Engaging a naval architect#

Sunwake SW-15 · SW-NA Rev 1 · August 2026

This commission covers design development, engineering, production information and build support for Sunwake, a 15.60 m owner-built plywood-and-epoxy solar-electric cruising catamaran. It is not a blank-sheet project. The mission, principal dimensions and arrangement are established; a preliminary lines plan, offsets, hydrostatics, energy model and bottom-up materials takeoff already exist. The naval architect is needed to refair and verify the hull, validate resistance, engineer the scantlings, stability and systems, and develop the panels into CNC-ready files. This basis should reduce the discovery work normally included in a custom commission.

1. Current design stage#

The custom-design profession runs a recognised sequence: owner's requirements, concept design, preliminary design, contract and detail design, production information, build support. Measured against it, Sunwake has completed the first stage unusually thoroughly and the second stage substantially.

The requested engagement is design development and engineering of a developed concept, a recognised mode of practice that should cost less and take less time than clean-sheet work. The first email should state this clearly and distinguish the designer's engineering authority from the owner's requirements authority.

The existing documents already define much of the professional scope. Each [ENG] tag in the specification, lines plan and construction study becomes a line item in the naval architect's statement of work. Open questions compiles those items and should be attached to the design agreement.

SW-LP01 serves as the geometry brief for the naval architect of record; fairing, verification and contract lines remain within their scope. This document sets out how to procure that work.

The outreach should also explain that the repository includes the calculation package, not only prose. The code in calc/ produces the hydrostatics, resistance and power model, energy budget, weight ledger and materials takeoff; derived results are committed in data/; and the drawings use the same geometry. A reviewer can change an assumption and regenerate the results, making a short paid review more useful.

2. Three engagement models#

Model A — naval architect of record develops the existing package. Recommended. The designer critiques and refairs the SW-LP01 lines, completes the required verification, engineers the structure to ISO 12215-5 and -7 and stability to ISO 12217-1 Category B, and delivers the kit files as designer and engineer of record. This is the least expensive and fastest custom route. It requires a designer who is comfortable developing owner work, which the Phase 0 review will establish.

Model B — full custom redraw from the brief. The designer starts from the mission, dimensions and styling references; SW-LP01 becomes a reference rather than parent geometry. This provides clear professional authorship and may suit a designer who prefers to use their own hull forms. Expect roughly 1.5 to 2 times Model A's fee and two to four additional months. The existing work still shortens the brief-development stage by defining displacement, LCB, clearance and weight policy.

Model C — adapt a proven stock design. Stock plans plus paid modifications typically cost about 20% less than clean-sheet work, and the plans themselves cost a few thousand dollars. No identified stock design combines this arrangement, traditional styling and electric system, so modification fees could approach Model A while giving less control over the result. Model C is retained mainly as a cost benchmark: a Skoota 36 study pack and Dix 430 kit price help calibrate the cost of panels, plans and kits per metre.

3. The staged process — gates, deliverables, money#

Run the engagement as staged fixed-fee phases with a sign-off gate between each. Money is committed one phase at a time, either party can stop at a gate, and every phase ends in documents the owner keeps. This is the profession's own pattern — the published references describe concept, preliminary and final design with staged progress payments — tightened for an owner-build that ends in a kit.

Phase 0 — paid design reviews, two or three designers in parallel. Request a written critique, proposed approach (adopt the lines, redraw or hybrid), staged fee proposal and current availability. Budget $500–2,500 per designer. This provides technical due diligence, a working-style check and comparable quotations while paying candidates to assess the existing lines. Gate G0: choose the designer and engagement model.

Phase 1 — concept validation and contract lines. Deliverables: refaired lines as SW-LP01 Rev 1, hydrostatics, the LCB and transom-immersion trade resolved, the general arrangement carried to dimensioned drawing, profile and styling drawings, an updated weight estimate and power check, resistance verification at the level the documents call for — CFD or tank work the designer will stand behind — and a written specification revision. Typical calendar six to ten weeks. Gate G1: lines and GA freeze. After this, geometry changes cost real money.

