Fly movement physics question

[Mangrove Cuckoo]

OK... the fly is not in the air though, it is in the water. Much like when presented from a drift boat.

So here is the "discussion" I have been having...

When a fly is swung downstream by an angler standing in a stream it generally follows an arc until it is directly down stream of the rod tip... on the dangle. Forget about mends, leader to flyline ratios, or amount of flyline on the water at this time.

OK so far?

So... what if some parameters are changed? As in when the angler is not anchored?

Assume the water is completely still, and it is the angler that is moving, like in a boat drifting due to a wind? Again a simplified case.

The fly will not travel in an arc like when swinging a fly because neither the fly nor the angler is anchored... right?

I believe I am correct. My argument is that the boat would travel in an arc if the fly became anchored, but the fly does not follow the same path as when swinging wet flies.

My buddy says it does. And, if not, "then what path does the fly take then smart ass?"

Um... help?

[Paul Arden]

Hi Gary, the fly will follow the line so in my opinion it will travel an arc. In fact this is a tactic so often used to use on hard fished Stillwaters. Ie cast out and walk along the bank, particularly with sinking lines.

If you cast a floating line straight out and walk along the bank you can see the curve in the line. Same thing on a drifting/moving boat etc.

In fact I think if the river flow was constant all the way along the line, which it never is of course, then the curve of the fly path would be identical if you were to walk along a stillwater bank at the same speed.

Cheers. Paul

[James9118]

Hi Gary,

Essentially your question is a 'frame of reference' one. In the first example the angler determines the frame of reference, whilst in the second example the water determines the frame of reference. If you standardise the frame of reference, to either, then you see that the problem (in a purely physics sense), is identical.

Obviously in real life there are differences, water does not flow in a laminar manner downstream for example, the water closer to the banks moves slower, there are eddys and all sorts of other things.

This is a similar question as to the nature of drag in air and whether it matters if it's the object moving or the air. When you get down to the level of the interaction between individual molecules I think it's quite easy to see that it doesn't matter, and on that scale the observer would not necessarily know which is moving, just that an interaction is happening.

Cheers, James

[Mangrove Cuckoo]

OK, thanks guys!

Paul,

When you walk / troll a fly along the bank, after a cast perpendicular (?) to the shore, what path does the fly follow? Along the curved layout that forms in the line? If so, how does that better present the fly to hard-fished trout?

James,

I figured it was a frame of reference thing. So, what if we change the frame of reference to that of a stationary fish?

When the angler is anchored, the fly can be swung across the face of a fish without any line or leader bothering it first. Does this hold true in the second scenario?

This discussion arose from my lack of experience fishing from drift boats. My buddy
has lots of it though. Of course, there are infinite numbers of variables in the real world.

And one of them is pertinent to some fishing I do where *both* the fish and the water is stationary. The flyline absolutely cannot travel above the fish, not in the air or in/on the water. Alike on a stream you can assume where a fish might lay, but you cannot see it.

So... how best to present the fly to the presumed fish?

[Paul Arden]

Hi Gary,

I think curved fly movement paths are a trigger. We use them on the dibble to induce a take, I often throw a curved cast for sedge feeders. On hard fished stillwaters I think fish just learn. Many years back I used to teach children, taught about 1000 kids one year, usually on small UK Stillwaters. That’s mostly where I practised that walking along the bank technique. On big Stillwaters you usually have currents that do this for you.

A good example is a fish chasing your fly to the boat. There are three main things you can try; speeding up (many species like this, eg many SW species and Snakehead etc), stopping and restarting (trout often take on the pause) and curving the fly/changing direction. That change of direction is a killer for me. If I’m fishing “blind” I *always* curve the fly before I lift off. Sometimes all the fish take on the dibble (or change of direction). Usually it’s about 1 in 3 or 1 in 4.

Cheers, Paul

[James9118]

Hi Gary,

A fish in a static position in running water and a fish in a static position in still water are not equivalent. There is no frame of reference that can be considered that equates the two.

Regards, James

[Mangrove Cuckoo]

OK, thanks James... I believe you just agreed with my side of the argument with my fishing buddy.

Since this is not working, I 'll ask a much simpler question:

Does anybody know of a book or video that discusses the ways to present a fly when fishing from a drift boat?

It seems that drift boat fishing is very popular in the western US, and even over here in the east when on the larger rivers, but I cannot find much in the way of instruction.

Thanks.

[Paul Arden]

I don’t know of any books Gary. There must be some. There is definitely a different set of skills particularly in line management, tactics, and so on.

When the angler is anchored, the fly can be swung across the face of a fish without any line or leader bothering it first. Does this hold true in the second scenario?

I think it still can but sometimes it can’t. The boat is moving slower than the current it is in, usually. Not always of course because it’s possible to row downstream faster than the current. But more often the opposite is the case, making the boat considerably slower than the current that the boat is in.

The fly may be in that same current, or one with the same speed, but most usually not. Mostly you are fishing into slower although sometimes faster water. So what matters I think for your discussion is boat downstream decent speed vs fly downstream descent speed. One or other can be faster and is constantly changing. If the boat is faster and you’re fishing streamers the leader will appear first, if the boat is slower the fly can appear first. I think that’s your discussion?

I can ask around for a series of articles on fishing drift boats from different contributors, guides etc? That might make for some interesting reading.

Cheers, Paul