Oh man, I could write a book on this adventure/business. But to make it shortish… this particular boat is too small for any full size boat propellers, even trolling motor props. But it’s too large for R/C boat style propellers - plus R/C boat props are designed for higher speeds, these things run at around 1-1.4m/s. It’s right in the no-mans land of props. Plus, finding solid propulsion has actually been a much bigger problem than one would have expected. We have a few boat sizes and I’ve tried a ton of stuff, the bigger USVs can handle a trolling motor; but it’s a lot of weight for a very low power motor, plus I’ve found that they somehow don’t last very long. When I use trolling motors on actual boats I never wear them out. But, on these USVs they burn out pretty quick; it might be the slightly higher voltage, or perhaps the fact that a motor will seemingly last forever when its used 3 hours per weekend. These boats accumulate alot of hours pretty fast… clients break trolling motors constantly. I’ve tried thrusters, such as the blue robotics T200s… they’re good, reliable, but are best in ideal conditions. Any weeds or plants… even a leaf… and it’s going to jam, plus they’re not very efficient. Even had a client suck a snake into a T200, which jamed it. haha. I’ve tried alot of random stuff and variations in between as well.
Also have some customers who operate these in ultra-high salinity environments; like 30%+ salinity. Cakes onto everything. That destroys most things, so I landed on having some custom 140kv and 200kv motors made, fully potted for use in corrosive environments. I installed the motors into some pods which I tig welded myself. The small pod works great with 5x5 R/C airplane props, the mid sized one does well with the 7x7 RC airplane props and the largest 9kw one can actually use a boat prop. The welded pods are nearly impossible to break. (Nearly impossible, not actually impossible: Somewhat overweight client fell out of the back of the truck and landed on the small boat (30 inch long) crushing the motor shaft assembly. Didn’t find out how that happened until someone else at the company slipped up and told me; they were trying to warranty it) Anyway, the airplane props have 50-60% efficiency improvement over the trolling motor props.
The motors, the airplane props, the product works great. However, I’m trying to move from a lower cost “get what you pay for” type market position to one of the better providers out there, goal is to be on par with Ocean Alpha or Oceanscience Teledyne but made here in the US…so the small details are starting to count. I need to make look and actually be a well engineered product; and the R/C airplane prop bolted on isn’t ideal. That said, I may stick with it and just focus on some MJF 3D printed or CNC’d housings to make it look nicer. If someone breaks an R/C airplane propeller, it’s $4. I can just include some extras and have happy customers, plus they actually work well.
Fun project: I built this manned/unmanned 15ft catamaran from a trashed McGregor Venture. Performs great with dual 140kv potted motors, 7x7 APC airplane props. Has R/C control (great for getting on/off the trailer), confusing people at the lake… it has an autopilot with bridged LAN and LTE connectivity, can cruise at 2 m/s for about 20 hours. Adding an Ouster lidar here soon as well. I’ve had more fun with this thing than nearly any boat I’ve previously owned. Just program a looping mission, open a beer, hop in a tube or relax on the deck and enjoy.
