Question on streamlining

[Matsya]

I read a lot of references to streamlining whenever there are equipment questions usually in relation to hoses and Jacket vs BP/Wings.

Why is streamlining so important? I can understand streamlining for say, car racing or flying where speed and fuel consumption are critical issues. But is it so crucial in diving? And if it is, then why?

 

[Packhorse]

Less drag thru the water means easyier faster and more efficent finning and that means that you use less air. In other works speed and fuel consumption. It also means there is less chance of entaglement.

 

[K9trnr]

Imagine walking down the street with wind and rain, and you have your umbrella open. It's being blown about a bit, and you have to expend more energy because the area being exposed to the elements either creates drag or pulls you along (perhaps in a direction you don't want to be pulled toward).

Water has a lot more resistance than air or rain. If you're not streamlined, your kick propulsion will be less effective. You will expend more energy and use more air. But streamlining is even more important for other reasons. If you have dangling hoses, you could get caught up on an object and enter into a potentially dangerous situation. You could also accidentally have a hose/console/octopus hit a coral or sponge or any number of other underwater organisms and kill or damage that organism.

You don't streamline for speed, but you can compare fuel consumption to air consumption. And even if the air consumption difference is minimal, the other benefits (reduced fatigued & reduced chance of damaging living organisms) are very much worth your taking the time to streamline.

 

[ScottB]

Try running through air... pretty easy right? Try running in a pool.. its a bit harder isnt it?

Having a hose hanging off you wouldnt snag too much air,.. but water is quite a bit more dense, .. about 64 pounds per cubic foot..

For every action there must be an equal and opposite reaction.. if you move forward 1 foot, and your body has a frontal surface area of 2 feet.. you just moved roughly 128 pounds of water
add an extra foot of surface area for hanging hoses and inflated wings (say if you are overweighted and have to keep air in your BC to keep from sinking).. and now you have to move 192 pounds of water to advance that 1 foot..

So in that example, you would have to expend 50% more energy to move forward

Take care,
Scott

Reason for edit : correct a spelling mistake and finish my analogy

 

[PerroneFord]

Water is about 30x more dense than air. So every fin kick is trying to push a LOT of mass with a lot of drag through the water. Less drag equal less air trying to kick your way through it. So the "fuel consmption" is the air in your tank!

Where things go wrong is people begin to eliminate things that have nearly no bearing on drag. As in air, a sphere, or cylindrical shape presenting it's side to the wind or water, presents VERY little drag. Eliminating a LP hose will not cause a perceptible difference in drag. When you look at a diver moving through the water, the shoulders and head are breaking the plane of the water in front of the diver. This is why technical divers place pockets on their thighs. That plane of water has already been broken by the shoulders. They are in the slipstream.

What causes a LOT of drag is tanks. This is why going to 2 tanks won't give you twice the time. The extra drag induced is high. This is one reason I don't like tank mounted pony bottles (among many). You incur the drag of adding a second tank, but since you don't breathe it, you gain none of the benefit in terms of air consumption. Better to use double tanks and get some breathing gas for all that extra drag, or put the pony behind the shoulder and keep it from adding so much drag.

 

[Matsya]

Water is about 30x more dense than air. So every fin kick is trying to push a LOT of mass with a lot of drag through the water. Less drag equal less air trying to kick your way through it. So the "fuel consmption" is the air in your tank!

Where things go wrong is people begin to eliminate things that have nearly no bearing on drag. As in air, a sphere, or cylindrical shape presenting it's side to the wind or water, presents VERY little drag. Eliminating a LP hose will not cause a perceptible difference in drag. When you look at a diver moving through the water, the shoulders and head are breaking the plane of the water in front of the diver. This is why technical divers place pockets on their thighs. That plane of water has already been broken by the shoulders. They are in the slipstream.

What causes a LOT of drag is tanks. This is why going to 2 tanks won't give you twice the time. The extra drag induced is high. This is one reason I don't like tank mounted pony bottles (among many). You incur the drag of adding a second tank, but since you don't breathe it, you gain none of the benefit in terms of air consumption. Better to use double tanks and get some breathing gas for all that extra drag, or put the pony behind the shoulder and keep it from adding so much drag.

Thanks Perrone. I understand that air consumption will increase with drag. I was curious to know whether it is significant in terms of practical recreational diving - for example, I move very slowly in the water seeing the sights as I go and am in no hurry. In such a situation will drag have a significant impact on my air consumption?
ScottB's answer gives me an idea. But what if, in the scenario that he used, i cut my speed by half? Would my air consumption remain roughly the same?

 

[Mako Mark]

I read a lot of references to streamlining whenever there are equipment questions usually in relation to hoses and Jacket vs BP/Wings.

Why is streamlining so important? I can understand streamlining for say, car racing or flying where speed and fuel consumption are critical issues. But is it so crucial in diving? And if it is, then why?

Dude, I love your question. You are right, race cars need a little more streamlining, but water is slightly more dense. So your hands, hoses and handbags are things that make a huge difference.

Just look at the 100m sprinters, they are running through air and they wear body suits to reduce frictin. Imagine how much difference there is in water that is 800 times more dense than air.

In other words, an ounce of stream lining is worth a stone of extra energy

 

[MikeFerrara]

Thanks Perrone. I understand that air consumption will increase with drag. I was curious to know whether it is significant in terms of practical recreational diving - for example, I move very slowly in the water seeing the sights as I go and am in no hurry. In such a situation will drag have a significant impact on my air consumption?
ScottB's answer gives me an idea. But what if, in the scenario that he used, i cut my speed by half? Would my air consumption remain roughly the same?

If you don't move, then wether or not you're streamline won't effect gas consumption at all. Usually divers do some moving though and water is over 800 times as dense as air so any movenment at all is a lot more work...why add to that if you don't have to?

There are other advantages to being streamline. One has already been mentioned and that is a tidy rig that is close to your body will rub, bump and drag on less of your surroundings preserving the equipment, the vis and the environment.

Another is functionality. If everything is streamline and secure, you're probably more likely to know where exactly where it is and be able to use it.

 

[Mako Mark]

Mike, you have become so esoteric since the CVsE thread. We need your wisdom and instruction on this.

Matsya, you will have many times in your future dive career when youbecome breathless. when this happens, you have dine something wrong and streamlining could have helped.

becoming breathless as mike will (I hope) confirm, can kill you.

This is the importance of streamlining.

 

[del_mo]

Along this same vein, what has perplexed me on streamlining is watching tech or other talented divers cruise along (how I wish I could do what they do, and I try and try and try) with their knees bent and their lower legs vertical. To me this is very unstreamlined and doesn't make sense in a no-silt situation. Am I missing something here? Are we talking about giving up just a couple breaths of air? Is it because the kick is more effective and offsets the drag? Do they do it because they can and it looks cool and it shows a level of competence?