Blackwood
Contributor
I can throw a water bottle from the ground floor onto the roof of my house. Think I can do the same thing with you?
sudden uncontrolled ascent!
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I can throw a water bottle from the ground floor onto the roof of my house. Think I can do the same thing with you?
Dear Ninamoon,
I am so glad that you are alright. I had a friend go into an uncontrolled ascent from 80 ft on a high altitude dive. He complained of a headache after that!!! He too was lucky.
Learning to use all your dump valves is important. For little dumps, when you are heads up, you can use your low pressure inflater hose dump. However, many times, especially when I'm hunting crabs or picking up stuff from the bottom, the "butt dump" is the one to use. If fact, when I'm struggling
with a big dungeness crab or two, I may reach back there and pull it and pounce on them. Sometimes when I'm navigating (compass fun) the murky waters of the Pacific NW, we are doing some ups and down over volcanic reefs and sand bars (with my hands and arms tucked in close to my chest) and I'm using my shoulder dump - just barely tugging on it does the trick. And using your own lungs brings you up and down as well - it's really fun when diving down and up and over submerged reefs with deep inhaling and exhaling - kicking like crazy! Also, as others have said, you really don't have to add much air to your BCD at all to make a difference in your buoyancy - just a squirt will usually do. This is especially true when you ad a little bit at a time on the way down. Be encouraged - after a while, you don't even have to think about it, it's like riding a bicycle and it feels so natural.
I love diving. Warm or cold, murky or clear, shallow or deep, salt or fresh water - there is really nothing else like it.
Enjoy!!!
TheScubaBOB
Contributor
Sure if you can scale yourself up to the same relative size of myself to the water bottle!
How does this statement make any sense?
In my example the forces involved would scale up from the small scale test to the full scale test.
In your "comment" they would not...
Seriously, why not just take me up on the offer, let's compare videos of the actual experiment.
Blackwood
Contributor
First, I may have came off as an ass, but I didn't intend to. I often post in a ...roundabout manner rather than simply coming out and saying what I'm thinking.
In your experiment, only SOME of the forces will (may) scale analogously. Even though a human with dive gear isn't shaped remotely like a bottle (and thus the drag coefficient is different), I'll concede the drag force. It's probably close enough. The buoyant force will scale with volume.
However, the density (and thus weight) of your bottle is something like 1/1000th that of a human body (assuming it's mostly air and we're mostly water, on top of which you'd have to add dive weights, a scuba cylinder, etc., which more than offset plastic).
It's one thing to make a few grams pop completely out of the water. It's something entirely else to do the same with >100 pounds of meat, bone, fat and metal. The force required differs by orders of magnitude, and that's the point I was... suggesting in my reply (I can't toss up a bottle that weighs as much as a human body either).
TheScubaBOB
Contributor
Thank you for the more complete reply.
Your points are valid and would require me to conduct a second small scale test which would have me attach the bottle to the back of a Simula-Diver will scale size & weight matching that of a diver in relative size to the BC lift capacity of the bottle.
So first I'd determine the lift capacity of the bottle. Anyone know how BC manufacturers do this? Is it full bladder at x depth or full bladder at the surface?
Lets say for example I have a full size BC with 30lbs of lift and I determine that the bottle has 1 lbs of lift then I have a scale of 30:1, correct.
So now I need to make a Simula-Diver of the same scale. Using a diver of 180lbs (including weights & gear) I need a 6lbs Simula-Diver but it should also displace 1/30th of the water volume displaced by our full scale diver (so buoyancy is also to scale).
Or we could just go full scale and create a duct-tape body double of a diver and weight it the same as the actual diver then place it into the diver's gear, take it to depth anchor it to a platform & fully inflate the BC then release it for an uncontrolled ascent.
Maybe we should contact Mythbusters and ask them to do this!
It should also have the weight distributed so that rises vertically, like a diver would, no flare.
Blackwood
Contributor
Full bladder at any depth.
Displacement (in this case, the capacity of the bottle) * Density (of sea water).
cowdog77
Contributor
"When I went up on the boat, I had a little blood in my nostrils, but just a little bit (when I blew my nose later, no blood came out)."
______________________________
Actually, this is the item in the OP that concerns me the most....a newbie with an uncontrolled ascent from depth and then doing a self-recompression after noticing blood in the nostrils.
Really glad that she had no lasting repercussions and will probably be very aware of her buoyancy in the future.
______________________________
Actually, this is the item in the OP that concerns me the most....a newbie with an uncontrolled ascent from depth and then doing a self-recompression after noticing blood in the nostrils.
Really glad that she had no lasting repercussions and will probably be very aware of her buoyancy in the future.
Elkfriend
Registered
Do you really believe this?
mbwilliamn
Contributor
Originally Posted by scubazachary
you should have been able to control your asent buy swimming down, slowly. to slow your asent.
Elkfriend: Do you really believe this?
Yep....I have the computer log from an AOW student. He had an inflator malfunction...stopped the inflate, but couldn't dump air ...unfamiliar with new equipment, so he never found the rear dump. Head down and kicked for the bottom. What could have been an 80-90 fpm ascent from 60 ft never exceeded 30 fpm and he was able to hold for about a min at ~20 ft. Of course his SAC rate was over 1.3 CF/M!
you should have been able to control your asent buy swimming down, slowly. to slow your asent.
Elkfriend: Do you really believe this?
Yep....I have the computer log from an AOW student. He had an inflator malfunction...stopped the inflate, but couldn't dump air ...unfamiliar with new equipment, so he never found the rear dump. Head down and kicked for the bottom. What could have been an 80-90 fpm ascent from 60 ft never exceeded 30 fpm and he was able to hold for about a min at ~20 ft. Of course his SAC rate was over 1.3 CF/M!
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