I am looking in getting a fish finder.  I dont own a boat but i rent one at local lakes all the time.  I strap my electric motor on it and go out.  Any suggestions on a fish finder that would easily be portable i could take out with me.  I was thinking that hummingbrd smartcast but have heard mixed reviews.  Are there any other suggestions on one or should i just get the smartcast RF20 or 15 i think it is.

I wouldn't recommend the SmartCast. It's a neat gadget, and useful in a very limited way -like checking depth, finding large isolated cover pieces, and spotting large fish away from cover or bottom.

It has a "fish ID" feature that shows "fish" as a fish symbol, which may be effective at picking up large fish away from bottom amongst sparse vegetation, but it also marks any hard object such as rocks and wood as "fish".

The problem is it doesn't have a grayline feature, which would allow for some target separation and relative hardness differences.

Since you are in a boat the size of the unit is not such an issue, so any compact unit with as much pixels as you can afford would be better.