side imaging first impressions

I cashed in some WAF points and got the Humminbird low-end Side Imaging 792c2. The TD has to have a clear view out to the side, so for starters I just strapped it to the bottom of my kayak with
fastex.

Here's a tree.


Here's a mid-water bait ball, mostly to the left of the kayak. That might be a single fish and its shadow, at the far left (straight down from the 49).


Having the TD on the outside of the boat is a royal pain, plus it seems to cut my cruising speed by 1-2mph. I fish from a 21"-wide fiberglass SOT, so I've been experimenting with an in-hull mounting, by installing a bulkhead area in the bow that I can fill with water and just lay the TD inside. With my 2-3" of draft, I can shoot thru the water->fiberglass->water and get a decent image.

Here's the same tree (unfortunately not quite the same settings as above) with in-hull.


I think the in-hull reduces the sensitivity of the SI somewhat, but during my tests I was continuously bailing water back into my duct-tapped (and leaking) bulkhead, so I wasn't very methodical in comparison testing. Next time I'll use silicone seal.

It drained my 2.5AH NiMH in a bit over 2.5 hours. In the few hours I've had it out I've seen plenty of cool structure, and bait balls, but fish looks to be hard. The wake/bubble trail of a PB lasts for a long time on the SI. The GPS reportedly is annonying slow compared to Garmin, but as this is my first sonar with GPS, it seems adequate. I got it with the built-in Navionics 2006-era, but alas this can't be field-updated with the latest maps; if you buy the latest SD chip, you can install it in the single slot, but then you can't save images or routes. The higher-end 997 and 1197 have two slots, and also use 800KHz instead of 450KHz for the SI for increased detail.


mikechin
(who doesn't have time to fish anymore, and now is broke too)

thanks for the report on the side imaging.

I was wondering how well it would work on a yak, but at $1k for a unit, it's out of my reach at this time. One would have to win a couple MBF or yak tourneys to justify the cost.

Let us know if it is really worth the price.

Wow Mike! That is pretty dang cool. Those images are impressively clear.
I've got an additional side-scan TD that attaches to a trolling motor, and have been trying to figure out how to best mount it. I devised an external mount off the side of the yak with just metal braces and some plywood. But the drag is annoying. Maybe if you could figure a way to hang it off the back it would produce less drag? I don't know---just thinking/typing out loud. Sure, it would still have some drag, but probably not as much as a side-mount.
For internal mounting, what about gluing a small tupperware box to the side of the hull (inside), then use a variation of the pool-noodle technique, and fill the tipperware w/water each trip..? Again, just thinking out loud.

   

For in-hull mounting, I think you need the top of the TD to be below the waterline, and no air gaps between the sides of the TD and where your "acoustic couplant" (water, glycerin, k-y) contacts the inside of the hull.

I think there is a big learning curve for the SI, I expect a lot of teeth gnashing on my part as I get to know it. One thing on the 797, the relatively small screen makes it really difficult in bright sunshine or gnarly conditions to see the subtle shadows on the SI. Sometimes I don't spot stuff until I get the images home and am looking at them on the PC.

I seriously doubt it's worth the price in terms of tourney's won or fish brought home. For me it was the idea that I could finally see (imperfectly) underwater while I'm paddling.

mike

For in-hull mounting, I think you need the top of the TD to be below the waterline, and no air gaps between the sides of the TD and where your "acoustic couplant" (water, glycerin, k-y) contacts the inside of the hull.

I had one of those atSCWA and Humminbird Tech said it would not work (at least well) as a thru hull as the beams propagate at very shallow angles and it needs to be in the water to take full advantage of its mojo.

I was interested in your reports regarding the 792c2 SI.  I have had it for some time but really don't use the SI much because I've been ocean fishing most of the time.  I thought it might also help me spot baitballs in the ocean, that I might otherwise pass by since it is supposed to scan 150 feet to either side. But with no salmon season I really haven't tried to use it for this.

When I got it, I really didn't want to have the drag and cumbersomeness of having an external mount so I mounted it inside my Tarpon in a manner that insured the side scanners also had an unobstructed view through the sides of the hull.  I know that the manual says it can't be used through the hull, but I figured they were thinking about a regular boat hull where it would be more dense or have air gaps along the side of the transducer. I couldn't see any clear difference between the view inside and outside the hull in my rudimentary testing, but I really didn't test this in real world conditions.  So I would be very interested in knowing if you find that the resolution and detail is much less when you try to shoot through the hull. If so I may have to go that route.

