A Plague on Words: Laboring Oar

To “take the laboring oar” still seems to be a widely used expression.  Its meaning is fairly obvious, as the derivative word “laboring” provides a generous hint at the intended object:  to say “I’ll take the laboring oar” means “I’ll do most of the work.”  Then again, does it mean, “I’ll do all of the work”?  Already there seems a latent ambiguity, perhaps making the expression only marginally better than saying “I’ll do the lion’s share of the work," a desperately ambiguous and nonsensical expression.

Still, the expression isn’t all that strange until you take a look at the Webster’s Online Dictionary entry:

The oar which requires most strength and exertion; often used figuratively; as, to have, or pull, the laboring oar in some difficult undertaking.

It hardly seems intuitive, upon hearing the expression, that we are meant to start thinking about oars and boats and rowing and so forth.  But even once we’ve got all that mental equipment laid out, the question then arises:  What sort of oar is it that requires more “strength and exertion” than another?   Once we are taking the matter quite seriously, that is, are we to suppose the object of this particular oar is to take the expedition in a circle?  If the oar on one side is diligently laboring while the other idly flops around in the water, I don’t know what other conclusion can be drawn.  Unless we’re talking about a kayak paddle.  Is that it?  Am I only betraying my paucity of knowledge of matters nautical?

And: “often used figuratively”?  Are there such folks that do much talking about actual laboring oars, and actual non-laboring, idly-flopping oars?  If so, I find their ideas intriguing, and would like to subscribe to their newsletter.