Kurt,
Happy you've surfaced again on this thread, it's been a year!
I've been looking at my tabernackle project recently. Have a Bomar forehatch now with a nicro saucer vent in the middle.
Mast is going to roll forward when lowering and rest somehow in the pulpit. Have to raise my tab/base to about 4.5" so as to not crunch the vent.
I already cut the foot of the mast to the roll profile before painting it. Now I discover I have to recut two inches shorter and do the roll cutout again.
This means that I have to build UP the mast base onto something strong, load spreading but not cumbersome - that works with the compression load beam inside.
While I was fooling around with mockups to bring down to the boat for fitting,
got to thinking, that while the mast is under good control using the Bingham 'masting' model and Ballenger's single bolt in a SLOT tabernackle,
there are FORE & AFT forces that come into play when the mast is lowered under tension and pulled back up.
The base has strong forces working on it when the mast is moved.
When the mast is loose everything depends on bridle, backstay/boom, upper shroud, ropes and wires, winches and connections to keep it under control. As the stick is lowered, a lever force comes into play from the angling mast. Imco there is AFT pressure on the tabernacle. Just think what would happen if the hinge bolt came out while lowering the stick - see mast drill into the doghouse.
maybe not, but see mast wanting to shoot aft anywhich way it can. That pressure is all there when the mast is lowered under control.
Also trying to get a mental on how much fun it's going to be when decommishioning to get the mast loosened from the hinge bolt. There'll be a bit of wrassling with the cantilevered spar while attempting to keep it under control. See chaos in this. The tabernackle needs to be as immovable as a rock. In all directions. Including UP.
My riser hump is basically flat topped for the tab hinge plate footprint - with athwartship sloping sides. The hinge plate is predrilled for 5/16" flatheads that don't match the beam inside. Because the mast's real estate is a very short distance between the hatch cover and the nose of the doghouse the riser hump model just fits vertically front & back. To say that there is very little space for fore&aft bracing for any mast tabernackling hardware.
Should the plate be thru-bolted? Or lagged. The arguement for lagging is that if the mast in a blow decides to come down on its own, it may be wise to let the thing tear the immediate base off - rather than tear a hole in the deck, if it's all bolted together. Still in the hemhaw stage.
Am worried that a tall tubernackle will experience unfair bending forces when raising and lowering - unless braced.
Looking at the last photo in the series at post #243, imagine a double tube extension coming from the upright toward the doghose nose and at about that level. Couple of pins, to lock the tubernackle straight. Maybe a single tube brace is clipped on the mast and hinges from the top of the tube-horns to hook onto the doghouse.....?....
Holes in the old mast should be controlled so wear and corriosion are minimized. An accomodating slot is better in a support structure, which can be altered & changed as wanted. Just my opinions.
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