transducers for side and down imaging?

[oct.fisherman]

I'm in the market for a new humminbird depth finder. Probably going to buy one of the 800 series units. Just wondering is there any drawbacks using the trolling motor transducer for the side and down imaging units. I'll be fishing the flowage in late oct and early November, I'm sure the bow of my boat is going to be beaten by the waves as I slip down the channels.

Thank you

[BlueRanger]

I think a downimaging unit would be great on a trolling motor, but the main advantage would be for vertical fishing and being able to position more accurately over cribs, rock bars, weed edges, etc. because the edges would be defined more accurately than on a 2D unit (see attached sketch).

There are definitely some constraints to be aware of if you're thinking about mounting a sideimaging unit up front. For a good sideimaging picture, you need to be traveling in a fairly straight line at a steady speed - the screen is just a blur if you're standing still or turning. You're shooting a pair of narrow beams straight out to the sides, and when you turn you're essentially increasing the speed of the beam traveling over the bottom at an uneven rate - faster the farther it gets from the boat, and worse the faster/tighter the turn. An odd analogy, but it's kind of like making a snow angel - your fingertips cover a lot more distance than your upper arms in the same amount of time, and that's what's happening with the sideimaging beams when the transducer turns. It creates a motion blur that's worst at the edges of the screen. Again, see the attached sketch - I'll try to remember to make some demo screen shots next time I'm out and post them so you can see what it actually looks like on screen. Anyway, since you tend to be turning the boat a lot when you're running the trolling motor, it really limits the usefulness of having a sideimaging unit up front - particularly if the sideimaging transducer is mounted on the motor, because the motor turns a lot more than the boat itself - you might turn the motor 90 degrees to turn the boat 10 degrees.

Sideimaging works best as a surveying tool to help you scan an area using straight-line passes and either mentally visualize the structure to help you understand what you're casting to, or mark specific spots on GPS which you can then use for navigation or as virtual marker buoys for vertical fishing, and in general it's more efficient to do that from the console and not waste your battery doing it with the TM. You'll usually switch to a 2D view (conventional or downimaging) when you're actually fishing anyway. And putting a big, $234 transducer on the bottom of your trolling motor in the TFF is a risky idea. The catch-22 is that sometimes you'd really like to have those GPS points on your bow unit for fine positioning with the TM.

One idea would be to mount the main sideimaging transducer at the stern and a 2D puck on the trolling motor. With the accessory Y-cable, the unit will take depth and 2D data from the puck, and side- and down-imaging from the main transducer without the need for any manual switching. But then any GPS waypoints created in sideimaging view will be off by the length of the boat, which is fine as long as you're aware of that limitation. Still, I think that once you saw the things sideimaging does best, you'd find yourself wishing it was on the console so you could use it to cover larger areas using your big motor, unless of course you can afford to buy two and network them, eliminating most of the compromises...

For more information, Yahoo! has a great Humminbird users group with a discussion board, mounting photos and lots of screenshots. A couple factory guys chime in regularly to answer questions: http://groups.yahoo.com/group/sideimaging/

[oct.fisherman]

I did decide to go with a switch. And a hardware item for the unit similar to a flat screen tv wall mount with swivil arm that's going to attach to the consloe. Then turn the switch to the bow transduser turn the unit around on the mount so I can see it when running the trolling motor. I hope it works and comes together as planned.

Thank you for your input. I was hoping for your response.

David

[BlueRanger]

In that setup, the transducer switch is the right way to go.

I have mine on a RAM mount - one thing to pay attention to when mounting it is to leave enough slack in the cables so you can spin it around easily without having the cables bind. I've tried looking at the sideimaging from the bow on occasion, but everything is essentially upside-down and the sides are reversed, so it gets disorienting. It would actually look more accurate to just flip it upside-down - I wish the software had a "reverse view" setting. I have an old Eagle 2D on the trolling motor and I think I'll eventually switch to a Humminbird 700-series 2D or downimaging unit and network them so I can mark my GPS waypoints for cribs, rock piles, etc. from the console then share them to the bow unit. The locations will be off by a few feet, but should put me close enough to find them with the sonar. Was just checking out the XM Weather module - would be pretty cool to see approaching storms on the fishfinder!

[AndrewR]

That's really good info, Bill. Helps me a lot too because I'm in the "same boat" as David.

I'm dumping my Garmins for Humminbirds next year. Gonna buy over the winter and then install before it's showtime again in spring. Looking at a 597Ci HD or 788ci HD SI to mount to the console (I like their price and GPS feature - but unsure whether to go down image or side image).... But it's a toss-up between either. And then perhaps either the 570 DI or 586c HD to have on the casting deck and connected to the PowerDrive. For a small boat like mine these seem to be logical choices. Really helps to have a trolling motor with built-in universal sonar as you have no need to worry about crashing the transducer into rocks or wood. Although its signal strength is questionable at times but I'd like to blame that on my Garmin Fishfinder 240's because they aren't powerful to begin with.

A lot of these units either come in single beam or dual beam. What is the difference?

