The probably chief cause of keel bolt failure is: they are not
removable for inspection.
Stainless steels are 'very' subject to 'crevice corrosion' and fatigue
failure, mostly a combination of the two modes of failure. Worse, the
maximum stres on a keel boat is 'cantilever stress' ... very hard to
predict since the loads and actions are 'variable to unforseen'.
Aiarcraft have the almost same problem with cantilever stress ... but
those wing root bolts are REMOVEABLE and thus are able to be
periodically inspected.
So, keel bolt failure is a functional design failure due to the bolts
not being able to be removed and periodically inspected.

Encapsulated (iron) keels are not a panacea, as if the cavity is
penetrated and water enters, the rust (ferric) that forms is less
dense than the original metal (iron) and the encapsulated keel will
'push' itself apart ... then the balllast will simply fall out if the
rust formation is that great.

So, from the above it seems that a encapsulated keel with solid lead
internal ballast would probably be the 'best'.

"RichH" wrote in message
...
The probably chief cause of keel bolt failure is: they are not
removable for inspection.
Stainless steels are 'very' subject to 'crevice corrosion' and fatigue
failure, mostly a combination of the two modes of failure. Worse, the
maximum stres on a keel boat is 'cantilever stress' ... very hard to
predict since the loads and actions are 'variable to unforseen'.
Aiarcraft have the almost same problem with cantilever stress ... but
those wing root bolts are REMOVEABLE and thus are able to be
periodically inspected.
So, keel bolt failure is a functional design failure due to the bolts
not being able to be removed and periodically inspected.

Encapsulated (iron) keels are not a panacea, as if the cavity is
penetrated and water enters, the rust (ferric) that forms is less
dense than the original metal (iron) and the encapsulated keel will
'push' itself apart ... then the balllast will simply fall out if the
rust formation is that great.

So, from the above it seems that a encapsulated keel with solid lead
internal ballast would probably be the 'best'.


I think the best keel is a drop keel and water ballast just like that which
the Macgregor 26 series of fine and respected sailboats uses. You have NEVER
heard of one single solitary Mac26 with a keel falling off of it, have you?

--
Gregory Hall

On Jun 10, 7:50 am, RichH wrote:
The probably chief cause of keel bolt failure is: they are not
removable for inspection.

As I said before, just looking at the pictures in the link I think the
failure was of the hull bottom (or structural keel of the vessel) and
not the keel bolts. Hull failure is not uncommon in hard groundings
on lightly built, fin keeled boats but I think that is a separate
topic.

Stainless steels are 'very' subject to 'crevice corrosion' and fatigue
failure, mostly a combination of the two modes of failure. Worse, the
maximum stres on a keel boat is 'cantilever stress' ... very hard to
predict since the loads and actions are 'variable to unforseen'.

The "Received Wisdom" is that stainless is not the best choice for
keel bolts because it is subject to crevice corrosion and wasting in
an wet, low oxygen environment. Fatigue failure can be engineered
around. I haven't looked into it but my guess is that the time to
ductility exhaustion of the typical set of ss keel bolts would be on
the order of forever and a day. Cantilevers and sheer stress are
pretty well understood for bolts and beams. And, in the case of keels
where weight isn't generally a concern designers can be, and generally
are, very conservative.

... So, keel bolt failure is a functional design failure due to the bolts
not being able to be removed and periodically inspected.

Kinda Zen statistics, but my feeling is that most keel bolt failures,
as opposed to keel failures, are on fairly new racing boats and
probably result from over aggressive designs or constructions errors.
In any case, keel bolt failure is very rare. Yes, it would be good if
the bolts were easy to inspect and yes, stainless isn't the best
choice for them, but in practice, the fleet is holding up very well.

... So, from the above it seems that a encapsulated keel with solid lead
internal ballast would probably be the 'best'.

Well, you haven't sold me yet. Keel bolts can be made of things other
than stainless. Even stainless bolts seem to be holding up well. If
the bottom of the boat fails the point is moot anyway.

-- Tom.

On Jun 10, 3:01 pm, " wrote:
On Jun 10, 7:50 am, RichH wrote:

The probably chief cause of keel bolt failure is: they are not
removable for inspection.

