Slow, controlled ascent

[DallasNewbie]

This may be a stupid question, please forgive the newbie if it is. Aircraft have a mechanical vertical speed indicator. Because the pressure change is much more rapid under water, this would either work much better or much worse than in air. Were mechanical VSI's ever used for scuba diving before computers?

 

[Green_Manelishi]

This may be a stupid question, please forgive the newbie if it is. Aircraft have a mechanical vertical speed indicator. Because the pressure change is much more rapid under water, this would either work much better or much worse than in air. Were mechanical VSI's ever used for scuba diving before computers?

Many of the 'puters (even the simple digital DG/BT) are calculating your vertical speed and will beep or "flash" when your ascent rate exceeds programmed limits. That's about as much a VSI as you are likely to find for diving. It would be interesting to know if someone is making a unit that will flash the ascent rate in FPM or MPM rather than wait 'till you are speeding. Actually, it would probably be better than a "you are going too fast".

 

[ShakaZulu]

http://www.dtmag.com/06-04-articles.shtml reference the article about avoiding DCS, some really good tips in there.

I like to divide my ascend in halves, wait there for a minute and then ascend to 15ft for the 3 min stop. Use my bubbles, stuff and SPG to control the rate.

 

[simbrooks]

Many of the 'puters (even the simple digital DG/BT) are calculating your vertical speed and will beep or "flash" when your ascent rate exceeds programmed limits. That's about as much a VSI as you are likely to find for diving. It would be interesting to know if someone is making a unit that will flash the ascent rate in FPM or MPM rather than wait 'till you are speeding. Actually, it would probably be better than a "you are going too fast".

Although it doesnt state it as a direct speed, my little Suunto shows a bar on the right hand side indicating the approx speed. It goes something like this (however i havent got the manual in front of me and they have moved the Suunto site recently) 1 bar ~ <6fpm, 2 bars ~ 6-18fpm, 3 bars ~ 18-33fpm, 4 bars = 33-45fpm, 4 bars and "Slow" and flashing, you have hit the jackpot at >45fpm - usually if i get that its because i shot my right arm up to protect my head rather than my left arm, but anyway. So if you keep an eye on the number of bars and the stuff you have a good idea of how fast you are moving upwards (the more important direction for most people to control). I typically try to keep at around 1-3 bars.

Other methods i have heard to help in the speedometer with a BT and depth guage are splitting up the ascent into sections and timing 5ft ascents (min 10 sec) and the like to get a better idea, rather than trying to guess if you are going 30fpm.

 

[Doc Intrepid]

Suppose you don't have a dive computer.

How do you make a slow, controlled ascent at 60 (or 30) ft/min? Or can you go 5 ft (looking at depth gauge), then, pause 10 seconds, then, go another 5 ft, pause again, repeat?

Thanks!

As noted by some above,...

If you're ascending at a rate of 30' per minute, then you're ascending 10' every 20 seconds.

On the surface take a look at the second hand of your watch as it ticks off 20 seconds. That's 10 feet of ascent.

Underwater simply practice with your bottom timer. Its easier (as UP noted) with something to use as a reference for vertical scale - best is a line (anchor line, float line, whatever). It takes some practice, but eventually you'll be able to rise slow and controlled, covering 10' or so every 20 seconds.

Hope that answers your question.

 

[hdtran]

It's not a big deal when ascending a line; I can grab the line with my left hand, count "one mississippi, two mississipi"; grab with the right hand about one foot up; repeat... That's how I ascended on my checkout dives. Now, I will confess that when my head was about one foot from the surface (you can tell because you're bobbing a lot due to the wave motion), I ascended more rapidly than recommended... Some practice is in order here.

I was more interested in how to ascend gently without a reference line, and not necessarily trusting the DM to ascend slowly... (And not spending $$ on a computer). I've gotten lots of good advice here, and will try to remember & practice.

Thanks a bunch!