Report for Cargo Ship Challenge

The Gang of Eight

Anyole High School

Team Members

Captain Edward Smith
William Froude
Hyman Rickover
Grace Hopper
Rosie T. Riveter
Lenah Higbee
Phoebe Ann Moses
Isambard Kingdom Brunel
Advisor: Mr. Wiedorn

Table of Contents





Preliminary Design

Drawing the Lines

Propeller Design

Construction of the Hull







Appendix A: Safety

Appendix B: Team Members

Appendix C: Scheduling and Accomplishment

Appendix D: Material Resources

Appendix E: Tools and Machines

Appendix F: Working Drawings


This report is written to reduce the obstacles to entry to the Maryland Engineering Challenges Cargo Ship Challenge by providing a sample solution. The goal of this challenge is to design and construct a radio controlled model cargo ship to travel around a specified course carrying 40 pounds of sugar. Our ship is 60 inches long, has a beam of 11 inches and a design draft of 4 inches. A Kelvin 850962 motor drives a single 3 ½ inch five bladed propeller. We expect our model to take 30 seconds to complete the course for a Required Freight Rate of $0.90. This is a design challenge in which all eight team members were introduced to engineering as a career.

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A local Baltimore company would like our team to design a bulk carrier cargo ship to deliver 40,000 tons of processed sugar to remote ports. The shortest wharf on the expected route is 600 feet long and the minimum depth in any port is 40 feet. As part of our solution we need to build a 1" to 10'0" scale, radio controlled model to be tested in the inner harbor.

The competition involves five main components: a written report submitted two weeks prior to the actual competition, an oral report on the day of the competition, the actual design and construction of the entry, the reliability of the entry, and the demonstrated performance.

We are required to design a mono-hull ship to meet the requirements and construct a 1" to 10'0" (1:120) scale model with the hull constructed of any rigid material. The model should be robust enough to withstand minor collisions and must have enough watertight integrity to protect the cargo, the propulsion plant and the radio controls. The model should conform to the constraints listed below.

Up to 5 bonus points will be awarded by the judges to vessels that are consistently ready to test when called, need few repairs, and operate reliably.

The performance of the vessel will be based on Required Freight Rate (how much the operator must charge per ton·mile to break even). The vessel with the lowest Required Freight Rate (RFR) will be declared the performance winner.

Once loaded, each entry will perform a timed run consisting of getting underway from a wharf, running a specified course around buoys, and maneuvering back alongside the wharf. This simplified formula for Required Freight Rate will be used:

RFR = (L+T)/(CD)

L = Length of Vessel
T = Time to run course in seconds
C = Pounds of Cargo carried
D = Scale Distance of course (considered to be 2.5 scale miles).

Example: 50" Long model with a full load of 10 bags (40 pounds) around course in 2 minutes
RFR = (50+120)/(40x2.5) = 170/100 = $1.70 per ton mile

The design is subject to many constraints

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In this section we will explain the science, technology, engineering, and mathematics involved in the challenge.

The Cargo

The cargo we will carry is ten, 4 pound bags of sugar. A 4 pound bag of sugar is 7 inches high, 4 ½ inches wide and 4 inches deep.

Throughout the report we will talk about three faces of the bag, the front, the top, and the side. The front has the main label and its dimensions are the height (bottom to top) and the width (side to side). The dimensions of the top are the width and the depth (front to back). The dimensions of the side are the height and the depth.

Ship Geometry

For definitions of various measurement click here.

Ship's lines drawings look like this.

Here is a close-up of another body plan

Using Archimedes’ principle to determine draft

For a boat to float, it must generate a buoyant force equal to its weight. The buoyant force is generated by displacing water and can be determined using Archimedes' principle.

A body fully or partially immersed in a fluid is buoyed up by a force equal to the weight of fluid displaced.

To determine the displacement, first calculate the underwater volume of the hull. This may be done by measuring the submerged area of each section and then integrating over the length of the boat using Simpson's rule. Multiply the underwater volume of the hull by the specific weight of water (ρg or "rho-gee") which is 64 ft3 / 2240 lbs for salt water and 62.4 ft3 / 2240 lbs for fresh water. For smaller boats use 0.577 ounces per cubic inch. The product of the volume and the specific weight will be the weight of water displaced. By Archimedes' principle, this is also the buoyant force.

For a Rectangular Barge

Find the total weight by adding up the weight of the cargo, hull, machinery, etc.

