Design Chart for Preventing Outboard Motors From Entering Boats updated

Back in July 2016, we posted a chart for use in designing and testing outboard motors in a way to prevent them from breaking off and entering boats when striking submerged objects.

Today we are posting an updated / enhanced version of that chart. The new chart specifically identifies three more potential design / testing paths to achieve the objective.

Flip In Design Chart

Flip In Design Chart

One of the new paths focuses on designing the outboard so it will not break off and enter the boat. This can be done by making sure the skeg breaks away before the gearcase / lower unit breaks off, and by making sure the lower unit / gearcase breaks off before the swivel bracket or other mounting components break.

Another path calls for the establishment of jackplate performance standards / requirements.

Mercury outboard on jack plate. 2017 Tulsa Boat Show.

Mercury outboard on jack plate. 2017 Tulsa Boat Show.

Jack plates are regularly being inserted between the boat and the outboard with:

  1. No requirements being placed upon their structural integrity
  2. No consideration to their performance during an impact at speed
  3. No requirement for them to physically prevent the outboard from slipping up and out of the track, such as by use of a safety cable
  4. No consideration to the changes in geometry they bring that influence the forces, stresses, and strains felt by the outboard and transom

Please note we are not saying or implying that the Bob’s Machine jack plate in the photo above may not be of the highest quality and meet all needs of the application. We are saying we are not seeing any jack plate standards, requirements, or testing procedures in place to assure that is so, not only of this particular jack plate, but of all jack plates in general.

The final new path recognizes Failsafe Testing is the procedure by which to verify no parts from the outboard will enter the boat during collisions with floating or submerged objects.

The new chart has also been inserted into the original post.

Outboards breaking off and flipping into boats with their propellers still running has particularly been associated with bass boats and tournament bass boats.


  1. Khorae Olivier

    I really like how you discussed the changes in outboard motor design to keep the motor from breaking off and entering the boat. My uncle owns a small boat with an outboard motor and I’m always afraid we might capsize or get injured by the motor. Thank you for the information about how certain pieces being designed to break first to keep more dangerous ones away.

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