True trolling Depth?

[FT]

Hey Everyone. Does anybody know if there is a formula for figuring out true down rigger depth at the ball? For an example: If you have 135 feet of cable out on a 12 pound ball and your speed is 2.2mph, where is your true depth at? Around 118? I did not know if there was a chart out there or a formula you could plug number in to figure out the answer.

[momay4000]

FT,

I've often thought about this as well, but I typically use my fish finder to look where the ball it located b/c I'm not even sure how accurate the line counter is on my rigger in the first place. However, using the Pythagorean Theorem, you can probably figure it out:

Since the sum of the square of the sides of a right angle triangle equals the square of the hypotenuse, you can probably calculate true depth. a2 +b2 = c2

For example, "side" a=true depth of the ball, "side" b= distance the ball is dragging back from the boat, "side" c= amount of cable out. Since a2+b2=c2, then a = sq. rt. of (c2-b2)

Thus true depth = the square root of [(cable out)2 - (approximate distance back)2]

So, if you have 120' of cable out and it looks to be about 40' back from the boat, the true depth will be the square root of [(120*120)- (40*40)] = about 113' down

- Chris

[ray koziatek]

huh? i ant touching that formula..but 110 down with 120 ft cable out is in the ballpark if you have a down temp then check temp at a standstill,check rigger depth (ball on graph) and you know about where you are .then get up to trolling speed and start letting out cable till you show same temp on down temp ....this will get you in the approx ft per depth zone ..course down or mid currents will come into play so ya gotta learn to take that into account ..ive been 100 ft down with little blowback due to down currents and ive been down 100ft with major blowback.. the downspeed and temps are your best tools with varing conditions (currents) thats why so many people say there down probe is the most important tool for catching fish....but we all have put many fish in the boat before implemting that tool ,so ya ant gotta have one but it will be a nice addition when you use it.

[goin hungry]

I hate math, so I'm going with Ray on this one. It won't show true depth, but if you adjust your fish finder to read the balls, then you can see where they are in relation to the "bottom" - keep in mind that now the FF is shooting at an angle, so it too will read deeper than actual depth. Now, if the finder shows fish at 80 you can move the balls to that depth. It may not be actual depth, but that's where the fish are, so true depth won't matter. Keep in mind that with most of this stuff it's about finding out what works, and then duplicating it. - i.e., the counter on my downrigger may be wrong, but I know I'm getting fish when it says 80ft, so that's what I'm going to keep setting at until the rods stop firing. Of course, none of this will help if you can't get on the fish in the first place, which is what happened to me last weekend, so what do I know....

[Born to Fish]

Cannon snt gives back depth.

I will check actual vs the counter on the DR next trip and see what the difference is.

[FT]

Thanks for all the answers. The problem I am running into is that I have not marked anything on my fish finder for sometime now. I am just fishing tempture and was fishing down this weekend sometimes at 160 and catching fish. This was putting me into fish. I think I need some 220 sandpaper to clean the reading on the boat. Once again thanks for all your help

[on the lam]

Pretty much as Ray said.too many variables to be exact i feel, depth, current, coated/non coated cable 10 # ball or a 20# shark? all different answers. when u have time run your rigger out 100 in 110 and head in until you hit bottom at trolling speed. that will give you a pretty good idea.

[Shade]

Does this help?

Cable Length and distance back from desired Depth and estimated angle

20 degrees 30 degrees 40 degrees

Desired Cable Back Cable Back Cable Back Cable Back

Depth Length Length Length Length

in feet

10 11 4 12 6 13 8 14 10

20 21 7 23 12 26 17 28 20

30 32 11 35 17 39 25 42 30

40 43 15 46 23 52 34 57 40

50 53 16 58 29 65 42 71 50

60 64 22 69 35 78 50 85 60

70 74 25 81 40 91 59 99 70

80 85 29 92 46 104 67 113 80

90 96 33 104 52 117 76 127 90

100 106 36 115 58 131 84 141 100

125 133 45 144 72 163 105 177 125

150 160 55 173 87 198 128 212 150

175 186 64 202 101 228 147 247 175

200 216 73 231 115 261 168 283 200

225 239 82 260 130 294 189 318 225

250 266 91 289 144 326 210 354 250

DEPTH - DISTANCE FROM CABLE TO THE WATER

BACK - THE DISTANCE FROM THE BOAT TO THE BALL

ANGLE - DEGREES FROM DOWNRIGGER TO THE CABLE

Shade

[Shade]

