Shore power and DC fast charging for electric boats: a practical guide

Charging is where electric-boat ownership meets infrastructure — and where the gap between what is technically possible and what is operationally practical is widest. Below: the two charging modes (AC shore power and DC fast charging), how to size the on-board charger from the supply you'll actually plug into, and why the battery system, not the charger, often sets the real limit.

→ The spec calculator works out your pack size and charge time for a given charger →

The two modes, briefly

AC shore power uses the marina's pedestal — commonly 16 A or 32 A single-phase at 230 V in Europe, 30 A at 120 V or 50 A at 120/240 V in the US, and three-phase on some larger berths. The boat's on-board charger (OBC) converts AC to DC and feeds the pack.

DC fast charge bypasses the OBC entirely. A high-power charger ashore feeds DC directly to the pack through a dedicated inlet, with the boat's BMS setting current and voltage limits over a data link.

For coastal and harbour-hopping cruising, AC shore power is the day-to-day reality. For passage planning or commercial fleet operation, DC fast charge changes what is possible — but only at marinas that have it.

Sizing your on-board AC charger

The OBC is the bottleneck on AC charging. Get this right and you avoid two failure modes: chargers oversized for typical pedestals (wasted cost, wasted weight) and chargers undersized for overnight pack recovery (boat sits at the dock half-charged).

Rule of thumb

Decide how long you can wait — overnight is the usual answer — and how much of the pack you'll typically refill. Then:

OBC_min (kW) ≈ kWh to refill ÷ (hours available × 0.9)

The 0.9 is the calculator's charger efficiency. Refilling 20% to 95% (75% of the pack) in 9 hours:

• 30 kWh pack: 22.5 kWh ÷ (9 × 0.9) ≈ 2.8 kW
• 60 kWh pack: 45 kWh ÷ 8.1 ≈ 5.6 kW
• 100 kWh pack: 75 kWh ÷ 8.1 ≈ 9.3 kW

Allow extra time if you charge to the top: the calculator adds 10% for the slow final stage when the target is 90% or more.

What pedestals deliver in practice

Those are the arithmetic ceilings, not what you'll get. Pedestals are often shared or limited below their rating, and running a breaker at its full rating for hours invites nuisance trips. Set your charger's input current limit below the pedestal rating; many marine chargers and inverter/chargers have one.

Single-phase or three-phase OBC?

A single-phase 32 A supply tops out at about 7.4 kW, which refills about 60 kWh overnight at best. Larger packs need either a three-phase supply and charger, or more hours. Check what your home berth actually offers before choosing; a three-phase charger is no faster on a single-phase pedestal. The single vs three-phase guide covers the hardware.

High-power DC charging — where it actually stands

This is the part of marine charging most often described as more settled than it is. Road-vehicle DC fast charging has a mature standards stack; leisure-marine DC charging does not yet have a settled equivalent. What exists in practice is a small number of marina installations, several vendor-specific inlet and communication schemes, and ongoing standardisation work that has not converged into something you can simply specify by number.

That has three practical consequences at spec time:

1. Interoperability is not guaranteed. A DC inlet fitted today is tied to a vendor's ecosystem to a degree an AC shore-power inlet is not. Ask the charger supplier directly which marina networks their inlet has been commissioned against.
2. Billing and roaming are unsettled. Some operators use the back-end protocols of road charging networks, which helps roaming, but that's a vendor choice rather than a requirement.
3. Isolation architecture is a design conversation. Because no standard dictates it for you, how the pack BMS and the inlet isolate — and whether they do so as a unit — is something to agree explicitly with your supplier and surveyor.

The honest planning assumption for a cruising boat specified now is that AC shore power is your charging strategy and DC fast charge is an opportunistic bonus on a small number of routes. If a supplier quotes you a specific standard number as settled, ask them for the published document before you design around it.

Sizing your DC fast-charge inlet

The inlet sets one ceiling on charge power, and the battery system sets another, usually lower. Take Victron's Lithium NG system:

• Each 51.2 V, 100 Ah battery (5.12 kWh) accepts up to 100 A continuous, 1C.
• Twelve of them make a 61 kWh bank, so the cells together would accept 1,200 A.
• The largest Lynx Smart BMS NG is rated 1,000 A continuous, so the BMS caps charging at 1,000 A, about 54 kW at a typical 54 V charging voltage.

At that rate, 20% to 80% (37 kWh) takes about 41 minutes. An inlet or shore charger rated at 150 kW would make no difference, because the battery system takes no more. Size a DC inlet to what your battery and BMS can accept, with modest headroom for a future upgrade.

A realistic charging architecture for 2026

For a 14 m cruiser with a 60 kWh pack used mostly in coastal cruising:

• Primary: 11 kW three-phase OBC, 32 A three-phase shore inlet. Overnight recovery from any reasonable marina pedestal.
• Secondary: 16 A single-phase fallback for older marinas. Slower (3.5 kW) but ubiquitous.
• Optional: a DC fast-charge inlet sized to the battery system's limit, for charging at equipped marinas. It's worth the cost only if you sail routes with several equipped sites, and it may tie you to one vendor's system.
• Where it fits: solar for hotel load at anchor. A 14 m boat has room for more panels than a 30-footer, but area is still the limit; see the solar guide.

For pure coastal day-sailing, the secondary alone is often enough. For active cruising in mainland Europe, the primary becomes the daily driver. The fast-charge inlet is genuinely useful only on routes where you already know participating marinas exist along the way — verify before specifying.

What not to do

Three patterns to avoid:

1. Oversizing the OBC to "future-proof". A charger bigger than your pedestals can feed costs more, weighs more and produces more heat for no gain. Size it to the supply you'll actually use most.
2. Treating DC fast charge as a substitute for AC charging. Where it exists at all, it's on a few routes. Treat it as the motorway services, not the home garage.
3. Skipping the galvanic isolator. A galvanic isolator or isolation transformer on the shore-power AC inlet protects against stray-current corrosion on your underwater metal. This is not optional for a boat that spends time at the dock.

Sources

Checked on 7 November 2026:

• Victron Energy — Lithium NG batteries datasheet: nominal energy and maximum continuous charge current (1C) of the 51.2 V, 100 Ah battery
• Victron Energy — Lynx Smart BMS NG 500 A / 1000 A continuous ratings: see the sources in our Lynx Smart BMS NG guide
• The calculator's charging model: 90% charger efficiency and the 10% allowance for charging to 90% or more