Upwind Buddy - T-200 on a surfski to power through long upwind paddling

I’ve been building a little helper to go upwind in a surfski (ocean racing kayak). I love to do downwinds in the surfski, which consists of surfing open ocean waves, and sometimes we do the “upwind” part by car, i.e. shuttle around with two cars. But sometimes I’m alone and that means paddling upwind. So I’ve 'been mulling over using a T-200 for a while. My typ solo tour is paddling ~4mi upwind, surfing 6mi downwind, and then closing the loop with 2-3mi back upwind. It’s that last section that is tough because at that time I’ve gone 1-1/2 hours at full exertion and am facing 20-30 minutes of slog.

The concept is to have a T-200 on an arm that I can lower for the upwind section and raise for going downwind. I don’t have good photos at the moment but do have a bunch of questions :sweat_smile:.

Here’s a view of the mount showing the electronics box and, to the right, the arm going down into the water with the T-200 (not visible):

Here’s a view of the arm raised up in “downwind” position:

The controls are my own design and construction. I’m using the Basic ESC and use a power monitoring chip (INA233) to monitor the battery state as well as power consumption. I use this to provide a small number of power levels where the T-200 runs at constant power irrespective of load. For the first two runs I used 66W, 120W, and 200W settings.

The battery is a 70Wh 5S1P pack (21700 cells rated at 4.2Ah and 45A continuous draw) with a cheapo BMS. I have temperature sensors for ESC, BMS, and battery and limit the power when things get too hot, which they did until I added a fan and reflective tape on the lid.

For safety I have an IMU that can detect when the surfski tips by more than 45 degrees in which case the motor turns off 'cause I’m probably going for a swim at that moment…

A big constraint for the whole shebang is weight. The surfski weighs 26lbs (it’s a middle of the road carbon-kevlar construction). My entire contraption weighs in at 5.2lbs. There’s room for improvement but not a whole lot.

I did some upwind runs in 1ft waves as well as 2ft-3ft waves (that’s overhead when seated in the surfski). In the taller stuff I normally go at 4mph or a tad more, in the smaller stuff 5mph or a bit more. (On flat no-wind I paddle at 7mph or more and downwind it’s 8mph-10mph avg and over 15mph peak)

What I’m finding is that the T-200 with my contraption kind’a hits the wall around 5mph. So going upwind I feel the power of the motor but it looses it as soon as I apply any real paddling power myself. Essentially, if I do nothing, speed is an anemic 3mph, if even that. As soon as I start paddling, even very leisurely, the motor helps me get to 5mph (@200W, a bit less at 120W) but then very quickly looses it above 5mph, e.g., I can feel the drag: it’s as if the 200W were almost entirely consumed by the resistance of the arm+thruster.

Here are some photos of the arm (and my test pool :laughing:):

So I’m wondering where to go next… I have some minor improvements I can do to the arm in terms of streamlining things, but it’s not like it’s awful right now. I’m wondering whether I’m just getting beyond the design envelope of the T-200 not in terms of power but in terms of water flow speed.

I know the T-200 can consume more than 200W but I’d have to add another 5 cells which adds almost another lb (350g just the cells) and even then the run time will barely exceed 30 minutes, which is marginally worth it.

I’ve seen the M-200 but am not sure how to design a prop and shroud, plus I may just hit the same issue.

I’d love to hear if anyone has suggestions…

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