Topic: 1198 settings for viewing bottom of seabed

[joeskippy]

Hi, I have an 1198 and use it for prawning (shrimping to some of you. ) I live in Australia and during summer we cast net for prawns in typically 4-7 metres of water (13-23 feet) I have my unit set to bottom lock at 15 feet , as the prawns are on the bottom of the seabed.
 I'm wondering whether I should have it set on 200khz or higher to get clearer readings? also, are there other settings that might improve my readings. The prawns are about 5-7 inches long and only seem to be visible in reasonable congregations. Cheers.

[sfw1960]

I would use side & down imaging in 800 KHz and run the sensitivity @ 12 to see what that does for you.

[Humminbird_Greg]

Keep in mind that prawns do not have any skeletal structure and not much (if any) air bladder which will make them hard to see individually with sonar.  Higher frequencies and high sensitivity settings will help but will also clutter the display.  I would try what The 800KhZ Si sonar as Robert (sfw1960) said but would also try the SwitchFire menu in the Max Mode setting for the 2D sonar and run 200kHz only.

PS: Send a boat load of those prawns over here.  We got these small little things called shrimp and I would love to sink my teeth into something a little larger!

[sfw1960]

Funny stuff Greg!
FWIW those big'Nz chew like an old Goodyear.... 
The 200 KHz Max Mode is a great idea - but I can see clouds of Daphnia when chasing bluegill on the SI/DI so I figure it'll work on the Prawns.... sometimes you just have to make a little guess work into fact. LOL!
I may not always see the bluegills, but I can taste the results!!!!!

[Humminbird_Greg]

Those are Water Fleas Robert?  I’m guessing that these are in great concentrations as they look it from the pics you posted.

FWIW: I’ve had Tiger Prawns before and I thought they were quite good (and huge!).

[sfw1960]

I  think so Greg - that was an inland body of water & the bluegills digest them rather quickly so it's hard to tell what kind of critters they are, the larger plankton, zoo-plankton type bugs...
Daphnia is what I was suspect of, so quite possible.
I think they are between a 1/16 and 1/8 long guessing....
I had one user INSIST it was  a boat wake's turbulence, yeah 30 feet down...BIG PROP!!! LOL!




BTW Big farm raised Tiger's may be a whole other ball game - but I can "suffer" with  some 20/30's OK....   

[joeskippy]

Thanks for the help so far, This is about the size of them. You wouls think they would be easy to spot.,

[sfw1960]

HOLY big buggers is RIGHT!!!


MMMMMMmmmmm mmmmmmmmmmmmm....
Yum yum, gimme some!!!!      

Got any screen shots to show too??
<drool...>

[rnvinc]

Get the hot sauce...!!!

Rickie

[sfw1960]

NNNNNNNNNNNNNNNNNNice!!!!!

Get the hot sauce...!!!

Rickie

"I put dat $|-|*** on Ev'y ThaNGGG!"

LOL!!
Ohhhhh maannnnnnnnnnnn..... I can almost hear Mr. Greg droolin' all the way up here!!   

[Doc Stressor]

Anything with a different density that water will show up well on your machine. Crustaceans like gulf shrimp or krill have hard exoskeletons that will block the bottom signal if they are thick enough. Even squid are fairly easy to spot because their internal exoskeleton (pen) has a different density that water. In general, the higher the frequency you use the better the return.

The swim bladder story is sort of overblown. Many fish that don't use their swim bladder such as Spanish mackerel will show up on the screen. A lot has to do with the transducer though. Ocean king salmon, which don't use their swim bladder when chasing prey in the water column, will show up nicely with an Airmar Tm260 but not with the stock Humminbird transducer.

[rk_diver]

sfw1960; Without knowing the history behind your snapshot of Daphnia you posted, I would have to agree with the user who insisted what you were seeing is indeed air bubbles blocking the transducer pings. This is a very common error but logical if you think about it. The prop wash area is full of air bubbles, of which air is the best blocker of a sonar ping. If your snapshot was taken as you crossed the path another boat or your own had recently made the air bubbles will still be present (they do stay in the water column for a while, though I've never tested the time duration). As you travel through the (narrow) path full of air bubbles remember, though the air bubbles may only be in the first three(?, again, never measured) feet of the water column your transducers ping signal, as it goes through the air bubbles, will be fully surrounded (and mostly blocked) by them. That's why you see the "intereference" you're seeing on your snapshot. So each ping cycle you generate as you go through the first 3' of the water column will be greatly blocked, hence the image you saw. It looks like you're seeing a column of Daphnia but in reality your pings are being blocked by oxygenated water. However, if you were traveling through an area that hadn't had any recent boat traffic then it's something else. The best thing to do is test it yourself the next time your out. Run a trail and circle on back through it and compare your results. On our chain of lakes it's illegal to make a wake within 200' of shore. A savvy sheriff's officer could write tickets by observing a boat making a wake, driving through the prop wash and checking the distance from shore (other variables involved obviously). Rick

[sfw1960]

 
Prop wash GENERALLY doesn't go 40 feet down, also the bubbles would have risen up from hours ago as this shot was taken well after midnight and all other boats had left long ago.
Riddle me that??
LOL

[Humminbird_Greg]

I doubt it was prop wash due to no other boats being in that area but not knowing this information: prop wash could appear at the 40 foot mark in the Di sonar because this sonar is derived from the Si sonar and the air bubbles could have been 40 feet away from the transducer just under the surface of the water.  Remember, the Di sonar is showing you distance which may not represent the same water depth.

[sfw1960]

Dang it Greg!
Is this a ploy to get me to add a dedicated DI machine to the last Ethernet switch port??
 
I blew away the original files off the card so I don't have the file attributes to show that info.
I copied this series around 2:45 PM to the SSD, but I assure you it was in the dark and alone with one fishing partner.
I am selling my trusty 798ci SI to my stepson, and an 859ci HD will take it's place on the bow and become my new ice machine. I am going to have to be creative with a small Lazy Susan bearing and custom gimbal to fit that puppy in a 6 gallon bucket with a 12 amp SLA.

Is it safe to say there's no prop wash off a MK PD65v2 & wouldn't cause these results since I am running a 60" shaft on a Deep V walk Thru?
We were the only ones around and had been trolling well under 1.5MPH for some time on a lake just under 800 acres.
One of the reasons I like to walleye fish is the lack of "participants" that like to terrorize the weeds, water & "innocent bystanders" at night.
 

Would anyone dispute that this is a boat sitting "face down" in the mud?



I had run across it before on my 797 a few years ago, but  being a single card slot machine I felt it more desirable to have a map card than snap shot capability. I probably should have swung around and adjusted the machine for a better shot, but I was fishing and it probably would have looked a lot better if I had things slowed down, tweaked up and maybe even shot at 800 KHz instead without TM steering "creases".
Yes I have seen prop wash from the blaster wake boats & dual V8's all cranked up on Hardy Pond many times in the summer during the day chasing Bluegill.
One night I did forget the plug and ...OOPS!
Pumping out the results of trying to fill the lower deck was easily visible with the bubble stream of the bilge pump.
Did I mention ...OOPS!???

[Humminbird_Greg]

"Is this a ploy to get me to add a dedicated DI machine to the last Ethernet switch port??"
Oh no, you are on to me now Robert... 

Probably no prop wash, not that I ever remember seeing any prop wash from a trolling motor but they could do it.

Who hasn't forgotten the plug every now and then? 

[rnvinc]

Who hasn't forgotten the plug every now and then? 

Guilty as charged your Honor ...

Rickie