Home' Afloat : AFLOAT October 2015 Contents 58 AFLOAT.com.au October 2015
two wire pins, albeit
slightly thicker than
on the G4). These are
called Dichroic lamps.
Most commonly used
is the MR16 with a base
for a G5.3 holder, which
have a diameter of 50mm at the widest
point and pins spaced 5,3mm apart. Less
common are the smaller MR11 with a GU4
base, which have a 35mm diameter.
Then there are the festoon lamps.
These look a bit like a glass fuse, but they
have a pointed contact at either
end. Here the length is critical to
ensure that they fit properly into the
holder, most common are lengths
of 30mm, 37mm and about 42mm.
A variation are the festoon lamps
conforming to a German standard,
that have concave, dimpled contacts at
each end, as used in Aquasignal Series
25 navigation lights.
Less common are
wedge lamps, which
are all glass, again
peanut shaped, but
with the glass flattend
at one end with
two very thin wire
over the flat end. They are identified by
a T suffix and the nominal width at the
flattened end, e.g the T5 or T10.
For all lamps, apart from the shape
and base dimensions, the Volts for the
circuit they are to be fitted in, and Watts
that define the desired brightness, must
While the use of incandescent lamps is
rapidly on the wane, it is still useful to know
what the differences in the lamps available
are, even if for no other reason than to be
able to define what LED replacement to
by Kurt Küpper*
* Kurt Küpper is director of Aquavolt
Electric Boat Parts. Tel: 02 9417 8455
So what else would you like to know? You are welcome to send in questions about
boat electrics or suggestions for topics that you would like explained.
used on boats
We are often approached by
customers looking to purchase
a lamp (globe) or an LED
replacement for an incandescent lamp
who have some difficulty in explaining
what exactly it is they require. A standard
lamp, or a boat lamp, or a 12Volt lamp is
what they ask for.
Unfortunately there are many
standards, so it may be useful to run
through the most common types of lamp
bases used to make it easier to specify
exactly what you are after the next time
you need something.
Traditionally many lamps had either
a bayonet cap or a screw base. The base
is inserted into the holder, then twisted
clockwise a few degrees while being
pushed against the contact springs to lock
the lamp into place. The size most will be
familiar with is the 22mm diameter base
used in household lamps.
On boats and in the automotive
industry 15mm diameter bases are more
commonly used. For indicator lights and
instrument lighting, even smaller lamps
with 9mm or 7mm diameter bases are
Also specified are the number of
electrical contacts at the bottom of the
base – single or double.
The bayonet cap base is
identified by the letters BA,
then the base diameter, then an
BA15D lamp with have a 15mm
diameter bayonet cap base with
two contacts. More descriptors defining
the shape and size of the lamp are often
added, but these are not so important.
An exception to note
though are the BAY15D
bases, which have their two
retaining pins at different
heights on the base (aka
‘staggered pins’). This is
usually done to ensure that
the lamp can only be fitted one way into
the base when there are two filaments in
the lamp, e.g. for automotive tail and brake
lights. On boats these bases are used for
navigation lights to make it less likely to fit
a lamp with a filament at a height that will
not optimally light up the lens of the light.
Less common nowadays are
Edison Screw type bases, which
as the name suggests require the
lamp to be screwed into the base.
Here the household size has a
27mm base, also used are 14mm
and 10mm bases. They are identified by
the letters ES and the nominal thread
diameter, e.g . ES14.
In more modern boats, halogen
lamps are extensively used. Most
common is the G4 type, which is
all glass, the shape of an unshelled
peanut (they don’t grow in plastic
packets!) with two thin wire contact
pins spaced 4mm apart.
Also used are halogen lamps with an
integral, cone-shaped reflector (also with
Aquavolt has moved a
few doors closer to the
Roseville Bridge from
No11 to No29E.
We look forward to
welcoming you to our
29E Babbage Rd, E-Roseville NSW 2069
Tel: 02 9417 8455
Fax 02 9417 8423
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