13.6 Shipboard Carpentry, Woodworking & Cement Box Emergency Repairs

13.6 Shipboard Carpentry, Woodworking & Cement Box Emergency Repairs

While merchant ships are constructed from steel, timber and carpentry remain essential for shipboard damage control, cargo seaworthiness, and emergency hull maintenance. General Purpose (GP) Ratings must be proficient in using woodworking hand tools, truing timber stock, fabricating framing joints, recognizing timber defects and fungal rot, and executing temporary emergency repairs. For suitable local leakage, the responsible officers may direct construction of an emergency cement box as a temporary containment measure. Ratings prepare timber and assist under supervision; the damage and repair require assessment before further service.

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1. Shipboard Carpentry Workshop Safety & Hand Tools

The ship's carpentry store contains woodworking hand tools and powered machinery such as table circular saws, band saws, and wood lathes. Timber dust and wood shavings present an acute fire and respiratory hazard in enclosed shipboard spaces.

                         HAND WOODWORKING SAWS
         RIP SAW (4.5 - 6 TPI):                CROSS-CUT SAW (6 - 8 TPI):
         Chisel-shaped teeth; cuts             Knife-edge beveled teeth;
         parallel along wood grain.            slices across wood fibers.
             /|  /|  /|  /|                        /\  /\  /\  /\
            / | / | / | / |                       /  \/  \/  \/  \
           +--+---+---+---+                      +----+---+---+---+
         TENON (BACK) SAW (12 - 14 TPI):
         Brass/steel reinforced back spine; fine joinery cuts for tenons and laps.
         ======================================== (Rigid Spine)
         vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv (Fine teeth)

Safety Rules in the Carpentry Shop

1. Dust & Fire Hazard: Fine wood dust has an explosive surface-to-mass ratio and causes respiratory irritation; wear certified dust masks. Sawdust and shavings must be swept daily into covered steel bins. Hot work (welding, cutting, grinding) is strictly forbidden in or adjacent to the carpentry store.
2. Machinery Safety: Always feed timber into table circular saws using a push stick. Riving knives (positioned within $3\text{ to }8\text{ mm}$ of blade teeth) and crown guards must always be locked in place to prevent violent workpiece kickback.
3. Chisel Handling Discipline: Keep chisels razor sharp; dull chisels slip under force and cause severe puncture wounds. Never hold timber with one hand while pushing a chisel toward it; clamp the piece securely in a vice and keep both hands behind the cutting edge.

Woodworking Hand Saws

Wood grain consists of directional cellular fibers requiring specific tooth profiles:

• Rip Saw: Large teeth ($4.5\text{ to }6\text{ TPI}$) filed straight across at $90^\circ$ to act like miniature chisels, designed to rip fibers parallel along the wood grain.
• Cross-Cut Saw: Medium teeth ($6\text{ to }8\text{ TPI}$) filed with alternating bevels ($45^\circ\text{ to }60^\circ$) that slice wood fibers cleanly across the grain.
• Tenon (Back) Saw: Fine teeth ($12\text{ to }14\text{ TPI}$) reinforced with a heavy folded brass or rolled-steel back spine that prevents thin blade buckling, producing accurate, shallow cuts for mortise-and-tenon and lap joints.
• Compass / Keyhole Saw: Narrow tapered blade for cutting curved internal apertures and circular pipe penetrations in plywood bulkheads.

Hand Planes: Types, Tuning & The Cap Iron

• Jack Plane ($350\text{ to }400\text{ mm}$ sole length): General-purpose plane for rapid preliminary stock removal and rough sizing of sawn timber.
• Smoothing Plane ($200\text{ to }250\text{ mm}$ sole length): Compact finishing plane for fine surface smoothing and dressing joint mating faces.
• Plane Iron & Cap Iron (Chip Breaker): The cutting iron is ground to a $25^\circ$ primary bevel and honed to a $30^\circ$ cutting edge. A curved secondary blade—the cap iron (chip breaker)—is bolted tightly against the flat face of the plane iron, adjusted $1.0\text{ to }1.5\text{ mm}$ behind the cutting edge ($0.5\text{ mm}$ for smoothing). The cap iron curls and breaks shavings immediately, preventing the blade from tearing deep into the wood grain.

