Automatic Dive Safety Line Tender - Design Questions from a Mechanical Engineer

[DragonTSD]

Hello Everyone,

I'm brand new to this forum. I have to admit that I'm not a diver (did some scuba diving at a resort once...haha). I may be tasked with designing an automatic dive saftey line tender buoy, and I'd like to hear any thoughts the experts might have.


The buoy will keep slight tension on the line to minimize fouling, and pay out a minimum of 400 ft of min 750 lb test safety line to the diver. I'm assuming (although it's not speficially stated in the requirements) that I need to make it capable of retrieving a diver at an acceptable ascent rate to prevent nitrogen narcosis and decompression syndrome. I also need to make the tension strong enough to resist paying out due to cross currents, but slight enough so as not to adversely affect descent or diver function at the target depth.

I have a number of questions but I'd like to ask them during a discussion. If anyone has any information they'd like to add, or any features you think are key, please respond. Please also respond if you've ever seen anything like what I am describing (I find it hard to believe that nothing like this exists already). Problem statement follows:

***Description of the problem:

The US Navy Diving manual requires divers to be tended either by hand or via a buoy that marks their location. This tending line can produce significant drag on the diver and is a fouling hazard that has caused multiple incidents over the years.

***What the solution needs to do:

The solution must provide a tending line via a buoy such that a slight tension is maintained on the line to the diver. The buoy needs to properly mark the diver's location with minimal slack in the line to eliminate the risk of entanglement or snagging on the bottom. The system should minimize line payout due to surf or current pull, without compromising diver tending.

Specific performance parameters follow:
. System must contain at least 400 feet of line.
. Buoy must be highly visible, and at least 10 inches in diameter.
. Line must have a breaking strength of at least 750 lb.

Thank you.

AJ

---------- Post Merged on August 22nd, 2012 at 10:03 AM ---------- Previous Post was on August 21st, 2012 at 10:25 AM ----------

Am I asking the wrong crowd?

 

[Aqua-Andy]

Why 400'? chances are if your going that deep you will not be dragging a flag, 130' would be plenty enough. But the whole idea seams like a "solution in search of a problem". In diving it is best to keep it simple. I use a simple plastic line holder with polypropylene line. The poly line floats so any excess will float up over you, and the whole thing costs under $15.

 

[raftingtigger]

I use a simple plastic line holder with polypropylene line. The poly line floats so any excess will float up over you, .

I saw a California free diver using a 50' length of polypo line connected to his speargun as a dropped gun finder. He reports that the line just slithers through the kelp. I don't think this would work if the line has any knots or a buoy on it.

I'm curious as to the conditions and reason that Aqua-Andy uses such a line.

 

[knotical]

The combination of "slight tension", "minimal slack" and current seems to ignore physics. Whenever the diver needs to change position horizontally even in calm water, there will be significant water resistance on a 750 lb test line (unless he moves very slowly). Throw in even a bit of current and the issue mushrooms.
The only solution I can envision is either a DPV or something like an ROV that automatically follows the diver around, somewhat like those golf carts that followed golfers around the course. To retrieve the diver, there would need to be a slack (or nearly slack) line connecting the DPV or ROV to the diver. The slack line could be used to tell the ROV which way to move.

But before looking for solutions, there needs to be some effort expended on writing (or re-writing) the "requirements". I'd guess that the people who wrote the requirements didn't do the math. Without defining (with numbers and units) the parameters of "slight tension", "minimal slack", and "surf or current pull" it is not a valid requirement set <not testable>. (I used to write requirements for the Air Force as part of my job.)

 

[Tigerman]

Why 400'? chances are if your going that deep you will not be dragging a flag, 130' would be plenty enough. But the whole idea seams like a "solution in search of a problem". In diving it is best to keep it simple. I use a simple plastic line holder with polypropylene line. The poly line floats so any excess will float up over you, and the whole thing costs under $15.

Probably because they might want to use it for not only rec depths and possibly also not only vertically?
From his reference to the US Navy diving manual this might not be aimed at the average resort diver..

 

[Aqua-Andy]

I saw a California free diver using a 50' length of polypo line connected to his speargun as a dropped gun finder. He reports that the line just slithers through the kelp. I don't think this would work if the line has any knots or a buoy on it.

I'm curious as to the conditions and reason that Aqua-Andy uses such a line.

Reason for such a line? It came already on the holder, it is 1/8" poly BTW. The conditions I use this in are open water diving in lakes and ocean, no kelp forest around here. Anything other than open water diving the flag is flying over the boat or no flag at all (boats can't go into an overhead environment).

 

[DragonTSD]

Thanks for replying everyone.

Knotical, Aqua-Andy, The information I've been given is a call for a concept design that will be developed further by engineers...if my idea gets forwarded, I could be the one developing it. I haven't been given any other information, but whoever wrote the baseline requirements had their reasons. I understand that drag, payout, current and the like will be problematic, but I don't think it flies in the face of physics as much as you think it does. A lot of intelligence can be designed into mechanical systems.

To be clear, I'm not really looking for solutions, I can develop those on my own. What I'd like to leverage is your experience.

For example; I added the bit about retrieving a diver after I read a mishap report about two divers who lost their lives on an ice dive and had to be retrieved by their tenders after they failed to respond to line-pull signals. Articles: USGCC Healy Dive Accident Final Report

I am unfamiliar with the specific function of a tender as well as the intricacies of the job. Ideally, i think this system would replace as much of a dive tender's job as possible, replacing human reliability with mechanical reliability (and, perhaps more importantly, predictability). is that practical?

 

[dumpsterDiver]

This is what you may want...The system (reel) must be controlled by the diver. There would be three settings on the reel:

One setting would be locked.. the reel will not spool out any line and the system can hold 100 lbs of force or so without releasing line.

The second setting would be slight tension, if the line becomes slack, the reel will pull in line and keep a slight tension of maybe 2-3 lbs max. this would be used on ascent primarily or when the diver begins to swim into the current.

The third setting would be released (free spool), the line would be released with near zero tension... to be used on descent.

I would love to see this work... but i doubt it.