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Author Topic:   Depthsounder Accuracy At Speed
pcrussell50 posted 04-13-2010 02:16 AM ET (US)   Profile for pcrussell50   Send Email to pcrussell50  
Do [depth sounders] have a fast enough refresh rate to map the bottom while under way at say, 25 to 30-MPH? Or are they for the most part just used at trolling speeds? An admittedly inexhaustive scan of the manual did not reveal anything. My 1985 Sport 13 came with a Lowrance X-30, black and white LCD depthfinder/sonar. When I bought my boat, I was not too into fishing. Now I'm a lot more into it than I was, and have reached a stage where I (think) I have enough knowledge to want to know what the bottom looks like in the area I fish a mile or two radius around the opening of the Santa Barbara harbor.

So anyway, after storing it while I wasn't using it, I put the unit back into it's bracket and and hooked up the power and transducer wires and got it working.


cohasett73 posted 04-13-2010 07:31 AM ET (US)     Profile for cohasett73  Send Email to cohasett73     
From my experience Pete, I would say trolling speed gets better results. I have used Hummingbird for twenty years, with mixed results. Advertisements claim they are effective at WOT. I have never been able to make that claim. For bottom contour I started using a Lowrance GPS. To get a positive ID of marks on sonar I drop a fish camera.
Tom from Rubicon,WI
deepwater posted 04-13-2010 12:24 PM ET (US)     Profile for deepwater  Send Email to deepwater     
I dont think there is a unit that we can afford that would map the bottom at that speed,,The Impulse 2800 I baught new in 1988 could tell between a fish and a floating bag and show flounder on the bottom,,At any speed above 5 mph I would be ahead of the return echo by dozens of yards in about 2 minutes and on plane I was past the bottom area by hundreds of yards,,The fastest units I saw were old "Flasher" units that just showed bottom and were hard to read
TRAFFICLAWYER posted 04-13-2010 01:21 PM ET (US)     Profile for TRAFFICLAWYER    
My Furuno holds bottom at speeds of 40mph+ and depths of 500-600 feet easily.
gnr posted 04-13-2010 01:33 PM ET (US)     Profile for gnr    
My experience has shown that the ability to map bottom at speed is dependent on getting the transducer set up perfectly.

I have no experience with high end units, only inexpensive units. I have been able to get a bottom reading at speed in most cases.

fishgutz posted 04-13-2010 05:56 PM ET (US)     Profile for fishgutz  Send Email to fishgutz     
I have an Eagle locator. Eagle is made by Lowrance. They use the Eagle brand to fit in between Lowrance models. Mine tracks the bottom without fault at 40 plus miles per hour. I had a Raymarine on my boat before. It was very problematic. On my old Alumacraft I had a Humminbird that worked pretty good to 25 miles per hour. The rivets on the bottom of the hull disturbed the water flow under the transducer and it would be a bit glitchy at speed.

Some things to consider are pixel size and the display speed. Large pixels and a slow display speed will be less accurate than small pixels and a fast display speed.

SJUAE posted 04-13-2010 09:04 PM ET (US)     Profile for SJUAE  Send Email to SJUAE     

It depends on what you mean by "map the bottom"

If you are refering to newer technology like structure scan that can show very high level of detail these only operate up to 15mph

If you are refering to most newer sonar/fish finders then these will lock and track the bottom contours at high speed and large depths.

The level of detailed displayed is dependant on your system, screend size/specification and speed

The difference of display between slow and fast speed is the information on the screen can represent from just a few feet travelled to 100(s) depending on your speed and scroll rate

ie a small trench could just show as little dip at high speed or look like the grand canyon at slow speed


dburton posted 04-13-2010 09:33 PM ET (US)     Profile for dburton  Send Email to dburton     
Here is a link to the manual in case you don't have one.


contender posted 04-13-2010 10:22 PM ET (US)     Profile for contender  Send Email to contender     
Deepwater: I have a Impluse 2800 still brand new in a box, has everything, the sender, bracket, instructons. Purchased it in a flea market back in 1988-89. Never installed it...
pcrussell50 posted 04-14-2010 02:30 AM ET (US)     Profile for pcrussell50  Send Email to pcrussell50     
Guy, thanks. So far I have learned 100% more about these contraptions than I knew before I asked. And Doug, thanks for that. I downloaded and saved a copy of the manual.

A quickie question about transducers. From the look of mine, it's sealed and looks pretty robust and simple. Mine is on the transom and aimed so it's tilted forward. IOW, so the conical "beam" paints forward. In deep enough water, the cone will paint in front of the boat. Is that typical?


deepwater posted 04-14-2010 05:30 PM ET (US)     Profile for deepwater  Send Email to deepwater     
Contender,,When I picked out mine it was in the $600+ range and touted as very selective in what you saw on the screen,,A fish symbol was a fish and nothing but a fish and the size of the fish on the screen got bigger as the fish in the water got bigger,,The depth was listed at 900' and mine would do some extra but the mapping was not good at any speed,,I could outrun the screen by hundreds of yards at only low plane speeds,,That is the only thing I did not like about it because at even low speeds you were over the sandbar before you knew it ,,I guess its the screen speed and the processing of what the unit is seeing and what you program in to see or filter out what you dont need to see on the screen that will give you real time over bottom info
fluke posted 04-14-2010 06:22 PM ET (US)     Profile for fluke  Send Email to fluke     
Peter there's some good info on transducer install on this site, I think it should be level when on plane. If you get out to 4mile at the derricks your going to love your finder, the pinnacles come up quick from 145' to 116', I used to go out there in my 13' sport. If you have a gps I can give you some coodinates.
JMARTIN posted 04-14-2010 06:42 PM ET (US)     Profile for JMARTIN  Send Email to JMARTIN     
The transducer should be aimed straight down, not tipped forward. My Lowrance works at speed, beats me how but it does and is surprisingly accurate at speed. My buddies Eagle does not. Both are relatively new. I am guessing that the transducer on mine is positioned better than my buddies. I think we have his mounted too high and are getting some air or turbulence at speed.


jimh posted 04-14-2010 09:38 PM ET (US)     Profile for jimh  Send Email to jimh     
[Moved this discussion about SONAR and electronics to SMALL BOAT ELECTRICAL.]
jimh posted 04-14-2010 09:42 PM ET (US)     Profile for jimh  Send Email to jimh     
Please see this prior discussion on this topic:

SONAR Depth Sounding and Boat Speed

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