Snorkel designs vary based on bore diameter and length, and should be chosen based on a snorkeler’s needs and body type. Generally, the larger you are the larger the diameter of your snorkel should be, as it will allow more air to pass through.
If the bore is too wide, however, it may be more difficult to clear water from the snorkel. The width of a snorkel should not exceed 1 inch (2,5 cm).
Similarly, although longer snorkels allow a swimmer to breath air at a deeper level, they also make it more difficult to take in air and during long dives may cause buildup of stale air in the tube. Most snorkels measure between 12 and 18 inches (30-45cm), but choose one that feels comfortable for you.
Keep your hands away from Snorkels with a closing valve on top as they can cause pendulum respiration!!!
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Description of the different kinds of Snorkels: