too many boaters, having a flat battery is
Without power they can’t even use
the radio to call
out the lifeboat.
They are condemned to
drift like ancient
alone on a wide, wide sea.
Lost without the GPS and
unable even to eat without the
microwave, which is probably as well, since the pump for the heads is also
Looking for an Electrical Panel?
And when, if ever they do
reach the marina again, the
skipper with his long, gray beard and glittering eye is first ashore,
in his skinny hand, not a wedding guest but the power lead.
Before even tying up, shore
power is reviving the
blinking lights and tweeting gadgetry, causing lights across the town
as power is sucked from the local grid.
So how much power is needed?
Well the short answer is that
it isn’t necessary to
My first little cruiser had
But then she had no radio and
no proper navigation lights
and no electronic depth sounder to name but a few of the aids which,
would be loath to set off without now.
Navigation was all DR
pilotage, GPS being still but a
twinkle in someone’s eye.
Night sailing entailed keeping
a constant watch and
taking huge detours around anything which did have lights showing, and
clutching a torch in the hopes that shining it on the sail might make
visible in an emergency.
However, those were primitive
Nowadays it seems, even to
rather silly not to take advantage of the miraculous advances which
made in the use, generation and storage of electricity on board small
Unfortunately there is a huge
Electricity and water do not
mix, nor do electronic
devices like damp environments.
So while it may be silly not
to take advantage of these
inventions, it is even sillier to be totally dependent on them.
I am pleased to boast that I
have rewired a previous boat
and that I installed the complete wiring system on Mignonne which, does
However, I must admit to
having less understanding of the
logic of the average circuit diagram than of an Australian Aborigines
And some of my wiring is more
Rastafarian hair style than
For those who are in that
select group who repair the
Christmas tree lights by juggling a hand full of duff bulbs, kicking
when they still don’t work, then going out to buy a new set.
Never fear if I can get my
boat electrics to work, so can
However, for the best
practical and technical help and
C Payne, marine electrician and best selling author of
Electrical and Electronics Bible” as well as many other boating books
sailboats and yacht systems.
The basic set up on a boat
is akin to that on your car.
need a battery to start the engine and
while the engine is running
it will be turning an alternator which produces enough electricity to
re-charge the battery and run the lights, the radio and such like.
However, anyone who has
switched their car engine off but
left the lights on, will know that the cranking battery will soon go
So on a boat, where you
want to use power while the engine is off, when sailing or at anchor
need at least one more ‘domestic’
This is the normal car type starting battery.
It is designed to give occasional short bursts of a large
amount of current specifically to turn the engine starter motor.
But it doesn’t like being used for long periods nor will it
take kindly to being run flat.
These are designed for use on electric trucks, golf carts and
the like, which are deeply discharged every day.
They are long lasting as they can tolerate numerous deep
discharges and recharge cycles.
However, they are large, heavy and expensive.
These are the usual ‘Domestic’ or deep cycle batteries found
on small boats.
They are designed to provide small DC (direct current)
voltages but over a longer period.
They have slightly thicker lead plates than ordinary cranking
so they can withstand deeper discharges and are much more tolerant of
being run flat.
However, they are of the unsealed lead acid type, so must be
maintained by topping up the cells with deionized water.
This also means that they will spill acid if tipped over, and
produce oxygen and hydrogen gas if they are overcharged, this
must be vented to avoid explosion.
These leisure batteries give you the most power for your
they have a shorter life expectancy than more expensive batteries.
With these the acid is gel-like therefore unlikely to leak if
the battery is tipped over.
An ideal ‘domestic’ battery that can withstand many charge
They are maintenance-free and have a low self-discharge rate.
Absorbed Glass Mat (AGM) Batteries
These (AGM) batteries avoid leakage by containing the acid
within glassfibre mats in between the plates.
They can accept high charging voltages and many charging
They are particularly suitable for high current applications.
They are maintenance free.
Spiral Cell Batteries
These also use glass-fibre mats to contain the acid but the
lead plates are larger, thinner and wound in a spiral.
They can accept higher charge rates and tolerate much more
shaking and vibration.
They are expensive.
Lithium Ion Batteries
The latest developments in high capacity lithium-ion
beginning to provide a viable alternative to traditional lead acid
While they are about three times the price of a normal
leisure battery they are reputed to last three times as long,
And they are about a third of the weight of an equivalent
Lithium Ion batteries have a level power curve, which means
have full power until the battery is dead, so little warning time
before you have no power.
But they can take many deep discharges and can be
charged up to
90-94% of their capacity in a third the time of a lead acid battery.
However, charging needs to be closely controlled.
Whether or not weight is an issue on your boat they might be
worth the investment in the future if the price begins to drop.
Faulty electrics and
poorly installed electrical systems are a source of potential hazard to
Short circuits and
cables are both common causes of boat fires.
While complicated wiring
systems are best left for the
qualified electrician part of everyone’s routine maintenance should
involve checking for any worn or damaged cables or wires and having
repaired or replaced.
Check that cables particularly
battery cables are
Make sure that your fuses and
correctly rated for the circuits they protect.
And reduce any potential risks
from flammable hydrogen
gas, produced when charging your batteries, by stowing them in a secure
But above all learn how to
cope without any electrical
power or associated gadgetry.
Don’t allow electrics to
become an albatross
weighing you down, spoiling your enjoyment or putting you in
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I am perfectly aware that the majority of Wooden Boat aficionados are sensible folk. However, I need to point out that I am an amateur wooden boat enthusiast simply writing in order to try to help other amateur wooden boat enthusiasts. And while I take every care to ensure that the information in DIY Wood Boat.com is correct, anyone acting on the information on this website does so at their own risk.