I know you can buy a "through hull" transducer for the unit but I think the dimensions are significantly larger than the P15 hollowed out area will accomodate.

When I changed to a P15 I thought about altering the transducer, using carbon fiber reinforcement to allow it to be mounted in the P15 transducer hollow by the back scupper.  But the size of the standard transducer would just barely fit and it would require fabricating some sort of stem to hold it into the scupper hole since the normal transducer support is way off center. 

Here's some pics of my current through hull set up for my P15.  The front and back ends are cut from closed cell foam so they can flex with the hull.  The top is acrylic.  The little box is just needed to accomodate the mounts on the tranducer.  I could have just had a flat top if I was willing to cut off the mounts but thought I better keep them.  I have a small plug to hold in and release the water.

Keep me posted on how your experience is with the  external vs. through hull applications.

Doug

Hey Doug,

I saw from the downrigger post that you also have a 797 SI. What are using to power it, and where did you mount the transducer?

I use 2x10 NiMH AA's (diode-or'd), lasts a day if I'm lucky.

I have my transducer in the bow between two bulkheads that I fill with water. I do see fish on the SI, but not a lot and not easily. Structure is great, tho.

mikechin

Hi Mike,

I actually had posted some questions on one of your threads awhile back because I saw that you were the only other yakker that I knew had a 797.  I didn't see any response so maybe you didn't see my post.

I had compared the SI image with a thru hull and outside the hull positioning and thought they looked comparable so I decided for an thru hull mounting to save on the hassle and drag of an outside mounting.  But I have never thought my SI images were very detailed.  So when you posted your results, it got me wondering whether I would get better detail if I put the transducer outside.  As it is, I really don't use the SI and feel it's kind of a waste because the 797 definitely is a battery hog.  I have to use a PowerSonic 1290 F2, 9 Ah battery to get about 7-9 hours continuous use (more if I turn down the brightness of the LCD).  I actually got an additional battery slab, PS-1220 with 2.5 Ah, that I can add to the 1290, but that was because I was running out of gas with the 1290.  Turns out that my old 1290 was running out of steam so since I bought a new 1290 I don't think I'd really need the add on 1220 for the usual 7-8 hour paddles I do.

With my downrigger, I'd need additional power and I don't want to add more weight so I'm considering a lithium iron phospate battery.  Very pricey, but the only real way to get an advantage of significantly more Ah with less weight.  This is the same technology that is being developed for the electric cars of the future. The Lithium chem reaction also avoids the Peukert's effect which makes a lead acid battery's capacity decrease with greater power draw.  So a Lithium battery of the same Ah rating actually gives considerably more power than a lead acid battery of the same capacity rating. A 20 Ah lithium iron phosphate battery weighs around 6.5 lbs.  Lithium iron phosphate has less capacity/weight than lithium manganese or cobalt batteries, but is much safer and won't burn up or explode (not a nice thought if you have it inside your kayak's hull).  Plus they can be charged up to 2000 times.  I stuff the batteries in the dry box you can get from Hook 1.

I'm really interested in finding out if you are getting more useful results with your SI feature and whether you have determined if shooting through the hull significantly degrades the details on the SI.

Doug

Hi Doug,

Sorry I didn't see the Nov posting earlier, your in-hull mount is similar to mine (except way more nice). I've experimented with different heights of water above the top of the TD (the puck part, not the mount), I think I get better SI results with at least 1" over it. Too little and it starts to fuzz. Also, I think I'm getting better SI by having the TD clamped to one of the closed foam bulkheads. Before I had it duct-taped, and could slide around a bit, and I think I could see paddling effects.

I haven't been totally methodical about comparing inside versus shoot-thru, testing in Del Valle and once in Disco Bay, but the drag and hassle factor of having it outside outweighs any image improvement (which honestly I don't see)

Most of my fish spotting on SI has been in the water column area (20' or more depth). Stripers (or carp maybe) leave high-contrast marks; trout are fainter, maybe also because they don't school as tight. I've seen stuff on the SI that I never picked up on the 2D; embarrassingly, the converse has also been true. I've also caught fish that didn't show up on either, and couldn't buy a bite when surrounded on both.

