One thing to watch out for in a tabernacle if you want to use it to actually remove the mast from your boat, or if you want to get the mast down to a level, where you can work on the masthead from the dock without a very tall step ladder is that the mast base should be elevated so that the mast will fully lower without hitting the forward hatch.
This is not the case on my boat, so I cannot lower the mast far enough to do work on the masthead. Indeed, the mast step is now a stainless steel plate instead of the original teak mast base, so the mast pivot point is actually lower. You might be surprised how that forward hatch interferes with lowering the mast. On my last boat, I can stand on the top step of a five stepladder on the dock and perform some work on the masthead, but it's a dangerous stretch. Also a higher mast step would better facilitate running lines back to the cockpit for the halyards, downhaul, reefing lines etc.
For the purpose of crawling under bridges the normal height of the mast step is just fine, but you will need a new mast step, since for a tabernacle, the mast step should l be stainless steel with raised sides and a bolt run through the mast. The forward edge of the mast will have to be cut in a radius, and a block with a similar radius cut and inserted in the bottom end of the mast through which a hole will be drilled. Matching holes are drilled through both port and starboard sides of the mast. A bolt is inserted through the mast, block and both starboard and port sides of the stainless steel mast base. The mast does not rest on this bolt, but on the base itself. The radius on the leading edge of the mast permits the mast to fall forward in the lowering operation.
To lower the mast, I break the backstay at the tensioning device, and attach the top end of the backstay to the end of the boom. A pelican hook is provided to ease this operation. I use the top of the backstay (from mast top to boom) and mainsheet (from boom to traveler) to lower the mast. You have to physically lift the boom by hand to get it started down. Now putting a backstay-tensioning device in mid-backstay is sort of loony, because you cannot tension the upper part of the backstay without unwinding wire on the lower part. In other words, you need to have one end of the tensioning device connected to something that does not twist. However locating these things at deck level means that if you are underway with the motor running and you wish to adjust the backstay tensioning device, you have to close the lazarette hatch on the running motor, and crawl out of the cockpit, sit m lie or kneel facing aft and tighten the device. That was not something that I wanted to so, I raised my tensioning device to boom level, and devised a simple "wrench" to stabilize the lower portion of the device (and lower section of the backstay, while I tension the backstay. I made it with hardware store parts for a few bucks.
Another feature of a well-designed tabernacle rig is that boom guys on either side running from the upper shroud turnbuckle to the aft end of the boom. These boom guys are very important. They prevent the boom from flopping to one side or the other. The tabernacle rig has good lateral stability, but very poor transverse stability. You do not want to place any pressure to port or starboard during the operation. In my photos, the boom guys are black in color. It is also wise and some consider essential to utilize a "bridle". The bridle runs from the boom guy attachment point (pivot point) on the upper shroud either to the base of the aft lower shroud (at deck level) or to another deck location aft of the lower shroud. I made my bridle a permanent section of my lifeline system. That line is white in my photos and runs from a deck fitting (eye bolt) at the forward end of my spiffy teak boarding step forward to the upper shroud turnbuckle boom guy attachment point. This bridle prevents the upper shroud from bending at deck level, and causes it to bend instead at the pivot point, which is parallel with (level with) the mast base. I did not use a bridle on my Catalina 22, but that was a much lighter boat, and mast, and I did not design that set-up. Suffice it to say that adding a bridle is wise if not essential on an Ariel.
Note: DO NOT install a "running" bridle/boom guy. That was the way my boat was rigged when I bought it. The bridles and boom guys were one continuous line that ran through blocks. The way I saw that set-up, the ability of the bridle and boom guys to self adjust in a "running" bridle/boom guy reduced, if it did not eliminate, lateral stability of the tabernacle rig.
Raising the mast is just the reverse of lowering it. What goes down comes up. It is important to have a boom vang, or so the theory goes. The further that you lower the mast, the heavier it is to lift. The forward hatch is the limiting factor. Of course it pays to have a long mainsheet.
This photo shows the upper shroud turnbuckle and the shackle used as the pivot point attachment shackle for the boom guys and lower lifelines including the section of the lifeline that serves as a "bridle". It is important to seize the pin on this shackle so that it wil not work free. The forward end of the black boom guy is shown. The pelican hook on the aft lower shroud has been released and is resting on the lower life line, where it will remain during the tabernacle operation.
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