keel stepped/deck stepped masts
 

On Thu, 08 Apr 2004 19:14:39 GMT, Jack Dale
wrote:

I have heard stories, uncorroborated, of keel-stepped masts carrying
away the coach roof during dismasting.
===========================================

That can happen, and also the interior can be trashed by the mast butt
whipping around below decks. For that reason, it's very important
(and required by the ORC regs), that the mast butt be mechanically
fastened to the mast step in a secure manner.

I've had some personal experience with this issue since my old Cal-34
started out as deck stepped. As others have pointed out, almost any
kind of rigging failure with a deck stepped mast results in a total
dismasting with the entire rig in the water trying to hole the boat.
Been there, done that, and it's ugly. When I went to re-rig the boat
we did a lot of research. Ben Hall personally told me that keel
stepped masts are about 25% stronger than a comparable deck stepped
mast because of the extra support at the deck. Ben has engineered and
built a lot of masts and should know.

Personally, I would never go offshore again with a deck stepped mast.

keel stepped/deck stepped masts
 

"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. He
is currently building a 90' cat with an unstayed rotating mast but that is
an intirely different problem. No compresson loads there, but at one time
he was considering a stayed mast and must have done the thinking on it.

keel stepped/deck stepped masts
 

"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. He
is currently building a 90' cat with an unstayed rotating mast but that is
an intirely different problem. No compresson loads there, but at one time
he was considering a stayed mast and must have done the thinking on it.

keel stepped/deck stepped masts
 

On Thu, 08 Apr 2004 19:14:39 GMT, Jack Dale
wrote:

I have heard stories, uncorroborated, of keel-stepped masts carrying
away the coach roof during dismasting.

Me, too. But if the choice is a big hole in the roof or a big hole at
the waterline....G

There are probably well and poorly designed keel and deck stepped
masts. A good solid step and a well engineered compression post are
necessary on a deck-stepped mast.

Absolutely. This is key in anything, and from what I've seen of them,
I wouldn't sneer at a Pacific Seacraft for a second. I simply indicate
a slight personal preference that, if not met, would in no sense be a
deal breaker.

Of course, I always like stowing stuff in hammocks secured to the
keel-stepped mast, too...G

R.

keel stepped/deck stepped masts
 

On Thu, 08 Apr 2004 19:14:39 GMT, Jack Dale
wrote:

I have heard stories, uncorroborated, of keel-stepped masts carrying
away the coach roof during dismasting.

Me, too. But if the choice is a big hole in the roof or a big hole at
the waterline....G

There are probably well and poorly designed keel and deck stepped
masts. A good solid step and a well engineered compression post are
necessary on a deck-stepped mast.

Absolutely. This is key in anything, and from what I've seen of them,
I wouldn't sneer at a Pacific Seacraft for a second. I simply indicate
a slight personal preference that, if not met, would in no sense be a
deal breaker.

Of course, I always like stowing stuff in hammocks secured to the
keel-stepped mast, too...G

R.

keel stepped/deck stepped masts
 

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

keel stepped/deck stepped masts
 

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

keel stepped/deck stepped masts
 

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

keel stepped/deck stepped masts
 

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

keel stepped/deck stepped masts
 

On Wed, 14 Apr 2004 03:44:54 -0500, "QLW" wrote:
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.

============================================

I think this is one of those cases where theory and the real world
break down, probably because of faulty assumptions supplied to the
theory. In the real world of squalls, knock downs, luffing sails and
accidental jibes there are many asymmetric side loads generated which
are trying to force the mast out of column.

That's when the extra support provided by the deck becomes the most
useful.