Open engineering questions#
Sunwake SW-15 · SW-ENG Rev 1 · August 2026
This register gathers every item in the repository marked [ENG]: work that still needs calculation, CFD, FEA, a vendor answer or a professional signature. Until then, the figures remain a preliminary sizing basis. The numbered list is intended to accompany the design contract as a statement of work and to give the naval architect a clear view of what remains unresolved.
In the status column, gating means other work depends on the answer; scheduled assigns the item to a contract phase; and open means an owner decision or vendor answer is still needed but is not yet holding up the work.
A. Decisions that hold up other work#
| # | Item | Status | Where it lives |
|---|
| A1 | Naval architect of record. Commission paid design reviews from two or three candidates, then use a staged contract. The remaining engineering work depends on this appointment. | gating | NA engagement |
| A2 | The Bahamas draft decision. The 0.95 m depth to the propeller tips meets the constraint with no allowance. Options are to refair at BWL 1.45–1.50 m (draft to about 0.637 m, props to about 0.91 m, no measurable power cost and wider berths), arrive light, or accept the current line. The decision affects the lines and all work based on them. | gating | lines plan finding 2 |
| A3 | The underwriter's written conditions, especially on battery certification, obtained before any high-voltage hardware is ordered. The answer decides whether the pack is bought as a certified sealed product or engineered from cells, which is a five-figure difference and a schedule difference. | gating | electrical and insurability |
| A4 | The drive rating reference plane, pinned in writing in the RFQ. DC input at the bus gives 0.94C at sprint and passes; shaft output gives 1.04C and fails the ≤ 1C constraint. | gating | power and energy §4 |
| A5 | The generator RFQ, which can issue immediately — the requirement set is settled and does not wait on A1. | open | generator selection |
| # | Item | Status |
|---|
| B1 | Twin-hull interference sweep at s/L. The Michell model puts a 20–24 % favourable dip at 7–7.5 kt and a 45–48 % penalty at 8.5–9 kt — directly on the silent cruise and the single-generator passage speed. This is the highest-priority CFD check in the package. | scheduled, Phase 1 |
| B2 | Resistance verification, 6–15 kt, at the level the designer stands behind — their own CFD, subcontracted CFD, tank, or calibrated empirical. Absolutes carry ±25–30 %. | scheduled, Phase 1 |
| B3 | Four strakes against round bilge at matched hydrostatics, to check the facet ladder's few tenths of a percent. | scheduled, Phase 1 |
| B4 | Chine placement at refair. The as-drawn hull sits above the idealised four-strake point because the closure solve chose chine heights to carry section area, not to minimise girth. A further two or three tenths of a percent may be available through the refair. | scheduled, Phase 1 |
| B5 | The chine 2 run-out at the transom. The boot seam's turn grows from about 4° amidships to 28° at station 10. Whether chine 2 should sweep up through the waterline to the transom corner is a refair question, taken with the unrolling check. | scheduled, Phase 1 |
| B6 | LCB held at 53.5–54.5 % LWL through the refair, and the maximum-section position settled — the faired interpolant peaks at 60 % where the original solve reported 57 %. | scheduled, Phase 1 |
| B7 | Transom and platform immersion trade in the 6–10 kt band; platform length sweep. | scheduled, Phase 1 |
| B8 | Skeg wake into the propeller plane. An uneven wake into the blades could be an important source of noise on an otherwise quiet electric boat. A smaller deflector strut is the lower-drag fallback. | scheduled, Phase 1 |
| B9 | Stern foil (Hull Vane class), yes or no. It targets the Froude band where the losses live. Evidence on slender catamarans is thin. One CFD question. | open |
| B10 | Form factors per variant, rather than one 1.10 carried across all of them. | scheduled |
| B11 | Propulsive efficiency of 0.58 confirmed from the motor map and a self-propulsion estimate; final propeller pitch and DAR follow. | scheduled, Phase 2 |
