I’ve made several of the birdsmouth shaft paddles. I found a blog or something about 10 years ago where the guy mentioned how to do the birdsmouth. In his plan, the shaft was cut with a real long angle- like 75-80 degrees at the end and then that long angle face was simply epoxied right to the blade. The idea was epoxy is strong enough to hold.
I made a few real nice paddles this way. The birdsmouth shaft is really a nice shaft and ultralight and strong… and I even made them a little bit oval in shape for ergonomics … but over the years they have either started to seperate at the shaft/blade union or have separated completely already. I made 5 or 6 of them and maybe have one intact still. I wouldn’t do that.
Instead- There were other designs where a normal or bent shaft blade was made with a Tenon and the tenon is inserted and epoxied into the hollow birdsmouth shaft. I would think that would be a good design.