Propeller Advance Ratio J

Dimensionless speed ratio J = V_A / (n·D) - the horizontal axis of every propeller open-water chart.

Propulsion

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Formula, assumptions, and limits

J = \frac{V_A}{n \cdot D}

Symbol	Meaning	Unit
$V_A$	Advance velocity at propeller disk	m/s
$n$	Shaft revolutions per second	rev/s
$D$	Propeller diameter	m
$J$	Advance ratio

Source: SNAME PNA Vol II Ch.6; Carlton - Marine Propellers and Propulsion

Dimensionless speed ratio J = V_A / (n\u00b7D) - the horizontal axis of every propeller open-water chart.