This solenoid should do the job, but you need a 12V power supply and use the Arduino as a relay.
https://www.aliexpress.com/item/P13-27-13mm-12V-Holding-Lifting-Magnet-Electromagnet-Lift-1Kg-Solenoid-2W/32804819433.html
You could of course wind your own, you can find the calculations here...
I suggest the following:
1) Carry additional weight on the OC2 so that all paddlers 'pull' the same weight.
2) Don't do the test when it is windy, but if there is light wind, just sit on the water for say 30sec and see how much you drift. Add/deduct this from the result.
The data will give you a...