PAGE 24 • WINTER 2007 THE JOURNAL OF THE AMERICAN SAILING ASSOCIATION
INSTRUCTOR TIP
By Capt. Paul Mirenda
Marine Battery Switch Operation
M
ost cruising sailboats have two batteries or
Using position number 1 while motoring, only the
banks of batteries which are isolated from each
starting battery is charged. Under sail, battery number 1
other, but are connected to a battery switch.
provides power to the electrical system if left in this
Battery number 1 is normally used to start the engine
position. This is not recommended since battery number
while battery number 2 provides power for the electrical
1 should be kept fully charged.
system. The battery switch has positions labeled as: 1, 2,
All and Off.
Position number 2 charges only the deep cycle battery
used to power the electrical system when
The purpose of the battery switch is twofold:
motoring. It draws power only from this battery
When motoring, the switch determines
when sailing with the engine off.
which battery is being charged by the
alternator. In position 1 or 2, only the
In the all position, the alternator charges
battery selected is charged while in the
both batteries when motoring. Both
“All” position, both batteries or banks of
batteries are simultaneously discharging
batteries are being charged. It is wise to
while under sail. Move from “All” to
recharge both batteries often while
number 2 each time the engine is stopped
motoring as marine batteries should never
to begin sailing.
be discharged past 50 percent to insure
longer battery life.
In the off position, neither battery is charged
while the engine is running. Under sail, no battery
Under sail, this switch determines which battery will
power is being used. When plugged into dock power, both
provide power to the electrical system. Keep this switch
batteries are charged regardless of the battery position.
in position number 2 while sailing so only battery
number 2 is used. This way, if battery number 2 runs
Note: Although common on sailboats, this type of switch
down you can still start the engine by selecting battery
may not be found on some newer high-tech boats. In this
number 1.
case, refer to the manual. Additionally, if you own a used
boat that had any wiring done by a former owner, check
If this switch is left in the “All” position while sailing,
to be sure that your switch has been wired with position
both batteries are discharging. This could run down both
1 being the starting battery and position 2 as the house
batteries, resulting in no power and no way to start the
battery.
engine. It is wise to carry a solar panel on extended
cruises as a backup in case you make this mistake.
Paul Mirenda is a USCG Licensed Captain since 1992 and ASA
Certified Sailing Instructor since 1988.
AMERICAN SAILING ASSOCIATION
P.O. BOX 12079, MARINA DEL REY, CA
PRESORTED
90295-3079 TEL: 310/822-7171
STANDARD
U.S. POSTAGE
WWW.AMERICAN-SAILING.COM
PAID
ANAHEIM, CA
PERMIT NO. 514
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