You should be able to buy a western basin map for around 10$ at most bait shops. it will have all the reefs marked with depths and your lat. And lon. Assuming you have a cumpus that should be all you need. I did it this way for years before I got a fancy GPS with navionics and lake chip. Gps can fail and it's good to know how to get around without it. Good luck and safe boating !