To find the underwater volume, take the total weight (which is equal to the displacement, Δ) and divide by the specific weight.

V = Δ / ρg

The underwater volume is equal to the length (L) times the beam (B) times the draft (T).


If you know the Length (L) and Beam (B), you can divide the volume (V) by both to get the draft (T).

T = V / LB

Or if you know the Length (L), you can calculate the Beam (B) needed to limit the Draft (T) to a certain amount.

B = V / LT

Will it stay upright?

In order for your boat to stay upright, the meta-center (M) must be above the center of gravity.

To find the center of gravity

Divide the weight into groups (e.g., cargo, hull, machinery).

For each group, multiply the weight of the group by the height of the center of gravity of the group (above the keel). Add up the products and divide by the displacement (Δ).

KG = {wKg + wKg + wKg} / Δ

For the cargo the height of the center of gravity can be approximated by half the height of the cargo. Depending on how the bags of sugar are arranged, the Kg for the cargo is about half the height (or width, or depth) of the bag. You can add the thickness of the hull below the cargo is you would like.

For the other weights you can take your best guess of the height of the machinery etc. If you can weigh things, good. If not, make an intelligent estimate.

To find the center of buoyancy

For a rectangular (or nearly so) barges you can use half the draft for KB


For your hull, the center of buoyancy will be a little above half the draft, estimate as 0.6T or 0.7T and you won't be too far off.

To find the metacentric radius (BM)

The metacentric radius (BM) is the second moment of area of the waterplane (I) divided by the underwater volume (V).

BM = I / V

If the waterplane were a rectangle, the second moment of area of the waterplane (I) would be the Length (L) times the Beam (B) cubed divided by 12.

I = LB3 / 12

Since your waterplane is not a rectangle, take 80 or 90% of that value. If you have a more detailed lines drawing, you can find I using simpson's rule.

To find the metacentric height (GM)

KB + BM = KM
KM - KG = GM

The boat will be initially stable if the GM is positive. The rules of this challenge require a GM of at least 0.75 inches.

Another Explanation

Factors in Resistance

In the age of sail, the total sail area in a design was based on rules of thumb and centuries of experience. These rules of thumb were passed from father to son, until Samuel Pepys the famous diarist traded his family's knowledge for a position in the admiralty.

In the 1800's steam replaced sail, but no one was sure how big a motor was required to power a boat. William Froude solved this problem by developing a method of predicting ship resistance (and hence powering requirements) from model tests. In doing so, he divided resistance into three parts. Based on Froude's work, Total Resistance consists of frictional resistance, wavemaking resistance, and other minor factors.

Frictional Resistance

Results from the friction between the skin of the boat and the surrounding water. For a smooth hull, this resistance depends only on the wetted surface area of the hull. The frictional resistance increases as the square of boat speed.

Wave Making Resistance

A boat underway produces a characteristic wave pattern consisting of transverse and divergent waves. The wave pattern travels at the speed of the boat. Since the group velocity of the waves is on half of the wave velocity (celerity), energy must be continuously supplied to produce the wave pattern.

Longer waves travel faster, faster waves are longer

The speed of a wave in deep water is

c (ft/sec) = 2.41 times the square root of the length of the wave in feet
Hull speed (ft/sec) = 2.41 times the square root of boat length in feet
Hull speed (knots) = 1.34 times the square root of boat length in feet.

Other Stuff

There are other minor factors in resistance, such as form resistance. Additionally, basic model tests do not account for the resistance of appendage (such as the rudder). These must be accounted for separately.

Propeller Design

We need to specify four things to get our propeller made: the diameter, the pitch, the number of blades, and the Blade Area Ratio. We will also specify that we want a 13/64 (5mm) shaft diameter to match our running gear.

The diameter of the propeller is limited to the draft, since no part of the ship can go past the draft limit and the top of the propeller should be underwater.

The pitch of the propeller is how far it would advance through the water in one rotation. It is measured in distance units (feet or inches). A propeller with a pitch equal to the diameter is known as a “square” propeller. Propellers with pitch more than the diameter are for speed. Propellers with the pitch less than the diameter are for power.

The maximum possible ship speed that a propeller can produce is a factor of the pitch (P) and the revolutions per second (N) of the shaft. Since a propeller advances one pitch per revolution, the speed of the ship in feet per second is equal to the pitch in feet times the shaft speed in revolutions per second.

