How accurate are ALL depthfinders?

waterinthefuel

Commander
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Nov 15, 2003
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2,729
I was just wondering, since we don't exactly have tapemeasures onboard to check our depthfinders, how accurate are they? We assume they are close, but are they 10% off and we just don't care?<br /><br />I was just curious. It seems that nobody disputes the accuracy of sonar, just whether one unit displays the bottom better than another.
 

Texasmark

Supreme Mariner
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Dec 20, 2005
Messages
14,797
Re: How accurate are ALL depthfinders?

I have tested mine on different boats with different types. They are very accurate but remember it's meauring from the transducer bottom to the bottom of whatever water you are running in....so take this into account when you read it. Like if you mount it on the outside of the transom at the bottom of the boat (give or take a couple of inches) you can run (idle around) in a couple of feet (recorded on the sonar) and not drag bottom regardless of what shape your hull is.<br /><br />Course you will be stirring up the bottom and see mud/sand in your propwash.<br /><br /><br />Mark
 

Silvertip

Supreme Mariner
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Sep 22, 2003
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28,771
Re: How accurate are ALL depthfinders?

Let's put it this way -- they are accurate enough such that "WHEN THE DEPTH OF YOUR DRAFT IS GREATER THAN THE INDICATED DEPTH OF THE WATER YOU ARE MOST DEFINITELY AGROUND!"
 

waterinthefuel

Commander
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Nov 15, 2003
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2,729
Re: How accurate are ALL depthfinders?

LOL Upinsmoke!<br /><br />Texas, my Garmin 240 has a "keel offset" feature so you put how far beneath the water line your transducer is and it takes that into account when it gives you your depth.<br /><br />I was just curious to know if they were accurate. I mean they show down to the tenths of a foot. Good grief, what is that, a tad over an inch? LOL<br /><br />I thought it was hilarious whenever a boats wake hit my stationary boat and you could see the bottom on the depthfinder as having "waves" at exactly the same rate as the waves that were htting my boat. It also gave me a good idea of the scale I was seeing, so one foot wave equaled about 1/4 inch on the display. That was neat!
 

DangerDan

Petty Officer 1st Class
Joined
May 21, 2005
Messages
260
Re: How accurate are ALL depthfinders?

This thread caught my eye as I run the same FF in my lil flat bottom jet boat as my 23 ft. Lake boat. I use a Humminbird 981C and also wondered the accuracy of the FF when in say 4" of water. It doesn't seem to really read to accurate any shallower that a foot or two.
 

glasply1

Petty Officer 2nd Class
Joined
Jan 20, 2006
Messages
171
Re: How accurate are ALL depthfinders?

I compared the results of my depth finder with that of my downrigger when it hit bottom in deep water with the engine at idle. Very similar numbers and plenty close enough for deep water stuff. For shallow water areas I use my kicker motor and raise the outdrive on the main engine. I learned the hard way.
 

Chunder06

Petty Officer 2nd Class
Joined
Apr 17, 2006
Messages
124
Re: How accurate are ALL depthfinders?

You could always do a Samuel Clemens and mark the twain.
 

jtexas

Fleet Admiral
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Oct 13, 2003
Messages
8,646
Re: How accurate are ALL depthfinders?

Shallow enough water, I've checked with fishing rods, & texas-rigged worms - seem to be pretty accurate. My eagle fismark320 seems to consistently lose bottom at 1.6 feet - so far that hasn't been an issue - manual says don't rely on reading less than 2 feet anyway.
 

jch7450

Petty Officer 1st Class
Joined
Apr 13, 2003
Messages
230
Re: How accurate are ALL depthfinders?

The truth is>>>>. most are all from about the same technology
 
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