Are trim and buoyancy fundamentally related?

[Nasser]

I would say buoyancy and weight distribution are related to trim.

 

[Bogtrotter]

Yes they can exist independent of one another. But I would say during the act of scuba diving, which involves striving for the most efficient means of propulsion and control within the water column, they are fundamentally related.

 

[The Chairman]

Who hasn't admired those effortless divers. They're in perfect control and seem to use no energy during their dives, adjusting their depths magically, never creating a silt out, never scull and their air seems to last forever! Some say, this takes at least a hundred dives, but I've got a few lessons that will make you feel and look a lot better on your very next dive. This will be a multi-part discussion about how to master Neutral Buoyancy. They will be "The Importance of Horizontal Trim", "How to Establish Trim", "Bubble Management" and "Breathing Techniques". Consider this my Christmas present to all my students, past, present and future.

It's my personal opinion that these discussions and demonstrations should be a part of every open water class, but alas they are not. However, this thread is only to discuss the physics of trim and how it affects neutral buoyancy and not the importance of when or where it should be taught. PLEASE KEEP ON TOPIC.

Disclaimer... if the following picture epitomizes your concept of neutral buoyancy, then this thread may not be for you. In fact, it might just piss you off!

Horrible Diver Buoyancy/Trim

Almost everyone knows the physical law that for every action, there is an equal and opposite reaction. This is the beginning of understanding physics for divers. Don't worry, this won't be painful. I've taken a bit of time to create some animated GIFs to demonstrate what I'm writing about. As for testing your comprehension, your final exam will be on the reef.

For our purposes today, we'll be quantifying kick propulsion as a vector. A vector has both amplitude and direction which can be broken down to indicate both it's vertical and horizontal components. We're not going to worry about left or right in this discussion so we can keep this simple. All we are worried about is propulsion as it relates to vertical and horizontal components.

So, let's look at a nicely trimmed, horizontal diver. Of course, we're not talking about Christmas ornaments, but their attitude in the water, which should be mostly flat and horizontal.

Notice the propulsion vector being generated by the diver's kick. It's going straight behind him with no upwards or downwards element. This diver will control their depth by using their lungs rather than adjusting their propulsion angle and we'll cover how to do that in a couple of installments. Now let's look at a badly trimmed diver. We can see that his propulsion is not horizontal anymore but rather has a downward element to it.

While this is pretty as a picture, it's not giving us a real clue as to what is really happening. In order to do that, we are going to separate the resultant vector into its horizontal and vertical component vectors. They are smaller, but when added together, they become the bigger resultant vector seen above.

Notice the small vector representing the downward propulsionhappening here. The diver must compensate for this downward propulsion by adding more weight or letting out air in their BC to keep them moving horizontally. This is a slight angle as I've seen many, many divers with a 45o angle or worse! The larger the angle in regards to horizontal, the more force is being directed downwards rather than rearwards. That means you have to overweight yourself even more and that you're wasting a lot of energy pushing yourself up instead of forward like the horizontal diver. Good exercise, sure, but what happens when you stop? Here's a side by side comparison of these two divers at rest. The horizontally trimmed diver is on the left.

See? When the horizontally trimmed diver stops, he just stays there. Unfortunately, once the badly trimmed diver stops, he has no upward force to keep him neutral, so he starts to sink. This is where people start to scull with their hands or they add some air to their BC. Sculling and playing with your BC all the time are two major indicators that your trim is off: way off. That horizontal diver can just relax and look at whatever he stopped to admire. The badly trimmed diver has chased away whatever he wanted to look at with his flailing hands. Even worse, he gets the 'rototiller' award for kicking the crap out of the reef when he starts up again. While it's still your choice, it's pretty obvious from a physics standpoint that getting horizontal will improve your diving. You'll use less energy, which means your air will last longer and your drive will be far more enjoyable.

 

[RayfromTX]

First, I am new and so this is the pov of a new scubadiver.

Scuba diving is a four dimensional activity that is closest in my opinion, to slow motion flight. There is a pov that it is best performed in a skydiver position. That is a pov with merit and sound basis for many of the activities engaged in by divers.

