Removable Tabernacle

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Removable Tabernacle

Postby JonLee on Mon Apr 30, 2012 1:06 pm

I am planning on making my tabernacle removable. I don't think that I'm going to store my PocketShip in the garage, but it'd be nice to be able to pull it in from time to time for maintenance or whatever.

I see in some of Pete's posts that he added a fairly large doubler inside the cabin to help take the loads. I wondering if anybody else has down a removable tabernacle and how you've handled it in terms of bolt size/patterns, doubler plates inside the cabin, and other considerations. Any guidance on how big/thick a doubler should be?
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Re: Removable Tabernacle

Postby aschilpp on Thu May 03, 2012 10:40 pm

I made my tabernacle removable but did not include the doubler. In hindsight I think it's probably a good feature to include for peace of mind but I have yet to have any issues other than seeing some flex when I push on the tabernacle after it's bolted in. Under sail I have noticed no issues. I built my tabernacle to spec and countersunk 4 3/8" bolts in a vertical line towards the bottom. I then epoxied the heads of the bolts in place leaving only the threaded ends protruding from the aft side. The interior of the tabernacle is completely smooth and the bolt heads are buried. I drilled the corresponding oversized holes into the forward cabin wall and lined them with thickened epoxy and drilled the appropriate sized holes through the epoxy lining. The bolts slide through and with a rubber washer and nuts the tabernacle is secured. It's not exactly beautiful on the interior but I was after function here. I can assemble and disassemble in about 5 minutes. I will try and include some photos soon.
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Re: Removable Tabernacle

Postby tattoo on Wed May 09, 2012 8:35 am

My Tattoo has a removable tabernacle. A month after her maiden voyage (Oct '10) on a windy day the mast/tabernacle unit pulled the bulkhead away from the cabin roof / bulkhead joint. There appeared to be several causes. First, the cleat glued to the bulkhead was made of cheap pine. Analysis showed that the wood separated rather than the glue joint. Second, I had not wrapped the bulkhead / cabin roof edge with fiberglass. And (possibly) third, the mast shrouds could have been tighter. My fix was to pull the bulkhead back into place, reglue it, and wrap the bulkhead / cabin roof edge with fiberglass. I also tightened the mast shrouds. As an extra precaution I installed a 1/8" x 1-1/2" SS "L" bracket on the inside (with the short part of the "L" under the top 1/2" bolt and the long part bolted under the roof at its centerline). A year later (on a windy day) the same failure occured! At the instant of failure, the "L" bracket was severly bent, but its presence limited the damage. Lesson learned: A reconstituted epoxy joint is a poor substitute for a joint made of properly prepared surfaces. Also, I had not improved the poor quality of the wood used for the cleat.

The second repair included a 3/4" plywood doubler (on the inside of the bulkhead) that extened from Dorade box to Dorade box and from just under the cleat (at the cabin roof) down to the level of the anchor deck. There was a second (smaller) 3/4" doubler that covered about 4" (of the top) of the big doubler and the cleat. That doubler was then fastened to the cabin roof with six 1" x #10 FHWS screwed into it from the top of the cabin roof. The top of smaller doubler / inside of cabin roof joint was also glued with epoxy. The bulkhead/large doubler/small doubler surfaces were made fast with epoxy & screws. This fix (completed over the winter) has not failed in several days of sailing in strong winds.

Tattoo's tabernacle is attached with two 1/2" carrige bolts spaced as far apart as possible. The round heads are supported with 1-1/2" washers (with the 1/2" holes made square). That increases the bearing surface by a factor of 2.8. The washer and head are not countersunk into the tabernacle and are therefore supported by the full 3/4" thinkness of the tabernacle. The countersinking is not necessary due to the fact that the mast (at its foot) is kept away from the tabernacle with a 3/4" spacer for the purpose of setting the proper "rake." That leaves enough clearance for the carriage bolt heads and washers. The 1-1/2" washers have four small "tabs" cut into their edges. Two of the (opposite) tabs "dig in" to the wood resisting clockwise turning ... the other two resisting anti-clockwise turning.

The doublers were made with an attractive profile and the edges well rounded over. They were painted white and blend in quite well with the inside appearance of the cabin. They do not get in the way and are hardly noticable. I'm fairly confident that there will not be another similar failure.

