How to Choose the Right Inverter Size for Your Yacht

One of the most important decisions for recreational boat owners looking to upgrade their onboard electrical systems is choosing the right marine inverter. An inverter allows you to power AC appliances such as air conditioning, refrigeration, entertainment systems, and kitchen devices while at anchor or underway—without relying on shore power or running a generator 24/7.

But selecting the correct inverter size isn’t always straightforward. Too small, and you risk tripping the system or leaving key comforts offline. Too large, and you could overspend or face unnecessary energy losses. In this comprehensive guide, we’ll break down how to calculate the right inverter capacity for your yacht, with a special focus on trusted brands like Victron Energy and Mastervolt.

1. What Does a Marine Inverter Do?

A marine inverter converts DC battery power into AC electricity, allowing you to run appliances designed for household voltage. Onboard systems such as air conditioning, microwave ovens, TVs, and induction cooktops typically require AC power.

Marine inverters are available in different sizes, measured in watts or kilowatts, and selecting the right capacity ensures both efficiency and reliability.

2. Key Terms to Understand Before Choosing an Inverter

• Continuous Power Rating: The amount of power the inverter can supply continuously (e.g., 2000W).

• Surge Power Rating: The inverter's ability to handle short bursts of high-demand devices (e.g., starting an A/C compressor).

• Pure Sine Wave vs. Modified Sine Wave: Most sensitive electronics require pure sine wave inverters for clean, stable power.

• Battery Bank Size: The inverter draws from your battery bank, so larger loads require appropriately sized batteries.

3. Step-by-Step Guide to Calculating Inverter Size for Your Boat

Step 1: List All AC Appliances You Intend to Power

Examples include:

• Marine air conditioner (Dometic or CTM): 1000W to 5000W depending on BTU rating

• Refrigerator/freezer (Isotherm or Vitrifrigo): 80W to 300W

• Microwave: 1000W

• Induction cooktop: 1500W to 2000W

• Entertainment system: 200W to 500W

• Lighting: Varies but usually 100W or less

Step 2: Identify Continuous and Peak Loads

• Add up the continuous running watts of all appliances you might use simultaneously.

• Identify any appliances with high startup surges (typically motors or compressors).

For example:

• Air conditioner: 1500W continuous, 4000W surge

• Refrigerator: 100W continuous, 500W surge

• TV: 150W

• Total continuous load: 1750W + 100W + 150W = 2000W

• Peak surge: 4000W

Step 3: Apply a Safety Margin

Add 20-30% to your maximum continuous wattage to account for inefficiencies and unplanned loads.

• 2000W + 30% = 2600W

Step 4: Select an Inverter Size

In this example, you would choose an inverter with:

• Continuous power: 2600W or higher

• Surge capacity: at least 4000W

The Victron MultiPlus 3000VA or Mastervolt CombiMaster 3000 are excellent choices in this power range.

4. Choosing the Right Type of Inverter: Standalone vs. Inverter/Charger

A. Standalone Inverters:

• Ideal for smaller boats or minimal AC loads.

• Require separate battery chargers.

B. Inverter/Chargers (All-in-One):

• Automatically switch between shore power and inverter.

• Built-in smart chargers maintain battery health.

• Recommended for medium to large yachts.

Victron MultiPlus and Mastervolt Mass Combi are both popular inverter/charger solutions.

5. Sizing Considerations for Marine Air Conditioning Systems

Air conditioning is typically the largest AC load on most yachts.

• A 12,000 BTU marine A/C unit can draw 1200W to 1500W continuously.

• Surge demands may briefly spike above 3000W.

To run marine air conditioning from battery power:

• Choose an inverter that matches the surge rating.

• Consider adding soft start kits to reduce startup demands.

• Ensure battery bank capacity supports sustained use.

Read our guide on Upgrading Marine A/C Systems for detailed cooling system advice.

6. Battery Bank Sizing: The Often-Overlooked Factor

Even the best inverter is only as effective as the battery bank supplying it. Here’s how to size your battery bank:

• Identify total amp-hour (Ah) demand for the duration you want to run your systems.

• Multiply total AC wattage by hours of use to calculate energy need (Wh).

• Divide watt-hours by system voltage (12V, 24V, or 48V) to determine Ah required.

For example:

• 2000W x 4 hours = 8000Wh

• 8000Wh / 24V = 333Ah

For lithium battery systems, consider Victron Smart Lithium solutions for higher energy density and faster recharge times.

7. Additional Tips for Choosing the Right Inverter

A. Think About Future Expansion:

• Will you add more electronics later?

• Opt for an inverter slightly larger than your immediate needs.

B. Consider Charging Speed:

• Higher-wattage inverter/chargers will also recharge batteries faster when plugged into shore power.

C. Efficiency Ratings:

• Choose inverters with high efficiency (>90%) to minimize wasted energy.

D. Remote Monitoring:

• Victron GX Touch or Mastervolt EasyView panels allow real-time monitoring.

8. Recommended Inverter Models for Recreational Yachts

Victron Energy:

• Victron MultiPlus 12/3000/120-50: A popular choice for mid-sized yachts.

• Victron Quattro: For larger vessels with dual AC inputs.

Mastervolt:

• CombiMaster 3000W: Compact and efficient with smart charging.

• Mass Combi Ultra Series: For larger yachts with higher loads.

9. Professional Installation Considerations

Proper inverter installation is critical for:

• Safety compliance (ABYC standards)

• Cable sizing (marine-grade tinned copper)

• Grounding and circuit protection

Consult a certified marine electrician for complex installations or if integrating with multiple systems (autopilot, radar, solar, etc.).

10. Power Your Yacht Efficiently with S & S Dockside Marine Supply

Choosing the right inverter size for your yacht ensures you can enjoy the comfort and convenience of household appliances without overloading your electrical system. By carefully calculating your continuous and surge power needs, matching them with a quality inverter from Victron or Mastervolt, and ensuring proper battery support, you’ll create a reliable and efficient onboard power solution.

At S & S Dockside Marine Supply, we offer a full range of marine inverters, inverter/chargers, battery banks, and installation accessories to help you design the perfect electrical system for your recreational boat. Our team can assist you in selecting the right products for your specific needs and ensure you get the most out of your time on the water.

Visit S & S Dockside Marine Supply to explore premium marine power solutions that keep your adventures powered and comfortable.