I don’t have a problem with swimming per se, I could easily swim out to a boat etc.
I can’t fully submerge and go to the bottom, I’m too buoyant. I’m not fat, if anything skinny and told I look like a junky.
At this point I am about to give up, but if I need to swim down to retrieve a macguffin I’m out of luck.
Let some breath out of your lungs and try it.
Not enough muscle and bone vs relatively big lungs. yes, do try to make a full expiration before you go down. Do some weight training.
If you are fairly tall and thin the odds are you have a relatively large lung volume. Air obviously is more buoyant than even fat. Muscle is a bit denser than water but not much (maybe 6% denser). Most non-obese people, meaning those who do not have the junky build, still have enough of it (and thick enough and dense enough bones) to offset the buoyancy of residual lung volume. You don’t.
Hold a weight as you sink and when you to get the macguffin and drop it as you pick the macguffin up. Or, again, work-out.
I float very easily. People have commented on it at the pool. But I have no problem swimming down to the bottom of the deep end (13’).
It’s just something you learn to do.
And don’t let out air. That’s not the main issue.
We all float down here?
Do you really need that MacGuffin down there anyway? It’s probably just a red herring.
What is a MacGuffin?
Why would somebody want to catch one?
Are there McGuffins out there, are they related in some way?
Fight The Ignorance! 
Hey, I’ve experienced the same thing, I thought it was just me! Pleased to hear I am not alone.
We were snorkelling in Bali, I had a t shirt on to protect my shoulders, some other snorkellers suggested we dive down to see a lion fish on the seabed. So we tried. But no matter how hard I tried, or how much air I exhaled, I just couldn’t get down to the ocean floor! We resurfaced and made three attempts. On the final attempt my husband reached up and grabbed my t shirt and pulled me down the last bit. I don’t think I could have done so otherwise. (105 lbs!)
The fish was a very cool thing to see and all, but when I got out I was all, WTF happened there?
I think it’s an egg Macmuffin that has been regurgitated…not sure so don’t quote me on that.
Now this is a conundrum…I suppose it depends on how hungry you are.
next question…
My x-wife would sink like a rock…could not stay on top of the water with out floatation. She had a rather ample buttox (that was not hard to look at) …maybe you have a similar backside?
Scuba divers wear weights to counter their natural buoyancy.
Don’t feel special.
An easy solution would be a rope with a weight on one end and a float on the other.
Drop it where you want to dive and pull yourself down.
Or get a weight belt and weights.
Don’t forget that it does not take a lot of weight to make it very hard to swim back up. If you do not have an alternate way to get your weights back up you will spend a lot of time collecting rocks or buying lead.
What is the main issue, then? Like the OP and some others, I’m unable to swim down.
Most people are too buoyant to completely submerge. Unless you’re extremely athletic, you’ll need to either propel yourself downwards, or carry weights.
You do the breast stroke in a downward direction. It is not at all mysterious or hard to do.
There are different ways to get started. The best is: lying flat on your belly, bend at the waist and turn your head down, flip your feet up into the air (you use a sweeping motion with your arms to keep your head down), the weight of your feet gives you the initial momentum. Learned to do that by the time I was 8.
For beginners, while vertical, give a big push and kick up, when sinking back down let your legs go back so you start sinking in at an angle. Once all the way under straighten out horizontally and start the breast stroke. Angle down more to gain depth.
I do the later when I want to swim underwater on my back (but angling the other way). I’ll do 1.5 lengths of a 25m pool that way. It actually seems easier than on my front.
Letting out your breath when snorkeling is extremely bad thing to do. Never do it. Never. (And as I said, you shouldn’t do it all. But with snorkeling you need air to clear the tube.) The buoyancy change from letting out your breath doesn’t make that much difference. Swimming technique is what matters.
If you’re snorkeling, you presumably have fins which makes underwater propulsion quite easy.
Your rib cage occupies pretty much the same space no matter how much air is in your lungs.
Weights are properly used to establish neutral buoyancy - not to cause you to sink, just to let your swimming direction determine your depth.
Ideally, you would stay at whatever depth you set.
:dubious:
Then why does it move in an out with each breath?
I’ve let the air out of my lungs and sunk to the bottom of a pool quite often. Without letting the air out of my lungs I didn’t sink.
When in college my friends and I used to do that and then try to walk across the bottom to the other side of the pool.
Wait really? I didn’t know divers wore weights, huh. This makes me feel a little better.
Yep, it also helps since, as the SCUBA tank empties, it gets lighter and more buoyant.
My dives would start with my body slightly facing upward as I moved horizontally (the kicks would propel me slightly upward to counteract the weight-belt). Then toward the end of the dive my body would face slightly downward to counteract the increasing buoyancy of the tank.
Paying attention to your body position during horizontal movement can be helpful in judging your remaining air supply.
Thought about the exhaling issue and came up with this point of view.
Let’s say for simplicity your buoyancy after exhaling is the same magnitude as your buoyancy with your lungs full, just the sign has changed.
So, with lungs full, you have to swim down with effort but going up is much easier.
With lungs less-than-full, you have to swim up with effort but going down is much easier.
Note the symmetry in both cases. One way is easier, one way is harder.
My preference is to have the going up (you know, to where the air is) be the easier part.
If you can swim up to the surface with negative buoyancy, you can swim down from the surface with positive buoyancy. Plus you have a longer time underwater with greater safety.
Your rib cage expands with inspiration. Lung volume typically varies by roughly 500 ml between normal inspiration and expiration and full breath in to full breath out is typically a bit more than a L for a normal adult male.
The goal ftg is be roughly the overall density of the water you are swimming in. Thus very little effort will propel you down and the same very little will propel you up. Note salt water is denser thus most scuba diving in salt water require weights to become neutral density. You do not want to make the effort of swimming down carrying an inner tube just so the inner tube will carry you up.
Here’s a good hypothetical illustration using a moderately built individual with typical lung volumes.
Our open is very thin: lung volume represents a larger fraction of his/her total volume than it does a heavier person.
If you want we can do the math: we’d just need to know grude’s weight and make a guess at percent body fat (height and thus BMI would help make the guess a bit more educated).