# Piloting A Boat

Teacher Edition Contents

Skill, Tools, & Craftsmanship

Cutting & Drying Fish
Sharpening
Nails, Pegs, & Lashings
Falling Trees &
Small-Scale Logging
Guns
Chainsaw Clutch & Chain
Ice Pick

Shelters

Wood Stoves
Wall Tents
Steambaths
Insulation & Vapor Barriers
Gas Lamps & Gas Stoves

Travel

Piloting A Boat
Boat Design
Magnetos & Spark Plugs
Carburetors
Compression
Outboard Motor Lower Unit

Outboard Motor Cooling System
Dogsleds
Snowmachine Tracks
Snowmachine Clutch
Snowshoes
Winter Trails

## Activities

1. 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 wiay he would travel if he was piloting a boat on that stretch of river.

2. 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.

3. 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.

4. 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 downstream. Do this again, releasing the same stick in several points across the river from the original release point. Measure the time it takes to reach the same downstream point. Compare their results.

One way I have done this is to tie a weight on one end of a 120’ rope. Tie a good float (5 gallon can) at the 20’ mark and another float on the other end. When this is thrown in the river, the weight holds the floats in the river, and the floats are always 100’ apart. An object can be released by the upper float and the time to the bottom float is recorded. Divide the seconds necessary to travel the 100’ into 68.2, and you will have the speed in miles per hour.

5. 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.

6. 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.

7. 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?

The biggest waves are in the middle, and the waves by the lee shore are the smallest.

8. 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?

It is measurable.

9. 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!

10. 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 boat?

It is more noticeable with a planing boat.

12. Pour water out of a teapot that has a spout. Observe. Where is the strongest flow of water? Which is stronger, gravity or momentum?

The strongest flow of water is at the bottom. Gravity is stronger than the momentum of the water coming out of the spout.

13. 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.

This will help you understand what is happening in the different bends of a river, particularly the smaller, swifter ones.

14. Design a boat that would trap air under the boat so it will travel on a cushion of air.

I built a boat with a concave bottom. It got on step instantly, and trapped air, causing the boat to skim wonderfully. However, it didn’t corner well at all, and it pounded terribly in waves.

## Student Response

1. What are the three main forces working on the water in a river?

Gravity, friction, and inertia

2. Draw a typical bend in a local river. Identify the deep and shallow places. Estimate what the current will be in 5 places on the river.

3. Why is the current next to a river bank slower than the current in the middle?

Friction with the bank.

4. 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.

5. What are the three priorities a pilot operates by when traveling upstream?

Water deep enough

Shortest distance

Least current

6. 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.

7. Draw a picture showing a boat in ground effect and another in deep water.

The boat in ground effect should be traveling higher than the one in deep water.

8. Why are the waves caused by wind larger in the middle of the river than on the sides of the river?

Waves are caused by friction between the water and the air. The current is less next to the bank. So the combined velocity of the current and wind are less against the bank than they are in the middle of the river.

9. Draw a picture of a boat that is traveling at the best angle for waves.

Bow down

10. Draw a picture of a boat that is traveling at the best angle for calm water.

Bow slightly up to keep some of the boat’s surface out of contact with the water.

11. Why do small choppy waves help a boat travel a little faster?

Air is trapped under the boat. Friction with air is less than with water.

12. What are three things to remember or do when traveling at dusk?

Don’t spoil your night vision. Have running lights. Don’t travel in the dark, even if you know the river.

## Math

1. Pete can travel 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?

\$6

2. A boat travels at 16 mph relative to the water. The river’s 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 trip?

3.14 against the current and .88 with the current. Total 4.02 hours

3. 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?

2.75 total

4. Compare the trip in current and the trip on the lake. Why do you think there is a difference?

You would think that the round trip would be the same in the current and on the lake, but the fact is, the boat is in the negative force of the river longer than it is in the positive force, so it takes longer to make a 22 mile round trip in a river than on a lake.

5. An outboard motor uses 4 gallons per hour. It can go 21 miles per hour. How many miles per gallon does it use?

5.25 mpg

6. Another outboard uses 3.2 gallons per hour, and goes 18 miles per hour. Which outboard is more economical?

5. 625 mpg

7. Which of the above outboards is more economical going upstream for 72 miles on a river with an average current of 12 miles per hour?

The one using 4 gal per hour and going 21 mph because the speed relative to the current of the faster boat is greater.

21 mph - 12 mph = 9 mph ground speed

18 mph – 12 mph = 6 mph ground speed

The slower boat is slightly more efficient in calm water, but is far less efficient against a current.