[BlueRanger]

Dual beam just means you can choose between two transducers in a single housing. In the case of the 2D and SI units, you get a 200kHz element with a 20 degree cone angle that's standard with the single beam units, and an additional 83kHz element with a 60 degree cone angle. In theory, a lower frequency has better penetration and a higher frequency has better definition, but instead they've used the enhanced penetration of the 83kHz beam to allow it to be spread over a much wider area, so its use is limited to depths of about 60 feet, which covers most of our fishing. As an aside, there isn't really a perfectly sharp cone being projected from the transducer - the sound radiates in all directions, just like a loudspeaker - it's just much louder when you're standing right in front of it, and diminishes the further you move off-axis. Humminbird specifies their cone angles at the -10dB point, which means that with the 83kHz beam, once you get to 30 degrees off-axis in any direction (60 degrees total spread) you have 1/10 the power that's going straight down. Lowrance claims up to 120 degree coverage with their units, but doesn't specify the relative dB at that point so there's no way of knowing whether it's really projecting a wider beam.

Anyway, you can choose either beam, view both in a split view or both in a combined view. The 200kHz beam gives you better definition of structure under the boat, while the 83kHz beam picks up more fish that are off to the side. When you're in combined view with fish ID turned on, the fish symbols appear in two colors so you know whether they're in the narrow beam and directly under the boat or the wide beam and further to the sides. Sensitivity is controlled at two levels - the first push of the Menu button brings up the XPress menu - the most commonly used controls specific to the view you're using, and adjusting sensitivity there affects both beams. A second push brings up the main menus, and the sonar tab has an 83kHz sensitivity control that basically controls the balance relative to the 200kHz beam. Boosting it shows more small targets off to the sides, but at the expense of additional screen clutter. Cut it a little and it will only pick up the larger targets off to the sides.

On the new DI models, the approach is different - you get 200kHz/25 degree and 455 kHz/16 degree beams, with the 455kHz providing very high target definition, probably better for separating fish from the bottom. I think the assumption is that you'll use the DI view for wide coverage fish-finding. Personally, I don't find myself using downimaging much, and I think you'd find a lot of good uses for the sideimaging, especially since you fish a lot of different water - it's a great exploring tool. For example, in places like the river, you'd be able to pick up submerged current breaks, washout holes behind boulders, etc. and you'd probably be able to see if there were fish holding in those spots.

[Ruff Fish]

Blue, once again, has great advice for you guys. I have a Humminbird w/side imaging on my console. I use it to map out areas of the TFF, then get up front and use my smaller Humminbird w/the trolling motor's built-in universal. As Blue said, there are times that I wish that I had the waypoints on my littler unit, and maybe the down imaging, too...but other than that, I am supremely happy with what I've got. With the side imaging, you'd be amazed how far off some of the maps of the TFF are for showing the original river channel. Seeing a bunch of stumps off to the side, that aren't on the map...pretty cool, too. I often times wish that my console swiveled, but I think I get more disoriented than most other guys when the stuff is upside down and/or backwards.

[wally1]

Have either of you guys had issues with your units losing your depth reading when trimmed out? I was with a guy the other day and he was giving me a demo on his Bird 997 SI, and he said once he gets above 15 mph, he loses his depth reading. Other than that, I was pretty impressed by what it would do.

[Ruff Fish]

Have either of you guys had issues with your units losing your depth reading when trimmed out? I was with a guy the other day and he was giving me a demo on his Bird 997 SI, and he said once he gets above 15 mph, he loses his depth reading. Other than that, I was pretty impressed by what it would do.

I thought that I had heard that is common at higher speeds. I think I may have had mine adjusted perfectly at one time (transducer angle and such.) I think I had to be over 24mph to lose it, and I only lost it sometimes. I had the same problem with my old Eagle at even lower speeds than that. I bashed my transducer recently at a boat landing (don't ask). I have the one hanging on the outside of the transom. I didn't seem to lose the depth very often before, but I am losing it more often now. I'm working on seeing if I can't get it back to what I had.

[BlueRanger]

My main SI transducer is mounted well above the hull bottom such that it's completely out of the water at planing speed, so it loses its picture at about 6 mph. That's a pretty common approach, especially on fiberglass hulls, to protect the expensive transducer from impact. I have a shoot-through-hull 2D transducer for high speed running, and it works fine at any speed I would run in water where I feel the need to pay attention to it.

[oct.fisherman]

I going to install my Transducer this weekend. DI SI 898ci . Any advice? I have a transducer installed on the back now for a small Garmin. Does it matter what side of the back the transducer is on? I assume the other trans wont create problems.

[BlueRanger]

The Garmin shouldn't interfere with the sideimaging but if it's using 83kHz or 200kHz you might have interference with the 2D that affects both units. I know my 997 doesn't turn any of the sonar beams off when they're not being displayed on screen, because when I switch views (say going back and forth from a split-screen with GPS/map and 2D to full-screen sideimaging) the sonar recording on both views is uninterrupted.

The manual gives pretty detailed transducer mounting guidelines, but again, these are the kind of questions where I would definitely look to the Yahoo! sideimaging group. There are tons of pictures of how other people have mounted theirs, and if you post a question you can probably get advice from people who have an identical or very similar boat.