Variable weight dives and hydro drag

[RLdiver]

unclejake,
Yeah... it is a brass knuckle, some shells, screws, a key, plastic, paint can opener and dive weights. I made it in an automotive funnel...Did a test fit of all the solid lead and it seemed ass though when I poured the resign in it would have completely covered the weights.. It didn't so I scrambled for anything to bring the height of the resign above the lead.

Here is the video we took...
[ame=http://www.myspace.com/video/333663432/sea-tiger/32349508]SEA TIGER Video by Riley - Myspace Video[/ame]

efattah,
I think were you went wrong is... you pulling it up before you dove. Maybe at 50+ meters it really wouldn't have made a difference in your Blackout. But, when we did it the diver who had just dove pulled it up for the next guy. It worked out to be about 15 minutes between dives with two divers. Just my thoughts. I do agree with your...don't know it's a bad dive until it's too late.

Riley

 

[Unclejake]

A little more sled progress this week. The brake wasn't strong enough so we changed it around a bit and it now holds 50kgs on dry rope.

We also moved the ballast to make it more streamlined, but in truth it will not need much additional ballast as the sled itself will be in the order of 15 kgs

 

[Stavros]

Using a lanyard on the sled has me a bit concerned. I am building it to minimise any snag points, but you can't eliminate them all and still have a functioning device.

Eric's post (above) makes it clear that a lanyard is required - but how to safely do it with a head down sled plunging into darkness? I think it was Natalia whose team decided against using a lanyard on the sled. A lanyard could help save your life if you B/O at -30m but it could cost you your life if it got tangled at -100m

Does anyone have any experience with those cyalume glow sticks below 100m?

Hi All,

I have done a few sled dives myself and organised a lot more both in VAR and NLT.

A few quick comments I thought might be relevant:

1. Natalia (I presume you are referring to Molchanova) always wore a lanyard at least during her VAR training with us for the record attempt. In general nobody gets on the sled without a lanyard. We are not using a traditional lanyard but a belt lanyard similar to the ones you see in CNF dives. The actual line connecting diver to the dive line is a 4mm high tension line with a stainless steel ring around the diveline instead of a carabiner.

2. The rope guide points at the top and bottom of the sled you made out of alloy - give a thought to trying teflon. Its easier to work with and causes even less friction.

3. Nice but complicated brake design. There is a good chance of someone getting tangled on the bicycle break. I usually go with commercial high quality sailing clutches. They are robust, made exactly for the purpose we need them and they work.

4. A traditional head up sled using a bent-knee bar with the amount of weight you have on the sled on you picture and a diver wearing a 7mm suit and no weights would start the descent (first 30-40m) with a very slow speed - less than 1m/sec. Thats for a normal diver - someone as big and with the lung size of Dave M. would probably not allow the sled to even start. We are normally using a minimum of 20kg for smaller divers not wishing to go much more than 1-1,5m/s and we go up to 35kg on the sled for me to go with about 1,8-2,3m/s on a HEAD UP sled. We have played around with head down use of the sled and it is a lot faster. Main reason is the diver's hydrodynamics. A straightened out diver (like Herb did on his 214m dive) is a LOT faster that a bent knee diver. So you will need less weight and the sled will be fast.

5. You do not need fairings or any other contraption to add drag and make your sled even more complicated. There is no discomfort on the diver due to water around him/her - I always find the feeling relaxing. Just make sure you have a very tight fitting suit otherwise you will get flushed. It is very easy to have your hood fly off if you look down going at 2m/s...

6.Manually lifting a sled up from 130m loaded with 25kg + the bottom weight? rofl Please video the first attempt and put it up on Youtube
In short forget about it. When I was young dum and first had a sled (20kg+15kg bottom) I once brought it up from 65m. It took 3 of us close to 1hour to get back up. Next thing I did was buy a winch.

