Finally got a weekend to work on the first prototype for a scupper-based Torqeedo mount. It took a few hours to build (more time to shop for the parts
), and I tried it today with good results.
The idea was to have a mount that can be close to a front-riding position, but also usable on the back. That called for the scuppers to be used. The Hollaender system for pipe structures makes it trivial to build, very light and rock-solid. It could also be done using PVC (with some trickery in the scupper-inserted section to maximize the area filled by the pipes.
The hardest parts were:
* To eliminate rotation of the motor shaft without resourcing to a fixed (as in "glued") attachment: in my previous attempt using Tom Kirkman's method I wasn't able to fix the shaft reliably using the pipe conduits for long (after a while, the vibration loosened the grip). So I used 30 mm aluminum shaft collars. In this first prototype I used two collars on top, the lower one drilled to pass a couple nails into the PVC holder to eliminate rotation, the other (on top) to keep the nails in place. My next prototype will tap the shaft collar and the PVC container so that a bolt can be used instead (and no second collar). For now, the chosen design keeps the shaft solidly rotation-free.
* To produce a good fit between the vertical pipes and the scuppers. The scuppers have a diameter that is (a) not uniform and (b) not-standard, which means hard to perfectly fit for any specific pipe size (PVC or Hollaender). I could have used other pipes that fit better, but at the extra complication of drilling the fixtures out of blocks (nylon, wood, etc.) as opposed to using pre-fit fixtures. Not interested in the extra work.
The system as built is
* Very light
* Very easily taken apart using a simple hex key
* Able to be fit onto the boat in less than a minute
* Usable as-is on any of the two scupper sets, and easy to lift with one hand from any of them on approach to the beach
* Very adaptable in terms of motor depth: I just need to loosen two hex set bolts to slide the motor up or down as needed (same hex key as to loosen the structure
)
* Totally reversible from side to side in about a minute.
Enhancements planned for prototype 2 (very, very simple to build now that the measurements are perfectly understood):
* Using nylon 5/16-18 bolts instead of the Hollaender system set screws. This requires tapping the pipes, and continuing the thread from the fixtures into the pipe, which takes a little extra time. The nylon bolts provide safety as they will brake on impact of the motor agains rocks or bottom, letting the axis rotate circularly towards the back and the motor to come up naturally as a result (just as the threaded rod I used in the TK design). Right now, it is very simple to loosen the set screw on the elbow outside the boat, but time may not be available to do so: a nylon one would simply just break and let the motor up.
* Using bolts through the collar shaft and into the PVC tube containing the shaft (no nails, no second collar)
* Possibly adding a "tiller" to rotate the motor on its axis after removing the bolts in the point above (I am not sure there is a real benefit to that, the kayak has a rudder). Notice that the upper and lower shaft collars transform the PVC "tee" in which the shaft is centered into a bushing of sorts.
* Possibly adding the aluminum "wing". I have not observed "cavitation" (sorry, I use the term loosely, because it has been used already in the thread), so I don't know if i will need to. I would prefer to avoid it because it would sacrifice the ability to move the motor up and down as needed) (The area below the PVC tee is submerged and it would change in length).
After trying it today, I am optimistic about the design. I will update when the second version is finished. And thanks for this very useful thread, and all the information shared in it.