Marine Generator Sizing Calculator

REF: MAR-GEN-SIZE-802

Determine the recommended electrical power output (kW / kVA) for your marine genset based on continuous operating loads, inductive motor starting surges, and recommended reserve capacity. Proper sizing prevents both engine overload and long-term carbon buildup caused by light-load "wet stacking."

Navigating Marine Generator Sizing Rules

Selecting a marine generator requires a careful balance. Installing an undersized generator will trip circuit breakers during peak inductive motor start cycles, while selecting an excessively oversized generator leads to engine glazing and unburnt fuel residue.

Key Engineering Rules & Considerations:

• Inductive Inrush Current (Surge): Electric motors—such as air conditioning compressors, watermakers, and refrigeration units—require 2 to 4 times their normal operating wattage for a brief split-second during startup. Soft-start kits can reduce this inrush by up to 60%.
• The 70% - 80% Continuous Load Rule: Diesel generators operate most efficiently and last longest when subjected to a steady continuous load of 70% to 80% of their rated capacity.
• Wet Stacking Risk (Underloading): Running a marine diesel generator consistently under 30% of its rated capacity prevents cylinder walls from reaching optimal operating temperatures. This leads to unburnt fuel leaking into the exhaust system, known as "wet stacking."
• Power Factor (PF): AC generator ratings are calculated at a standard power factor of 0.8. Real-world continuous kilowatt (kW) needs are calculated as: kVA = kW ÷ 0.8.