Wood Chisels & The Wooden Mallet Rule

• Firmer Chisel: Heavy rectangular blade with square edges for general shaping and chopping.
• Bevel-Edge Chisel: Longitudinal edges beveled at $45^\circ$ to clean out acute corners of dovetails and narrow recesses.
• Mortise Chisel: Extra-thick square cross-section engineered to withstand heavy prying forces when cutting deep mortise cavities.

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2. Planing Practice: Face Side, Face Edge & Winding Sticks

Squaring up rough timber requires four sequential steps:

                      SQUARING UP TIMBER: FACE MARKS
                   Face Side Mark (Loop)
                            \
                    +--------@---------------------+
                   /        /                     /|
                  /                              / |
                 +------------------------------+  |
                 | <--- Face Edge Mark (V-Arrow)|  |
                 |      (Points to Face Side)   |  |
                 +------------------------------+/

1. Face Side (Reference Plane): Plane the widest face flat using a jack plane. Test flatness longitudinally, transversely, and diagonally with a straight edge. When flat, mark it with the traditional Face Side Mark (a pencil loop).
2. Face Edge (Reference Edge): Plane an adjacent narrow edge straight. Periodically check with a try square placed against the proven Face Side. When straight and square ($90^\circ$), draw the Face Edge Mark (a 'V' pointing directly toward the face side loop). All subsequent gauge scribing must originate strictly from these two reference surfaces.
3. Marking Gauge Sizing: Scribe final width and thickness lines with a marking gauge referenced against the Face Edge and Face Side.
4. Planing to Gauge Lines: Plane away waste stock on the opposite un-marked surfaces down to the scribed lines.

Detecting Twist with Winding Sticks

A board may appear straight along its edges yet suffer from helical twist (in wind). Place two matched, identical winding sticks across opposite ends of the board. Sight across the top edges from one end: if the edges remain parallel across the horizon, the board is true; if they cross out of parallel, the board is in wind, requiring high diagonal corners to be planed down.

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3. Wood Framing Joints in Marine Service

                            MARINE TIMBER JOINTS
         TEE HALVING JOINT:                     MORTISE & TENON JOINT:
           Mating Member                          Tenon (1/3 Stock Thickness)
            +---------+                             +----+
            |  t / 2  |                             |    |=========+ (Rail)
            +---------+                             |    |=========+
                 |                                  +----+
                 v                                    |
          +--------------+                            v
          | Cutout t / 2 |                     +---------------+
          +--------------+                     |    Mortise    | (Stile / Post)
           (Main Beam)                         +---------------+

• Halving (Lap) Joints: Half the thickness ($t/2$) is cut from each timber so faces sit flush in the same plane:
  • Tee Halving: Joins an upright or intermediate strut to a continuous runner at $90^\circ$ for framing damage control screens and cement shuttering boxes.
  • Corner Lap: Joins two timbers at a $90^\circ$ corner frame, fastened with screws or bolts.
  • Cross Halving: Intersects two battens in the same plane.
• Mortise and Tenon Joint: Provides maximum rigidity against racking loads in structural framing. The tenon thickness is cut to one-third the timber stock thickness ($t/3$), fitting snugly into a matching mortise cavity chiseled in the mating post. Joints are locked with waterproof marine glue and driven hardwood pins (trenails) or through-bolts.

