The Installation Guide recommends placing the thruster as far forward as possible for leverage and as deep as possible (at least 1x the tunnel diameter below the waterline) to prevent air suction.
Regular upkeep is the only way to avoid the $10,000–$15,000 cost of a full unit replacement. QL Bow thrusters - moegster.no
The QL range was designed for vessels from 22 to 75 feet. Common models listed in the QL Thruster Programme include: