Issue 1
April 2012
Section 10
Electrics and Instruments
Original Arrangements
When these boats were built, very little was fitted as standard. All interior and navigation lights,
the battery, and log and echo sounder were all 'standard' extras. A 'cable loom' and switch panel
were fitted, but it is now unclear about what facilities these provided. The wiring diagram in the
Reference Library
Wiring
Diagram
gives a good indication of how the various electrical items could
have been wired. Advances in technology, members' ingenuity, and the depth of their pockets,
have resulted in boats now equipped in vastly different ways.
Batteries
Most boats now carry two batteries with a change-over switch such that either can be used for
engine starting, or to feed domestic needs. If only one battery is fitted, it must have an isolating
switch. The primary engine battery should be located close to the engine to minimize voltage
drop when starting an in-board engine. Charging is usually done by the engine alternator, and
often via a 'split' arrangement whereby the charge is fed only to the 'low' unit; an article in the
Reference Library, below, describes one method. Batteries require maintenance, particularly in
terms of cleaning corrosion from the terminals and greasing them, though few now need the
electrolyte to be topped up. Securing arrangements for these heavy items need to be robust to
withstand the abrupt motion of the boat in rough water. Given the propensity for all 23s to list to
port, placing one battery on the starboard side of the boat is a useful ploy. Leisure-type batteries
are the most suitable for marine use, since they can stand being discharged to a lower level than
standard car batteries. But no unit should be discharged to less than 50% of its capacity
otherwise its life will be shortened. A condition meter is useful in this context, such as available
from
RS
Wiring
All wire used on boats, both for 12 volt and mains wiring, should be multi-strand and not solid;
the latter can fracture with vibration. Ideally, this should be tinned copper wire, and it MUST be
heavy enough to carry the current of the items(s) it is serving, otherwise it can overheat and
cause a fire. The table below gives an indication of different sized wires and their current-carrying
capacities:
Sample data re current carrying capacity etc
Each piece of equipment served should be protected by an individual fuse; the item below 'Fuses'
covers this topic in depth.
The weakest points of any electrical circuit are usually the connections, and particularly so in a
marine environment. Deck connectors are very susceptible to corrosion – and difficult to clean.
On one 23SL, all the mast cables are routed through deck glands and are connected inside the
boat, in the ceiling recess in the forepeak, as pictured below.
24
Dia of strands
(mm)
No strands
Approx area
mm
2
Approx max
capacity (Amps)
0.2
24
0.75
4.5
0.3
14
1
9
0.3
21
1.5
13
0.3
28
2
17
0.3
44
3
27