Sorry I tried to put it in content but it will not let me. If anyone wants to see this in scale give me an email address. I tried to post it but it will not post like a picture. If anyone knows how to post an excell sheet forward info to me and I will try again.

What it tells you is if your cable is 30 degrees from the back of you boat you need to have 58' of cable out. So with 58' of cable out your ball is 50' down and 29' from the back of the boat. This is based on 2.5 mph/ 10lb ball and spoon 15' off the ball.

Something I found on the internet and I think it was from the Oak.

Shade

[LongLine]

Shade - Copy/paste the excel file into msPaint. (should be listed under accessories on your computer - actually I use photshop but paint works ok) Crop & save as a j-peg. Upload to photobucket, copy into reply.

Tom B.

(LongLine)

[skipper19]

Just to make things more complicated (sorry), the cable never goes exatly straight to the ball when trolling. The cable curves back with the flow of water resistance against it (and it gets worse with fleas or junk clinging to the cable). The ball is closer to the boat than you think by swinging with gravity and trying to reach a point under the downrigger arm.

[chowder]

Just to make things more complicated (sorry), the cable never goes exatly straight to the ball when trolling. The cable curves back with the flow of water resistance against it (and it gets worse with fleas or junk clinging to the cable). The ball is closer to the boat than you think by swinging with gravity and trying to reach a point under the downrigger arm.

This is a really good point. Under Monday's conditions off Port Bay(N/S troll) it seemed like I had to let out 140' of coated depth raider cable to target Kings at 100' w/ a 13# pancake + probe @ 2.3-2.4 down w/ 40# spoon rod on the rigger. The blowback was extreme enough that I couldn't see the weights on the graph after they were in place.

[jekyll]

It seems a good place and time to mention that the FF shows how far the balls are from the transducer, not how deep they are. Just a reminder.

This all makes my head hurt. Run them out till you plow, catch a laker and take notes. I'm hard on my balls.

[Mickey Finn]

There are lots of variables but one thing I do alot, especially when fishing near bottom is after I've been trolling for a minute of so is to drop the ball to the bottom and see what the counter says. If I was trolling in 130 feet of water, I might hit bottom with 145 or 150 feet of cable. Now I can just lift the ball up say 20 feet if thats where I want to be. The key is to give enough time for blow back to be set. I drop till I hit bottom, lift it one foot, then wait 30 secconds or a minute and then hit bottom again. Now I know where bottom is and can just bring the ball up from there. This doesn't work that well when fishing way above the bottom but works great if you are near bottom. I don't however recommend doing this with your probe rigger. I try to keep that one from hitting bottom.

[Finders Keepers]

I use 15lb sharks with standard non-coated cable (no probe yet) and if trolling at 2.7 on the surface, I lose the sharks at 60 ft with nothing attached to them. I typically never see my rigger weights when trolling deeper than 50 ft, but on other boats I have seen them mark the weights down to 100+ ft. Is this because they have the transducer tipped back instead of level? I have thought about doing that...

[Iceman]

My Lowrance Dual Frequency sonar marks my 20 lb sharks down to 300' with no problem. You need the 50khz frequency wide cone angle to see the weights.

[Finders Keepers]

I have tried using the 50 kHz and I still lose the weights off the chart. Last time out I was running the weights with 85 and 95 ft of cable out with one line attached to each and I couldn't see them on either frequency...

[Iceman]

Is the filtering turned of for the surface & down signal? These need to be set to off or on the lowest setting to get maximum sonar performance. You also need to have the sensitivity at at least 75% of the scale or higher to get a strong enough signal. What sonar unit do you have?

