I have a Lowrance 15MT. I can not get the unit to display fish arches. Fish, or what appear to be fish, show up as vertical lines. Do I need to adjust my transducer? Please help.

If your transducer is reading the correct depth, then its not the transducer.

Correct me if I am wrong but you will only get arches if the boat is moving other wise they will show as horizontal lines not vertical...?

I sure wish Lowrance would put on seminars up in N. Minnesota..... if any Lowrance people are viewing.

I am getting accurate bottom readings....these arches appear while trolling 3 mph.

I beleive stinkycat is right you get arches when the transducer cone moves over a fish and a wiggly horizontal line when a fish swims through the transducer cone
I may have this wrong too but I believe that is how it works

I went from an Eagle locator to a Humminbird two years ago. Granted these are not the top end, colour units that everyone seems to have but work for me. The Eagle showed arches nearly all the time. I switched to a better more powerful Humminbird and seldom do I see the aches that I was so accustomed to. I talked to Humminbird about this and they said that I would seldom get arches because everything just has to be right like how fast the target passes throught the sonar cone, chart speed and other variables. I sometimes get the lines that you refer to but I mark that up to the fish sitting in the sonar cone and not moving. I find this does not happen that often. Even when anchored the boat is still moving side to side a bit. With practice and catching what I see on the screen I can now identify the marks on the screen as fish.

W5

I also believe, but correct me if I am wrong because I am not sure if this is correct, that if the boat was not moving and a fish is under the transducer and the fish is also not moving..... wouldn't you have a continuous straight line that would go all the way across your screen until the fish or boat moved?

the only way you will get a vertical line is if the boat is not moving and the fish is not moving.

the reason you get a arch is this

the sonar reads the distance away the target (fish) is from the transducer. Thats all it does.

When a fish swims into the cone of sound from the t\d, its at first furthest away from the t\d. so the sonar shows it lower in the water (start of the bottom of the arch). As it swims closer to the boat, the sonar thinks its getting shallower since its getting closer to the t\d and shows it higher in the water until it is as close as its going to get (top part of the arch) then it swims past and away from the t\d, and the sonar now thinks its deeper in the water and displays the downward sloping of the arch until the fish is out odf the cone angle.

it also works this way if the fish is not moving but the boat is passing over it.

when you get a partial arch, the fish is on the edge of the cone and does not pass directky under it

if neither the boat or fish are moving, then all it shows is a vertical line since the fish is keeping the same distance away from the t\d and the sonar is showing it at a constant depth

its all explained on the Lowarnce site on how sonar works

vertical = straight up and down

horizontal = straight left to right

which is it?

Vertical lines sound more like interference, possible from another sounder? Horizontal lines might be fish, or another object, which is not passing through the cone very quickly.

The answers have already been given ... but you could change to the fish symbol, but that has its own problems. I had a lowrance that only showed the bottom (never any fish), it was defective and Lowarnace replaced it for free.

It was hard to figure out.

karpbuster

sorry should have said horizontal

it was early lol

Tim is right

I will try and turn down my chart speed and see if that helps...tahnks for all who replied.

What is your boat speed when you get vertitcal lines?

I rarely see fish arches and I'm comfortable that this is how my electronics should operate. While simulators do a good job showing arches, I think the real world on the lake reality is quite different. If you do a little math, noting the scale you're electronics is set on, to see an arch the size you see on the simulators, either the boat or the fish has to be zooming along. No way to have time to catch such a fish.

That 15-MT is a dual-frequency unit isn't it? Do you have the dual frequency transducer? IIRC, it has a narrow sonar beam (10-12 degrees?) in the 200KHz setting.

My boat has a Lowrance 334C with both a 20 degree (Lowrance) and 12 degree (Airmar) 200 KHz transducer. I see clear fish arches with the 20 degree, but only near-vertical lines for fish with the 12 degree.

The difference may be:
- The 20 degree transducer is adjusted to look straight down at trolling speeds and gives nice, symmetrical arches. When I had it pointed too far forward or sternward, the arches became very lopsided, just lines with a slight hook at the top. The 12 degree transducer mount required me to point the transducer forward and what I see for fish marks looks like the front part of the arch, with no detectable hook at the top.

You may be able to adjust your transducer angle and see fish arches. Playing with transducer angle sure makes a difference in the shape of fish marks I see.