# Ben's Website

Serious musings

The EMA senior design spans two semesters; the first develops an idea into a consumer product, while the second tasks us to design an airplane, submarine, or spaceship. Over the first semester David Aguilar, Lisa McGill, Scott Sardina, Jordan Wachs, and I developed BoomAlert, a device to warn sailboat crews of dangerous boom movements. See also my spring design, LEVITATE.

If you want to watch our final presentation instead of reading, seek to 1:50 here.

BoomAlert alerts sailboat crew to dangerous motions of the sailboat boom known as autojibes. These occur when sailing with the wind and are due to poor captainship or random, unanticipable, changes in the wind. Immediately before the autojibe the sail is typically full-out, nearly perpendicular with the centerline of the boat. As the wind changes direction the boom quickly accelerates and swings across the cockpit to the other side of the boat, reaching rotational velocities of >2 rad/sec. These angular velocities are not very dangerous near the pivot point (gooseneck), but can reach 5-10 mph where the crew sits. If a crewmember is unaware, they can be struck by the boom, as seen here: (I would embed, but the video owner doesn't want anyone to see his video. Begrudgingly, a link.)

To overcome this problem, BoomAlert senses boom accelerations and alerts the crew by aural and visual means. Here are the major parts:

## Accelerometer Housing #

We began our design with a sail on Lake Mendota to characterize sailboat boom movements. With a waterproof camera attached to the mast, looking upward at the underside of the boom, Dave simulated autojibes while I recorded videos of the boom sweeping from side to side. Returning to land, we analyzed these videos and determined angular positions, velocities, and accelerations. Based on these results, we decided to measure boom acceleration and trigger the alerts when acceleration crosses a user-set threshold. This threshold is determined by boom length and crew position along the boom, so that BoomAlert can be used on any size of boat.

The accelerometer box holds a 3-axis accelerometer which communicates with a microcontroller by the I2C two-wire serial communication protocol.

## Control Box #

The control box contains the system electronics, power supplies, and alert devices.  An Atmel ATMega 368 microcontroller compares the accelerometer readings against the acceleration threshold, and depending on the boom's position, alerts the sailors to the motion.

## Documents #

View our slides [2.2MB]