Port Credit Marine Survey
& Yacht Delivery
9. Reading The Water

I have taken hundreds of photographs of currents and eddies trying to illustrate a few of the following points but I am not enough of a photographer to do a good job catching the subtleties of these with a digital camera (or any other kind), but I do have a few shots that may help along with a couple of diagrams. With some practice you should almost always be able to sight the deeper water in a current. Whether it is deep enough is another matter.

The river - Mark Twain once made a living as a Mississippi River pilot and the river pilots of today although backed up by many other methods still heavily rely on their local knowledge of a particular river and an understanding of river dynamics and how they affect underwater topography. I do not claim to be an expert in this field however I do remember high school geography classes on river formation and I am a fairly observant person. If I was really good at this I would be making $200k working 8 days a month as a river pilot but I do have a few tips. The key to successful river or inlet cruising is observation and continual learning. 

River Basics -The chart at right shows the primary factor of concern to boaters.

As a river bends, centrifugal force causes the bulk of the current to scour a deeper channel on the outside of the curve. The deeper water is almost always at the outside of a bend. The slower moving water on the inside of the curve is more easily affected by shore and bottom friction thereby causing back eddies which deposit silt on the downstream inside of the curve. This is complicated somewhat by river currents being opposed by tidal currents but is generally true.

The Yeocomico River shown below is a good example of this phenomena. The above water topography also gives clues to what may be under water. If there are high banks on one side of a river and low banks on the other, the high banks have likely been eroded by faster and therefore deeper water. The low sloping bank marked by yellow dots continues about 75 yards into the river where water is 2’ deep. The black dotted line shows the path of the boat going downstream, hard against the far high bank in 18’ of water on the outside curve.

"X" Shows position of the boat in the photo

When traveling in 12’ of water with a light chop, a still patch probably indicates a shallow spot as the friction with the shoal slows the water down. When passing close by a shallow spot, the water accelerating around it may give your boat a little push to one side. If you over correct (natural reaction) you may run into the bank.

Photo 1. Section A shows moderately rough water therefore faster and deeper. Section B shows the transition area between deep & shallow where faster and slower water fight each other. Section C shows relatively still water indicating a shallow bank.

Photo 2. Same thing but more subtle in this shot. Close observation of surface effects will go a long way to keeping you off the shoals.

Photo 3. the boat (A) had passed us 2 minutes before. His wake hitting a shallow bank (B) told us we were too far west even though well within the marked channel.

Unlike the Bahamas or the keys, until you are well into Florida the water is largely opaque and the colour of the water tells you little about what’s under the surface.

The water here was so still and opaque that without the wake of the distant boat (A) which passed us two full minutes before this shot was taken) shown hitting a shoal at point (B) we may not have seen the bank.

Occasionally you will see lightly coloured areas that appear to be sand banks but are often just light sand stirred up by currents. Slow down anyway.

Chapter 10. Marks On the Charts.

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