Nobody has solved this problem yet so maybe it's time to take another look..........
The Bottom Sensor/Collision Reference and Prevention (BS/CRAP) System:I duct taped a piece of an old busted fly rod to the very front of my yak, extending down below the depth of the fins with a comfortable margin of safety. (Lightly taped so it retains flexibility.) At the top, I stuck a golf tee through the center of a Lil Debbie miniature cherry pie pan (stiff aluminum foil - easy to work with and cherry is my favorite) and then down into the tip guide and taped it firmly to the rod. I then bent the side of the pie pan down into a notch which rests in the end of a piece of PVC pipe that runs down to the sail mount.
This is getting a bit more difficult to describe than it seemed... Let me just take you through the operation of the system, explaining the elements as I go.....
When the fly rod encounters the bottom or an obstacle, it wiggles and shakes a steel ball bearing off of the golf tee, into the pie pan and down the PVC pipe, making contact with two wires mounted in the pipe. This completes a circuit, powered by the fishfinder power supply and provides current through an ignition coil from a Model A Ford coupe to a set of contacts on the operator's seat, causing the operator to rise abruptly. With pressure thus removed from the seat, a spring-loaded cord is released which pulls two ping-pong paddles, hinged one on either side of the boat, rapidly forward, thus arresting forward momentum and immediately imparting sternway to move the boat away from the potential collision. Because the rapid rearward acceleration could cause the operator, who is already in an awkward position at this point, to suffer whiplash and/or spinal vertebrae extension, a safety device consisting of a spring-mounted length of 2x4, mounted with a pivot between the operator''s legs, is provided. To protect the operator, upon rising from the seat, the release of seat pressure also releases the restraint holding the length of 2x4, which, by spring action, rises to catch the operator, arrest his continued forward motion and return him to his seat.
Now, I realize that some minor refinements may be necessary but this system will reliably give sufficient warning so that the operator can get 'fins up' before damaging them on either the bottom or a submerged obstacle, thereby solving a major problem, the severity and extent of which can be deduced from the large number of previous posts on this topic.
And they laughed at the Wright Brothers, who only made bicycles! Hah!