Pete McCrary, Tattoo's builder and skipper.
Pete McCrary, launched Tattoo Oct '10.
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Re: Removable Tabernacle

Postby bobsastro on Wed Jun 20, 2012 7:04 am

I'm currently working on an aluminium folding tabernacle due to a need to lower it to get my Pocketship in my garage on the trailer. It's basically 5mm 5083 aluminium plate, same dimensions as the wooden tabernacle, with an additional part bolted to the forward cockpit sole to act as the hinge plate. The back plate of the tabernacle will be bolted through the cabin forward bulkhead through a 10mm doubled aluminium plate about 30 x 20cm (12 in x 8 in for you Yanks). It'll all be painted the same colour as the cabin/decks, so hopefully it won't upset the wooden traditionalists too much. My Pocketship is just about at the bottom painting stage, so I should be able to install it and see how it looks in a month or so. I'll post some images then.

Cheers,
Bob in Sydney, Aust
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Re: Removable Tabernacle

Postby bobsastro on Sun Sep 02, 2012 2:34 am

Finally finished folding tabernacle and installed it. As you will see from the images, I need it to get in and out of my garage. It wasn't a cheap exercise, all in 5mm 5083 marine alloy, laser cut, and welded, but I'm pretty sure I'll lose the stick before this breaks or rips out of the #2 bulkhead (I have an approx. 1' x 1' 10mm alloy backing plate inside the cabin. Only months away from sailing, hooray......

cheers,
Bob in Sydney

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Re: Removable Tabernacle

Postby jwv630 on Tue Sep 04, 2012 12:59 pm

Pete (and Everyone):

Sounds like a nasty fault! If you had to do it all over again from the start, what would you do differently regarding this particular issue? I'm trying to learn from others mistakes; make enough of them on my own.....

Many, many thanks. I've benefitted much from your gracious advice here.

Regards,
Jimmy Vitale
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Re: Removable Tabernacle

Postby tattoo on Tue Sep 04, 2012 3:13 pm

1. I would use white oak for the cleat at the top edge of the bulkhead. The cheap stuff that I used pulled apart. 2. I would be careful to wrap the fwd bulkhead/cabin roof edge with double fiberglass. I didn't have any fiberglass over that edge at all. And 3, I would have a doubler on the inside as suggested by John Harris' sketch. Also, I wouldn't countersiink any of the carriage bolt heads into the inside of the tabernacle (there's space there for the bolt heads because of the rake of the mast). I think the bolts need the entire thickness of the tabernacle's back side. Countersinking makes a bolt "pull thru" more likely under extreme stress. And I'd put 1.5" washers under each carriage bolt head.

But I really like Bob's all metal folding one! If I could afford it, that's what I'd do. Manassas machine shop labor is $80 to $120 per hour, minimum! And the machinist would require professional quality drawings to work from. Welding labor/hour may be a bit less. Maybe Bob Sastro could let us know the machine shop man-hours required for his job.
Pete McCrary, launched Tattoo Oct '10.
tattoo
 
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Re: Removable Tabernacle

Postby jwv630 on Tue Sep 04, 2012 7:11 pm

Pete:

Many thanks. I'm going to incorporate your thoughts into my building plan.

Regards,
Jimmy Vitale
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Re: Removable Tabernacle

Postby bobsastro on Thu Nov 22, 2012 5:07 pm

Dear Peter, just noticed your questions in your last post regarding my folding tabernacle. I made some simple drawings from the full-size plans, and bought a half-sheet of the 10mm aluminium for about $150 (AUD is about the same as USD), got a local laser-cutter to cut out the pieces for about the same, and with some difficulty, found a welder willing to work on such a small job. That cost me $300, so the all-up cost was about $600. Way too expensive, I agree, but I really didn't trust the idea of a removeable wooden one. Just a bit more detail: I used a couple of SS countersunk head machine screws (8mm) through bulkhead 2, threaded through the 10mm aluminium backup plate in the cabin so I could screw it on from the outside, but I still use washers and wingnuts on the inside for additional strength. I'm just waiting for a surveyor's report so I can get my insurance, and I'll be launching in a couple of weeks. Cheers, Bob
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Re: Removable Tabernacle

Postby hood on Fri Oct 17, 2014 2:14 pm

I welded the two Corner profile bars of 10 mm aluminum
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