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Full Version: [CA11] Stern drive AXIOM RV transducer installation
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Hello folks,

I wish to upgrade a Raymarine C-70 MFD with a thru hull 50/200 kHz transducer to an AXIOM 9 RV for a 2006 27’ Sea Ray Amberjack 270 equipped with a single I/O engine and a transom dead rise of 21 degrees. I am very anxious regarding the selection of the appropriate transducer and its location. There appears to be no perfect solution for a RV transducer for this stern drive application. As the bottom of the keel is rounded (please refer to the first of the three attached pics) this apparently rules out the use of a single RV-200 thru hull transducer which requires a flat surface. Also, I’m hesitant to attempt to replace the existing thru hull transducer since, while it is believed to be an Air Mar, there is no tag attached so that the exact model is unknown, and without that the exact diameter is unknown. I thought that the installation of a pair of RV-2xx thru hull transducers between the keel and the first chine (please refer to the first of the three attached pics) would be a good choice, but my mechanic said that he would not do that, because that is where a bunk trailer pad would most likely lie. Although I don’t own a trailer the mechanic uses one to transport the boat. I also considered the installation of a pair of RV-2xx thru hull transducers located forward of the water intakes that are located on each side of the keel (please refer to the first of the three attached pics), but there appears to be insufficient room to do so in the bilge, as the fuel tank is located forward of the water intakes (please refer to the second of the three attached pics).
The local Raymarine rep recommended the installation of a RV100 which could be connected via a Y cable with the existing 50/200 kHz thru hull transducer. With such an installation it is realized that the performance of the side scan on the side of the outdrive opposite to that of the RV100 will not be optimal.
For such an installation, where on the transome would be the best place to locate a RV-100? Please refer to the third of the three attached pics. The blue tape on both sides of the transom indicates where the water intakes, which can be seen in the second pic, are located. The speed/temp sensor on the starboard side can be removed, if necessary, as it is attached to the current C-70, which is to be replaced with the AXIOM 9. The sensor on the port side is for a Fish Hawk down speed/temp/depth unit.

Thanks in advance for any suggestions,
Welcome to the Raymarine Forum SeaBat,

This hull indeed poses challenge due to the currently installed thru-hulls, numerous chines, and the potential for damaging installed RV2xx transducers when trailering. With all hull features and thru-hulls forward of the transom, it would be quite challenging for any transom mounted transducer to be provided with a non-aerated flow of water across its face at planing speeds ... would recommend relying on the 50kHz/200kHz transducer presently installed for tracking bottom while on plane should a RV-100 be installed. The location to starboard where you have placed the blue tape would be my first choice should a RV-100 Transom Mounted RealVision Transducer be installed. At speeds below plane, it is unlikely that the water pick-up forward of the transducer will cause aeration of the water. Should the RV-100 be installed with a stern drive, then the possibility of creating a sonar blind spot is indeed possible ... moving the transducer further outboard to the location of the speed/temp transducer would seem to increase the sonar blind spot. Have you considered relocating the water pickups further aft to then permit the RV-2xx transducers to be installed in the locations presently occupied by the water pick ups?
Thanks Chuck for the analysis.
Yes, I had thought about moving back the water intakes as a potential solution, but not for very long, as I am anxious about the number of holes in the hull that would result.
What I am revisiting, though, is replacing the existing Airmar 50/200 kHz thru hull transducer w/ a RV-200. As can be seen w/ the two attached pics, there is a flat area in the hull that is about 3” in diameter where the Airmar transducer is installed. Now, if the Airmar transducer and flange, which is the outer of the two rings, were removed, the flat area would no longer be level with the keel. But a boat builder, who looked at the area today, believes that he could manufacturer a spacer that would bring up that 3” diameter area to be level with the keel again, so that when the RV-200 is installed in that area the top of the RV-200 would be level with the bottom of the keel, but would not be flush. There would be gaps between the hull and the RV-200 on both sides of the keel. The diameter of the RV-200 is greater than that of the Airmar by 3/8” but that would not be a problem. Would there be any problems with such an installation?

Thanks in advance for any suggestions,

You may want to consult the boat builder whom you referenced or another skilled in repairing/modifying fiberglass hulls to create a flat mounting surface on the bottom which fully supports the RealVision transducer and would permit a non-turbulent flow of water across the face of the transducer. Given the cost of hauling boats, the better option may be to install a low profile 50kHz/200kHz tilted element thru-hull transducer or in-hull 50kHz/200kHz transducer to support tracking bottom while on plane should the fiberglass work perform cause an aerated flow of water to flow across the face of the RealVision transducer while it is on plane.
Thanks Chuck,

At this point I have decided to put the boat in the water and wait until mid season, when the boat is usually out for maintenance, or the end of the season to install new transducer(s). I'm planning on purchasing a trailer before the end of the season, so I'll wait and see where the bunks are located before selecting a transducer(s).
In the mean time I would like to use the AXIOM 9 with the existing transducer, which is presenting its own difficulties, which may be best addressed in a separate thread.

You're welcome.
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