A Si unit can be used on the bow but unless you are moving the boat (and therefore the transducer) in the same manner as you would a transom mounted transducer; the results will differ. Try searching this and other web sites for information on bow or trolling motor mounted Si units.
Most who use an Si unit on the bow use a trolling motor mounted transducer, but you could opt to use a transom mounted transducer if you want to.