| B12 | Beam sensitivity confirmed by CFD if the A2 refair is taken. The thin-ship result shows no power penalty for added beam at fixed length and displacement; confirm that result before relying on it in the design. | open |
C. Structure#
| # | Item | Status |
|---|
| C1 | ISO 12215-5 local scantling book. The shell schedule in the specification is a sizing basis, not an approved figure. | scheduled, Phase 2 |
| C2 | ISO 12215-7 global load case book, multihull. | scheduled, Phase 2 |
| C3 | FEA of a whole-bridge model including the roof as a stressed panel and the wet deck as a shear web. | scheduled, Phase 2 |
| C4 | FEA of the wet-deck slam panel at about 28 kN/m² over a 0.25 m² patch. | scheduled, Phase 2 |
| C5 | Topsides at 12 mm against 9 mm plus stringers. About 94 m², about 135 kg, and a row shift in the plywood schedule. This is the largest open scantling choice on the boat. | scheduled, Phase 2 |
| C6 | Beam webs at 18 mm against doubled 15 mm. Shifts about ten sheets. | scheduled, Phase 2 |
| C7 | Okoume against meranti below the chines. The bottoms already carry the heaviest sheathing schedule, which may make the tougher substrate unnecessary. Decide this with the panel calculations. | scheduled, Phase 2 |
| C8 | Rudder stock and bearing design; appendage design generally. | scheduled, Phase 2 |
| C9 | ISO 12217-1 Category B stability calculation, plus the inclining experiment and the stability booklet at completion. | scheduled, Phase 2 |
| C10 | Unsinkable-by-calculation verification and the downflooding review. | scheduled, Phase 2 |
| C11 | Panel development and unrolling, with a strain report per strake showing that each flat panel stays within the bending limits of the specified plywood thickness. This check is essential to a workable stitch-and-glue kit. | scheduled, Phase 3 |
| C12 | Insulation and condensation model for April and October in Maine — a dew-point map, taken with the ventilation scheme, and particularly for the sleeping hulls. | scheduled, Phase 2 |
D. Weight#
| # | Item | Status |
|---|
| D1 | Weight ledger to Rev 1 with vendor masses, and the power model re-run behind it. The exchange rate is about 0.11 kt at solar noon per 500 kg. | scheduled, Phase 2 |
| D2 | Reconcile the materials takeoff against the ledger's structural groups. The current gap is 880 kg, about 17 %, attributed to framing and solid timber, bedding, fasteners, hardware backing and margin. Plausible, but it should be itemised. | scheduled |
| D3 | Use the kit nest for the first parts-based mass check, because it counts individual components instead of integrated areas. | scheduled, Phase 3 |
| D4 | The 20 kg substitution rule made mutual — the designer countersigns substitutions above threshold. | contract term |
E. Electrical, propulsion and vendor selection#
| # | Item | Status |
|---|
| E1 | Drive rating reference plane — see A4. | gating |
| E2 | Motor, inverter, generator and battery vendor selection matrix, weighted for US East Coast service network depth. | scheduled |
| E3 | Battery cell format at 352 V and 64 kWh per hull (a 110S × 180 Ah prismatic class against blade), and confirmation of the two-minute sprint rating. | RFQ |
| E4 | CCS: keep or delete, decided at quotation. Deleting saves $15–25k and costs the lunch-stop half charge. It is the least off-the-shelf item on the boat. | open, at quotation |
| E5 | CCS EVCC implementation and interoperability plan if it is kept. | scheduled |
| E6 | Parallel operation and droop share between the two generator sets across cross-tied buses; CAN protocol documentation as a quotation deliverable. | RFQ |
| E7 | Generator load-dump rating at contactor opening under load; keel-cooling option; calorifier takeoff circuit. | RFQ |
| E8 | Measured generator fuel map (g/kWh against load) and sound pressure at the 16 kW operating point as well as at rated output. | RFQ |
| E9 | Witnessed generator sound demonstration at 16 kW, factory or reference vessel, before order. | RFQ |
| E10 | HVO (EN 15940) warranty statement in writing from the engine vendor. | RFQ |
| E11 | Belt drive rating sign-off; propeller final sizing from the vendor motor map. | scheduled, Phase 2 |
| E12 | EMC plan — inverters against VHF and AIS antennas on a boat with 3.53 m of air draft and a folding mast. | scheduled, Phase 2 |
