16 inchs
On a large charter boat with an experienced captain, yes.
Less and less sunlight is getting through the water the deeper you get. As such it does not receive the warming effects of the upper water levels. Also the heat from beneath the crust is not strong...
No. They are not real so you can't see something that is not real.
You prolly shouldn't go deeper then you do and use more lube maybe. It's possible you bump into the cervix.