Marine Diesel Generators
Air conditioning at anchor, a full galley, a watermaker humming in the background: all of it runs on your generator. We sell and install marine diesel generators from Kohler, Phasor, Westerbeke, NextGen and Fischer Panda, from compact 3.5 kW sets for center consoles and sailboats to 40 kW units for large yachts. Most models are priced on request because the right configuration depends on your boat. Request a quote and we'll size it with you. Or open our sizing guide below.
+ Marine Generator Buying Guide: Sizing, Fixed vs. Variable Speed, Brands and FAQs
Sizing a Marine Diesel Generator: Our 4-Step Method
Generators fail early for one reason more than any other: someone guessed the size. Here's the process our technicians use before quoting.
- List every AC load you'll run at the same time. Not everything aboard, just what overlaps on a hot afternoon at anchor.
- Add running watts. Use nameplates where you can; the table below gives typical figures.
- Account for the largest startup surge. Compressors on air conditioners and refrigerators briefly pull several times their running load.
- Add 20–25% headroom. Diesels like to work at 60–80% load. Lightly loaded diesels wet-stack and carbon up.
| Typical load | Running watts (approx.) |
|---|---|
| Marine AC, 12,000 BTU | 1,100–1,300 W |
| Marine AC, 16,000 BTU | 1,500–1,800 W |
| Watermaker, AC-driven | 1,000–2,500 W |
| Battery charger, 60–100 A | 900–1,600 W |
| Water heater | 1,000–1,500 W |
| Microwave or induction burner | 1,200–1,800 W |
| Refrigerator / freezer (AC) | 150–400 W |
Example: two 16,000 BTU AC units, a 60 A charger and a fridge add up to roughly 4.6 kW running. Add surge and headroom, and a 6.5–8 kW set is the honest answer, not the 4.5 kW that "should be enough." For a deeper walkthrough, read our marine generator buyer's guide.
Small Marine Diesel Generators (3.5 to 7 kW)
Space is the enemy on boats under 40 feet. Compact diesels fit where a traditional genset never could. The NextGen Ultra Compact line offers 3.5, 5.5 and 9.5 kW models; Fischer Panda builds a 3.5 kW variable-speed inverter generator; and the Phasor K3 6.5 kW compact series runs at a quiet 1,800 RPM. A 3.5 kW marine diesel generator will carry one mid-size AC unit plus small loads. Anything more and you'll want 5.5 kW or above.
Fixed Speed vs. Variable Speed
1,800 RPM Fixed Speed
Traditional, proven, easy to service anywhere. Heavier and larger for its output, but quiet and long-lived. Most Kohler marine generators and Westerbeke generators in our lineup fall here.
Variable Speed / Inverter
Engine speed follows the load, so a lightly loaded set idles down, burns less fuel and makes less noise. Electronics produce clean power for sensitive gear. The trade-off: more complex electronics and a higher purchase price.
Brands We Carry
- Kohler: the widest range here, roughly 9 to 40 kW, single- and three-phase, with digital remote panels.
- Phasor: compact and ignition-protected PMG models, popular on center consoles and express cruisers.
- Westerbeke: a long-standing name in marine power with deep parts support. Running a gas boat? See our low-CO gasoline marine generators.
- NextGen: ultra-compact sets built for tight engine rooms.
- Fischer Panda: lightweight, sound-shielded diesels with variable-speed options.
Installation and Service in Miami
A generator is only as good as its install: exhaust routing, water-lift muffler height, raw water intake, fuel supply and sound shielding all matter. Our technicians install new gensets, replace tired ones and handle routine service across South Florida. See our marine services, or browse all marine generators including gasoline models.
Marine Diesel Generator FAQs
What size generator does my boat need?
Add the running watts of everything you'll use at once, allow for the largest compressor startup, then add 20–25% headroom. Most 30–40 foot boats running air conditioning land between 5.5 and 9 kW.
Why diesel instead of gasoline?
Diesel is safer to store aboard, more fuel-efficient and longer-lived under load. Gas boats sometimes choose a gasoline genset to carry one fuel, and we stock low-CO gasoline models for that.
How much does a marine diesel generator cost?
Price depends on output, brand, single- or three-phase power and options, and installation adds labor for exhaust, fuel and raw water plumbing. Compact 3.5–6.5 kW sets sit at the low end; 20–40 kW yacht sets cost considerably more. Request a quote with your boat and loads and we'll price the right model.
How many hours does a marine diesel generator last?
With proper load and maintenance, many run 10,000+ hours. Chronic light loading shortens that more than anything.
Our Brands