Phase 2 — engineering. The [ENG] register executed: ISO 12215-5 local scantlings and -7 global load book, ISO 12217-1 Category B stability calculation, structure drawings (bulkheads, box beams, wet-deck, skegs with sacrificial tips, rudders and stocks), appendage design, condensation and insulation review, and the systems one-lines. On the electrical side the 352 V one-line is coordinated with the high-voltage integrator and the insurance broker per electrical architecture and insurability: the naval architect engineers structure and interfaces, the integrator owns high-voltage execution, and the 24 V house side follows ABYC E-11 and E-13. Weight ledger to Rev 1 with vendor masses; power model re-run. Typical calendar three to five months. Gate G2: engineering freeze. The underwriter's written conditions should be in hand before this gate closes.

Phase 3 — production information, the kit. Everything in §7 below: developability verification, unrolled panels with marking geometry, nesting, layered DXF cut files, jig drawings, laminate and tape schedules keyed to part IDs, bill of materials, build manual. Ends with a pilot cut — one bulkhead and one full-length strake — assembled dry before the full sheet order is released. Typical calendar two to four months, overlapping Phase 2's tail. Gate G3: kit release to the cutter. See cutting the kit.

Phase 4 — build support. Hourly or on retainer: query turnaround, site visits at the structural milestones (hull join, beams, wet-deck closure — the same visits that feed the insurance photo log), vendor-substitution review against the 20 kg rule, and commissioning and trials support against the SW-800 acceptance list. Published guidance is blunt that construction-phase support can cost as much as the design itself if loosely scoped. Cap it in the contract with a named visit schedule and an hourly band.

Fee planning bands#

Industry references frame custom design at 7–10% of build cost (Sponberg) or 6–8% on an hourly basis for 40–80 ft (Kasten, who argues hourly runs cheaper than commission; commission basis 10–12%). Those percentages assume a professional yard build, and on an owner-build they compute against professional-equivalent cost rather than the owner's materials bill. Use fixed bands instead. These bracket the project's own budget line.

Model B adds roughly 50–100% to Phases 1 and 2. CNC cutting is a separate line: the construction and kit studies carry a $10–14k cutting premium on top of sheet stock for the roughly 250 sheets this boat consumes.

4. Who to shortlist#

Three pools: remote-friendly designers anywhere, Maine and New England, and electric-boat specialists. Contact routes are in §10.

Consider pricing a paired design team. Proportion is the main aesthetic risk: freeboard against length, house mass on a 7.29 m beam and the final sheer. Hylan could develop the character drawings for the sheer, stem, trunks, glazing and fascia while an engineering-led naval architect owns geometry, structure and the kit. If this arrangement is used, both contracts must assign authority clearly: geometry and structure to the naval architect of record, character drawings to the stylist, and conflict resolution to the owner.

Not shortlisted: Schionning and Grainger, whose DuFlex kit cats use modern styling; Malcolm Tennant, whose practice appears inactive; and round-bilge composite powercat firms without relevant taped-seam plywood experience.

Vetting beyond the paid review. Ask for work in this construction method, not only catamarans, and request at least one owner-builder reference. Ask the reference about query turnaround and mid-build errors. Ask who cut the last three kits and whether those cutters are available as references. Confirm professional liability cover; many small practices do not carry it, making documentation and contract terms especially important. Ask for a firm start date because established designers may be booked two to four quarters ahead.

5. Approaching a designer with a developed concept#

A developed owner package can either save a designer time or suggest that the owner will resist professional judgment. The initial approach should make the intended working relationship clear.

