A 5, 6,
D 1, 2, 3
F = MA
Most Alaskans live or hunt on rivers. On almost every Alaskan
river there are a few people who really know how to pilot a boat.
They are river scientists who operate by basic principles the rest
of us need to learn.
Once we are able to read a book, we have the skills to read other
books. Once we are able to read a certain river, we discover that
we have the skills to read other rivers also. The signs and patterns
are common to all rivers. Repeated travel helps us learn the river
better. However, a good pilot can travel a completely strange river
and sight read it the same way you would read a new book.
With identical boats, an experienced pilot can go from one place
to another faster than an inexperienced pilot. How is this possible?
He understands the forces working for and against his boat, for
and against the river.
Three Main Forces
are three main forces working on the water in a river.
- Gravity pulling the water downward towards the sea.
The steeper the incline, the greater the velocity of the water.
- Momentum of the water goes around a bend. Inertia causes
most of the water to go to the outside of the bends.
- Friction with banks and river bottom.
The river channel is often deeper on the outside of bends.
On the inside of the bends, the current is slack.
Look at the following drawings of a typical bend in a swift river.
The two forces, gravity and inertia, are sometimes working together
and sometimes competing. In the first drawing, the slope of the
river isnt too steep, so inertia carries most of the water
to the outside of the bend, creating a swift deep channel there.
In the second drawing, the water is flowing down a steep slope.
Inertia is working to carry water to the outside of the bend, but
the drop is so great, gravity forces the water to fall to the shortest
distance which is on the inside of the bend. Gravity overrides inertia.
If the pilot understands these forces and how they interact, he
can understand almost all river situations in Alaska.
When the current slows, and its ability to carry sediment also
decreases, an island or sandbar forms in the middle of the river.
The channel goes to either or both sides of the island.
Other islands are formed when the river channel erodes its way
through the banks, separating large land segments.
As the pilot looks at the river while going upstream, the priorities
- Water deep enough for his boat and motor
- Shortest distance
- The least resistance from the current
The pilot looks at the stretch of water in front of the boat.
Math and science blur together as decisions are continually made
figuring the best path to travel. Where are the snags, eddies, slack
current, straightest paths, and shallowest waters?
The Current Varies
The current is slower close to the riverbank than in the middle
of the river. Friction with the riverbank and bottom of the river
in the shallow places slows the current. If you measure the current
across a river, you will find that it varies tremendously from place
Salmon are aware of this and travel the path of least resistance
in their journey upstream. They prefer the shallows at night because
they feel safe, but swim on the bottom in the middle of the river
during daylight in order to avoid detection.
The current might be six miles per hour (mph) in the middle, eight
mph five feet from the cutbank, two to three mph right against the
bank, two mph on the sandbar side of the river in the shallow places,
and minus two mph in the eddy.
A good river pilot takes advantage of all slack current. Against
a cutbank, the water swirls backwards due to friction with the bank.
Sometimes the stumps and brush keep a good pilot away from those
back currents, but traveling close to the cutbank adds several miles
per hour to the boats speed as it goes upstream.
The water swirls backwards in eddies. The current is actually
going in the opposite direction from the rest of the river. Good
pilots search for eddies.
Fish rest in eddies and use the current to assist in the upstream
effort. The opposing currents hold a net in perfect position to
catch the fish as they head upstream. Because of this, good pilots
watch out for nets as they travel the eddies.
Rocks and Snags
The current swirls in low pressure areas behind rocks and snags.
A good pilot enters a place with slack current behind a rock, gains
speed, and shoots out before crashing into the rock.
In very shallow water, an experienced pilot knows that the water
is deeper right beside snags and rocks, as the water intended for
the snag is diverted aside, creating a mini-channel deep enough
for the boat.
A pilot must decide which path upriver gives the least resistance.
Obviously it isnt worth crossing a wide river to get a little
help from an eddy. There is a constant give and take in this regard,
constant decision-making by the pilot.
