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Author Topic:   RAYMARINE Depth Finder Reading False Bottom
Chriscz posted 09-20-2011 10:16 AM ET (US)   Profile for Chriscz   Send Email to Chriscz  
I have a Raymarine unit with a DSM 250 depth sounder module. When trolling with a down rigger, periodically the unit interprets the down rigger weights as the bottom. For example, when I am in 330-feet of water and I lower the down rigger weight to 70-feet, the depth finder changes and marks the bottom depth at 70. I have tried adjusting the gain get it to break free, turning the unit off and then back on, zooming in on different depths. Nothing works. The only thing that works is raising up the down rigger. This does not happen all the time, perhaps 30-percent of the time, and sometime the unit breaks free by itself. Any suggestions? Thanks
Jefecinco posted 09-20-2011 07:18 PM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
Try reducing the sensitivity setting.--Butch
jimh posted 09-20-2011 09:59 PM ET (US)     Profile for jimh  Send Email to jimh     
Please try setting the depth range using a manual setting instead of automatic. Let us know if this helps with your problem of the SONAR falsely sensing the weighted balls of the down-rigger as bottom echoes.
Mr T posted 09-27-2011 11:09 AM ET (US)     Profile for Mr T  Send Email to Mr T     
I have a raymarine A65 unit that runs the dual frequency 50/200 P58 transducer. From your description, it sounds like we have the same setup. I have had that same problem with this unit and also with a raymarine DS500x unit as well. In both cases, I would be able to read the bottom while running in dual frequency mode with the 50kHz, but the 200kHz would lock in on the dowrigger ball. Cycling the power woud sometimes resolve the issue, but not consistently. The resolution turned out to be replacement of the transducer. A local supplier explanined to me that the P58 transducer is an OEM version of the P66 unit, and was made with lower build quality and less shielding than the 66 to meet price point requirements. According to him the element begins to delaminate from the epoxy coating inside the housing and causes this phenomenom. Typically this occurs from an impact while running the boat. I did replace the transducer on both units and in each case it resolved the issue. I would have liked to update to the P66, but the plug has been updated for the newer raymarine head unit, and it does not match the older syle on mine. I find it a bit disappointing that both times, the interval time for replacement was right around 2 years.
jimh posted 09-27-2011 04:13 PM ET (US)     Profile for jimh  Send Email to jimh     
Mr T--that sounds like very good advice. I pity the fool who does not take it.
David Pendleton posted 09-27-2011 06:42 PM ET (US)     Profile for David Pendleton  Send Email to David Pendleton     
I see what you did there, Jim.

How do I get diet Coke out of a keyboard?

jimh posted 09-27-2011 09:41 PM ET (US)     Profile for jimh  Send Email to jimh     
Diet Coke is not harmful to keyboards. Invert the keyboard over an absorbent towel. Allow it to dry, perhaps helping with an elevated ambient temperature. All should be fine. I guess you just have to be of a certain age to get that one.
Chriscz posted 09-29-2011 10:19 AM ET (US)     Profile for Chriscz  Send Email to Chriscz     
I have been trying a number of adjustments and manual settings to get the unit to break free of the false bottom readings. Thanks for the tips, please don't "quit yo jibber-jabber" because still no luck. It does break free but not based on any pattern or event I can discern. It's sounds like the next step might be as MrT suggests.
Any recommendations on a good transducer?
jimh posted 09-29-2011 01:49 PM ET (US)     Profile for jimh  Send Email to jimh     
Try an AIRMAR SONAR transducer. The may have been the OEM for the RAYMARINE transducer.
Mr T posted 10-01-2011 04:35 AM ET (US)     Profile for Mr T  Send Email to Mr T     
Jim is correct on the manufacturer.
Airmar has a very good website with a lot of good information. This is a good page to reference.

As stated before, the P58 and P66 transducers are both a mid level performance design using s single element for both frequencies. If you are serious about getting a better view of what is down below, consider upgrading to a unit with more elements. More elements make for a better defined image displayed. The TM258 is the next step up with 4 elements versus the single element on the P58 and P66.
The next step is the top of the line TM260 and TM270W which run 7 elements in the 50kHZ range. I have a friend running the TM260 on a Furuno FCV620, and the resolution is quite impressive.

Chriscz posted 10-01-2011 11:20 AM ET (US)     Profile for Chriscz  Send Email to Chriscz     
Thank Mr T, I'll check out the other airmars. Do you know if the higher end transducers work well with the older DSM250 I have? Or do I need to go to the DSM300?
Mr T posted 10-03-2011 10:39 AM ET (US)     Profile for Mr T  Send Email to Mr T     
Yes, it will work. The DSM 250 is like the P58 transducer, a price point entry to get the chartplotter/fish finder package to sell. The main difference is the output power. The DSM250 puts out a maximum of 600 Watts power compared to 1000 watts for the DSM300. For deep water ocean fishing, it may be needed but I have not found it a requirement. I fish local lakes for kokanee salmon, trout and king salmon, and very seldom do I find myself looking below 150-200 ft. At that point, they are below any level I want to fish. In the ocean, most of the fish I wish to target are above that level as well.
The cost of a DSM300 is around 600-700 dollars as of today, which I find to be a factor when I consider the age of the unit I am interfacing to. The A65 I own is now over 5 years old and I would not put that kind of cost into a unit that old.
The performance benefit in the case of a transducer upgrade comes from the use of more elements more than anything else.
The single biggest issue is getting the right plug from any transducer you choose to match up with the electronics. If you find the right one for your needs you can always solder the right plug on. I am likely to take that step when I replace the current P58 when it fails, as I am sure it will in the next year or so based on experience. When that happens I will go with the P66 and have a plug soldered on or do it myself.

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