My Original Tabernacle
I could see no way to use the standard Stevenson
tabernacle with my round mast. Since I was building a birdsmouth hollow
mast I needed something besides the large outside hinges. My tabernacle
was a slight modification of ideas from Craig Gleason. It uses a tenon
on the top of the compression post (lower part) and a mortise on the mast
proper that swings down. The tabernacle portion of the mast is octagonal
as shown.
My Problems with this Design
I started building this design before I realized
all the implications. Most notably, when the sail and gaff are lowered
on the boom, in order to lower the mast the pivot point would have
to be an extra foot or so higher to allow clearance for the mortised part
to swing out. I solved this by raising the compression post (lower part)
another foot, but this has some other undesirables.
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In my case it meant that I could no longer
get the boat in my garage with the mast stepped.
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The mast doesn't fit on the boom crutch properly.
If you use a mast with the same overall height because the pivot point
is higher, the mast is made shorter. (I cut mine shorter to make the mast
the proper height. Then I realized I should have left it higher.)
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The mast has a much higher angle and looks
funny. I like the mast paralleling the boom when down, like the Stevensons
have done.
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It makes the boat harder to cover.
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The bolts on the outside of the mast have
heads that catch my sail lacing.
I am somewhat concerned about the strength
of the tenon and the mortise, although it seems quite strong. As built
the tenon fits very snugly and there is virtually no play in the mast.
Another Idea
I am trying to eliminate the tenon and use
a hinge more like the Stevensons original design. I am considering a hinge
internal to the mast. Here is a drawing. There are two hinges: a 4" door
hinge mounted flush to the cut in the mast and another smaller on the outside
of the mast similar to the Stevensons design. The smaller is only to hold
the mast together when upright. The heaviest door hinge I can find uses
1/8" steel. I think that will be strong enough even though I will have
to cut off one section.
Concerns
My biggest concern is about the screws in
the end grain of the mast, and whether they will hold well enough. This
drawing only shows 1" screws. I plan to use at least 3" screws. Another
concern is the notch to allow it to pivot. This reduces the surface area
of the contacting parts. I suspect that it will not reduce the strength
much.
Testing
I purchased a heavy duty welding hinge.
This allowed me drill my own 3/8" holes as desired. Unfortunately it did
not close flat, but I found some machine screws that would fill the gap
and hold the mast vertical. Before trying the hardware out on the real
mast, I decided to test the hardware out on a piece of 4x4 cedar fence
post. I extended it with a 2x4 to get it about the length of the mast so
that I could apply some side to side force and see how the design holds
together.
The mast stands up by itself without the
aid of any support.
With the mast down, I put quite a bit of
force on the end of the mast wiggling it more than I would expect it during
normal usage and the hinge was quite stable.
