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Old 09-07-2016, 09:15 PM   #21
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My understanding is that the so-called structure scan side sounded are only good up to maybe 100' then they lose it. Maybe some who has one can confirm. I tried one once and couldn't get it to work at all so replaced it with a Furuno which worked perfectly. Anyway, if you want depth and contour readings below 100', forget about structure scan.
I have Humminbird Side Imaging or what is generically called side scan on my center console. It can work in >100 ft depths with a big BUT. Boat speed over 6 mph severely degrades performance. Yes you can read depth at higher speeds but the unit is barely functioning as a depthfinder at that point.
Limitations come from a typical trawler in the way of installations. The vast majority of boat installations use a transom mount transducer. Some manufacturers now have through hull bronze transducers (one for each hull side) needed for inboard boats. The first ones were ordinary plastic! The side scan transom mount transducer must be mounted absolutely level. If its not mounted at the bottom (or very close) of the Vee, when on plane, there becomes an air gap between the TD and the side opposite the TD and that side will read poorly. Rudders, Trim tabs, and keels also interfere with the side imaging.
There is a significant learning curve to interpret the SS display.
In the 2 full seasons of owning Irish Lady, not once have I thought that it would have better to have my HB SI on board instead of simply reading Active Captain anchorage reports. Yes it will show the difference between smooth sand and jetty rocks on the bottom, but not discarded tow cables, ropes, or flat snags. You would have a hard time finding your lost anchor unless it was huge.
In summary, unless you plan to slowly search for underwater structure for fishing or diving, side scan is 99% waste of time and money for a trawler yacht.
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Old 09-07-2016, 09:30 PM   #22
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Another vote for graphic depth display vs digital.
If you are installing Chart Plotter / GPS you won't need a separate fish finder just a compatible transducer & processor box that provides graphical depth...
You will have to decide if speed (in add'n to GPS) & water temp are important as they are different Xducer options

You can then customize screen displays w/ other info or full depth display to use when approaching anchorages etc.
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Old 09-08-2016, 07:43 AM   #23
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You will have to decide if speed (in add'n to GPS) & water temp are important as they are different Xducer options.
Bacchus makes several good points. As for speed, I've never used a paddlewheel speed sensor that worked for more than a week or two before getting fouled. And even before they're fouled, I haven't found them terribly accurate.

Much as I'd like to know STW, and compare that to SOG to derive the set and drift of the current, I've never been able to get to that level of accuracy.

For me, the speed sensor isn't worth paying extra for.
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Old 09-08-2016, 09:27 AM   #24
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As for speed, I've never used a paddlewheel speed sensor that worked for more than a week or two before getting fouled. And even before they're fouled, I haven't found them terribly accurate.

For me, the speed sensor isn't worth paying extra for.
I've had a paddle wheel that worked OK in fresh water - but did jam occasionally - a quick reverse cleared it most times
Calibration was OK at low OR high speed but would not be accurate for both

Bottom line I agree and went w/ depth and Temp but skipped the speed option when replacing mine a year ago
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Old 09-08-2016, 09:33 AM   #25
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Just numbers wont work for me. In shallow or stirred up water the digital only displays may quit while the scanning display usually shows some info on bottom trend even if the return is not strong enough to display numbers.
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Old 09-08-2016, 10:49 AM   #26
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I suppose the fact that I have not fished since I was 16 years old should be mentioned. I do sometimes think that I might like to take up fishing but so far I haven't been interested enough to try.
I know exactly what you are wrestling with. I don't fish as much as I used to but searching for wrecks is a neat past time! Raymarine's Chirp (Down vision Sonar) will do both. Mine is said to work as deep as 600 ft but I find that 300 feet is more accurate.

The first photo (Taken from the Web) shows good definition at 150 feet.
The second photo (also from the Web) at about 30 ft.
IMO, fishing at 150 or less is where the Chirp performs the best. (In fact i would say it's incredible!)
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Old 09-09-2016, 04:39 AM   #27
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I suppose the fact that I have not fished since I was 16 years old should be mentioned. I do sometimes think that I might like to take up fishing but so far I haven't been interested enough to try.
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Originally Posted by Codger2 View Post
I know exactly what you are wrestling with. I don't fish as much as I used to but searching for wrecks is a neat past time! Raymarine's Chirp (Down vision Sonar) will do both. Mine is said to work as deep as 600 ft but I find that 300 feet is more accurate.

The first photo (Taken from the Web) shows good definition at 150 feet.
The second photo (also from the Web) at about 30 ft.
IMO, fishing at 150 or less is where the Chirp performs the best. (In fact i would say it's incredible!)
So,
I can see that there is amazing detail in these pictures but as I look, I can't figure out what it is I'm looking at in that 150' shot.
It kind of appears to look like a sunken trawler or something...I've just been looking at videos on YouTube that explain the use of basic fish finders. I have much to learn apparently.

I am leaning toward the CHIRP system. Mostly due to the fact that it appears to be so much better at showing detail and now I'm simply curious about what's down there!

Thanks for the pictures,
Bruce
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Old 09-09-2016, 07:51 AM   #28
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[QUOTE=Bruce B;477927]
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I can see that there is amazing detail in these pictures but as I look, I can't figure out what it is I'm looking at in that 150' shot.
It kind of appears to look like a sunken trawler or something...

Codger, looks to me like the 49m pic was taken by a side-scanning or forward-scanning unit? I don't know if the down-vision units can create what looks like a lateral view?

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Old 09-09-2016, 10:19 AM   #29
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[QUOTE=ranger42c;477966]
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Codger, looks to me like the 49m pic was taken by a side-scanning or forward-scanning unit? I don't know if the down-vision units can create what looks like a lateral view?
That's a damn good question! I hadn't thought of that! The other picture, though, is typically what I'm seeing. I plan to cruise over some wreck symbols on my plotter and see what i can pick up.
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Old 09-09-2016, 12:38 PM   #30
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Part of my work at the salt mine involves underwater search and recovery, usually stuff people try and dispose of, but occasionally people themselves. We use a high end sidescan sonar that cost nearly as much as my trawler. I think part of the issue is that the manufacturers of consumer equipment publish demos that are hand pick screen frames that are unrealistic in normal operation.

There's an art to sonar interpretation as opposed to just "sonar viewing." If you are expecting regular photos of the sea floor with consumer sidescan, you are going to be disappointed. I put the Garmin sidescan transducers in the trawler, but I've only been on one trip since (gotta pay the bills.). I've included a pair of screen shots from that trip.

I was pleasantly surprised at the performance of the Garmin sidescan. Given the limitations from purely a physics standpoint, they do well for what they are.

If you look close you can see the halocline in both standard and structure view.
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This shot is when I ran over a raised rock ridge. A decent return about 300' out from the boat, considering the transducers are at the surface and not a towed fish.
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If I ever manage to get two days off in a row I'm planning on heading out to the islands to play with my new toy. Lobster season is rapidly approaching...
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Old 09-10-2016, 05:38 PM   #31
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I have a Hummingbird plotter/fishfinder at the low end for price. I have it at the upper helm and a second mount on the dinghy. I find the ff part very useful on the dinghy, but I rarely (can't think when was the last time) use it on the big boat. The plotter display shows the depth at all times and the screen is small, so taking up some of the screen with ff display is not something I would do unless I thought it would be useful.
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