A boat lifts when traveling in shallow water. The pilot hears
the motor speed up as the boat lifts. The shallower the water is,
the more lift there is, but there is also a greater the chance of
hitting bottom. This is why the pilot pays close attention to the
sound of the motor.
When the boat is in deep water, the water is pushed down and away
from the bottom of the boat. The boat sinks to some extent.
In shallow water, the water is pushed downward and away from the
bottom of the boat, but it cannot move downward because the bottom
of the river is solid. The boat pushes down. The water and bottom
Some waves are caused by the current moving around underwater
waves are created by wind blowing over the waters surface.
When the current and wind are moving in the same direction, the
waves are small. When the current and waves go against each other,
the combined velocities can be great, causing large waves. This
explains why some sections in a river can have no waves, and another
section of the same bend can have whitecaps. On one section of the
river, the wind blows directly against the current. On another section
it is crosswise. In another section, the wind is blowing with the
This is particularly distressing when rafting logs or firewood.
The pilot feels totally safe on one section of the river, rounds
a bend, and gets into huge whitecaps that threaten the safety of
the boat and raft.
Wind generated waves are smaller against the bank. Why is this?
The current against the bank is slower than it is in the middle
of the river, and therefore the combined velocities of the wind
and water is less. The waves in the middle are bigger because the
combined velocities of the unobstructed wind and current going against
each other are greater.
boats have ridges
that trap air under the boat
Another consideration of piloting a boat concerns the friction
of the boat against the water. The more surface that is in contact
with the water, the more friction there is.
A boat that has the bow too low will have a lot of surface to
A boat that has the bow too high will plow the water, and pound
in the waves. A good pilot adjusts the angle of the boat by shifting
the load and changing the tilt on the engine.
trap air under the boat. The air, once under the boat, becomes flat
bubbles that greatly reduce the friction with the water. This effect
is very noticeable when coming from a small creek onto a larger
river on a windy day. The boat accelerates when it hits the small
choppy waves and breaks free from the drag of smooth water. The
boat decelerates considerably when it comes from a river with small
choppy waves and enters a smooth creek.
Reading the River
It is very hard to read a river when it is windy. Whatever sign
might be presented by the snags and rocks is masked by the waves
from the wind. It is like trying to read a book in the dark.
It is also very hard to read a river when there is little or no
current. Some of my greatest disasters have been on windy days or
in dead water.
When there is adequate current, shallows, rocks, and stumps all
give sign of their presence and are easy to read.
Going upstream in a swift river is easy because all the obstacles
are obvious and the boat is traveling slowly against the current
allowing time to look and think.
Going downstream is another story. The rocks and other obstacles
are covered with water. The boat is going so fast there is little
reaction time. Going downstream is more difficult and dangerous.
Years ago, people pulled their boats up the river. The tops of
the banks were cleared of brush. They were lined with hard packed
trails. Even today, people who break down while downriver from their
village sometimes line up to get home. With one rope, the boat is
very hard to steer. Two ropes easily steer the boat in and out around
snags and obstacles.
Travel at Dusk
Good pilots learn to protect their night vision, as it is quite
easy to read the channel in twilight after the sun has gone down.
The glare from the surface of the water highlights all of the signs
the pilot is looking for. It takes most people fifteen to twenty
minutes to develop night vision.
Artificial lights are a hindrance unless they are extremely bright.
The glare from the water makes visibility worse and ruins night
vision. It is important to have running lights, not for the pilots
vision, but so boats will not collide.
Years ago a boatload of people ran over a swimming moose at night.
Five people drowned. Travel in full darkness is not wise at all.
- Watch a video about a swift river or go to a swift section
of a local river. Discuss the route you would go to take advantage
of all the areas with slack current. Draw a map of a section of
that river. Ask one of the elders in your village which way they
would travel if they were piloting a boat on that stretch of river.
- Imagine that you are a salmon going upstream in that river.
Color the path you would swim during the day in blue. Color the
path you would swim at night in black.
- Draw a typical stretch of river in your location, or where
you go to hunt. In your imagination, estimate the current in different
parts of the river.
