Underwater Streamline

[UaVaj]

For reduce drag underwater.

Should one focus on shorter larger profile or smaller long profile?

Example. Is it better to have a longer and smaller diameter tank or a shorter and larger diameter tank?

What are your thoughts.

 

[Blue982]

From a background in engineering, the biggest reductions in drag are usually gained when you reduce your frontal profile. This kind of drag is called "form drag." Friction coming from the length of the tank would be what's called "skin friction." Using your example, your tank should be longer and skinnier. However, because the diameter of tanks varies so little and they're already decently streamlined, the effect of a skinnier tank is negligible (so small it can be ignored).

 

[wadedeeper]

LOL...I have to know, how much are you really hoping to reduce by your long or short profile?

You want to reduce drag...get rid of the danglers hanging from your BCD. Reduce hoses and go hoseless computer. get rid of the octo and go alternate air source. make sure your BCD is properly sized and not one of those typical HUGE bladder styles (Tech BCDs tend to have larger BCDs whereas a mroe recreational BCD hugs your body a little better...or at least that is how my Tech rig is as compared to my recreational rig is).

keep your fins cleared of burrs...you'd be amazed at the difference of that and using a silicone spray to keep them clean and in good shape. keep your hands at your waist and make sure your kicks are effortless.

I have reduced my drag to as little I can. I don't worry about profile of my tank because I switch tanks depending on dive type (i.e deep, shallow, whatever). I have two hoses...one to my reg and one to my BCD/alternate air then my transmitter.

 

[elmer fudd]

To build on the OP's question, what are peoples thoughts regarding the bottoms of tanks and tank boots and how they affect streamlining? It seems to me that that big flat surface running perpendicular to the direction of travel just can't be good for streamlining. I've been thinking of making a slide on cone just for something to tinker and experiment with, (I enjoy doing that stuff almost as much as I like to dive).

 

[dumpsterDiver]

To build on the OP's question, what are peoples thoughts regarding the bottoms of tanks and tank boots and how they affect streamlining? It seems to me that that big flat surface running perpendicular to the direction of travel just can't be good for streamlining. I've been thinking of making a slide on cone just for something to tinker and experiment with, (I enjoy doing that stuff almost as much as I like to dive).

Working on the leading edge will be more beneficial than trying to put a cone on the end of the tank. These people have greatly reduced their coefficient of drag:

http://www.freakingnews.com/pictures/5500/Political-Coneheads--5606.jpg

 

[kanonfodr]

Trying to streamline a scuba diver by changing tanks is about like trying to streamline a brick by changing the color of it, IMO. While deleting hoses is a nice thought, I don't put enough trust in wireless signals and batteries to ditch my analog, hosed SPG.

Streamlining a diver is more about body position and staying completely in line with the intended direction of travel while maintaining a low frontal cross section. Granted, I can feel the difference between when I hold my arms under me and when I put my arms back to my waist but that could have adverse effects on trim or comfort for a diver in a drysuit, not to mention that's more movement if I have to communicate with my buddy, check my hoseless computer, or shoot an azimuth to get us back to shore. In short, suck it up, you're not a fish. A diver in the water is not going to be anywhere near perfectly streamlined, instead we will only be less un-streamlined.

That being said, gear can make a difference. Deleting hoses may as well, but then you could possibly give up redundancy or functionality which IMO comes before being super-streamlined. But most would argue that the diver makes the gear, not vice versa. I've seen rec divers in poodle jackets with much better trim than tech divers in Hog rigs and thus they were more streamlined. Instead of focusing on gear, work on yourself first. Then when you notice your gear having the same deficiencies repeatedly over the course of many dives you can start looking at changing your rig.

Peace,
Greg

 

[ajduplessis]

To build on the OP's question, what are peoples thoughts regarding the bottoms of tanks and tank boots and how they affect streamlining?

I doubt that the boot on a tank will have any noticeable increase in drag, however I am of a school where you don't "hide" any possible issues. What I am trying to here is that tanks can rust. The boots generally retain moisture for long periods, and people don’t remove them on a regular basis. I also don’t like the hose protectors on regulator setups as they too can hide possible issue. All diving equipment must have a zero potential of hiding/covering up problems.

The other thing I don’t like about boots are the fact that it encourage people to let the tanks stand upright. IMO a tank must lay down at all times.

 

[UaVaj]

in regard to the tank diameter and length. I do understand that the difference in drag between these two setup is negligible. however becuase I do have a choice. I might as well pick the one with less drag.

just incase some of you did not get it. say I want to buy a can of soda. 2 machine side by side. machine A charges 50¢. machine B charges 49¢. obviously 1¢ does not make a difference. given a choice. I might as well go with machine B.

back to the tank example. since all fast fish of the ocean are long and skinny. given a choice. I will go with a longer and smaller diameter tank for reduce drag.



I am only so tall (can not adjust that length).. so I will consider reducing my overall diameter by using slimmer gears.

 

[elmer fudd]

Working on the leading edge will be more beneficial than trying to put a cone on the end of the tank. These people have greatly reduced their coefficient of drag:

The front of the tank already has a fairly aerodynamic profile. The regulators sure don't, but the tank and valve form a nice cone shape. The butt end of the tank however is about the worst aerodynamic profile you could get, especially an aluminum tank or a steel tank with a boot.

I doubt that the boot on a tank will have any noticeable reduction in drag

The reason I ask about the boot is because on a steel tank it takes what would be a hemisphere and gives it straight 90 degree edges. Now obviously a hemisphere is a pretty poor trailing edge, but it still beats the hell out of a flat surface running perpendicular to the direction of travel.

What I'm actually thinking of doing is taking a traffic cone, cutting off the bottom, cutting a series of slits in the sides and then wrapping some duct tape around it to make it slide up over the bottom of my tank like a tank boot. No, this isn't going to become part of my regular kit. It's going to be more of an experimental thing. I'm curious what affect it will have on my speed and SAC rate.

 

[Adobo]

The front of the tank already has a fairly aerodynamic profile. The regulators sure don't, but the tank and valve form a nice cone shape. The butt end of the tank however is about the worst aerodynamic profile you could get, especially an aluminum tank or a steel tank with a boot.



The reason I ask about the boot is because on a steel tank it takes what would be a hemisphere and gives it straight 90 degree edges. Now obviously a hemisphere is a pretty poor trailing edge, but it still beats the hell out of a flat surface running perpendicular to the direction of travel.

What I'm actually thinking of doing is taking a traffic cone, cutting off the bottom, cutting a series of slits in the sides and then wrapping some duct tape around it to make it slide up over the bottom of my tank like a tank boot. No, this isn't going to become part of my regular kit. It's going to be more of an experimental thing. I'm curious what affect it will have on my speed and SAC rate.

This might be interesting as a stand-alone experiment but from a whole diver perspective, it's like treating split ends when you have a hatchet wound.