Scuba Trim Case Study - Adam (Trim tips) 

A small point, but tanks of any kind don't change trim as they empty; the whole tank gets more buoyant. The reason the back end goes up is the weight of the first stage holding the front down. But the net effect is you will be losing 2kg or whatever from the position of the centre of the tank as you burn the gas. I agree about the effect of the wet suit with depth and you can compensate for that with how much you extend your legs and where you hold your arms. But for me the best way with this sort of rig is to use a wing-style BC, so the lift is right with the cylinder, and as much as possible concentrate the weight around your centre of buoyancy. It takes a bit of playing about but trim pockets and a backplate help and when you get it right you'll find your trim stays pretty good at any pitch or roll angle you happen to be in. If I use a weight belt I put the weights at the back for this reason. Well, it works for me.

Thanks for adding your thoughts and experience, Tim.

Thanks for the great tip, Ron 👍

Some great points here, Wes. Thanks for contributing to the conversation 👍

Great point about the balanced rig, Max. I’d love to see a vid of your trim work. Sounds like you are working with an interesting set of variables.

Thanks, Nick 👍

Let us know how it turns out! Please post up there again after your pool.

@@DiscoveryDiversTokyo Hello Jim. I did the actual pool test today using a Zeagle Ranger back inflate. I can tell it’s what I want for my first BCD. It doesn’t have to be a Zeagle but back inflate for sure. I was able to get in the horizontal position and stay that way pretty easily. I also tested it at the surface with too much air, not enough air and then found the right amount. I did all that to go from each extreme to feel the differences in each situation and it’s not difficult to lean back a little and have my legs out front without feeling like my upper body was being pushed foreword. Of course I was in a calm pool and not in the ocean with some chop. This model has most everything I was looking for in a back inflate. I wanted the cummerbund and a few pockets. This model has that along with enough D rings to snap a few items to as needed. The pockets for me would be for some trauma shears and maybe a small light and they were low enough for me to use without looking as I tried both sides while in the water. I believe this model can be outfitted to twin tanks as needed so it looks like a good one to get to allow me to advance without another good investment. Speaking of a tank…it had two tight fitting straps that took a little more work than what I have used with the metal clasp Scuba Pro BCD’s (which are very easy in my book) but it wasn’t a deal breaker and it may even be better since it had two straps on the tank? What I didn’t care for was the weight dump apparatus. I watched a few videos of how it works when releasing it and how to re-cock the system. The weights definitely drop as they should and I think it is easier to just pull the one red t handle but it’s just different than what I have seen. Is it better or worse? I really don’t know I guess experience and preferences come into play there. In the end it was great and I will look at a few other back inflate BCD’s. This one is pretty tempting but I have seen an Aqua Lung and Scuba Pro I want to look into. Any suggestions or pros and cons on an model would be appreciated. I’m sure if I picked one of the brands I mentioned and it had the cummerbund and a few pockets I would be happy. 👌 Don

You’re right, TPL…I hate to use BP/W as every answer 😜

Great comment, AJ 👍

HI ALex. Thanks for the Q. Regarding this Q, "If you do this but you are head heavy shouldn't your head sink?" in a wetsuit, your legs will go heavy and sink. Try it out yourself. For the drysuit case you are referencing, is this person still head-heavy? If head-heavy in drysuit, I'd consider heavier fins, look at weight placement as you are, and look at tank choice. When I'm in drysuit, my dream tank is 14L steel for the lenght, but almost never possible in my area. Short, heavy tanks like a 10L steel (short) are the worst choice for someone with a head heavy trim issue. You are on teh right track, to first get the weighiting right, then distribute that weight in the best way possible to achieve passive trim that is as good as possible. From there, the diver will have to manipulate, arm/leg psotion and adjust as air is breathed down from the tank (as taht balance will change over the dive).

Actually Dutch Springs quarry is a very well known quarry in Pennsylvania that has been used by divers all over the northeast US for training for years. Has a fire truck, school bus, and even an airplane sunk in there! So lots to see!