Week 4 & 5 - Building Boats
Hello again!
Coming onto week 4 lesson, we were given a lecture on buoyancy, drag and stability. On week 5, we were taught about the propulsion force of the motor propeller. After that, we are to build a surface vessel with styrofoam as the only floatable material. Before that, we must calculate the amount of styrofoam needed to allow the vessel to float stably as according to the requirements given.
The surface vessel is subjected to the following maximum size constraints:
- Length < 30 cm Width < 20 cm Height < 20 cm
- Operating water depth < 15 cm (including the propeller diameter)
The given materials were:
• 1x or 2x Big basin or tank of water
• 2x cans of soft drinks (as the "cargo" of the boat)
• 1x protractor.
• 4x 9V mini pumps + 4 toy propellers
• Half a sheet of polystyrene foam
• Some steel wiring
• Some perforated steel bands
• Some ice-cream sticks
• Weighing scale (digital)
• Screws and nuts and cable ties
• Hot glue gun as needed
• 1 tube of POR UHU glue
THE VOLUMETRIC CALCULATIONS
Taking all the size constraints to consideration, we started on our boat experiment. The first thing we needed to do was the calculations. We were tasked to calculate the amount of styrofoam required to create our floating device.
Mass of bottle = 362g
Mass of boat with motor = 150g
Safety factor = 3
W = mg
= (0.362 * 9.81) + (0.150 * 9.81)
= 7.67142
Buoyancy Force = safety factor * W
= 3 * 7.67142
= 23.01426
Buoyancy Force = ρ * v * g
= 1000 * v * 9.81
23.01426 N = 1000 * v * 9.81
v = 23.01426 N / (1000 * 9.81)
= 2.346 x 10^-3 Cubic Meters
= 2346 Cubic Centimeters
Dimensions = 20cm x 25cm x 6cm
DESIGNS FOR THE BOAT
Designs for the floats
Overall design for the boat.
We decided to design it in an aerodynamic kind of design so that there would be less drag and higher efficiency of movement. We were told that a streamlined design would reduce the drag as it has a low drag coefficient of 0.4.
We did a test on whether the vessel would float and it did, but the weight of the cans were too much, and the vessel sunk. Therefore, after much discussion among the team, we've decided to change our designs.
Improved designs:
BUILDING & FIRST TRY
Designing the boat
Retrofitting a propeller onto a waterproofed mini pump
Cutting styrofoam
First prototype of our surface vessel.
First try with two cans, the vessel would sink in, leaving only 3cm of styrofoam left above water level. And so, we changed the design to decrease its surface area to water so that there would be lesser pressure on the vessel.
SECOND TRY
We changed the design into a slimmer one, using the same platform we cut off the sides and glued it to the middle of floats. Then we used some ice cream sticks as the base support for the platform. After that, we proceeded to test it out with a 700g bottle. And finally, it is able to float with the weight placed on the platform. To mount the bottle on top of the platform, we took a piece of steel band and attached it onto the platform, so that the bottle is secured and would not fall off.
Voila! It floats!
THE MOTORS
Moving on, we attached the given motors onto the vessel. Later on, we proceed to soldering. We connected the live and neutral wires in parallel separately.
Once we were done with the soldering, we brought it out the test in the tub of water prepared.
Voila! It works!
THE EXPERIMENTS
1. The buoyancy test
Materials:
- Marbles
- Ziplock bags
We were to fill the bags with marble while also taking note of the weight of the bag. But before that, we must calculate the metacentric height.
Metacentric height is determined using the data we collected in the Overturning Moment (OM) vs angle of roll experiment.
W = 0.512 * 9.81
= 5.0220
W * mg tan θ = mx
mg = (0.301 * 17) / (5.022 * tan2θ )
= 2.185074057 cm
≈ 2.19 cm
After determining the metacentric height, we proceeded on with the experiment, which is the Overturning Moment (OM) vs angle of roll experiment.
We collected the data and collated them into a table and graph as shown below.
2. Propulsion test
Materials:
- Fishing wire
- DC power supply
- Thrust meter
Using the fishing wire, we tied it to both sides of the boat and tied its ends to hook onto the lever of the thrust meter. We then connect the motor to the DC power supply and then slowly increased its voltage level from 0V to 9V.
Recording the data displayed on the thrust meter.
ANGLE FINDER
Next, we had to build an angle finder to be able to gauge the angle of lateral roll for . We built ours using steel wiring, styrofoam, a protractor and some blue tack.
VIDEO
SUMMARY
The process of building a floatable device is not as easy as it looks. We learnt that we should not have designed it with the mindset of making it look "cool" and instead, should've gone for a more realistic and simplistic approach. After many failures and also help from our classmates from other groups, we have made a boat that can float and carry heavy objects. We've also had lots of help from our classmates on the calculations of buoyancy force, amount of styrofoam used, metacentric height etc etc.
THANKS FOR READING! :)
Edited by : Natalie
