Raising the mast using a tall mast crutch could allow the mast to clear the cabin top on many boats with a mast up forward in an aft facing tabernacle. It would beat keel stepping with a gin pole. I needed a somewhat tall mast crutch anyway for single handed lifting with the rig pictured below.

Imagine the mast in the picture below being drawn into an aft facing tabernacle. Should be workable with some masts and with less people power.  The gin pole pivot here was at the mast pivot. I used temporary baby stays to keep the mast from swaying. Their pivot point had to stay level with the mast's pivot point. As the mast is further drawn into our imaginary tabernacle that side to side support will be needed less. Poles with junk masts stepped further forward would have a shorter lever arm and may need more power at the block and falls.

I also thought about a gin pole that would attach rigidly to the top and bottom of the tabernacle with perhaps a tensioning line to the bow also connected at above the mast's midpoint and pull the mast close to upright, until it came to close to 2 blocks and then the rest by hand.

When planning to convert I considered a tabernacle with a midpoint pivot for clearing the cabin and transporting the mast in the tabernacle while staying away from the area of greatest stress at the tabernacle top. This would also provided greater side to side support sooner as the mast was raised and brought into the tabernacle both above and below the pivot. It would require a 2 1/2 sided tabernacle.

So many ideas, so many boats, just one life, or so they say.

larger images in my album

Arne Kverneland wrote:

The fine thing with tabernacles is that they surround the mast, kind of. Since we know that the strength of any beam varies with the cube of its dimensions, it doesn’t take a rocket scientist to design a tabernacle at least as strong as the mast. Even an open U-shaped tabernacle should hold well. I guess I would add 2-3 “horse-shoes” of metal or plywood to support the open U-profile.

Btw, David Ty. presented a real Colombie-egg here, recently, by suggesting that the open U should face aft. On smaller boats, with fairly light masts, one can then just walk the mast up, right into the recess of the tabernacle.

Arne

This kind of small boat's tabernacle is useful, because it doesn't need a through pin at the point of maximum stress, at the top of the tabernacle. To use it successfully, the mast must be pushed up from a point above the CG, which places a limit on the practical length. 

It occurs to me that it could be useful in larger sizes too, if a pin is put through the heel of the mast to keep it in place during raising and lowering. This will avoid having to make a clamped-on band for an aluminium mast (so that there is no stress-raising hole through the tube). The push can then be from below the CG.The limiting factor on mast size will then be the manpower needed, and problems of control. Here's a clue as to how it can be done.

We really don't like putting holes through aluminium masts at deck level, the point of maximum stress. It's proven to be the cause of fatigue failures. I recommend a clamped-on band with the pivot pin just behind the mast tube. This arrangement is similar to that used with a wooden mast in a tabernacle. 

In one of the JRA magazines, Pete hill wrote a piece about making tabernacles. It's worth reading.