I agree with Woodster
Ken
Having an easy to use device made for the application you are using it is the best way to go (it will cost a bit more however.) At least look into it. I have been happy with ours.take a look at the Garmin 400 series chartplotters they are pretty good for what they are and you can usually find them on sale and if you buy one of any kind at all mind you they will be obsolete just after you mount it in your boat..... via superseded by a newer model
Ken