◣ The Sunwake Project

Electrical architecture and insurability#

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

This document explains the relationship between Sunwake's electrical design and its insurance requirements. A 352 V propulsion bus falls outside ordinary recreational boat electrics and requires automotive-style controls: insulation monitoring, interlocks, service disconnects and documented conformity. Underwriters will need evidence that qualified people engineered, installed and witnessed the system. The SW-300 architecture in the design specification includes that evidence from the outset, so much of the technical specification can also support the insurance submission.

1. Where the voltage line sits#

The US recreational standards regime draws its high-voltage line at 60 V DC. Sunwake's propulsion bus is 352 V nominal, with a 308–394 V window, and remains above that threshold in normal operation.

At 352 V, fewer people are qualified to install, survey, certify and repair the system, and a simple electrician's sign-off is no longer sufficient. A documented conformity package is required. In return, the system can accept a 120 kW CCS charge, connect 15 kWp of solar through high-voltage MPPTs with practical conductor sizes, and propel a 12.70 t boat without unmanageable cabling.

SW-300 was written around E-30 and ISO 16315 from the start, including insulation monitoring per hull, an HVIL loop, crash-signal contactors, labelled manual service disconnects and a one-line diagram. These specification deliverables also form the core of the insurance evidence. They must be produced during design and construction, because reconstructing them after launch may not satisfy an underwriter.

2. Underwriting criteria#

Research across broker commentary, published owner accounts and carrier practice points the same direction: insurers do not price volts. They price provenance, conformity and paperwork, with lithium chemistry as the tripwire that triggers scrutiny at any voltage.

Professional installation per ABYC is the accepted pattern. Insurance companies lean on ABYC standards to decide whether a boat is insurable at all; a certified-technician lithium installation is routinely accepted, while a do-it-yourself installation can void or deny coverage. The consistent advice is to contact the insurer before the work is done, not after (PKYS, Yachting Monthly).

Limited loss data makes underwriters cautious. Brokers cite a lack of reliable information on lithium batteries in boats. The managing director of Pantaenius UK identifies owner retrofits as the main concern and notes that professionally built vessels pose fewer problems (Marine Industry News). That distinction matters here because the hull is owner-built but the high-voltage system is professionally engineered and commissioned.

Owner-involved high-voltage projects have limited precedent. A UK builder's 6 m catamaran with 120 kWh and EV motors, despite surveyor approval, was refused by several insurers over roughly two years before Pantaenius covered it in 2024. His earlier 360 V-class Torqeedo Deep Blue RIB was never insured (Practical Boat Owner). Production boats using comparable systems are routinely insured. The difference is the builder, installation process and documentation, not voltage alone.

The owner-built wooden hull is a separate underwriting issue. US mass-market carriers including BoatUS/GEICO, Progressive and Allstate commonly decline wooden or home-built boats and state-issued "Z" hull identification numbers. Owner reports more often identify specialty markets such as Hagerty marine and Markel, with coverage conditioned on survey (Small Craft Advisor reader poll). The submission must address both the hull and the propulsion system together.

Battery listing is the rising bar. US underwriting conversation increasingly references UL 1973 listed or DNV type-approved battery products. An owner-assembled pack of A-grade prismatic cells has no listing and no one standing behind it. At 352 V, the working assumption should be a professionally built and certified pack — and anything looser should be raised as an explicit underwriter question rather than carried as an assumption. This has direct cost consequences for the 128 kWh installed capacity and for the trays, cabling and protection already sized to 192 kWh; see build timeline and cost.

Relevant claims context. BoatUS attributes 26 % of boat fires to off-boat sources, about 47 % to ordinary AC/DC wiring and engine-electrical faults, and 8 % to batteries, mostly lead-acid voltage-regulator failures (claims breakdown). The submission should note that Sunwake has a new, documented electrical system with no engine alternators, fuel-fired galley or legacy wiring.

3. Required insurance work#

Both precedent lines exist separately. Home-built wooden and plywood hulls get insured through specialty markets. Professionally installed high-voltage propulsion gets insured on production boats. Sunwake is the combination, and the combination has thin precedent — so the insurance pathway is engineered like any other system on the boat, with a schedule and named deliverables.

Engage a specialist broker pre-contract. Get the underwriter's requirements in writing before any high-voltage hardware is ordered. Insurability is a design deliverable with a place in the open questions list, not a procurement task for the year of launch.

Builder's risk cover during construction, converting to agreed value at launch. Hull-in-build cover through the build years, with the survey cadence agreed at inception, then a normal agreed-value yacht policy from commissioning.

The provenance file. Assemble this record throughout the build:

Prefer listed or type-approved major components. The generator and drive candidates in the current matrix already carry marine certifications; see generator selection. The propulsion battery is the item to buy certified rather than improvise, and the isolated on-board chargers, isolation transformers and MPPTs should be chosen from products with marine listings even where a cheaper industrial equivalent exists.

Registration and HIN strategy. Avoid the state "Z" HIN auto-decline pattern where possible: USCG documentation plus surveyor-supported valuation, and target the specialty markets from the outset — Hagerty marine, Markel, Concept Special Risks, Falvey, Chubb at the upper end, with Pantaenius' US availability to be confirmed by the broker.

Premium planning figure. US coastal agreed-value yacht cover typically runs about 0.8–1.5 %/yr of insured value. Until quotations arrive, use the top of that band and allow for lithium-related deductibles, suppression requirements and a lay-up warranty. On a roughly $1.0M build this is about $8–15k/yr. This is a market planning figure, not a quote.

