"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.