It should be noted that many skydivers gave up that position long ago to pursue another form of skydiving called freeflying that involves 4 dimensional choreography is any position other than belly flying. A good skydiver can do all those things and a great skydiver doesn't say that one is better than another, they just fly and help others to do the same. Their brains process the 3 dimensions with movement in a way that is unlimited by a set of guidelines. They typically are not the same types that enjoy creating precision freefall formations of 100 or more people. I used to think that they were too lazy to build their belly flying skills. I soon discovered that to be a false belief.

I have watched DMs in Cozumel drifting along vertically and in perfect control able to easily scan 360 degrees and quickly transition to horizontal trim and anything in between as the situation called for it. They seem to be fish. I personally want to develop all the skills to allow me to do anything in the horizontal position as well as being a four dimensional freeform scuba fish.

An argument about this subject seems to be born out of concerns regarding people with none of these skills. If you want to be a good scuba diver, you need all those skills. There are simply too many kinds of diving to make the argument that one way is better than another. Context matters. As for me, I will continue to work on the fundamental skills of being trim and horizontal in the water with an awareness of where all my parts are. I'm a long way from that.

Oh, and in answer to the question of the thread as worded? Absolutely! I don't think that was really the topic of the argument in the other thread from which this thread was born.

 

[RayfromTX]

If you look like this, then you're doing it wrong:

View attachment 410473​

In the other thread, our OP referred to being both "trim and neutral" as a parlor trick. The picture above is the parlor trick.

Who hasn't admired those effortless divers. They're in perfect control and seem to use no energy during their dives, adjusting their depths magically, never creating a silt out, never scull and their air seems to last forever! Some say, this takes at least a hundred dives, but I've got a few lessons that will make you feel and look a lot better on your very next dive. This will be a multi-part discussion about how to master Neutral Buoyancy. They will be "The Importance of Horizontal Trim", "How to Establish Trim", "Bubble Management" and "Breathing Techniques". Consider this my Christmas present to all my students, past, present and future.

It's my personal opinion that these discussions and demonstrations should be a part of every open water class, but alas they are not. However, this thread is only to discuss the physics of trim and how it affects neutral buoyancy and not the importance of when or where it should be taught. PLEASE KEEP ON TOPIC.

Disclaimer... if the following picture epitomizes your concept of neutral buoyancy, then this thread may not be for you. In fact, it might just piss you off!

View attachment 410474​

Horrible Diver Buoyancy/Trim

Almost everyone knows the physical law that for every action, there is an equal and opposite reaction. This is the beginning of understanding physics for divers. Don't worry, this won't be painful. I've taken a bit of time to create some animated GIFs to demonstrate what I'm writing about. As for testing your comprehension, your final exam will be on the reef.

For our purposes today, we'll be quantifying kick propulsion as a vector. A vector has both amplitude and direction which can be broken down to indicate both it's vertical and horizontal components. We're not going to worry about left or right in this discussion so we can keep this simple. All we are worried about is propulsion as it relates to vertical and horizontal components.

So, let's look at a nicely trimmed, horizontal diver. Of course, we're not talking about Christmas ornaments, but their attitude in the water, which should be mostly flat and horizontal.

​

Notice the propulsion vector being generated by the diver's kick. It's going straight behind him with no upwards or downwards element. This diver will control their depth by using their lungs rather than adjusting their propulsion angle and we'll cover how to do that in a couple of installments. Now let's look at a badly trimmed diver. We can see that his propulsion is not horizontal anymore but rather has a downward element to it.

​

While this is pretty as a picture, it's not giving us a real clue as to what is really happening. In order to do that, we are going to separate the resultant vector into its horizontal and vertical component vectors. They are smaller, but when added together, they become the bigger resultant vector seen above.

​

Notice the small vector representing the downward propulsionhappening here. The diver must compensate for this downward propulsion by adding more weight or letting out air in their BC to keep them moving horizontally. This is a slight angle as I've seen many, many divers with a 45o angle or worse! The larger the angle in regards to horizontal, the more force is being directed downwards rather than rearwards. That means you have to overweight yourself even more and that you're wasting a lot of energy pushing yourself up instead of forward like the horizontal diver. Good exercise, sure, but what happens when you stop? Here's a side by side comparison of these two divers at rest. The horizontally trimmed diver is on the left.

