On Thu, 15 Apr 2004 13:39:15 -0400, Wayne.B
wrote:

On Thu, 15 Apr 2004 12:38:06 GMT, (Steven
Shelikoff) wrote:
I'm not so sure about that. If, when there are sideloads in squalls,
knockdowns, etc., the deck stepped mast failed by remining in one piece
but slipping out of it's step, then I'd agree that a keel stepped mast
would solve that problem ... if it didn't snap at the deck. But most
of the mast failures I've see are when it snaps somewhere aloft, like at
the spreaders. How it's stepped doesn't make a difference when it
breaks up there.
=====================================

The issue of whether or not the mast fails as one piece or multiple
pieces is separate from the structural considerations.

Here's a different way to view the situation: A keel stepped mast is
cantilevered at the deck and thus derives extra support. A deck
stepped mast is essentially pivoted at the deck rather than supported
by it.

That's exactly how I am viewing it. But the support at the deck of a
keel stepped mast is not going to do a damn thing to keep the mast from
breaking if the rigging fails in rough weather. If anything, I'd think
you'd have a slightly better chance of salvaging a deck stepped mast
after a catastrophy and jury rigging it up again since, if it does come
down with a pivot at the step, you've got a chance it may still be in
one piece. Of course it all depends on what breaks and how it comes
down. The only mast I've ever had come down due to rigging failure was
on a deck stepped boat and everything was salvagable. Lose the rigging
on a keel stepped mast and you're pretty much guaranteed to break it.

Another difference between them is that, when the boat is parked at the
slip, you can take the rigging down and not have the mast fall over if
it's keel stepped. But then it's also a little tougher to get the mast
up and down when you want to if it's keel stepped because you have to
lift it up a bit.

And the last difference I can think of is that you don't have to worry
about a compressed compression post and attendent deck sag with a keel
stepped mast.

Steve

Steven Shelikoff wrote:
On Thu, 15 Apr 2004 15:44:47 GMT, Rich Hampel
wrote:


I'm not so sure about that. If, when there are sideloads in squalls,
knockdowns, etc., the deck stepped mast failed by remining in one piece
but slipping out of it's step, then I'd agree that a keel stepped mast
would solve that problem ... if it didn't snap at the deck. But most
of the mast failures I've see are when it snaps somewhere aloft, like at
the spreaders. How it's stepped doesn't make a difference when it
breaks up there.


Mast failure (usually at midsection) is usually due to some rigging
failure that permits the mast to move 'out of column' and permits
catastrophic buckling failure when the compressional loads get off
center. Doesnt matter if its deck stepped of keel stepped, if the
rigging support fails and the mast deflects catastrophically .... the
latent compression load finishes the job.


Exactly. Which is why I don't think it makes all that much difference.

Steve

When my SC22 mast folded into a right angle and spiked into the
water beside the boat, it was because there was no compression box
inside the mast at the point where the spreader was through bolted.
When I built up a new mast from the extrusion, I put a piece of
square aluminium tube inside for the bolt to pass through. I
positioned it with a long stick and duct tape which tore off once I
had secured the box with 2 pop rivets one above, one below, one on
each side, just there to retain it in place when the spraeader bolt
was removed. I had single lowers, as installed by South Coast. I do
not know if the mast was original factory equipment or not.

The side load in a gust caused the spreader and lower shroud mast
tang stresses to crush the mast at that point. I was watching it
when it went. We salvaged the mast lashed it alongside and rescued
the mainsail, there was no other damage except the tabernacle was
partially torn off the deck and bent somewhat.

Lack of a compression box at the spreaders is the most common
failure in design that I know of. Check your spreader mounts.

Mast pumping may have been the root cause, the final straw, so to
speak. Keel stepped mast / deck partners migh have prevented some of
that, while providing a fulcrum to develop gooseneck loads and crush
the mast at the partners in a manner different from those expressed
in a deck stepped system without them.

It seems to me that the main difference between deck and keel steps
in some boats is that the tabernacle bolts passing through the deck
might shear, as most of them seem relatively flimsy. The tabernacle
would never let the mast base get away, as it was all secured
together with bolts. A wad of 1/2 round convex bog faired all around
the base of the tabernacle might help, there.

