I have a Humminbird which I use more as a depth finder. It's much cheaper
than many yet works great. It also gives you the water temperature and you
can buy a speedometer attachment. You can change the graphics to several
different formats. There is an elapsed time counter. It has an adjustable
depth alarm. You get reasonably good graphics of the bottom. I've had it
show depths of over 500 feet and it works well underway. It's also easy to
read in bright sun. It shows battery power and there is a self-diagnostic
feature. My only criticism is that you cannot switch to metric measurement
but that's a minor point.