Recommissioning Judy B's "Bijou"
a 1977 Catalina 27 Sailboat - June 2004

Problem: The upper port bulkhead had pulled loose from the lower one

Solution: Install a new bulkhead and attach it more securely. Reinforce the lower port bulkhead.

Job Description:
  • fabricate and install a new upper port bulkhead using 1/2" Hydrotek plywood
  • Reinforce the lower port bulkhead (between hull and the settee), using 1/2" Hydrotek plywood. Double the thickness of the lower bulkhead from 1/2" to 1"
  • fabricate 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
  • Reinstall and rebed the chainplate, and reattach the port cap shroud.
  • Re-tune the rig

 

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":

  1. 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.

  2. 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:

  1. 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.

  2. All fasteners are through bolted. There are no self tapping screws anywhere.

  3. The shanks of the bolts are smooth, not threaded, wherever they contact wood and/or fiberglass.

  4. 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.

  5. 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.

Above: The new bulkhead, prior to installing the trim on the locker. The inspection port in the settee seatback was installed to provide access for through bolting the bulkhead to the settee.

 

Above: Three 1/4" bolts anchoring the port bulkhead to the bulkhead underneath the settee.

 

Above: There are three 1/4" though-bolts anchoring the new bulkhead to the back of the settee.

 

Above: There is a separate bulkhead underneath the settee, connecting the settee to the hull. To strengthen the bulkhead underneath the settee and to provide more bearing surface for the bolts, we epoxied a piece of 1/2" thick Hydrotek to the original bulkhead under the settee (held in place by four screws while the epoxy cured). There are three 1/4" though-bolts attaching the new port bulkhead to the settee bulkhead.

 

Above: The edges of the new plywood used for the bulkhead and top of the locker.

The bulkhead is 1/2" Hydrotek, with 9 plies. It is solid meranti, no fir, and is very dense and compression resistant.

The new top on the locker is a piece of good quality, 1/2" marine-grade plywood with a teak veneer; it's 4 ply.

 

HYDROTEK BS1088

The following information is from Almquist Lumber, http://www.almquistlumber.com/plywoods.htm

Hydrotek is a multiply marine plywood that is superior to all standard Meranti plywood currently produced. Both face and inner plies are constructed from whole piece, color-matched, Meranti veneers. Hydrotek is used in boat building applications where only the best will do. Hydrotek's durable rating will ensure that you are using a marine plywood that will last a lifetime.

Technical Specifications:

Properties: Hydrotek has excellent machining properties as it can be easily sawn and bored leaving smooth edges. It also has good nailing and screw-holding properties and is easy to stain and glue. Hydrotek meranti has superior durability and insulation properties compared to other timbers commonly used in marine applications such as Okoume, Pine, Spruce, Fir and Hemlock. Due to the multiply construction, its strength properties are superior to other marine plywood available.

Face Veneers: No structural defects allowed/Appearance grade face and back, color matched (pink/red)
Core Veneers: All core veneers are comprised of whole piece veneers ensuring absolutely no core voids.Glue: WBP1088 (Phenolic)
Bending Strength: 92 N/mm2
Modules of Elasticity: 11400 N/mm2
Compression Parallel to Grain: 52.9 N/mm2
Impact Strength: 0.74 N/mm2
Durability: DURABLE
Movement: STABLE
Working Properties: GOOD

Certified by Lloyds of London

Hydrotek Marine Plywood is a top quality Red Meranti plywood conforming to BS 1088 (certified by Lloyd's of London) marine specifications. Very attractive face veneers, void-free multiply core, and quite reasonably priced.

THICKNESS # OF PLIES. SIZE (PRICE EA 10 OR MORE - prices as of June 2004)
4 mm 3 ply 4' x 8' $25.60 ($23.10 ea)
6 mm 5 ply 4' x 8' $29.50 ($26.60 ea)
9 mm 7 ply 4' x 8' $39.40 ($35.50 ea)
12 mm 9 ply 4' x 8' $50.70 ($45.80 ea)
18 mm 13 ply 4'x 8' $75.40 ($68.70 ea)

 


 

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