Terry K

Steven Shelikoff wrote:
On Thu, 15 Apr 2004 15:44:47 GMT, Rich Hampel
wrote:


I'm not so sure about that. If, when there are sideloads in squalls,
knockdowns, etc., the deck stepped mast failed by remining in one piece
but slipping out of it's step, then I'd agree that a keel stepped mast
would solve that problem ... if it didn't snap at the deck. But most
of the mast failures I've see are when it snaps somewhere aloft, like at
the spreaders. How it's stepped doesn't make a difference when it
breaks up there.


Mast failure (usually at midsection) is usually due to some rigging
failure that permits the mast to move 'out of column' and permits
catastrophic buckling failure when the compressional loads get off
center. Doesnt matter if its deck stepped of keel stepped, if the
rigging support fails and the mast deflects catastrophically .... the
latent compression load finishes the job.


Exactly. Which is why I don't think it makes all that much difference.

Steve

When my SC22 mast folded into a right angle and spiked into the
water beside the boat, it was because there was no compression box
inside the mast at the point where the spreader was through bolted.
When I built up a new mast from the extrusion, I put a piece of
square aluminium tube inside for the bolt to pass through. I
positioned it with a long stick and duct tape which tore off once I
had secured the box with 2 pop rivets one above, one below, one on
each side, just there to retain it in place when the spraeader bolt
was removed. I had single lowers, as installed by South Coast. I do
not know if the mast was original factory equipment or not.

The side load in a gust caused the spreader and lower shroud mast
tang stresses to crush the mast at that point. I was watching it
when it went. We salvaged the mast lashed it alongside and rescued
the mainsail, there was no other damage except the tabernacle was
partially torn off the deck and bent somewhat.

Lack of a compression box at the spreaders is the most common
failure in design that I know of. Check your spreader mounts.

Mast pumping may have been the root cause, the final straw, so to
speak. Keel stepped mast / deck partners migh have prevented some of
that, while providing a fulcrum to develop gooseneck loads and crush
the mast at the partners in a manner different from those expressed
in a deck stepped system without them.

It seems to me that the main difference between deck and keel steps
in some boats is that the tabernacle bolts passing through the deck
might shear, as most of them seem relatively flimsy. The tabernacle
would never let the mast base get away, as it was all secured
together with bolts. A wad of 1/2 round convex bog faired all around
the base of the tabernacle might help, there.

Terry K

Not that I plan for failure, but I do plan against. I've been told
that, if one is in a position to be towed for a distance in adverse
conditions, leading the tow line to the mast is much stronger than
leading it to some cleat. Unless the mast base on a deck stepped mast
were to go, say, a foot up into the interior of the mast and everything
was bolted to a compression post running to the keel, I'd think that
deck-stepped masts would be more likely to pull loose. A keel-stepped
mast is directly supported horizontally by the deck and would seem to be
better able to resist/sustain the shocks and tugs of the tow line.

john

Not that I plan for failure, but I do plan against. I've been told
that, if one is in a position to be towed for a distance in adverse
conditions, leading the tow line to the mast is much stronger than
leading it to some cleat. Unless the mast base on a deck stepped mast
were to go, say, a foot up into the interior of the mast and everything
was bolted to a compression post running to the keel, I'd think that
deck-stepped masts would be more likely to pull loose. A keel-stepped
mast is directly supported horizontally by the deck and would seem to be
better able to resist/sustain the shocks and tugs of the tow line.

john

On Sat, 24 Apr 2004 15:31:19 GMT, Steve Studley
wrote:

On Thu, 15 Apr 2004 19:03:55 GMT, Rich Hampel
wrote:

Relativisticly the keel stepped is perhaps better if you have rig
failure and NO LOAD on the rigging. But if you have extreme deflection
at the deck interface and create deformation such as a 'teeny notch'
where it goes through the deck ..... step out of the way, its coming
DOWN.

Try working with an unstayed rig, everything changes.
Of course, I'm only running a junk-rig on a small (21' ) boat, but...

Seems to me that deck stepping an unstayed rig is an exercise in
futility.

Steve

On Sat, 24 Apr 2004 15:31:19 GMT, Steve Studley
wrote:

On Thu, 15 Apr 2004 19:03:55 GMT, Rich Hampel
wrote:

Relativisticly the keel stepped is perhaps better if you have rig
failure and NO LOAD on the rigging. But if you have extreme deflection
at the deck interface and create deformation such as a 'teeny notch'
where it goes through the deck ..... step out of the way, its coming
DOWN.

Try working with an unstayed rig, everything changes.
Of course, I'm only running a junk-rig on a small (21' ) boat, but...

Seems to me that deck stepping an unstayed rig is an exercise in
futility.

Steve