once crevice corrosion starts it
is more difficult to prevent it from continuing. If there is any
doubt about the integrity of the part, it's time to replace it.
Fair winds and safe sailing!
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Lowell Richardson, Owner
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Catalina Direct
10210 Systems Parkway Suite 390
Sacramento, CA 95827
Order Desk: 800/959-SAIL (7245)
Email: CD1@CatalinaDirect.com
