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Author Topic:   RAYMARINE DRAGONFLY SONAR: Poor Results at Planing Speed
sjp2 posted 07-13-2014 05:33 PM ET (US)   Profile for sjp2  
[In the course of a long discussion, now deleted, we find out that on the transom of a 1991 Boston Whaler 13-footer, mounted 11-inches from keel centerline, is a Raymarine CPT-60 transom mount transducer, connected to a Raymarine DRAGONFLY SONAR.] The picture is fine at idle speed but drops off to non-existant at any more than that. [The transducer] is level with the bottom of the hull. [Seeks] help with the position of the transducer.
fishgutz posted 07-13-2014 06:33 PM ET (US)     Profile for fishgutz  Send Email to fishgutz     
You just have to experiment with lowering it or changing the angle (front to back). I've installed a few of these and I've always had to play around with positioning to get them to work. Also make sure you don't have any wires bundled with the transducer wire. I had a problem with a Raymarine unit that gave false readings and froze up coming into shallows because the transducer wire was bundled with the main wire harness.
sjp2 posted 07-14-2014 05:26 PM ET (US)     Profile for sjp2    
The transducer throws up a fair bit of spray at speed, so I assume it is deep enough in the water.

Looking at the boat on the trailer, the back of the transducer is slightly higher than the front. Would this angle would be increased when the stern is in the water ?

jimh posted 07-14-2014 07:15 PM ET (US)     Profile for jimh  Send Email to jimh     
You can get the factory's advice on installation of a transducer from html#fathometer

The above is an on-line re-creation of the owner's manual in hypertext that I authored a few years ago. It can give you a lot of useful information about your Boston Whaler boat.

With the transducer only 11-inches off keel centerline, it should remain in the water when the boat is on plane. That sounds like a good location, but you have to look forward on the hull bottom from the transom to see if there are any hull strakes in line with the transducer.

The orientation of the transducer angle fore-and-aft when on the trailer is not particularly important. The orientation with regard to the waterline when in the water is important. Usually a SONAR transducer is mounted with the leading edge, that is, the part that enters the water first when the boat is going ahead, to be not as deeply immersed as the trailing edge.

The first place to look for a remedy to the problem you have is to adjust the depth of immersion of the transducer into the water. If you can without risk, look over the transom while the boat is running on plane and see how the SONAR transducer and water are meeting. In order to work properly, the transducer has to be in clean water, that is, water that is not full of air and turbulence. You should be able to see this by looking over the transom and observing the water flow on the transducer.

All transducers create some spray. It is not clear to me that one could deduce the proper position of a transducer by noting whether or not it is making spray. Spray is an artifact of having a SONAR transducer on the transom. You have to live with the spray created when the transducer is working well at speed. You cannot really tune the position of the transducer for spray and expect that will lead to the best position for SONAR operation.

In almost every case, the performance of the SONAR at high speed operation is entirely determined by the mounting location and the depth of immersion.

sjp2 posted 07-15-2014 05:34 AM ET (US)     Profile for sjp2    
The transducer is about 7-inches long. When a straightedge is put along the bottom of the boat and transducer, it lined up the bottom of the boat at middle of the beginning of the transducer. but showed 1/8-inch at the end of it, that is, the end was higher. [This] might be the problem. [The transducer position has] been adjusted but I have yet to test it.
jimh posted 07-15-2014 08:28 AM ET (US)     Profile for jimh  Send Email to jimh     
Re the CPT-60, see

for the installation instructions. See Section 4.1, "Mounting the transducer."

Contact Raymarine technical support. Inquire with Raymarine technical support if there is an expectation that the DOWNVISION function of the sounder will be able to operate at planing speeds. Often these complex side-scaning SONAR units do not work above idle speed.

Based on your narrative of the present position of the transducer, it is probably not sufficiently immersed in the water at planing speed to work effectively. It is very normal and typical that the working surface of the transducer must project well below the bottom of the boat if the system is to work at planing speed.

The image linked below shows the mounting of a SONAR transducer on the hull of a Boston Whaler boat in a view that gives a good indication of the relationship of the working surface of the transducer to the hull bottom: transducerMountingCloseUp.jpeg

jimh posted 07-16-2014 06:53 AM ET (US)     Profile for jimh  Send Email to jimh     
[Incorporated much information drawn out in the discussion into the initial posting--jimh]
jimh posted 07-18-2014 09:20 AM ET (US)     Profile for jimh  Send Email to jimh     
If there is any fore-and-aft tilt to a SONAR transducer, it is generally preferred for the trailing edge to be lower (more immersed in the water) than the leading edge. That orientation tends to prevent air bubbles from flowing over the actual working surface of the transducer.

From what I can tell from your narrative description, the present installation of the CPT-60 transducer is with the trailing edge higher (less immersed in the water) than the leading edge. That orientation tends to permit air bubbles to flow upward and across the working surface of the transducer.

As all comments have suggested, the most likely cause of the problem you are experiencing with the Raymarine Dragonfly SONAR is a result of poor transducer position. The first place to look for a remedy to the problem is in the location, depth of immersion, and orientation of the transducer.

gnr posted 07-23-2014 01:58 PM ET (US)     Profile for gnr    
I recently installed a Dragonfly on my 17.

I had similiar results as you on the initial test run and figured I just needed to dial it in.

At one point I left the helm in control of my buddy and went back to eyeball the transducer while on plane. (note: it was what seemed like an unusual amount of rooster tail being kicked up that caught my eye and prompted me to check it out.

To my surprise the transducer was releasing from the catch that is supposed to hold it in place in the bracket and had assumed a vertical position against the transom.

When we came back down to idle speed the transducer re-assumed its horizontal position and all was well.

Tightening down the screw that adjusts the tension required to release the transducer in the event of a bottom strike seemed to have solved the problem.

I noted the seemingly over engineered and under constructed design of the transducer mounting bracket when I installed it.

The unit itself has been a real pleasure though.

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