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from a 24-volt battery bank, keeping the UPS or another 12-
volt battery (for generator, electronics/communication or
main engine start for instance) charged using a modern
three-stage charge profile. Finally, converters are also avail-
able with full electrical isolation between the 12 and 24-volt
supplies. This may be a desirable attribute for SSB or other
communication installations aboard aluminum or steel ves-
sels, where maximum galvanic protection is sought.
It’s worth noting that an undersized equalizer will cause bat-
teries to cycle more frequently, shortening their life. Gener-
ally, my experience has been that converters, because they
draw power evenly from the 24-volt bank, contribute to
slightly longer battery life when compared to a properly
sized equalizer. Equalizers, on the other hand, are more
adept at providing high current for starters and other am-
pere-hungry devices.
With the equalizer or converter installation, all of the vessels
charging systems, alternators, shore power chargers, in-
verter chargers etc, are 24 volt, simplifying the installation
considerably. Independent 12 and 24 volt systems require
duplication of all of these items.
Installation Issues and Expense
Whichever composite 12/24-volt system is chosen, com-
pletely isolated, converted or equalized, properly sizing both
12 and 24-volt supplies is critical. Calculations for daily use
are performed just as they would be for a single voltage sys-
tem. Under sizing the system, regardless of variety, is false
economy at best as this typically leads to battery failures or
poor performance. Opting for a composite 12/24-volt sys-
tem is done, primarily, to save space in wire sizing and ex-
pense. Taking a short cut will negate this benefit.
It would be unfair to complete this discussion of 24-volt e
trical systems without mentioning two particularly irksom
drawbacks to 24-volt equipment. It is sometimes difficult
source and obtain. Peruse your favorite marine retailer’s
catalog and look over the selection of 12-volt bilge pump
Now, have a look at the 24-volt selection, all three or four
them (my top of the line wholesale catalog offers six 24-v
models out of a total of 41 different pumps of all voltage
The 24 volt pumps, and other 24 volt gear, is typically mo
expensive than its 12-volt brethren, although in the afore-
mentioned pump survey the 24-volt models were just a f
dollars more than the same capacity 12-volt version.
In addition to the possible added expense and narrower s
lection present in the 24-volt world, 24-volt equipment is
simply more difficult to obtain. If you are cruising and you
24-volt starter solenoid fails, even a well-stocked electric
repair shop may be unable to get you going without havin
to order parts.
Having said all that about the drawbacks of 24-volt gear,
and many builders of medium- and larger-sized craft beli
the advantages of a 24-volt electrical system far outweig
the potential shortcomings. Whether you are preparing to
purchase a new vessel or refit an older one, give this effi-
ciency enhancing, space, weight and dollar saving option
close look.
A former full service yard manager and longtime techni
writer, the author now works with boat builders, owners
others in the industry as, Steve D’Antonio Marine Consult
His book on mari
systems will be published by McGraw Hill next year.
Boat Load Capacity
, Persons Capacity, and the
Mysterious Number 141
(continued from page 14)
result discriminated against the typical boating family of two
adults and two children whose combined weight would not
normally exceed 500 pounds. The Coast Guard does not
believe that permitting a typical boating family of four per-
sons in a boat with a 500-pound persons capacity will ad-
versely affect boating safety.
On the other hand, a boat with a persons capacity of 320
pounds is not allowed to carry more than 2 persons accord-
ing to the formula adopted. The Coast Guard believes that
the small, lightweight boats with persons capacities of less
than 320 pounds cannot safely accommodate three per-
sons, even if one or more of the persons is a child. The small
lightweight boats are generally very unstable and are easily
affected by the motions of persons on board.
Is it a violation of any Federal law for a boat operator to ex-
ceed the values displayed on the U.S. Coast Guard Maximum
Capacities label?
No. The information displayed on the U.S. Coast Guard M
mum Capacities label is intended for the use of the boat
operator as a guide in loading a boat, and, if the boat is o
board powered, in powering a boat. There is no violation
Federal laws if a boat operator exceeds the values displa
on the label.
However, some states consider overloading or overpower
a boat beyond the values displayed on the capacity label
violation and may cite an operator who exceeds posted li
its. In addition, some insurance companies will not insur
boat that is powered with a larger motor than the Maxim
Horsepower Capacity displayed on the label, and some b
manufacturers will void any applicable warranties for the
same reason.