Materials takeoff: plywood, glass and epoxy#
Sunwake SW-15 · SW-QS01 / SW-QS02 Rev 0 · August 2026
Bottom-up quantity schedules for the taped-seam plywood and epoxy structure, including the plywood species decision. Computing the schedules from panel areas provides sheet, cloth and resin quantities with explicit waste factors. Everything here is generated by calc/sunwake/materials.py and exported to data/ply_schedule.csv and data/glass_schedule.csv. [ENG throughout: the scantlings behind these areas are the sizing basis, not approved figures; the CNC kit nest supersedes this document the day it exists.]
1. Plywood species#
Okoume BS 1088 for all primary structure. Meranti below the chines is the only live variant. Nothing uncertified goes in the boat.
Every panel is epoxy-encapsulated and glass-sheathed, and everything is painted — there is no bright plywood anywhere. That removes appearance from the decision and leaves weight, cost and toughness.
| Species | For | Against | Role here |
|---|---|---|---|
| Okoume BS 1088 | Lightest structural marine plywood, about 450–480 kg/m³; best stiffness for its weight; bends and machines beautifully; available in 1220 × 2500 and 1530 × 3050 blanks, which is worth about 20 % fewer puzzle joints in the long strakes | Most expensive; zero natural rot resistance — it survives only as a fully encapsulated composite; soft faces dent; the cheap end of the market is full of fake BS 1088 stamps | Baseline: hulls, decks, bulkheads, house, roof — everything big, curved or high |
| Meranti BS 1088 (Hydrotek class) | 30–40 % cheaper; harder, tougher faces with much better abrasion and impact resistance; moderately rot-durable in its own right, a second line of defence behind the epoxy | About 15 % heavier — all-meranti adds roughly 485 kg of structure; stiffer to pull into the forefoot; mostly 4 × 8 sheets, so more joints; density varies mill to mill; a 15 mm sheet at about 28 kg is not a one-person sheet, 50 sheets running | Optional bottoms only; the fallback if okoume quotes are high |
| Sapele or khaya BS 1088 | Durable, strong, beautiful bright | Heavier than meranti at okoume prices, and the aesthetic premium is wasted on a paint-everything boat | Skip as sheet stock |
| Douglas fir marine (APA) | Domestic, cheaper, stiff, decent rot resistance | Notorious face-checking and print-through, adding work to the 950-hour fairing allowance | Strongback, jigs and cradles only |
| BS 6566 or "exterior" tropical | Cheap | Thinner faces, laxer core rules, glue lines often weather-and-boil-proof in name only. Much of what is sold online as BS 1088 is really this | Patterns and temporary work — never in the boat |
| Baltic birch | Void-free, cheap, machines superbly | Heavy at about 680 kg/m³, and birch rots eagerly | Interior furniture cores, drawers, jigs, CNC fixtures |
This is a cost-and-weight choice, not a quality grade. Going all-meranti saves roughly $10–15k and adds about 485 kg of structure, which the model prices at −0.11 knots at solar noon, permanently. On a boat whose entire premise is drag and weight discipline that is a bad trade.
The useful hybrid option is meranti below the chines, adding grounding and beaching toughness where it is needed and carrying the extra mass low in the boat. It adds roughly 100–150 kg and costs within a few thousand dollars of all-okoume. Decide it with the naval architect at scantling stage; the bottoms already carry the heaviest sheathing schedule, which may make the tougher substrate redundant. [ENG: rule on okoume against meranti bottoms with the 12215-5 panel work.]
Procurement controls#
- All-okoume construction, faces and core. Reject okoume-faced ceiba or fuma cores — lighter still, but punky and weak.
- Real certification: a Lloyd's Register or BM TRADA-programme stamp, not "conforms to BS 1088" printed on an edge.
- One vetted supplier, and a destructive sample before the volume order — boil coupons and try to peel the glue lines. Store flat, dry, stickered, off the floor.
- Quote both species and all three formats — 1220 × 2440, 1220 × 2500 and 1530 × 3050. Big blanks are where a 5 × 10 router earns its premium; see cutting the kit.
- Ask the naval architect which mill is currently good. Mills drift year to year and they will know.
2. Plywood schedule (SW-QS01)#
Counts in 4 × 8 ft equivalent sheets (2.973 m²). Purchase quantities carry nesting and cutting waste by class — 1.16 for long strakes rising to 1.30 for furniture — plus a 5 % learning-curve scrap allowance. Order quantities round up to the next five.
