How low do you go?

[Tod]

How far from the bottom should the towfish be? What if the fish had a bottom feeler that controlled the vertical


stabilizer mechanically? If it came to large rocks or something it would help direct it over. Mite look bad on the display


but maybe it saved the fish. How does the transducer array get a large vertical angle and small horizontal? Why is the


transducer array horizontal, would it be better vertical? Next week I’m going to talk to a company that makes piezo


eliments and ask them some of these questions. I think we can make our own array for a lot less. Cable question: how


do you look at both sides, do you need two circuits i.e. 3 or 4 wires too the fish. I’m looking at a RG-58 A/U twinaxial


cable 20g 100ohm strand 500 feet for $264. Will that work for both left and right or at all?

[Patrick Duffy]

Re: How low do you go?

Todd,


I'll try to answer a couple of the questions ...


>How far from the bottom should the towfish be?


Very close to the bottom. This is why Sture used Stainless Steel. On his website, he mentioned that it has to be a tough fish to withstand hitting rocks ... a certainty. This is why I went with Delrin (stronger than PVC, but just as easy to work with) and plan on needing extra parts (fin section most likely). This is also why I wanted to hook another transducer in the bottom of the fish to tell me how far the fish would be off the bottom.


I mentione in an earlier post that I considered hooking a Lowrance PD-W transducer (same as in my fish) to a Lowrance 3500 depth finder. I forget how much power the 3500 has, but there was not enough to go over a 60 cable. Another possibility would be to feed the extra (depth) transducer into another fishfinder (more power than the 3500 depth finder).


I drew a rough graph to get an idea on the coverage I would have with a 20 degree transducer. 1" equals 50' in depth (on the side of the paper) and 1" equals 50' in distance (the bottom of the paper ... represents flat ocean bottom).


Once you do that make a 20 degree angle and move it at various depths to see what your coverage will be. Also, remember that with Dan's unit you will on have one side coverage (1000' max, 600' more likely for better resolution) and tou will soon see that you MUST be very near the bottom.


Now do this same graph with an 8 degree beam and you'll understand my earlier post on selection of beams (20 vs. .


What if the fish had a bottom feeler that controlled the vertical


>stabilizer mechanically? If it came to large rocks or something it would help direct it over. Mite look bad on the display


You are towing the "fish" at a very low speed ... trollong. I would be surprised if anything would have time to react with outdrops of rocks. You would likely hit it before the fish could react ... if it has the capability to even turn at such slow trolling speeds.


>but maybe it saved the fish. How does the transducer array get a large vertical angle and small horizontal?


You got me ... I'm stuck with an off the shelf 20 degree conical beam (Lowrance PD-W).


Why is the


>transducer array horizontal, would it be better vertical?


I'll leave this one for someone else.


Next week I’m going to talk to a company that makes piezo


>eliments and ask them some of these questions. I think we can make our own array for a lot less.


I would be curious to know what Sture used.


Cable question: how


>do you look at both sides, do you need two circuits i.e. 3 or 4 wires too the fish. I’m looking at a RG-58 A/U twinaxial


>cable 20g 100ohm strand 500 feet for $264. Will that work for both left and right or at all?


This could be done with Dan's fish. However, you might need to hook the other (additional) side into another paper graph. The diameter of the fish would double in size also (since the present design calls for 2" Scehdule 80 PVC) because it can only house one array of transdcuers.


In a recent e-mail exchange with Sture (on electronics cable and towing cable), he mentioned that he uses I use a 8 x 0.5 mm square cable. His electronics mainly located in the towfish and needs at least 7 wires to conrol it from the surface.


Parallel with the cable he has a 10mm rope wich takes the force.


Patrick