Hi Rick and welcome to the forum!
I agree with Wayne about the 200 kHz about the disturbance issue, but I would rather turn off the Bird for high speed runs if the Ray is giving the better readings.
I have a dual engine boat as well and mounted my transducer in the middle of the outdrives. The distance to the propellers is about 36 cm.
The pictures and recordings are fine as long as I keep the revs down to 1500 rpm. Raising the revs results in disturbance on the pictures and recordings.
I've been out with my colleagues of the water police in the last weeks. They have a dual break through transducer set up on their boat. I was amazed how good their pictures are even at high speed. Especially the 2d sonar is Cristal clear compared to my 981. I think this is because their transducers are far away from the propellers (approx. 4 -5 meters).
Thinking about it I realized that I had much better (clearer) pictures as well when I was using my tow fish. I will propably go for a new mounting position next year to get more distance to the props. I guess the props are producing noise in the frequencies the sonar is using and staying away from the source of the noise will give me better results.
Stay away as far as possible from your propellers.
Best regards and wishes