OP
trpltongue
Registered
I've tried to put an illustration together to highlight what I'm experiencing.
A divers trim can be broken into three sections: 1) Upper body to Hips, 2) Hips to knees, 3) Knees to feet. It is split into 3 sections because each section is separated by a rotating joint.
The first diver is neutrally buoyant in each of the three sections. 1) Upper body due to BCD and trim weights, 2) Hips to knees due to wetsuit and body composition, 3) knees to feet due to wetsuit, fins, and body composition. This diver can maintain any position they like underwater with no continuous effort required.
The second diver is neutrally buoyant in the upper body only, and negatively buoyant everywhere else. This diver will ALWAYS experience a downward moment of inertia around the hips and knees. The only way for this diver to maintain correct trim (without kicking) is to lock the hip and knee joints to prevent rotation AND to add weight in the front of their body to counterbalance the negative weight from their lower body preventing a "seahorse" position. This can be done, but it is tiring.
Alternatively, you can make the knee to feet section positively buoyant with fins/boots/etc., such that it counterbalances the negative buoyancy of the hip to knee section and makes the lower body neutral overall.
My wife and daughter are like the upper diver, naturally neutral in the water. I am like the second diver.
View media item 200785
A divers trim can be broken into three sections: 1) Upper body to Hips, 2) Hips to knees, 3) Knees to feet. It is split into 3 sections because each section is separated by a rotating joint.
The first diver is neutrally buoyant in each of the three sections. 1) Upper body due to BCD and trim weights, 2) Hips to knees due to wetsuit and body composition, 3) knees to feet due to wetsuit, fins, and body composition. This diver can maintain any position they like underwater with no continuous effort required.
The second diver is neutrally buoyant in the upper body only, and negatively buoyant everywhere else. This diver will ALWAYS experience a downward moment of inertia around the hips and knees. The only way for this diver to maintain correct trim (without kicking) is to lock the hip and knee joints to prevent rotation AND to add weight in the front of their body to counterbalance the negative weight from their lower body preventing a "seahorse" position. This can be done, but it is tiring.
Alternatively, you can make the knee to feet section positively buoyant with fins/boots/etc., such that it counterbalances the negative buoyancy of the hip to knee section and makes the lower body neutral overall.
My wife and daughter are like the upper diver, naturally neutral in the water. I am like the second diver.
View media item 200785
The weather was a bit crap so viz was only about 7-8 meters and the water was a little chilly at 19C but it was a great trip with a few Sand Tiger sharks (or grey nurse sharks as the Aussie's call them), loggerhead turtles, huge cod, leapord sharks, rays, etc.