| E13 | Failure-modes review of the steer-by-wire overlay on the hydraulic steering. | scheduled, Phase 2 |
| E14 | Fridge and freezer keel-cooled condensers — whether to share the heat-pump loop. | open |
| E15 | The 96 V packaged-ecosystem alternative. A single-vendor, dealer-supported, owner-installable system at roughly a quarter of the high-voltage package's hardware cost. It would rule out the twin DC generator architecture and CCS, and reduce the sprint to about 12.5 kt. Assess it as a fourth architecture and as a fallback if high-voltage quotations are too high. Dealer RFQ questions are in build timeline and cost. | open |
F. Insurability and compliance#
| # | Item | Status |
|---|
| F1 | Specialist broker engaged pre-contract, and the question list run — see A3. | gating |
| F2 | Whether the propulsion battery must be a listed or type-approved product (UL 1973, DNV type approval) or whether a professionally engineered and signed pack from A-grade cells is acceptable, and in whose name that sign-off sits. | gating |
| F3 | Who is acceptable to certify conformity — an ABYC-certified technician, a manufacturer-trained installer, an IMCI/CE module route, a class surveyor. | gating |
| F4 | Builder's risk terms across a multi-year owner build; staged survey cadence; commissioning witness requirements. | open |
| F5 | Exclusions or conditions around DC fast charging, shore charging, and unattended charging at the dock. | open |
| F6 | Fire detection and suppression conditions for the battery bays and generator enclosures beyond the specified fit. | open |
| F7 | Registration and HIN strategy — USCG documentation with surveyor-supported valuation, avoiding the state-issued HIN auto-decline pattern. | open |
| F8 | The high-voltage integrator: two or three candidates willing to commission in an owner's shed with staged sign-offs, and their own liability cover confirmed. | gating |
| F9 | Approved high-voltage repair network on the US East Coast, and how a mid-Loop casualty would be handled. | open |
G. Production, procurement and the build#
| # | Item | Status |
|---|
| G1 | Puzzle joints against scarfed blanks, decided jointly with the cutter before nesting starts. | scheduled, Phase 3 |
| G2 | Pilot cut protocol — one bulkhead and one full-length strake, dry-fitted — before the full sheet order releases. | scheduled, Phase 3 |
| G3 | Cutter selection, and whether to buy the router. Nothing needs deciding before the design contract is signed provided the package is specified cutter-agnostic. | open |
| G4 | Okoume and meranti quotes in all three sheet formats, plus the naval architect's mill preference. | open |
| G5 | Shed: at least 17 × 9.5 m with 4 m clear, heatable. Or a smaller bay plus rented space for the join. | open |
| G6 | The professional boatbuilder, if the crewed scenario is taken — interviewed and signed in Phase 0, starting on kit day. | open |
H. Owner decisions still outstanding#
| # | Item |
|---|
| H1 | Trunk lights over the queens — an aesthetic gate, and one of the two decisions the general arrangement waits on. |
| H2 | The character drawing: the sprung sheer, the spoon stem, the platforms. The other gate. |
| H3 | Beam overall at 7.29 m or trimmed back to 7.1 m at the after flare. It costs nothing hydrodynamic; it may cost a berth or a haul-out. |
| H4 | Fuel tankage at 600 L or grown toward 800–1,000 L. A few thousand dollars and 160–320 kg for a third more passage range. |
| H5 | Watermaker fitted or omitted. |
| H6 | Winter storage: heated shed against outdoors with the battery bay on shore power. |
| H7 | Final boat name. The current designation is a placeholder. |
Using this register#
For the naval architect, sections B, C and D form the main statement of work; the items marked "scheduled" in section E require coordination with the integrator. The high-voltage integrator's scope is section E together with F8.
For the owner, A1 through A5 are the immediate priorities, in that order. A5 can proceed while A1 is being resolved.
Reviewers should focus first on B1, B2 and A4, in that order, followed by the modelling assumptions at the end of power and energy §9. The figures can be reproduced with python calc/scripts/run_all.py, but the underlying assumptions still need independent review.