Cruising Helmsman - July 2018

Of course as we age these transitions take
longer than when we were younger.
Despite our eyes remarkable flexibility,
we can help them adjust to this change
by wearing sunglasses during daytime;
especially out to sea where we have both
the direct sunlight plus the reflections off
the deck and water. As daylight fades our
eyes will naturally adapt to the lower light
levels so that by night time we are as well
prepared as possible.
Once the sun has set we now need to
retain our night vision, which can be
destroyed rapidly by looking into any bright
lights irrespective of colour. The current
most popular method is to equip our
internal spaces with low intensity red lights.
This has been the solution to the perennial
problem of maintaining night vision in
boats for a long time. The warships at the
Australian Maritime Museum used this
technique while they were in active service.
This has been proven to help retain
our night vision, however there is recent

research suggesting that low level cyan-

green light maybe a better alternative

since this is the region where rods are

most sensitive. It also has the added

benefit of retaining the ability we have

of detecting other colours, on maps for

instance. Whatever solution you choose

the important message is low level light

irrespective of the colour.

However we are not all as disciplined as

the Navy so while Editor Phil was visiting

a sailing club a clever sailor told him of

his method of keeping white lights away

from the cockpit crew. He had installed

a switch that automatically turned the

white cabin lights off and turned red lights

on automatically when the navigation

lights were switched on. Unfortunately he

did not explain how he did this so here are

some thoughts how I might do it.

A technique my friend used was to place

a simple curtain across his companionway.

He was colour-blind and had trouble with

some colours including red so the blind

was a great method of keeping his night

vision intact.

He was an interesting person to share a

watch with as there were things he could

see that I could not. His curtain was made

of heavy canvas weighted at the bottom. It

kept out unwanted sightseers, rain and, at

night, kept any stray light in. Any technique

you choose to use needs some intelligence

so it is not possible for every situation to be

covered. Think how you use the boat and

adapt it, but the ideas here might just help.

Having a small light in the compass,

whether it is red or, like mine, a dull

white light, will also help preserve night

vision. Most chartplotters have a night

mode where the brighter screen image is

reduced. Some do this automatically but

you may need to reduce it even more by

placing a piece of smoky film or plastic

over the screen if brightness controls are

not available or adequate. Do not forget

the other instruments that are back-lit,

they may need to be made night friendly.

23

http://www.mysailing.com.au

CLOCKWISE FROM LEFT: The

various switch typed commonly

used in yacht switch panels.

The computer screen viewed

through polarised lenses in the

correct orientation.

A computer display is polarised

and so will be blocked if viewed

through polarised lenses

in the wrong orientation.

The LCD GPS screen is

polarised and so will be blocked

if viewed through polarised

lenses in the wrong orientation.

Switch types used

in these circuits

SPST Single Pole Single Throw(simple on/off switch)

SPDT Single Pole Double Throw(Two outputs)*

DPST

Double Pole Single Throw

(simple on/off with two

circuits. Both groups of

contacts move together)

DPDT

Double Pole Double Throw

Both groups of contacts

move together*

*These have a centre off position