Speed control during a drift dive

[Hank49]

and then there is always the trusty reef hook, invented by a photoprapher...

I swear Catherine, you change you avatar more often then I change my underwear...

 

[knotical]

Neat topic !

Sailboats can sail faster than the wind, and at other times, into the wind. In both cases the sailboats are moving at an angle to the wind. Perhaps similar physics could be applied to divers and currents.

Even the question of just drifting is not trivial. Will an object (the diver) eventually drift at the same speed as the current, or will it always be a bit less because some of the water will flow past you?

I’m not sure how, or even if depth actually affects your speed. I suspect it simply puts you in water moving at different speeds.

Any fluid dynamics experts on board?

 

[Firefyter]

maybe not what you're looking for, but on a couple of drift dives I've done I turned into the current and just let it carry me along backwards - if I wanted to slow down I kicked a bit. For direction and extra forward movement I just did a backward kick, which is very easy with the current. I'd check my direction by looking back between my legs occassionaly. I was mostly having fun watching the other divers - sometimes they are more interesting than the fish

Aloha, Tim

I did this same thing for an entire hour on a pretty fast drift dive last year in PDC, Mexico. You're right, it was just as much fun watching the other divers...LOL.

 

[Jim Baldwin]

Accepting the fact that one can control their speed while drifting by changing their depth, I heard a couple of things recently that my little pea brain is having a hard time accepting.

After a swift dive in Cozumel, a VERY experienced instructor/diver commented that he could speed up by sticking his fins out like a sail. Shortly after that a very inexperienced diver (but highly educated) mentioned she could slow down by sticking her fins out like a brake.

It seems to me that in theory it doesn't matter where you are spread eagle or in a cannonball, if you don't fin or paddle and stay at a constant depth, your speed will not change but continue at the speed of the current you are in.

I have made numerous drift dives in Cozumel and I find that I can control my speed by staying closer to the reef and by not giving the current more surface area to move me.

I have seen new and experienced divers that are not familiar with drift diving finning a lot, moving their hands and trying to stay more vertical. They move through the water faster than those of us who stay horizontial and allow the current to move us..

I carry my camera on almost every dive and althought I don't hold on I am normally always the last one in the group. My wife will be slightly ahead of me and sometimes we have to kick hard to catch up with the group.

Once we catch up we will quit finning and simply allow the current to carry us. The rest of the group will get ahead. After a couple of days of diving and discussing diving techniques we see these divers slowing down and ultimately they use less air and see more.

Nothing scientific just my experience from a practical standpoint.

 

[TheRedHead]

I have made numerous drift dives in Cozumel and I find that I can control my speed by staying closer to the reef and by not giving the current more surface area to move me.

Quite true and you can also duck behind something and stop with 1 finger in the sand or a light touch on a piece of dead coral. If you don't want to see you DM pulling his hair out, do not drag your fins or hook into anything in Cozumel.

 

[ba_hiker]

Neat topic !

Sailboats can sail faster than the wind, and at other times, into the wind. In both cases the sailboats are moving at an angle to the wind. Perhaps similar physics could be applied to divers and currents.

Sailboats can do this by playing with the interaction of the wind in the sails, and the water against the keel (or center/dagger board) and the rudder. It is because they can manage enrgy in two different medums at the same time that the don't just get blown in the direction of the wind.

Perhaps if you had a keel and rudder in the sand??

 

[DA Aquamaster]

Hank had it right.. You can slow down by staying close to the reef or bottom as the turbulent flow there is significantly slower than the laminar flow in mid water.

When drift diving in fast rivers (5-7 kts) it was common to drag your fin tips on the sandy/rocky bottom, but that was mostly to ensure they did not end up in the faster water overhead as that could and often would flip you end for end. The differnece that 2 or 3 ft could make could be as much as 2-4 kts in water velocity.

 

[BarryNL]

Speaking of drag, how about your dive position ? If I am in a streamlined position, will the current move me slower ?

That's a bit like asking if you'll move faster along a conveyer belt if you lay down in a Superman position.

 

[Old Diver]

This is rather like hot air baloons drifting; shape is almost of no factor, the giant chicken moves at the same rate as the goodyear blimp, assuming that the blimp turns the engines off. The example of the sailboat earlier in the thread involves energy input: a sail is a wing in use and converts air flow into energy as lift relative to air movement. The keel is a case of directed drag to give bite to oppose the wings pull.
For an experiment try sailing an innertube, if you dont supply a keel surface of some sort before the wind is all you are gonna go.

 

[langs15]

I swear Catherine, you change you avatar more often then I change my underwear...

That, is just--wrong!