• Lead with the mission and the decision record, not the geometry. The first email should open with what the boat is for and what has already been decided. SW-LP01 arrives labelled as what it is — a geometry brief, explicitly offered for critique and refairing, with no authorship pride attached.
• Pay for a critique. Ask the designer to identify errors and weak assumptions. Engineering authority belongs to the designer; requirements authority remains with the owner.
• Be prepared for a proposed redraw. Use the paid review to understand the technical reasons before choosing Model A or B.
• Control requirements changes. Continue the existing revision discipline and dated owner decisions. Changes after each gate should use priced change notes, which allows the designer to quote a defined scope.

6. The design agreement — terms that matter#

Use staged fixed fees tied to named deliverables, with a right to stop at each gate and payment on acceptance. The agreement should also cover the following.

1. Scope by document. The compiled [ENG] register in open questions attached as the statement of work; anything added later is a priced change note.
2. Standards basis named. ISO 12215-5 and -7, ISO 12217-1 Category B, ABYC E-11, E-13, E-30, A-31 and TE-4, ISO 16315 — the specification's list verbatim, so that the insurance provenance file and the design contract cite one list and not two.
3. Engineer-of-record deliverables for the underwriter. Conformity statement, stability book, staged weight reports, high-voltage one-line — the provenance file described in electrical architecture and insurability, made a contract deliverable rather than a favour.
4. Intellectual property and licence. The industry norm is that the designer keeps copyright and the owner buys the right to build one boat, with royalties around 1.5% from a second hull. Negotiate specifics: native CAD (.3dm and STEP) and layered DXF cut files delivered to the owner or directly to the cutter; the owner's concept documents and calculation code remain the owner's; credit language agreed both ways.
5. Revision allowance. For example two GA iterations inside Phase 1, with further iterations as change notes. This protects both sides.
6. Performance language. Predictions are estimates, not warranties, consistent with the project's stated ±25–30% model uncertainty.
7. Support terms. Visit schedule (join, beams, closure, commissioning), hourly band, query turnaround target.
8. Substitution rule. The 20 kg vendor-substitution ledger made mutual — the designer signs off substitutions above the threshold.

7. From agreed design to cut files#

Phase 3 should include every item below.

Geometry. A faired 3D surface model (native Rhino .3dm plus STEP), with hull panels held developable and verified. Require an unrolling and strain report per strake showing that each flat panel stays within the tolerance of the specified plywood. Hidden strain in an unrolled freeform panel makes assembly difficult. Sunwake's four developable strakes per side were chosen to support this construction method, and SW-LP01 already calls for the check.

Drawings. Contract lines plan; general arrangement; construction sections at every bulkhead; structural plan (bulkheads, box beams, wet-deck, skeg roots, rudder stocks); appendages; systems one-lines; jig and strongback drawing with datums and alignment marks.

Panel developments. Every strake, bulkhead, web, beam flange and trunk side unrolled with marking geometry engraved: station ticks, waterline, chine and tape-centreline marks, part IDs, grain and face orientation, and bevel-where-needed annotations.

Nesting and cut files. Parts nested to 1220 × 2440 sheets by thickness — roughly 250 sheets for this boat — with the panel-joint strategy, puzzle joints versus scarfed blanks, decided jointly with the cutter before nesting starts. Layered DXF (outer cut, inner cuts, engrave, drill) with kerf and tab conventions set to the specific machine, plus a cut schedule reconciling nest counts to the sheet order.

Schedules and manual. Laminate and tape schedule keyed to part IDs (tape widths, stagger, fillet radii); hardware blocking map; the fastener-free-bottom rule carried through; bill of materials; build-sequence manual keyed to kit part numbers; and a weight ledger updated from nested part masses. The nest provides the first mass check based on individual parts.

Pilot cut, then release. Cut one bulkhead and one full-length strake first and check fit, kerf, joint tightness and engraving legibility. Release the full sheet order only after they pass; this short check can prevent a five-figure error.