4. Architecture and failure containment#

The SW-300 architecture addresses the failure-containment questions an underwriter is likely to ask.

Two mirrored propulsion islands, one per hull, cross-tied. 128 kWh of LFP total, in sealed, insulated and heated trays under the berth platforms. Trays, cabling and protection are sized for 192 kWh so future capacity can be added by changing modules. A casualty in one hull does not disable propulsion in the other.

Cross-tie with contactor, manual disconnect and Class aR fusing at both ends, normally closed and opened automatically by a differential fault, so the two banks separate when required.

Protection scheme. Class T / aR fusing at every source and every bank, sized per the 2025 E-11 AIC scaling for lithium chemistry. This demonstrates that the protection can interrupt the pack's available fault current.

Insulation monitoring device per hull, with helm alarm. An IMD provides warning of insulation degradation before a fault and is a basic feature of a properly engineered high-voltage installation.

HVIL interlock loop through every high-voltage connector, cover and both manual service disconnects. Opening any protected point drops the contactors before access is possible.

Labelled manual service disconnects, one per hull and accessible while wearing gloves, plus crash-signal contactors on an inertia switch. First responders and yard technicians have a known isolation point, and a collision opens the system automatically.

Cold-charge hard lockout below +2 °C cell temperature, with discharge derate below −5 °C and heated trays. This addresses lithium plating during cold-weather operation and lay-up in Maine.

Fire detection and suppression per battery bay. Per-tray smoke and heat sensing, aerosol suppression per bay, a thermal-runaway vent duct from each tray to a topside clamshell, and automatic high-voltage isolation on detection. Generator enclosures receive clean-agent flood, fuel shutoff and shutdown. These measures belong in the specification and should be identified in the submission; see SW-400.4.

Protected 24 V house bus. Four isolated DC-DC converters, n+1, feed a 24 V system with LFP buffer batteries. Navigation, bilge pumps, steering, VHF, fire and CO detection, and the IMD alarms continue for at least eight hours after a high-voltage shutdown. The boat therefore remains navigable and able to pump and communicate during an isolation event.

Orange segregated cabling in bonded metallic trays, with 100 mm separation or a barrier from low-voltage runs and glands throughout. This makes the routing and separation readily verifiable during survey.

Monitoring and alarm philosophy per SW-320: three alarm classes with distinct tones, and high water, fire, high-voltage isolation and CO hardwired as act-now alarms. These repeat to telemetry, including during winter lay-up.

[ENG] The engineer of record settles the following before the integrator RFQ closes: final AIC calculation and fuse selection against the as-procured pack's short-circuit contribution; IMD threshold and response-time settings; HVIL loop architecture where it crosses between hulls; and the arc-flash labelling basis for the one-line.

5. Questions for the broker and underwriter#

Run this list, in writing, with two or three specialist brokers before committing to hardware.

  1. Will you write an owner-built plywood/epoxy multihull with professionally installed 352 V propulsion? Under what named conditions?
  2. Which standards conformity do you require — ABYC E-30, E-13, E-11 (2025), ISO 16315 — and who is acceptable to certify it: an ABYC-certified technician, a manufacturer-trained installer, an IMCI/CE module route, a class surveyor?
  3. Must the propulsion battery be a listed or type-approved product (UL 1973 / DNV TA), or is a professionally engineered and signed pack from A-grade cells acceptable? In whose name is that sign-off?
  4. Builder's risk terms across a multi-year owner build; staged-survey cadence; commissioning witness requirements.
  5. Any exclusions or conditions around DC fast charging (CCS at up to 120 kW), shore charging through the isolation transformers, or unattended charging at the dock?
  6. Fire detection and suppression conditions for the battery bays and generator enclosures beyond the SW-400.4 fit as specified?
  7. Navigation limits — coastal Maine, the ICW, the Great Loop, Gulf Stream and Bahamas windows — lay-up warranty terms for a November-to-March haul-out, and lightning claims practice on a carbon-free plywood boat with ABYC TE-4 protection.
  8. Approved high-voltage repair network on the US East Coast and along the Loop, and how a mid-passage high-voltage casualty would be handled.

6. Open items#

The items are ordered by dependency.

  1. Identify two or three specialist brokers with both classic/wooden-hull and hybrid-propulsion experience, and run the §5 list — before the high-voltage integrator RFQ. The underwriter's answer to question 3 decides whether the 128 kWh pack is procured as a certified product or engineered and signed on this boat, and that decision changes the integrator's scope, the schedule and a six-figure line item. Asking the integrator first and the underwriter second inverts the dependency and risks paying twice.
  2. Confirm Pantaenius' US availability and Hagerty marine's appetite for a documented owner build of this quality class.
  3. Ask the drive and generator vendors for their certified-installer networks. An installer the equipment vendor stands behind is also an installer the underwriter can accept, and the overlap between those two lists is the shortlist.
  4. Revisit the pack procurement basis once question 3 is answered, and feed the result into build timeline and cost. Certified-pack pricing may be closer to the professional line item already carried than the cell-level arithmetic suggests; it will not be cheaper.
  5. Fix the provenance file's owner — one person responsible for the photo log, the survey bookings and the document set, from first panel to sea trial. A provenance file assembled retroactively is not a provenance file. See open questions.

The design intent behind all of this is set out in the design brief; the binding requirements are SW-300 (electrical), SW-320 (monitoring), SW-400.4 (fire) and SW-800 (trials) in the design specification.

Sources#

Accessed August 2026.

Named insurers reflect published accounts and reader reports, not quotes or endorsements. Underwriter appetites change with the reinsurance cycle; re-verify everything through a broker at pre-contract stage.