Recently I decided to tackle an issue with my kit that had been bugging me. When trying to maintain a stationary position I would go head down unless I was constantly fining and struggling. With the help of my team I was able to solve this puzzling mystery and move a lot closer to ideal trim. The following is an account of the steps I went through. I hope they can shortcut you to better trim yourself. To qualify what I am talking about I will start off with my stats and gear configuration.

Height: 6′ 2″
Weight: 275 lbs
Gear:
Tanks: Double PST 130 cu ft
Wing: Halcyon Evolve (doughnut wing)
Backplate: Halcyon SS
Lights: 2 Backups and OMS Phantom 10w Canister
Inflation: 6cu ft Luxfer
Bands: Dive Rite 3″ bands
Manifold: Sea Elite 300 bar
Regulators: Apeks DS4
Exposure: Bare CT 200 undergarment, Bare ATR HD Trilam suit converted to turbo soles

Problem: When trying to maintain a horizontal position with knees bent, fins above the tanks I was constantly struggling to stop from going head down. This leads to the only relaxing position being the checkmark position, see picture below for example. When in swimming mode using the frog kick, I was able to be slightly more horizontal but once stopped if I wasn’t struggling I was flipping head over heels. The constant struggling to keep in trim was wreaking havoc on my back and stopping me from progressing with other skills.

The first thing to do is decide you have had enough and want to get the problem licked. Like many divers I spent my dives diving and not working on stuff like this. It has been almost a year since my DIRF course and while other things had improved my “head heavy” issue hadn’t magically gone away. Go figure. I am not sure where I missed this in my training but it cam as a revelation to me. Here is how to tell if you if you CAN trim out with your current configuration. Get horizontal in the water and stop moving. If you start going head down, correct your trim and repeat. This time extend your legs all the way straight and stop moving. If you still go head down then you have to redistribute the weight of your rig. There are several ways of doing this.

Move your bands up as high as you can (usually to where the curve starts)
Move your backplate up one hole (if you have multiple holes)
Get some heavy fins like Turtles or Jets???

I had already done the above and repeating the trim check I was not able to stay horizontal even with legs extended. I talked to John Millar, a member of our dive team who agreed to spend some time in the shallows with me working on the issue. I knew I had to add some weight to the bottom of my rig but wasn’t sure how much. So to test my theory as to how head heavy I really was and get a quantifiable number we did the following.

I tied a loop of cave line around a washer.
Wing nut on the washer to the back, lower bold of my tanks.
Tied some cave line loops onto several 2 lb weights.
I brought a double ender to the dive site with me.

Started the dive with 2 lbs snapped to the bottom bolt of my tanks. Due to the length of the loops and the double ender, the weight ended up right near the bottom of the tanks. Dropped down to 10 ft and tried to extend my legs, stop moving, still did a face plant. On the surface, John said I started flat but he saw my head sink. Added 2 lbs, repeated. With 4 lbs on the bottom of the tanks I was much slower to pitch forward. On the surface John added 2 more lbs. Repeating the test again with my legs extended I was able to stay flat. Low and behold my head started to rise. It was almost too slow to perceive at first, but once I started going up I was able to halt and return to the horizontal position by bending my knees bringing my fins in closer to the tanks.

Very satisfied that I was able to find a way to maintain horizontal trim I was somewhat confused as to how I would add 6 lbs to the bottom of my tanks. I certainly couldn’t leave the 2 lbs weights snapped to a piece of cave line. I had a V weight that I considered cutting in half and putting only on the bottom bolt. Any way you sliced it I was going to have to ADD weight to an already HEAVY rig. Speaking with a team member late one night, I was told “exactly what my problem was”, which I had heard many times before without positive results. Oren suggested that I needed to change backplates and maybe add a tail weight, but changing to an aluminum plate would most likely fix everything. I was defiantly skeptical but was willing to give anything a try. Here is the theory. A stainless steel backplate weighs 6+ lbs, which is distributed along the axis of the tanks but higher up than where you need the weight. By changing to an aluminum plate you reduce the overall weight of the rig by about ~5 lbs and move your pivot point up higher. If that doesn’t get you close enough you can add a tail weight to finish off your balancing act. Up to a 5 lb weight can be added and you will have essentially the same weight you started with, but redistributed to where you need it.

The above theory seems to have worked for me. I am 4 dives post backplate change and added a 5.25 lb tail weight. Other team members tell me that my trim is improved, valve drills are coming a tiny bit easier and my back doesn’t hurt as much after the dive. I am still not perfect but if you look at the difference in trimf rom a year ago until now it has greatly improoved. At this point I would say that the above steps solved my head down problem. I hope these steps get you on the fast track to good trim.

Funny enough, after I got through this I started seeing Al plates with tail weights all over the place. LOL. I still have my ss plate for down south diving singles or aluminum tanks.

Cheers

Chris Phinney
Liquid Archaeology

This entry was posted on Monday, December 3rd, 2007 at 9:41 pm and is filed under Skills and Equipment. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.