Who cuts. The designer need not own a router; the file-to-cutter interface is routine. Candidates: Hewes & Company Marine Division in Blue Hill, Maine — an established kit-cutter for outside designers including Vivier, an hour from a Downeast build shed, and fluent in exactly this workflow; Chesapeake Light Craft in Annapolis, which runs a custom CNC cutting service alongside its kit business; or any competent 5 × 10 CNC shop if the designer supplies toolpath-ready files. Bring the cutter into the conversation at Phase 3 kickoff, not after nesting — joint strategy, blank sizes and kerf are their variables. Sheet sourcing (okoume versus meranti, BS1088 certification, sample-sheet destructive check) runs per construction and should be quoted in parallel so that kit release and plywood delivery land together. Details in cutting the kit.

8. Calendar#

From first email to first cut, with a designer available in a normal window.

The Phase 0 assumption in build timeline and cost — design contracted and kit ordered inside months one to four — is achievable only under Model A with a designer who has immediate bandwidth. Treat months one to four as the post-contract clock and the first three rows above as the pre-contract runway, which starts now. If a first-choice designer quotes a two-quarter wait, the runway absorbs it: broker questions, generator RFQ, plywood quotes, shed search and the air-conditioning styling decision all run in parallel and none of them require the naval architect.

9. The next thirty days#

1. Confirm the [ENG] register is complete and numbered. It is compiled in open questions; read it once more as a stranger would, because it is the statement-of-work attachment and most of the outreach's credibility.
2. Send the first-contact email (§10) with the short brief attached to three or four candidates — Devlin and Dix, being the stitch-and-glue native who drew the inspiration boat and the proven big-plywood-cat kit pipeline, plus the Maine slot: Stephens Waring, Hylan & Brown, or both. Hylan's review request can be scoped narrower — profile, house and proportions — if he demurs on the multihull engineering.
3. Commission the paid reviews. Interviews on receipt, not batched at the end.
4. In parallel: send the broker question list before any high-voltage commitment; issue the generator RFQ; obtain okoume and meranti quotes; search for a shed; and settle the air-conditioning styling decision required for the GA.
5. Write the decision memo at G0 — designer and engagement model — into the repository as a dated owner decision, per house convention.

10. First-contact email#

Subject: Design commission enquiry — 15.6 m solar-electric catamaran, stitch and glue, Maine

Dear ____,

We are a couple in coastal Maine planning an owner-built solar-electric cruising catamaran in taped-seam plywood and epoxy — classic Downeast character on two slender hulls, roughly 7–8 kt silent cruise, with a small HVO generator plant for range. The design is developed: 15.60 m LOA, 7.29 m beam, 12.70 t half load, four developable strakes per side, 352 V propulsion with 128 kWh, 15 kWp of solar and two 20 kW variable-speed DC generators. We have a design brief, an engineering-level specification, a preliminary lines plan with a full table of offsets and computed hydrostatics, a hull-form study, power and solar models, an accommodation study, a construction feasibility study with a bottom-up materials takeoff, a generator selection, and an electrical and insurability study. Every number in those documents comes out of a calculation package that travels with them, so any assumption you want to challenge can be changed and re-run.

We are looking for the naval architect of record to critique that package, own the lines, engineer the structure to ISO 12215 and 12217 and ABYC, and carry the design through CNC kit files and build support. The hull is owner-built; the high-voltage system will be professionally engineered and commissioned.

As a first step we would like to commission a short paid design review — a few hours against our short brief (attached) and the fuller document set, ending in your written critique, your proposed approach, a staged fee proposal, and your availability. Would you quote us a fee for that review and let us know your current lead time?

[Signature, phone, location]

Attach only the short brief. Send the full set — specification, lines plan with offsets, construction study, power model, [ENG] register and repository access — after the designer expresses interest. Follow up once after two weeks.

