Buoyancy, Body Type and Trim

[Frog Dude]

This a modified copy of my response to another post concerning BMI and how the distribution of fat and muscle affect not only buoyancy but the trim of the body at rest while submerged. The information is based on actual in pool testing and may be of benefit to many divers. I chose to start a new thread to save anyone that may gain something from this the agony of wading through 4 pages of discussion.
“WARNING” This is something you want to try at home. At least in a pool.

The results are in.
Test subject 6’1” 187lb. 16 % body fat (measured biometrically immediately prior to test).
Fresh water pool.
Equipment:
Mask and snorkel: considered neutral, captive air volume will offset negative mass.
Booties: approximately .5 pounds positive each. 1 pound total positive.
Fins: the Scubapro Jet fins, definitely negative and discarded for this test. I chose the Scubapro Veloce adjustable to use. The fins would be considered overall slightly positive. The tip of the blade protruded ¼ inch above the water with the remaining hanging down.
Farmer johns: 3/16” neoprene with knee pads. Positive 7.3 pounds.
Shortie: 3/16” neoprene. Positive 7 pounds.

Water Test:
Human test subject with mask and snorkel only:
Defiantly negative. Normal breathing caused subject to submerge below snorkel depth.

Human test subject with mask, snorkel and farmer john:
At rest, the subject was able to maintain snorkel depth. With arms comfortably extended and legs straight the body assumed a feet down angle approximately 45 degrees from the surface.

Human test subject with mask, snorkel, farmer john and booties:
At rest, the subject was able to maintain snorkel depth. With arms comfortably extended and the legs straight the body assumed a horizontal floating position.

Human test subject with mask, snorkel and shortie:
At rest, the subject was able to maintain snorkel depth. With arms comfortably extended and the legs straight the body assumed a vertical position with the legs down.

Human test subject with mask, snorkel, shortie and booties:
At rest, the subject was able to maintain snorkel depth. With arms comfortably extended and the legs comfortably bent at the knee the body assumed a horizontal position with the soles of the feet slightly horizontal and below the horizontal plane of the subjects back.
This was the most comfortable position of all the above mentioned and the subjects standard diving configuration, less booties.

The conclusions drawn from the above test prove that body fat to muscle ratio DOES have a direct bearing on overall buoyancy and that the distribution of the fat and muscle will affect the overall trim.
With this information divers bodies can be placed into three categories in regard to trim.

Triangle: Wide at the top, point at the bottom.
The wide line at the top symbolizes the upper body that coincides with the area where the available buoyancy has the most adjustability. Via a BC and weight. The narrow point at the bottom symbolizes the feet and the area that has the least amount of natural buoyancy and very few options to adjust. The triangles center of gravity in the water is located about mid chest.

The Square: Uniform distribution of natural buoyancy and larger envelope of adjustability. These people naturally float, a few border on triangles if their feet sink but the thighs float.
The squares center of gravity in the water is located about the abdomen close to waist.

The Pear. The center of buoyancy is located in the hips. May have sinking feet but they are closer to the center of buoyancy and will require less to compensate. If the torso is heavy it is compensated by the BC.
The pear center of gravity in the water is located about hips.

Current equipment technology is designed for the majority of the diving consumers of whom most have a fat distribution condusive to a horizontal floating position. Divers that don’t fit into that mold and continue in the sport learn to compensate by the many aforementioned means or just learning to accept a feet lower position and dive accordingly.
Copyright2006 Frog Dude

 

[TSandM]

Forgive me, but since the variables you played with all have to do with exposure protection and equipment, how do you draw any conclusions about the effect of body composition on buoyancy and trim?

 

[Frog Dude]

Body composition determines whether you sink or float without any ancillary equipment.
Whether you sink or float determines your buoyancy and is the datum you start from to select the correct equipment to facilitate an adjustable buoyancy for the dive planed.
The equipment selected and location of where placed on the body will determine your final trim. The understanding of your body style (Triangle, Square or Pear) will help determine the placement of the necessary, positively or negatively buoyant components to achieve the desired trim. What you may consider exposure protection must also be considered positive ballast and a tool to be used to achieve a desired trim.
The water test reflected the minimum (for my body composition) ballast required to achieve a horizontal trim on the surface.
By using the 3 body type (Triangle, Square or Pear) model I know, beforehand that with my body type, adding weight in the conventional manner (weight belt) will cause my feet and legs to sink.
Without medical modification, diets or workouts you are stuck with what you got. Understand what you are working with have an idea of where to start will make the task easer.
New concepts are often misunderstood. My original dive buddies would say “We don’t need pressure gauges, we got a reserve with the K valve”.

