New HDS/SS questions

[WaveWacker]

Well...after running various hds units with SS I have some questions that came up that I'm hoping someone can clear up here. So let's first set up a scenario.

20 ft of water running the SS screen Left and right out to 50ft.

The question lies in is one seeing 20' straight down and then 30' of bottom off to the side of the boat either way? OR (as it was explained to me) is the SS beam hitting the bottom 20' off to the side of the boat and you're seeing what's on the bottom 30' out from there?

If it is the later...what's picking up the 20' L/R of the boat? DS and/or broadband sounder? Only thing that seems weird is when I'm marking some fish on the DS/broadband sounder, they seem to show up just above bottom on my SS. that would have me believing that it's shooting straight down then out. Also it seems very coincidental that the SS beam would be hitting bottom out to the side of the boat at the same depth of water that one is in but it makes no sense to have the 10, 20, 30, etc. marks on the bottom of the screen if it isn't actually that distance out to the side of the boat. Hopefully this makes sense and thanks for any clarification.

[TruthWalleyes]

I would bet that it explains how the sonar works in the manual. I have h-bird Si and i don't think the side scan operates any differently.

[PerchJerker]

Side Scan and Side Imaging shoot out to the sides and down to the bottom at an angle --- because they shoot out to the sides at an angle, instead of straight down, they don't really see right below the boat. And what they do see close to the boat is the very edge of the transducer cone, the weakest part of the cone / signal.

For down scan, Lowrance has a seperate tranducer element that shoots straight down. For down imaging on their SI units, HB uses software to draw an interpretation of the weak edges of the left and right cones where they are closest to the boat --- for down imaging on their DI units HB has a transducer element that shoots straight down.

To answer the question in the OPs scenario, side scan is looking off to the side and down, but it doesn't actually hit the bottom until it is 20 feet away from the boat. It then shows you whats on the bottom from 20 to 50 feet away from the boat. And, what many people don't understand, it also shows you everything above the bottom ---- that's how you can mark fish in the "dead zone" below the boat with your side scan ---- they are fish that are up off the bottom so the side scan transducer cone hits them and marks them before it hits and marks bottom (ie. it shows you stuff closer to the boat than where it starts showing the bottom).

Hope that helps ---- it's hard to explain without having screen shots to look at.

[WaveWacker]

I also proposed this confustion to "the Doc" himself and his reply was completely different. He states that one has to take into consideration water depth first and then figure out how far you are seeing. Even though a possible weaker signal, straight down (or slightly off to the side) is the closest distance to the bottom and hence should show up first. This coorresponds to the DS depth as well. In other words...I did find it funny that with all the time on the water running SS that in 99.9%+ of the time the distance to the side of the boat that the SS beam was "hitting" bottom was EXACTLY the same as the depth.

????

[Nick Kuhn]

It becomes a distance problem. If you are in 20 feet of water and have it set to 75 feet left and right, the actual edge of the screen is 72.285 feet left and right. So any time you left/right setting is at least triple the depth, the edge of the screen is pretty close to correct. However, something in the middle of the left screen will not be 37.5 feet left, but rather 31.75 feet left. So yes, it's a few feet off, but not anymore so than your GPS would be if you tried to renavigate to that spot. Just use your judgement and know that objects to the side of the boat are slightly closer than they appear.

[PerchJerker]

I also proposed this confustion to "the Doc" himself and his reply was completely different.

Are you sure you didn't misunderstand him? In his DVD he explains it pretty much like I tried to explain it above.

I would have to look back at the specs, which I don't have here, but I believe for 800 khz the beam shoots down at a 45 degree angle --- that's why water depth and bottom distance would correspond. 455 khz shoots out at a much different angle, I don't recall exactly what it is (455 khz works better is water that is deeper than I usually fish, I usually run mine on 800 khz).

[WaveWacker]

Directly from Doc given the exact same example:

The side scan "sees" directly below the boat so the 20 ft to the side is actually the bottom below the boat.

This corresponds to his anology at the beginning of the SS video when he had a print out of a SS screen. Fold the paper in 1/2 along the "burst" line. Then again back on or opposite on the bottom. A 45 degree angle cone would still "see" straight down. Also, let's assume we are on a consistent depth large flat. A straight line at a 45 degree angle will be longer then the line straight down.

When you think of it...the only way one would read the same depth on the SS depth cursors compared to the Down scan/sonar would be if the bottom got shallow enough at said angle and that distance matched up with the actual depth.

[PerchJerker]

Some of what you're saying is right, but some of what you're saying does not make sense. It's hard to explain without diagrams.

side scan "sees" directly below the boat so the 20 ft to the side is actually the bottom below the boat.

[WaveWacker]

Geez...now I really have my head turning. I'm not saying your wrong at all PerchJerker but there are just some certain thoughts that have me thinking both ways.

I will agree that the side scan may not see "directly" down. However, I still am not convinced that in 20' of water the bottom that is being displayed is 20' to the side of the boat either.

I was under the belief that all sonar works by sending/pinging "beams" of sonar out in a straight line which when/if they hit something, travel straight back and the strength of tha return extrapolated out to provide us with the visual translation.

I'm probably totally wrong with this and maybe there is something in the HDS unit itself that makes a change but in 20' of water (on regular sonar and downscan) the bottom shows up on SS around 20'. In other words a "beam" of sonar is making contact with bottom ~20' away from the transducer. Well on a flat bottom, the closest distance to ~ 20' would be closer to the boat than 20' to the side. A2 + B2 = C2 proves this and here was where my straight line quoting came into play above. A straight line drawn from a transducer over 20' of water out to a point 20' to the side of the boat yields a length of ~28.3'. This distance is what would be "reported" back to the transducer as the depth.

Like I said, maybe there is something in the untit itself that calibrates or adjusts for this???

I guess it's time to jump in the boat and drive around spending some more time to figure out how to personalize my setting for me.