Suspect Depth Reading with C120W/DSM30/SS60

[TideRace]

I have a C120W display connected to a DSM30 sounder module and SS60 transducer. I have noticed that the depth reading reported by the Raymarine system is always different than the depth reading reported by my Furuno 585/B164 system, although the offset is not consistent. Usually they are off by 5-6' but I have seen a difference of 12'.

The transducers are at the same depth in the hull, approximately 4' apart, fore and aft.

Referencing shallow water depths in my harbor and depth data from charts offshore, I am inclined to believe the Furuno.

1. Could this be a software (update) issue for the C120W and/or DSM30?

2. Is there a calibration function for the DSM30?

3. Is there an Operation Manual for the DSM30 (I haven't been able to find one)? There are many features and settings that I may want or need to explore or adjust but I'm not finding it intuitively obvious to do so without a manual.

Thanks for any help.

[Chuck - Raymarine - Moderator]

Welcome to the Raymarine Forum TideRace,



A1. Could this be a software (update) issue for the C120W and/or DSM30?
A1) No.

Q2. Is there a calibration function for the DSM30?
A2. Unless one has applied a waterline offset (positive depth offset value indicative of the depth of each transducer below the waterline) and tide accounted for, then comparisons should neither be made between the fishfinders nor to spot soundings. The Fishfinder application's menu includes a Fishfinder Set-up menu from which a Transducer Settings menu may be selected. The latter menu includes a Depth Offset feature which may be used to adjust the reported depths to equal one another. I suspect that these transducers are also both of tilted element designs rather than the 0 degree versions of these transducers. Should these transducer not be perfectly aligned with one another, then the beam of the transmitted energy from one or possibly both of the transducers may not be directed straight downward. This may also occur when the boat is rolling and the transducers are installed on opposite sides of the keel. Should you desire to have them equal one another, then the Depth Offset feature may be used to do so. However, I do not suspect that you will find the difference to be so great when operating in shallow water.

Q3. Is there an Operation Manual for the DSM30 (I haven't been able to find one)? There are many features and settings that I may want or need to explore or adjust but I'm not finding it intuitively obvious to do so without a manual.
A3. Raymarine only produced installation documentation for the DSM30/300. The fishfinder features supported by the DSM30/300 are documented within Chapter 12 - Using the Fishfinder of the C-Series Widescreen MFD User Reference Handbook.

[TideRace]

Thank you for the quick and detailed reply.
Differences in beam angle relative to straight down makes sense given the Furuno with the B164 mounted at the greater deadrise angle further forward in the hull is reporting the greater depth. I'm not seeing a feature in the Furuno manual that would allow me to enter a beam angle to get a corrected depth and I'm assuming that there isn't one in the DSM30 either.
Now that I realize that the specified mounting angle range is actually a depth error range, I'll try to remount each transducer to get the beam angles vertical. So much for the nice smooth hull surface.

[Chuck - Raymarine - Moderator]

TideRace,

Q1. I'm assuming that there isn't one (beam angle configuration setting) in the DSM30 either.
A1. Raymarine's depth sounding products do not include this feature. Raymarine, as well as Airmar, Inc., offer 0 degree transducers as well as 12 degree and 20 degree tilted element transducers to support installation on hulls having 8-15 degree and 16-24 degree deadrise respectively in the location where the transducer will be installed. When a second through hull depth transducer is installed onboard a boat, the transducer would typically be installed on opposite sides of the keel (most common) or side by side. Install a depth transducer aft of another thru-hull transducer may expose the aft transducer to an aerated flow of water when the vessel is operating a planing speeds and speeds approaching plane. If the transducers are of the correct model for the amount of hull deadrise in the installation locations, and have been correctly oriented within the present installation location, then I would be inclined to simply note which of the two systems are providing the more accurate depth value when needing depth information.