I want to emphasize again that, in my opinion, there is nothing bad, wrong, immoral, unethical, or foolish in using or just preferring a double blade in a canoe for some or all purposes. It's just that I take the position that the single blade is preferable, probably because I actually define "canoeing" as controlling a canoe with a single blade (as does the USCA).
Hopefully without offense, I'd like to use two quotations from above to demonstrate why I claim that the availability of a double blade (rhetorically, crack cocaine) either deadens the motivation to continue developing single blade skills or preemtively kills off any single blade motivation at the outset.
my most efficient solo is a Phoenix, and it doesn't sit-and-switch very well because it's not that efficient of a boat - it's not meant to go straight. So if I want to make miles on deep flatwater I will often use a double to get up a lake
I will concede that most people, regardless of skill level, can probably propel a canoe a bit faster with a double blade than a single blade, at least for some period of time. But I can interpret the quoted explanation as a rationalization that deadens the motivation to continue developing single blade skills—i.e, I need to use a double blade because my canoe is too turny to use a single blade for long distances.
Well, all canoes want to turn away from the single blade forward stroke. That's the very reason to learn the the various and blendable single blade correction strokes in the first place. But what about canoes that are very turny? It doesn't matter; they all can be driven straight and controlled with practiced single blade technique.
The maximally turnable canoes are highly rockered whitewater canoes, and NO skilled whitewater canoeist uses a double blade. They go straight with goon strokes or J strokes or cross-forward strokes, depending on the situation. In hard whitewater in the turniest canoes, where constant second-to-second decisions are required, at penalty of risking one's canoe or even life, NO proficient whitewater canoeist (rarae aves aside) uses a double blade.
Therefore, a claim that a double blade is needed to chew up miles in a turnier-than-average touring canoe is, to me, mainly a rationalization, a rationalization that deadens the motivation to improve, use and become comfortable with available single blade skills.
like my friend who paddled the Allagash from the stern of a tandem boat with a double blade. He is primarily a kayaker (whitewater and and sea kayak) who gets in a canoe for wilderness trips. He is not really interested in working on his single blade technique - just getting his gear to the campsite.
Here is a clear example of how the availabiliy of the double blade preemptively kills off any initial motivation to learn single blade skills, in this case with kayaker who is quite happy to continue using his familiar double blade. The much worse case is that the same thing happens with far too many beginning canoeists. They just grab a double blade at the outset, the addiction sets in, and that's the end of it—farewell single blade; I hardly knew ye.
The extrapolation of all this is that we have a population of canoeists, at all ages and skill levels, who could significantly improve their single blade skill arsenal, even though they may be content and mostly effective with what they are doing. Worse, the population of single blading canoeists is declining, and the availability of both formal and informal single blade trainers is declining along with it.
It all bothers me. So, I choose to continue to be an advocate for the single blade, notwithstanding the truth of my first sentence in this post.
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