Refit energy sailboat winter layup 2026-2027 — complete workshop checklist

Winter layup is the only time of the year when the boat can be immobilized for 4-6 weeks without impacting the sailing program. It is the optimal window for a complete energy refit: removal of the lead-acid pack, lithium installation, alternator rewiring, addition of solar, full monitoring. This article describes the Skysat workshop method in 7 steps.

For in-depth coverage by topic, see our energy cluster articles: lithium pack sizing, BMS comparison, DC-DC converters.

Why winter layup = optimal refit window

1. Boat immobilized 4-6 weeks: energy refit possible without interrupting sailing.
2. Material prices: stable off-season (vs +8-12% in May-June for popular brands).
3. Workshop teams available: Oct-Mar = full capacity, vs Jun-Aug = saturation.
4. Seasonal electrical conditions: spring commissioning = warm conditions for battery + solar testing.

Step 1 — Current system audit

Written, documented, photo-referenced inventory:

• Current battery type (lead-acid, AGM, gel, lithium), nominal capacity, age, condition (measured residual capacity).
• Electrical diagram: retrieve original boatyard diagram or redraw if lost.
• 24 h consumption measured with shunt over 1-2 weeks of typical sailing. See sizing method.
• Recent failures: what tends to fail? Alternator regulator, shore charger, sensors?

Step 2 — Target sizing

Theoretical calculation of target capacity:

1. Inventory of 24 h consumption by load (see sizing method step 1).
2. Simultaneity coefficient 0.65-0.75.
3. Safety margin 30%.
4. Useful DoD 80% for lithium.
5. Final nominal capacity = increased demand / 0.8.

On a typical 40 ft offshore cruising sailboat: gross consumption 145 Ah/24h → sim 0.7 → 100 Ah/24h → +30% margin → 130 Ah/24h → DoD 80% → nominal capacity 165 Ah.

Step 3 — BMS and batteries

BMS selection based on program (see BMS comparison):

• Standard offshore cruising: Victron Lynx Smart BMS 500 (~ 1,020 € HT) + 12.8V/200Ah Smart lithium battery (~ 1,180 € HT).
• Yacht with CZone: Mastervolt MLi Ultra 12/3000 (~ 2,600 € HT, integrated BMS).
• Offshore racing: MG Energy 24V 304Ah (~ 2,990 € HT).

Step 4 — Alternator/DC-DC chain

Switching to lithium requires alternator-side modifications (see lithium plug & play):

• LFP-compatible alternator regulator: Wakespeed WS500, Balmar MC-614, or Victron Orion XS solution.
• DC-DC protection: Orion XS 1400 (~ 350 € HT) limits current to a safe value.
• Class T fuse: 600 A in series with lithium battery (rated at BMS max current + 20%).

Step 5 — Solar and complementary energy sources

If the program includes extended anchoring or offshore sailing without daily engine charging:

• Solar: 1 Wp per Ah nominal lithium (standard workshop ratio). 200 Wp minimum for 200 Ah, 400 Wp for 400 Ah.
• MPPT: Victron SmartSolar MPPT 100/30 (~ 140 € HT) up to 400 Wp.
• Wind turbine: only in very windy areas (>15 knots average offshore). Not relevant in the Mediterranean.
• Hydrogenerator: 500-1,000 W under continuous sailing. Excellent for offshore racing.

Step 6 — Shunt and monitoring

Essential for tracking state of charge and detecting anomalies:

• Victron BMV-712 Smart (~ 215 € HT): 500 A shunt + Bluetooth + 30-day history.
• Cerbo GX: central monitoring server for the entire Victron system (BMS, MPPT, charger). Compatible with smartphone app and VRM cloud.
• Alarms configured at the switchboard: low battery voltage + BMS overheating.

Step 7 — Testing and commissioning

Before relaunching:

1. Full charge with shore charger and SOC verification at 100%.
2. Controlled discharge test to 80% DoD on known load.
3. Engine start test with and without separate starter battery.
4. Load dump test: disconnect BMS while alternator is charging; verify transient absorber functions.
5. Shunt calibration and BMS programming with final thresholds.
6. Documentation handed to client: final diagram, user manual, emergency procedure.

3 real-world cases — complete winter layup refit

Case 1 — Refit of a Bénéteau Oceanis 40 (2024-2025)

Scope: conversion from 300 Ah lead-acid pack → 200 Ah Victron 12.8V Smart lithium + Lynx Smart BMS 500 + Orion XS 1400 alternator protection + replacement of shore charger with MultiPlus 12/3000-120 + addition of 200 Wp solar panels + BMV-712 monitoring. Total workshop time 4 weeks + 8,500 € HT materials + 3,500 € HT labor = 12,000 € HT. Commissioned April 2025, estimated payback 4 years (vs lead-acid replacement every 6-8 years).

Case 2 — Refit of a Lagoon 42 charter catamaran (Mediterranean, 2025-2026)

Broader scope: conversion to 24 V lithium pack (2 × 200 Ah Victron) + Orion-Tr 24/12 for 12 V equipment + 600 Wp solar panels + maintained diesel generator + Cerbo GX central monitoring + Touch 70 switchboard display. Workshop time 6 weeks + 18,000 € HT materials + 8,000 € HT labor = 26,000 € HT. Rationale: intensive charter use, critical autonomy for high-season rentals.

Case 3 — Refit of an IMOCA Initiatives-Cœur (2024-2025)

Dedicated offshore racing. MG Energy 24 V 304 Ah HE Series pack (maximum cycle life) + 2 × Orion XS alternator protection + 800 Wp semi-rigid solar panels + Watt&Sea hydrogenerator + full Cerbo GX monitoring + satellite telemetry. Workshop time 8 weeks + 32,000 € HT materials + 12,000 € HT labor = 44,000 € HT. IMOCA racing standard.

Excluded alternatives — rejected solutions

• Replacing lead-acid with lead-acid to save money: false economy. Initial differential 1,500-2,500 € HT vs lithium, but lead-acid lifespan 7-10 years vs lithium 15-20 years = lithium pays off over 12-15 years. Over the typical boat ownership period (10+ years), lithium wins.
• Energy refit without monitoring (BMV-712): tempting to cut 200-300 € from the budget. Mistake. Without shunt + app, it is impossible to diagnose faults or optimize consumption. Do not neglect this.
• Staggered refit over 2 winters: compromise on system coherence. Better to do everything in one winter, even if it means delaying by one year if not ready.
• Wind turbine refit: good idea in very windy areas (northern Brittany, Scandinavia) but not relevant in the Mediterranean. Prefer solar + hydrogenerator if needed.

Useful resources — during the refit

• Clean electrical diagram: Excel or Visio with batteries / loads / fuses / cable cross-sections. Updated after every modification.
• BMS documentation: manufacturer manual kept on board (Victron, Mastervolt, MG Energy publish PDFs).
• Monitoring app: VictronConnect or VRM Cloud for remote monitoring during winter. Cerbo GX enables email alerts for faults.
• Maintenance log: record antifouling dates, cell cleaning, replacement of consumables. Useful for insurance and resale.

Skysat operates an integrated workshop in Carnac (Brittany) with 4 teams specialized in marine energy. This article reflects our standard method applied to 80+ sailboat refits 2022-2026. 2026 HT prices are indicative distributor prices.