7. Looking at your sled and the weight position combined with the length of the sled I think you will get the sled pivoting around the weight point going down at an angle and creating a lot of drag. Remember you placed your ballast in the middle of it and right next to it you placed the handlebar were the diver is going to be causing all the drag of the sled. So drag at a distance from the middle point and all the weight at the middle point means a sled pivoting around that point. I would place the weight a lot closer to the bottom of the sled or place it lower and to the other side of the diver.

I will try and upload some dive profiles (I have changed laptops a couple of months back and most of my profiles died with my last laptop)

Cheers
Stavros Kastrinakis
Freediving Club Greece

 

[Unclejake]

Stavros, your points are gratefully received.

In response:

1) I thought I read that she had a b/o at -40m some distance from the line without a lanyard. I could be confused with someone else. Thank-you for your clarification

2) Noted. We worked with what we had, but anything softer on the rope sounds good.

3) I guess he brake looks more complex that it is, due to some weight reducing holes drilled in it and some bracing. The holes give it a better gravity balance. The design was that the brake would be enclosed by the fairing so a snag risk was greatly reduced (see point 5). I looked at rope clutches and considered them difficult to operate remotely (this would be less of a problem with a head up sled)

4) Thank you

5) Really?? No fairing would save heaps of work and make the sled much more manageable for transport. I will need to cover the brake and throttle if we have no fairing (to prevent transport damage and to reduce the lanyard snag risk). I will think about that hard. It is an appealing direction.

6) A winch is highly desirable, but there are no funds available for it at this point and I do not have the time to build one out of old car parts. The davit I have designed uses rope clutches (Lewmar D1) which act like a one way ratchet. I had hoped that this would allow the boatmen to haul the sled up 1 meter at a time. The sled will be deployed off a 5.8m RIB so space is at a premium.

7) I completely agree with you but there are two factors that dictated the ballast position. A) I needed to allow for installation and removal of the ballast with the fairing in place, B) The sled is longer than you see in the photos. There is a removable tail that screws into the sled. At this point the tail tube is around 1,100mm long. I too worry that the sled will 'tip over' under brakes or with the drag of the diver. We have not tested it yet. If we abandon the fairing then I can place the ballast at the very bottom of the sled. This would be my preferred solution but I had been very keen on a fairing until now.

Lastly: One question: 8) If you could moderate the speed of your sled during the descent, would you ever do so?

Thank you very much for your input.

UJ

 

[Jouskari]

I´ve done some diving with sleds so some quick comments:

A "standing up" -sled is more comfortable equalizingvise in my opinion. You can hunch over and find the most optimal position. "Heads down" again is optimal to support CWT training, but in my opininon not as comfortable going down. Especially if using mask as one hand is needed to equlaize.

Speeds at 2 m/s or over are fast. It will, as Stavros said, rip the hood or mask of your head if you look in the wrong direction (not nice in cold dark waters). I almost lost my mask coming up from 72 m with Only One Apneas sled. That was 1,8 m/ s.

I´m really interested in the fairing -consept. Atleast I experienced some "turbulence" going down and up in a standing position. In my opininon you could be pioneers in that area and experiment?


I really like the "auto brake" -concept. The automatic brake is really good if you have a sticky ear and you need to brake fast. At 2 m/s , it takes only 5 s to burst an eardrum at worst. Also, using a lanyard that is connected to the line above the sled can still easily lead to a situation where you are tangled to a sled that is pulling you down into darkenss at 2 m/s and your last equalization was 20 m ago. So having a break that activates when everything goes wrong is really nice (user just releases grip). However this brake setup would not work on a No-limits sled as you would not need to brake on the way up. Instead you need a quick-release for the lan-yard to be able to deco at 20-15 m.

Also, remember to put some kind of spring or other damping on the bottomplate (Herbert used tennisballs and coke bottles). Hitting your teeth on the bar at 2 m/s hurts.


- J

 

[Stavros]

Stavros, your points are gratefully received.

