The essentials in 30 seconds
- Batteries: follow the manual. Victron: keep lithium on charge, or (nearly) full and then disconnected. Mastervolt MLI Ultra without shore power: above 80%, safety relay on LOCK OFF, top-up recommended every 100 days.
- Lithium and cold: Victron only allows charging between +5 and +50 °C; the BMS must switch the chargers off.
- Removable displays go home, software updates happen over the winter, on a stable power supply.
- Speed sensor: blanking plug in, housing drained before the frost, no pressure washer on transducers; at relaunch, check for leaks immediately and again within 3 hours (Airmar).
- In spring, measure before you sail: about 60 Ω and at least 9 V on the NMEA 2000 network, VHF SWR, autopilot tested at the dock.
Contents
This checklist covers onboard electronics and battery storage during the lay-up; the energy refit itself (battery bank, charging, lithium conversion) has its own method in our winter energy refit checklist. General rule: the manufacturer's manual beats dockside habits, and it differs from one brand to the next.
Batteries: store them by the manual
A bank “at rest” keeps draining (alarms, relays, standby loads, charger back-current), as Victron's Lithium Smart manual points out. After a BMS low-voltage shutdown, roughly 1 Ah per 100 Ah is left: from there, 10 mA is enough to damage a 200 Ah battery left discharged for more than 8 days. Before you leave, read the current on your battery monitor with everything switched off (SmartShunt, BMV…): any draw you cannot explain is a load to track down.
| Battery | Manufacturer's instruction | Watch out |
|---|---|---|
| Victron Lithium Smart (e.g. 12.8 V/330 Ah) | Kept on charge, or (nearly) full and then the DC system disconnected: battery switch, fuses pulled or positive terminal off. A BMS shutdown is a last resort only. | Charging only between +5 and +50 °C. |
| Mastervolt MLI Ultra (12/3000, 12/6000, 24/6000) | Idle for more than 3 months. With shore power: loads off, float at 13.5 V (27.0 V on 24 V). Without: above 80%, safety relay on LOCK OFF, MasterBus powering not on “Always on”, top-up above 80% recommended every 100 days. | Below −5 °C, the battery may not accept charge current. |
| Victron AGM and Gel | Up to a year without recharging if kept cool. Storage mode on Victron chargers: 13.2 to 13.5 V (12 V), with a short absorption boost every week. | Self-discharge below 2% per month at 20 °C, doubling with every +10 °C. |
| Mastervolt AGM 12 V | “Keep battery in charged condition”; recharge when the open-circuit voltage drops below 12.3 V, and at least every 9 months below 20 °C. | Self-discharge about 3% per month at 20 °C. |
Workshop trap: lithium, charger and cold. Keeping lithium on charge over winter only works if something stops the charge below the minimum temperature. With Victron, the BMS controls the chargers, with a default threshold of +5 °C, because a cell charged below that suffers permanent damage. The manual also requires at least 2 hours of absorption per month, and any charger “storage” mode set to float voltage (13.5 V for a 12.8 V battery). Otherwise: nearly full, then disconnected.
Displays and chartplotters: remove, protect, update
Check each unit's storage temperature range (−20 to 70 °C for Garmin's VHF 115/215, for example): Garmin excludes damage outside that range from its warranty. Then there is moisture: in rare cases, fogging can appear under the glass of Garmin chartplotters after large temperature swings; a hydrophobic patch lets the vapour out as the screen warms up, and Garmin recommends storing the unit somewhere warmer, such as the house or garage, when it is not in use.
- Bracket-mounted display: take it home, photograph the connections first, protect the plugs left aboard.
- Flush-mounted display: leave it aboard, powered off, boat ventilated, sun cover on (Raymarine asks for it whenever the unit is not in use, against UV). Removing it disturbs the mounting gasket and rear connectors: a job to plan, not a winter reflex.
- Cleaning: power off, damp cloth, no solvents and no pressure washer (Raymarine).
Updates: now, not in April. An interrupted update can leave the unit not functioning properly, warns Raymarine, which asks for a reliable power supply and a backup of important files first; its full package covers Axiom displays and networked products, via Wi-Fi or microSD. On Garmin GPSMAP units, the memory card prepared with Garmin Express goes in once the plotter has fully booted and stays in until the restart is complete. Also check when your chart update subscription runs out (our chart comparison).
Transducers and through-hulls at haul-out
Out of the water, through-hull fittings can be checked from both sides. For a paddlewheel sensor in a valved through-hull housing, such as the Airmar DST810, Airmar's instructions call for:
- no power sanding or pressure washing on the sensor, which may weaken its structure or damage internal components: tell the yard;
- the blanking plug in as soon as the boat comes out (or after a week in salt water), O-rings intact and lubricated, cap nut hand-tight, safety wire back on;
- once ashore, the plug removed to let the water drain, then reinserted, otherwise freezing water can crack the plastic;
- cleaning with a Scotch-Brite pad and mild detergent, without scratching the face, never with solvents;
- water-based antifouling made for transducers, never ketone-based, every 6 months or at the start of each season.
