About 15 years ago a friend had an aluminum vessel ~40' designed by Tanton,
a French naval architect who lives in this area (or at least did at that
time).

Tanton insisted that the mast be keel stepped. The issue he was concerned
about was mast pumping. If a deck stepped mast starts to pump it can
theoretically jump out of the step. How the mast gets into this mode, I
don't know.

Now, this boat was for blue water, and this friend has sailed around the
world at least once. As far as I know, he still has the boat.

I also had an Aluminum vessel that was French designed and built. The mast
was deck stepped.

Bill

"QLW" wrote in message
...
Steve,
As I suspected, my Engineer Friend went on in great detail to explain why
stepping the mast on the deck or on the keel has no effect on the strength
of the mast in compression. While some small benefit could conceivably be
gained by helping to keep the mast in column, he claimed that would only
occur in the case of a flawed design. If the mast were stepped on a
poorly
supported deck then all of the thinking changes...but that's a deck
problem
not a mast problem. Good reasons for either stepping the mast on the
keel
or on the deck can be argued, but compressive strength is not one of
them.

"Steve Christensen" wrote in message
...
In article , QLW says...


"Tom Dacon" wrote in message
...
It's a mechanical engineering issue. A mast (called a column by
mechanical
engineers) that's supported only at the ends is less strong in
compression
than a column that's supported at two points at one end. The support
at
the
mast step, for a keel-stepped mast, allows the mast to take more
compression
before failing than a deck-stepped mast can. Because the stays and
shrouds
take sailing loads almost parallel to the mast, the mast column comes
under
significant compression load.

While I like the idea of a keel stepped mast, I'm skeptical about the
reasoning above. I'm not an engineer but I have a good friend that
is...and he has a lot of aircract and boat design experience...so I'll
run
this thread by him this afternoon and get his input before saying more.



I hope your friend agrees with the above post, since this IS the
accepted
wisdom
wrt rigs. Deck stepped masts get less support than keel stepped masts.
Therefore the deck stepped mast must be larger - and heavier - in cross
section
to make up for it. It's always an option, but it adds weight aloft.

Steve Christensen