Have used the TT40 on our offshore inline boards.It can be done,but they pull pretty hard.Had to double up our rubber bands to keep the flag up.If you look at dive chart for TT30 need 125 lead to get to 30ft deep.We use tadpoles #2 on our harnesses and if we need to go deeper put on a 3oz sinker.The 3oz sinker pulls less than TT40 and will get you down deeper than 30fow.