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