Variable weight dives and hydro drag

[Unclejake]

This corner of the forum seems fairly quiet.

I am wondering what those of you who practice variable weight dives think about sleds with or without fairings?

Is the water pressure against you as you descend quickly uncomfortable and does it add to stress?

I am whacking together a head down sled and I plan to include a fairing to keep the water flow on the diver to a minimum.

Lastly - how fast is a fast sled? 3 meters per second?

Regards,
UJ

 

[Simos]

I would guess maybe 2 m/s, if that. Last no limits dive I remember was 101m and took 2min7sec
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[Unclejake]

Did the sled have a fairing or any other type of hydrodynamic aid?

Could anyone post dive watch screen shots of their sled dives?

Sorry for all the questions. Thanks heaps.

 

[Simos]

Sorry have no idea, I just read about the dive. I do seem to remember seeing a sled with fairings (herbert's?) but not sure. The only sled I have ever used didn't have any...
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[Unclejake]

Sorry Simos, I assumed that you had done the dive yourself - hence the question.

Sled information isn't as easy to come by as I thought it might be but a few very kind people have sent me some photos of what they have built in the past.

Thanks again. I will post some photos of what I am building once it is a little more progressed.

 

[Mullins]

Looking at the graphs on Patrick Musimu's site, it appears he was doing about 1.8-1.9m/s on the descent and then coming up faster. Herbert's descents were faster, from memory.

 

[Unclejake]

Patrick was using lift?

 

[Mullins]

Yeah both were no limits dives. I recall Herbert going very fast on the second part of his descent but not sure of the numbers. Somebody here should have them handy...

 

[Unclejake]

As the volumetric change on the inner ear decreases (at depth) one could progressively increase the descent speed, or doesn't it work like that?

 

[Mullins]

'zackly. Past 100m or so you can go like a rocket. I don't think Herbert equalised at all in the last 30-40m.

 

[Unclejake]

I will keep that in mind next time I am past -100m

....or maybe I will just go have a cigarette and a beer.

You guys are special.

 

[Unclejake]

Has anyone got some sled dive profiles they could share?

 

[trux]

Check out the History of NLT records at ApneaMania. Though, plenty of links are now broken there - it is Bill Stromberg's website and was interlinked with the old AIDA server, but since it was transferred to the new version, some image links stopped working. Try contacting Bill Extreme here on DB - perhaps he can fix it. Or look up the DB archive - there are plenty of profiles here too.

This is the info about Herberts 214 NLT dive:

16 seconds at 22 meter.
74 seconds from 22 to 214 meter.
54 seconds from 214 to 60m
50 seconds from 60m to 9.5m
54 seconds from 9.5m to surface.

07 seconds deeper than 214m
20 seconds deeper than 200m
53 seconds deeper than 150m
90 seconds deeper than 100m

Highest speed reached going down 3.1m/s
Highest speed reached going up 4.0m/s

 

[Simos]

54s from 9.5m to surface - gotta love the deco stop!

 

[efattah]

54s from 9.5m to surface - gotta love the deco stop!

Herbert told me that the 214m dive didn't even feel like a 2 minute static. He said he could have extended the deco stop for several minutes. In fact I think in the future a no-limits diver should do a 1 minute deco stop at 20m, and then a 2 or 3 minute deco stop at 8-10m. In that sense the whole dive should last around 6 minutes, which is totally fine for an expert.

 

[Mullins]

Pretty sure there were some dive profiles published on Yasemin's site too, but I can't find them just now. They were variable weight dives so would more relevant to what we're trying to do. They were also done on a more 'normal' sled than Herbert's one.

 

[Unclejake]

Thanks for that info Trux. It is greatly appreciated. As Mullins rightly points out, it is the descent speed (and any increase in velocity at depth) that I am most interested in.

I was after the information for dive planning and also to compare the performance of the sled we are building to other sleds around the globe.

We are building a head down sled so I guess a target of 2m/s is a good one. The diver can always slow his/her descent by rolling off the throttle a bit.

As a related aside: Building a speed controllable head down sled seems to be way harder that a head up sled (due to the need to have the brake controls remotely operated by an inverted diver). I would build a NLTs sled next if it wasn't for the fact that it is so likely to kill the adventurous.

 

[azapa]

I wonder why you are building it specifically heads down? any reason?

The only one I ever rode was heads down, it was fun, but nearly all others are heads up, mostly to facilitate equalization during those fast descent speeds.

 

[Simos]

I wonder why you are building it specifically heads down? any reason?

The only one I ever rode was heads down, it was fun, but nearly all others are heads up, mostly to facilitate equalization during those fast descent speeds.

Exactly my thoughts. If you are trying go make it go fast then better to be head up otherwise I wouldn't worry too much about it being hydro-dynamic etc
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[chrismar]

It's a CWT training tool, hence head down.

I don't think anyone in NZ has any desire to set a sled record. AIDA NZ doesn't accept NLT NR attempts anyway.