Temper said:
Having it break while in fast water wouldnt be good.
I wasn't thinking of a break as much as an issue of control and comfort in the hand. A paddle isn't stronger than a plank, but it much less effective and harder to use but at somepoint between a finished product and a flat piece of wood there are going to be diminishing returns.
You would want to be careful to round out the contours as if you leave it just rough cuts from the axe chopping the cracks can propogate but he does much further and produces a nicely finished product, he has the time of course, just interested in more of a survival view on the same situation.
Also, consider the extra time in making a useable paddle because the material is ill suited, taking more time sourcing it but being assured of not only a strong paddle, but one that is easy to work with is IMHO the sensible thing to do.
Of course you can't always find what you want, but in the places he was, fallen wood was anything but scarce.
Yes, how well you knew the enviroment would be an issue, plus you should be noting the river when you are working along it anyway so it isn't a blind search. You outlined exactly the reason why the decision isn't trival, every minute you spend looking for a more ideal wood you could be already working on an existing one and you have to weigh this against the extra time it takes on problematic wood.
-Cliff
