California Solar Regatta – Propulsion

The SMUD Solar Regatta was established to promote renewable energy through solar technology and innovation. For our Senior Project, we designed and built the Propulsion System of Cal Poly’s boat.

Without A Paddle: A Cal Poly Senior Project

The Cal Poly 2020 Solar Regatta Team consisted of two senior project teams. Up a Creek focused on the boat’s hull, while Without a Paddle (that’s us!) took on all things propulsion.

Niko Banks

Design Lead

Designed and manufactured propellers, conducted testing and analysis of solar panel energy conversion and motor efficiency, and assisted with CAD modeling.

Nathan Carlson

Systems Lead

Coordinated between sponsors, advisors, faculty and peers to ensure both the Hull and Propulsion Teams worked together to design a boat that met competition requirements.

Eric Rinell

Manufacturing Lead

Designed gearbox and motor mount. Reviewed designs for manufacturability. CNC programmed and machined the gearbox. Performed CAD integration with Hull Team.

Alex Larson

Test Lead

Designed and manufactured  the rudder.  Put together testing plans for custom manufactured components.  Solutions expert resource for teammates.

General Overview

Play Video

Technical Overview

Play Video

Our Project's Digital Poster

Problem Statement

Design and build a propulsion system for a solar powered boat to compete in the 9th Annual SMUD Solar Regatta. The propulsion system will be powered by either the solar panels or the battery (depending on the race) and will be suited to maximize scores in all three races.

Competition Overview

The SMUD Solar Regatta consists of three races (Endurance, Sprint, and Slalom) as well as a presentation and various bonus awards.

The Endurance Race is scored on how many laps are completed in 25 minutes (battery power only).
The Slalom Race is scored on the time it takes to navigate around the buoys (solar panels only).
The Sprint Race is scored on the time it takes to travel 100 yards, starting from rest (solar panels only).

Design Constraints

  • Maximum boat dimensions: 20’ x 8’ x 5’
  • Solar Panels and Battery are only allowed forms of energy storage (no capacitors)

Propulsion Design Layout

Two propulsion units were chosen for the final design for a number of reasons, including:

  • Multiple, smaller propellers are more efficient than one larger propeller
  • Improved stability over a single unit in the center

Other notable design choices:

  • Steering system designed with cable system in order to be adaptable to different pontoon configurations
  • Each propulsion unit rotates to provide steering rather than changing speeds of each propeller- keep each propeller at max efficiency speed
  • Gearbox machined out of aluminum for ease of manufacturing
  • Propellers 3D-printed for ease of manufacturing and comparatively low cost
  • Rudder has a wood core for shape laminated with carbon fiber to keep it light but also strong enough to support gearbox and propeller
  • Solar panels planned to articulate toward the sun to provide maximum power input
Layout of components for one unit
Transparent view of the gearbox.

This project was sponsored by Cal Poly Mechanical Engineering, SMUD, and Electric Motor Wholesale.

Design Concept

Exploded view of a single unit

The chosen design was to have two propulsion systems, one on the back of each pontoon. The CAD model of a single propulsion unit allowed the dimensions and tolerances to be finalized for each component of the subsystem.

Propeller Analysis

Traditional propeller performance curve (non-dimensional)
Dimensioned performance curve

Through analysis, a propeller diameter of 9″ and an operating speed of 900 RPM was chosen to provide the maximum possible efficiency. The torque and speed of the propeller were designed to coincide with the same torque and speed required for high motor efficiency.

Using the dimensioned performance curve the top boat speed was determined to be 7.3mph. Each unit, at 900 RPM, produces 11.25 lbf of thrust at an efficiency of 80%.

Manufacturing Process and Components

5-Axis CNC gearbox
Laser Cut Airfoils
3D Printed Propellers

We used the manufacturing process that best fit the part and application:

  • CNC machining for tight tolerance aluminum parts
  • 3D printing for small complex parts
  • Laser cutting for wood
  • Carbon composites for strong and smooth submerged surfaces
  • Sheet metal for simple but strong components

Design Verification/Testing

Solar Panel Testing (panel shaded)
Motor Test Jig

Solar Panel Output – The solar panels specified output (235 Watts) were verified using a PV test device. The panels were also tested in their response to changing lighting conditions. It was found that a head-sized shadow reduced power by nearly 30% and that angling the panels away from the sun caused a significant power drop.

Motor TestingA dynamometer was used to generate torque-speed curves for the motor. Early motor testing led us to purchase a higher KV motor (faster) and an electronic speed controller better suited for its operation.

Final Design

Specifications of One Unit:
Weight – 6.5 lbs
Height – 34 Inches
Thrust – 11.25 lbf
Boat Top Speed – 7.3 mph

CAD model of one unit
Propulsion units mounted on the hull

Custom Components

  • Propeller
  • Gearbox Housing
  • Rudder
  • Motor Mount
  • Mounting Bracket

Stock Components

  • Bearings
  • Bevel Gears
  • Drive Shafts
  • Carbon Downtube
  • Electric Motors
  • Box Tubing
  • Fasteners

Future Application

This design and manufacturing processes will be used by the 2021 Cal Poly Solar Regatta team. The prototype unit we manufactured will be used for testing and optimization before completing two final units to be used in competition next year. This design could also be modified for personal use for boats with low speed requirements such as fishing trollers and water taxis.


Improvements to be made for next years design

  • Solar tracking to get maximum power from solar cells
  • Gearbox design to simplify manufacturing
  • Custom electrical regulator to reduce losses
  • Utilize a water channel to perform flow visualization on the propellers and rudder.
  • Design different propellers for each race to ensure the maximum efficiency under different conditions
  • Verify simulation results and confirm the model matches the unit’s performance

CAD Gallery

Propulsion systems attached to the hull
Single propulsion unit
Exploded view of propulsion unit
Exploded view of the hinge
Exploded view of the gearbox
Transparent view of the gearbox
Rudder tilting mechanism

Manufacturing Gallery

Gearbox housing first operation machining in progress
Housing second operation in progress
First article completed housing
Partial 3D print of propeller prototype
Finished 3D printed propeller
Tested materials and print settings on scaled propellers
3D printed motor mount in progress
Laser cutting airfoil sections for the rudder

From all of us at Up a Creek Without a Paddle, Thank You!


First off, a huge thanks to our project advisor Dr. Brian Self for helping our team throughout the year, he was always a voice of reason and encouragement. Special thanks to Dr. Peter Schuster for being our senior project coordinator, and for working with Dr. Self to adeptly transition to a virtual workspace our last quarter.  We could not have completed this project without the support and funding from Cal Poly and the Mechanical Engineering Department, we were very thankful for this opportunity. Thank you to SMUD for hosting this competition and for sponsoring our team, we were sad you had to cancel the 2020 competition, but Cal Poly is excited to participate again in 2021!

A list of other individuals that assisted in our design includes: Hans Mayer, Andrew Davol, Dale Dolan, Ali Dehghan Banadaki, Majid Poshton, and Eric Pulse.  This project was successful because of your support and insight, thank you.

Have a Question About this Senior Project?

Send an email to to be connected with the project team. Please include the title of the senior project you’re inquiring about in the subject line.

Interested in Sponsoring a Mechanical Engineering Senior Project?

Visit our Sponsorship Page to learn more!

Check Out More Projects!

Visit our ME Senior Projects Page to view the latest Mechanical Engineering senior projects from the class of 2021!


Share on facebook
Share on twitter
Share on linkedin