Hi Amy
I have just placed an order for a new Northcraft 6.3 RIB, which should be ready in a couple of months, so it's good to meet another 'Northcrafter' on here! I would be very interested to hear about your set up - engine and prop details etc., and what you think of the boat - handling, build quality and how it's standing up to wear and tear.
As for the depth sounder, if you just want to know what's under the boat then I agree with MikeCC - fit a fishfinder. This seems like a pretty good deal (but there are lots of other options on the Cactus site):
http://www.cactusnav.com/product_inf...roducts_id=509
Regards
David