1. Search and Recovery Recovery 1 SR v1.2 Copyright © BSAC 2009 Recovery Operations

2. Search and Recovery Recovery 2 SR v1.2 Copyright © BSAC 2009 Outline Buoyancy for lifting Weight in water Lifting bags Attaching lifting bags Air requirements The lift Is it legal?

3. Search and Recovery Recovery 3 SR v1.2 Copyright © BSAC 2009 Buoyancy for lifting Gas will displace its own volume of water Displaced water  BUOYANCY ●1 litre of water weighs 1 kg ●every litre of water displaced provides 1 kg buoyancy ●volume of gas required to displace each litre increases with depth (Boyles Law) Gas expands on ascent ●speed of ascent increases ●excess gas must be able to escape

4. Search and Recovery Recovery 4 SR v1.2 Copyright © BSAC 2009 Buoyancy required Weight of object? ●weigh one ●ask… ●estimate volume and density Weight in water ●water displaced by object provides upthrust ●weight in water reduced by weight of water displaced (Archimedes Principle) Buoyancy required = = weight in air – weight of water displaced

5. Search and Recovery Recovery 5 SR v1.2 Copyright © BSAC 2009 Example – weight of block Example – concrete mooring block 1 m  1 m  0.5 m Volume= 0.5 m 3 Density of concrete2323 kg/m 3 Weight of block volume  density = 0.5  2323 = 1162 kg

6. Search and Recovery Recovery 6 SR v1.2 Copyright © BSAC 2009 Example - buoyancy required Volume of water displaced = 0.5 m 3 Weight of water displaced = 0.5  1000 = 500 kg Buoyancy required = weight of block minus weight of water displaced = 1162 – 500 = 662 kg Use lifting bag of 700 –750 kg capacity

7. Search and Recovery Recovery 7 SR v1.2 Copyright © BSAC 2009 Lifting bags Custom made in various sizes Capacities Shape Control devices Size to use ●avoid uncontrolled ascent ●just big enough when full ●expanding gas escapes

8. Search and Recovery Recovery 8 SR v1.2 Copyright © BSAC 2009 Attaching lifting bags Choose strong attachment points Use pre-prepared equipment Strops for larger objects Use lift tray for delicate or awkward items Effect of equipment on personal buoyancy ●messenger line to send equipment to work site Several small bags versus one large one

9. Search and Recovery Recovery 9 SR v1.2 Copyright © BSAC 2009 Multiple lift bags Fill multiple bags evenly topping off ‘control’ bag last

10. Search and Recovery Recovery 10 SR v1.2 Copyright © BSAC 2009 Air requirements Know how much gas is needed Gas needed (litres) = weight of object in water (kg)  absolute pressure (bar) Use dedicated air cylinder unless very little needed Filling the bags ●don’t use primary regulator ●AS ●blow gun ●separate supply

11. Search and Recovery Recovery 11 SR v1.2 Copyright © BSAC 2009 The lift Check all attachments are secure Once all bags are filled top up ‘control’ slowly until lift-off Object can ‘stick’ in sea bed Precautions ●plan who will do what, where and when ●dry run or shallow water rehearsal ●never ride up on the lift ●never remain under the lift – move clear At surface secure the object then lift aboard/tow ashore ●do not underestimate the difficulty of this phase

12. Search and Recovery Recovery 12 SR v1.2 Copyright © BSAC 2009 Staged lift Line plus pre-prepared loops (approx every 5 m) Requires two bags Most of the work is carried out in shallow water Good for ‘breaking out’ of sea bed

13. Search and Recovery Recovery 13 SR v1.2 Copyright © BSAC 2009 Legal aspects All wrecks are owned by someone Receiver of Wreck ●anything recovered must be reported (even if you own the wreck) ●if not lifted, no obligation to report it Military remains ●terminology ○war graves ○derelicts ●appropriate respect ●look but don’t touch ●some subject to exclusion zones

14. Search and Recovery Recovery 14 SR v1.2 Copyright © BSAC 2009 Legal aspects ‘ Unknown’ old wreck – 100 yrs + ●mark position ●do not disturb ●report to appropriate authority ●Protected Wreck status ●Nautical Archaeological Society for advice/training Health & Safety Executive (UK) – payment for diving work

15. Search and Recovery Recovery 15 SR v1.2 Copyright © BSAC 2009 Summary Estimate mass of object to be moved Allow for sticking in sea bed Use several small bags rather than one large one Use dedicated air source for filling bags Ensure object is securely attached Never ride up on the lift Never get beneath the lift Plan for getting the object onto the boat or ashore Comply with legal requirements

16. Search and Recovery Recovery 16 SR v1.2 Copyright © BSAC 2009