by 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.