Paul I have Lowrance Gen 2 which you've seen on the boat ,the down imaging is good but you have to do it at a very slow speed about 3 knts to get a clear sounding.Havent used mine much but it is impressive when I do,you can see individual branches of weed etc.
If he looks on there web site or utube he will see it in action
I can run my head unit at home if u want to have a play
Nige