As I said before, just looking at the pictures in the link I think the
failure was of the hull bottom (or structural keel of the vessel) and
not the keel bolts. Hull failure is not uncommon in hard groundings
on lightly built, fin keeled boats but I think that is a separate
topic.

Stainless steels are 'very' subject to 'crevice corrosion' and fatigue
failure, mostly a combination of the two modes of failure. Worse, the
maximum stres on a keel boat is 'cantilever stress' ... very hard to
predict since the loads and actions are 'variable to unforseen'.

The "Received Wisdom" is that stainless is not the best choice for
keel bolts because it is subject to crevice corrosion and wasting in
an wet, low oxygen environment. Fatigue failure can be engineered
around. I haven't looked into it but my guess is that the time to
ductility exhaustion of the typical set of ss keel bolts would be on
the order of forever and a day. Cantilevers and sheer stress are
pretty well understood for bolts and beams. And, in the case of keels
where weight isn't generally a concern designers can be, and generally
are, very conservative.

... So, keel bolt failure is a functional design failure due to the bolts
not being able to be removed and periodically inspected.

Kinda Zen statistics, but my feeling is that most keel bolt failures,
as opposed to keel failures, are on fairly new racing boats and
probably result from over aggressive designs or constructions errors.
In any case, keel bolt failure is very rare. Yes, it would be good if
the bolts were easy to inspect and yes, stainless isn't the best
choice for them, but in practice, the fleet is holding up very well.

... So, from the above it seems that a encapsulated keel with solid lead
internal ballast would probably be the 'best'.

Well, you haven't sold me yet. Keel bolts can be made of things other
than stainless. Even stainless bolts seem to be holding up well. If
the bottom of the boat fails the point is moot anyway.

-- Tom.

In spite of the beliefs of most people here, the Mac 26 really is a
much safer boat than most heavily built cruising boats. If one
integrates safety over the life of the boat, I think you would find
the Mac 26 to be far safer than a heavily built boat with a deep
keel. The deep keeled boat may be safer in a certain unusual
situation (being out in a hurricane in deep water) but the Mac 26 can
more easily avoid such weather by going into a shallow entrance that
the deep keeled boat cannot.

wrote in message
...
In spite of the beliefs of most people here, the Mac 26 really is a
much safer boat than most heavily built cruising boats. If one
integrates safety over the life of the boat, I think you would find
the Mac 26 to be far safer than a heavily built boat with a deep
keel. The deep keeled boat may be safer in a certain unusual
situation (being out in a hurricane in deep water) but the Mac 26 can
more easily avoid such weather by going into a shallow entrance that
the deep keeled boat cannot.


Truer words have rarely been spoken. The Mac 26 is a very safe boat as
evidenced by its unparallel safety record.

And, the Mac 26 can get to that shallow entrance a lot faster than any
sailboat other than perhaps a racing multihull.

--
Gregory Hall

"I haven't looked into it but my guess is that the time to
ductility exhaustion of the typical set of ss keel bolts would be on
the order of forever and a day. Cantilevers and sheer stress are
pretty well understood for bolts and beams. And, in the case of keels
where weight isn't generally a concern designers can be, and
generally
are, very conservative".

Ductility exhaustion? What are you doing drawing wire? Sorry but
once 300 series stainless gets loaded above its endurance limit it
typicallly only lasts approx 1 million load cycles - doesnt matter if
its rigging, keelbolts, chainplates. If the endurance load factor (at
about 30kpsi) is exceeded, 1 million cycles is about all you get
You bet that cantilever stress is well understood thats why bridges,
aircraft wings, etc. dont fall off. That sailboats constantly have to
have rigging replaced, on some - keels & rudder shafts, etc. keep
falling off ... would tell any prudent engineer/designer that
'something is wrong' in the 'typical design'.

On Jun 10, 1:36 pm, RichH wrote:
....
once 300 series stainless gets loaded above its endurance limit it
typicallly only lasts approx 1 million load cycles - doesnt matter if
its rigging, keelbolts, chainplates. If the endurance load factor (at
about 30kpsi) is exceeded, 1 million cycles is about all you get...

