Professional BoatBuilder - April-May 2018

32 Professional BoatBuilder

HIGH SPEED: Foiling, Part 1

floppy drive. And here’s where it gets

a bit more academic: Larsen derived

the control law using the Linear Qua-

dratic Regulator algorithm coded in

Visual Basic. Its control gains vary

with speed. The differential equation

of height is:

ddh/ddt = k*(α–(dh/dt)/v) – g

where h = height; α = angle of attack

measured from the zero-lift angle

relative to the boat’s coordinate

system; k = the bow foil’s lift slope;

g = the gravitational constant; and

v = velocity.

Using Xfoil, a free software for sub-

sonic airfoil development, he designed

and built a new aluminum bow strut,

carbon fiber bow foil, aft foil, and side

struts. He also added a foil-position

sensor, an rpm sensor, a new bow

foil actuator, a servo valve/manifold,

and electronic interface to the com-

puter. The actuated bow foil is oper-

ated by hydraulics with a custom-

built throw cylinder and a fast Rexroth

high-performance servo valve that

opens fully in 10 milliseconds.

To measure the distance from the

gunwale to the water, which deter-

mines foiling height, Larsen added

two Senix Toughsonic 14 ultrasonic

sensors, which he installed in the bow

at 15° angles. An ADXL 203 acceler-

ometer is also mounted in the bow,

while the impeller for the knotmeter

system’s parameters on a 10" (254mm)

sunlight-readable LCD screen in the

cockpit, the update speed is 75 Hz.

Larsen programmed the computer

with 1,500 lines of code in C++. About

half is reserved for the display, the rest

for the control algorithm and interfac-

ing subroutines. A Borland C++ 5.02

compiler generates the executable

code, which is transferred to the

SBC0489 flash memory through its

Talaria’s 133-MHz, 64-bit CPU is an

industrial computer with the neces-

sary interface capability. It’s a SBC0489

from Micro/sys, with a total of 16

channels of analog-to-digital convert-

ers (ADC), 1-MB flash memory, four

channels of digital-to-analog convert-

ers (DAC), a RS232 interface, VGA

screen driver, and a floppy disk port.

While executing the flight-control

software and displaying the control

Left—The custom-programmed LCD monitor displays vital data including speed, rudder angle, roll rate, and foiling height.

Right—Talaria’s “brain,” an industrial 133-MHz, 64-bit central processing unit, sits unceremoniously on the aft bunk, surrounded

by coils of cables.

A view of the stern reveals the extension of the outdrive shaft, which keeps the

propeller submerged when foiling, and Talaria’s anhedral rear foils.

DIETER LOIBNER (ALL)

Foiling172-ADFinal.indd 32 2/21/18 7:39 PM