We’ll probably specify the pitch in inches and then have to convert to feet to use the formula. For ship speed, we’ll try and obtain hull speed with no slip, and the actual speed will end up being something less. Normally, propellers have an odd number of blades to reduce vibration. We should probably go with 3 or 5 blades.

The Blade Area Ratio is the ratio of the total blade area to the disk area. The disk area is the area of the circle with the same diameter as the propeller.

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When we constructed the fiberglass hull we had to wear dusk masks and vinyl gloves. Other than that a list of general safety rules is provided in appendix A.

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Preliminary Design

Let's make a box the size of our sugar cargo and see what draft it has and if it is stable—we’ll start with the bags top up, front forward, in a neat line 10 bags long.

First Configuration

This box carrying bags of sugar is 40 inches long, 4½ inches wide, and 7 inches tall. It weighs 40 pounds. How far does it sink into the water?

Archimedes' principle says that we need to displace 40 pounds of water. The first thing is to figure out how many cubic inches of water this is. Fresh water weighs about 62.4 pounds per cubic foot. So we need 40/62.4 cubic feet. That is 0.64 cubic feet. Since there are 12x12x12 or 1728 cubic inches in a cubic foot, we need 0.64 x 1728 cubic inches or 1108 cubic inches. We know two of the dimension of this volume, the Length (L) and Beam (B). Therefore the draft (T) is:

T = 1108 in3 / (40 in X 4.5 in.) = 6.1 inches

Well, that won't work. The draft is limited to 4 inches. Let's reverse the problem, how much beam do I need to limit the draft to 4 inches.

B = 1108 in3 / (40 in X 4 in.) = 6.9 inches

But is it stable? We need to find three distances, KB, BM, and KG and then compute GM. The constraint is not only a positive GM, but a GM over 0.75 inches.

KB is half the draft or 2 inches.
BM is I / volume or BM = L B3 / 12 / 1108 in3 = 40 in (6.9 in)3 / 12 / 1108 in3 = 0.98 inches
Add these up to find KM = 2.98 inches
KG is half the height of cargo or 3.5 inches. G is above M and we are unstable, the box will turn over.

So let's change the problem and find the beam to get a GM of 0.75. This is tricky, because as you increase the beam, the draft goes down. We’ll increase beam by 1 inch per iteration starting with 9 inches.

Nine Inch Beam

Remember, the total volume is 1108 cubic inches. The length is 40 inches, if the beam is 9 inches let’s find the draft.

T = 1108 in3/ (40 in. x 9 in.) = 3.1 inches

So KB is 1.65 inches

BM = I / V = 40 in. x (9 in.)3 / 12 / 1108 in3 = 2.19 inches
KM = 2.19 in. + 1.65 in. = 3.84 inches
GM = 3.84 in. – 3.5 in. = 0.34 inches, which is stable but does not yet have the required 0.75 inches.

But if I need more that 9 inches of beam, why not put the bags side by side and reduce the required length?

This leads to our second configuration.

Second Configuration

Ten bags of sugar top up, front forward, in 5 rows of 2. This box of sugar is 20 inches long, 9 inches wide, and 7 inches tall. What is the draft?

T = 1108 in3 / (20 in X 9 in) = 6.15 inches, which is too much.

This time, let’s make the box longer to get the draft below 4 inches.

L = 1108 in3 / (9 in X 4 in) = 30.8 inches

Is it stable?

KB = 2 inches
BM = L B3 / 12 / 1108 in3 = 30 in (9 in)3 / 12 / 1108 in3 = 1.68 inches
Add these up to find KM = 3.68 inches
KG is half the height or 3.5 inches. M is above G and we are stable. But GM is 0.18 inches, less than the required 0.75 inches.

Let’s see what happens with a 10 inch beam. With the increased beam, we can make the length 30 inches and still have the draft we need.

Ten Inch Beam

With a length of 30 inches, a beam of 10 inches, and a volume of 1108 cubic inches what is the draft?

T = 1108 in3 / (30 in. x 10 in.) = 3.7 inches

Do we have the required GM?

KB = T / 2 = 1.85 in
BM = 30 * 103 / 12 / 1108 in3= 2.25 inches
KM = KB + BM = 1.85 in. + 2.25 in. = 4.1 inches
GM = KM – KG = 4.1 in. – 3.5 in. = 0.6 inches

So we are almost there. Let's try an 11 inch beam.

