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It’s not in
our nature to look backwards. Whether we’re walking or driving,
our focus is naturally directed forward. This does have its disadvantages,
however, not the least of which is a blissful unawareness of any problems
we may have left in our path.
That characteristic
takes on special import when we’re driving our boats, because
unlike Reeboks and Volvos, boats create a palpable disturbance that
if of sufficient size can cause substantial damage. The formal name
for this is, of course, wake, and today a lot of boaters and landlubbers
are concerned with it. In more and more places, governments are passing
laws designed to essentially ban wakes through the imposition of speed
limits. This movement will have a direct affect on how you will pursue
your favorite pastime in the future.
Technically, a wake
is any disturbance caused by an object that displaces water. In its
smallest and most innocuous form, a wake is the ripple formed by tossing
a pebble into a pond. That is obviously not the kind that’;s causing
speed limit signs to proliferate along waterways at about the same rate
as Zebra mussels.
Wake is a function
of an object’s mass, shape, and velocity. Without getting wrapped
up in hydrodynamic theory and arcane formulae, a vessel’s waterline
length—from where the bow enters the water to where the stern
leaves the water—dictates its displacement speed, which is how
fast it can travel through the water without causing a big wave. To
go faster than displacement speed, a hull must plane—climb on
top of the water and glide over it, instead of plow through it.
All this is relevant
because of the findings of a study conducted by the Stevens Institute
of Technology of Hoboken, New Jersey, on wave patterns in New York Harbor
and the damage they cause both shoreside and waterborne property. After
placing sensors on the harbor bottom, Stevens scientists determined
that the harbor’s wave patterns were generated not by tides and
currents but by vessel traffic, mainly ferries, which have proliferated
in recent years. They set about finding ways to minimize the size and
number of the waves.
What’s surprising
is that after all their research, the Stevens scientists did not recommend
the imposition of speed limits. In fact, Michael S. Bruno, director
of Stevens’ Davidson Laboratory, told The New York Times, “Just
throwing a speed limit on the harbor might be the worst thing you could
do.” He pointed out that ferries generate most of their wake not
at low or high speeds, but in the transition zone between the two—when
the vessels are between displacement and planing modes. The same is
true of pleasureboats.
This is something most
boaters have known all along. You need only look aft while on a high-speed
planing boat to see that the wake is small—not as small as when
the boat is at displacement speeds, but much smaller than when she’s
trying to get over the hump. This simple conclusion might be something
those government agencies should take into account the next time they
decide to attack a wake problem by simply posting a 9-mph speed limit.
It might lessen the wake for some vessels, but for others it just might
be the point at which they generate their largest wake—and the most
damage.
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