Trim versus buoyancy

[MNScuba]

Hey, good suggestion. I'll try that this week when I go out on Wednesday or Thursday... Will be interesting to see what happens. I'm always up for improving my skills! (Lord knows I need improvement, haha!)

 

[Uncle Pug]

Chris.... do it shallow.... at the beginning of a dive.... if fact make it your dive.... spend a tank playing with it....

The eyes closed bit isn't something to be doing at 90' after a 30 minute dive

 

[MikeS]

Mike and UP,

Thanks for the input, it has given me a lot of things to try!

UP,

One point I’m still not clear about, semantically does trim include body positioning? If so, does that mean that you can have good trim with not so good weighting, compensated for by body position?

Back to the three-step program, in step two what is the correct body orientation to check proper weighting, horizontal as in the real test?

If so what should I expect to happen if I go heads up vertical? If I tend to rotate back to horizontal, since I can’t move weight without messing up the horizontal trim, is this where body position comes in?

Also, wearing a wetsuit, if my weighting is perfect at 15 fsw (per the real test)what will tend to happen when I descend to 60 or 100 feet and my wetsuit compresses?

Thanks,
Mike

 

[Uncle Pug]

trim has to do with position... I suggest being trimmed for the horizontal position of least drag. It is effected through weight placement and body mechanics.

In this horizontal position your forward movement is not producing planing forces that cause you to ascend or descend... forces that many divers must counter with additional weight or vise versa... consequently when correctly trimmed and you stop forward motion you neither sink nor rise... unlike the poor fellow who does not have proper horizontal trim.

Balance has to do with the positioning of weights on your body and rig that allow you to remain in a stable position... you can be balanced so that you are super-stable vertically with tons of ankle weights and a horse-collar BC... or balanced so that you are super-stable horizontally with belly mounted weights and a rear inflation wing. Obviously we don't want that much stability! So we compromise... but realize that you will be balanced for either predominantly horizontal positioning or predominantly vertical positioning. A great many divers are worried about being unconscious at the surface and drowning with their face in the water... so they elect to balance themselves for heads up vertical stability... during the dive itself they have to swim (with great drag) at a 45 degree angle finning like mad to keep themselves off the bottom. I call them rototillers.

Since I want to be trimmed to swim horizontally and avoid the planing effects of motion and reduce drag as much as possible... I want to balance my weighting in favor of the horizontal position.

BTW... to answer your question about wetsuit compression at depth and the correct way to compensate for this loss of buoyancy... use the aptly named buoyancy compensator!

 

[MikeS]

Uncle Pug once bubbled...
trim BTW... to answer your question about wetsuit compression at depth and the correct way to compensate for this loss of buoyancy... use the aptly named buoyancy compensator!

Ha, Ha, funny answer but out of context as the issue at hand was trim not buoyancy.

To clarify the question, as the wetsuit compresses and air is added to the BC to compensate, will Balance shift as lift is moved from your legs and arms to your back (in the case of back inflation) and if so what can be done to compensate?

For example, with a 7 mil wetsuit, if I adjust weighting so that I “can get horizontal and remain horizontal without any movement to compensate” at 15 fsw, what should I expect if I then drop to 100 fsw and attempt the same exercise.

Another in the unending stream of questions:

Assuming that I have made the decision to adjust trim for horizontal swimming, but for some reason I would like to temporarily be in a vertical orientation, say to dump air from my BC, is there a proper technique for changing orientation? I think that now I just bend my knees and use my arm/hands to rotate up. At that point if I were to remain motionless I would eventually rotate back to horizontal.

Mike

 

[MikeFerrara]

Remember...If we get our center of gravity close or the same as our center of buoyancy we can maintain any position due to the lack of apposing forces. Depending on the equipment being used we may not get it perfect but we can get darned close. When you achieve this you can hover in any position. I don't settle for being balanced for horizantal or vertical. I try to get balanced so I can maintain which ever I want. With both single and doubles, horizantal is no problem. With my doubles FULL, at the surface, there is a SLIGHT tendance to go on my back. This is because those double 104's filled to 3500 or higher are very neg. With some of the gas gone it's all balanced again. With a single al 80 it's all dead nuts on. I can maintain any position at depth and I am not pushed on my face at the surface. Obviously this depends on both equipment and your body. There is usually some compromise involved and one should opt to maintain the horizantal position.

 

[Uncle Pug]

MikeS once bubbled...
is there a proper technique for changing orientation?

Just don't place your weights in such a way that you are balanced to be super-stable horizontally (or vertically)... as Mike F. says you can balance yourself to where any position can be assumed and maintained... though I really think that it is impossible to have both CG and CB coincide. In reality the best possible distribution of weight will still fall short of that ideal and you will be balanced in favor of one or more positions over others.... this actually can be a very small differential and easily overcome by body positioning.

To answer your question concerning wetsuit compression effecting the ability to trim out horizontally.... nah.