Marine & boatbuilding
Marine plywood thickness guide, by boat part
Short answer: pick the thickness by the job. 4–6 mm for curved panels, linings and ceilings; 9–12 mm for cabinetry and light bulkheads; 12–18 mm for structural bulkheads and soles; 18–25 mm for decks, transoms and load-bearing structure. Whatever the thickness, use IS 710 BWP grade for anything marine — the grade matters more than the millimetre.
These are discussion ranges, not scantlings. Final thickness, lay-up, joints, fastenings and coatings for any vessel must follow the designer or naval architect and the applicable build or class rules. Unsupported span, framing, craft size, speed and expected loads govern the answer, and they differ from boat to boat.
Thickness by application
| Thickness | Typical marine use |
|---|---|
| 4–6 mm | Curved/bending panels, hull linings, ceilings, light fit-out |
| 9 mm | Cabinetry, lockers, light partitions, furniture |
| 12 mm | Bulkheads, general joinery, cabin soles (light craft) |
| 15–18 mm | Structural bulkheads, soles, decks, framing |
| 18–25 mm | Decks, transoms, stringers, load-bearing structure |
Bending vs structural
Thin panels (4–6 mm) take a curve without forcing and are right for hull skins formed over a frame and for linings. As the part carries load — bulkheads, soles, decks — step up the thickness for stiffness and screw-holding. For transoms that carry an outboard or hardware, thickness and any laminated build-up must come from the vessel designer: doubling a panel only works if the orientation, adhesive, surface preparation, cure and load transfer are specified with it.
Grade matters more than thickness
A thick board with a poor glue line will still delaminate. For any marine application, specify IS 710 BWP — a board bonded with a BWP-type adhesive conforming to IS 848, with a full hardwood core. See IS 710 vs IS 303 for why commercial grades don't belong below the waterline.
Finishing
Even marine ply lasts longer sealed. Epoxy-coat or seal cut edges and faces, especially on decks and transoms, to keep water out of the end grain. See our marine plywood grades and sizes.
FAQ
What thickness marine plywood for a boat deck?
Typically 18–25 mm IS 710 BWP for decks and transoms, depending on span and load; lighter craft may use 15–18 mm.
What thickness for a bulkhead?
12–18 mm for structural bulkheads; 9–12 mm where the bulkhead is light or non-structural.
What is the thinnest marine plywood for bending?
4–6 mm panels bend over a frame for linings and light skins without forcing. Hull skin thickness itself is a scantling decision, not a rule of thumb.
Does the grade matter more than the thickness?
Yes — use IS 710 BWP for anything marine. A thick commercial-grade board will still fail at the glue line in water.
What thickness marine plywood for a bulkhead?
12-18 mm for structural bulkheads; 9-12 mm where the bulkhead is light or non-structural.
Building or fitting out?
Send your cutting list and grade and we'll quote IS 710 marine plywood within one business day, FOB Cochin.