How long is a short blast and how long is a prolonged blast?
Short about 1 second, prolonged 4 to 6 seconds.
Rule 32 (b), (c).
Part of the convention Sound and light signals
A whistle is any sound-signalling appliance capable of producing the prescribed blasts. A short blast lasts about 1 second. A prolonged blast lasts from 4 to 6 seconds.
At sea it looks like this
Five short blasts means five crisp one-second blasts, not five long ones: long ones would say something else entirely.
The rule says«The term “short blast” means a blast of about one second's duration. The term “prolonged blast” means a blast of from four to six seconds' duration».
Sound signals
Sound signals
≈1 s / 4-6 sShort and prolonged blast