Excessive Keel Bolt Corrosion on 1988 F36

Posted by Nick Piediscalzi (nickpied@…>)

I just bought a 1988 F36. The seller said they had 6 keel bolts
replaced in 2004. Apparently, they hauled the boat for a bottom job
and noticed the keel was loose.

My surveyor and a keel specialist noted that one bolt (not sure if
it’s original one or new) is showing excessive galvonic pitting.
Another has some galvonic pitting, but not enough to be of concern.
We’ll be removing the nuts to determine how serious the problem is.
All other bolts are fine.

Fortunately, I got a substantial price reduction as an allowance for
potential keel bolt replacement, so it’s not financially problematic.

So, I’m wondering if anyone has experience with keel bolt corrosion
and can shed some light on this situation. Specifically:

  1. Why would 6 (of 7) bolts need to be replaced so relatively early
    in the boat’s life? Does it indicate some larger, continuing
    problem? Should I be worried, especially since I’ll be sailing it
    up to San Francisco where it will be berthed and regularly sailed in
    25-30 knot winds?

  2. How could bolts that apparently weren’t corroded 2 years ago be
    corroded now so quickly? There’s no indication of oxygen
    deprivation. Could it be an electrical leakage problem? I don’t
    know what the zinc consumption rate has been.

Many thanks!

Posted by Dave_Benjamin (dave_benjamin@…>)

Perhaps they just had the bolts tightened in 2004 rather than
replaced. Is there paperwork showing the bolts were replaced? Or
you’ve got one heck of a galvanic corrosion problem happening. Might
have to look for some zinc nuts. That might actually do the trick;-)

If the the thru-hulls are metal are they bonded? (8 ga green wire
run between all of them?) How was the rest of the underwater metal?
Is anything grounded to the keel, say a SSB using the keel as a
groundplane or something like that? Is a galvanic isolator installed?
Weird.

— In freedomyachts2003@yahoogroups.com, “Nick Piediscalzi”
<nickpied@…> wrote:

I just bought a 1988 F36. The seller said they had 6 keel bolts
replaced in 2004. Apparently, they hauled the boat for a bottom
job
and noticed the keel was loose.

My surveyor and a keel specialist noted that one bolt (not sure if
it’s original one or new) is showing excessive galvonic pitting.
Another has some galvonic pitting, but not enough to be of
concern.
We’ll be removing the nuts to determine how serious the problem
is.
All other bolts are fine.

Fortunately, I got a substantial price reduction as an allowance
for
potential keel bolt replacement, so it’s not financially
problematic.

So, I’m wondering if anyone has experience with keel bolt
corrosion
and can shed some light on this situation. Specifically:

  1. Why would 6 (of 7) bolts need to be replaced so relatively
    early
    in the boat’s life? Does it indicate some larger, continuing
    problem? Should I be worried, especially since I’ll be sailing it
    up to San Francisco where it will be berthed and regularly sailed
    in
    25-30 knot winds?

  2. How could bolts that apparently weren’t corroded 2 years ago be
    corroded now so quickly? There’s no indication of oxygen
    deprivation. Could it be an electrical leakage problem? I don’t
    know what the zinc consumption rate has been.

Many thanks!

Posted by michel.capel (michel.capel@…>)

Galvanic corrosion can pop up on any metal connected with the water.
I think you need more zincs closer to the keel-hull joint. Make sure
these zincs are electrically connected to the keel and the engine
and shaft. Check if the wire connected between one of the keel bolts
and the engine is not corroded.

You could also look into the situation around your berth; is there
are metal walls around the marina, these could be electrically
protected against corrosion. If your boat is close to them, it
suffers. In this case, hanging zincs overboard on a wire connected
to the boat’s metal could protect you. These zincs will also show
what’s happening with stray currents.

good luck
michel

— In freedomyachts2003@yahoogroups.com, “Nick Piediscalzi”
<nickpied@…> wrote:

I just bought a 1988 F36. The seller said they had 6 keel bolts
replaced in 2004. Apparently, they hauled the boat for a bottom
job
and noticed the keel was loose.

My surveyor and a keel specialist noted that one bolt (not sure if
it’s original one or new) is showing excessive galvonic pitting.
Another has some galvonic pitting, but not enough to be of
concern.
We’ll be removing the nuts to determine how serious the problem
is.
All other bolts are fine.

Fortunately, I got a substantial price reduction as an allowance
for
potential keel bolt replacement, so it’s not financially
problematic.

So, I’m wondering if anyone has experience with keel bolt
corrosion
and can shed some light on this situation. Specifically:

  1. Why would 6 (of 7) bolts need to be replaced so relatively
    early
    in the boat’s life? Does it indicate some larger, continuing
    problem? Should I be worried, especially since I’ll be sailing it
    up to San Francisco where it will be berthed and regularly sailed
    in
    25-30 knot winds?

  2. How could bolts that apparently weren’t corroded 2 years ago be
    corroded now so quickly? There’s no indication of oxygen
    deprivation. Could it be an electrical leakage problem? I don’t
    know what the zinc consumption rate has been.

Many thanks!

Posted by macks011 (macks04@…>)

You’re either in a “hot” marina or you have a larger elec, problem.
If you don’t have the skills, you need to get a competent marine
elec. to diagnose and fix the problem. Galvanic action on keel bolts
before it is seen elsewhere is very puzzeling.


— In freedomyachts2003@yahoogroups.com, “Nick Piediscalzi”
<nickpied@…> wrote:

I just bought a 1988 F36. The seller said they had 6 keel bolts
replaced in 2004. Apparently, they hauled the boat for a bottom
job
and noticed the keel was loose.

My surveyor and a keel specialist noted that one bolt (not sure if
it’s original one or new) is showing excessive galvonic pitting.
Another has some galvonic pitting, but not enough to be of
concern.
We’ll be removing the nuts to determine how serious the problem
is.
All other bolts are fine.

Fortunately, I got a substantial price reduction as an allowance
for
potential keel bolt replacement, so it’s not financially
problematic.

So, I’m wondering if anyone has experience with keel bolt
corrosion
and can shed some light on this situation. Specifically:

  1. Why would 6 (of 7) bolts need to be replaced so relatively
    early
    in the boat’s life? Does it indicate some larger, continuing
    problem? Should I be worried, especially since I’ll be sailing it
    up to San Francisco where it will be berthed and regularly sailed
    in
    25-30 knot winds?

  2. How could bolts that apparently weren’t corroded 2 years ago be
    corroded now so quickly? There’s no indication of oxygen
    deprivation. Could it be an electrical leakage problem? I don’t
    know what the zinc consumption rate has been.

Many thanks!