Interesting Temporary Buoyancy Issue

[tursiops]

All of this does not change the fact however, that for a reasonably skilled diver head first is not much worse than feet first. I can do both styles of descents in addition to a horizontal trim descent in a drysuit, and what is doable in such a balloon is certainly doable in a wetsuit.

Please correct me, if I'm wrong.

I'll try and say this again: Going down head-first using fins to help the descent is risky, since it may mean one is not sufficiently weighted to maintain a comfortable safety stop at the end of a dive, with the suit uncompressed (back at 5m depth) plus lost gas from the tank.
The fact that YOU can do a head-first dive does not make it a good recommendation, it only means it is possible. I can't...because I can't equalize well when upside down.

 

[Subcooled]

Most photos I've seen of diving legends tend to show a person in a bathing suit, triple tanks, double hose reg, flippers and mask on forehead if not in the water. Excluding photos from ads selling wetsuits, I haven't seen very many vintage photos that include exposure protection. I've seen a few, but not a lot.

Maybe that is because with diving legends I mean people who dived in Finland in 1950's
The water is pretty cold here.

Globally:
The cousteau team wore neoprene (painted in silver: look at the films) although Hans Hass with his wife did (as you said):
https://ichef.bbci.co.uk/news/624/mcs/media/images/80680000/jpg/_80680051_lotte-and-hans.jpg

my understanding is that the main reason things aren't done in the way that the legends did it is primarily to improve safety.

That is correct.

I do not understand however, how diving feet first would be better than head first, unless very inexperienced and scared. In the former situation you will use the corrugated hose to let our air while in the latter case you will use the rear dump. If you dive dry, both ways are doable (all air around your neck or in your boots but both doable), but the often easiest way is in a horzontal position.

 

[Subcooled]

I'll try and say this again: Going down head-first using fins to help the descent is risky, since it may mean one is not sufficiently weighted to maintain a comfortable safety stop at the end of a dive, with the suit uncompressed (back at 5m depth) plus lost gas from the tank.
The fact that YOU can do a head-first dive does not make it a good recommendation, it only means it is possible. I can't...because I can't equalize well when upside down.

You are correct. Finning down means trouble making a controlled ascent.
(This does not depend on orientation but on forced descent by finning "using fins to help the descent")

The amount of actual risk depends on depth and time and physical shape and hydration and many other factors of course, but I have to admit that as a general rule, the need to fin down means increased risk.

 

[tursiops]

You are correct. Finning down means trouble making a controlled ascent.

The amount of actual risk depends on depth and time of course, but I have to admit that as a general rule, the need to fin down means increased risk.

Additionally, at some inland diving sites the bottom is full of snags sticking up, and the viz is very bad; much better to hit those snags with your fins than with your head.

 

[TMHeimer]

At least to me it is...

Hello All,

I did an ocean dive last Saturday with 18 lbs. on my weight belt. I was wearing a 1.5 mil wetsuit, a 2/5 mil hooded vest, and a 5 mil wetsuit over all of it. Warm as toast, by the way, with 50 degree water.

I had enough trouble descending that my dive buddy suggested that I needed a little more weight. However, once I worked at it and was submerged for a while, I found 18 lbs. to actually be a bit too much. When fully exhaling, I could lay on the bottom and stay there while breathing. So I don't want more weight.

What seemed to do the trick was giving up on a vertical descent and just diving down, headfirst, with a few fin kicks. Releasing air from my BC was also easier because I used the release valve at the bottom of the vest since it was then closest to the surface. That method seemed more foolproof than getting the hose extended just right and hoping no air was trapped someplace.

My guess is that I had all kinds of air trapped in my suits which was eventually squeezed out by the pressure. I also assume my breathing got better as I relaxed and that helped too, but I suspect air in the suits was the main culprit.

Is getting down with a few fin kicks and head down frowned upon? Is there a better solution you would recommend, given my situation? I am open to any and all suggestions...except for add more weight.

Thank you all.

I've also done the head first descent on occasion. Just bought a new BCD, larger than my old one, so I imagine there is more air trapped in that when doing the initial descent. I dropped 2 pounds and found that it was just too much of a hassle wiggling around to descend, so I added the 2 pounds back. All is good. A pound or two more than necessary doesn't noticeably affect my type of diving.

 

[Subcooled]

Additionally, at some inland diving sites the bottom is full of snags sticking up, and the viz is very bad; much better to hit those snags with your fins than with your head.

A valid point. While diving in bad visibility (=muddy rivers) I always descend feet first, for the very reason you stated, then get on my knees, then get in horizontal position. If visibility is good though, I want to see the things before the are up my ***

 

[rick00001967]

The issue might be that holding a safety stop is difficult without contsantly finning down.

100% true

there were two assumptions on my part.

A - that when we were discussing going head first and finning down, that it meant a dive similar to when snorkeling. i did not assume we meant kicking as of your life depended on it.

and 2 - that the diver had previously done a proper weight check. which imho would be testing weighting at about 10 feet with low gas in the tank (no more than 500 psi - less would be better) and then dumping all the gas out of the bcd. then adjust weight until you are neutral or slightly negative.

 

[Patrick Star]

Thank you all.

Let me add these observations to the mix, in light of the comments so far. When it was time to ascend (with about 1000 psi left in my tank), I wanted to try doing so without adding any air to my BC. I wanted to see if the suit compression process reversing itself, along with less air in the tank, would make me buoyant enough to ascend but not too buoyant for a safety stop. I ended up struggling to ascend, finning fairly hard, and then resorting to adding air to my BC to get me up.

The 18 lbs. recommendation was as a result of a formal buoyance check in a salt water pool, with a known adjustment for the salinity difference with the ocean. Actually, the check said 16 lbs. and it was recommended that I add 2 additional lbs. for a cushion, and to work toward removing it during subsequent dives.

IF it actually was air trapped in the suits and eventually purged, as opposed to compression of the material itself (which will come and go in equal measure as I descend/ascend), it seems to be an explanation of what I experienced. I just feel that if I add more weight, I will be fighting being a paperweight on the bottom. If I then have to add air to my BC at depth, this appears to not be the best way to move about with good trim.

Thank you again for your advice and suggestions.

 

[tursiops]

If you are weighted properly, you WILL need to add air at the bottom, because (a) you will be 5 lbs heavy to compensate for the air you have not yet used up, AND your suit will be compressed. Sorry.

 

[Patrick Star]

If you are weighted properly, you WILL need to add air at the bottom, because (a) you will be 5 lbs heavy to compensate for the air you have not yet used up, AND your suit will be compressed. Sorry.

Makes sense. I just thought air in your BC was mostly for the surface.