Eleven Inch Beam

With a length of 30 inches, a beam of 11 inches, and a volume of 1108 cubic inches what is the draft?

T = 1108 in3 / (30 in. x 11 in.) = 3.4 inches

Do we have the required GM?

KB = T / 2 = 1.7 in
BM = 30 in. * 113 / 12 / 1108 in3 = 3 inches
KM = KB + BM = 1.7 in. + 3 in. = 4.7 inches
GM = KM – KG = 4.7 in. – 3.5 in. = 1.1 inches

So it looks like we have it. Our cargo section by itself is 30 inches long, 11 inch beam, and will have a 3.4 inch draft. If we add a bow and an engineering section, we will have a ship.

Overall Length

The propulsion system should take about 15 inches from the back of the rudder to the back of the motor.

A full length ship of 60 inches will likely maximize speed. With 30 inches of cargo and 21 inches of propulsion we are left with 9 inches for a bow. This is more than the required 10% for a collision bulkhead.

So my hull is going to have a shaped bow that is 9 inches long, followed by 30 inches of parallel mid-body for cargo, followed by 21 inches for propulsion which is plenty of length to give good flow into the propeller.

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Drawing the Lines

Off to draw the lines for a cargo ship that is 60 inches long, 11 inches beam, 8 inches depth (the total height of the sides), and 4 inches draft.

Well, that didn’t work. We tried to draw a set of lines by hand but got so confused we gave up.

Then Bill decided to try drawing the lines using AutoDesk Inventor. This is the best that he could come up with.

So we didn’t like that and couldn’t finish it.

So George says that since we designed a ship in three parts, we should draw three parts; a bow, a parallel midbody, and a stern/propulsion plant.

So George went off and instead of trying to use AutoDesk Inventor Professional 2013 to make a set of lines drawings, he made a 3D model of the ship. We liked it except for three things. First, the sizes were wrong. The beam was only 10 ½ inches, the bow was only 6 inches long, and the stern was 24 inches long. Second, the way the stern section was drawn, the propeller hit the hull.

Then Izzy said that he could fix everything, he took George’s work and modified it to have a 9 inch bow, 30 inch midbody, and 21 inch propulsion section. First he modeled the cargo compartment, a box of 1 inch pink foam. Note that the turn of the bilge is rounded.

Next he made a bow. In this picture it is shown from underneath. The round of the bilge in the cargo compartment is extended around the bow. When we actually carve it out of pink foam, we may give it more shape.

It took Izzy several tries to model a stern section that had room for the engine (hand drill), the running gear, and the propeller. Again, this model will guide us when we carve it out of pink foam.

Our first try.

Izzy's second try. This one show from below. Still not enough room for the propeller.

Izzy's third and final try.

His superstructure is designed to look like a ship. The deck house covers the handle of the upside down hand drill. The whole thing comes off for access to the machinery.

He also designed a forecastle to go on top of the bow.

And a hatch cover.

Here is what it looks like assembled.

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Propeller Design

We decided to ignore slip and find the pitch for hull speed.

The length of our ship is 60 inches which is 5 Feet

Hull Speed for 5 feet of length is 5.4 ft/sec or 64.8 in/sec.

Hull Speed = 2.26*(5 feet)½ which is about 5 ft/sec.
OR 5 ft/sec x 12in/1 feet = 60 in/sec.

The Kelvin motor is rated for 12,800 rpm at 30 volts. Since we will be running at 12 volts, we'll estimate 6000 rpm, which is 100 revolutions per second.

N = (6000 rev/min) x (1 min / 60 sec) = 100 rev/sec

For the ship to have a speed (V) of 60 inches per second while the propeller is spinning at 100 revolutions per second, or propeller has to have a pitch of about 6.5 inches

V = P x N
P = V / N
P = 60 in per sec / 100 rev per sec
P = 0.6 inches

At a diameter of 3 inches, this is a pitch/diameter (P/D) ratio of 0.2. At a diameter of 2.8 inches, this is a pitch/diameter (P/D) ratio of 0.214. It should be easy to find a propeller like this.

The prop we have on hand is 2 ¾ diameter, 1 ¼ Pitch propeller that comes with the Midwest Products Company, Inc Boat Running Hardware Kit #828. Looks like this will do fine, it might even be a little overloaded.

