1. Supplementary Diver Training Workshop Buoyancy and Trim BTW v1.16 VA1 Copyright © BSAC 2008-10

2. Buoyancy Workshop BTW v1.16 VA2 Copyright © BSAC 2008-10 Aims Understand issues affecting buoyancy and trim Be able to hold position in water at any depth ●Horizontal to reduce drag ●Horizontal for decompression ●Legs positioned to avoid disturbing seabed ●Head down ●Head up To improve on or reconfirm your personal buoyancy and trim

3. Buoyancy Workshop Symptoms Yo-yoing Unplanned rapid descents Constant inflation/deflation Failure to inflate ‘Winding up’ on SMB/DSMB Excessive finning High gas consumption Over-inflation ●Gas burping from drysuit or BCD ●Gas migration in drysuit or BCD ●Effects of Boyle’s law ●Rapid ascents near the surface BTW v1.16 VA3 Copyright © BSAC 2008-10

4. Buoyancy Workshop Causes Too much weight Too little weight Equipment configuration Equipment malfunction ●Dump valve failure ●Inflator freeflow/disconnection Dropped weights Dragged upwards Up/down-currents BTW v1.16 VA4 Copyright © BSAC 2008-10

5. Buoyancy Workshop Prevention Control ●Awareness, concentration etc ●Anticipation ●Breathing Equipment maintenance Planning and practice ●Emergency gas dump ●Quick releases ●Dive planning – up/down currents Correct weighting BTW v1.16 VA5 Copyright © BSAC 2008-10

6. Buoyancy Workshop Overweighting Signs Rapid descents, sinking Rapid ascents Finning to maintain position Sinking when finning stopped Venting/adding gas Drysuit unable to retain gas BCD close to full inflation Excessive gas consumption Failure to adjust for fresh water Failure to adjust for a new configuration BTW v1.16 VA6 Copyright © BSAC 2008-10

7. Buoyancy Workshop Correct Weighting Correct weight distribution Equipment configurations Buoyancy change due to gas consumption Normal breathing No suit, wetsuit or drysuit? Clothing Relaxation Salt v fresh Adjust weighting if anything changes BTW v1.16 VA7 Copyright © BSAC 2008-10

8. Buoyancy Workshop Weight Guide Fail-safe method is a buoyancy check in water! Adjustments ●Fresh/salt change 2 to 3 kg ●+/- for different configurations ●Keep a personal record Starting point for beginners ●UK 7 % body weight (fresh) ●10 % body weight (sea) ●Extra for buoyancy check Diving abroad ●Thinner suit/less equipment ●Buoyant cylinders ●Checkout dive Don’t wear more weight than needed BTW v1.16 VA8 Copyright © BSAC 2008-10

9. Buoyancy Workshop Drysuit v BC (Optional slide) BC only? ●Not possible - suit squeeze Drysuit only? ●Easy to manage ●Limited buoyancy available ●Gas migration / venting Drysuit + BC? ●High lift capability ●Higher task loading Safe diving Experienced divers Simple config Personal choice Consider buddy/CBL Beginners Drysuit only Experienced divers Heavy config Drysuit + BC Caution basic skill high little lift needed large BTW v1.16 VA9 Copyright © BSAC 2008-10

10. Buoyancy Workshop Trim Pitch ●Forward ●Backward ●Roll BTW v1.16 VA10 Copyright © BSAC 2008-10

11. Buoyancy Workshop Why Trim? To overcome ●Problems of gas migration ●Equipment imbalance (fitting) ●Poor balance ie over-finning ●Kicking up silt ●Damaging marine life To improve ●Comfort ●Swimming efficiency ●Gas consumption ●Diving & u/w control ●Relaxation BTW v1.16 VA11 Copyright © BSAC 2008-10

12. Buoyancy Workshop Body Positions Horizontal / head down ●Decompression ●Observing seabed ●Travelling Visual field Vertical / head up ●Observing scenery ●Observing surface Avoid contact / silting ●Impact with seabed / reef ●Wash from fins Negative/positively buoyant BTW v1.16 VA12 Copyright © BSAC 2008-10

13. Buoyancy Workshop Trim Solutions Weight belt configurations Kit configurations ●Trim check ●Redistribute weight/cylinder ●Ditchable weight BCD Leg position Streamlining Experiment! BTW v1.16 VA13 Copyright © BSAC 2008-10

14. Buoyancy Workshop Practical Overview Basic Lesson Content ●Record weight/s ●In-water weight check ●Vertical descent, 6 m stop ●Stop 1 m above seabed or hold station at planned depth ●Trim checks ●Ascent with stationary unassisted stops at 12, 9, 6, 5, 4, 3, 2 and 1 m ●Adjustment for neutral buoyancy ●Task loading exercises depending on divers experience and level of performance ●Repeat the above ●Compare performances Dive 1 – 15 m max Dive 2 – 12 m max 1 min stop 2 min stops Trim checks Dive profile BTW v1.16 VA14 Copyright © BSAC 2008-10

15. Buoyancy Workshop Standards Black +2m +1m 0 -1m -2m -3m +3m Silver Gold Unacceptable Beginner - Bronze SD/Assistant instructor +1 m DL/Open Water Instructor +0.5 m Advanced/Technical Diver +0.3 m BTW v1.16 VA15 Copyright © BSAC 2008-10 Ocean Diver +2 m

16. Buoyancy Workshop Summary Buoyancy issues Symptoms, causes & prevention Correct weighting Drysuit v BC Trim & body positioning Practical overview Standards BTW v1.16 VA16 Copyright © BSAC 2008-10