heavy legs

[michaelb51]

A pound of feathers ...

If a cross section of ones anatomy was taken and the specific gravity measured if the result is greater than 1, it will sink. This is basic physics.
...
Frog Dude

Someone else mentioned teeter totter. This is also basic physics. We're negotiating semantics on an issue I'm happy to say we've unwittingly agreed about. You win. I'll climb down slowly.

But: people don't trim buoyancy by changing fat/muscle ratio. They trim by moving movable parts. The observation and description (fat floats, muscle sinks) does help us understand one of the reasons people have to be individually weight and balanced.

It also begs an absurd question: is fat safer than muscle? After all, when the going gets tough, floating might be regarded as safer than sinking. And fat doesn't cramp, to my knowledge. If you start the thread, I'll join you there.

Michael B.
[BMI: 18%]

 

[ReefHound]

Think of your body as a see-saw.

Pete

Put a hinge in the middle of the see-saw and it doesn't matter how much weight you put at one end, it won't stop the other end from hanging down. Frog Dude is the only one I've seen here that seems to understand this. If your feet are denser than water they will sink down, no matter how high you wear your tank/weights, unless your head is so heavy it's sinking faster. Your hips are a movable hinge and you cannot transmit leverage through a hinge that freely moves in the direction of the force vectors.

 

[michaelb51]

I get your point, ReefHound and concede the logic, I don't think anyone is arguing against the vector math, but I still somewhat disagree with the final assertion.

Perhaps metaphor is inadequate to describe these phenomena. As Frog Dude pointed out, the forces can be viewed at fixed stations along the body's axis. Lift doesn't just occur at the center of lift, it just coincidentally totals same on both sides of that point. The few ounces which account for most foot sink or foot float simply will not overcome the balance of tensions at the hip to cause it to bend forward, even when I totally relax. So it is fairly easy to misdiagnose the reasons for pitch up or pitch down moments. I still pivot almost as a unit, even if I dress in jetfins without my boots.

That said, the best stability should occur if every station along the body is neutral, or neutralized and the CL is placed as high as possible above the CW. So I agree, and floating (or better, neutralizing) at the feet is preferrable to the other solutions, in my opinion. Many people also disagree with that, choosing instead to move the CW forward even if analysis proves the feet sink. They observe for themselves satisfactory results, and neither their head and torso nor their legs actually droop, unless you snatch them out of the water by the back of the weight belt. Or so it seems to me. But maybe my hips just need oiling.

 

[Frog Dude]

ReefHound,
You nailed the point I was trying to confer with the hinge example. Maybe I was too obtuse with the verbiage I used to describe the variables involved to solve dumps problem.
Michaelb
Rather than agonize over the physics of weight distribution and BMI I am trying the pipe insulation on my fin straps. My hypothesis is that I may gain enough positive buoyancy to compensate for the foot drop. If it works, that is the answer for dump to try. It may take a section of swim noodle but if it doesn’t interfere with an efficient kicking stroke and it solves the problem all the math is just mental exercise.

Dump,
We will find a solution for you if you haven’t gotten disgusted and forgotten about this thread.

Frog Dude
50 + and still fit.

 

[spectrum]

We all want to help the guy but we need to READ what the problem is.
Legs sinking AT REST (Not Kicking) is when he has the problem.

Good point!

If he chooses not to use a frog kick he may want to employ a frog like posture when at rest. By bending his legs upward at the knees he can temporarilly move his center of gravity.

It is also possible that his swimming trim is poor but with body posturing is unknowingly generating the right lift to feel like he is swimming OK.

When stopping it can help to pay attention to the bubble in your BC, especially a back inflate. The air may be biased to the top thus forcing the feet down. By intentionally dipping the head the bubble will shift to the bottom providing more lift to the lower extremeties.

Pete

 

[ReefHound]

Many people also disagree with that, choosing instead to move the CW forward even if analysis proves the feet sink. They observe for themselves satisfactory results, and neither their head and torso nor their legs actually droop, unless you snatch them out of the water by the back of the weight belt. Or so it seems to me. But maybe my hips just need oiling.

I suspect that many achieve horizontal trim by maintaining tension throughout their body to prevent the hinge movement and allow the forces of leverage to extend through, while those who cannot are taking the advice to "relax" while diving a little too literally. You will often see it said that it helps to arch your back slightly, which also requires tension.

Bending the knees helps a lot and also allows those who need a slight bit of finning to keep the feet up to do so while remaining stationary by alternating a slight forward and reverse finning movement.

BTW, anyone know what fin models are positive?

 

[jbd]

I concur with all jdb’s recommendations except #1 (a good style to develop while diving) but not relevant when motionless. If the general consensus will accept a horizontal hover to include the legs bent up at the knees in a stable freefall “frog” position the CG will move toward the head and reduce the effective feet down moment.

Frog Dude,
Your second sentence does two things 1.) It contradicts your disagreement with my first recommendation; 2.) States the exact reason why I suggested the frog kick, because with the execution of the frog kick you recover to the glide position which has your body motionless--essentially a hover. So actually I think we are in agreement

Which brings us back to the original problem.
I am surprised that nobody zoned in on the physique issue that is the root cause of dump’s problem. This was brought into focus by his subsequent post.
Quote: “i dont use weight or a weight belt. I am 5 ft 7in weight 235 lbs powerlifter. so i sink with no problems.

We didn't have that info until he posted it later as you noted. This is one reason it is so hard to make accurate recommendations for proper weighting and trim over the internet

i will try to add a little to the top of the tank.”

Which is exactly what he shouldn't do until he has tried all the other options first. Unnecessary additional weight will only create problems with bouyancy control.

BTW jdb the drills used when I received training with my first BC we were taught to pivot on our fin tips. Breath control was stressed and to pass the drill you had to stay within a +- 3 inch span for 20 minutes.
FD

Which is good a good thing in general, and not a bad thing to practice from time to time, but IMO, there are better drills which I use in the OW course and are in the bouyancy control seminar(similar to Peak Performance Bouyancy).

 

[dkktsunami]

A suggestion for feet that continue to sink after reducing amount of weight, after shifting weight upward, after changing body position, after doing everything possible:

Neoprene dive "socks" worn under booties. H20dyssey makes thse in 3 and 5 mil. When all else fails increase the bouyancy of the feet.

 

[Whale Whisperer]

Dump, I'm in a similar situation, I'm 5'6" and weigh 200 lbs. I sink like a rock and I don't dive with weights. So the most I could do was raise the position of my tank (without banging my head on it) and adjust my swiming posture by Arching my back and tilting my head up kinda like Superman ha ha. Tilting your head up promotes my back to arch and also streamlines my body. Then I'll position my arms straight out in from of me with my hands together and my legs straight while I'm swiming forward. Anytime I want to slow down and/or hover I'll bend my legs straight up 90 degrees. This along with my arms in front moves my center of gravity foreward and really helps my trim out. You're neck will feel sore if you're tilting your head just right for a few dives, but it will feel better and natural later down the line. Give it a try, it worked for me, it may work for you.

EDIT: I forgot mention that my legs are sinkers too

 

[dump]

thinks for all of the replies. ill try some of the suggestions the next time iam in the water. some very good ideas. thanks