I hope to get more time on it in the Bay, looking for fish in shallow water, but I think it's more difficult to pick them out against the bottom.

In whitecaps, the water column area gets messed up from wave action. The bottom area is still great of seeing structure.

Seeing SI fish at >100' + is really problematic given the limited horizontal pixels; a big fish is only going to be 2-3 pixels. I did a "find the sunken sailboat" test in the North Sailing Basin in Berkeley; even with only shooting left or right settings it was tough with the 200-300' settings to see enough pixels to make sense of something the size of a car.

I haven't had it in the ocean, but I would think it would be terrific for seeing of bait schools. I have used it a lot to keep track of schooling fish ("aha, they're mainly off to the left now").

For anyone else considering these, I recommend mounting the TD in the bow; the SI is sensitive to water turbulence, and you'll be looking at water-column clouds from your paddling if you stern mount it.

mikechin

Mike,

What's your thinking on why the SI works better with water on top of the transducer?  I made my tank just deep enough to cover the transducer completely because I figured the SI beams would be aimed laterally and downward.  But I didn't think I'd need water above the top of the transducer.

What's your thinking on why the SI works better with water on top of the transducer?  I

Hi Doug,

The top of my bulkhead setup is open, so I'm guessing the water sloshes around as I paddle. The effect I saw wasn't dramatic, but I remember it being correlated with yak motion. I stopped, popped the hatch to see that the water level was barely covering the top (I think I had intentionally put in less water before starting to see what I could get away with), and then filled it to be about 1" above.

Maybe your setup will be less affected since it's sealed? It might also be a function of how deep below the waterline the TD actually sits (inside the hull).

I think I read somewhere that Humminbird recommends setting the TD as deep as possible for best SI results.

It would also be nice to know how long the puddle needs to be; I made mine oversize so that I have an inch of water before and and inch after. I guess I could stick in more foam to see if there's any degradation. But I'm pretty sure I'm carrying more water than in necessary.

I read someguy is using Lithium-ions from portable tools (Sony, DeWalt) for FFinders. Are those prone to fire?

mikechin

Are those prone to fire?

I don't know about the Sony batteries.  They may still be lithium ion batteries--usually either lithium cobalt or manganese.  These chemistries offer the highest ratio of capacity to weight and therefore are attractive in implementations where light weight is given a high priority such as laptops.  But from what I understand, the lithium is more unstable in these forms and is immersed in a fluid that can catch on fire, even explode.  That's why I have shied away from trying these batteries in the past: Had visions of seeing the bow of my kayak glowing brightly just before the whole front end melted and I went under.

Lithium iron phosphate batteries are the newest technology.  The use of nanotechnology in the carbon cathode has greatly enhanced its efficiency and it is much more stable and safe and can be charged over 2000 times.  The DeWalt 36 volt lithium batteries are made by A123 and I think this company is also under contract to produce the batteries for the GM Volt.  Since the company doesn't sell their batteries to end users, techies who use the cells to make model airplane or electric bike battery packs, buy them in bulk on Ebay, disassemble them and repackage them in suitable packs. I have considered using the Makita Lithium 3 Ah packs because they are 18 volt and my FF/GPS can use 12-20 volts.  But they are only 3Ah and I don't know if you can really just put them in parallel because lithium batteries are tricky in the way they work together.  Each cell needs to be charged and balanced individually under the control of specially designed circuit boards so connecting two packs may mess things up.

I will probably get the LiFePO4 made by Thunder Sky.  Buying four 3.3 volt, 20 Ah batteries and putting them in series you can get a near 12 volt pack with 20 Ah that weighs about 6.5 lbs.  That's the best solution I've seen so far. Still quite expensive.  Once electric vehicles become a reality, these batteries should become much more affordable.

Maybe someday we can hook up so I can see if your SI results are better than what I'm getting.

Doug

Hey Doug,

Send me a PM if you want to do some SI comparison testing, great idea.

Altho I haven't measured current draw vs. supply voltage yet, if the 797 wide input range is just linearly regulated, then a 90+% efficient buck converter would gain 10-20% runtime over a raw battery output of 12V or more if the output were set to 10V.

mike