75' of anchor line is kinda short, depends on where and how you anchor, a good rule of thumb is 3 times depth to the length of line. Thats what I use over sand or mud, over rock you could probably double the line. So 75' would be good for 25' depth, also, always good to have a quick release method to the boat. Another thing I do when diving off my kayak is let my float and 100' of line go with the current. Swim against the current and pay close attention to where my float is. That way if I get fatigued, I can pull myself back to my kayak. If a current starts rippin, you'll be in for one hell of a swim.
Congrats on gettin a boat to utilize, take your time and practice patience when learning, dont rush to learn and dont let your boat give you a baptism by fire. Lookin forward to reading about your progress. You'll soon find too that shore dives are so much more less complicated and easy compared to all the responsibility of having a boat. Listen to Fins if he helps you. Your in for alot of work as well as fun. JTF
I dont exactly understand why I need 2/3rd more line then what the depth is is it just for the current thing? or would it be a bad idea to use it in 35-45 feet of water?