- If it is possible, measure the current in a cross section of
that river. If you have no way to accurately measure, release
a stick on the sandbar side, timing how long it takes to pass
a certain point 100 feet downstream. Do this again, releasing
the same stick in several points across the river from the original
release point. Measure the seconds it takes to go 100 feet. Compare
their results. Tell students to divide the number 68 by the number
of seconds it takes a stick to float 100 feet. The result is miles
- At each of the above points measure the depth of the river.
The easiest way might be to put a weight on a string, putting
a knot at every foot in a string. Counting the knots as they slip
through the fingers will give the depth in feet.
- Observe islands in your river. Do you think the river widened,
depositing the islands, or did the island occur because the river
cut a new channel? Either might be the case.
- The next time there are waves on your river caused by wind,
note the bends they occur on, the direction of the wind, and the
relationship of the wind to the current. Where are the biggest
waves? Are the waves as large by the shore?
- If possible, drive the boat from a river where there are choppy
waves into a creek where the water is flat. Can you feel the difference
in the speed of the boat?
- While piloting a boat in deep water, set the throttle so the
boat is barely on step. Cruise to the sandbar side of the river
and notice the increase in speed of the boat and motor. Be careful
not to hit bottom!
- Listen and watch closely the next time you are in a boat. Hum
in tune with the motor. Does the pitch of the motor get higher
when you pass through shallow water? In and out of eddies? Do
you think this effect is more noticeable with a planing or displacement
- Ask the people in your village about the dangerous places on
your local rivers. What stories can they tell about close encounters?
- Pour water out of a teapot that has a spout. Observe. Where
is the strongest flow of water? Which is stronger, gravity or
- Put a piece of plywood on a slant. Pour water from the teapot
across the top end. Observe and mark where most of the water flows.
Tilt the plywood up and down changing the angle, again observing
and marking the greater flow of water. At what angle does gravity
exert the greater force, pulling the flow of water downward instead
of yielding to momentum? Try to keep the water flow and pressure
the same while changing the angle.
- Design a boat that would trap air under the boat so it will
travel on a cushion of air.
Momentum is strong. Water pours out
Gravity is stronger pulling
water down more
What are the three main forces working on the water in a river?
- Draw a typical bend in a local river. Identify the deep and
shallow places. Estimate what the current will be in five places
on the river.
- Why is the current next to a river bank slower than the current
in the middle?
- In the picture to the right, tell how fast you think the water
might be going in the different places circled if the current
in the middle is 6 mph.
- What are the three priorities a pilot operates by when traveling
- Draw a picture of a typical bend in a river. Draw a big rock
in the middle of the river. Draw the path a boat might take.
- Draw a picture showing a boat in ground effect and another
in deep water.
- Why are the waves caused by wind larger in the middle of the
river than on the sides of the river?
- Draw a picture of a boat that is traveling at the best angle
- Draw a picture of a boat that is traveling at the best angle
for calm water.
- Why do small choppy waves help a boat travel a little faster?
- What are three things to remember or do when traveling at dusk?
- Pete can travel the from the store to his cabin in 3.5 hours.
His son can make the same trip in 4 hours. If gas is $3 per gallon
and the motor uses 4 gallons per hour, how much more does it cost
his son to make the same trip?
- A boat travels at 16 mph relative to the water. The rivers
current averages 9 mph. How long will it take to make a round
trip of 22 miles each way? What is the total time of the 44 mile
- A boat travels at 16 mph. How long will it take to make a round
trip of 22 miles each way across a lake? What is the total time
of the 44 mile trip?
- Compare the trip in current and the trip on the lake. Why do
you think there is a difference?
- An outboard motor uses 4 gallons per hour. It can go 21 miles
per hour. How many miles per gallon does it use?
- Another outboard uses 3.2 gallons per hour, and goes 18 miles
per hour. Which outboard is more economical?
- Which of the above outboards is more economical going upstream
for 72 miles on a river with an average current of 12 miles per