Bubble Speed

[madmole]

Actually its quite easy, the bigger bubbles shoot off and there always seems to be very small pin head size bubbles around in the water. Check it out on your next dive.

That was until I got my Inspiration

In green water its easy to spot them as they appear white against it. I can believe its harder to see them if its really bright (like cozumel) but we dont get dives like that in the Thames

The really small bubbles travel at about 5 m/min, ditch them and find another small one about every 3-5 seconds. This was the method I used prior to 84 and my first computer (DecoBrain). Now I use the bubbles and my winding rate on the lazy blob

By the way, the VR3 has a sliding scale from 0-20 m/min and you can tell your ascent rate to nearly the nearest m/min on it. Much better than the course grads on most units (vyper for example)

But I do agree that all the meters show you what you have done, not what you are doing. But they are better than nought and have taught a lot of people to SLOW DOWN

 

[MSilvia]

So long as you keep a fairly constant exhalation as you ascend, the tiniest bubbles are, I think, a pretty good indicator. Don't fix on a single bubble though... always look for the one that isn't passing others. It's not "use a bubble as a reference," but "use your smallest bubbles as a reference."

 

[Uncle Pug]

... use the Stuff Luke...

 

[MSilvia]

The Stuff that doesn't ascend with you is going to be better than the stuff that does.

 

[Uncle Pug]

...you don't want to ascend (or descend)... but just float there with the stuff for a minute or three or more.

 

[MSilvia]

It never even occurred to me to use floaties as a reference for safety stops. Bubbles are definately not so good for that, huh?

 

[Spectre]

sheck33 once bubbled...
how on earth are you going to pick 'the smallest' bubbles in a mess of bubbles of all sizes

What's the point here... a slow ascent.

Don't bother thinking 'smallest' bubbles. Think 'slowest' bubbles. They by nature'll be the smallest anyway, and it's not the size of the bubbles you care about anyway, it's the speed of 'em.

 

[The Iceni]

sheck33 once bubbled...
of course you already know the end bubble size on the surface, it will be V initial x (D/10 + 1) where D is depth in meters)

Come on you lot. Is this a wind-up?

I have, on occassion, looked at the bubbles as they ascend and I have NEVER seen a spherical bubble bigger than about a couple of centimetres in diameter. What I have seen is that the larger bubbles form a dome shape, like a jellyfish, which sheds thousands and thousands of sattelite bubbles from its skirt as it riggles on rising to the surface.

One thing for sure. Whenever a diver is below me when I am in the boat, I have never seen a giant spherical bubble hit the surface! They seem to rise as the domed sheets I described above accompanied by perhaps millions of smaller bubbles gently fizzing as they surface.

No doubt a physicist can explain but I am sure it is something to do with suface tension.

In any case there are plenty of small bubbles, the size of those in a carbonated drink, which rise at respectable rate before they too break up as they expand. Some even seem to disappear (probably the gas in them dissolves as the Laplace pressure is exceeded.)

I'll stick to looking at all that the crud suspended in the water, with just a little help from my computer and reel! In my humble opinion the days of using bubbles to judge the rate of ascent are long gone.

ut:

 

[Dr Deco]

Dear Readers :

Rise time

From Stokes’ Law, I calculate that roughly a 1mm in diameter bubble would rise at 1 ft/sec. See ATTACHMENT. This naturally assumes that there are not any currents etc to disturb it. Basically we are looking to find very small bubbles.

Dr Deco :doctor: