@Skidder I watched those technique videos on Friday. I've watched a few videos on technique but this was the first one which suggested imagining putting the paddle in mud and then using the core to pull yourself forward rather than using your arms to pull the paddle back to you.
Saturday i got out and did around 4 miles, my core has been killing over the weekend from it! I definitely tired in the last mile and my technique suffered. Not helped my a fairly heavy headwind. At one point an old man on the side was stopped to chat to me and i was being blown backwards and had to paddle just to stay level with him. That really tested my balance as it's much harder on this board to balance without having that forward momentum.
Shows i have a long way to go before i can think about 4-5hr paddles!
Good work, I've really been trying to work on the hip hinge and core.
Had a similar experience to you on Sat. Did about 13-14k total. Downriver then back up. After rain got the flow up end of last week and with a headwind way back was sloooow.