30 is a lot. If you are willing to go with separate speed and depth
transducers, they sell a depth transducer
with a tilted element that will compensate for your dead rise. Your speed shouldn't be a problem.
Our old depth transducer was mounted on a 20* dead rise and we would have problems with it not giving depth readings in rough water
and not seeing as deep as the specs allow. The not seeing as deep was never an issue, but the rough water
was - we would be in narrow channels with boat
wakes and disturbed water that would prevent the depth from working properly.
Our new tilted element sounder works perfectly.