[TG] RV-100 placement

[jharcnc]

hi Chuck et al

Looking for guidance on ideal placement on my 21 Whaler Outrage - see attached pics. System works well but the RV-100 will lose bottom at speeds above 20 mph or so.

Last season I had it mounted on the lower port strake as you can see from the orange circle and drill holes. I knew going in that the port side mount was less desirable (my prop turns clockwise), but hoped for the best. It worked flawlessly trolling and at low speeds but again would lose bottom.

Thinking of trying it on the starboard side of the engine, marked by the red circle. Thoughts?

I would prefer it a little closer to the centerline but it might conflict with the engine. As well, I plan on mounting it so the bottom edge of the RV-100 is level with the lowest edge of the hull.

Thoughts? Thank you!

[Tom - Raymarine - Moderator]

Hello jharcnc,

It might well be that the transducer location relative to the engine and prop-rotation isn't the cause of the problem:

Sounder performance is dependent on the relative signal strengths of the bottom/fish echoes and the background noise (there is always some background noise, both in the electronics and the outside environment.) The larger the difference in these signal levels, the better the sounder images. If a sounder gives good images when stationary or moving slowly but doesn’t perform well at speed then the cause is either a higher-than-normal background noise level or a lower-than-normal signal level. Increased noise comes from hull vibration, water flow and turbulence around the transducer, and electrical interference from the engine ignition and charging. Decreased bottom/fish echo signal levels occur because of air across the face of the transducer, which blocks the echoes coming back to the transducer. There’s a lot of information on all this and some in-depth diagnosis detail at https://forum.raymarine.com/showthread.php?tid=9371

To see what’s causing the problem in your instance – high noise, aeration or a combination of the two – what we’d want to do is get clear, full-screen images of your sounder screen when under way at a range of speeds, with the sounder set up in our standard diagnostic gain mode of Manual 65% Gain, manual 15% Intensity and manual 0% Surface Filter. That lets us see what changes as you speed up, as objectively as possible. It’s important to put the SOG value up on screen when you do this, to use an appropriate manual Range, and to turn off Bottom Lock, Bottom Fill and White Line display modes beforehand. Full details and instructions are on that FAQ page.

If you can post back some images, we can go to the next step to solving the problem for you. If the problem isn't aeration then moving the transducer may well not solve it.

On your question though - I would be wary of putting the transducer upstream of the engine, that can interfere with water flow into the intakes apart from anything else.

Regards,
Tom