It will get a little expensive, but this is one of the scenarios where you might consider a
http://www.humminbird.com/Products/AS-SILR-Y/ and 2 SI transducers.
I saw a YouTube video where the guy mounted the transducer at an angle on the right side of the hull .... I wouldn't recommend doing that if you want to get good SI images. With one side angled down, one side will be "hot" and the other side "dim".
Well, might as well go ahead and post the link.....but I would not recommend this.
https://www.youtube.com/watch?v=9CTFjn4rB9oA second option would be to epoxy an actual thru hull transducer... not shoot thru.... but not many people want to drill a hughe hole in their transom.
I'd go with 2 SI transducers.... one on each side....and if that hull will support a shoot thru, put a 2D transducer in the bilge to get high speed depth readings.....You may have to talk to Yamaha to find out if the hull will support the shoot thru 2D and if they can tell you a likely place to put it.