Altitude Drift Dives

[WillHartNZ]

Quick wee hypothetical question regarding drift dives at altitude.

As it is not recommended to mix altitudes on the same day of diving, how would one go about performing a river drift dive at altitude?

Do you work based on your starting altitude or finishing altitude when planning the dive? Or is it better off to just not do the dive?

 

[Jax]

Wow! Just how much altitude do you loose in this river!?!?!? :shocked2:

 

[Bill Parker]

I guess you could drift dive down a class 5 white water river but getting bent would be the least of your worries.

 

[shoredivr]

Where exactly is this dive planned?

 

[WillHartNZ]

There's no dive actually planned at this stage... probably only likely to lose 50-100m over the entire dive. BTW it's only a grade 2 (maybe 3) river (on the dodgy sections)

 

[Bill Parker]

100m is a small altitude change. I'm assuming depths would be so shallow
(<30ft) that blowing your NDLs would be unlikely anyway. According to
my EAD higher altitudes mean less time at a particular depth so I'd plug
in the highest altitude and the deepest depth you'll experience during
the dive. You'll probably discover you'll run out of air long before you hit
your NDL. You'd keep an eye on your computer during the dive. You'd
have to check you manual but many computers make adjustments for
altitude although they don't have planning features for altitude dive.
With my computer I can set the depth and it will calculate the time but
it does it at the current altitude so I have to already be at the same
altitude as the dive site for it to work as a planning tool. Be safe.

 

[boulderjohn]

As it is not recommended to mix altitudes on the same day of diving, ...

I don't see why you can't mix altitudes on the same day of diving. If it is in some literature somewhere, I must have missed it.

I just skimmed through the instructor manual for the PADI altitude course, and it is not mentioned at all. The closest thing I can come to it is the recommendation not to do more than 2 altitude dives in a day. that recommendation I find a bit silly. I have no idea why that would be the case, and I have done as many as 7 (obviously relatively short) altitude dives in a busy day.

The altitude change you are considering is very minor in the grand scheme of things, and, as has been mentioned, your dive would be so shallow that it would not matter. You would essentially be doing a prolonged safety stop the entire time.

 

[Scared Silly]

As said, I would plan the dive for the highest altitude and deepest depth. That said the bigger issues might be arriving from a lower altitude to the dive site and afterwards if any of the travel requires travel over a pass that is higher than the diver site.

While OT before doing an EVA astronauts breath pure O2 for several hours to purge N2 so that they do not suffer DCS while doing the EVA which is in a low atmosphere environment. Depending on the altitude you might want to do the same - spend some time at the altitude before doing the dive.

My only other suggestion is wear a helmet.

 

[scagrotto]

probably only likely to lose 50-100m over the entire dive. BTW it's only a grade 2 (maybe 3) river (on the dodgy sections)

I'd love to hear all the details. How long is the dive expected to last, and how far are you planning on drifting? I can imagine a hypothetical river with a gradient of 100'/mile (about 20m/km) that's only class 2, but it would be really ripping right along. I'd expect most class 2 or 3 rivers to have gradients well under half of that, and that losing 50m of elevation would mean you're expecting to drift at least 5km.

I've got no qualms about swimming class 3 rapids, but even with really good viz I'm not sure I'd want to do them as scuba dives.