Master Neutral Buoyancy: The Importance of Horizontal Trim (Simple Vector Physics)

[markmud]

We're way ahead of ourselves here. There will be a thread about getting trim... This is only about why to get trim. Until you understand the need, it will never be much of a priority. Just be patient. The discussion will come in due time.

Roger!

markm

 

[Steve_C]

Hello NetDoc and BoulderJohn,

Where do you like to position the tank on ones back?
I see many divers with their tank half way down their butt.

For us trolls, diving a rental AL80 it is going to hit my butt and that is with the first stage as high as I want it. I am short. If diving my own tanks which are HP100s and shorter they fit me great.

---------- Post added December 23rd, 2015 at 08:21 PM ----------

When I go in the water wearing nothing but shorts, I sink to the bottom (fresh water or salt water). So what I have been trying to figure out for 20 years is how to get my legs not to sink.

Are you saying that you do this with tank and BCD but no extra weight? Other folks are telling you to move or add weight but if you are already negative that seems maybe suboptimal.

 

[TMHeimer]

Same here.

When I go in the water wearing nothing but shorts, I sink to the bottom (fresh water or salt water). So what I have been trying to figure out for 20 years is how to get my legs not to sink.

Same problem here. Assuming you're talking scuba and not just swimming, what about the most positively buoyant fins you can find? And/or a pair of ankle floats that you can find at any LDS--Oh wait, those don't exist (yet?).

 

[NAM001]

In you intent of can it be made more easier ? NO. there is no magic number to do when you rent gear and attempt to be perfect. The only thing you can arm your self is UNDERSTANDING of how things work. With that understanding you can control the most impacting variations of your diving. If you trim on a catalina tank at home then rent them when you can. minimize changes in the problem. Own your own bcd or bpw and then that will be a constant. Know the differences in your wet suits and that will be a value you have to change with great accuracy. Have the appropriate fins for using a shorty and a full wet suit. Have the adjusting weights of 1 for every 40 of your weight fully rigged for salt water conversion. This can be done with lead or changing BP's from steel to al. With that information your can adapt to good control of your trim and buoyancy no matter where you go. Knowledge and application is the key to all.

As a new diver, I *think* what I need to know next is how to Establish Trim. The importance was reasonably clear from my OW training, and made clearer from your first post, so thanks! But the path to getting comfortable with Trim looks like a lot of trial and error over many dives, made more complicated by vacation diving and rental equipment. If there's a way to be more efficient about it, I'd love to know.

---------- Post added December 24th, 2015 at 08:29 AM ----------

Most people undertstand and obtain neutral buoyancy. it is not hard. what is hard is being 5# over weighted and comping with the wing and then deelling with the depth change problems of a bubble in the wing. If they understood they would nt have as much weight and use less air in the wing to comp with and not have to vent fill vent fill and use their air up. Trim , a whole different mater requires neutral buoyancy to start with. If you understand trig you know just how much additional opposition to forward motion is put in effect with a given angle. You may be swimming 40 feet up hill but only moving 30 ft horizontally. There is 25% of your energy and air lost to poor horizontal trim. Until you can get to that attitude (trim angle) in the water your breathing is almost moot. getting there is the tough part for the majority. I look for ward to the rest of DOC's articles..

I'm not understanding why all the criticism. It's pretty freaking elementary the way NetDoc illustrated it. Whatever your trim is will be the direction you go, up or down. Once you establish neutral buoyancy, stay horizontal and you should not have to adjust your buoyancy again unless you ascend or descend to a different depth. Pretty freaking simple. Use your breathing and lungs to make minor changes to your buoyancy if you want to get closer or further away from something.

 

[Jim Lapenta]

One of the keys to good buoyancy and trim is to practice. As much as possible, whenever possible. Also take the attitude that EVERY dive is a skills dive. Even on the simple swim around and look at pretty fishies or playing in the pool. Take a portion of that dive, 5-15 minutes, and pick a skill to work on while maintaining good buoyancy and trim. Mask remove and replace, reg replace, adjust weight belt if using one. Try to do all of this while remaining horizontal and not changing depth by more than a foot to begin with.
Don't get frustrated if you change by two the first few times. More than five feet change?:shocked2: Better go back to the pool and stay out of OW for a while.

As for problems you may anticipate with rental gear. If possible rent as many DIFFERENT set ups as you can. Try different sizes. When I was working for one shop as a DM I grabbed whatever was closest in the rental locker to assist with pool sessions. Used steel and al tanks. Sometimes the BC would fit. Other times it would not. I normally wear a medium/large jacket BC depending on the mfg. I would be in everything from a small to an XXL. It didn't matter. Quick weight check, make a few adjustments, get the "feel" of the rig, and within a few minutes go through the session neutral, in trim, and look like there was nothing unusual going on.

I have seen DM's, AI's, and Instructors who have problems when switching between rigs like this. There is no excuse for that. As a newer diver who does not yet own their own gear you have a chance to expand your knowledge and skills in a myriad of ways. Don't tie yourself to that one specific BC and reg set up until you have a clear idea of what you want and done your own research.

 

[JBFG]

We're way ahead of ourselves here. There will be a thread about getting trim... This is only about why to get trim. Until you understand the need, it will never be much of a priority. Just be patient. The discussion will come in due time.

I can't hardly wait!

 

[scubadada]

For us trolls, diving a rental AL80 it is going to hit my butt and that is with the first stage as high as I want it. I am short. If diving my own tanks which are HP100s and shorter they fit me great.

That's funny, a HP100 is O.8 inches shorter than an AL80

 

[stuartv]

That's funny, a HP100 is O.8 inches shorter than an AL80

HP100s are about 2" shorter than an AL80.

Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan

 

[LowVizWiz]

Do you have access to a pool up there?

In January? Are you serious? LOL yes I do.

 

[NAM001]

Untill i got in my mid 40's i had the same problem leg heavy and chest neutral with full longs. then a little fat set in and I'm ok now

Same here.

When I go in the water wearing nothing but shorts, I sink to the bottom (fresh water or salt water). So what I have been trying to figure out for 20 years is how to get my legs not to sink.