Originally posted 2018-03-07 23:57:10.
99 Problems….and your TRIM is one!
by Andy Davis.
The short article outlines the most common trim problems experienced by scuba divers and how to overcome them.
In scuba diving, our trim is the position and angle of our body in the water. Ideally, that trim should be in flat and horizontal. This is a good thing because it makes us much more streamlined in the water. Being streamlined reduces our exertion when moving through water and consequently lowers our gas consumption.
The other benefit of having a good horizontal trim position is that your feet/fins are held higher above you. This helps prevent unintended disturbance of the bottom; which can reduce visibility underwater. Kicking up silt is an annoyance for photographers and fish-spotters. For wreck and cave divers it is a distinct hazard to safety.
I’ve noticed a tendency for novice-intermediate divers to focus predominantly on equipment variables in their pursuit of perfect trim. Yes, the ubiquitous ‘trim weights’ solution. This equipment-focused approach is often blinkered to the exclusion of human factors, including counter-productive habits and weak diving posture.
From my experience teaching hundreds of divers how to attain perfect trim, here are the most common weaknesses. Do note – my list is in order of importance and significance:
1. You Were Conditioned to Drop Your Legs. Prior (bad) training conditions divers to instinctively drop their knees. This is typical of scuba courses where the instructor teaches skills from a kneeling position and/or encourages students to revert to a vertical diving position whenever static or practicing buoyancy. Once conditioned, it gets further ingrained as (uncorrected) experience is accumulated. Bad habits and undesirable responses require significant focus and dedicated practice to eliminate. For more explanation see my article – ‘Learning Scuba Skills On Your Knees – Negative Habitual Response Conditioning‘.
You dive how you train. Bad training leads to problematic diving.
2. Not understanding what proper horizontal trim ‘feels like’. Proper horizontal trim initially feels like you’re a little head down. Divers might initially feel like they are horizontal, but are actually feet-down and out of trim. In proper horizontal trim you should be able to tuck your chin into your chest and see behind you.
Student practicing proper trim position on dry land prior to foundational skills training session.
3. Incorrect body posture. The shoulders, hips and knees must be level at all times. This requires the head to be held chin up and the knees / shoulders to be ‘lifted’ with an arch in the spine. The biggest failure is weak hips…. allowing the knees to drop… which pulls the diver into a feet down position. Bend the knees 90 degrees, shortening the lever-weight of your legs. Experiment with different arm positions, as these influence balance also. Practice body posture on dry land.
4. Over-weighting. Carrying superfluous weight necessitates adding more gas to the BCD. This exacerbates the complications from gas movement around the BCD (see #5) and buoyancy-ballast balancing (see #6). For more details on getting your weighting fine-tuned, read my article: Perfect Scuba Weighting
5. Not ‘balancing the bubble’. Gas moves around your BCD. It always moves to the highest point. The diver needs to shift this gas and hold it where they need the lift to support themselves in trim. Get a little ‘ass high’ to move the bubble down nearer the hips. Don’t let it rise to the shoulders.
The gas in your BCD moves. Place it where you need it, to achieve the right trim.
6. Incorrect distribution of ballast and buoyancy. Yes, BOTH. Typical configuration with heavy weight belt below the fulcrum (balance point on the torso) and buoyancy high on the torso gives a see-saw effect outline legs down. Distribute weight to balance the ‘see-saw’. Consider where your BCD holds gas along that balance point.
7. Relative buoyancy characteristics of equipment. Heavy fins at the end of long levers (the legs) have an obvious effect. Try a less negative pair of fins. Try more buoyant booties etc. Think in detail how everything you wear when diving influences your balance and whether it contributes to, or ruins, a natural trim position.
For instance, see this article on neutrally buoyancy fins; Warm Water Diving Fins
About the Author
Andy Davis is a RAID, PADI TecRec, ANDI, BSAC and SSI qualified independent technical diving instructor who specializes in teaching advanced sidemount, trimix and wreck exploration diving courses across South East Asia. Currently residing in ‘wreck diving heaven’ at Subic Bay, Philippines, he has amassed more than 9000 open circuit and CCR dives over 27 years of diving across the globe.
Andy has published many magazine articles on technical diving, has written course materials for dive training agency syllabus, tests and reviews diving gear for major manufacturers and consults with the Philippines Underwater Archaeology Society.
He is currently writing a series of books to be published on advanced diving topics. Prior to becoming a professional technical diving educator in 2006, Andy was a commissioned officer in the Royal Air Force and has served in Iraq, Afghanistan, Belize and Cyprus.