To get the maximum effect, we plan to order a 3.5 inch propeller with a 0.5 inch pitch. This is a speed propeller. We decided to pick 5 bladed propeller with a blade-area ratio of 1.1. It will be designed for a 13/64" (5mm) shaft to match the running gear we got from Midwest Products.

a 3D printed propellerWe e mailed these specs to Mr. Wiedorn, who sent them off to David Taylor. We got back an STL file and 3D printed the propeller. Look at the picture for another propeller being 3D printed.

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Construction of the Hull

We bought some ½ inch pink foam and some 2 inch pink foam.

For the cargo section, we made the box out of the ½ inch pink foam and rounded the turn of the bilge.

For the bow, we cut out the top view of the bow on four pieces of 2 inch pink foam using a band saw. We stacked them up and glued them together with stick glue. This gave us a pile 8 inches high. We then shaped the turn of the bilge using a SurForm file and sandpaper. We also gave the bow more shape than is shown in the 3D CAD model.

For a collision bulkhead, we cut a piece of lauan plywood and stuck it on the back end of the bow. We then glued the cargo compartment behind the collision bulkhead.

For the stern section we stacked two pieces of 2 inch pink foam together and shaped them to the above water part. We stacked two other pieces together and cut and shaped them for the underwater section. We glued these two parts together, faired the joint, and glued them to the back end of the cargo compartment.

Another idea we considered was to make the stern section out of thin Plywood in flat pieces. Maybe we can design one using Delftship

We flipped the hull over and covered it with packing tape. We then inserted the running gear into the hull and greased it up heavily to make sure the epoxy would not stick to it. We raised the hull up on some scrap 2x4 to make it easier to fiberglass.

We then fiberglassed a hull over the pink foam. We used two layers of 3 ounce fabric (three would have been better). We tried to use plenty of epoxy to make the hull smooth.

Next day we came back and turned the hull over. We trimmed the fiberglass to the gunwhales using a dremel tool and cut-off wheel. We left the pink foam intact in the bow. The cargo compartment was already hollow. In the stern section, we carved out the pink foam as much as needed to support outfitting.

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We epoxied a square tube into the stern. The brass rod that was our propeller shaft fit inside the square tube, but left room at the corners so that an debris would fall out.

The rudder was constructed of balsa wood covered with fiberglass. We drilled a small hole in the end of the rudder shaft and put a small nail through the hole, this prevented the rudder from slipping on the shaft as the rudder turns from right to left.

Rosie suggested that we 3D print a back up rudder. Our design had a hole through it for the 5/32 rod. We like it and brought it to the competition. Next year we'll just use this rudder.

At the top of the tube on the stern of the ship we mounted a servo driving a crank arm designed for a steerable nose wheel of an RC airplane. Works real well. We always wiggle the rudder back and forth before we put the ship in the water to make sure every thing is working well.

Radio Controls

The ship is driven by a two-channel remote control via an RC speed control (see appendix D). One channel moves the rudder, the other controls the Kelvin motor. The rudder servo is mounted on the stern moving the nylon stearing arm.

The antenna for the RC receiver is mounted inside the mast which is on top of our pilot house.


The running gear is a threaded rod in a tube. We bought a model running gear to use with our custom propeller. The propeller is held in place with a nut and a propeller dog. We packed the tube with vaseline to keep the water out and the friction down.

The motor is mounted in line with the shaft and connected with a flexible joint to the shaft. The power comes from the batteries through the RC speed controller. The batteries are two rehargable 12V batteries that we bought at the battery warehouse. The batteries are wired in series to obtain a higher voltage.

This model shows how propulsion could be arranged. It is about 15 inches from the back of the rudder to the front of the motor.


This report is a work in progress, check back frequently for updates


This report is a work in progress, check back frequently for updates

Hatch Cover

This report is a work in progress, check back frequently for updates

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In this section, we will tell you all the things we changed as we tested our boat. Since we probably won't finish until the night before the challenge, we probably won't write anything here.

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A list of team members and their contributions is provided in appendix B. Appendix C provides our initial schedule and a description of what we accomplished each day. A list of materials used in this challenge, including an estimate of the cost of donated materials is provided in appendix D, the total cost was $376. Appendix E lists and describes special tools and machines used in this challenge. Working drawings are included in appendix F.

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It was a long and hard challenge, but we loved it and most of us will end up engineers. Lenah will even end up having a ship named after her. Izzy's Great Eastern will lay the first under-ocean telegraph cable across the Atlantic. Rosie will have a museum dedicated to her. Bill will be the most famous of all naval architects. Hyman will be known as the father of a whole branch of the navy. Grace will be one of the first women admirals. Annie will ride with Buffalo Bill. And Ed, well Ed will have his name always associated with the most famous ship ever.

