[Public-list] Tabernacle

[Gordon Laco]

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.

Gord








> 
> 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
> of 
> 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
> much 
> 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
> above 
> 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
> two  
> 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
> on  
> 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,
> at  
> least 4 or five inches in diameter I would think, that had their bases fixed
> in  
> 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. :)
> 
> Lee
> 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.
> 
> Gord
> 
> 
> 
> 
> 
>>  Gord,
>> 
>> Besides being in the choir, what is a  tabernacle?
>> 
>> -bob
>> 
> 
> 
> 
> 
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