Only the cement is allowed to touch the water. It can not be bigger than 19cm in Length by 10cm in height. It also has to hold twice it's Weight.
Just displace more water than the boat weighs.
The boat is made out of floatable materials. I would save myself in the same way I would save myself in a regular canoe ...... swim to shore and help save anyone with me. = )
Get some window screen and make it in the shape of your boat. rub concrete into the screen and let it dry. Test will it hold water? If YES, trim off any excess screen If NO, rub on another coat of cement, let it dry and test again for water tightness. Repeat until it is water tight You are done
it just has to float, nothing else? How deep can it be? assuming 10cm. The maximum volume, if you shape it like a box, is 19*10*10 = 1900 cm? density of water at 20C = 0.998 g/cm? density of cement = 3.1 g/cm? so the weight of the water displaced is about 1900 g or 1.9 kg. and that is the maximum weight of the boat total with load. I'd keep it to 1 kg to have some margin. That means the cement part can be only 0.66 kg, or 1.4 pounds. That is not much. How about if you make a box 18x9x9 cm out of a light wood, and coat it with 1 cm of cement? That would take a cement volume of: 18x9x3 + 9x9x2 = 486+162= 648 cm? x 1cm = 648 cm? this would weigh 648 cm? x 3.1 g/cm? = 2000 g, too high So you will need a very thin coating of cement, 3 mm, which will get you a weight of 660 grams. difficult. .
