Offshore Electrical Systems
                                    Presented by Ron Romaine

The proper offshore system consists of a design to meet YOUR needs.  Quality
equipment that is properly installed, inspected and maintained regularly and
managed properly will give you years of service.

Designing a system starts with figuring your daily consumption expressed in
amp-hours (Ah).  Ah is the number of amps used over time (10 amps per hour =
10 Ah ).  To figure daily consumption add up your 24 hour usage of lights,
radios, blender etc. to arrive at amp-hours consumed per day.  Once we know
daily consumption, multiply by 2 to figure capacity required for a one day
supply (100Ah x 2 = 200Ah).

Following the 50% rule is a must for longer battery life.  The 50% rule is to
not discharge the batteries more than 50% of total capacity and the battery
will deliver the maximum amp hours over it's life.  One day supply is not
enough time between recharging cycles for most voyaging yachts, therefore
multiply your daily capacity by the number of days desired to go before
recharging (200Ah X 3 days = 600Ah supply).  This means we can use 300Ah
before reaching 50% discharge or 3 days at 100Ahs.  600Ah can be arrived at by
using three 8D batteries (210Ah each @ 12vdc) or  four 4D (170Ah each @
12vdc), seven Group 27 (85Ah each @ 12vdc) or six GC-2 (180Ah @ 6vdc)
batteries.  Weight is between 450 and 550 pounds for the different

Marine storage batteries come in two basic types, wet cell and gel cell.  Each
have advantages and disadvantages.  A third type, absorbed glass mat batteries
are sold in the marine market however will not address glass mat batteries as
they are not as well suited for deep cycle use as wet and gel types.

Wet cell batteries are common and inexpensive.  The primary drawbacks to wet
cells is they have to be maintained (with distilled water only), ventilated
properly and contained in full boxes or enclosures.  The sulfuric acid fumes
created while charging will corrode near by materials and if overcharged, wet
cell batteries can render the boat uninhabitable.  They also will not accept a
charge as quickly as gel batteries, requiring a longer charging cycle and less
efficiency for the charging system.  The advantage is a wider selection of
sizes and lower initial cost.  The average life of a properly maintained wet
cell battery is 5 years.

Gel cell batteries do not need distilled water, ventilation or boxes.  They
have no liquid to spill or replace and they don't give off gases to
contaminate your environment.  The batteries come in most sizes and can be
mounted on there side or end.  They are truly maintenance free.  The
disadvantage is initial cost, but they last 8 - 10 years when properly charged
and used.  For the long term, gel batteries are very desirable and are a good
match for a modern high power charging system.

Once you have determined what your battery capacity will be to fit your needs
and your boat, design a charging system to recharge the batteries easily.  The
main engine fit with a suitable high output alternator is the most powerful
tool to quickly recharge a depleted battery bank.  Check your engine for
horsepower rating, alternator V belt width and alternator "foot" mounting
arrangement.  For example: 35hp, 1/2" belt and 2" single mounting foot.

At full output high output alternators use from 7hp for a 100 amp type to 9hp
for a 200 amp model.  If your engine has 18hp then half the power will go to
driving a 200 amp unit!  This wouldn't be a wise decision as you may want all
your power going to your propeller while motoring.   It is possible to use a
regulator with a current limit adjustment that would limit the horsepower
required of the engine.  This would allow you to use a larger output
alternator while at ancor for full output and use current limiting while
underway to lessen the horsepower draw on the motor.

Great care must be taken to properly mount the alternator to the engine.  If
the alternator is out of alignment or loose it will self destruct.  Be sure to
use a grade 8 bolt for the pivot bolt not stainless steel.  Stainless is too
brittle to use around the engine.  Most alternators will only need one belt if
it is a 1/2" width.  If your engine has only a 3/8" pully on the alternator
and engine you may need double belts.  The belt(s) should be a Heavy Duty type
with cogs on the inside for longer life.  Gates belts are the best for this
type of use.

Next, a quality multi - step regulator is needed to get a fast and full charge
from the alternator to the batteries.  A three step type regulator should be
considered for maximum charging efficiency and care for the batteries.
Choose one that will  adjust to your type of batteries (gel or wet) and if
needed, current limiting.  The faster you get to full charge the less running
time will be needed.

The difference between wet or gel battery charging is considerable and
precision is required to achieve full charge.  Wet cell batteries will accept
in charging amps between 25% - 40% of the total Ah rating.  For example a 200
Ah battery will accept between 50 and 80 amps in the bulk charge (step one).
A gel  cell battery will  accept 50% of the Ah rating (i.e.100 amps) in the
bulk charge.  Once the batteries reach the absorption stage (step two), the
voltage will be constant and the amps will decrease to 25% of Ah capacity down
to 5% of capacity.  The absorption voltage for  wet cells is 14.4 vdc, for gel
cells it is 14.2 vdc.  The regulator must be able to adjust to the required
voltage depending on which battery type you have installed.  The third and
last stage is "float" and both types of batteries should be set at 13.65 vdc
to keep the batteries fully charged.

All the systems on the boat MUST be inspected and maintained properly on a
regular basis.  This will help prevent failures and problems that plague many
sailors.  All equipment and systems should be installed with care to prevent
water damage, corrosion and physical damage.  If you don't know already, boats
are a very harsh environment for anything electrical.  All wire connections
should be soldered and heat shrunk to insure water tight integrity.  Keep
things DRY and CLEAN!!

Lastly, you need to manage your use vs. supply to abide by the 50% discharge
rule and keep your systems with the proper voltage.  This can be done with a
simple amp / volt meter, but they lack accuracy and require close accounting
of amps being used.  The volt reading of a battery  doesn't  give you an
indication of the state of charge while it is in use.  Monitor systems that
keep track of amps, volts and Ahs consumed take the guess work out of managing
your supply and give you the information all in one place.  There are many
types of monitors in different price ranges with a wide range of information
and accuracy.  With a good monitor, management is easy.  Consult with a marine
professional to help with choosing the right system for you.  Accurate
monitoring is key to the longevity of your well designed and properly charged
battery system.

In conclusion, if you take the time to design a system for your needs, install
it properly, use quality equipment, maintain & inspect the system and properly
manage your supply you will be among the many sailors who have more time for
FUN on their voyages.


If you should have a question , give Ron Romaine a call at:

                                           Farallon Electronics
                                           2346 B Marinship Way
                                           Sausalito, CA 94965
                                           (415) 331-1924

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