Icarus, a human powered cardboard boat

Mark Battley, November 2000

Gidday from NZ. Here are a few pictures of my HPB (Human Powered Boat) "Icarus", which was built in 1993 for the local "cardboard cup" event, and raced almost every year until this year when the event was sadly not held. With a few rebuilds along the way... that cardboard does get soggy!

Icarus is a one person pedal/propeller design, main center hull with outriggers. Puller prop at the bow, pilot facing forwards. It was always the fastest local single person boat (quicker than single racing kayaks with skilled paddlers), only ever beaten in speed by a two person k2 kayak replica (whom I understand won the 1993 Crystal Lake IL international event), and a similar two person HPB.

There are more notes about construction and performance scattered through this simple webpage…..

Icarus in motion

Front propellers (model aircraft)

The propellers were placed at the bow so that they would act in undisturbed water, to reduce draft, and to minimise the length of the driveshaft. The main disadvantage of this layout is that they are a bit too close to the surface, and in choppy conditions sometimes one or more blade can come out of the water, resulting in cavitation. Using two, two blade propellers helped reduce the effect of this, and also seemed to improve acceleration from rest.

The other problem with this layout is that Icarus is very difficult to steer at low speed. A rear propeller just in front of the rudder should enable the use of thrust to steer. At speed steering is not a problem.

 

Another view from the bow

And from the stern, showing the simple rudder, and the elegant use of duct tape!

Sometimes the cardboard gets soggy…. Repair time!

The bow section removed for a rebuild, note the layout of the drive system.

The overall ratio used is from about 6:1 to 8:1 depending on the propellers. To achieve this with conventional bicycle parts I used two chains, with a standard rear cluster as an intermediate idler (machined a fitting for an internal bearing). For example you can get 8:1 from a 52 chainwheel driving a 13 on the cluster (4:1), then a 24 on the cluster driving a 12 on the final drive (in my case a custom made 90 degree gearbox, driving the propeller shaft) gives another 2:1, 8:1 overall. The cluster acts as an adjustable (but fixed when in use) tensioner. The drive system has been completely reliable, apart from the second race when it hit weed and sheared the drive pins at the propeller. Hardened pins (drill blanks) solved that. The steel driveshaft runs in nylon bushes in an aluminium shaft tube. The universal joint between the gearbox and the driveshaft is from a socket set.

In the first trial one of the small hulls came off causing a capsize, and enabling me to discover that it is indeed possible to release from Look clipless bicycle pedals while underwater! Probably not a consideration for the pedal designers…

 Repair process underway, showing internal structure

As is required for the class, the hulls are all cardboard, and "single pot" glues and paint used. Other materials (mainly aluminium) are used for the drive system, and to join the hulls together. Even the seat is cardboard, although supported by the aluminium frame.

New one piece outside skin, that duct tape is wonderful stuff!

The start of a Class 2 Cardboard Cup race, well ahead by the first buoy

Note the surface piercing prop on the left boat. Lots of spray, not a lot of speed. But it seemed to float a lot higher than planned, which probably didn't help! The blue boat on the right was also propeller powered. I'm not sure what the central boat is using, it shouldn't have paddles in a class 2 race.

Nearly to the second buoy, the competitors yet to reach the first

More competition in the regional final: crowded around the first mark

The biggest problem that Icarus has is poor acceleration compared to paddle powered craft. It is necessary to feed in power very gently until the boat speed reaches an adequate level for the prop pitch, or you get cavitation. Then you can put in as much power as your legs will let you. So in a competitive race against paddle craft I have to go wide to stay away from flailing paddles, and rely on speed to take the long way home….

Relying on a good top speed and taking the long way on the outside of the other boats

This was one of the closest races, the start was a bit of a mess, and I had to go quite wide around the other boats.

Straight line to the finish….

Made it!

Presently (October 2000) Icarus is officially "resting", in need of another hull rebuild. It is a shame that the cardboard cup competition seems to have died here, unless I can stir it up again I plan to transplant the frame and drive system to a spare fibreglass hull I have.

If I rebuild Icarus as a cardboard HPB the main improvements would be a longer, thinner main hull, and a rear mounted propeller.

I haven't yet figured out how to make hydrofoils out of cardboard that have adequate strength….

Update 1st November 2000:

I've just ordered a 15x25" human powered boat prop from http://www.bolly.com.au, measured up my spare fibreglass hull (a flat deck "ski" based on a racing kayak hull), and finished the basic design of the revised drivetrain... Icarus will live again soon!

Credits

Icarus would not happened without the support of my work (Industrial Research Limited), who sponsored the race entries and put up with the mess we made in the work labs.

The real key to its success has been the great workmates and friends who helped design, build, test and race Icarus. Many have helped over the years, but those deserving particular mention are Richard Wong (design, construction, testing, and long suffering race day pit crew), Chris Murphy (superb machining skills: the gearbox and drivetrain have never failed), John dePont (building, repair and pit crew), Andrew Lush (hull building and high quality repairs), and Magnus Burman (hull repair, race day pit crew, general assistance and much appreciated abuse). Thanks guys!