Not sure if it is here to stay, but there is a pressure crack already, which says it has some substance. If the wind doesn’t come up in the next couple of days, this might be it.
I am going to try to keep up on the ice reports, but I never will tell you the ice is safe. I wouldn’t go out on this yet, simply because of the open water you can see near shore. But there are people fishing in the bays already around Alburg, North Hero, and Isle La Motte.
I will try to make ice reports a steady part of this blog while I slog through the paper on seiches in the thermoclines in the Broad Lake. I would like to go into a little more depth than reported here, though it is accurate as far as it goes, and if possible, find something in the original paper fishermen can actually use. Hopefully, I can have an article by next week.
UPDATE: Ice largely broken up, but not entirely.
Or somebody decided to make one of those “flash crowds” on the ice at the Isle La Motte bridge.
The St. Louis Arch is probably the most familiar example of a catenary curve to Americans.
Catenaries are important to the troller because it is the basic shape that a trolled line takes on if it has some kind of terminal tackle, such as a lead weight and a lure, attached. If you imagine a heavy weight at the end of your line, and a fair amount of line out, the line will take on a steep curve at the weight, gradually becoming a shallower curve near the boat. You see than that the depth increase per foot of line out is greatest near the weight, and continues to diminish as more and more line is let out.
The way an engineer would solve the problem of depth vs line out, is to calculate a formula for the curve by the looking at the basic laws of classical mechanics to determine the fundamental drivers; in this case the unit weight of the line, its diameter, and the towing +- the current speed. He or she would then perform a series of manipulations and calculations to get the depth at any point on the curve. I will be publishing a set of tables like that in the next week or so, but I cannot possibly cover every possible combination of leader length, line time, blades or no blades, lure or live bait, etc.. So I am going to present here a way to measure the depth of your presentation that relies strictly on measurements that can be taken from the boat using simple carpenter’s tools, a pencil, paper, and some addition and some way to measure the line out. You can mark your line with a tape measure and spray paint if you want to keep strictly in the realm of carpenters tools, or you can use a line counting reel. This is an extension of my post regarding the “Guestimator Tool,” which only works on lead core line with a minimal type of terminal tackle.
The important thing to remember is that this curve keeps roughly the same shape, no matter how much line is out, as long as you don’t hit the bottom 😉 Imagine a sheet of paper covering the image, level, and revealing the curve as you slide the paper from bottom to top. The curve as it is revealed will be the curve as the line enters the water.
Your task is to measure the angle of the line at different points as the line goes out, creating a series of triangles, for which you have the angle and the approximate hypotenuse. From this you can calculate the depth gained from each section of line using trig. Add them up, and you have a decent measure of the depth of the end tackle. If you are using a long leader, do the measurements for the leader as well. This technique will only work if you use a neutrally-buoyant, weighted, or diving bait. If you want to run a Jitterbug on the end, you are on your own.
Make up whatever kind of angle measurement apparatus you can with the stuff in your tool box, or from the local hardware store to measure the angle of the line in degrees as accurately as you can. Use the following table to estimate the depth increase (Factor) for the section of line you let out.
Make up a table for your measurements, using the example as a guide:
|Line Out||Length||Angle||Factor||Depth||Running Total|
Use the running total to get the depth at 10, 20, 30, and 40 ft. The smaller the sections the more accurate, in theory, but measurement error will probably erase any gains by trying to get too cute. If you do this once, or better yet, a few times for each rig and take the averages for each speed or set of conditions you wish to know the table, you can have a create a set of personalized depth charts for your gear. Laminate them, and keep them on your boat. The beauty of this method is that it takes into account local conditions. Any pre-calculated tables would inevitably ignore many factors to make the math workable, like doing the measurements on a cold, still, lake. When our like is “cold and still”, we are fishing through the ice.
This technique will also work for divers, which create the same kind of curves
This allows you to make a *rough* guess as to what the drop per color at your current position. So, if you have four colors out, and you let out a new color, it will show the depth gained by the next color let out. As you can probably guess, you do this by comparing the angle of the line out to the guestimator and reading off the number.
One of the biggest problems with fishing for cold water species is depth control. Of course you can solve this problem with expensive down riggers, but I am a cheapskate with a mathematical bent and a little background in classical physics. A search of the web turned up little more than rules of thumb. There was one interesting scientific paper which took an engineering approach to the problem: “Sink depth of trolled fishing lines” G Spolek – Sports Engineering.
What Spolek did was to make some simplifying assumptions about the behavior of weighted line and developed a simple model for calculating the depth of a trolled lead core line based on its weight, its diameter and trolling speed. In any case where drag is involved the drag increases with the square of the speed unlike that of other factors. He then validated his model by depth and speed measurements.
Professor Spolek’s paper has already been referenced in Fly Fisherman Magazine in reference to sink depths of wet flies, if you are interested in that kind of thing.
What I did was to measure diameters of lead core line with calipers and a feeler gauge (+/- .05 mm) and measured one color of the line to the nearest gram – if no published data were available. I then calculated the specific gravity theoretically and ran the numbers through Professor Spolek’s model. This gives a speed dependent view of depth to line out. At 2.5 MPH I get roughly 5 ft down per color, which agrees with observations seen around the net, and on lead core line web sites. As you can see from the table below, however speed, diameter, and the line’s grain weight vary this number considerably.
Sink Depth in Feet per Color
|Speed – MPH||Kerplunk #18||Kerplunk #27||Cabella #12||Cortland LC 13|
I had assumed while doing the above calculations that the lead core line would take on a catenary shape as more line was paid out, based on my interpretation of this Wikipedia article which touches on, but does not completely explain the problem of calculating the depth of a towed cable. Once I went to the trouble of creating a model which took catenary effects into account the effects cancel out. It turned out that there are no additive effects on a simple lead core line, that it lays straight in the water; with the small exception of density changes due to temperature changes. So theoretically, one could use this table to calculate the depth out to ten colors or more. According to this model then, ten colors of Kerplunk #18 at 1.5 MPH could get you deeper than 100 ft, assuming no current, and that your lure was of neutral buoyancy, such as a light salmon spoon.