|
|
|
|
|||||
|
||||||
From: delviento2 (no email)
Date: Wed Apr 11 2007 - 08:09:18 EDT
Respectfully, I disagree with Jeff. The pinched spaghetti
illustration does not work because a keel-stepped mast is
not "pinched" where it goes through the deck, in fact, it is not
attached to the deck in any way. If the mast were attached to (or
made contact with) the deck, both the mast and the deck/cabin top
would be damaged by the forces from the mast movement. In fact, I
would argue that the shorter deck-stepped mast may be stiffer.
To all: there is no definition of a blue water- or offshore-capable
boat that stipulates a keel-stepped mast. Some of the most stout
boats in the world feature deck-stepped masts (like the HC 33,
Westsail 32, and Hallberg-Rassy mentioned here).
The biggest difference between the two configurations (keel- vs. deck-
stepped) is that a vessel with a deck-stepped mast has to withstand
tremendous compression forces on the deck/cabin top, from the weight
of the mast/sails (compounded by the increased g-forces on a pitching
vessel and compounded by the force of the sails on certain points of
sail). Correspondingly, the interior design of any deck-stepped
vessel is restricted by the requirement that a substantial/primary
bulkhead be situated directly beneath where the mast is stepped. On
many production, deck-stepped coastal cruisers, these compression
loads are not addressed substantially and years of use will result in
the primary bulkheads beneath the mast becoming "de-tabbed" from the
hull and the deck will flex visibly under load.
Alternatively, some designers combine deck stiffners and a
compression post inside (kind of a hybrid between the keel- and deck-
stepped design). A keel-stepped mast features a mast protruding into
the cabin, but is otherwise free of the cabin-top compression loads
and the corresponding bulkhead requirement.
I agree with Jeff's assessment of rig loss, it is bad regardless. It
may be with a keel-stepped mast you stand a better chance of
retaining a portion of the stick for use as jury rig, it may be that
you rip a gaping hole in the deck during a roll-over. At least with a
deck-stepped mast everything is external to the vessel.
Sincerely,
Michael Robertson
--- In , "Jeff Stander" <jeff at dot dot dot >
wrote:
>
> The main point of having a keel stepped mast is that the mast is
> stiffer. Try holding a single piece of (uncooked) spaghetti at one
> end between your thumb and forfinger. Have someone else wiggle it
> from the other end. Now try the same experiment by pinching it at
> one and and a couple of inches furthur along. It is significantly
> stiffer.
>
> So, keel-stepped masts are stiffer, can use lighter rigging, and
> areusually stronger. My preference is for keel-stepped masts. My
> opinion is that many boats have deck-stepped masts as a concession
to
> below-decks interior design.
>
> The water ingress can be dealt with. As for rig loss? Well, I am
> not making my decisions on the easiest rig to deal with in a
> disaster. If the rig goes it's going to be a mess anyway.
>
> Regards
>
> Jeff
> s/v Beatrix (KP44 #276 1980)
> www.svbeatrix.com
>
|