diff --git a/libraries/SITL/SIM_Sailboat.cpp b/libraries/SITL/SIM_Sailboat.cpp
new file mode 100644
index 0000000000..9e0e38c6da
--- /dev/null
+++ b/libraries/SITL/SIM_Sailboat.cpp
@@ -0,0 +1,180 @@
+/*
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see .
+ */
+/*
+ Sailboat simulator class
+
+ see explanation of lift and drag explained here: https://en.wikipedia.org/wiki/Forces_on_sails
+
+ To-Do: add heel handling by calculating lateral force from wind vs gravity force from heel to arrive at roll rate or acceleration
+*/
+
+#include "SIM_Sailboat.h"
+#include
+#include
+#include
+
+namespace SITL {
+
+Sailboat::Sailboat(const char *home_str, const char *frame_str) :
+ Aircraft(home_str, frame_str),
+ max_wheel_turn(35),
+ turning_circle(1.8)
+{
+}
+
+// calculate the lift and drag as values from 0 to 1
+// given an apparent wind speed in m/s and angle-of-attack in degrees
+void Sailboat::calc_lift_and_drag(float wind_speed, float angle_of_attack_deg, float& lift, float& drag)
+{
+ // check extremes
+ if (angle_of_attack_deg <= 0.0f) {
+ lift = lift_curve[0];
+ drag = drag_curve[0];
+ return;
+ }
+ if (angle_of_attack_deg >= 170.0f) {
+ lift = lift_curve[17];
+ drag = drag_curve[17];
+ return;
+ }
+
+ uint8_t index = constrain_int16(angle_of_attack_deg / 10, 0, 17);
+ float remainder = angle_of_attack_deg - (index * 10.0f);
+ lift = linear_interpolate(lift_curve[index], lift_curve[index+1], remainder, 0.0f, 10.0f);
+ drag = linear_interpolate(drag_curve[index], drag_curve[index+1], remainder, 0.0f, 10.0f);
+
+ // apply scaling by wind speed
+ lift *= wind_speed;
+ drag *= wind_speed;
+}
+
+/*
+ return turning circle (diameter) in meters for steering angle proportion in degrees
+*/
+float Sailboat::turn_circle(float steering)
+{
+ if (fabsf(steering) < 1.0e-6) {
+ return 0;
+ }
+ return turning_circle * sinf(radians(max_wheel_turn)) / sinf(radians(steering*max_wheel_turn));
+}
+
+/*
+ return yaw rate in degrees/second given steering_angle and speed
+*/
+float Sailboat::calc_yaw_rate(float steering, float speed)
+{
+ if (fabsf(steering) < 1.0e-6 or fabsf(speed) < 1.0e-6) {
+ return 0;
+ }
+ float d = turn_circle(steering);
+ float c = M_PI * d;
+ float t = c / speed;
+ float rate = 360.0f / t;
+ return rate;
+}
+
+/*
+ return lateral acceleration in m/s/s
+*/
+float Sailboat::calc_lat_accel(float steering_angle, float speed)
+{
+ float yaw_rate = calc_yaw_rate(steering_angle, speed);
+ float accel = radians(yaw_rate) * speed;
+ return accel;
+}
+
+/*
+ update the sailboat simulation by one time step
+ */
+void Sailboat::update(const struct sitl_input &input)
+{
+ // update wind
+ update_wind(input);
+
+ // in sailboats the steering controls the rudder, the throttle controls the main sail position
+ float steering = 2*((input.servos[0]-1000)/1000.0f - 0.5f);
+
+ // calculate mainsail angle from servo output 4, 0 to 90 degrees
+ float mainsail_angle_bf = constrain_float((input.servos[3]-1000)/1000.0f * 90.0f, 0.0f, 90.0f);
+
+ // calculate apparent wind in earth-frame (this is the direction the wind is coming from)
+ Vector3f wind_apparent_ef = wind_ef + velocity_ef;
+ const float wind_apparent_dir_ef = degrees(atan2f(wind_apparent_ef.y, wind_apparent_ef.x));
+ const float wind_apparent_speed = safe_sqrt(sq(wind_apparent_ef.x)+sq(wind_apparent_ef.y));
+
+ // calculate angle-of-attack from wind to mainsail
+ float aoa_deg = MAX(fabsf(wrap_180(wind_apparent_dir_ef - degrees(AP::ahrs().yaw))) - mainsail_angle_bf, 0);
+
+ // calculate Lift force (perpendicular to wind direction) and Drag force (parallel to wind direction)
+ float lift_wf, drag_wf;
+ calc_lift_and_drag(wind_apparent_speed, aoa_deg, lift_wf, drag_wf);
+
+ // rotate lift and drag from wind frame into body frame
+ const float wind_to_veh_rot_angle_deg = wrap_180(180 + wind_apparent_dir_ef - degrees(AP::ahrs().yaw));
+ const float sin_rot_rad = sinf(radians(wind_to_veh_rot_angle_deg));
+ const float cos_rot_rad = cosf(radians(wind_to_veh_rot_angle_deg));
+ const float force_fwd = fabsf((lift_wf * sin_rot_rad)) + (drag_wf * cos_rot_rad);
+
+ // how much time has passed?
