Can you have proper weighting if you are not in a horizontal trim?

[cb5150]

Sorry, too long to read...but, "yes" is the answer.

 

[DivemasterDennis]

I just ewant to add to the discussion that once you are in proper trim, you should be able to hover in about any position: vertical, horizontal, inverted, head stand, whatever. That ability is of course impacted by how much air is in your bcd or wing, so proper weighting is crucial as well, so that the least air possible is in the bcd when at depth. Lets face it ultimate buoyancy and trim control is a life long learning, practicing and improving process that encompasses proper amount of weight, proper placement of weight, equipment selection and familiarity, use of breathing to control the finer points of buoyancy and trim, and constant revision of all these factors as one's body changes, gear is replaced, and conditions vary. It's a wonderful challenge, and keeps ever diver worth their salt in a learning mode.
DivemasterDZennis

 

[tracydr]

I just want to add as well. You will never be perfectly weighted for the entire dive because air weighs. You weight yourself to be properly weighted at the end of a dive to hold a stop in 10-15 feet of water with about 500 psi in your tank. That means,for the rest of your dive you are always somewhat overweighted.
Weighting is dynamic,as is neutrality,since we must also compensate for suit compression.

 

[raftingtigger]

Some posters are getting my point and others are not. Yes I am reinventing the wheel - or at least reminding people the wheel has been invented.

Neutral buoyancy and trim ARE different. My point, which several posters have agreed with, is that the only way to KICK and stay at a STABLE DEPTH is to be in a horizontal trim.

Why am I bringing this up? A lot of divers believe they can KICK in a head-up trim AND be neutrally buoyant at the SAME time. These divers are therefore inadvertently over-weighting themselves. How much over-weighting depends on how hard they kick and how head-up their trim is (and probably a few other minor factors). I see a lot (majority?) of divers swim in a head-up and fin down (coincidentally a silting) kick - including a lot of instructors. This means that a large number of divers are over-weighted. *sarcasm* a completely new thought *end sarcasm*.

I posted this in the Basic forum so that new divers can see why they should strive for horizontal trim. This is a mental evolution I went through when I restarted diving a few years ago. I was one of the slightly over-weighted head-up trim divers. Any pilot should see the truth of this as it is the same as the 4 forces in flight.

---------- Post added October 16th, 2013 at 09:55 AM ----------

I just want to add as well. You will never be perfectly weighted for the entire dive because air weighs. You weight yourself to be properly weighted at the end of a dive to hold a stop in 10-15 feet of water with about 500 psi in your tank. That means,for the rest of your dive you are always somewhat overweighted.
Weighting is dynamic,as is neutrality,since we must also compensate for suit compression.

You are absolutely correct. I should have said neutrally buoyant in the title, but I wanted to catch attention. This point should have been made in the body of the post. Unless there is a way to dive with no flexible air spaces (lungs do count), every time you change depth you need to adjust buoyancy to maintain neutrality.

---------- Post added October 16th, 2013 at 09:58 AM ----------

Sorry, too long to read...but, "yes" is the answer.

Don't just read the title. It was meant to catch attention. Read the entire thing and you may (or may not) want to change your answer.

 

[DBailey]

Neutral buoyancy and trim ARE different. My point, which several posters have agreed with, is that the only way to KICK and stay at a STABLE DEPTH is to be in a horizontal trim.

From a physics point of view, you don't have to be a horizontal trim to stay at a stable depth when you kick. Your kick must have a pure horizontal component to it in order to maintain that stable depth. One could be vertical and neutrally buoyant, but as long as the kick only has a horizontal component, then the stable depth will be maintained. Also, one could have perfect trim and neutrally buoyant, but if the kick has any vertical component, then the stable depth will not be maintained.

From a real world application, yes it would be easier to maintain a stable depth in a more horiztonal trim since the kicks tend to have a "mostly" horizontal component.

A lot of divers believe they can KICK in a head-up trim AND be neutrally buoyant at the SAME time.

Neutrally buoyant while kicking is still neutrally buoyant. How neutral buoyancy is achieved is not a requirement of being neutrally buoyant.

For new divers, it might be easier to say "If you stop kicking, you should be hovering."

 

[raftingtigger]

"If you stop kicking, you should be hovering."

Absolutely agree. But that doesn't tell the diver (new or otherwise) how to get to that point. The whole point of the post is to explain how to get to the point where they hover when they stop kicking.

