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Underwater Search & Recovery Techniques

    Caution      

While these techniques have worked well for me, I am not advocating their use by others. I am not a trained professional nor a certified instructor.
Lift (recovery)

Underwater lifting is physics coupled with safety concerns. Your choice for lift methods will depend upon the value , bottom composition, distance from land recovery point, water depth, visibility, size and weight.

For small items throwing it in a mesh bag or recovery container is simple and easy and is not covered here except to identify certain technicques to maintain an objects value. Items which may oxidize when removed from water should be placed into a sealed water filled container before reaching the surface. Items which have forensics value should be recoverd using the specific techniques expected to retain the most information for study and should not be handled excessively or exposed to contamination of outside materials which will confuse the data collection.

Physics : when calculating the lift requirements you must take into account the objects weight in air minus the water it displaces When transitioning from water to air you must take into account the effective total weight, plus any portion of the object that breaches the air/water barrier loses it's 62-64 lbs of support per cu ft.

MaterialDensitylbs per cu ft   MaterialDensitylbs per cu ft
Pure water 1.00 62.4Sea Water 1.03 64.08
 
Aluminum 2.64 165   Ice 0.92 57.4
Brass, Cast 8.56 534 Iron, cast 7.21 450
Bronze 8.16 509 Iron , wrought 7.77 485
Cement, Portland 1.6 100 Lead, cast 11.35 708
Cement, mortar 2.16 135 Limestone 2.61 163
Concrete, Gravel 2.4 150 Marble 2.56 160
Concrete, Limesone w/Portland 2.37 148 Mercury @ 32oF 13.61 849
Gold, 24kt 19.29 1204 Porcelain 2.4 1550
Granite 2.69 168 Steel, cast 7.85 490
Hydrochloric Acid 40% 1.2 75 Tin, cast 7.36 459

( under construction )
Surface Lift
Single Lift
Multi Stage

pro/cons
pro - safest for divers - attach and leave the water or observe at a distance.
con - brute force requirement might be a problem for non-commerical vessels

Buoyant Lift - Lift Bag , Drum - open bottom, resticted bottom, pillow
Single Stage
Multi Stage

Combo Lift (Surface + Buoyant)

think displacement

salt water / fresh water differences

next: Preservation



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