Why is the length and diameter of a snorkel limited?

Question

Why is the length and diameter of a snorkel limited?

Answer 1

Length is limited due to the dead air space.  When you exhale, the oxygen content of the exhale air is lower and is referred to as dead air.  This dead air is in the tube of snorkel.  When you inhale again, the first part of the breathe would be only dead air.  If you had a long snorkel, you'd never get fresh air on an inhale.

I think the diameter is only limited on the small side.  Too small of a diameter and you won't be able to inhale enough air.

On the large side of the diameter discussion, I think it is a factor of a large diameter would be harder to clear if water entered the snorkle.  Also, a large diameter snorkle would be limited by the size of the persons mouth.