[Terry Coging]

Drifting in a boat. Exploring the Loch. Reading the signs. Blending with nature. My favourite way of fishing.
There are so many variable to consider that it never becomes boring. Even a blank can be a rewarding and memorable day. Oh! and we can do it sitting down 
It also exposes our personalities. A few days spent with a boat partner will soon show up our character and nature. I've made life long friends from sharing a boat.

As most forum members will know, I have a passion for long trout rods and light lines.  During the past 6 years, I've been experimenting and refining the 'wafting' technique, as I call it. The foundation of this pleasurable style of fishing is based on geometry.  Put simply, a longer rod with lighter line will fish a dibbled fly for longer and further from the boat. But there is a lot more to it than that. So many variables.

I am currently thinking about some sort of equation that can be applied when drifting 'loch style' in or near the surface. The variables are a mathematical challenge, but my physicist  pals think that there could be something in my muse.  Maybe when I list the variables they will think otherwise 

In the meantime I can list the constants - rod length, line weight and profile, typical rig etc. Then some assumptions as a base - wind speed, boat speed etc.

Your comments to my muse are welcome - for instance - what could be assumed as an average speed of a boat drifting  with a wind of 10mph? Lots of variable there?

It pays to take a fresh look sometimes 



 

[Robert MacDonald-Lewis]

There are likely to be a few levels of complexity to this one. While the target accuracy will drive the complexity required.

While line weight and profile are constant for one angler, these could vary significantly from angler to angler. Typical rigging could introduce significant variations. I know from my group of fishing friends we all use different materials and diameters of materials. The diameter and stiffness of the material will impact the angle and shape of the line through the air.

Aerodynamic properties and weights of flies would also have to be considered.

To investigate further, you may need to define a series of sensitivities for each variable. Presenting the results in an easily digestible/usable format could be challenging.

Someone with more experience in dapping may be able to provide more useful insight.

[Terry Coging]

Thanks for your input Robert. The elements of the great puzzle that you mentioned are being constantly tested.
An interesting aspect of this study is the spill over experience gained, that applies to regular sized rods and lines.
An example of this is the affect of wind turbulence in front of the boat. How your line and flies behave when the wind direction is reversed close to the boat and why it can sometimes be better to finish around the end of the boat. I've been doing this for over 50 years but not really considered why.

[Hamish Young]

I'll add some things to this topic later today, as drift rate is very applicable to maritime search planning which I may have some qualifications in  fishing from dinghies I consider myself reasonably well-versed/experienced, so I will hopefully contribute something useful later 

[James Laraway]

how about a variable in relation to loss of concentration from getting a sore/numb arse from sitting in a boat too long - this definitely leads to less fish in the boat 

[Hamish Young]

Your comments to my muse are welcome - for instance - what could be assumed as an average speed of a boat drifting  with a wind of 10mph? Lots of variable there?

Within the Search & Rescue (SAR) community this is a type of modelling  which owes some of its routes to the recovery of downed airmen during WW2.  A great deal of effort was made to determine the drift rates of different objects in the water and that is still something that is being fine tuned today.

The rate of speed of any drifting object is largely (but not exclusively)  influenced by two things:

1. Leeway speed of the object - this is percentage of mean wind speed and is calculated downwind only, no divergence. This speed is obviously different on the size of the drifting object. So a fibreglass boat will typically drift at a different rate when compared to a proportionally similar wooden boat in the same conditions.

2. Total water current (TWC). Now this is funky and whilst more commonly applied to the saltwater than freshwater because of tidal effect,  it is actually relevant to large lochs and stillwaters - hugely relevant. Other than tide, TWC is influenced by many things - depth of water, continual effect of a wind from a constant direction (this is called 'fetch'), heat/cold.  If you've heard of thermoclines and can imagine what stratification looks like then very loosely that is also how TWC can be perceived, the top layer of water can be moving at a very different rate (faster) compared to the rest.

The resulting drift direction and speed is a vector sum of the objects leeway speed and total water current. But we're not interested in the resulting drift direction here, the question was really one about drift speed and that is essentially determining the leeway rate of the object. If a person in the water has minimal leeway and a sailing boat has significant leeway then determining the percentage rate of wind speed for the type of craft you are in is almost entirely just 'taking a punt' - some call that an educated guess.

Sure, there are SAR graphs and tables that give an indicative/generic rate for different objects, but there's no hard and fast rule - too many variables.  As a general rule of thumb, I have found that in freshwater if you allow 20% of the wind speed up to a force 4 and 30% above, you'll have a good baseline of the uncontrolled drift speed.

H

[Terry Coging]

Excellent Hamish. Thank you for that valuable info. I never gave a thought to the difference between surface water speed compared to the main body of water - even though I was conscious of it from coarse fishing. Interestingly, my rule of thumb was going to be 10mph wind = 2mph drift. So we agree on that.
The dynamics of the top 2 or 3 feet of water is probably a case study in itself. How it influences the behaviour of fly life and feeding trout.  Thermoclines nearer the shore can be 'reasoned out' easier.

[Mike Barrio]

Drift speed: I imagine that the use of ( and perhaps size of ) a drogue would need to be taken into account Terry?

[John Wastle]

This is interesting. I have always assumed about 1mph give or take a significant margin due to the boat. based on experience of long open water drifts on the likes of Leven, Harray, Watten.

The only empirical example I have is from an continuous end to end drift of Loch Merkland in a steady NW wind  A nice steady fishing wind of perhaps 8mph that alligned perfectly with the far shore and required minimal adjustments. Merkland is about 3m long and it took around 4h to complete. That was in a well ballasted fibreglass boat that behaved pretty well.

Strava or similar would be a useful tool to collect more detailed information on drift speeds. Worth some trial in the new season.

[Terry Coging]

Think you are right about 1mph being more typical John. I like to drift faster than average when  wafting, unless the fish are down a bit. When wafting the flies are touching down two or three times more often than with the usual cast and pull angler. This is part of the reason why it works so well.
My own boat drifts quite fast even with the drogue out, because it sits on the water instead of in the water. Don't use it much nowadays though.
Maybe 2mph on Shin, Assynt and Veyatie is not unusual? - always looking for calmer drifts on those Lochs.
Always wanted to fish Merkland - what is it like?

[John Wastle]

Merkland is a nice loch to fish Terry. A decent stamp of fish that are usually looking up. It has a sporadic mafyfly hatch in June which can be fun.

You will certainly drift at 2mph or more in a decent blow, especially on the big lochs when surface current takes an effect.

My default is to cover the water avoid a drogue  unless I have to due to high wind, fishing a sinker, tighly packed fish or to control a badly drifting boat.