At stresses less than that the bolts will essentially never fatigue,
right? I'm looking at a worked example of an ABS keel bolt
worksheet. Since you're using psi I'm converting to USA units. 10
keel bolts of 0.83" (at the thread root) support a 7,175 lb keel with
a cg 2' below the joint. Even assuming half the bolts aren't doing
anything the maximum static stress on those bolts are going to be an
order of magnitude below their endurance load. Hydrodynamic loads on
the keel max out at about the same order. Day in and day out you'll
never approach the endurance limit of ABS sized bolts. On top of that
your typical designer is going to use the next size up off the shelf
rod. As you'd expect with those kind of scantlings keel bolt failure
is extremely rare. Fatigue isn't normally an issue.

... That sailboats constantly have to
have rigging replaced, on some - keels & rudder shafts, etc. keep
falling off ... would tell any prudent engineer/designer that
'something is wrong' in the 'typical design'.

Rigging is a different story with very different compromises. Keel
failure is so rare that I think each case needs to be looked at
individually. There is no evident systemic problem with keel bolts as
a class.

-- Tom.

Tom --- simply go back to basic structural engineering basics.

All metal has a service life based on fatigue. Even below the
endurance fatigue limit, applied cyclical stress will develop
microcracks between the grain structure. Such propagation is minimal
but continuously additive to applied cyclical stress. At or above the
endurance limit the fatigue become more 'predictable', below the limit
the fatigue is 'not so' predictable. The inevitable failure for ALL
metals in cyclical stress service is embrittlement and crystaline or
fatigue failure. Fatigue failure at scantiling design values with
Safety Factor of 4X (typical ocean service) still but rarely happen.
Only when the stress design approaches FS=6 does fatigue failure
become rare; but rare doesnt exclude some failure. I repeat: The
inevitable failure for ALL metals in cyclical stress service is
embrittlement and crystaline or fatigue failure ... this WILL
eventually happen to rigging, rigging supports and keel bolts on
boats.

At stresses less than that the bolts will essentially never fatigue,
right? *I'm looking at a worked example of an ABS keel bolt
worksheet. *Since you're using psi I'm converting to USA units. *10
keel bolts of 0.83" (at the thread root) support a 7,175 lb keel with
a cg 2' below the joint. *Even assuming half the bolts aren't doing
anything the maximum static stress on those bolts are going to be an
order of magnitude below their endurance load. *Hydrodynamic loads on
the keel max out at about the same order. *Day in and day out you'll
never approach the endurance limit of ABS sized bolts. *On top of that
your typical designer is going to use the next size up off the shelf
rod. *As you'd expect with those kind of scantlings keel bolt failure
is extremely rare. *Fatigue isn't normally an issue.

... *That sailboats constantly have to
have rigging replaced, on some - keels & rudder shafts, etc. keep
falling off ... would tell any prudent engineer/designer that
'something is wrong' in the 'typical design'.

Rigging is a different story with very different compromises. *Keel
failure is so rare that I think each case needs to be looked at
individually. *There is no evident systemic problem with keel bolts as
a class.

-- Tom.

On Tue, 10 Jun 2008 19:10:59 -0400, "Gregory Hall"
wrote:

And, the Mac 26 can get to that shallow entrance a lot faster than any
sailboat other than perhaps a racing multihull.

A scows are good for 25, but not in big waves.

Casady

On Tue, 10 Jun 2008 19:10:59 -0400, "Gregory Hall"
wrote:


wrote in message
...
In spite of the beliefs of most people here, the Mac 26 really is a
much safer boat than most heavily built cruising boats. If one
integrates safety over the life of the boat, I think you would find
the Mac 26 to be far safer than a heavily built boat with a deep
keel. The deep keeled boat may be safer in a certain unusual
situation (being out in a hurricane in deep water) but the Mac 26 can
more easily avoid such weather by going into a shallow entrance that
the deep keeled boat cannot.


Truer words have rarely been spoken. The Mac 26 is a very safe boat as
evidenced by its unparallel safety record.

And, the Mac 26 can get to that shallow entrance a lot faster than any
sailboat other than perhaps a racing multihull.

Good grief. Have either of you ever sailed more than 20 miles
offshore ?