In order to determine the ampere draw of your vessel, you need to know what electrical equipment you have and what the 12-volt amp draw is. The following is a list of typical 12-volt equipment aboard most boats and their average amp draw per hour.

12-VOLT ITEM
Bilge Pump (500 gph) ——— 2.0 AMP Draw
Bilge Pump (1000 gph) ——– 2.9 AMP Draw
Bilge Pump (1500 gph) ——– 4.9 AMP Draw
Bilge Pump (2000 gph) ——– 8.4 AMP Draw

Navigation Lights (3 mile) — 1.5 AMP Draw
Live Well Pump ————— 7.0 AMP Draw
Fresh Water Pump————– 4.0 AMP Draw
Refrigerator (12v) ———— 6.0 AMP Draw
Ice Maker——————— 6.0 AMP Draw
Head (Macerator) ————- 9.0 AMP Draw
Anchor Windlass (900lb) ——- 75 AMP Draw
12v. Housing Lighting——— 15 per 10 Watts AMP Draw
Spot Lights (100k cp) ——— 8.0 AMP Draw
Spreader Lights (3k cp)——- 3.0 AMP Draw
Radar (24 mile) ————– 5.0 AMP Draw
GPS ————————— 0.80 AMP Draw
LORAN————————- 0.70 AMP Draw
VHF Radio - transmit———- 6.0 AMP Draw
VHF Radio - receive———– 0.50 AMP Draw
Depth Sounder (LCD)———– 1.0 AMP Draw
Depth Sounder (Color)——— 3.0 AMP Draw
SSB - Transmit—————- 3.0 AMP Draw

INVERTERS*
SSB receive——————- 2.5 AMP Draw
Autopilot——————— 5.0 AMP Draw
Stereo (50 watt) ————– 0.50 AMP Draw
Fan————————— 1.0 AMP Draw

TROLLING MOTORS (12VOLT)
24lb Thrust——————- 27 AMP Draw
30lb Thrust——————- 30 AMP Draw
36lb Thrust——————- 36 AMP Draw
42lb Thrust——————- 40 AMP Draw
55lb Thrust——————- 55 AMP Draw

*Inverters vary on 12-volt amp draw depending on 115-volt A/C draw. It is generally recommended by the manufacturer’s that you have 20% of your inverter’s voltage capacity in battery amp hour capacity in battery amp hour capacity. This should provide 1 hour of full inverter capacity. However, be sure to add additional 12-volt amp draws.

Additionally, the above amp draws are for “on-time” while the batteries are being used. Remember, a refrigerator, fresh water pump, head macerator, etc only draws power intermittently.

The information provided here has been reproduced courtesy of the Mercury Marine. Wholesale Marine reproduced this information 08/13/08