Cardboard boats

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A cardboard boat

Problem[edit | edit source]

Get Invited to a Cardboard Boat Competition
cardboard boat competition 2010
cardboard boat competition 2008

Civic groups such as a Rotary Club(s) and school engineering departments/clubs can sponsor a fun, family event such as such as a cardboard boat competition. They are a great way to begin building an engineering program at a high school or community college.

The competitions judge speed, themes, demolition survival, most dramatic sinking, best mechanical aid, rube goldberg award, etc.

Get a copy of the rules .. they will typically explain that years "themes" which translates into awards, pictures of the boat in the news and marketing campaigns.

Some competitions have materials that are used to design and build cardboard boats on the spot in the hours before the competition.

Some cardboard boats can cost a thousand dollars and are reused year after year. Some are built over a four week period, are designed to win various prizes, and are thrown away at the end of the race.

The problem is that you have been asked to build a cardboard boat or enter a quick build competition. This can not be avoided for political, fund raising, community building, program growing, student recruitment reasons. Cardboard boats can be simple or a bottomless pit of $20 gallons of wood glue, paint and cardboard debris all mixed together on a floor that will take a year to clean.

Conceive[edit | edit source]

Boat Name

The design should start with a unique name for the boat. This has to be backed up by a narrative or story. This ideally is on a piece of paper that is handed to judges and verbally told to people passing by the boat, in funding raising presentations, and design reviews. The goal is to maximize attention.

Planned Sinking/Staying Dry
competitive racing
cardboard boat sinking .. video

Most competitions differ from an Olympic rowing race in that the boats should sink. Everyone should get wet. The audience anticipates sinking.

The goal of staying dry destroys competitions. It is possible to build cardboard boats where everyone stays dry. But if everyone stays dry, there is no drama. This is why most competitions have a demolition derby at the end.

One of these requirements has to be chosen:

  • sink in a certain way
  • stay dry
  • build without engineering and see what happens

Maximize Attention
Round Cardboard Boat ... liquid nail sealed with contact cement

These are situations that don't maximize attention:

  • Boat rolls over at the dock, dumps everyone in the water and instantly becomes soaked in water
  • Boat design is too heavy and can not be carried in the parade in front of the judges. Want boat to sink in front of the judges, not be abandoned at the end of the race.
  • Boat takes on water, doesn't sink, but becomes too heavy.

Then there are the boats that invite ridicule because they don't go anywhere. Round boats may be easy to defend in the demolition phase, but offense requires chasing down the enemy. Round boats that only spin in circles usually win a futility award.

A crew
Team moving very heavy cardboard boat.

Building a boat without a crew that is ultimately going to paddle it in a competition is an invitation to disaster. The crew needs to

  • train if the boat is going to be fast
  • willing to get wet
  • practice carrying the boat in the parade
  • practice getting in and out of the boat without tipping over

Transportation to the Site/Expect Damage

How are you going to Move It?

Expect damage .. and plan on fixing it

Demolition or transportation to storage

Most boats will be demolished. If the boat is to be saved, a crew is needed to transport the boat to storage. Timing is critical. The race organizers typically demolish most boats. Saving the boat requires planning ahead.

Design[edit | edit source]

  • There is free software for hull design here. Need to install windows xp mode to run it.
  • Lots of build pictures and video are below
Draw the Boat
Stretched hat boat drawing in Pro/E

Most programs such as sketchup have rulers. There are pre-drawn boats at 3D Warehouse. A ruler in sketchup can be used to cut the cardboard to the correct dimension. Autodesk Inventor can compute the center of gravity once drawn.

Make models of the boat

Can use models to raise money

Origami Boats

Dragon Designs

Corrugated Fiberboard Sources


Cardboard boxes are used everywhere. But they can not be found because they are compressed into a steel box by a compactor. Asking a retail store to not put boxes in a compactor causes problems because usually have no where to store the boxes. Refrigerator boxes are the best for building anything. But to get the box one has to hang around a store where refrigerators are sold.


Cardboard is recyclable. Some institution have dumpsters dedicated to cardboard that are not baled or compressed. These boxes are typically smaller in size. Big boats become more difficult to build without large boxes. The best boxes in these dumpsters are usually related to computers and electronics.


