Proper rate of descent?

My history: 10 official dives under my belt, with a lot of time in my swimming pool. All my dives have been warm water boat dives. I am feeling very good in the water, and those instructors with whom I have dived have commented that my skills are good for such a new diver.

I was reading an article in Dive Training Mag that says the correct way to descend is to vent air a the surface so that a slow descent rate is achieved, then slowly add air on the way down to maintain a constant, slow descent rate.

I realized that when I descend, I dump all the air at the surface, kick down until the wetsuit compresses, then let the descent commence at a pretty fast rate, in a nearly horizontal or even head down position, clearing every few feet. When I'm near the bottom, I start adding air in bursts. I stop a few feet above the bottom, then make any final adjustments to get neutrally bouyant.

The difference between my method and Dive Training's method seems significant. Is my way a poorer way to descend, or is it just a different way to descend? For me, it works fine and just seems a natural way to do it. It's also more fun.

Thanks for any advice.

It's going to depend on the type of dive you're doing.

If you're doing a standard warm water, no/low current dive, then there's no reason to rush it, and I'd abide by the Dive Training Mag's suggestion, to make sure you're equalizing well and often (always without losing site of your depth, and descent rate, which applies to all dives).

If you're doing a drift/negative buoyancy dive, you want to get to depth, along with your buddy/group, as quickly as possible, so you're not separated too much in the current, and you descend as quickly as you can, while safely equalizing.

Scubasailor:

Thanks for any advice.

Click to expand...

Depends on the dive. If you're out over a wall with navy blue water stretching out below you for thousands of feet I wouldn't be in such a hurry...

Equalizing is the main concern. Also that you don't slam into the bottom. Other than that, I go as fast as I can to get down there.

There was a discussion about this not too long ago, in which Walter offered that somebody (but I don't remember who) prescribes a maximum descent rate of 60 fpm. I'm not at all sure what the basis for the recommendation is. There is some evidence that narcosis is worsened by rapid descents, if you are going to sufficient depth where it is an issue. But I certainly know technical divers who descend by pointing the scooters straight down and hitting the trigger!

For me, one of the biggest considerations in descents is keeping the team together. Descents are one of the "unstable" periods of the dive -- that's when you're likely to discover equipment that isn't working or isn't adjusted properly, or that your ears don't want to dive that day. If the team members all decide to plummet, considerable separation may occur, which makes it difficult to detect a teammate having issues and difficult to assist them. Controlled descents, keeping eye contact, make for a safer strategy to me.

Your way seems OK to me as long as your ears hold up.

I guess it depends on the situation. Leading students or other divers I descend slowly and upright, adding air as necessary to slow my descent, making sure to emphasise equalisation every few feet to encourage good dive habits. With just another DM or instructor buddy, I just hit my dump valve and drop/swim down like a rock as it's just quicker that way.

I'm not sure it really matters all that much, although you should perhaps be setting a good example if there are less experienced divers present. Whatever you do, just make sure you and your buddy maintain an appropriate level of communication throughout the descent. It's no use if you get down to 30m and suddenly realise your buddy is still at 6m with equalization problems.

There are some things that you should consider

- can you stop your descent at any time (ie. is it under control?).

- Is your buddy team cohesive? The tempo of the slowest diver determines the rate at which you can descend.

R..

This largely depends upon the breathing mixture you're using. If you're breathing air and your diving above say 100 feet, the only limitation is equalizing your ear pressure. Deeper than 100 feet you should not descend faster than 60 fpm, as a faster rate seems to increase the effects of nitrogen narcosis.

For saturation diving (as a matter of interest) the descent rate is varied from 30 fpm to usually 0.5 fpm as a fast descent rate will cause HPNS. Also a slow descent reduces Hyperbaric arthralgia (joint pain which occurs during compression).

In-particular:

0–60 fsw, 30 fpm max
60–250 fsw, 10 fpm max
250–750 fsw, 3 fpm max
750–1000 fsw, 2 fpm
1000-1500 fsw, 1 fpm

Again these are maximums, but I always order a 0.5 fpm descent, across the board.

IMHO, CO2 build up is the main concern here.

An uncontrolled rate of descent can led divers into rapid breathing that causes CO2 levels to increase. CO2 buildup is accepted in the literature as one of the factors that can intensify narcosis and O2 toxicity.