[Public-list] Tabernacle

[FINNUS505 at aol.com]

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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