Recommissioning Judy B's "Bijou"
|
|
Job Description:
|
I
discovered the problem while rebedding the chainplate on the deck. When
I detached the shroud from the chainplate, the bulkhead dropped down 1/2".
The bulkhead was loose.
When the shrouds was tensioned, the upper edge of the bulkhead was pressing against the underside of the deck.
As originally installed, the bulkhead was bolted to the bulkhead panel under the settee with 3 or 4 quarter-inch machine screws. The threads of the bolts were contacting the wood and fiberglass of the settee bulkhead, and had caused the hole to enlarge.
There were also 2 or 3 more #10 self-tapping screws holding it to the backrest of the settee. Over time, the threads "egged out" the holes in the fiberglass.
After we removed the OEM plywood bulkhead, we inspected it. We didn't find any signs of rot. However, it did have compression damage where the chainplate bolts were. Two chainplate bolts had been over-tightened and the fender washers were fairly small, so the plywood grain was crushed around the bolts. The plywood had been weakened right there. That was an additional potential point of failure.
Several factors had contributed to the failure of the original bulkhead,
pulling it loose from the hull and lifting it up about 1/2":
- The threads on all the fasteners were cutting into the fiberglass
and wood. The factory should have used bolts that had a smooth, unthreaded
surface where they contacted wood and fiberglass. Instead of self tapping
screws, they should have used through bolts with unthreaded surfaces
where they contacted the wood and fiberglass.
- The lower bulkhead (attaching the settee to the hull) was pretty thin
to provide adequate bearing surface for the loads. (At least it was
the link in the system).
The lower bulkhead connects the port settee to the hull with fiberglass tabbing. The bulkhead was made of plywood approximately 1/4" thick, and the fiberglass settee edge was thinner than 1/4" thick. Together they were less than 1/2" thick.
The upper port bulkhead was attached to the lower bulkhead with 1/4" bolts through the (almost) 1/2" thick plywood. We increasex the thickness of the lower bulkhead to about 1" to provide more bearing surface for the through-bolts.
In comparison, the chainplates were attached to the upper bulkhead with four 3/8" bolts through 1/2" plywood. That's a lot more bearing surface.
The replacement installation corrects many of the weaknesses in the original design:
- The plywood is 1/2" Hydrotek. It's a 9-ply, BS1088 standard,
certified by Lloyds of London. It's the strongest marine plywood available.
There are NO voids. All exposed edges were coated with epoxy before
it was installed. The old "marine plywood" was only 4 or 5
plies, and had visible voids. The OEM plywood was not a high quality
marine plywood.
- All fasteners are through bolted. There are no self tapping screws
anywhere.
- The shanks of the bolts are smooth, not threaded, wherever they contact
wood and/or fiberglass.
- The bulkhead attaching the settee to the hull was built up by adding
a piece of 1/2" hydrotek, to provide more bearing surface for the
through bolts. It is screwed onto the OEM 1/4" plywood bulkhead
and fiberglass tabbing at the top and bottom, as well as epoxied with
thickened epoxy.
- The bulkhead is attached to the backrest of the settee with through-bolts,
not self tapping screws. We installed an inspection port in the backrest
of the settee to provide access.
Materials and Labor to repair:
I didn't have enough free time to do the work myself, so I hired Svendsen's Boatyard in Alameda to do the work.
- Fabricate and install a new port bulkhead made from Hydrotek plywood
- fabricate and install a reinforcing bulkhead under the port settee
- fabricated and install a new top on the locker, made from teak veneer marine plywood
- install an inspection port to facilitate through-bolting behind the settee
- Reinstalled and rebed the chainplate, and reattach the port cap shroud.
Nine Hours of Labor: Dave Wilson at Svendsen's Boatyard completed the job from start to finish in about nine hours, using materials that Svendsens keeps in inventory. He has replaced hundreds of bulkheads, and worked very efficiently. (I'm sure it would have taken me at least three times as long.)
$110 in Materials: The Hydrotek and teak plywood cost about $60. Miscellaneous bolts, epoxy, gloves, sandpaper, etc. cost another $50.
