Depth finder ???? up--down--up

BobH

BobH

Member
May 28, 2010
51
cent fl
Boat Info
2006 185 Sport
Engines
V-6 190HP
Took the boat yesterday on a river and twice touched bottom!!! Just prior to touching the depth finder went from 4 to 10 then like 245??? My wife who was up front looking for Manatee kinda alerted me " How deep is the water here ?" "Uh it is 4 no wait 10 what the hell". bump bump bump!!!! Fortunately we were at idle power and speed.
Is there anyway to get these meters more accurate?? It will work fine then out of the blue it will read something ridicoulous.
Thanks
BobH
 
The depth finders on boats were designed by northerners! From Labor Day to Memorial Day they were programmed to give inaccurate readings thereby making winter boating in the south less enjoyable!
 
I'm assuming you're using the factory setup. I also had strange readings using the factory unit in shallow water...sometimes. Enough actually that I made sure that when I purchased a chart plotter, I connected the the included transom mounted transducer as well. Now, when I'm in known shallow water, I have two readings staring back at me from the console. The Garmin tends to be a bit more accurate in shallow water and with the display set to "depth", it gives a much b better depiction of whats going on beneath your boat.
 
You have to go back to the basics to understand what the issue is. Depth gauges are sonar devices. The transducer sends out a sound pulse and then receives the reflected pulse back. In its simplest form as a depth gauge, the instrument is measuring the time between the pulse being sent and received, knows the speed of sound in water and then does the math. The difference between simple depth gauges and fish finders is that the instrument is not only timing the roundtrip pulse time, but also measuring the characteristics of the returned pulses. From the differences from the original pulse pattern it determines if there are thermal layers and or fish.

In shallow water these things all start to have problems. In BobH's case it sounds like he was moving over a bottom where the bottom had peaks and valleys. This would mean that as he moved over this surface the depth gauge might start to see conflicting results, i.e. pulses having been sent into a valley arriving back at the same time a pulse from a peak returned. And in the case of really shallow water, the pulse might return too fast for the gauge to read.

We boat in shallow water that is exacerbated by a big tide swing (11 feet). I found that incorporating the depth display into my MFD that is mounted in my line of sight has probably done the most to prevent kissing the bottom.

I'd suggest a fish finder with a good visible display as a solution. Here are some numbers to help determine how much its worth; new BIII props $ 1000-1300 on eBay, $1600-1800 at your dealer, BIII props sent to the prop shop for truing and nick removal, $ 500.00 minimum. Decent fish finder; $ 300.00 to $ 400.00.

Henry
 
I think part of your issue MAY have been that since you were in shallow water you were churning up silt and the depth gauge was 'bouncing' off the silt and not the hard bottom. This typically happens in shallow water and will also happen if you follow someone else in the wake, the air pockets (bubbles) will return false readings as well. Silt on the bottom here is FL is also very light meaning lots of water mixed in the floating debris just off the bottom meaning it is hard to get a good reading in parts that are very silty.
 
You probably have the exact same depth finder I do - Humminbird 600.

http://www.humminbird.com/PDF/hdr600.pdf

For what it is worth, I'm on a lot of shallow water lakes, some I've come to know quite well, and can predict the depth, and also know areas where the depth jumps all over very quickly - the lake bottom is just that inconsistent. So, some of your quick reading changes from 4 to 10' may be accurate. You may also be passing over the occasional submerged car or God knows in a river. The sudden jump to a very high depth that does not make sense is something I have not experienced. I know that when I found some submerged concrete this summer, my gauge dropped from 5' to 2' just as the ugly noise started. I replayed what happened in my mind several times, God knows what I really saw on the gauge. The silt comments by trit21 also make sense, I've seen that issue come up on CSR before.

I've seen mine read sudden low depth at anchor. It may read 10 - 11' for a long time, and suddenly read 3' for a moment. I've wondered if maybe a large fish or something just passed under the transducer. Or if age and issues are making it flakey.

I like Henry's tutorial on depth gauges. Our Alpha props aren't quite so expensive, but his point is well taken. If you spend a lot of time on water you are not familiar with, or a river that changes its channels after every storm, you may want to revise your Christmas list.
 
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Thanks fellow Sea Ray ers' ... All great info . I usually but the depth chart for the area but not yesterday. Also have looked into a new Garmin or Fish finder. For now I'll monitor for erratic operation
BobH
 
Also keep in mind the readings are typically of ground behind or under the stern and not what's up ahead. Bottom composition and dissolved solids in the water can have an effect on readings also. Mostly these instruments are for reference as to the general depth in any given area and not a replacement for due diligence in shallow water.
 
Here's another tidbit for you. I too run a Humminbird depth gauge. We boat in several lakes and most of the time the gauge works perfect regardless of how fast or slow we're going.
But one lake in particular, the numbers bounce all over the place, even though the depth is constant. The water looks fairly clean, but close inspection, there are lots of tiny algae particulars suspended in the water, so my assumption is it's bouncing off all the debris. On this HB unit, you can't adjust the sensitivity of the sending/pickup reader.
On my previous boat, I had a fish finder and it had way more adjustments, and I could adjust to get more accurate readings at this particular lake.
Sort of backs up what others have said already, that it has lots to do with the debris in the water.
 
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Follow up-----I went out a few weeks back in the inland waterway near Clearwater and the factory gauge was reading constantly anywhere from 450 - 550 ft while i watched the bottom and walked in the water.
Looking for a nice replacement that fits in factory opening. Ant suggestions would be appreciated,
BobH
 
Does your depth finder have a transom mount transducer or through hull? The stock depth finder on my 205 would read crazy because Sea Ray installed a 0 degree transducer in a 20 degree hull so it shot out kinda sideways. Your issue sounds a little different but regardless I would seriously consider a fish finder/chart plotter with a ram mount. Not only will you never loose bottom untill below 2 feet but you have GPS trails and a sonar image. If you have a through hull transducer it Will perform better at high speed compared to a transom mount. It would be worth the $500-$1000 it would cost.
 
When I replaced ours I went with the Raymarine ST40 that although rectangular requires a round hole the same size as the round gauge. I also went with RM because the data can displayed on our C80. This is just basic depth as fishing is not allowed on the 280 by royal decree.

I would strongly recommend any depth display be integrated to a MFD (if you have one) for the simple reason that the depth display will probably be more visible. Also having a low depth warning that is set once is a big plus. The OEM gauge we had before had low depth warning, but it had to be set at every startup. Needless to say it got forgotten more often than not.

Henry


Sent from my iPad using Tapatalk HD
 
Took the boat out the other day and noticed the depth finder was accurate with the motor off and key on..... Is there a common place that maybe providing electrical interference? My transducer is located in the bottom of the hull about 4 feet from transom
Thanks
BobH
 
If that were the case, how deep would the water be when it does 2ft?

Sent from my Nexus 10 using Tapatalk 4
 
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