​

See? When the horizontally trimmed diver stops, he just stays there. Unfortunately, once the badly trimmed diver stops, he has no upward force to keep him neutral, so he starts to sink. This is where people start to scull with their hands or they add some air to their BC. Sculling and playing with your BC all the time are two major indicators that your trim is off: way off. That horizontal diver can just relax and look at whatever he stopped to admire. The badly trimmed diver has chased away whatever he wanted to look at with his flailing hands. Even worse, he gets the 'rototiller' award for kicking the crap out of the reef when he starts up again. While it's still your choice, it's pretty obvious from a physics standpoint that getting horizontal will improve your diving. You'll use less energy, which means your air will last longer and your drive will be far more enjoyable. I'll post the second installment in a day or two on how to establish horizontal trim. I bet you have a number of ideas already!

I really wish I could take your class.

 

[Colliam7]

I think I'll change my opinion to - trim is the position we hold in the water. Buoyancy is how we maintain our depth. Propulsion is how we move forwards and backwards. Whilst they are independent of each other they can combine to give us the result we want.

I was going to reply to your original post, but this one is easier. I agree with your description above. Frankly, I agree with part of the premise of your OP, that trim and buoyancy are NOT the same thing, and can be achieved independently. I do think they are indirectly related, and propulsion enhances that indirect relationship. Andy has provided a good exposition. And, your statement, above, is a good summary. Thanks for raising an interesting discussion.

 

[Colliam7]

I would say buoyancy and weight distribution are related to trim.

Hmm. To extend that line of reasoning: buoyancy is related to weight, and weight distribution is related to trim. So, 'proper weighting' (how much and where) influences both buoyancy and trim.

 

[Lorenzoid]

How can any two things be "fundamentally" related if you are willing to factor in a third factor, such as thrust? Thrust/propulsion is a red herring. The answer is that fundamentally, i.e., without any other inputs such as thrust, buoyancy and trim are unrelated. That is, one can theoretically be neutrally buoyant in any trim (orientation). They are unrelated to each other, so long as you don't factor in anything else, which is what "fundamentally" means to me.

 

[RayfromTX]

How can any two things be "fundamentally" related if you are willing to factor in a third factor, such as thrust? Thrust/propulsion is a red herring. The answer is that fundamentally, i.e., without any other inputs such as thrust, buoyancy and trim are unrelated. That is, one can theoretically be neutrally buoyant in any trim (orientation). They are unrelated to each other, so long as you don't factor in anything else, which is what "fundamentally" means to me.

Technically correct but it isn't what the argument was or the reason for the thread. If you go back and read the original posts in the other thread where Charlie and Pete were arguing, then the question is more involved than just a semantic discussion of definition. It might have been helpful to move those posts over here to put the question in context.

 

[The Chairman]

They are unrelated to each other, so long as you don't factor in anything else, which is what "fundamentally" means to me.

So, you dive without kicking? Maybe you can start the No Kicking Scuba School?

At the core of effortless diving is control. People with bad trim have to continually adjust their buoyancy depending on their thrust. They scull, they flail, they silt, they do everything but maintain control. So, what's the upside to this? Rly? What's the upside to all the wasted energy? What's the upside to scaring the crap out of the fish you're there to see? What's the upside to hoovering through your air because you can't gently hover?

It doesn't matter where your propulsion comes from, if you're not neutral and flying flat, bad things can happen quickly. I was on the bone line in Ginnie Springs. It was my first solo cave dive and I was a bit nervous, but not terribly so. I knew I was coming to the end of the line and would be making a jump to the main line and heading on back home. All of a sudden I am hit with a cave light to my right. It was a solo diver on a scooter and I apparently surprised him as much as he surprised me. We both stopped. I stayed perfectly neutral while he floated up into the ceiling. He was using his trim to compensate for not being neutral, so when he stopped he went kaboom! I was able to acquire the gold line before the brief silt storm hit, so it was all good for me. Being Ginnie, it all cleared out in a second or so... but it illustrated to me that you need to integrate trim with buoyancy to maintain real control.