Missed this thread 1st time round, as I was offshore - thought I might add something to it. Of course, some of you guys actually preserving aircraft might know more, but I've a lot of experience of salt water and metals...
Different areas of sea have different amounts of salinity, but apart from the Dead Sea, it isn't vastly different. I work in the ROV industry using heavy workclass equipment, and occasionally if we change location (ie - a different sea) we often have to recalibrate our sonar equipment due to the change of salinity affecting the speed of sound in water, the difference between the upper and lower levels being about 200mtr/sec. Temperature also has a big difference in the speed of corrosion of metals. We carry Temperature / Salinity probes so the surveyors can calibrate their doodahs attached to our vehicle. Seabed temperature in the North Sea is typically 2-5 C, but in shallower Med waters can be a lot higher. Temps down to about 500ft have been recorded at about 20C.
Originally Posted by dsinnett
Indeed. Depending on the quality of aluminium, it will corrode quite quickly in salt water. Most of our equipment we put underwater is made of aluminium, and needs sacrificial anodes to protect it, usually zinc. Our stuff is quite thick, but I'd imagine lightweight stuff would rot pretty quickly without protection.
Originally Posted by steven_wh
Lack of oxygen does slow it down, but metals at depth corrode just as well. Depending on how tight an oil company has been in paying for anodes for their subsea equipment, we can see corrosion starting on equipment in 2000m deep equipment within months. Again, depends on several factors like salinity, quality of metal, directly exposed surface area, different alloys, or metals / minerals in contact with structures which may act as cathodic protectors. Another thing to take into account at depth is bacteria. One company I used to work for had big problems in deep, warm water off of West Africa when anerobic bacteria was found to be eating our main lift umbilical cable strands (basically wire rope cable with electrical and fibre optic cable conductors running down the middle internally). Over 3000m down, you do not want to be dropping $2m of equipment on the seabed!
Originally Posted by DaveF68
Deep water wrecks like Titanic point the way for this. The rusticles hanging off the structure is the result of bacteria eating the ferrous metals out of the ships hull. She's getting fragile and is a matter of time before she collapses in on her self. She's only lasted this long, as it is heavy gauge metal, unlike a lighter aircraft. Titanic also does not have ferocious ocean currents or wave action affecting her, since she sits in about 13,000ft of water.
For channel sunk aircraft, the tide and shifting seabed is also going to be as bad as being in salt water. Sediment propelled by tide and wave action in the relatively shallow waters of the channel are going to sandblast any airframe. I've worked in bits of the channel with subsea currents running to 5kts+. Being buried under tons of sand as the seabed moves, or getting dragged by a moving seabed or fishing nets is all going to add to the destruction of any WWII era airframe. Perhaps there is a reason for the fact the biggest bits that seem to get salvaged are engine blocks....
Again, other people might have different experiences to me, but what I've written is after a long history of looking at aluminium and other metal structures under the sea..... Pity the only aircraft wreck I've had to recover was an F-16 in the med - very little left of that!
Hope I've been a little bit informative.
Last edited by WL747; 25th September 2008 at 22:52.
"I've never killed a man, but I've read many obituaries with a great deal of satisfaction" - Mark Twain