The essentials in 30 seconds
- Pure sine is mandatory in marine. Modified square-wave inverters damage laptop charger transformers and poorly power compressor fridges. Pure sine = 99% of sailboat use in 2026.
- Sizing = continuous power AND peak load. A 1,200 W coffee machine draws 2,000 W on startup (3-5 sec). A 1,200 W "smooth" inverter will overload and shut down. Always size the inverter at 150% of continuous consumption.
- 2026 standards: Victron Phoenix 12/1600 Smart (~ $540 ex-VAT) for occasional use. MultiPlus 12/3000-120 for continuous use with shore power charger integrated.
- Idle loss counts. Inverter in standby draws 0.3-0.8 A continuously. Over 24 h unused = 7-20 Ah loss. Always use an accessible ON/OFF switch.
- Workshop installed budget for 35-45 ft sailboat: ~ $700-1,200 ex-VAT (inverter + wiring + protection + switch), excluding battery bank which depends on lithium sizing (see our sizing article).
The DC/AC inverter bridges your 12/24 V battery bank and the 230 V world. It converts the battery’s DC voltage into a clean sine wave, allowing household equipment (coffee machine, laptop, absorption fridge, electronic chargers) to run. But without correct sizing, it’s the most temperamental piece of gear on board.
This article explains the difference between pure sine and modified square-wave, provides a sizing method, presents the Victron and Mastervolt ranges stocked by Skysat, and gives installation rules. For the battery bank powering the inverter, see our lithium bank sizing article.
Why pure sine, not modified square-wave
Two inverter technologies coexist: modified square-wave (stepped waveform) and pure sine (sine wave close to the EDF grid).
- Modified square-wave: cheaper, slightly higher efficiency, but high harmonic distortion. Damages: transformers (laptop chargers, camera chargers), induction motors (fridge compressors, fans), medical equipment.
- Pure sine: voltage identical to the grid, powers everything without issues. 20-30% surcharge vs modified square-wave, but justified as soon as you go beyond basic smartphone charging.
In modern 2026 sailboats, pure sine is the de facto standard. Unless using very specific equipment (incandescent lighting only), go pure sine.
Sizing — workshop method
4-step calculation:
- List all 230 V equipment used simultaneously. Coffee machine (1,000-1,500 W) + laptop (90 W) + absorption fridge (300 W on startup). Total continuous: ~1,400 W.
- Identify startup peak load. For coffee machines and fridges, multiply continuous power by 1.5-2.0. Estimated peak: ~2,100 W.
- Choose inverter at 150% of continuous consumption. Continuous 1,400 W × 1.5 = minimum 2,100 W inverter. Round up to the next range: 2,000-2,500 W inverter.
- Check peak load compatibility: the 2,000 W Victron inverter handles ~4,000 W peaks for 1-2 seconds (datasheet). Compatible with coffee machine/fridge startup.
For light occasional use (laptop + USB chargers only): Phoenix 12/1600 Smart (~ $540 ex-VAT) is more than enough.
Victron Phoenix range
Entry and mid-market Victron range, pure sine, 12 V and 24 V.
- Phoenix 12/500 Smart: ~ $270 ex-VAT. Small uses: laptop, USB chargers, 230 V lighting.
- Phoenix 12/1200 Smart: ~ $470 ex-VAT. Light coffee machines, drills, small tools.
- Phoenix 12/1600 Smart: ~ $540 ex-VAT. Skysat’s workshop reference for 35-45 ft sailboats. 3,000 W peak (2-5 sec).
- Phoenix 24/1600 Smart: ~ $580 ex-VAT. 24 V version for sailboats with 24 V architecture.
- Phoenix 12/2000 Smart: ~ $850 ex-VAT. Fridge compressor + coffee machine + tools.
- Phoenix 12/3000 Smart: ~ $1,250 ex-VAT. Heavy continuous use.
Mastervolt Mass Sine range
Direct competitor to Victron with MasterBus / CZone integration for configured yachts.
- Mass Sine 12/1500: ~ $720 ex-VAT. More expensive than Victron at equivalent power, but native MasterBus integration.
- Mass Sine 12/2000: ~ $980 ex-VAT.
- Mass Sine 12/2500: ~ $1,250 ex-VAT.
Mastervolt is preferred on new Bénéteau/Jeanneau/Bavaria yachts equipped with CZone (native dashboard integration).
Inverter-charger combo
For intensive use and regular harbor stays, consider the all-in-one inverter + shore charger unit (Victron MultiPlus).
- MultiPlus 12/3000-120: 3,000 W inverter + 120 A shore charger in one box. ~ $1,850 ex-VAT. At the dock, it functions as a charger; at anchor, as an inverter. Automatic transfer in under 20 ms.
- MultiPlus II 48/3000: ~ $1,950 ex-VAT. 48 V version for large hybrid parks + solar.
If you plan to replace your shore charger and install an inverter, the MultiPlus saves on wiring and space.
