I took the prototype to a quite location on the river to test and record a video of it in action. The location below is 5 minutes from a parking place so very accessible, has a public path running very close, the flow is slow, the banks are low and the river is 5m wide. All in all, this would be a good location if things proceed well.
A floatation test was carried out and the structure floated well, with the top vertical paddle proud of the water, but I appreciate that this version is probably 2/3 of my planned size so another floatation test will be required. I do plan to make the paddles deeper so the text will sit more proud of the water so any sinking of the paddle should be countered by this.
The video below shows the paddle in action. It turned slowly, if with a slight struggle, and the sound of the paddles slapping the water was enjoyable. I do like how the sound gives the impression of a swimmer or treading water rather than a finely tuned machine.
The main issue was the swivel hooks which once under tension by the rope, failed to turn so the rope twisted instead, which eventually led to the paddle coming to a standstill. It was obviously raising itself out of the water as well, as the rope shortened, then just sat motionless. Swivel hooks are clearly not the answer and a low friction motion is required that caters for the fact that the paddles are being pulled downstream under force. An axle through each paddle seems like an obvious solution as there would then be little sideways tension on the rotating parts. There are many options for this which will be experimented with.
The other aspect for evaluation is the font I’ve used, which is a stencil font. This was in anticipation of the letters being cut out as I’ve done here. While I like how the light shines through the letters and the water trickles through as well, the font is not sufficiently readable from a distance. Yes, the paddles will be bigger in the actual design but readability is critical. Also, this particular font has military symbolism which is distracting and irrelevant. It highlights how important the choice of font is. Engraved letters have more potential in both readability and more flexibility in terms of font choice.
An examination afterwards revealed that the wood glue had come away on one of the paddles. Wood glue did mean that no visible fixings had to be used which was a design choice so if I use glue on the actual piece it will have to be done well. Alternatively, I could use fixings that were in keeping with the rest of the structure. The wood itself did not swell or deteriorate at all which suggests that a protective coating would not be required.
Summary & next steps
Some success was had but design modifications are required. The mechanics of rotation are absolutely critical as if the paddles fail to turn it will fail as an outcome. The first drawing below has been my initial plan of how to put together 5 paddles on the river, so a single wire will be suspended at water level, each paddle will have a hollow section running through it and turn around the wire (with spacers between the paddles to keep them apart). I now appreciate how the force of the river will push the structure downstream into an arc and introduce sideways forces, increase friction and make rotation harder. It may not work and will be a lot of effect to rectify.
The second design shows an alternate way to structure the piece. A line above the surface of the water will suspend each paddle independently, hung like a puppet that is dancing on the water. The line will be easier to secure away from the bank in firmer ground, each paddle can find its own level on the water if slight slack is included in the vertical wires suspending it over the water. Also the forces are spread around more evenly, being taken by the wire across the river rather than being on the axles going through the paddles. There is also something architecturally pleasing about the second design, the design has become more visible and part of the piece, more Bauhaus. I will try to consult with an engineer or artist with experience with kinetic sculpture before proceeding but I am now favouring this second design.