In response:

1) I thought I read that she had a b/o at -40m some distance from the line without a lanyard. I could be confused with someone else. Thank-you for your clarification

2) Noted. We worked with what we had, but anything softer on the rope sounds good.

3) I guess he brake looks more complex that it is, due to some weight reducing holes drilled in it and some bracing. The holes give it a better gravity balance. The design was that the brake would be enclosed by the fairing so a snag risk was greatly reduced (see point 5). I looked at rope clutches and considered them difficult to operate remotely (this would be less of a problem with a head up sled)

4) Thank you

5) Really?? No fairing would save heaps of work and make the sled much more manageable for transport. I will need to cover the brake and throttle if we have no fairing (to prevent transport damage and to reduce the lanyard snag risk). I will think about that hard. It is an appealing direction.

6) A winch is highly desirable, but there are no funds available for it at this point and I do not have the time to build one out of old car parts. The davit I have designed uses rope clutches (Lewmar D1) which act like a one way ratchet. I had hoped that this would allow the boatmen to haul the sled up 1 meter at a time. The sled will be deployed off a 5.8m RIB so space is at a premium.

7) I completely agree with you but there are two factors that dictated the ballast position. A) I needed to allow for installation and removal of the ballast with the fairing in place, B) The sled is longer than you see in the photos. There is a removable tail that screws into the sled. At this point the tail tube is around 1,100mm long. I too worry that the sled will 'tip over' under brakes or with the drag of the diver. We have not tested it yet. If we abandon the fairing then I can place the ballast at the very bottom of the sled. This would be my preferred solution but I had been very keen on a fairing until now.

Lastly: One question: 8) If you could moderate the speed of your sled during the descent, would you ever do so?

Thank you very much for your input.

UJ

Hallo Again,

1. That was Yasmin who from her blog posting followed very unsafe diving practices which led to a deep blackout. Natalia never had a BO on her sled training (nor had anybody else on our events) and always wears a lanyard on the sled same as everybody else.

2. Try it - you'll love it

3. I agree on your point but what you have at the moment even though very cool looking and ultra high tech is scaring me a bit. For example - unless you create a big cover for the whole mechanism it is a prime snagging point. You will not believe the points a lanyard will get stuck on - I had one case where it got caught on a polished stainless D shaped mooring point on the sled with absolutely no surface which could cause a snag...and yet it did. So a break like that is a magnet for lanyards to get caught on. Other thing would be the stainless (I presume) bike cable will most likely get stiffer with time salt and rust (well we know that stainless is just staining less) so you might end up with a break that does not work unless rigorously maintained (which is always a problem for equipment that see a lot of use)

4. U R Welcome

5. I would say skip it -the only sled with a real fairing design that worked was Umberto's old torpedo sled which cost a fortune and was a nightmare to setup and run - of course those were the days when one had a Navy Frigate watching over each dive session and 100 assistants to short out details like setting up. This is not the case nowadays when you will most likely be setting up yourself before the dives...so the easier a sled is to setup the more you will use it...a very complicated sled will just collect dust in your storeroom after a couple of dive sessions

6. Well it will still be a lot of fun seeing your team pull up 40kgs from 130m please video the whole thing

Ok I will be nice and helpful - since you have a 5,8m rib you already have a motor that can lift the sled up. Will you set permanent mooring on your dive site or are you planning to drift (bad idea) ? Let me know what your setup will be and I will tell you how to bring the sled up without a lot of sweating and swearing .

7. Skip the fairing and setup the sled properly. A head down diver is nice and hydrodynamic - forget about adding more metal that will just make the sled a nightmare to use.

8. Hehehheheh - the important question.... No I would not...my idea is you ride a sled when you have shorted out equalization...if not why are you riding a 30kg piece of metal going down at 2m/s? I will personally never use my sled's break during the descent or ascent (I leave the sled at 30m during the ascend for my slew deco ascend of course)... I prefer staying focused on my equalization and mouthfill during my dives rather than trying and play around with breaks and gadgets because I failed in my equalization and mouthfill...but a word of warning - I am funny when riding my sled so do not follow my example

Stavros

 

[Unclejake]

Stavros, your posts delight me. 1 through 8 are treasure.