Model comparison table
| Model | Continuous power | Peak | Efficiency | Price ex-VAT |
|---|---|---|---|---|
| Victron Phoenix 12/500 | 500 W | 900 W | 89% | ~ $270 |
| Victron Phoenix 12/1200 | 1,200 W | 2,200 W | 91% | ~ $470 |
| Victron Phoenix 12/1600 | 1,600 W | 3,000 W | 92% | ~ $540 |
| Victron Phoenix 12/2000 | 2,000 W | 4,000 W | 92% | ~ $850 |
| Victron MultiPlus 12/3000-120 | 3,000 W + 120 A charger | 6,000 W | 93% | ~ $1,850 |
| Mastervolt Mass Sine 12/2000 | 2,000 W | 4,000 W | 93% | ~ $980 |
Workshop installation — technical rules
Skysat workshop rules
- DC cable sized for max current. 12/1600 W inverter → 130 A continuous → 35 mm² cable minimum, length ≤ 1 m if possible. Too thin = voltage drop → inverter shuts down on undervoltage.
- Fuse class T or MEGA in series with battery. Rated at 1.5× nominal current. 1,600 W inverter = 200 A class T fuse.
- Accessible ON/OFF switch. Inverter in standby draws 0.3-0.8 A. Physical button at the helm = 5 min install = 100-300 Ah saved per year at anchor.
- Mandatory ventilation. 1,600 W inverter produces 100-150 W of heat at full load. Ventilated compartment required, never in a closed locker.
- AC earth bonding. The inverter’s 230 V output must be bonded to the boat’s ground for safety. ISO 13297 standard.
FAQ — Practical inverter use
12 V or 24 V inverter?
12 V if your bank is 12 V (95% of pleasure sailboats). 24 V if bank is 24 V (yachts ≥ 45 ft). Converting 12→24 V to power the inverter is inefficient; better to use a direct inverter matching your bank voltage.
Can you use the inverter while sailing (engine running)?
Yes, in fact it’s optimal — the alternator recharges the bank while compensating for inverter consumption. Watch for startup peaks: on small banks (< 200 Ah), voltage dips briefly and the alternator may overcompensate. Prefer starting the inverter with the engine running.
What is the standby loss of a modern inverter?
Victron Phoenix 12/1600 Smart: 0.4 A standby (4.8 W). Over 24 h unused: 9.6 Ah. Over 1 year at anchor: 3,500 Ah lost if never turned off. Hence the need for an ON/OFF switch.
Can the inverter power an air conditioner?
Theoretically yes but not recommended. Marine AC draws 500-1,500 W continuously. On batteries, autonomy is limited to a few hours max. Prefer a generator or shore power for extended harbor stays.
Inverter-charger combo or separate units?
Combo (MultiPlus) if you plan to use both intensively (long anchorages + harbor stays). Separate units if the shore charger is already in place and you only need to add an inverter. Combo wins on space/wiring, loses on maintenance flexibility.
3 real-world workshop cases — inverter install
Case 1 — Bavaria 41 cruising family sailboat
Inverter installed in 2024: Victron Phoenix 12/1600 Smart (~ $540 ex-VAT) + accessible ON/OFF switch in cabin + 200 A class T fuse. Typical use: coffee machine (1,200 W startup) in the morning at anchor, USB chargers while sailing. Average 24 h consumption: 30-40 Ah (including standby loss). The customer confirms: "Coffee at anchor changes the quality of the cruise."
Case 2 — Lagoon 42 offshore catamaran
Victron MultiPlus 12/3000-120 inverter-charger combo (~ $1,850 ex-VAT) replacing the existing shore charger. Benefits: automatic transfer dock↔battery in < 20 ms, continuous 230 V power at anchor (1,200 W AC possible for 2-3 h), space saved in the technical locker. 6 h workshop install. Total install $2,200 ex-VAT.
Case 3 — 8 m coastal solo sailboat
Small need: laptop charging + phone chargers. Phoenix 12/500 Smart (~ $270 ex-VAT). 2 h install, 80 A class T fuse + switch. Total install ~ $380 ex-VAT. The customer confirms: "For my usage, it’s exactly the right power — not oversized, not frustrating."
Excluded alternatives — inverters not selected
- Chinese modified square-wave inverters (250-350 $ ex-VAT in 2,000 W): to be avoided in marine. Waveform degrades laptop chargers and fridge compressors within months. Attractive price promise, but reduced lifespan and risk of damaging powered equipment.
- All-in-one "combo" inverters (generator + inverter integrated): practical for very large units (yacht ≥ 60 ft), but expensive and complex to maintain. Prefer separate components under 50 ft.
- Inverters without integrated ON/OFF switch: some entry-level models lack a physical power button. Standby loss (0.5-1 A continuous) then consumes 4-8 kWh per month. Always choose a model with ON/OFF or add an external switch.
Specific case — powering an absorption fridge when off-grid
An absorption fridge (Dometic, Vitrifrigo) draws 90-300 W in cycle, with startup peaks 2-3× continuous consumption. For a 200 W average fridge:
- 24 h consumption: 200 W × 12 h cycle = 2.4 kWh = 200 Ah at 12 V.
- Inverter sizing: Phoenix 12/1200 minimum (for ~600 W startup peak).
- Battery bank: 400-500 Ah lithium minimum for 2-3 days autonomy without recharge.
For this specific use, the MultiPlus 12/3000-120 combo (~ $1,850 ex-VAT) is our standard: integrated 120 A shore charger + automatic transfer. The customer gets their AC coffee even on long anchorages.
Skysat distributes Victron Energy and Mastervolt. 2026 ex-VAT prices are indicative distributor prices.
