Old time Radars

And a trip out on the bridge wing to listen. Those breakers could probably be heard miles away.


The sea at the time was reported 4 meter swell and 2 meters seas. From the wing of a ship underway how far out can that be heard in average conditions?

For reference here’s some values from COLREGS

Length of vessel in metres 1/3-octave band level at 1 m in dB referred to 2x10-5 N/m2 Audibility range in nautical miles
200 or more 143 2
75 but less than 200 138 1.5
20 but less than 75 130 1

At 130 db, equivalent to a jackhammer, hearing protection is recommended, the distance is one mile. For 140 db, equivalent to gunshots it’s 2 miles.

Listening to detect breakers was a method we used on ships with no functioning radar, or other electronic means of navigation, when I sailed Australia to PNG and other South Pacific Islands, where charts were not always reliable and no navigation aids, like lighthouses and buoys around the islands…
We obviously didn’t have anything to measure the exact distance when you could detect the reef by the sound, but it was far enough to turn around and wait for daylight, or until the first cooking fires were lite on shore, before approaching again.
On clear nights you could see the breakers at about the same time you heard them

BTW; the first indication of the existence of a reef, or an island, was the changing motion of the ship from the backwash.

I do not expect that anybody sailing on modern ships, with all kinds of electronic aids to navigation would even notice backwash, or think of listening for breakers.

PS> I was Ch.Officer on two ships in this trade, from 1968-70. Here they are:
Slidre, built 1938:
FRE54119660120001 SLIDRE

Slidre Timur, built 1952:

Don’t be fooled by the radar scanners you see. The Decca Mk.1 radars on both did not work and no spare parts available to get them to work.

PS> Both ended up as wreck. Slidre Timur on Parker Reef, Qld. in 1971. Slidre of Gabgab Beach, Guam in 1976.


“Don’t be fooled by the radar scanners you see. The Decca Mk.1 radars on both did not work and no spare parts available to get them to work.” :laughing: Racal Decca!

Back then, radars were a luxury. You could count on them to go dark just before you needed them most, like when you are about to enter the Dover strait, especially in poor visibility and heavy traffic.

When I first joined the Slidre in Jan 1968 there were a stack of receiving crystal available.
To get the radar to work for a short period (20 min. or so) I had to climb up to the scanner to replace the blown ones. We run out before going to Australia in April 1968.
That was only done when the radar was ABSOLUTELY needed. (Usually in atrocious weather)

PS>The crystals blew because the TR Cell that was supposed to protect them from the outgoing signals were faulty. No replacement was available.

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We also had no spare cell but also no crystals. Sometimes the T/R cell was okay but the keep-alive voltage of 300 - 800 V negative was missing or too low. Gas discharge tubes take time to turn on, and longer to turn off again. Often a keep-alive is used to prime the cell ready for action, that voltage did keep the gas in the T/R cell just below the point of ionization.
A small portion of the transmitted radar signal was let through the cell to serve as the main bang, zero range signal on the display.

When I went to sea we were the first lot that were taught radar in school. After the examinations we got a certificate to proof it.

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“PS>The crystals blew because the TR Cell that was supposed to protect them from the outgoing signals were faulty. No replacement was available.”

We are going of topic but need to respond to this statement.
In 1950 Decca launched their first commercial radar type 159 with 9 inch display and double cheese array, 4ft and upmast transceiver. The Dutch Willem Ruys was outfitted with this radar. This radar was followed quickly by the type 12 with 12 inch display and reflection plotter with same array/transceiver.
In 1952 Decca introduced the type 45 with 6 ft double cheese array and upmast transceiver and in 1955 this was followed by the TM46 with true motion. All these radars had the double cheese arrays, upper part for transmission and lower part for receiving. They had no TR cell. In the late sixties the 45 and TM46 transceivers were field modified and fitted with a TR cell, believe it was a QF45, reason being that when in close proximity of another ship or with strong return signals like in the Panama Canal they would blow up or deteriorate the receive crystal.
In 67/68 the Johnson liners, equipped with 45 radars, had NO TR-cells.
We would advise captains not to use the radar while transiting the Canal.
159 display
159B array

TM46 display with true motion unit.

From the pictures it appears that both ships have the double cheese antennas, difficult to guess whether it is the 4 or 6 ft. I left the Caribbean in 1981 and up to that time we had ample spares, including salvaged replacement upmast transceiver trays!

Needless to say that due to not having waveguide losses the radar-pictures on these early systems were excellent!

Decca was highly popular and fairly reliable. In 1979 they had 50% of the marine radar market. That has changed big time, they only have a fraction now.

Found a schematic diagram of the type 159 and 12 transceiver and apparently the TR was optional. Note on diagram: “A BTH BS52 gas TR switch was included in some models to protect the mixer crystal. When present, it is inserted in the receiving waveguide directly after the RF unit input flange.”


all i can say folks is i was usually far from land and any sound of breakers even now gives me the heebie jeebies.

My second ship only had the one radar and it was forbidden to use it in daylight (unless it was foggy of course).
When it broke the Old Man questioned whether or not it was possible to fix it with a valve out of the TV.
It wasn’t.


And whatever you do, never, ever turn it off. Leave it on stand by, even in port for dayds at a time. Turning it on and off will “blow out the tubes.”

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That’s me at nineteen showing my muscles…

I am sitting in front of the BTH radar cabin with the double cheese antenna, some called it a double half moon antenna. The cabin was stuffed, apart from the radar transmitter, with spare parts and measuring equipment. Never seen so much spares. There were two universal voltage and current meters, soldering irons and an oscilloscope. The cabin had an electric heater and ventilation system system for cold and warm weather. The second mate got rich on the maintenance. He used to retire quite often with his smokes in the cabin for “maintenance”.

The captain’s nightorders said, amongst other things, “If the radar has to be switched on wake the captain”. Needless to say that during the sleeping hours of the captain the radar was never switched on. That was a dangerous little sentence…


Everyone knows it would need a valve out of the fresh water system. . . . .

Us second mates had a full on day. My cabin had an alarm for the gyro and one for each hospital. Mercury pots, clamps and latitude riders, just think what you young 'uns are missing out on.