Equipment

[jpanayotou]

Gday divers,

I am a university design student and am focusing on designing a dpv for my final year project. I am hoping for continuous positive feedback from the following questions:

Regarding oxygen cylinders/tanks, are there any specifications detailing dimensions, weight and brands of existing tanks? How is the weight affected in and out of the water? Why are the tanks made of such heavy materials, are there any alternatives?

What is the direct purpose of BCD's and weight belts, and how are they controlled during a dive?

Are there any specific details regarding the rate of ascent and descent at various levels during a dive, and the maximum speeds that can be achieved? This needs to be considered in reflection to a dpv.

Would it be possible, and would there be personal and market interest in a dpv that enables you to connect a tank, BCD, weight belts, etc (all necessary equipment) to the u/w vehicle? My primary concern is your hands will be operating the dpv, allowing minimum interaction with the marine life. An immediate thought on the design is to combine all necessary equipment into the single unit of the dpv, however allowing the user to detach and separate the oxygen cylinder to support them for a short period of time.

What is your personal interest and comments on directing a dpv towards a scuba diving market, aiming to expand the exploration of the underwater environment to a wider target market?

Your feedback is greatly appreciated, and I hope to hear positive constructive criticism towards my project shortly.

Kindest regards,


John

 

[Spectre]

Originally posted by jpanayotou
Regarding oxygen cylinders/tanks

Some quick starting points:

http://www.abysmal.com/pages/features-cylinders.html
http://www.omsdive.com/cyl_spec.html

The above two links show some examples of the size and weights of tanks, and their bouyancy [their weight in water].

I have no real answers as to the weight of the metals used, other than that the air pressure in the tanks is quite severe [an exploding 3000 psi tank can send a firetruck 50 feet into the air]. It's a lot of power to have to hold back.

What is the direct purpose of BCD's and weight belts, and how are they controlled during a dive?

Mainly your exposure suit is the main cause of bouyancy, not to mention that a body will naturally float. You have to offset that bouyancy with weight to allow yourself to sink. Once you can sink, boyle's law will go into effect on any air pockets [expecially in exposure suits], and cause you to continue to sink. The BC is then used to offset the negative bouyancy that you've created, to enable yourself to reach neutral bouyancy. As you decend, Boyle's law acts on the air in your BC thus making you negatively bouyant again. You have to add air to keep your neutral bouyancy. As you ascend, the air expands and you have to remove air from your BC to keep from uncontrollably ascending.

Are there any specific details regarding the rate of ascent and descent at various levels during a dive, and the maximum speeds that can be achieved? This needs to be considered in reflection to a dpv.

The common practice is no more than 60 ft/minute. Many dive computers require to to ascend slower than that. The descent rate is a little less rigid, but you have to equalize the pressure in your sinuses/ears/mask as they compress on descent, so that sort of controls your decent speed. [It's pretty easy to blow capilaries in your eyes from the pressure in your mask if you don't clear early and often. No damage, no real pain, but you sure look funny for a few days! ] The ascent rate limits are tough to explain in a quick e-mail, but it has to do with decompression sickness. The concept is fairly easy to understand... if you shake up a bottle of soda, and then open it really fast, the bubbles come out of the solution and make a mess. If you open that bottle really slowly, it lets off the excess gas slowly and it doesn't explode everywhere. There has actually been documented cases of blood being drawn from people with serious [& fatal] cases of Decompression sickness, where the blood is just foam.

Would it be possible, and would there be personal and market interest in a dpv that enables you to connect a tank, BCD, weight belts, etc (all necessary equipment) to the u/w vehicle?

No answers, just one question to throw back. If you are naturally positively bouyant, and all your stuff is on a vehicle that you are holding, and you accidentally let go... you'll ascend. If you ascend uncontrollably... see foaming blood comment above. Now the other thing is your weight would need to be distributed around your center of balance. If all your weight is on something your holding, and your positively bouyant, it would have to be negative. If it's negative and your positive, you and it are now vertical in the water. [or fighting to stay horizonal].

Your feedback is greatly appreciated, and I hope to hear positive constructive criticism towards my project shortly.

If you are truely serious about this project, you may want to look into getting Open Water diving certification. Nothing beats practical experience. One quote that I think sums it up quite well is "Never trust a bald barber". If you want to design something for divers, you'd be best to become one yourself!

-Jeff

 

[Rick Murchison]

Originally posted by jpanayotou
Regarding oxygen cylinders/tanks, are there any specifications detailing dimensions, weight and brands of existing tanks?

I assume you mean "air" or "breathing gas" vice "oxygen" cylinders. There are lots of tables claiming to give the dimensions, weights etc of tanks on the net. Few of them are accurate. If you want accuracy you're going to have to get out in the field and test the tanks yourself.

How is the weight affected in and out of the water? Why are the tanks made of such heavy materials, are there any alternatives?

Buoyancy (weight decrease due to submersion) is equal to the water displaced by the tank, and varies with each size tank. In general, a tank will displace about as much as it weighs empty or a bit less, a notable exception being the standard Aluminum 80, which displaces a few pounds more when empty. Tanks for diving need to sink easily, or the diver will have to carry a bunch of extra weight to get down. Lighter altrernatives would therefore be impractical.

What is the direct purpose of BCD's and weight belts, and how are they controlled during a dive?

BCD's assist the diver in maintaining neutral buoyancy at depth, and positive flotation on the surface. It is controlled by adding and dumping air. The air can be provided manually by blowing into an inflation tube but is almost exclusively provided from the breathing gas cylinder with a manually controlled power inflator. Weight belts are there to overcome the positive puoyancy of the diver's total rig so the diver is able to descend (with no air in the BC).

Are there any specific details regarding the rate of ascent and descent at various levels during a dive, and the maximum speeds that can be achieved? This needs to be considered in reflection to a dpv.

Yes. Buy the books for any beginning diving course and read up. Or buy the NOAA diving manual.

Would it be possible, and would there be personal and market interest in a dpv that enables you to connect a tank, BCD, weight belts, etc (all necessary equipment) to the u/w vehicle? My primary concern is your hands will be operating the dpv, allowing minimum interaction with the marine life. An immediate thought on the design is to combine all necessary equipment into the single unit of the dpv, however allowing the user to detach and separate the oxygen cylinder to support them for a short period of time.

The unit already exists.

What is your personal interest and comments on directing a dpv towards a scuba diving market, aiming to expand the exploration of the underwater environment to a wider target market?

Plenty of DPVs are available - shoot for a price advantage over the competition and you'll be successful.

Rick

 

[Scottri]

I'll test the prototype for free! Sounds like a fun project.


Good luck,

Scott