Tip du jour

[The Iceni]

Uncle Pug once bubbled...

We don't even hold onto the spool...

It would seem there must be at least two schools of thought on this one. In the UK I was taught to ascend the SMB line winding in as we go (whether from depth or from mid-water).

It take it from your reply, Uncle Pug, that this is NOT universal practice. While winding in does mean that the reel is not at depth, all set to snag on wreckage or whatever, and the line does not need to be recovered after getting onto the boat it does seem to encourage "hanging on" at the expense of good bouyancy control.

Perhaps leaving the SMB line hanging as an external and additional visual reference encourages more accurate ascents/bouyancy control.

At least there will be less task loading during the ascent.

Is that the reasoning behind what you say?

I was also taught to take a spare depth guage/dive timer when doing extended range diving. You may lose your buddy and your computer may also fail on a dive but I doubt both depth guages would ever fail at the same time! We are also advised to carry a spare mask and an alternative air supply. (Oddly, I think it is called redundancy!)

 

[Rick Murchison]

Dr Paul Thomas once bubbled...
It would seem there must be at least two schools of thought on this one. In the UK I was taught to ascend the SMB line winding in as we go (whether from depth or from mid-water).

It take it from your reply, Uncle Pug, that this is NOT universal practice. While winding in does mean that the reel is not at depth, all set to snag on wreckage or whatever, and the line does not need to be recovered after getting onto the boat it does seem to encourage "hanging on" at the expense of good bouyancy control.

We still wind the spool up as we ascend between stops, Doc, we just clip it off (to itself) and let it hang free at each stop depth.
Rick

 

[The Iceni]

While we may insist on driving on the left I didn't think we were so completely out of step with normal practice across the pond.

Thanks for clearing that one up, Rick

 

[Rick Murchison]

Dr Paul Thomas once bubbled...
While we may insist on driving on the left I didn't think we were so completely out of step with normal practice across the pond.

Thanks for clearing that one up, Rick

Two countries separated by a common language...
Rick

 

[otter-cat]

Uncle Pug once bubbled...
I watch the stuff and use it as a visual cue... if the stuff is going up then I am going down... and if the stuff is going down then I am going up... and what ever the rate of ascent/descent of the stuff... that is my rate of descent/ascent.

Watching the stuff I can make a slow controlled ascent without ever looking at my depth gauge/computer.

I too watch the plentiful stuff in the water column for a visual reference during ascents, descents and stops here in the PNW. I also like watching the little critters who swim around do so...but it makes me wonder sometimes about using them to gauge ascent/descent rates.


If they are collectively moving up or down (up to get more light or food, down to escape predation or just slow downward movement of particulate matter due to gravity) wouldn't this throw off our visual cue to our rate of motion? If we are moving down, and the particles are moving down, then our estimated descent rate based on using them as a "fixed" reference will be an underestimate. If we are rising and the stuff is rising, we will think our ascent is slower than it really is. If the stuff and the diver are going in opposite directions, then estimates of ascent/descent rates will be overestimates.

Of course the key word in all this is ESTIMATE, and as long the "stuff" is not moving very fast, it will not throw your estimate off very much. In general, the stuff-watching technique of gauging your own motion through the water column is neat and effective. But I wonder if it has an impact when trying to do those extremely slow and controlled depth changes.

 

[Uncle Pug]

Dr Paul Thomas once bubbled...
Thanks for clearing that one up, Rick

 

[Uncle Pug]

otter-cat once bubbled...
it makes me wonder sometimes about using them to gauge ascent/descent rates.

The little stuff is very static in its position in the water column... unless there is significant current upwelling/downwelling... remember I am talking about the really small stuff.... not the little fish that are schooling up and down all over the place feeding and being fed upon.

 

[otter-cat]

I think I know which "really small" stuff you're talking about. Those tiny little "flakes" that comprise the ubiquitous specks in the water column.

I'm not completely certain of this, but I believe that most of that "stuff" is actually slowly filtering down through the water. I don't know what the rate is, so it may be far too slow to have any noticeable impact on our estimates of our ascent/descent rates (as I said, I use this method as well.) But if, hypothetically, it was descending at a rate of, say, 2 inches per minute, and you were trying to descend at 1 fpm, then you would have to descend 14" per minute instead of 12 in order to descend 1 foot below a set of reference particles in one minute.

So your actual rate would be...1 + 2/12 = 1.167 fpm, or about 17% faster than your estimate.

I guess whether the motion of the particles is important to consider would depend on how slow you wanted your motion to be, how close to your desired speed you need to be, and of course, how fast (or slow) those particles are moving.

My personal feeling is that if you are doing ascents and descents slowly enough that the slow-but-unknown rate of particle motion will significantly impact your rate estimate, then you are probably going slowly enough that even with the impact on your rate estimation you are still going to be travelling at a safe rate.

I was basically just wondering if there was a noticeable effect (I think about this type of thing sometimes during safety stops) although I have little worry that if there is one, it would be enough to cause any problems.

Does anyone know how fast that really little stuff moves through the water?

Just curious.
otter-cat

 

[Uncle Pug]

otter-cat once bubbled...
Does anyone know how fast that really little stuff moves through the water?

If it is living stuff it might move around in the water but the excursions are of no significant distance.

If it is sedimentary in nature where did it come from... stuff dropping from the clouds and then sinking into the abyss at 2ipm?

However if it is stuff moving with the water, ie. DP... then no matter what you try to do... you will be moving right along with it!

Relax, enjoy the stuff. It is perhaps the best reference you could possibly have to bring your ascent to a millennial crawl.

BTW... while at your safety stop... enjoying the stuff... think of all those poor suffering divers who dive in water so devoid of stuff that visibility is 200~300'.

 

[otter-cat]

...for all those divers suffering through that particle-free 200-foot vis!

But I believe that much of that small particulate matter is detritus from other sources in the water column (i.e. very small fish and plankton excretions and carcasses.) These exist as a semi-constant source of particulate matter that slowly rains down to the bottom, where it provides nutrients for organisms lower in the water column or on/in the sediments. Some of it becomes part of the sediment.

So it's not raining from the clouds at 2 ipm, it's "raining" from organisms in the water, mostly plankton, I think. As for the 2 ipm figure, I made that up; I really don't know what the actual figure is, but would be interested in finding out. Maybe I'll look it up when I get home tonight.

If stuff moves with the water, as you pointed out UP, "then no matter what you try to do... you will be moving right along with it." But in fairly static conditions, it slowly moves downward.

I agree that the stuff IS a great reference to use to slow an ascent to a "millenial crawl!"

otter-cat