Mine Sweepers

[norgale]

I'm watching the Caine Mutiny and I thought mine sweepers were all made out of wood. This ship is all metal. I missed something somewhere,ya think?
Pete

[CG Bob]

The ADMIRABLE (http://www.navsource.org/archives/11/02136.htm) class minesweepers used the same steel hull as the PCE's (Dumas USS WHITEHALL (http://www.navsource.org/archives/12/02856.htm) kit). Degaussing (http://www.fas.org/man/dod-101/sys/ship/weaps/degaussing.htm) systems changed the magnetic characteristics of the hull so magnetic detonators wouldn't explode.

Incidently, the degaussing system makes a ship "virtually invisible"; and this maybe one of the rumors or part of the conspiracy theory behind the USS ELDRIDGE (DE 173) and the Philadelphia experiment.

[jeno]

Many WW1 destroyers were converted to mine sweeping destroyers during WW2

[nick_75au]

Technology has caught up with them, now made of fibreglass, the Australian boats were at the time the largest moulded single monocoque skin with no ribs or framework.

The fibreglass providing increased shock resistance and a low magnetic signature when compared to conventional metal-hulled vessels.
Nick

[mfr02]

Many WW1 destroyers were converted to mine sweeping destroyers during WW2
Dont forget the change in technology - WW1, no magnetic mines, these were new for WW2, along with acoustic mines and pressure mines. These, having been put into operation, immediately caused counter measures.
Most minesweepers were small, and many were requisitioned fishing boats, which were wood anyway. Degaussing didn't just happen on sweepers. most ships got fitted in WW2.

[norgale]

I read about a "wiper" which is a long wire with 2000 amps of power in it being dragged under the ship as an inexpensive way to counter the magnetic field of the ship. That must have been pretty dangerous never mind how many fish would be killed. That's a lot of amps. How would that much amperage be generated onboard a ship? Pete

[mfr02]

You could be thinking about the LL Sweep, two cables towed out behind the sweeper and fed with current from an on-board generator and arranged so that they would separate, giving a very wide "ship". The idea was to detonate magnetic mines over as wide a corridor as possible, preferably when the minesweeper was well clear. There are stories of close detonations destroying the ships crockery and much of the glass.

[norgale]

Might be the same thing mfr02 but in the article it called the wire a "wipe".

[TEMEAD]

Norgale
as a former navy electrican we were responsible for the ships degaussing systems. what i think you are discribing is the process of deperming. Deperming is a procedure for erasing the permanent magnetism from ships and submarines ( submarines have no degaussing systems) to camouflage them against magnetic detection vessels and enemy marine mines.

A sea-going metal-hulled ship or submarine, by its very nature, develops a magnetic signature as it travels due to a magneto-mechanical interaction with the Earth's magnetic field. This signature can be exploited by magnetic mines, or facilitate the detection of a submarine by ships or aircraft with magnetic anomaly detection (MAD) equipment. Navies use the deperming procedure, in conjunction with degaussing, as a countermeasure against this.

Specialized deperming facilities, such as the United States Navy's Lambert's Point Deperming Station are used to perform the procedure. Heavy gauge copper cables are wrapped around the hull and superstructure of the vessel, and very high electrical currents (as high as 4000 amps) are pulsed through the cables. This has the effect of "resetting" the ship's magnetic signature. It is also possible to assign a specific signature that is best suited to the particular area of the world the ship will operate in. Over time the deperm will begin to degrade and the procedure must be redone periodically to maintain the desired effect.

[Shaun Hendricks]

Must've played merry heck with any CRT's and magnetically sensitive instruments inside the ship!

[TEMEAD]

magnetically sensitive equipment would be removed if possible prior to deperming and all CRT's already have a built in deguassing coil to maintain the alignment of the electron guns

[TEMEAD]

Norgale, We also had a magnetic sweep tail which was pulled behind the ship and was pulsed with either a positive or a negative DC voltage at a high amperage to create a magnetic field in the hopes of exploding any magnetic mines in the area.

[Prins Willem]

The Caine in the movie was depicted by USS Thompson DMS 38. According to wikipedia in Herman Wouk's book the Caine was a converted four piper. In 1954 there were no four pipers left so the Navy let them uses a contemporary ship. DMS's were destroyers fitted with sweep gear as opposed to mission specific vessels. Look up YMS minesweepers for examples of wood hulled dedicated ships. Cousteau's Calypso was a YMS.

Peterson Builders in Sturgeon Bay WI was the leading builder of wood hulled vessels. Just before they closed shop they built the Avenger class MCM along with Marinette Marine. During WWII they made several subchasers for the Navy.

[norgale]

Well that certainly is a lot of information. I never would have imagined that they could wrap a whole ship in copper wire to demagnetize it or change it's magnetic field. Pretty interesting especially when you realize how much more there is to a ship than just putting the pieces together and setting it in the water. Maybe if a mine was attracted to the ships metal they could reverse the polarity of the ship and repel the mine. Too simple hey? My seventh grade science kicking in, Ha! Pete

[nick_75au]

There are mines now that can discriminate a single ship out of a class of ships and only detonate for that ship. They have pressure, magnetic and acoustic sensors and a microcomputer.
Most mines sit on the seabed, very few countries would use floating mines nowadays. The scariest would be the captor mine which sits on the bottom awaiting its victim and releases a Mark 46 Mod 4 torpedo. Its primary use is for submarines.
Mine hunting close to the heart as I am a plank owner M85 HMAS Gascoyne. We did do some mine sweeping as well using essentially the same Oropesa sweep invented at the end of WW1. It was developed from side trawling gear substituting cutters for the net and using a float to set the depth of the wire.
Nick

[mfr02]

The magnetic mines, as opposed to limpet mines, were not actually attracted to the ship. The idea was that a large object like a ship hull passing over, or near enough, would alter the ambient magnetic field strength, and trigger the mine.
The limpet, on the other hand, was an explosive charge with a brutal great magnet to fix it to a steel hull until it was no longer wanted, and had to be placed by hand.

[norgale]

The torpedo thing is scary. Is there no limit to the destruction that people can think up for each other? Glad I'm not in the subs. Pete