Degowsing Gear

[philipmthompson]

Does anyone remember the Degowsing Gear that used to run all the way round a tankers deck underneath the handrail,I was told it gave off an anti magnetic force that detected mines ,i cant remember it ever being used and i done a couple of years or more with BP,we went through a mine field up the Baltic but we had a pilot on board,maybe it was used then.PHIL

[Jim Brady]

Hi Phil,our you a "Scouser" or you sailed with "Scousers"it's actually called the Degaussing Gear,but like you I always thought it was the Degowsing Gear.I know it was definitely still aboard the Millais,when I was gallley boy I used to stand on the cover of it to dump the rosie over the wall,and I think it was still aboard the Eastbury whenI sailed on her.
Regards.
Jim.B.

[Lou Barron]

hi guys it was used on most ships in the war it was for the magnectic mines and also on ships i was on we had what they called paravanesi think that is how it is spelt these was used on the mine sweepers to they were but into use going in and out of some ports i do remember one time of seeing a floating mine and a mine sweeperblowing it up that was going up the firth of clyde

[robpage]

egaussing
Degaussing refers to the process of neutralising the magnetic field around an object. The process can be applied to any magnetic material, but originated during World War II when then Commander Charles F Goodeve RNVR developed the process as a countermeasure against Germany's magnetic mines, deployed against the British fleet.The copper wire fitted to Merchant vessels was at the cost of H.M.Government . The newest ship I ever sailed on with this fitted was built around1960. There were also often large sections in holds etc that had gone missing , and the copper had fetched a good price ashore


The magnetic mine contained a sensitive magnetic sensor, calibrated in milligauss. One milligauss is one thousandth of a gauss, the measurement unit of a magnetic field, named after the German mathematician and physicist Carl Friedrich Gauss. These highly sensitive detectors could detect the passage of a ship above them as it concentrated and distorted the earth's magnetic field, and they were set to trigger the mine when the signal reached its maximum, indicating the ship was at its closest approach. Unlike contact mines, which detonate against the target with the intention of causing a hole, the magnetic mine is a proximity device, intended to disable or destroy its target through the distortion caused by the blast or shock wave generated by its explosion.

Magnetic hysteresis means that degaussing is not generally able to reduce the magnetic field around an object to zero, nor would this be desirable as the mere presence of a magnetic material in the earth's magnetic field will distort and concentrate it. Goodeve's system was developed to produce a known residual, or bias, field in the vessel being degaussed. This bias field was set to be equal and opposite to that of the vessel, with the result that it effectively cancelled out the distortion the vessel caused as it passed through the earth's magnetic field, making it temporarily indistinguishable from the magnetic background.
Although the system was very successful, it was not a permanent solution, and had to be used correctly. As ships pass through the earth's magnetic field, it tends to magnetise them, and orders were issued instructing captains to make frequent changes to their direction of travel in an effort to minimise this effect. Degaussed vessels had to return to port at regular intervals (between four and six months) to have the process repeated. The polarity of the signal was dependent on their direction of travel, meaning that different magnetic polarities had to be used dependent on whether they were operating in the northern or southern hemisphere.

The original method of degaussing ships was referred to as Coiling, and required required each ship to be equipped with its own set of degaussing coils and supporting equipment to power them and generate the required electromagnetic field. While this method had the advantages of being able to maintain the vessel's magnetic bias continuously, and reverse its polarity for operation in either hemisphere, its complexity and cost meant it was not suitable for installation in all the ships that needed it. This method was used on many British cruisers and battleships, protecting them as they were deployed around the world during the conflict.

Goodeve developed a much simpler and cost-effective for degaussing vessels, known as wiping. Instead of installing coils and control gear in every ship, Goodeve reversed the system and located the equipment at land based Degaussing Stations. Ships would visit these sites periodically, and a cable carrying the degaussing current would be dragged over the hull. The electromagnetic field generated by a high current passing through the cable induced the required magnetic bias into the hull as the cable passed over it, with magnetic hysteresis maintaining the bias thereafter. The cables were substantial, carrying current in the order of 2,000 A. Although there were fears that the constant pounding of the sea, and inherent vibrations in the ship would lead to the bias being dissipated, the main problem was magnetisation of the hull as it passed through the earth's magnetic field and, as noted above, this was minimised by ensuring frequent changes of direction were made whenever possible. The bias on wiped ships gradually weakened over time, and they would be scheduled to visit a Degaussing Station to have their bias restored two or three times each year.


A similar result can be achieved using external coils without dragging the cable over the hull, in which case the process simply referred to as degaussing. In this operation, the coils are either located beneath, or floated around the the ship. Rather than dragging the heavy coils over the hull to distribute the electromagnetic field, a higher initial current (anything from 3,000 A to 4,000 A) is used to generate a larger field. By reducing the magnetising current slowly, and avoiding a rapid collapse of the induced magnetic field, magnetic hysteresis acts to maintains the bias in the hull.

