Measurement of marine propeller pitch
Assuming you want to carry out these measurements on a bench rather than under water ...

A common method for machine vision applications to measure heights in a cost effective manner is to use a laser line-scan to generate a line across the surface to be measured. An off-axis camera is used to view the line.



Figure 1. A 3D vision application using a laser line generator and a 2D camera.

The result is shown in Figure 1. The height of the pixel on the image relative to the base-line is proportional to the height of the object relative to the background.

As with all vision applications the system does present some difficulties in calibration and elimination of lens aberration.

A simpler method would be to make a stand for a laser distance sensor and a turntable for your propeller. I can't find any with USB interface but there are plenty of industrial types with 0 - 10 V analog out that you should be able to interface with a USB voltmeter of some sort.



Figure 2. Omron HS-ZL range of sensors is one of many.

One advantage of this is a visible spot so you know exactly where you're measuring and it's non contact so you have little mechanical work to do.

Add a protractor to your turntable for reference and make the sensor slide radially at a fixed height above the turntable. With a reference point for the tip of the prop you should be able to quickly run a series of measurements at at set of angles and radii.



Figure 3. Prop measurement system.