Weeks 4 and 5 - Boat design and calculations

For week 4 and 5, we are required to build a boat and test the buoyancy of the boat as well as to find the force exerted by the motors. 

There is also limit as to how big our boat can be:

• Length < 30 cm
• Width < 20 cm
• Height < 20 cm
• Operating water depth < 15 cm

Constructing the boat over this limit can be done, however, marks will be deducted in doing so.

Here are some photos of our boat design on paper:

Figure 1

Figure 2

Figure 3 

Figure 4

Our team designed a boat with 2 frames on the side while the middle is empty, as seen in figure 5. This type of design are known as catamarans. Only metal rings are used to link the 2 frames, as well as to hold 2 cans as required. Polystyrene, also known as Styrofoam, is being used as the base to allow the boat to float.

Figure 5 (GPS World, 2016)

The dimensions for our boat:

• Length = 29 cm
• Breathe = 19 cm
• Height = 19 cm
• Operating depth of motor = about 5 cm

Our team used the following materials to construct the boat:

• 1x protractor.
• 4x 9V  toy propellers
• Half a sheet of polystyrene foam 
• Some steel wiring
• Some perforated steel bands
• Some ice-cream sticks
• Screws and nuts and cable ties as needed.  

The machinery used to construct the boat:

• Scroll saw

Figure 6: Scroll saw

The tools used to construct boat:

Hot glue gun  

Digital weighing scale (digital)

File

Ruler

Styrofoam cutter

Figure 7: Hot Glue Gun

Figure 8: File

After spending about 2 weeks to build the boat, we are finally able to test it. Some of the photos taken during the prototyping process:

Figure 9

Figure 10

Figure 11: Complete Product 

The bottom of the twin-hull design, which features a streamlined bottom, allows the boat to move faster. Both hulls are joined together by lightweight ice-cream sticks, as well as metal bands to carry the load of the boat between both hulls, thus spreading the weight equally between both hulls.

Now, let's test it!

Test 1: Buoyancy

Firstly, with the 2 cans on the boat, we deliberately add as many marbles on the boat until the boat capsizes. This is to determine the maximum angle of longitudinal and lateral roll that the boat can sustain.

Photos of the tests:

Figure 12

Figure 13: Boat on the verge of capsizing

Buoyancy Calculation:

Formula for buoyancy calculation= p x V x g

Relevant weights (In Grams) :

Motor (x4) :108

Steel Band (x4):40

Cable Tie (x8) :8

Satay Stick (x2) :2

Marbl :6

Ice Cream Stick (x3) :6

Can of soft drinks (x2) :330

Buoyancy of boat with cans:

Total Mass with cans: 830g

Since W=mg

W=0.830kg x 9.8

   = 8.134N

Buoyancy force  =Weight 

For safety factor = BF x2

                           = 8.134N x 2

                           =16.268N

Volume of boat (Including cans):

Volume= BF/Gravitational force x density of water

Volume=16.268/9.8x1000

Volume=0.00166m^3

Volume=1660cm^3

During the ideation and brainstorming of the boat design we also took into account the drag that would be experienced by our boat. After much pondering and consideration we concluded that we would utilize a cone shaped head for our boat.The cone shaped head although does not posses the lowest drag coefficient was ideal for our boat as the shape was relatively easier to create and was more suited towards our design.

Below is the drag force experienced by our creation.

Drag Force=0.5 x C x p x A x V^2

where, 

C = drag coefficient,

p = density of water,

A = front surface area of the boat

V = the volume of the boat

Drag Force= 0.5 x 0.5 x 1000 x (0.00166)^2

                  =0.6889 x 10^-3Nm

The maximum angle is 35 degrees, about 50 marbles, before the boat capsized.

Figure 14: Angle measurements

Force for the boat to capsize=

Test 2: Propulsion

We are required to measure the thrust (in kg) with respect to the voltage supplied to the motors.

Figure 15: Results for force measured

We also use Excel to show the best-fit trend line of the data recorded and we can see that many data are apply the line of best fit.

Figure 16: Graph of force with respect to voltage

That's all for these 2 weeks folks. Stay tune for week 6 activity as well as our prototyping of our robot that can take pictures at 1.5 meters depth.

References

• GPS World (2016) Researchers to Test Water Drone for Bridge Inspections  Available at: http://gpsworld.com/researchers-to-test-water-drone-for-bridge-inspections/  (Assessed 19th November 2016)

Joel

Keith