| Thickness | Goes into | Net in boat | Purchase | Sheets → order | In-boat mass | Cost (mid) |
|---|---|---|---|---|---|---|
| 6 mm | furniture skins, laminated light frames, stem laminations, trim | 29 m² | 40 m² | 13 → 15 | 84 kg | $1.2k |
| 9 mm | house sides (51 m²), hull-cabin fit-out — platforms, soles, liners (32) — saloon furniture, frames and webs, head | 127 m² | 163 m² | 55 → 60 | 549 kg | $5.8k |
| 12 mm | topsides (94 m²), hull decks (50), roof (66), saloon sole, wet-deck grid, cockpit, transoms and platforms, skegs, trunk lights, doublers | 300 m² | 372 m² | 125 → 130 | 1,728 kg | $16.4k |
| 15 mm | hull bottoms (36 m²), watertight bulkheads (25), wet deck (29), box beams (20), generator, battery-island and tank foundations | 121 m² | 147 m² | 50 → 50 | 871 kg | $8.0k |
| Total | 577 m² | 722 m² | 243 → order 255 | 3.23 t | ≈ $31k |
Blended cost lands at about $123 a sheet, which is the upper half of the $94–133 band a mix this thick should sit in.
Carry 255 sheets as the purchase plan and 310 as the budget envelope until the kit nest exists. A bottom-up takeoff made before panel development always lands under the envelope; the envelope is what you budget against.
Purchase tranches#
Buy the plywood in stages to avoid storing and reconditioning the full order for two years.
| Tranche | Contents | Sheets |
|---|---|---|
| T1 — hulls complete | 25 × 15 mm, 42 × 12 mm, 5 × 9 mm | about 72 |
| T2 — join: wet deck, grid, box beams | most of the remaining 15 mm | about 40 |
| T3 — house, decks, roof | the bulk of the 12 mm | about 78 |
| T4 — interior including both hull cabins | about 45 m² of 9 mm, plus the 6 mm | about 65 |
Handling note: okoume at 15 mm is about 21.5 kg per 4 × 8 sheet, still a one-person sheet. The meranti alternative at about 28 kg is not, fifty sheets running.
[ENG fork] Beam webs may want 18 mm rather than doubled 15 mm; decide it in the 12215-7 global cases. That shifts about ten sheets.
3. Glass schedule (SW-QS02)#
Purchase carries 15 % cutting waste, 8 % on tape.
| Product | Purchase | Mass | Where |
|---|---|---|---|
| 600 g/m² biaxial | 132 m² | 79 kg | bottoms outside, forefoot, keel band, wet-deck underside, skegs, beds, local reinforcement |
| 450 g/m² biaxial | 460 m² | 207 kg | decks, roof, and all tape — about 330 m² of it: hull seams, twelve watertight bulkheads, wet-deck double laps, beams, frames, hull-cabin joins |
| 400 g/m² biaxial | 184 m² | 74 kg | bottoms inside, topsides outside, cockpit and transoms, trunk lights |
| 300 g/m² woven | 226 m² | 68 kg | topsides inside, house sides, wet-deck top, sole wear layer |
| Total | ≈ 1,000 m² | 428 kg | ≈ $5.7k |
Include the tape inventory. Sheathing alone comes to about 675 m² of purchase; the other third is tape, cut from 450 g/m² stock on the bench. Any takeoff that scales sheathing area and stops there will be a third light on glass.
4. Epoxy budget (SW-QS02)#
| Consumption | kg |
|---|---|
| Glass wet-out, 1:1 on stitched biaxial | 380 |
| Weave-fill coats on sheathed faces | 88 |
| Coating bare faces, two thin rolled coats, including hull-cabin interiors | 125 |
| Fillets, about 500 m of joins | 58 |
| Gluing and laminating: puzzle joints, scarfs, stem, doublers | 30 |
| Fairing compound, resin fraction | 45 |
| Losses, 8 % | 58 |
| Total | 784 kg · $7.8–10.2k drum-bought |
One resin system, drum-bought in two or three tranches, hardener speed chosen by season.
5. Rollup and reconciliation#
| This takeoff | |
|---|---|
| Plywood | 243 sheets calculated, 255 to order, 310 envelope · about $31k |
| Glass | about 1,000 m² · $5.7k |
| Epoxy | 784 kg · $7.8–10.2k |
| Combined | $44–47k |
That sits comfortably inside the structure-and-finish materials line in build timeline and cost, which also carries fairing, paint, glazing, hardware and interior materials.
Against the weight ledger. Plywood in boat 3.23 t plus cured laminate — glass, wet-out resin, coating and fillets — about 1.08 t gives 4.32 t of accounted structure. The ledger's structural groups (hull structure 3,150 kg, bridgedeck and beams 1,400 kg, and about 650 kg of house woodwork) total 5.20 t. The 880 kg gap, about 17 %, covers framing and solid timber, bedding, fasteners, hardware backing and margin. That allowance is consistent with the scope. Furniture plywood belongs to the interior group, not here. [ENG: reconcile at ledger Rev 1 with vendor masses.]
6. Next decisions#
Okoume and meranti quotes in hand, plus the naval architect's mill preference. Absent a surprise in the quotes the default is all-okoume.
The schedules here are superseded by the CNC kit nest the day it exists — and that nest will provide the first mass check based on individual parts instead of integrated areas. Until then this is the purchasing basis and the weight-ledger input.