[goin hungry]

Tim - it's probably not the unit, it's the angle that you have the transducer mount set. just keep tipping it back until you can see them, but keep in mind that this will now affect the depth reading, as the beam is now shooting back at an angle rather than straight down (although it will be minimal, especially at shallower depths).

[Finders Keepers]

I don't recall the exact model, but it is a Furuno unit similar to the LS4100 (dual freq, black & white screen). I will have to check the filtering for surface and down signal. I generally set the frequency gain as high as I can without getting a lot of scatter on the screen. The transducer is set so that it is flat with the bottom of the boat, as the instructions suggested. I will check the model and settings tomorrow when I'm out and see if that works.

[Finders Keepers]

My unit is the Furuno LS6100 and the filters were "on", so I turned them off and that helped. However, I still lost the weights below 65 ft. pulling lines. I didn't see any other settings to fiddle with, but we were hooking into fish and I may not have gone through all the screens. I think I may just tilt the transducer a bit. I have a second FF mounted on board that we use for shallow depths in the bay, I can always use that one if I need the true depth at any time. I still find it strange that I can't see the weights though. The only other factors I can think of are 1) I have been going by the SOG on the FF and not the new GPS that I am still getting accustomed to (can't get the SOG to display yet) and setting up (I need a set of maps on a flashcard) so I think I may be trucking along a lot faster than the FF says, or 2) I use 11' rods on the riggers and they are angled fairly high (say 60 or 70 degrees off of horizontal versus tipped down towards the back of the boat like I see on a lot of the charter boats) so when I keep them taught perhaps they are pulling up on the weights and creating more swayback. Once I get the GPS all situated I will be able to check the speed.

[Edd]

In the smallish lakes and reservoirs I fish, from speeds of <1 to 2.5+ I never lose the weights on the screen until I get into cross current. If the current is port to starboard and pretty strong I will lose the starboard weight and the port weight will show on the starboard side. I'm fishing as deep as 130 to maybe 150 for the land-lockers. My Scotty meters seldom are off more than a foot from the sonar. Mind you all, that I am not pulling anything as large as you do out there. I'm using a 10" Sling Blade (at the largest) and rolling 3 inch shad generally. So the gear you pull also has something to do with the location of the weight.

Edd

[mtboxess]

For Christmas ask Santa for a Temp Probe(Raider, Sub Troll, Cannon). Fish the temps!!!! Smartest buy I ever did. The currents in LO are gonna play with your head, man!!!!! For the record, I have the Furuno 585 and depending on the currents I can lose the ball at 60' also.

Dion

[billybono]

you say you havent marked a fish, but dont know where your balls are? if you arnet reading your balls on your graph, i wouldent worry about seeing fish on it........ because you got other problems

temp at the ball is more important than "seeing" fish on your graph anyways

and assuming your graph isnt junk, how is the angle of your transducer..... does it seem to work right in shallow water? skip out at more than a troll??? if your catching fish, are you duplicating any constant???

i need some more information to assess this situation.

but my gut tells me your running some old ass graph

[billybono]

My unit is the Furuno LS6100 and the filters were "on", so I turned them off and that helped. However, I still lost the weights below 65 ft. pulling lines. I didn't see any other settings to fiddle with, but we were hooking into fish and I may not have gone through all the screens. I think I may just tilt the transducer a bit. I have a second FF mounted on board that we use for shallow depths in the bay, I can always use that one if I need the true depth at any time. I still find it strange that I can't see the weights though. The only other factors I can think of are 1) I have been going by the SOG on the FF and not the new GPS that I am still getting accustomed to (can't get the SOG to display yet) and setting up (I need a set of maps on a flashcard) so I think I may be trucking along a lot faster than the FF says, or 2) I use 11' rods on the riggers and they are angled fairly high (say 60 or 70 degrees off of horizontal versus tipped down towards the back of the boat like I see on a lot of the charter boats) so when I keep them taught perhaps they are pulling up on the weights and creating more swayback. Once I get the GPS all situated I will be able to check the speed.

for 800 bucks get a new lowrance hd unit

end the guesswork