Frog Dude

 

[Charlie99]

With this information divers bodies can be placed into three categories in regard to trim.

Triangle: Wide at the top, point at the bottom.


The Square: Uniform distribution of natural buoyancy and larger envelope of adjustability.

The Pear. The center of buoyancy is located in the hips. May have sinking feet but they are closer to the center of buoyancy and will require less to compensate.

You forgot yet another very important distinction of types of people. This has to do with whether they have floaty feet or sinking feet.

AIRHEAD. Head goes up, feet go down. For an on land test, check color of hair. Very light colored hair, whether natural or bleached is a good indicator of an airhead.

BLOCKHEAD aka CEMENT HEAD. Head goes down, feet go up. Above water, these people can be identified by having a short discussion about any controversial topic. The excess cranial density will prevent penetration of the skull by any facts.

 

[adurso]

If I understand your post correctly you used one human subject with exposure protection as variables. How does one draw conclusions of other phenotypes? "J" valves have reserves, by the way....

 

[michaelb51]

The conclusions drawn from the above test prove that body fat to muscle ratio DOES have a direct bearing on overall buoyancy and that the distribution of the fat and muscle will affect the overall trim

No, they don't.

body fat to muscle ratio DOES have a direct bearing on overall buoyancy and ... the distribution of the fat and muscle will affect the overall trim

Yes, true statements, I believe.

 

[Frog Dude]

One only has to view the contents of a local swimming pool or beach to see examples of the three body types and see the buoyancy characteristics of each.
An understanding of human anatomy and basic physics is also helpful. The supporting evidence for other body types buoyancy issues are found on this forum using the search function.
Dividing body types into 3 groups is a simple, easy to understand (I thought) classification to assist in selecting ballast and where to locate the ballast to achieve the desired trim. This process must start with determining what your body type is.
This is a simple function. Jump into the water and breathe normally. If a part of your body starts to sink remember what part and how fast it sinks. Then decide which of the three groups you fit into. Repeat the process adding gear and making adjustments until you are satisfied with the results. If you are in the triangle group add negative ballast closer to you head and, or positive toward your feet. You may need to dive in warm water with farmer johns to ballast your lower half if you want a horizontal position at rest and a more efficient kicking position. .
Take time away from the computer bashing concepts you haven’t tried and develop better dive skills. There are some new divers that can use this information.


Michealb,
????????
Rather than semantics, try what I posted. If it works for you, good. If not you got some bottom time.
Win-win.

Frog Dude

 

[*Floater*]

I've noticed that small women (like my gf) tend to be more prone to head down trim than large men (like me), but this is just anecdotal.

Even in a jacket BC with positively buoyant fins my gf (5'6" and 100#) some times had issues with he feet pulling up during hang time. And when she moved to bp/w she had to move her tank all the way down below where top cam strap could be used to keep horizontal trim with an 12L aluminum tank, 7mm wetsuit, steel plate with light STA, oxycheq razor 30# wing in top position (which has a tiny rear bias in center of lift but is pretty neutral), 6 kg in weight pockets on the waist strap and slightly negative force fins. However, I think loosening the shoulder straps and tightening the crotch strap to drop the rig further down and switching to jet fins will sort her out. I'm a little nervous about what will happen when she tries doubles though in a few weeks time.

 

[TheRedHead]

Triangle: Wide at the top, point at the bottom.
The wide line at the top symbolizes the upper body that coincides with the area where the available buoyancy has the most adjustability. Via a BC and weight. The narrow point at the bottom symbolizes the feet and the area that has the least amount of natural buoyancy and very few options to adjust. The triangles center of gravity in the water is located about mid chest.

The Square: Uniform distribution of natural buoyancy and larger envelope of adjustability. These people naturally float, a few border on triangles if their feet sink but the thighs float.
The squares center of gravity in the water is located about the abdomen close to waist.

The Pear. The center of buoyancy is located in the hips. May have sinking feet but they are closer to the center of buoyancy and will require less to compensate. If the torso is heavy it is compensated by the BC.
The pear center of gravity in the water is located about hips.

You forgot the hourglass and the potbelly.