keel stepped/deck stepped masts
 

I have heard ppl say they would only have a keel stepped mast on an
offshore boat. Why? A well built deck stepped mast is as strong as a
keel stepped one and easier to put up or down. If either loses a
stay, it is coming down in a hurry? I fail to see the reason for this
odd preference.

keel stepped/deck stepped masts
 

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.

For offshore work, the ultimate compression strength of the mast is
important for situations like full knockdowns and capsizings. The additional
compression strength also comes into play if you lose a stay or a shroud,
and might just give you the additional reserve strength that would keep the
mast from coming down.

Tom Dacon

"Parallax" wrote in message
om...
I have heard ppl say they would only have a keel stepped mast on an
offshore boat. Why? A well built deck stepped mast is as strong as a
keel stepped one and easier to put up or down. If either loses a
stay, it is coming down in a hurry? I fail to see the reason for this
odd preference.

keel stepped/deck stepped masts
 

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.

For offshore work, the ultimate compression strength of the mast is
important for situations like full knockdowns and capsizings. The additional
compression strength also comes into play if you lose a stay or a shroud,
and might just give you the additional reserve strength that would keep the
mast from coming down.

Tom Dacon

"Parallax" wrote in message
om...
I have heard ppl say they would only have a keel stepped mast on an
offshore boat. Why? A well built deck stepped mast is as strong as a
keel stepped one and easier to put up or down. If either loses a
stay, it is coming down in a hurry? I fail to see the reason for this
odd preference.

keel stepped/deck stepped masts
 

On Thu, 8 Apr 2004 10:19:19 -0700, "Tom Dacon"
wrote:

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.

For offshore work, the ultimate compression strength of the mast is
important for situations like full knockdowns and capsizings. The additional
compression strength also comes into play if you lose a stay or a shroud,
and might just give you the additional reserve strength that would keep the
mast from coming down.

To that lucid engineering perspective, I would add the following
observations:

1) Dismastings MAY be better with a keel-stepped mast in the sense
that a deck-stepped mast will tend to fail in its entirely, whereas
even if you can salvage ten feet of keel stepped above the deck, you
may be able to rig a jury rig and keep going. Also, if a deck stepped
mast goes, you must IMMEDIATELY cut the shrouds still attached or the
mast will poke a hole in your hull...and this under very likely less
than ideal conditions.

2) Pluses of deck-stepped include no partners to leak water...no mast
boot, no Spartite, and, usually, more room and less obstruction in the
cabin.

3) Keel stepped masts are frequently heavier, but that weight can
translate to the mechanical advantage and lower CG mentioned above.
Also, deck flexing is avoided.

It's a matter of taste and intended use, mostly. I prefer keel stepped
on fiberglass boats, but see no objection to deck-stepped on steel
boats, mainly due to materials used and likely function of the boat. I
suppose the ideal compromise would be an aluminium deck stepped mast
on an aluminum boat! G

For the record, I have a keel stepped mast I am quite happy with.
YMMV.

R.

keel stepped/deck stepped masts
 

On Thu, 8 Apr 2004 10:19:19 -0700, "Tom Dacon"
wrote:

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.

For offshore work, the ultimate compression strength of the mast is
important for situations like full knockdowns and capsizings. The additional
compression strength also comes into play if you lose a stay or a shroud,
and might just give you the additional reserve strength that would keep the
mast from coming down.

To that lucid engineering perspective, I would add the following
observations:

1) Dismastings MAY be better with a keel-stepped mast in the sense
that a deck-stepped mast will tend to fail in its entirely, whereas
even if you can salvage ten feet of keel stepped above the deck, you
may be able to rig a jury rig and keep going. Also, if a deck stepped
mast goes, you must IMMEDIATELY cut the shrouds still attached or the
mast will poke a hole in your hull...and this under very likely less
than ideal conditions.

2) Pluses of deck-stepped include no partners to leak water...no mast
boot, no Spartite, and, usually, more room and less obstruction in the
cabin.

3) Keel stepped masts are frequently heavier, but that weight can
translate to the mechanical advantage and lower CG mentioned above.
Also, deck flexing is avoided.

It's a matter of taste and intended use, mostly. I prefer keel stepped
on fiberglass boats, but see no objection to deck-stepped on steel
boats, mainly due to materials used and likely function of the boat. I
suppose the ideal compromise would be an aluminium deck stepped mast
on an aluminum boat! G

For the record, I have a keel stepped mast I am quite happy with.
YMMV.

R.

keel stepped/deck stepped masts
 

On 8 Apr 2004 09:52:55 -0700, (Parallax) wrote:

I have heard ppl say they would only have a keel stepped mast on an
offshore boat. Why? A well built deck stepped mast is as strong as a
keel stepped one and easier to put up or down. If either loses a
stay, it is coming down in a hurry? I fail to see the reason for this
odd preference.

I used to be of the school that favored keel-stepped masts as be more
sound.

Some things that have changed my mind.

Pacific Seacraft builds very strong boats with deck-stepped masts, as
do some other builders.

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

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.

Jack

__________________________________________________
Jack Dale
Swiftsure Sailing Academy
Director
ISPA and CYA Instructor
http://www.swiftsuresailing.com
Phone: 1 (877) 470-SAIL (toll free)
__________________________________________________

keel stepped/deck stepped masts
 

On 8 Apr 2004 09:52:55 -0700, (Parallax) wrote:

I have heard ppl say they would only have a keel stepped mast on an
offshore boat. Why? A well built deck stepped mast is as strong as a
keel stepped one and easier to put up or down. If either loses a
stay, it is coming down in a hurry? I fail to see the reason for this
odd preference.

I used to be of the school that favored keel-stepped masts as be more
sound.

Some things that have changed my mind.

Pacific Seacraft builds very strong boats with deck-stepped masts, as
do some other builders.

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

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.

Jack

__________________________________________________
Jack Dale
Swiftsure Sailing Academy
Director
ISPA and CYA Instructor
http://www.swiftsuresailing.com
Phone: 1 (877) 470-SAIL (toll free)
__________________________________________________

keel stepped/deck stepped masts
 

I think one of the 2002 issues of Wooden Boat Magazine had a design article
by Ted Brewer in which he gave some reasons for preferring keel stepped
masts. Don't recall what they were though.

"Parallax" wrote in message
om...
I have heard ppl say they would only have a keel stepped mast on an
offshore boat. Why? A well built deck stepped mast is as strong as a
keel stepped one and easier to put up or down. If either loses a
stay, it is coming down in a hurry? I fail to see the reason for this
odd preference.

keel stepped/deck stepped masts
 

I think one of the 2002 issues of Wooden Boat Magazine had a design article
by Ted Brewer in which he gave some reasons for preferring keel stepped
masts. Don't recall what they were though.

"Parallax" wrote in message
om...
I have heard ppl say they would only have a keel stepped mast on an
offshore boat. Why? A well built deck stepped mast is as strong as a
keel stepped one and easier to put up or down. If either loses a
stay, it is coming down in a hurry? I fail to see the reason for this
odd preference.

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.