To set my depth I just take a sinker that I know will sink the float that I intend to use,and make a rough guess at the depth of the water.I do not have my hook tied on at this stage. I cast to the area I want to fish and simply see if the float has been dragged under,(too deep,in that case reel in and move the stopknot up the line),or if the float lies flat,(too shallow,reel in and move the knot down the line). Once the float is sitting perfectly just under the surface,I have the water depth. I now need to allow for the kelp which is about 3 to 4 feet high off the bottom,and I want to use an 18 inch snood,so I reel in and move the stopknot 5 foot 6 down the mainline which now means when I cast my bait out,I am just sitting on top of the kelp fronds,and attach the appropiate sinker to cock the float. A second stop knot tied just above the weight will prevent the loss of the float if the hook catches the kelp. As the tide rises or falls adjust periodically to suit.