by: Philip Thompson

Recently I worked with the manufacturer of the Motorguide trolling motors, adapted to the Harbor 20, to find solutions to what seemed like an unusually high number of problems. Below is the report prepared by them and a summary by me of the issues and what we should be doing to reduce the problems.

Firstly, these Motorguide motors were adapted by W. D. Schock to the Harbor 20 by removing the motor from the factory supplied shaft and screwing it to a stainless steel arm bracket that hinges into the aft compartment on the Harbor 20. They were not designed to drive a boat like a Harbor 20 at max throttle for extended periods, it was for slow speed trolling at low rev’s. This adaption is the root of many of the problems but they can be managed.

The majority of breakdowns are due to water intrusion into the motor. There are several ways this appears to be occurring.

  • Through the screw joint of the motor to the stainless steel arm bracket. Either this is not being sealed correctly when assembled or when paint on the motor portion breaks down, allowing corrosion to occur. Water wicks its way down the thread into the motor.


  • For some boats, through a hole in the top of the stainless steel arm bracket that feeds the electrical leads down to the motor. At some point, a rubber bushing was added to this hole to reduce the likely hood of this occurring. Many older boats are wide open. Extensive hosing in this compartment might have led to water intrusion. Also, possibly salt air.


  • Through either of two potential parts of the “T” intersection of the stainless steel arm bracket. 1) On some boats, where the electrical wires feed into the end of the short stainless steel cross arm that the long Stainless Steel motor arm rotates around or 2) Through either end of the coupler fitting on the end of the long arm for boats where the electrical wires enter at the top of the long arm. For # 1, water wicks along inside the tube until reaching the “T” joint and open end of the long arm and runs down inside the long arm. For #2, the water wicks into either side of the coupler until it enters the open end of the long arm and runs down it.


  • Through either of the two joints between where the three parts of the motor body are bolted together. Both joints have rubber “o”ring seals. Most motors I see have corrosion to the motor body. This either occurs with time or due to the external paint being chipped off while rotating the motor into the harbor. The corrosion eventually gets to the rubber “o” ring seals and breaks down the waterproof joint.


  • These motors are designed to run al low throttle to move a boat slowly while fishing. It is believed that running them at full throttle for an extended period (20 – 30 minutes) pushing a Harbor 20 may overheat the motor. If this occurs, the rubber seals may breakdown allowing water to enter.



With these areas of concern now identified, I will be working to find solutions or better solutions to eliminate or reduce this occurring. In the meantime, here are some recommendations… (click here to view the full article and photos in PDF)

One comment

  • Ross Watanabe

    Thanks Philip!!!

    Excellent article long overdue, as the motor is the only disappointing thing about the boat.

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