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4. Defects, Fungal Decay & Marine Borers in Timber

• Growth Defects & Shakes:
  • Knots: Branch bases; dead knots shrink and fall out, creating holes and weakening tensile strength.
  • Star Shakes: Cracks starting at the outer surface and narrowing inward toward the pith. Heart shakes instead extend outward from the pith.
  • Cup / Ring Shakes: Curved splits following annual growth rings, destroying shear resistance.
• Fungal Decay (Rot):
  • Dry Rot (Serpula lacrymans): Attacks damp timber and can spread by strands across non-wood surfaces to reach other damp wood. Affected wood shrinks, develops deep cubical cracking across and along the grain, and crumbles to brown powder. The name describes the dry, brittle damaged wood; continued decay still needs moisture.
  • Wet Rot (Coniophora puteana): Favours wetter timber in persistently damp locations such as bilge linings. Wood darkens, softens and loses strength. Control both rots by correcting leaks, ventilating and keeping sound timber dry; replace weakened timber as directed.
• Marine Borers (Shipworm, Teredo navalis): A wood-boring marine bivalve mollusk whose larvae penetrate submerged timber through microscopic pinholes, excavating long calcium-lined tunnels inside the wood. Timber appears sound externally while internally honeycombed, leading to sudden collapse under wave shock. Protection includes intact copper sheathing or preservative treatment specifically rated for marine-borer exposure, such as suitable marine-grade creosote treatment. Inspect sheathing and replace weakened timber.

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5. Shipboard Cement Box Emergency Repairs

A cement box is a timber form filled with cementitious material to contain suitable local leakage when immediate permanent repair is impracticable. Its use depends on the damage, available support and the responsible officers’ repair plan.

                 TEMPORARY CEMENT BOX — PRINCIPLE
       Damaged hull surrounded by sound supporting structure
       +====================(leak)====================+
       |                    ||                       |
       | Cementitious fill  ||  Drain through form    |
       +--------------------||-----------------------+
        Stout timber form   ||
        Shores to strong    [X] Open while placing/setting
        structure + wedges   v  Controlled drainage
       Form and shores resist water pressure and fill weight.
       Close only when the repair has sufficient strength.

Purpose & Repair Acceptance

A cement box is a temporary emergency repair:

• Record the damage, location, repair materials and inspections in the ship’s records and notify the company and Classification Society; involve the flag Administration as required.
• Class may accept a suitable local temporary repair with a specific deadline and restrictions. Serious structural damage can require prompt permanent repair or a direct voyage to repair facilities. The box does not itself authorize continued service until drydock.
• Inspect the repair and shores on every watch for leakage or movement, and report deterioration immediately.

Step-by-Step Construction Procedure

1. Assess and Prepare: The responsible officer selects a repair suitable for the damage and controls flooding and access. Clean oil, grease, paint and loose material from the contact area. Do not drill or alter damaged structural plating without an assessed repair instruction.
2. Arrange Controlled Drainage: Where the plan uses a relief pipe, lead water from the leak through the box to a controlled discharge. Keep the outlet open while placing and setting the fill. Pipe capacity must suit the inflow; monitor bilge level and pumping capacity. If water continues to flow through the fill, stop and reassess the arrangement.
3. Build the Timber Form: Fit stout planks or plywood around the damage, overlapping onto sound hull. Seal the contact edges to retain the mix. Choose form thickness, overlap and fastenings for the actual opening and load; fit the drain through the form where required.
4. Shore and Wedge: Brace the form against strong frames or bulkheads using sound timber shores and opposing folding wedges. The support carries the concrete weight and resists water pressure and movement. Provide reinforcement where the repair design requires it, and inspect the load path before filling.
5. Prepare the Specified Mix: Use the cement, clean aggregate and water proportions specified for the repair. Mortar contains cement and sand; concrete also contains coarse aggregate. Keep the mix cohesive and avoid excess water. Use a proprietary rapid-setting material only for a suitable application and follow its mixing instructions. Do not improvise sodium-silicate or calcium-chloride doses: setting time and early strength depend on the formulation and conditions. Wear gloves and eye protection against wet cement.
6. Place, Cure and Check: Place and compact the fill without voids or disturbance, maintaining the planned drainage. Protect and cure it as specified. A hard surface or an elapsed number of hours alone does not establish adequate strength. The responsible officer authorizes gradual drain closure when the repair can carry the load. Secure the outlet as designed, inspect for leakage and movement, and continue monitoring the box and shores.