Lost, broken or worn parts: replace them right away; broken valve: replace the housing at the next haul-out. The valve is not a watertight seal; only the insert or the blanking plug closes the hole. At relaunch: check immediately, then do not leave the boat more than 3 hours without checking again; a small leak can let a lot of water build up within 24 hours.
Mast down: sensors, antennas, connectors
With the mast down, B&G and Garmin both advise removing their wireless wind sensors, with different battery instructions:
- B&G WS320: masthead unit off the mast and battery removed for the winter so it does not drain; pairing with the base station must then be redone, on the ground, before the sensor goes back up.
- Garmin gWind Wireless 2: stored dry and in the light to keep the battery charged, between 0 and 35 °C; if stored in the dark, replace the battery at the start of the season.
At the mast foot, cap, bag and label every disconnected connector (VHF, instruments, radar, lights); Garmin even supplies weather caps for unused ports on its VHF radios, against contact corrosion. Check the VHF/AIS coax: mast foot and back of the radio, plus antenna and masthead connector if the mast is down. A corroded PL259 is remade on freshly cut cable (crimp PL259 for RG213/RG214); when the mast goes back up, an SWR check validates the whole antenna line (masthead vs pushpit VHF antenna).
NMEA 2000 network: corrosion and spring measurements
In its troubleshooting procedures, Raymarine asks for connections that are secure, clean and free from corrosion, or replaced: apply the same rule to the NMEA 2000 bus, starting with the connectors exposed to moisture (bilge, mast foot, lockers). On Micro-C networks, tees and terminators are common parts (B&G Micro-C tee, Navico TR-120 terminators). In spring, two measurements documented by Actisense:
- network powered down, about 60 Ω between NET-H and NET-L (two 120 Ω terminators in parallel); 120 Ω: one is missing, 40 Ω: one too many;
- at least 9 V between NET-S and NET-C at the end of each backbone leg, with a terminator removed for the measurement; the network must stay between 9 and 16 V.
Architecture and power: see our NMEA 2000 sailboat guide.
Autopilot and drive unit
Mechanical maintenance of the drive unit is covered in our drive unit maintenance article. Note the season's symptoms at haul-out while they are fresh, and plan a dockside test in spring, especially if the rudder, steering linkage or heading sensor has been touched. Watch what gets stowed near the heading sensor: Raymarine lists ferrous screws and tools, speakers, pumps, electric motors and high-current wiring, and asks for the sensor of its Evolution autopilots to be relocated if deviation reaches 15°.
Mistakes that cost you in spring
Each one comes from a manufacturer instruction quoted above, forgotten or misapplied:
- a lithium bank in BMS shutdown, drained by a forgotten load;
- a charger left connected to lithium in a cold boat, with no BMS charge cut-off;
- a speed-sensor blanking plug cracked by frost, or a paddlewheel seized for lack of a plug;
- a transducer pressure-washed or painted with the hull antifouling;
- mast-foot connectors left bare, then intermittent faults;
- an update started the day before departure, on a tired battery;
- a silent wireless wind sensor: flat battery or forgotten pairing.
Limits and pitfalls
- A manual covers a product range: for any battery other than those in the table, follow its own manual, latest revision.
- Winterizing is not repairing: a worn-out bank or a botched network calls for a refit.
- Doubtful through-hull (crack, weeping, valve): fix it ashore, not “we'll see once afloat”.
- Without a multimeter and an SWR meter, the checklist stays visual.
Workshop verdict
- Ashore, no shore power: bank charged then isolated as its manual says, removable displays and wireless sensors at home, speed sensor plugged and drained, connectors capped.
- Afloat all winter: the automatic bilge pump stays powered, so the bank does too, on a charger set according to the battery manual (table above). Speed sensor plugged if the boat sits for more than a week, regular visits.
- Electronics work this winter: updates after installation (Garmin requires it when fitting its through-hull transducers), then network measurements and an autopilot test before relaunch; see our electronics refit method.
Prefer to hand it over? The Skysat workshop in Carnac installs, configures and commissions onboard electronics and power systems (NMEA 2000 networks, autopilots, lithium). For updates or recommissioning before the season, describe your boat from our services page.
Sources
- Victron Energy: Lithium Smart battery manual (rev. 21); Gel and AGM datasheet.
- Mastervolt: MLI Ultra manual (10000019442/11); AGM 12 V manual (10000002887/09).
- Airmar: DST800/DST810 instructions (17-435-01 rev. 16).
- Garmin: installation instructions for through-hull transducers, VHF 115/215 and gWind Wireless 2; GPSMAP manual; NMEA 2000 technical reference; chartplotter fogging FAQ.
- Raymarine: LightHouse 4 updates; Axiom 2 Pro installation instructions (87443 rev. 7); Setup Evolution FAQ.
- B&G: WS320 installation manual (988-12029-001, 988-12029-002).
- Actisense: building and testing an NMEA 2000 network.