And all because they participated in the Maryland Engineering Challenges.

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The only adult who helped up was Mr. Wiedorn, and he didn't help much.
“We hereby certify that the majority of the ideas, design and work was originated and performed by the students, with limited assistance by adults, as described above.”

Edward Smith    William Froude    Hyman Rickover    Grace Hopper 
Rosie T. Riveter    Lenah Higbee    Phoebe Ann Moses
Isambard Kingdom Brunel    Paul A. Wiedorn

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Appendix A: Safety—Howard County General Safety Practices

The use of the Technology Lab is a privilege. Therefore, the following safety practices must be followed at all times.

  1. Follow all directions first time given.
  2. Be courteous in language and actions.
  3. Be on time and prepared to participate.
  4. Respect other people and their property.
  5. Eye protection must be worn while students are processing materials.
  6. Running and playing is not allowed in the Technology Lab.
  7. Throwing any object in the Technology Lab is not allowed.
  8. Students will only be able to use tools and machines while the Technology Teacher is in the Lab.
  9. Students should wear clothing that protects their arms, legs, and feet from injury.
  10. Students must pass all tool and machine tests with 100% accuracy before they are allowed to use them.
  11. Keep the floor and working surfaces clean and dry at all times.
  12. Hair that presents a safety hazard must be tied back.
  13. Respect all tools and machines.
  14. When in doubt, ask your teacher.
  15. Report any incident to the Teacher.
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Appendix B: Team Members

Click on each link to find out more about the namesake of each member of our team.

Captain Edward Smith—Cap lead our team and kept us all on track and tried to keep us off the icebergs.
William Froude—Bill did our hull design and calculated resistance and powering.
Hyman Rickover—Hyman designed and installed our propulsion system and made sure we followed all the rules.
Grace Hopper—Grace did our computer work.
Rosie T. Riveter—Rosie was the foreman of our construction team.
Lenah Higbee—“Nurse” helped to construct the ship and made sure that we were all safe.
Phoebe Ann Moses—Annie made sure that we were all straight shooters.
Isambard Kingdom Brunel—Izzy had the vision needed to make a really big ship.

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Appendix C: Scheduling and Accomplishment

As an after-school club, this challenge takes eight students all year to do.

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Appendix D: Material Resources

This report is a work in progress, check back frequently for updates


Approximate Cost

Turnigy i4X 4-Channel 2.4GHz AFHDS 2A Transmitter With Receiver (Mode 2)$37.95
Goolsky WP-1060-RTR Waterproof Brushed 2S-3S 60A ESC for 1/10 Tamiya Traxxas Redcat HSP HPI RC Car$25.99
Kelvin Motor, part number 850962 $9.95
Misc. minor parts$25.00
5-yards of 2 ounce fiberglass fabric from Fibre Glast.$29.45
Expoxy Resin Kit$64.95
Get a 1-1/4” Nylon Steering Arm Assembly from a hobby shop. Mine uses a 5/32 rod.$2.73
Alternative is a HPI Aluminum Steering Arm$10.99
8 inches of 5/32 rod.$5.23
5 inches of square tube that the rod just fits inside of.$2.39
3D print the rudder$15.00
2 inch pink foam.$29.00
½ inch pink foam.$14.47
Clear Packing Tape.$10.49
Lauan plywood. 8 inches times the beam.6.32
Boat Running Hardware SKU# 828 from Midwest Products—High-quality stuffing tube and prop shaft that are bushed on both ends and includes an injection molded prop with brass inserts.
Shaft - Diameter: 13/64", Length: 10-1/4"
Stuffing Box - Diameter: 5/16", Length: 8-7/16"
Prop - Diameter: 2-3/4", Pitch: 1-1/4", Shaft Thread: 5mm
We also made our own running gear and got a propeller by e mailing Doug Griggs at $??.??
One or two 12 Volt batteries. I bought small rechargeable lead acid from the Battery Warehouse. $21.99
Oh, and 10 4-lbs bags of sugar. Wrap and seal them in plastic.$23.90
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Appendix E: Tools and Machines

This report is a work in progress, check back frequently for updates

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Appendix F: Working Drawings

This report is a work in progress, check back frequently for updates

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©Last updated by P. A. Wiedorn, 14 November 2018