The degaussing process was not arbitrary, and had to be carried out accurately to be effective. Applying to much bias, or assigning the wring polarity could have disastrous results. In order to determine the required bias level, ships would visit a Degaussing Inspection Station, where they could be tested, and magnitude and polarity of their initial bias could be measured. Once they had been wiped, they could be retested to determine the effectiveness of the degaussing, and wiped again if the process had not had the required effect. Several passes could be required in some cases.

The inspection station comprised a shore based station which housed the test equipment, and a test loop which would have been laid on the seabed. In operation, the ship being tested would be required to pass over the test loop while the signal generated in the test loop would be detected by the equipment in the station. This would provide a recording of the magnetic signature of the vessel, which would be calibrated and used to determine the required setting of the degaussing equipment.
One such monitoring station is known to have existed at Portkil, on the Rosneath peninsula.


The same degaussing techniques were adopted by the Americans to provide similar protection to their steel hulled vessels, and created their own name to describe the process, which they referred to as deperming, a reference to removing or neutralising the inherent permanent magnetism of steel hull

The early wiping system only removed the overall bias of the hull. Later system have become more sophisticated, with monitoring and wiping of the magnetic signature taking place in all three axes to ensure that the bias is effective in all directions.

Development of magnetic mines has also continued, with their sensitivity being greatly increased by having them detect changed in the magnetic field around them, rather than the field itself. This means they can detect small anomalies produced by spots that wiping either misses or cannot reach.

So the mines advanced and the cables went to the scrap man , the calibration process was off the Tail of the Bank , and you steamed up and down several times , whilst the RN took your magnetic signature ,. I am pretty sure I only did this once around 1966 .

[Richard Quartermaine]

In 1947 it was on the Port Line seconded MV Lowlander (Formerly 'LEME" of Navigazione Libera Tristina - that's what our bed top covers had written on them).

Like you Phil, as the Engineers Boy/Saloon Boy I dumped the Rosie whilst standing on the cover. The tubular housing went right around the ship just above the scupper.
Richard Q

[Louis the Amigo]

Hi shipmates, I remember it well in my time at sea, After storms now and again ,one of them mines things would pop up some times,but we had a royal navy in them days, with mine sweepers to deal with them. I was allways lucky so never came across one only on the Quayside to put money in for the life-boats, but trawlers would sometimes catch one in they nets? or trawls' could be very nasty? but the fisherman had great skill on the wooded cynets in them days .

[Pat Marshall]

RMS Aragon was fitted with degaussing gear despite being laid down well after WW2. I used to have to switch it on prior to coming into the Thames Estuary, then off once berthed in the Royals. There was a slight hiccup when an official, presumably from the Admiralty, came aboard and found the box for adjusting the settings unlocked. A mild wigging and that was the end of it.

[Gulliver]

Thanks to Rob Page for that clear explanation of Degaussing in post # 4.Real text book stuff !
And to Quote from Pat:-
　
‘RMS Aragon was fitted with degaussing gear despite being laid down well after WW2’

　
Does anybody know when Degaussing Equipment ceased to be fitted to Merchant Ships?…or perhaps even which ship it was? Pat above mentions the ARAGON was fitted with it and she was built in 1959.I also read somewhere that certain BP Tankers built in 1959 were still being fitted with it too.
I have a feeling it was in the early to mid-1960's that fitting of it was discontinued..Of my ships of the period I remember the SHROPSHIRE,also built in 1959 was so equipped(although when I was on her in the early 70's it was disused). I remember the cableways running through the tweendecks,and the controls for it were in the focsle head.
I cannot remember whether another of my ships,the DERBYSHIRE built in 1966 was fitted,although I don't think so.
Another vessel I stood by building in 1974 was certainly not fitted with degaussing. Which makes me think that my timeline of early to mid 60’s might be correct?.Certainly all those ships mentioned above were 1959,so were probably the last.
Also Rob seems to remember his ship using the degaussing range in the Clyde around 1966.
　
　
I wonder if Degaussing Ranges are still marked on nautical charts? or if there are any Degaussing Stations still left.? They are charted designated areas which ships can traverse They have coils on the seabed leading to the degaussing station where readings of a ships magnetic signature by the range officer are passed to the ship for the adjustments to be made to the coil in the ship’s degaussing system.
So,anyone know the last ship(s) to be fitted with Degaussing Gear?
Gulliver
　
　
　
　

[Doc Vernon]

Nice interesting Post this one,and although i must admit not knowing much at all about it,i am reading a lot on the Subject now!

We live and learn! No matter how old we get!

The following is a Site which to me is very good as well, and possibly some would agree!
Its from the SN Site,hope mo one minds!
Thank for this Post

I must also say that there has been a lot posted here by others and this too is also very good reading! Thanks to all who have thus far contributed to this Post
Cheers

http://www.shipsnostalgia.com/guides/Degaussing

Some more info!

http://www.xs4all.nl/~eeuwen/Degaussing.htm

http://www.phys.unsw.edu.au/~tmb/The...troduction.PDF

I have given it a 5 Star Rating!

[Gordon Brown]

The wire around the ship helps to reduce the magnetisim which helps in the defence against magnetic mines. I once read that drydocks were built north- south for the same reason. Another principal is the Bassets Balls on a binical compass. These were used to reduce the magnetic field around the compass.