Larger people pushed faster in current?

[Slow]

I agree with the physics as you have presented it -- and thank you for your clear explanation -- but it is not in line with my experience, hence the post.

- Bill

It's definitely interesting.

From my noobish perspective, if I were in your shoes I'd ask someone to video me from the side to see if there's some trim I could improve (very likely true in my case) or some obvious streamlining thing.

I do amateur bicycle racing so I'm kinda a fiend on dialing in body position and streamlining of equipment. Small changes can yield massive gains in drag.

None of that should change your steady-state drifting speed though. If you're really drifting at different steady-state speed, it's gotta be that you're in a different current. I have no personal experience on that subject, but the comments above on distance from the bottom make a lot of sense...currents reduce as they get closer to the bottom.

Good luck...I look forward to experiencing such things myself. All my experience so far is in small and calm bodies of water.

 

[uncfnp]

Bill. Have you ever noticed if you are out pacing the small particulates in the water?

 

[billt4sf]

Bill. Have you ever noticed if you are out pacing the small particulates in the water?

No. great question.

 

[gcarter]

Are you possibly unconsciously finning to stabilize yourself or maintain position/trim?

 

[Lorenzoid]

Since the whole group is not doing exactly the same thing for the entire dive--some people slow themselves down, stop to look at something, turn around, etc.--it would be rare for the whole group to ever reach the point where the current is moving them along at the same speed. I suspect factors like your body size, orientation with respect to the current, how big your wing is (and how much air is in it), etc., would produce exactly the effect you're observing--that at some points in the dive you are being pushed along faster than more streamlined people.

 

[runsongas]

oblong object in lamilar steady state flow is a reasonable approximation during a drift dive

terminal velocity is dependent on drag force aka streamlining. the more streamlined you are, the lower the drag force coefficient and the higher terminal velocity. cross sectional area cancels out in steady state. mass only affects acceleration rate.

if you are moving faster than the rest of the group during a drift, it is more likely due to you being more streamlined.

if you find yourself being faster than the group, turn sideways to increase your drag to slow down

 

[rhwestfall]

you are not "pushed" by current, but actually grabbed/pulled. It is called friction. Bigger person has more surface area, thus more contact with the water to pull you along with it....

 

[tursiops]

oblong object in lamilar steady state flow is a reasonable approximation during a drift dive

terminal velocity is dependent on drag force aka streamlining. the more streamlined you are, the lower the drag force coefficient and the higher terminal velocity. cross sectional area cancels out in steady state. mass only affects acceleration rate.

if you are moving faster than the rest of the group during a drift, it is more likely due to you being more streamlined.

if you find yourself being faster than the group, turn sideways to increase your drag to slow down

I think this is confusing vertical movement due to gravity, and horizontal movement due to drag. There is no sideways equivalent to gravity, so no such thing as terminal velocity, where there is no more acceleration downwards because the drag forces (as the velocity increases) finally equal the gravity force. The streamlining comment is also for vertical movement due to gravity; more streamlining means less drag, so you achieve a higher velocity before the drag force matches the gravity force.

You can't be pushed along faster than the current speed.

 

[runsongas]

you aren't moving faster than the current, just at a higher proportion of the current speed than a less streamlined diver.

you reach an equilibrium between the normal force of the current against drag force to determine the steady state velocity.

maybe terminal velocity isnt the right term

 

[runsongas]

you are not "pushed" by current, but actually grabbed/pulled. It is called friction. Bigger person has more surface area, thus more contact with the water to pull you along with it....

if this were true, both a large and small diver would still only reach the same velocity as the current would exert no force once both divers had matched the speed of the current. as mass increases faster than surface area, a larger diver should be slower to accelerate also.