Master Neutral Buoyancy: The Importance of Horizontal Trim (Simple Vector Physics)

[tursiops]

Just means that you have not had a new student who had taught vector calculus and differential equations and worked with a number of engineers and applied mathematicians for 30 plus years PRIOR to starting scuba. My instructor was also trained as an engineer so we were vectors from day one. Probably not the typical situation.

Yes! This is the problem of dumbing things down and/or using terms that have specific meaning but using with one's own definitions. People who actually understand the material get confused by the inconsistencies and conflicting meanings. For example, amplitude and magnitude are not synonyms except in (incorrect) lay usage....the former can be positive or negative, the latter is always positive. So, getting input from the diversity of SB members is excellent; that has already redefined what the blue arrows mean!

 

[NAM001]

Hi DOC,

This article is long overdue. This is something that is so rooted in fundimentals it is a shame it is not part of OW/AOW classes. Too bad that it is the instructor and not the curriculum that determines the priority of of this part of a class. What you have described , in the submarine service is SPEED ANGLE/trim PLANES. In diving it is not so clear cut which is which to the beginner. Like an airplane speed carries more weight, generates more lift. angle or trim attitude generates more lift per unit of speed as the angle increases. and planes are the control surface that increases drag with speed. all these factors are intertwined and their effects drop to ZERO effect when speed goes away. Nothing is native to hovering beyond the short term. Thus it is a skill that needs to be worked on and you cant do that without an understanding of the basics you describe. I hope as the rest of your segments comes out those that live to pick will leave well enough alone so the beginners and many more advanced can pick something up from the presentation. Beyond breathing I rank buoyancy as the next most important skill a diver can master.

buoyancy is one thing trim is another. diving tends to blurr the two into one.

 

[Eric Sedletzky]

I like the graphics.
This to me is the natural way a diver should look travelling through the water, body in a straight line in relation to the direction of travel.
No feet up at a 90 degree angle with arms forward, to each his own and I know there are reasons people dive that way, but for my simple open water dives keeping my arms back and my body straight with feet straight back, not overkicking getting my feet and fins too far out of the slipstream means a very efficient glide and minimal drag. The idea being to pierce the smallest "hole" going through the thick mass of viscous liquid.
I think the biggest thing that throws off a divers attitude (trim position) in the water is when they have too much weight on a belt and too much air in their BC to offset it. The air collects up around the shoulders of the bladder and the heavy weightbelt (or pockets) pulls their middle section down making them go forward at a 45 degree angle. The biggest thing to me is to first get the weighting down exactly right, then work on distribution of remaining weight after that to achieve the "flat" attitude in relation to the direction of travel.
Also, many times divers think they are flat in the water and are exhibiting perfect trim, but then somebody will snap a photo of them and they still look like they are sloped uphill. This is evident when you see the front of the tank up at a 10 or 15 degree angle. This stems from the divers needing to have their heads up to see where they are going. If you put a diver in an exactly flat position it feels to them like their heads and front of body are actually going down hill a bit and it's becomes really a strain to keep the head up to look forward. For this reason there will always be a slight upward angle to a diver travelling forward. The only divers I see that can keep a perfectly parallel attitude towards the direction of travel are freedivers but then they don't always have their heads up either.

All of this then gets into gear: where the ballast is placed on the body and the resulting gear choices to achieve that, and voila! we have another debate about BP/W vs poodle jackets, steel vs aluminum tanks (and plates), and a number of other things.
This just illustrates how everything combined, including gear choices, play a factor in overall trim and buoyancy.

 

[stuartv]

Yes! This is the problem of dumbing things down and/or using terms that have specific meaning but using with one's own definitions. People who actually understand the material get confused by the inconsistencies and conflicting meanings. For example, amplitude and magnitude are not synonyms except in (incorrect) lay usage....the former can be positive or negative, the latter is always positive.

I agree with the first part. And it is true that amplitude and magnitude are not synonyms. But, technically, the last bit is incorrect. In Physics, amplitude is always positive. It is the distance from zero. Specifically, it is the absolute value of the distance from zero. Absolute value, in Mathematics, is, by definition, positive. The amplitude of a sine wave (for example) is always X, never "minus X".