11. Candidate contact points#

Suggested first contacts: Devlin, Dix, and one or both Maine firms, Stephens Waring and Hylan & Brown. This group covers the inspiration boat's designer, large plywood-cat kit experience and local styling expertise. Hylan's paid review could focus on profile, house and proportions, leaving the multihull engineering role open as described in §4. Add Woods, Hughes or Bedard for a second round or additional price comparisons.

12. The question list#

For the paid-review response and the interview that follows.

Approach and fit

1. Having read the package: what is wrong with it? What would you change first?
2. Would you develop our geometry from SW-LP01, redraw from the brief, or hybrid? Why?
3. Have you designed for taped-seam, developable-panel construction at 13–16 m? Which builds? May we speak with the builders?
4. Where your boats were built by owner-builders: how were queries, errors and substitutions handled mid-build?

Engineering scope

1. Will you act as engineer of record to ISO 12215-5 and -7 and ISO 12217-1 Category B, and produce the conformity documentation our insurance work requires — stability book, weight reports, one-lines, conformity statement?
2. What resistance verification do you stand behind at this Froude range — your own CFD, subcontracted CFD, tank, or calibrated empirical — and what does it cost as a line item?
3. How would you interface with a high-voltage integrator and a marine electrical engineer on the 352 V system? Where does your scope end?
4. Weight discipline: our ledger runs a 6% margin and a 20 kg substitution rule. Who polices it in your process?

Production information

1. Who produced the panel developments and nesting on your last three kits, and who cut them? May we talk to the cutter?
2. What is your developability verification — strain limits by plywood thickness, unroll method, marking-geometry conventions?
3. Puzzle joints or scarfed blanks, and who decides — you or the cutter?
4. Is a pilot-cut protocol, one bulkhead and one strake before kit release, part of your normal practice?
5. What exactly do we receive: native .3dm and STEP? Layered DXF? Build manual? Who owns the files, and may we send them directly to our cutter?

Commercials

1. Staged fixed fees with gates and kill rights — what are your phase structure and payment terms?
2. Revision allowance per phase, and change-note pricing beyond it?
3. Build-support terms: visit schedule, hourly band, query turnaround?
4. Licence terms: one-build licence, royalty norms, credit language?
5. Professional liability cover — yes or no, and if no, as is common in small practices, how do you handle error discovery mid-build?
6. Current backlog: when would you be available to start Phase 1?

13. Evaluation scorecard#

Score each candidate 1–5 per criterion after the paid review; weight and sum.

A candidate strong in method and engineering but weaker in styling can be paired with a styling consultant. Engineering competence must remain with the naval architect of record.

14. Sequencing notes#

• Run two or three paid reviews in parallel; budget $500–2,500 each.
• Write the decision memo at selection — designer and engagement model — into the repository as a dated owner decision.
• In parallel: send the insurance-broker question list before any high-voltage commitment; issue the generator RFQ; keep plywood and CNC quotations current; continue the shed search; and settle the air-conditioning styling decision.

Sources#

Accessed August 2026.

Process and fees

• Eric Sponberg — How to Commission a Yacht Design and Have It Built (PDF)
• Kasten Marine — Yacht Design Costs

Candidates

• Devlin design process
• Devlin design process in depth
• Devlin profile — Power & Motoryacht
• Dix Design — Dix 430
• Dix — plywood catamaran kits
• Woods Designs — power catamarans
• Woods — Skoota power cats introduction
• Kurt Hughes Multihull Designs
• Bedard Yacht Design
• Stephens Waring Design
• Stephens Waring electric lake tender — Maine Boats, Homes & Harbors
• Hylan & Brown — custom design
• Hylan & Brown profile — Maine Boats, Homes & Harbors

Kit cutting

• Hewes & Co. cutting for Vivier designs
• Hewes & Company — Maine Built Boats
• Chesapeake Light Craft — custom CNC cutting
• Professional BoatBuilder — CNC construction on the rise

Candidate descriptions reflect public information as of August 2026. Verify current capacity, services and terms directly in Phase 0.