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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Milestone 1: Brainstorming and Preliminary Design

Last Thursday, we learned about the factors to consider in designing a hull.

  • buoyancy: The boat needs to float! (and not sink)
  • stability: The boat should stay upright in rougher waters.
  • waterproofing: The internal components (namely the electrical system) should stay dry.

We also wanted to consider potential speed and maneuverability since the ultimate goal would be to complete the boat challenge course (preferably quickly and without unplanned incidents).

With all this in mind, we looked at various boat designs on the Internet and drew a few of our own.

ryantse1ryantse2ryantse3ryantse4ksmori1ksmori2cedricy1cedricy2ryanchee1ryanchee2

We got together and discussed what we would like to have on our boat. We quickly decided that building a wooden boat would be a good experience and a challenge in craftsmanship. We also opted for a one-hull design rather than a two-hull design because of maneuverability. Our mutually agreed upon design resembles Ryan Chee’s design 1. To reduce drag, we proposed an altered bottom that we can construct given enough time. However, this would be hard to fit to the boat due to the curvature of the sides.

proposed

Next week is incorporating electrical and propulsion systems and drafting the design in Rhino or SolidWorks. Yay!

Also, on Friday, our last team member arrived in Boston (delayed due to an unfortunate mosquito bite). Welcome, Shobs! We named the boat after you!