Amplitude and magnitude are not synonyms because amplitude is specific to an oscillating system and magnitude is not.

 

[The Chairman]

OK, I'm going to have to do a video for the next installment. Don't look for it this week. I'll post a link here when it comes out.

 

[tdallen]

Rather than continue with the next topic, "How to Establish Trim" I'll probably write "Bubble Management" next. I haven't decided, but it's obvious to me by the PMs I'm getting that many divers have never considered this aspect of their diving. It's confusing and surprising the hell out of them. What would y'all like to see next?

As a new diver, I *think* what I need to know next is how to Establish Trim. The importance was reasonably clear from my OW training, and made clearer from your first post, so thanks! But the path to getting comfortable with Trim looks like a lot of trial and error over many dives, made more complicated by vacation diving and rental equipment. If there's a way to be more efficient about it, I'd love to know.

 

[Basking Ridge Diver]

As a new diver, I *think* what I need to know next is how to Establish Trim. The importance was reasonably clear from my OW training, and made clearer from your first post, so thanks! But the path to getting comfortable with Trim looks like a lot of trial and error over many dives, made more complicated by vacation diving and rental equipment. If there's a way to be more efficient about it, I'd love to know.

A good instructor goes a long way in being more efficient or you can keep diving and trying on your own.
I have seen OW divers on their very first dives after certification look very efficient - I believe it was due to their instruction.
And owning your own gear does help too.

 

[archer1960]

As a new diver, I *think* what I need to know next is how to Establish Trim. The importance was reasonably clear from my OW training, and made clearer from your first post, so thanks! But the path to getting comfortable with Trim looks like a lot of trial and error over many dives, made more complicated by vacation diving and rental equipment. If there's a way to be more efficient about it, I'd love to know.

If you're willing to essentially "waste" a couple of dives, you can probably get this done relatively quickly. Rather than swimming around exploring and looking at things, you'll have to be willing to get in the water, see how your trim is, get back out of the water to move weights around, and go back in to test. Probably multiple times. In my case, I didn't do that; I dove once per week for 3 or 4 weeks in a row, making sure to spend some time in each dive just hanging motionless to see how my trim and overall weighting were, and then I made adjustments during the week before the next dive. AFter about 4 dives, I had it dialed in pretty well. Now I can hang motionless head up, head down, or horizontally as required, and hold a 6 ft depth with an empty BC at the end of the dive using just my lungs. I chose to use 6' instead of 15' because so much of my diving is in the shallows near shore, and I didn't want to have to fight to stay down to look at things.

 

[The Chairman]

As a new diver, I *think* what I need to know next is how to Establish Trim. The importance was reasonably clear from my OW training, and made clearer from your first post, so thanks! But the path to getting comfortable with Trim looks like a lot of trial and error over many dives, made more complicated by vacation diving and rental equipment. If there's a way to be more efficient about it, I'd love to know.

After a few PMs and a phone call or two, it appears that I've really hit a nerve here for many, many divers. In that respect, it's been decided that I need video to competently convey the next few concepts. In those videos I will show you how to do just this pretty effortlessly. If any instructors or dive enthusiasts in the area want to help me out, please let me know. I'll be heading to cave country right after Christmas for a week or so of petting wet rocks, but there's a lot of clear water up there and I would love to get a real videographer on this project. Let me know if you're available, or maybe we can do it early January at Jacobs Aquatic Center in Key Largo after the first of the year.

 

[dumpsterDiver]

I think making a few videos is a great idea. Videos sound easy, but in practice it is always more difficult than it seems.

One suggestion/challenge I offer: Make the video to include identical tanks that are filled to capacity and nearly empty. The change in buoyancy in a tank can be significant and problematic, especially for larger capacity steel tanks that hold like 8-9 lbs of air (or whatever it is). In other words, show that what you are doing works at both extremes of the range.

I personally think the changes in the weight of the tanks makes optimizing trim more challenging and the best solution might be something that works perfectly toward the middle of the range.