+ float delta_time = frame_time_us * 1.0e-6f;
+
+ // speed in m/s in body frame
+ Vector3f velocity_body = dcm.transposed() * velocity_ef;
+
+ // speed along x axis, +ve is forward
+ float speed = velocity_body.x;
+
+ // yaw rate in degrees/s
+ float yaw_rate = calc_yaw_rate(steering, speed);
+
+ gyro = Vector3f(0,0,radians(yaw_rate));
+
+ // update attitude
+ dcm.rotate(gyro * delta_time);
+ dcm.normalize();
+
+ // accel in body frame due acceleration from sail and deceleration from hull friction
+ accel_body = Vector3f((force_fwd * 1.0f) - (velocity_body.x * 0.5f), 0, 0);
+
+ // add in accel due to direction change
+ accel_body.y += radians(yaw_rate) * speed;
+
+ // now in earth frame
+ Vector3f accel_earth = dcm * accel_body;
+ accel_earth += Vector3f(0, 0, GRAVITY_MSS);
+
+ // we are on the ground, so our vertical accel is zero
+ accel_earth.z = 0;
+
+ // work out acceleration as seen by the accelerometers. It sees the kinematic
+ // acceleration (ie. real movement), plus gravity
+ accel_body = dcm.transposed() * (accel_earth + Vector3f(0, 0, -GRAVITY_MSS));
+
+ // new velocity vector
+ velocity_ef += accel_earth * delta_time;
+
+ // new position vector
+ position += velocity_ef * delta_time;
+
+ // update lat/lon/altitude
+ update_position();
+ time_advance();
+
+ // update magnetic field
+ update_mag_field_bf();
+}
+
+} // namespace SITL
diff --git a/libraries/SITL/SIM_Sailboat.h b/libraries/SITL/SIM_Sailboat.h
new file mode 100644
index 0000000000..911d1f29a5
--- /dev/null
+++ b/libraries/SITL/SIM_Sailboat.h
@@ -0,0 +1,56 @@
+/*
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see .
+ */
+/*
+ sailboat simulator class
+*/
+
+#pragma once
+
+#include "SIM_Aircraft.h"
+
+namespace SITL {
+
+/*
+ a sailboat simulator
+ */
+class Sailboat : public Aircraft {
+public:
+ Sailboat(const char *home_str, const char *frame_str);
+
+ /* update model by one time step */
+ void update(const struct sitl_input &input);
+
+ /* static object creator */
+ static Aircraft *create(const char *home_str, const char *frame_str) {
+ return new Sailboat(home_str, frame_str);
+ }
+
+private:
+
+ void calc_lift_and_drag(float wind_speed, float angle_of_attack_deg, float& lift, float& drag);
+ float turn_circle(float steering);
+ float calc_yaw_rate(float steering, float speed);
+ float calc_lat_accel(float steering_angle, float speed);
+
+ float max_wheel_turn;
+ float turning_circle;
+
+ // 10 point curves for lift and drag. index is angle/10deg
+ // angle-of-attack 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170+
+ float lift_curve[18] = {0.00f, 0.00f, 0.80f, 1.00f, 0.95f, 0.75f, 0.60f, 0.40f, 0.20f, 0.00f, 0.00f, 0.00f, 0.00f, 0.00f, 0.00f, 0.00f, 0.00f, 0.00f};
+ float drag_curve[18] = {0.10f, 0.10f, 0.12f, 0.15f, 0.20f, 0.27f, 0.35f, 0.50f, 0.70f, 1.00f, 0.70f, 0.50f, 0.35f, 0.27f, 0.20f, 0.15f, 0.12f, 0.10f};
+};
+
+} // namespace SITL