On Jun 11, 6:50 am, RichH wrote:
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. ...

You're onto something here. I saw a Bavaria in the Bay of Islands
that had gone aground and split the hull right aft of the keel right
along the line where they remove the core to "reinforce" hull at the
keel joint. It also looks like the J in the link Jeff posted had a
similar split but at the front of the keel right where the core is
replaced. I can't really see it well in the photos, but it looks like
the panel sandwich had a peel failure, too. Also, with the J the keel
ripped the hull open right along the reinforcement line (the bolts
didn't fail, the panel failed). So, yes, I think you're right on the
money with the stress riser issue. Just to be pedantic, the problem
would be the same even if they glassed over the metal part of the
keel. So, I think of these kinds of failures are hull panel failures
rather than keel joint failures and don't see them as a problem with
bolt on keels per se. But I'm willing to concede the point.

-- Tom.

The simple fact is that a cantilever ( a keel is a cantilever) is
inherently WEAK .... needing FOUR TIMES the strength to be equal of
any other 'simple beam in flexure' structure. Add a safety factor of
4 for offshore or 'hard usage' and you wind up with a minimum of
needing 16 times the strength ... then add fatigue/endurance, etc.
etc. etc. and you wind up with a very complicated structural
element. A cantilever with smooth transitions at the 'root' of the
cantilever is MUCH stronger simply by 'good structural design
practice'.