Corrugators are machines that make cardboard sheets that are 7 feet by 8 feet approximately. Around major cities there are companies that install and repair the machines and companies that operate them. Cardboard is cheaper to make locally from recycled pulp that it is to make centrally and ship. Cardboard is very much like concrete in this respect.

Don't say Cardboard

The best source of donated cardboard is a company with a corrugator. They typically have a loading dock, ship lots of stuff and are generally willing to donate sheets of corrugated fiberboard. Talking to them on the phone is difficult. If you say, "will you donate some cardboard boxes?" they will not know what you are talking about. Cardboard boxes are made of corrugated fiberboard. The term cardboard means too many different things. Expect packaging engineers and technicians to be immediately confused if you ask for a cardboard box. They will not understand what you are asking for. You are looking for "corrugated fiberboard sheets."

Cross Flutes

Flute standards have been relaxed since the corrugated fiberboard market has matured. There is no need to help organize it or protect consumers.

Cardboard boxes are all different

Overlap the Flutes

Cardboard tubes are sometimes illegal in competitions

Cardboard boxes are designed to stack and not compress. The flutes all run up and down. The sides are normally subjected to jiggling during transportation. Conclusion:

  • strong up and down
  • weak sideways

Some engineers take a statics class and material dynamics class. There are three major points from these classes that apply to cardboard boats:

  • triangles are strongest (trusses)
  • computing centers audio of mass and buoyancy help prevent tipping
  • pulp is not wood

Think of wood as a massive number of straws that are made of chains of paper clips. Water gets into these straws like a water balloon. The straws expand sealing all cracks. A wooden boat seals itself. Pulp is like a bunch of needles glued together. Building a cardboard boat involves just adding more glue. Water dissolves most glue, so the boat is covered with a sealant. But the sealant is meant to keep out the moisture in air, not water itself.

Wooden boats can be left in the water years. A cardboard boat instantly leaks and should only be in the water for minutes. Cardboard dissolves like toilet issue. All other issues are secondary.

These papers are something a packaging engineer would read:

Air Pressure cannon designed to spray occupants so they want to jump in water .. video

The problem is that too many people build cardboard boats that don't sink. Yet they don't want to take them home, so they get thrown away without sinking. Fewer boats sinking means that the cardboard boat event draws less of a crowd.

Some event organizers have tried to add demolition derbies at the end. But boats crashing into each other and poking at each other doesn't sink boats. Most audiences are not patient enough to wait hours for cardboard boats to sink on their own. How else could boats be sunk and people forced into the water?

  • Swim underwater with box cutters
  • Spray people with tomato juice so they want to get in the water
  • Fire projectiles through the cardboard boats

This stimulated another project called "Air Cannon".

Dramatic Sinking
Cardboard boat sinking ... wining the "most dramatic sinking" award ... can see the garbage boat ready to pick it up ... at the end the rescue boat comes

The boat should have a name and a story in order to win the award for the most dramatic sinking. In this case the boat was named "Free Ride" for having no crew because nobody wanted it. It was especially ugly and looked like it would sink.

Carrying Mechanism
Video of carrying a cardboard boat in a parade in front of the judges

The carrying mechanism should help get the boat out of the water without damaging it, and then continue to carry the boat in front of the judges. Think of a casket being carried in a funeral.

Decoration Support

There are usually "theme" awards. Some events have a design theme and awards are given that best match that theme. A hole can be drilled completely through the boat, filled with PVC pipe and then sealed at the bottom to create a place for a pole to be inserted later. Obviously, some planning was necessary for these boats:

  • Boat Building Pictures
One-Two Person Quick Build

Competitions held at a pool generally have the objective of racing in a straight line from one end to the other. Sitting in long narrow boats wins.

Competitions held on a lake generally require turning and thus the best boats are unstable .. hard to turn and go straight. This happens around 10 feet long with width of 30 inches.

The materials are typically cardboard, plastic and duct tape. Let the cardboard seams guide you. Wrap in a plastic bowl and tape to the cardboard.

