Tabernacle Forces

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Tabernacle Forces

Postby buckeye on Wed May 12, 2021 12:08 pm

So, i'm into the finish work now and hope to launch late June.
I plan to make my tabernacle removeable. I had already doubled the top of the interior of BH 2 and re-enforced the joint with double Tape on top of the overlapping glass.
But reading about some of the failures it does make sense that the foot of the sail will put significant forces on the tabernacle.

From a purely Mech-e standpoint, ideally you'd have mini-shrouds for the tabernacle pulling back against the forces exerted by the mast on it so they're not all transferred to the bolts / bulkhead. I don't see a way to do this as a practical matter. Particularly given the close proximity to the wide companionway. But I'm crazy enough to do it if I get a failure there.

I do expect to use turnbuckles on the shrouds so I can keep them tight, which i understand to be the first line of defense.
buckeye
 
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Re: Tabernacle Forces

Postby TassiePete on Thu May 13, 2021 6:19 pm

Kermadec's tabernacle is removable. I added two brackets ( 19mm hardwood ), which are epoxied and screwed through the internal backing plate and from underneath through the forward deck. The tabernacle fits snug and is through-bolted with 4 x 6mm countersunk bolts. The holes for these bolts were drilled 12 mm filled with thickened epoxy and re-drilled 6 mm and countersunk. There are drain holes in the brackets so that water doesn't pool under the tabernacle. So far everything stayed in place ...

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I wouldn't worry too much about any forward acting forces on the tabernacle by the boom, but keeping the rig tight is important. Make sure that the shrouds take all of the load of the forestay. Otherwise, the mast will be a long lever for the jib trying to pull the tabernacle off the boat. I am using synthetic shrouds and lashings, and I have had no issues maintaining tension. To setup/tune the rig, I place two small wooden blocks into the tabernacle behind the mast foot to set about twice the required rake. Once the shrouds are tight and lashed, I remove one of the wooden blocks and with the fore-stay (luff of the jib) really tight, the rake is about right.
TassiePete
 
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