"RichH" wrote in message
...
The additional problem with 'bolt on' keels is the concentration of
stress at the root of the keel and the mating structure. The Bavaria
line is the most stunning example of this stress anomaly wherin new
boats are losing their keels ... not as a failure of the keel nor its
attachment bolting but rather the mating FRG structure. This, to me,
is simply an unforseen 'concentration' of stresses which lead to a
very weak, prone to failure structure.
With an encapsulated keel system the lines of stress are allowed to
follow a 'more open' or less concentrated pathway over larger cross
section of the structure --- inherently safer but at a greater cost of
excess material/weight. My engineering eye usually is in an extreme
'wince' whenever I see a sharp inside corner anywhere near a
cantilever structure --- as thats the prime location of concentrated
lines of stress. Encapsulated keels usually always have 'smooth
transitions' in this critical area and thus avoid this 'stress
concentration'.

I am sure you are right about this. IMO the problem has become much worse
because the more modern designs of yacht are much more flat bottomed than
older designs such as my Catalina 38. On my boat the transition is quite
smooth but on modern boats it is almost 90 degrees.
Last year at my marina I looked at two almost new French built boats which
had suffered heavy groundings. The keels had not come off and all you could
see outside were some relatively small cracks in the outer glass layer.
However the flexing in the upward direction was such that major components
had failed inside the boats. The keels had to be removed and the boats took
all winter for the interior to be stripped out, repaired and put together
again.

On 2008-06-10 20:43:07 -0400, Dave said:

On Wed, 11 Jun 2008 00:06:06 GMT, Jere Lull said:

We have bolted-on cast iron -- not my favorite material, but what we
have.

That reminds me, Jere--thanks for the suggestion of putting Interprotect on
my boat's iron keel. Preparation was a bit of effort, but now touching it up
for the season is a job of just a few minutes. A great relief.

Hopefully, I also suggested and you used POR-15 first. After 15
seasons, our Interprotect is beginning to fail and I had to spend a day
on the keel. Maybe will blast and re-do Xan this winter.

--
Jere Lull
Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/

On 2008-06-11 12:50:16 -0400, RichH said:

The additional problem with 'bolt on' keels is the concentration of
stress at the root of the keel and the mating structure.

The concentration of stress also exists with fiberglass keels; both are
as a result of under-engineering coupled with (usually) a hard hit.

--
Jere Lull
Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/

On 2008-06-12 09:48:03 -0400, Dave said:

On Thu, 12 Jun 2008 07:10:00 GMT, Jere Lull said:

Hopefully, I also suggested and you used POR-15 first.

I don't recall whether or not you did, but I just ground all the rust off
and used Interprotects's primer wash before applying the barrier coat. Seems
to be holding up pretty well.

Well, you'll probably have a good decade before you have to do it again.

Barrier coats *slow* water and dissolved oxygen down, but nothing stops them.

Next time, I'll bang the big flakes off, leaving light rust, then do
the Zinc-something wash to convert the rust and provide a good POR
bond. Fill, fair, then probably whatever the best barrier coat is at
the time.

--
Jere Lull
Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/

On Tue, 10 Jun 2008 08:59:06 -0700 (PDT), "
wrote:

BTW, the boat is an early J-35 (fully cored), and apparently it had
grounded previously.

Yuck. It looks like the hull failed, not the ballast keel/sump
joint. I suspect the "outsideness" of the ballast was not a
contributing factor.

Yes, J35s had notoriously weak keel attachments. They depended on a
steel plate glassed into the laminate to provide sufficient hull
strength. One hard grounding was usually enough to shatter the
laminate in that area leaving the keel/hull area vulnerable to flexing
or complete failure. I personally know of several boats where this
happened. Repair required almost complete removal of the interior.

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 ?