Just purchased a Helix 10 Mega Chirp SI GPS. In reading and watching the enclosed video it states you have to have a clean site line from left to right for your SI to work properly. How much clearance between the lower unit of your OB and the transom of you boat do you need? the entire length of the transducer? If that is the case I fear I may need to make some boat modifications to accommodate the transducer. However what are my options? Any thoughts, ideas or experience would be greatly appreciated.