The shown area causes turbulence on the surface. The BB paddle is much quieter (also much heavier).
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Tony, that part of a Zav where the shaft transitions into the blade is sort of fat, and it's always been unclear to me whether I should consider it part of the shaft or blade. I don't need to sneak up in perfect silence very often, but if that bent Zav were my only paddle, I would simply not bury that fat transitional area in the water. If I had my straight Zav, I would palm roll it and do a full in-water slice return without burying that fat transition area.
You haven't commented on the palm rolling suggestions, which makes me suspect you don't palm roll. In my experience, most flatwater paddlers with straight paddles don't palm roll simply because they haven't been exposed to it. I didn't start using it regularly until 2009 when I was about 64 and Marc Orstein urged it upon me. I knew how to do it, but didn't use it in whitewater at all, where it's not really apt, and I didn't use it with any regularity in flatwater because I had mainly been using bent shaft paddles in flatwater since 1984. Even my "straight" flatwater paddle for 25 years was actually an asymmetrical 2.5° Lutra S curve blade, which is not really amenable to palm rolls.
If you have a straight, symmetrical-faced paddle, try teaching yourself palm rolls for the Indian and box strokes. They are not only quiet, but fun, and a nice change of pace from the J and other correction strokes.