Quote:
Originally Posted by ApS
It's not a theory, and it can be measured—but first—think of it this way:
If 100 cubic yards of "fill" were added to the channel bottom, would the speed of the current change?
Now take the displacement of all the boats in the channel, and think of that as "fill"—but at the top.
The more engines a boat has—the deeper the "V" of the hull—all that displacement has to be "displaced" to somewhere else—effectively, narrowing the channel.
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To measure the effect of your boat, put your GPS in a Styrofoam cooler, and float that GPS down a measured course—say, a hundred feet. Record the speed of the current. Then anchor your 26-footer in the channel, and measure the current with the same floating GPS device. You can expect the GPS to record a faster speed. Apply that reasoning to a large number of boats: that they're in motion is insignificant.
If the channel were narrow enough, you can see even a canoe can affect current speed. (And why I advocate starting one's boating-experience with a small boat—even building one—not jumping in with an over-sized boat).
It would, but not to the same measure as a 40-foot rowing scull. It's displacement that counts—not length. |
The law of physics is absolute Aps, to a degree anyway, your post made it seem like there would be a significant change in velocity in the channel based on the boats in it, I say that the change is so small for the typical traffic in the channel, even on a busy day, your chosen measurement instrument, a gps, would not detect it.
The 100 yards of fill you mentioned would be fixed in place, and cause a significant disruption of the water flow, depending on how it was placed, it could increase the current speed, really not pertinent to your theory..... A 40 foot boat floating with or against the current would cause a change so small, it would be undetectable to a person on a boat. Remember, we are talking millions of pounds of water moving versus a 10 or 15 thousand pound boat. So while in theory your assumption is correct, the current speed is affected by the boats in the current, in reality, in the Weirs channel, even on a busy day, the effect is pretty much undetectable. Moreover you have boats moving in both directions, which would tend to negate the effect.