I shall consider your points carefully over the coming days. I have an eagerly awaited spearfishing holiday starting soon which will give me time to ponder and not weld, grind, buff, nor linish.

9) I must make this sled robust enough so it is still available for use by Dave Mullins in 2012 as he trains to defend his CWT WR title.

:blackeye

 

[chrismar]

One important point which might have been missed. This sled will be used 90% of the time in Lake Taupo, so corrosion and salt build-up concerns are not major.

 

[Mullins]

Stavros - we normally anchor at the dive site. We could always leave the anchor on a buoy temporarily while we use the motor + a lift buoy to retrieve the sled.

I don't want to use a lanyard because it'll probably be more trouble than it's worth (no counterballast). But I might have to, simply because it's too dark to see where the line is

The sled is really just an EQ training device for when water temperature limits CWT depth. But I'd also like the option to go at 2.0m/s, just because.

 

[alonrivkind]

Hi Dave,
Just for curiosity-why not to dive with a counterballast?
If you are allready building a nice sled...
Alon

 

[Mullins]

It'd have to be very heavy and we won't be pushing the depth that hard anyway. Just doing CWT depths in thicker suits than normal.

 

[Unclejake]

I´m really interested in the fairing -consept. Atleast I experienced some "turbulence" going down and up in a standing position. In my opininon you could be pioneers in that area and experiment?

Thanks J, I figure we may indeed try the sled both with, and without a fairing.

A fairing makes the sled awkward to transport and deploy but it does reduce the lanyard snag risk (for us).

A fairing is lots of work to fabricate and may not be any faster that a naked sled but a fairing gives you something to stick decals on.

A fairing probably makes life worse in current and will significantly increase the retrieval effort but this sled is weak without the fairing frame I planned so it will need some extra bracing regardless.

Dunno. I will have a hard think and will probably just end up doing what ever is hardest. That's how we roll....

 

[Unclejake]

Some initial (shallowish) freshwater trails of the bare sled have proven that the brake works and have indicated that a fairing is not absolutely required (as a few of you have suggested). The ballast position needs more thought and experimentation, but I think we have a sled that with some minor changes will be good and manageable.

I have all of the New Zealand winter to finish any sled modifications so for now will turn my energies to the deployment davit and counter ballast system.

We shall see what ends up working soon

 

[shrek]

A very interesting thread, one point i noticed was the part about pulling the sled back to the surface by hand and the comments about the diver who just dived pulling the sled back up for the next guy.I don't know how close to getting the bends you guys are getting, my understanding was that doing physical activity after a dive increases your risk of triggering a case.
I'm not trying to knock what your doing i just thought it might be something to be concidered

 

[Jouskari]

Cool, its always nice to hear about progress and new findings. I would die for some pictures or video material though...

 

[Unclejake]

^ there are a couple of short videos about Jouskari. Perhaps Dave will post links, but be aware that these were inital tests and not everything was present (read: it looks a bit rough)

 

[Mullins]

First trial run using our expendable test-ginger (bit like the Stig on Top Gear).

 

[Unclejake]

Thnaks for posting those Dave.

As everyone will have noticed - the ballast needs to be moved to be more in line with the handlebars. Also - the handlebars can probably be a bit closer to the sled spine.

When we have a deployment davit the handlebars will be near to the surface. This will make the surface departure easier for the diver.

 

[Jouskari]

Awsome! Cool setup and it actually seems to work pretty good.

Excelent wiz you have there.

 

[Unclejake]

Almost a year later we have finally moved the ballast, but still the sled will be run with a short spine and may tilt. A davit will help with running the sled at full length but there are complexities involved with mounting a davit on the boat.

We didn't add a fairing and probably will not.

Perhaps some video next week after it gets tried out again. It has been a fun project.