Milestone 2: Optimization of Stability, Drag, and Propulsion

This week, we started to analyze our designs with some models and simplified calculations.

Buoyancy and Stability

Estimated weight of vessel + estimated weight of battery pack + weight of heaviest memberx2 = 3780N

Based on this value, the hull was adjusted (Rhino) such that the volume of the hull underwater was close to 3780N.

Cross-sections of the hull was taken, and tilted to a degree of 10 degrees to test stability by comparing the center of gravity with the center of buoyancy. As seen below, the latter is above the former, confirming the stability of the boat should it tilt to an angle of 10 degrees in the event of choppy waters.hull1

Drag

prop1

Desired Speed: 10-15 kts
Length: 2.4m
Estimated Weight of Vessel: 150kg
Heaviest Passenger: 80kg

Thrust

Screen Shot 2015-06-23 at 2.38.28 pm

η = (T × V) / (2π n × Q)

Assuming the ideal efficiency of 80%, we can find n x Q = 29.901 based on a speed of 10kts, and drag force of 29.22N.

Motors

http://www.hobbyking.com/hobbyking/store/__31677__Turnigy_AquaStar_4084_1050KV_Water_Cooled_Brushless_Motor.html

motor1amotor1b

http://alienpowersystem.com/shop/40mm/4070-inrunner-brushless-motor-rc-boat-2700kv-7600w/

motor2a motor2b

Propulsion

Based on our list of motor candidates, 2 battery packs of 12V will be sufficient. From the equations given in the lectures, we have deduced that nQ=30. This constant shows the trade-off between rotational speed of the propeller and its torque.

Electrical

Our battery packs will be placed right at the front of the boat to maintain neutral balance between the bow and stern, even though it will not be sufficient to keep the boat balanced.

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