I have an idea for a tabernacle to share. I was playing with tabernacle designs for my aluminum tube mast last night and woke up with a very different idea. All of the pivoting tabernacles I've seen pivot at or near the top. Because of the stress on the mast there, hinges are usually used on hollow masts as opposed to drilling and bolting. Drilling holes in freestanding aluminum masts is discouraged for good reason. One may be able to do that with a solid wood mast or one with very thick walls especially if there is some reinforcement around the hole. Phil Bolger specified reinforcement with a long 1/16 inch stainless steel plate held by a number of very small screws on the wood mast, along with the tabernacle, he designed and I successfully built for my O'day many years ago. My second attempt to build wooden mast was a disaster but that's another story. Tightening the large bolt through the two thick wood sides of the tabernacle locked the mast in. It was a strong simple arrangement that served well.

I have a scheme to be able to bolt through an aluminum tube mast to allow for a simple two sided tabernacle while keeping ample strength. First, the pivot point would be about midpoint vertically on the tabernacle. I think there there is no great lifting advantage to having the mast pivot at about 10% of length unless it is counter weighted, a great option with a boat with a bow well or if you pull downward from the mast base as Robert has. A wood plug would fill the tube to eight inches or so above where the hole would be drilled for the pivot bolt. The mast would be locked in the tabernacle by the pivot bolt in at this point providing good reinforcement side to side. The top and base of the mast would be clamped in as well. When you consider that this part of the mast does not need the same strength as at or above the partners, as seen in the tapered bury of stepped masts, I think this arrangement would stand up well.

Having the pivot below the top of the tabernacle has the advantage of locking the mast between the uprights to limit side to side sway when raised, more so as more of the mast goes higher and the bury moves more between the uprights. Pivoting at the tabernacle midpoint would, I think, give it a longer arm of side to side support going up and down. On my boat the mast would still clear the cabin top when horizontal. I made and used a gin pole and a short temporary stay bridles to single hand for my stayed mast last year. A gin pole alone attached at the pivot bolt would allow the same.

I have some good ideas and some wild ones as well. I'm pretty certain this one is sound but would appreciate any feedback.

Phil

P.S. I think I need to learn to shorten my posts.

Robert,

You still may be able to use temporary stays despite the narrow bow. For those kind of stays to work without needing to adjust them during raising or lowering they need to be horizontally in line with the mast's pivot point. What if you welded a small drilled angle iron ear at the back of each upright just below the pivot rod. Before raising or lowering the mast you could then then could the bolt something like a 7 or 8 foot 2”X6” piece of wood or a piece of aluminum channel to those ears giving you a wide base for the stays that, with the added height of the securing eye bolts at the ends, could be at the same level as the pivot.

I can see why you don't want to add much more weight up in the bow but have you thought about adding some triangular gussets or braces from the tabernacle base to somewhere near the top. It would add a bit more weight and windage but would give more support to the top. Dave Z's aluminum tabernacle has two really neat bars that give both lateral and fore aft support to the top of the tabernacle. Something like that may do the same on yours. I think he also anchors it to the bulkhead as well. A piece across the back, allowing room for your lifting rig, would also add strength and stiffness but I'm sure you thought of that as well.

How have you anchored the tabernacle bellow deck? The one tabernacle that I built was a very beefy simple two sided keel stepped one with a bolt through the middle of the square mast which was close to solid at that point. Working with hollow a round mast and trying to keep weight and windage down is very different.

You are right on the cable comealong. I've used one too many times but fortunately I am still in one piece and still have all my fingers. I admire your fabrication work.

Phil

Robert Leask wrote:

I am a little concerned about the torsional stresses when the mast is near horizontal, I think these tabernacles will be strong enough when the masts are raised but the leverage is very high when they're on the way up or down, and I'm worried that if the boat were rolling a lot it could permanenly deform them. I'm trying to think of a way to stiffen them without adding too much weight or clutter. Suggestions welcome.

Hi Robert,

That's been a concern for us, too. Last time, we decided to leave the sail bundle attached, knowing we had plenty of power to lift. And we did... with me pulling on the masthead from beach ahead of our dried out boat (no rocking).

Problem was, with the mast over halfway up, that bundle lifted from a little off-center, so swung across. The mast followed. I (over) corrected. It swung back. The mast followed. I (over) corrected. Repeat.

I eventually got it under control before we levered our tabernacle apart. Or ripped the hinge off. Or something I yet fail to imagine. But WHOA! I was sweating bullets! 

Got me thinking about this problem, and we thought this up:

Since, with your set-up, you can take it slow and hold position, how about a pair of temporary, running shrouds, tended every few feet of lift/drop (stretchy line will dampen travel but allow some progress between resets)?

To save a trip up the mast, you can tie them to a loop around the mast, and haul it up with the halyard (don't forget a downhaul line to bring it back to earth!). Maybe not all the way up, but to wherever the angle looks right (high and wide are both good, but work against each other).

We use this method to lift one mast to 45+deg with the other's halyard. Then pull it home from the beach. But love your come-along arrangement!

Good luck and work safe... that's a mighty big nutcracker!  8/

Dave Z

I'm just finishing tabernacles for my new 3 masted rig and hoping this link will work: 

https://app.box.com/s/mggikxpabes6w22h6gsse51k8mrw907p

The relevant pictures are titled MastDown 1 and 2. I made mine out of steel and will get them galvanized when I'm satisfied they are completely done. My idea for raising and lowering with a common chain come-along worked out very well, it can be easily and safely done with little effort, a one hand operation for the foremast at least. Will be trying the main mast shortly.

I am a little concerned about the torsional stresses when the mast is near horizontal, I think these tabernacles will be strong enough when the masts are raised but the leverage is very high when they're on the way up or down, and I'm worried that if the boat were rolling a lot it could permanenly deform them. I'm trying to think of a way to stiffen them without adding too much weight or clutter. Suggestions welcome.