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Author Topic:   transducer placement on a 22 revenge
180 posted 05-29-2002 10:31 PM ET (US)   Profile for 180   Send Email to 180  
I have a 1981 22' Revenge with a 175 merc and a 18 hp merc kicker (mounted starboard). I am wondering, where is the best place to mount the transducer for my fishfinder?
I recall reading a thread about this but I can not find it.
Thanks in advance for your help.
jimh posted 05-30-2002 10:19 AM ET (US)     Profile for jimh  Send Email to jimh     
With you main engine mounted on centerline and your auxillary engine mounted to starboard, the best place for your SONAR transducer is to the port side of keel centerline. This is not a compromise, because that is generally the preferred location.

Offset the transducer far enough from centerline to be clear of the motor. You do not want the transducer to disturb the flow of water to the motor or interfere with its turning. Also, check the hull undersides for any strakes. Do not mount the tranducer inline with any underwater strakes on the hull. Of course, don't offset it too far or it may come out of the water when on plane. Usually the correct location will suggest itself when you look for the other obstructions mentioned above.

The design of the transducer will determin how far below the line of the hull bottom the transducer must project. The mounting instructions should explain that to you.

In my experience, using the LOWRANCE "Skimmer" transducer, the depth can be quite critical. If you want to get good readings at high speeds, you may have to tweak it up or down slightly. When well positioned, you should be able to maintain good bottom echoes at high speeds. I don't know if you can spot a fish 6-inches off the bottom in 100-feet of water at 55 MPH, but you will be able to track the depth.

The problem with mounting the transducer too low is that it will tend to throw spray and add a bit of drag. The spray is probably the more troublesome, particularly if it bathes you nice new outboard cowling with a constant shower of water. Again, with the LOWRANCE skimmer transducer, spray can be minimized at the proper depth; just the bottom face of the transducer is in the water and it skims across without making a big roostertail.

I often see SONAR transducer installations where the cables have been routed through the transom drain holes. I dislike this. I don't say that it is horrible or should never be done, but I dislike it.

I prefer to route the cables up and over the transom. Installing them this way has these advantages:

--prevents the transom drain holes from being blocked. It is hard to imagine that people would go around recommending you reduce the size of the transom drains holes, yet people will fill them up with cables.

--gives you flexibility in relocating or servicing the transudcer. If you discover the transducer doesn't work well where you initially place it, it will be much easier to reroute the cable if it is not captivated by passing through the drain.

--keeps the cable out of the lower part of the motor well. The motor well is often filled with water, thus your cables will be sitting in water. By coming over the transom you can route the cables across the transom at a height above the normal waterline of the well.

--permits plugging the drains. In some situations you may decide to plug the transom drains and keep the motor well dry with a sump pump (This is mentioned in the article on transom brackets in the Reference Section.) If the drains are full of cables you will not be able to plug them when desired.

If you have multiple tranducers, say for distance/speed and temperature, in your situation you may be constrained to mounting them both on the same side of centerline.
(Again, if you route their cables through the drains you will now have two cables passing through the drains.)

When you drill the holes for the tranducer mounting, be careful to not crack the gel coat. It is very prudent to drill the mounting hole, say 1/8-inch, then by hand and using a large diamter drill, say 1/2-inch, to gently bevel the hole to remove more gel coat. The goal is to make the hole in the gel coat layer as large as the screw shank. If you do not do this you can crack the gel coat and small radial cracks will grow from the screw hole.

I usually test the hole by first running the screw into it. If it takes too much torque to install the screw, I make the hole incrementally larger.

It goes without saying (but I will say it) that you must seal the mounting holes and screws against water intrusion. They will be below the water line at all times. If water is allowed to intrude you can create many problems for yourself in the future.


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