Propellers

The relationship between cross-flow at a waterjet inlet and delivered thrust is not
fully understood. A direct thrust measurement system was designed for a waterjet
propelled, free running USV. To induce sway velocity at the waterjet inlet, which was
considered equivalent to the cross flow, circles of varying radii were performed at
Reynolds Numbers between 3.48 x 106 and 8.7 x 106 and radii from 2.7 to 6.3 boat
lengths. Sway velocities were less than twenty percent of mean forward speed with slip
angles that were less than 20°. Thrust Loading Coefficients were compared to sway as
a percent of forward speed. In small radius turns, no relationship was seen, while in
larger radius turns, peaks of sway velocity corresponded with drops in thrust, but this
was determined to be caused by reduced vehicle yaw in these intervals . Decoupling of
thrust and yaw rate is recommended for future research.

Designing a propeller for optimum performance on a human powered underwater vehicle presents a significant engineering challenge. The propeller must be highly efficient to utilize the inherently low power output of a human. Also, the propeller must be correctly matched to the maximum sustainable torque of the propulsor. This thesis experimentally investigates a minimum induced loss propeller design program and its application to a human powered underwater vehicle. The design program is based on the vortex theory of propellers. The work includes experimental measurements of the velocity and rotational rate of three propellers designed with the minimum induced loss propeller design program. This positively verifies the output of the design algorithm. Also, the research, through the use of an underwater ergometer, determines the maximum power and torque sustainable by a human pedaling underwater. Final results of the research show that the design algorithm overestimates the blade section angles by 25% because the design program neglects the influence of the wake of the vehicle.

The use of surface piercing propellers (SPPs) shows promise for high speed operation by virtually eliminating appendage drag, which can be as much as 30 percent of the total drag on a vehicle at high speeds. The scarcity of available systematic test data has made reliable performance prediction difficult. The primary objective of this research is to obtain experimental performance prediction data that can be used in SPP design. In a series of open water tests in a non-pressurized towing tank facility, force transducer measurements were taken at tip immersion ratios from 0.5 to .33, yaw angles from 0° to 30° and inclination angles from 0° to 15° over a range of advance ratios from 0.8 to 1.8. Force transducer measurements were taken for thrust, torque, side forces and moments. These results will help develop a baseline for the verification of SPP performance prediction.