Is buoyancy control more difficult with a thicker wetsuit?

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Run away ascents are common at the quarry we dive near Chicago. The new students have trouble descending then fly up to the surface. The wife and I try to perfect our skills there in 7mm farmer johns or drysuits so when we get to the caribbean we look like total rock stars! It always amazes us how effortless warm water diving is compared to Chicago when snow is flying.
 
Yes, DD explains it all well. If properly weighted with good trim and a fair bit of experience, cold water equipment shouldn't make much of a difference. Shallow water will be a bit more difficult I guess. You may have to pay a little more attention to exactly what you're doing. I still like my steel tank better, especially with the 7 mil farmer john suit, but even with the shortie. I know it's always at least a bit negative. I do a lot of cold shallow shore diving, which certainly helps.
 
BTW, the tanks make no difference in buoyancy. If you are weighted correctly, it doesn't matter if you're carrying lead to sink an aluminum tank, or just using a steel tank. Where steels can cause issues is with rotational stability. But for buoyancy, the only problem with steels is avoiding being overweighted.

What I have found interesting, though I don't see it, is the number of divers who prefer the standard aluminums (over compacts) because of the buoyancy bubble those divers say it provides.

IME newer divers have trouble distinguishing trim and buoyancy problems because those two tie so tightly into each other. Since steels tend to encourage better trim (generally speaking), they end up seeming to solve buoyancy problems for some divers.
 
Uh-huh.
 
I would say yes, because a thicker suit will have more variation in buoyancy than a thinner suit or no suit at all. Too, it would be more noticeable at around 24' where you were diving (at deeper depths it would just compress and stay that way in a more consistent way).

Ah, I see.

Also, it's possible your weighting was not as spot-on as it was with less exposure protection and/or a familiar tank/etc.

Absolutely. As a matter of fact, today when I did day 2 of the Advanced Open Water certification, we worked on buoyancy. A very well spent 45 minutes. The coolest thing I got from it is that the fin pivot is not just something you demonstrate during the open water course, but something you can use before every dive, to optimize your buoyancy for the ambient conditions. You add air to or remove air from your BCD until you can do the fin pivot without difficulty, and that means that you have the right amount of air in your BCD. I don't know why nobody told me that before.
 
Now dive with a thick suit... You have much more lead and when you get down the suit crushes a lot, losing 15 or more lbs of bouyancy at depth.. so... you have maybe 15 - 20 lbs of air in your bc to be neutral... what happens when you ascend? Your suit expands (increasing bouyancy) and the much larger volume of air in the BC expands the same relative amount, but since you started with much, much more air in the BC, the expansion is much, much more.

The wetsuit and the air in the BC represent an unstable equalibrium... Once you are balanced it is immediately thrown off when you descend.. you get heavier faster and when you come up you get lighter faster.

This is a fabulous explanation of the problem. Thank-you for the education!
 
the fin pivot is not just something you demonstrate during the open water course, but something you can use before every dive, to optimize your buoyancy for the ambient conditions. You add air to or remove air from your BCD until you can do the fin pivot without difficulty, and that means that you have the right amount of air in your BCD. I don't know why nobody told me that before.

The problem with this is that the fin pivot, as taught, requires contact with the bottom. In many places, if you make contact with the bottom, you are either damaging something, or destroying the visibility. Although the fin pivot can be a useful transitional step for new divers, the goal is to descend and arrest your descent BEFORE making contact with the bottom, and establish neutral buoyancy IN THE WATER COLUMN.

The IDEA of the fin pivot, which is that you want to reach a place where inhaling causes you to rise gently, and exhaling causes you to fall a little, is valid. But you really want to be able to do this, and check it, without making contact with the bottom, and preferably not in the head-up/feet-down position that the fin pivot encourages divers to assume.
 
A great thread for everyone to read. And also the responses illustrate why it is important to do a weight check whenever you change equipment or conditions, or even if you had a change in body weight and type since your last dive. That is why I advocate logging every dive. As you assemble data from a variety of conditions, locations and over time, recording equipment worn and used (and that means type of tank along with everything else) , where you dove, what you weighed, and what weight you added to dive , you create a reference library that will serve you as long as you are diving.
DivemasterDennis
 
The problem with this is that the fin pivot, as taught, requires contact with the bottom.... The IDEA of the fin pivot, which is that you want to reach a place where inhaling causes you to rise gently, and exhaling causes you to fall a little, is valid. But you really want to be able to do this, and check it, without making contact with the bottom, and preferably not in the head-up/feet-down position that the fin pivot encourages divers to assume.

I still feel a frisson of annoyance when I am reminded of the fin pivot. In all three (!) of the classes I took wherein this maneuver was taught, I had a problem with it. The thing is, I tend to be a bit "foot light," if anything. So whenever I would try to do the fin pivot, I would end up hovering horizontal and going up and down with each breath, instead of angled with my fins touching the bottom, like they were supposed to be. It was so frustrating.

But, did they ever mention that horizontal was actually better (for real diving), and that the whole goal of the exercise was just to see that we could use breath control for buoyancy adjustment? (Which I was able to do.) NooOOOoooo. They just kept emphasizing that it was The Fin Pivot and that my fins needed to be resting on the bottom so that I could do a proper one. At that early stage, I simply understood what they said to be true (that I couldn't do a proper fin pivot), but missed that they were adhering to the "letter of the law" and not the spirit of it. Had I only known that it would be fine not to dive at a foot-down angle, and have my fins touching the bottom, I could have saved some frustration.

(Now that I'm past the rank beginner stage, I think I probably could get myself into the fin pivot position, but I haven't tried.)

Blue Sparkle
 
That is why I advocate logging every dive. As you assemble data from a variety of conditions, locations and over time, recording equipment worn and used (and that means type of tank along with everything else) , where you dove, what you weighed, and what weight you added to dive , you create a reference library that will serve you as long as you are diving.
DivemasterDennis

I agree with this and have found it very useful for my own diving. As you recommend, in addition to data on the site/sights, I record water/air temperature, exposure protection worn, equipment worn, weight worn (and where positioned). I also note whether it all felt just right, or, conversely, whether I was chilly, a bit light on the last stop, fighting for trim, or etc. I find it very useful as a reference for subsequent dives.

To enhance this, after some number of dives I looked in my log book to see where I consistently had unused space or blanks, and where I was writing in the same things over and over (that did not have a designated area). I then worked with my usual buddy (a friendly computer geek), and we designed our own log book pages that had places for us to write the things we found useful.

We eliminated certain categories (or condensed them) and added or expanded others. For example: Not just a box for amount of weight, but a way to keep track of where we placed it: front, back low, tank etc. We sized the pages to fit in the commonly found zip-up 3-ring dive log notebook. When it comes time to print more, I may make a few more tweaks based on their usage.
 

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