Are trim and buoyancy fundamentally related?

[dmaziuk]

Airplanes are the worst possible analogy because their buoyancy and trim are fundamentally related -- by thrust, as everyone else's been pointing out. Which is the opposite of the point OP was trying to make. And then there's that lift vs drag issue on top.

 

[MichaelMc]

Airplanes are the worst possible analogy because their buoyancy and trim are fundamentally related -- by thrust, as everyone else's been pointing out. Which is the opposite of the point OP was trying to make. And then there's that lift vs drag issue on top.

How about civilian submarines as an analogy. They dive, hover, have motors maybe not aligned with motion, some are a bit like flat decks pushed through the water, Some are not streamlined. Some fly through the water. Almost like divers...

The flat deck one: Lake Tahoe Underwater Researchers Unveil Findings

 

[DevonDiver]

Airplanes are the worst possible analogy.. .

This...

Buoyancy is independent from thrust, but effect by it, relative to trim.

 

[NAM001]

This...
View attachment 410618

Buoyancy is independent from thrust, but effect by it, relative to trim.

You are correct. and that is why when attempting to master buoyancy and trim you get the buoyancy fixed first. it is the easiest one to conquer. The easiest factor to remove from the problem. And yet it is the one that if not handled first is masked by body angle and speed (thrust direction). I say this because both buoyancy and thrust direction . (body angle and speed) yeild the same result. IE up angle with thrust takes you to the surface. light buoyancy takes you to the surface.

 

[wKkaY]

Why would you get water up your nose? I feel a bit of tension in my head when hanging upside-down -- I guess blood knows that gravity is thataway even if the body feels weightless -- and I had a rental reg breathe slightly moist once or twice, but never water in my mask.

There's always a little water that wells up in the nose area of my mask. It doesn't bother me when looking down or ahead, but it goes up my nose when looking up at the surface.

 

[wKkaY]

You are correct. and that is why when attempting to master buoyancy and trim you get the buoyancy fixed first. it is the easiest one to conquer. The easiest factor to remove from the problem. And yet it is the one that if not handled first is masked by body angle and speed (thrust direction). I say this because both buoyancy and thrust direction . (body angle and speed) yeild the same result. IE up angle with thrust takes you to the surface. light buoyancy takes you to the surface.

I've watched a few UTD "Extreme Makeover" videos and they seem to follow that method.

For example this one:

 

[EricTheDood]

One can only go so far by simplifying diving into a physics lesson. Eventually you reach the realization that the squiggly thing attached to the dive gear, i.e. the human, controls the end result, both consciously and subconsciously.

The human who maintains trim tends to have good buoyancy.

The human who ignores trim may or may not have good buoyancy.

The human who has crappy buoyancy has even worse trim.

 

[dmaziuk]

There's always a little water that wells up in the nose area of my mask. It doesn't bother me when looking down or ahead, but it goes up my nose when looking up at the surface.

Yeah, ok. I guess I must subconsciously breathe out a little when turning upside-down: I've been doing flip turns while swimming laps for quite some time now... You need just a little positive pressure in your nose to stop the water from going there.

 

[TMHeimer]

I always talk about "blocking" the nose passageway off (Soft Pallet, I think--one of those anyway), when the nose is exposed to water....usually in response to no-mask breathing problems. TS&M pointed out years ago that in a certain head back position water will get through even if the passage is blocked, though I've yet to experience it myself (never tried it).

 

[DevonDiver]

When inverted water will get up the nose and into the sinus. It shouldn't go down the throat or interfere with mouth breathing.

Nonetheless, it is unpleasant. It can sting and it can make a diver feel panicked. It can also leave you vulnerable to nasal infections.

I recommend a sterile saline nasal flush/spray whenever you get water up your nose. That's a good idea anyway as a pre-dive habit.. as it helps clear the sinuses well.

Some higher-level overhead and sidemount training requires skills like inverted (upside down) and vertical (head down) mask clearing and remove/replace. It's a heinous skill to complete... you'll flood your sinuses for sure. But it does help one get used to having the claustrophobic sensation of water up your nose. It's my least favorite skill to demo LOL.