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.