mainstay at csolve.net
Thu Dec 15 12:28:19 PST 2005
The Shark class uses something similar - their version being a cast
aluminium 'thumb' in the heel of the mast that rides on a bar in the mast
step. The effect is the same as what you describe: if the mast goes out of
line on the way up or down, well it just does with nothing to restrict it.
> Tabernacle; non-choir kind; it can be done. Some thoughts. :)
> The Alberg 22 had a very interesting variation in it's tabernacle that I
> thought was an improvement over the traditional captive bolt design. Instead
> having the mast pivot on a bolt that was captive in the mast and the deck
> part of the tabernacle, which would tear up the deck if the mast moved too
> from side to side while raising or lowering, the bolt was captive in the
> mast, but it rode in a sort of saddle, a groove in the deck plate of the
> tabernacle that kept the pin from moving for and aft, but allowed the pin to
> move up
> and down, so that either end could raise significantly if the mast moved from
> side to side, without the bolt coming out of the groove.
> Another article I once read about making it easier to raise and lower a mast
> in a tabernacle addressed the problem of the shrouds being slack while the
> mast was going up until the mast was nearly vertical. The problem is with a
> cabin top stepped mast, the vertical pivot point of the tabernacle bolt is
> the vertical pivot point of the shroud attachment at the chainplate. This
> guy dealt with the problem by having a ring put into the upper shroud at the
> height of the mast step pivot point. Wires went from the ring down to the for
> and aft lower shrouds chainplates, making a triangle, with the apex being the
> ring. This, you remember, is at the height of the tabernacle pivot pin. As
> the mast goes up or down, the shroud tension remains constant.
> Granted, for a boat as large as an A30, that ring would have to be very
> strong, but if so, the system would definitely help. Maybe nicopressing the
> wires that lead to the lower shroud chainplates to the upper shroud at the
> height of the mast step pivot point would be a better way to do it on a big
> boat. Once the mast is stabilized from swinging side to side, rigging a pole
> the for face of the mast to get mechanical advantage to hold the weight of the
> mast while raising or lowering becomes so much easier.
> The tradtional way of stepping a mast without a crane is to use mast
> 'scissors'. For an A30, I would imagine you would need 2, 20 foot long beams,
> least 4 or five inches in diameter I would think, that had their bases fixed
> position at the chainplates, and their apex's joined at the top. Lines from
> the bow and stern to the apex would keep the scissors from swinging for and
> aft. A block and tackle from the apex to a bridle around the mast at the
> spreaders would lift the mast up, and the heel of the mast would be swung on
> to the
> step, or the mast could be raised by pivoting over a tabernacle. Cumbersome.
> Interesting problem to ponder, when it's 20 degrees outside. :)
> Stargazer #255
> In a message dated 12/15/2005 12:40:00 PM Eastern Standard Time,
> mainstay at csolve.net writes:
> Hi Bob -
> A tabernacle is a type of mast step. It involves two fairly massively
> constructed cheeks, port and starboard that in our boats would be approx. a
> foot or more high. The whole assembly would act as a hinge allowing the
> mast to be swung down aft.
> Picture the cheeks as having a base with vertical plates welded at 90
> degrees and set up so that the are just far enough apart so that the mast
> will stand between them. Then picture the mast as having a hole drilled
> through it for something like a 1" diameter pin. The pin would go through
> similar holes near the top of the tabernacle cheeks near the top...in my
> example that might be about 10" above the heel of the mast. When assembled,
> the mast would be held with its heel slightly above the old step, which is
> now the base of the tabernacle.
> If you were to want to raise or lower the stick without recourse to a crane,
> you would be able to run a halyard forward to the bow, then release the
> forestay and the forward lower shrouds. By easing the halyard you can lower
> your own mast, the base pivoting on the tabernacle pin. You can raise the
> mast the same way.
> Sounds great...
> But. If any sideways movement on the part of the mast happens on the way up
> or down, you can either tear the tabernacle out of your cabin top or bend
> the mast (imagine the leverage). Or, imagine a dismasting; you stand a good
> chance of tearing the tabernacle and a chunk of the cabin top out of the
> boat instead of just losing the rigging companont that failed. And, I think
> they are ugly, but that is my problem!
> I think that they are terrific for small boats that raise and lower their
> sticks often, and for motorsailers with stumpy rigs on boats that go under
> bridges often... I think that for boats like ours they open more potential
> problems than they solve.
> Bye the way - did you want to see pictures of my vang, and anchoring tackle
> setup? Did I ever send you photos? I just found some.
>> Besides being in the choir, what is a tabernacle?
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