How To Build a Paddleboat

Paddleboats are fun, but they are challenging to build. It will take longer to make a paddleboat too. Before you commit to making one, try making a paddle wheel. If it works out well, then proceed to build the paddle wheel housing and finally the rest.

The Paddle Wheel

A paddle wheel is a simple device. It is easiest to construct one with an even number of veins or blades sandwiched between two disks. A dowel is used as the hub.

Improvements on the paddle wheel include making triangular slits near the disk centers to let air escape through the housing vent. Viscous water drag is also reduced by the slits when the paddle is spinning. The length of these slits outward from the hub may only be a quarter inch.

When wood is used, the disks can be replaced by spanners. Spanners are wood strips that hold the veins apart. Viewed from the side, they form a hexagon if six veins are used, an octagon if eight are used. The wood grain runs the length of each spanner for strength. The paddle wheel instructions given here use spanners.

Though a paddle wheel can be built out of stiff plastic (from an ice-cream container lid or similar) these instructions will describe the construction using a thin light wood like 3/32 inch thick balsa. Some regulations may allow only wood and paper materials to be used for non-ornamental boat parts. The paddleboat described here is probably not the "best" possible design. It is meant as a starting point for your own design.

1. Trace 12 spanners. Each has a 3/4 inch top centered over a 3/8 inch bottom. Each is 3/8 inch tall. The sides slope at 30 degrees.
2. Cut the spanners out using a sharp exacto knife.
3. Draw the desired number of rectangular veins 1.5 inches long and 1 7/8 inches wide on a piece of 3/32 inch thick balsa.
4. Cut the veins out.
5. Cut a 3/16 inch diameter dowel to 2 1/8 inch length.
   
6. Stack all veins and sand square together. Hold together with masking tape while sanding the edges.
7. While still stacked, press a piece of good thin masking tape across the root edges of all the veins. Remove any tape sticking out around the vein roots.
8. Test wrap the taped root edges around the axle. They should fit tightly with no gap. Sand the axle thinner if there is a gap.
9. Sand the sides of each down if they are too "fat".
10. Glue the vein root-tape to the axle.
11. Test fit spanners and adjust.
12. Glue in spanners on one side of the paddle then the other.
13. With a tooth pick, apply extra glue around all vein joints.
14. Grease the edges of the spanners and veins with wood glue.
15. Cut or sand the ends of the axle to rounded points. They should protrude from the paddle wheel about an eighth inch on each side.
16. Paint and coat the paddle wheel with a liquid plastic so it is water-proof. Wipe the excess off the axle points. When dry, the tips can be waxed by rubbing softened paraffin on them.

The Paddle Housing

The paddle wheel is held above the water by a hub. A housing with an air inlet pressurizes blown air. Hub caps hold the paddle wheel axle in the housing and helps insure best spin. The size of the housing is 1/4 inch more than the paddle wheel to allow good clearance and to reduce viscous water drag.

1. Mark a 3 1/4 inch diameter circle on a piece of cardboard using a compass so the center is clearly marked.
2. Mark at the center, a 1/8 inch diameter circle.
3. Draw a line (called a chord) 3/8ths of an inch from the center across the circle. In the following instructions, use the larger piece of the circle, it will form the pattern for the sides of the paddle housing. The flat side of this piece is its "base".
4. Draw a line at right angles to the base 3/4 inch from the center. Extend it across the side of the housing side pattern. This line marks the rear of the housing.
5. Draw a line at right angles to the base 1/4 inch in front of and below the center down to the base.
6. Complete the vent triangle by drawing a line from the upper end of the previous line to a point about 1/4 inch in front of the previous line on the base.
7. Cut out the housing side pattern including the center hole and triangular air vent.
8. Using the pattern, draw two housing sides on 1/8 inch thick balsa. Line up the rear of the housing along the grain of the wood. Be sure to copy the vent and axle hole.
9. Cut out the housing sides. The arched edge of each housing side is called the "round".
10. Place the two housing sides together so the edges, center holes and vents all line up.
11. Sand the edges and holes until they are identical, being careful to preserve the shape and size as much as possible. The paddle may not spin freely in the housing if the size and shape of its sides are altered too much.
12. Use a flexible ruler or tape measure to find the arc-length of one round; about 3 and 5/8 inches.
13. Cut a rectangle measuring 2 1/8 inches wide and as long as the arc-length you found in the previous step on 3/16 inch thick balsa. Make sure the grain runs across the narrow width of the rectangle so it can bend over the round. This will cover the round.
14. Smear a SMALL amount of wood glue on the front of each housing side right where the round begins. Try not to get any glue on the base.
15. Press the edge of the round cover against the glue on the front of the housing sides.
16. Hold the pieces so the bases of the sides are at right angles to the narrow edge of the cover and flush with it. The cover should not be sandwiched between the sides, but in front of them. The cover should stick straight out, don't try to bend it over the round yet.
17. Let the joint dry.
18. Smear a LITTLE glue on the rest of the round edges.
19. Carefully bend the cover over the rounds. The edge of the cover should not overhang the round on the outside, but be flush with it. If there is an overhang, the paddle may not spin freely in the housing.
20. If the cover does not bend well or starts to crack, wipe off the glue, and set to steam on a rack over boiling water (outside toward steam). The wood will bend toward the round after a minute or two. Remove, glue and finish bending.
21. Use pins spaced every inch to hold the cover on the round until it is dry.
22. Smear more glue on the inside and outside of the round joint.
23. Finish the inside of the housing including the hole and vent so they are water-proof. Wax these areas also. Avoid getting finishing compounds on the edges and outside of the sides.
24. Cut two 1/2 inch squares out of 3/32 inch thick balsa.
    
25. Glue them over the axles holes on the outside of the housing just beyond the vents. These are the hub caps for the paddle wheel.
26. Finish the inside of the hub caps. These areas should be water-proof.
27. Carefully fan open the housing rear to fit the paddle wheel into the hubs.

The housing is ready to be mounted on a suitable hull and finished. Congratulations if you were able to follow all these instructions! Now you know why God did not ask Noah to build a paddleboat!

Two Good Paddleboat Hulls

You can put a paddle wheel on either a split hull or a flat hull. Since the split hull is described in the construction instructions for the catamaran and a good flat hull is described for the hydroplane, only the differences will be listed here.

Point of Balance

Placement of the balance point is a key to the success of a paddleboat. Too far forward and the nose will bury itself in water. Too far back or high and the boat wants to wheelie the whole race or worse yet, flip over backwards!

1. Make the weight of the boat as near the lower limit of legal weight as possible with your materials. The harder you can blow, the heavier your boat can be, but it will be slower than it would have been if it weighed less!
2. Place about an ounce of weight near the forward edge of the short deck. The nose tilts up a few degrees.
3. Place the weight low in the hull to increase sideways stability, but it is more spectacular if you tie up your weight in deck sculptures or thematic structures.