How the math works
Each device: watts × hours per day = watt-hours. Add them up, divide by 12 for amp-hours on a 12V system. Lead-acid batteries only give you about half their rated capacity before voltage sag becomes a problem; LiFePO4 gives you about 80%. Solar: divide daily watt-hours by ~4 peak sun hours for the panel wattage that replaces a day's draw.
Defaults come from real-world draws: a Starlink standard dish runs about 75W (50–100W depending on weather and the heater), the flat high-performance dish around 110W, a cell booster about 12W, a failover router about 10W. Edit every number to match your actual gear — your boat, your math.
This is planning math, not an electrical design. Size the power first, the electronics second — and when in doubt, add margin.