Close to where I live is a cenote. From ground level to the water below is 18 meters. The depth of the cenote is 160 meters. So hopefully I won’t hit bottom. My calculus days have been forgotten. I would like some answers, so I have fewer unknowns before attempting this action. I am 65 years old, a good swimmer and weigh 120 Kilograms. If some of you math/physics folks could help with these questions, I would appreciate it.
 How is the best way to enter the water? I am not planning on a swan dive. Going to enter feet first. I have done some jumps, and when I entered with feet flat it stung. So, I am thinking to point my toes downward. Or, would it be better to wear shoes?
1a. Should my arms be straight up over my head? I am thinking that a smooth entry would be better, right?
 How many seconds will I be flying? Before entering the water?
2a. Speed upon impact?

What would be the maximum depth of my penetration in the water?

Is there other information I should know?
For math folks and others, this question.
 Is this a really dumb thing to attempt?
Thank you for your time and your calculations.