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new safety system for constant weight...

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Well-Known Member
Oct 5, 2001
we've been thinking for some time about how we can develop a system that would allow us to safely dive to deeper depths.
in the past, i came up with an idea that could be used for free immersion and constant weight. i posted it to apneadiver. it worked in theory, but i was starting to think that it might not work in practice, or would be too costly, difficult to build. also, because it was non-portable, there was the risk that people would mess with it. sorry, i think i've lost the drawing i did of that contraption.... anyway, i've since though up of another system that can be used to retrieve a diver from depth, it's only suitable for constant weight though.
it's not as good as DRUMS but i think it's quite a good idea, and it's simple, cheap to make, and portable.
i'd appreciate any comments from anyone...... let me know if you've tried anything similar!
i've attached a doodle of the setup below... sorry, if it looks like it's been done by a 5 year old. :eek:



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this is pretty much the same system, that the german diver came up with (the guy with the bo, in the example on my 'rescue procedures' thread).
he hasn't tried it yet, we've just talked about it. i'll forward your sketch and will let you know when he replies.

thanks Roland.

there must be hundreds of ways of implementing this general idea - of a heavy weight that pulls up the bottom weight along with the leashed diver.
i'd be especially interested to here of any system that is simpler and/or easier to build. that example i gave was only the best system i could think of in 30mins, so there must be better ways of implementing the idea.
the nice thing about my example is that you can break it down into parts for easy transport... the rod, 2 small buoys and the reel. the reel wouldnt be very big...
for 90m of 10mm.... and reel diameter 30cm...
(each turn = 2 x pi x 0.155 = 0.974m)
(total of 90 / 0.974 = max 93 turns.)
the reel would need to be 93cm long with a single layer or 45cm with a double layer... assuming it's all neatly wound on! :)
so not very bulky at all really... whole lot should fit in the boot of a car.

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Great idea, here's a twist on it ...

Hi Alun,

This is a great idea. I did think of a few potential improvements that might be worth considering:

- The platform could be a triangle (most stable form) or a square (easy to fabricate, e.g. using pipe) with a buoy at each corner. If two buoys were used, I think that there is a potential stability problem and you would have the risk of getting the rope wrapped around the platform. Although this risk is probably small, the stakes are very high.

- Use one "leg" of the platform to hold the spool, and the other as the pulley, over which the rope is drawn.

- The square could have another bar in the middle that serves the function of separating the diver from the weight (the "anti-bonk bar").

- Consider putting the clutch on the weight rather than the platform, and letting the spool run free. In your design, the mechanical advantage of the weight is halved, thus requiring a larger weight. Although your design could give a faster ascent, I think that the drag effects would quickly erase that advantage (i.e. the ascent wouldn't be that much faster). Also, the lighter weight makes for a more portable rig and an easier retrieval in the event that you actually use the rig for a rescue.

I've attached a crude drawing


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i can see how a plane on the surface would be more stable, but i cant visualise how the rope could get wrapped around the bar because the line is always under tension.

i dont quite follow what you mean by putting the clutch on the weight and letting the reel run free. is there not a risk that the heavy weight will just unravel the reel and not lift the diver? i must be missing something. can you do a close up doodle on that part of the system please?


ps: 'bonk' means something different here in the UK. i'll let you guess what it might mean. :eek:
Anti-Anti Bonk Bar

Ok, I didn't mean to imply that this could be a form of contraceptive ;) In American slang, "bonk" can have the slightly profane meaning that you mentioned, but it is usually more innocent and can be used to mean "bump into painfully" (e.g. bonk your head). By now you are probably rolling on the floor laughing. Another meaning is to become completely exhausted (e.g. to bonk while running a marathon). OK off the floor!

Back to the rescue device. My basic suggestion is to fix the weight to the rope. The clutch is fixed to the weight and the weight/clutch assembly is pinned to the platform. To perform a rescue, pull the pin. Then the weight drops and hauls up the diver. The spool could just spin freely and line would pay off. Be sure that the line is not tied to the spool. I have a crude drawing below.

The advantage of this approach is that the line does not need to pay freely through the weight. In the "line through the weight" system, if the line tangled at depth (e.g. to the rope twisting about itself), the rescue system would stop hauling up the diver and you would be left with the prospect of diving down to untangle stuff.

One other suggestion that i have is to make the "little weight" soft (like an ankle weight or something). That way, you would minimize the risk of injuring the diver via impact as the heavy weight pulls the lighter weight up toward the diver.

Your argument about the tw-float system being stabilized by tension is probably right and it would probably work just fineT. I guess that my main suggestion is to ditch the "rope paying through the weight" system, though that may work just fine too.

I think I'll try building something like this this spring and see how it works. We have a site where we can test it to 30M under pretty controlled conditions.
oops forgot picture ...


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ok, i think i understand now. one thing though... i thought that having the weight draw line off the reel would introduce more resistance and reduce the descent speed. but perhaps that effect would be neglegible and your version would always be faster than my version.
i may have another think about it to see if there is an even simpler alternative.
oh, and a friend of mine suggested that the loops under the bar be replaced by little wheels - make sense. might make construction a little harder but probably worth it.

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