Two Person Boats Built before the Race
  • A box 1 x1 x 3 will float 180 pounds
  • Wide, flat Bottoms tend to be less “tippy” than V-shaped bottoms. One paddler, make 30 inches wide .. two 48 inches
  • Longer boats go faster, but they are harder to turn.
  • Boats shorter than 10 feet are difficult to steer straight.
  • 10-12 feet in length seems to be just about right.
  • Don’t make sides higher than 18 inches.
  • The lowest center of gravity (sitting in the bottom of the boat) is the most stable
  • Kneeling or standing will tip over boats

Big Boats

Big boats carry between 3 and 8 people. They are typically more expensive than purchasing a real boat. Even the simple canoes have to be engineered. A group of people have to work together. There has to be a design. There have to be last minute decisions. They take up a lot of space while building. The gluing/drying rhythm requires working a couple of hours every day ... for many days ... at times drying for a week is necessary. Rain has to be dealt with. The dust and debris can fill trash cans. They lead to a desire to re-use them year after year.

Big boats can be fast and look like an olympic rowing machine.

A majority are slow and win "theme" awards. They are similar to floats in a parade. They can have mechanical aids such as ribs formed from electrical conduit, and bicycle parts turning a propeller or wheel.

Big boats are logistically hard to test. The construction pictures are the most interesting.

Pollock Boat

The 20 cardboard sheets were donated from two different companies. It is impossible to purchase cardboard sheets this big. They are strange sizes .. 6 feet by 7 feet .. and you don't want to fold them. So transporting them 70 miles on freeway becomes an issue. About $800 was spent in 2008 on wood glue, liquid nail, wall board sealant and paint.

Expense Detail

A school donated tools: tarp, box cutters, saws, screw driver, caulking guns, T-square, 8 foot straight edge. Donated items:

Organization Item Number
TimBar 7' by 6.5' corrugated 24
PCA 7' by 6.5' corrugated 24
SafeWay paper bags 10
Giant paper bags 20

Tools from school: box cutters, saws, screw drivers, caulking gun

Consumables Cost
Rollers !!$15
Roller Brushes $15
Paint Brushes $20
Paint Tray $3
Tray Liners $3
Wood Glue $320
Contact Cement $30
Wallboard Sealant $210
Liquid Nail $84
Paper Bags $10
Paint $90
TOTAL $800

Implement[edit | edit source]


Smashing Cardboard together with weights while glue dries

Liquid Nail


Spreading Glue versus Painting

Holding Cardboard together while drying

Elevating cardboard while working on it


Forms Jigs

There are many ways to hold cardboard in place ...

  • clamps

Leaving screws in a boat can result in sharp wood screws appearing while sinking and cut people.

  • Wood glue dries (days) but is cheap.
  • All other forms of glue are either expensive or not strong enough.
  • Gorilla glue is good for quick repairs when the boat is wet during competition day .. otherwise don't use .. it foams up and requires moisture to cure

Apply thin coats of glue. Do not pour into crevasses and form puddles and expect it to harden into a block. Wood glue can form a hard shell with a liquid interior that is both not very strong and can explode into a mess.

Paint the glue on.


Cardboard is a lot like dry wall or Gypsum board.

Skinning the boat with paper bags



Testing Corrugated Fiberboard

Garbage boats clean up lakes .. expect cardboard to float for a while after the boat sinks ...

Cleanup of the work space cardboard debris is easy. It is the paint/glue/wallboard sealant mess that can be impossible. Chemicals, pressure washing don't work. Scrapping can damage the original concrete finish. Make someone responsible, give them tarps, work on grass as much as possible, plan small thin coats rather than one big thick coat.

Pouring glue into cracks is the single biggest mistake. One doesn't want to move the boat, tries to put it in storage position, and the tarps always spill liquids .. plan on it.

Operate[edit | edit source]

A typical competition involves races and parades. In some competitions, the rhythm is to race the boat in pairs, carry it back to the starting line and race again in tournament. In other competitions, everyone pushes off the shoreline at once.

There is usually a MC making announcements and a panel of judges that are continuously commenting on the boats. The judges typically start with a narrative supplied (or not supplied) by the builders. The judges run around the docs organizing the races.

The races identify the fastest boat through heats like a swimming meet. After all races, there is typically a demolition derby. Announcements at the end give out awards in other categories .. most dramatic sinking, most futile, most dramatic sinking, best of a theme, judges awards, etc.

Race Details


Water Route

Demo[edit | edit source]


Next Steps[edit | edit source]

  • Build established boat designs using corrugated fiberboard
  • Use old fiberglass forms to build corrugated fiberboard boats
  • Develop questionnaire for those requesting a boat be built that focuses on how the people want to get wet.
  1. bad engineering
  2. bad planning
  3. demolition derby
  4. planned failure mechanism
  5. unknown planned failure mechanism