Since people are looking for all the subtle exceptions, rather than at the broad principles, let me further clarify:

A lot of divers believe they can KICK in a head-up trim, be NEUTRALLY buoyant, and MAINTAIN A SPECIFIC DEPTH at the same time.

Finally if you can kick in a purely horizontal plane with your fins either above or below your CG, without rotating around your CG, then more power to you.

 

[dumpsterDiver]

My trim is not good. When I stop swimming, my feet sink and I will become more or less vertical. Since I dive openwater and not in caves or silty wrecks, this is not much of a hindrance. Obviously, a diver that is perfectly trimmed in a horizontal position is going to be more streamlined and will swim more efficiently in a straight line.

HOWEVER, some of this is an issue of comfort. If you are drifting and hunting and looking forward at the limits of visibility you are looking straight a head. If you are horizontal, this can be VERY uncomfortable for your neck because it requires constant and complete extension of the neck. If you have some neck problems, I am sure it is unhealthy. If you have a more reasonable attitude in the water, feet down a little, this is much better for your neck and much more comfortable.

In some situations, I could play around trying to achieve perfect trim, but it is not worth it. When I swim hard, I plane out flat and move efficiently. When I cruise slowly, my body angle is tilted up a little and when I am completely relaxed for an extended time, I will end up vertical more or less. I feel that the decrease in hydrodynamic efficiency is negligible. The important thing is that your trim is not so bad that you do not trim out when swimming.. If you are swimming hard and not planned out, then you ARE wasting a lot of energy.

It really is not a big deal at all. In my situation, there is NO easy solution. Sometime I wear a big steel tank with no lead. I can not add or subtract trim weights and the tank has a very limited potential for adjustment up and down.. so I am stuck with the trim I have when I use that tank and the total weight of the tank will change about 11 lbs during its use.

I have very little need to float around with zero movement in perfect trim. If that is the diver's goal, then go for it.

 

[fdog]

I just ewant to add to the discussion that once you are in proper trim, you should be able to hover in about any position: vertical, horizontal, inverted, head stand, whatever. That ability is of course impacted by how much air is in your bcd or wing, so proper weighting is crucial as well, so that the least air possible is in the bcd when at depth. Lets face it ultimate buoyancy and trim control is a life long learning, practicing and improving process that encompasses proper amount of weight, proper placement of weight, equipment selection and familiarity, use of breathing to control the finer points of buoyancy and trim, and constant revision of all these factors as one's body changes, gear is replaced, and conditions vary. It's a wonderful challenge, and keeps ever diver worth their salt in a learning mode.
DivemasterDZennis

Absolutely, +1.

For me personally, I never stop trying to improve.


All the best, James

 

[cb5150]

You're applying a one-size fits all approach to the argument for horizontal trim.

While there is always a need to strive for neutral buoyancy, proper horizontal trim is not always needed for every environment. Caves, yes. Wrecks, yes. Exploring close to the bottom, yes. Diving or drifting over a reef with 100' of visibility, I often like to hover neutrally in the Budda position or the Laz-E-Boy position to simply watch the other divers and the critters...and I'll put my horizontal hovering/trim skills up against anyone. Many times, I just sit back and smile at the passing turtles, rays and sharks while the others (in perfect horizontal trim) are waiting in line to get a picture of a small eel or fish. Kinda reminds me of the sheep that stand in line outside the Apple store whenever a new phone is being released.

If you want to float by me, perfectly weighted and horizontal...good for you. But don't be surprised when I float by you, perfectly weighted, vertical, head down feet up, smiling like an inmate who just escaped the asylum.

Peace.

 

[raftingtigger]

You're applying a one-size fits all approach to the argument for horizontal trim.

I agree with most of your post cb5150, but nothing in my post demands, or even suggests, that all diving occur in a horizontal trim position. There are lots of times that I prefer either a head-up or even fully vertical orientation - but neither do I expect to stay at a stable depth if kicking in that position.

None of my original post was to proselytize, it was to explain the physics involved. How each diver chooses to dive is up to them, their buddy, and the specific environment. However, to make intelligent choices the diver needs to know why things behave the way they do, and how to change things if they wish to.

So far I haven't read a post on this thread that disagrees with my physics explanation. I have seen posts where the poster didn't read, or carefully read what was written (shame on you); other cases where implied diving philosophy was disagreed with (not a problem except it is off topic, but what else is new on SB and it leads to some fun reading); and some that verified my understanding of the physics. At this point I'll step out of the discussion unless someone finds fault with my physics.