Here is comparison of latching systems. The different prototypes for roboat and other models from the community. The comparison is applied in all three stages of the latching process: homing, docking and garaging.

This step utilizes a tracking system to assist in guiding the AUV into the dock. This system is activated once the AUV is within a close range of distance to the docking station.

Ideally we should have an accurate sensor (≤40mm) that can detect the target from far away (≤1500m), work outdoors and with minimal cost.

GUIDING	ACCURACY (mm)	DISTANCE (m)	SENSOR	COST	POWER (W)	TEST
Camera-AprilTag	±10mm	2m	Camera	$100		In/Outdoors
Magnetic	±50mm	0.3m	Magnetic field	$10	---	Indoors
Electro-Magnetic	±50mm	0.3m	Magnetic field	$20		Indoors
IR sensors	±50mm	1m	IR Photodiodes	$10		Indoors
Indoors GPS	±50mm	10m	Ultrasound	$400		Indoors
Outdoors GPS	±50mm	1000m	RTK	$9876		---
IR camera	±50mm	0.5m	IR Camera	$500		Indoors
Lidar	±100mm	100m	VLP16	$6000		In/Outdoors

Table 1. Guiding methods for latching a roboat.

Docking specifically refers to joining the AUV to a static docking station.

DOCKING	GENDER	TOLERANCE (m)	ACTUATORS	POWER	TEST
Magnetic	Yes	20mm (Magnetic field)	---	---	Indoors
Electromagnets	Genderless	10mm (Magnetic field)	1 per electromagnet		Indoors
Arms	Yes	V-shape 200mm	2 per arm		In/Outdoors
Funnel	Yes	80mm (adjustable)	1 per funnel		Indoors
Gripper	Genderless	(200mm) Arm length	1 per gripper		In/Outdoors
Stinger	Yes	---	2 per set		---

Table 2. Docking methods for latching a roboat.

The garaging refers to how the vehicle is locked, securing its position. In this context, the locking mechanism can be as simple as a hook, or a more elaborated system that involve active devices, such as motorized-screws.

GARAGING	STRENGTH	JOINT TYPE	ACTUATORS	POWER	TEST
Magnetic	LOW (70N) - magnetic field	Rigid	---	---	Indoors
Electromagnets	LOW (70N) - magnetic field	Rigid	1 per electromagnet	2-100 W while latched	Indoors
Push and lock	High - Physical lock	Spherical	1 actuator for lock/unlock	0.5 W per operation	In/Outdoors
Motorized funnel	High - Physical lock	Spherical	1 actuator for lock/unlock	0.5 W per operation	In/Outdoors
Adaptive funnel	High - Physical lock	Spherical / Rigid	1 actuator for lock/unlock + 1 or 2 for ams	0.5 W per operation	Indoors
Gripper	High - Physical lock	Cylindrical pair	1 per gripper	0.5 W per operation	In/Outdoors
Stinger	High - Physical lock	Cylindrical pair	2 actuators	0.5 W per operation	---

Table 3. Garaging methods for latching a roboat.

Mechanical and bio-inpired prototypes, methodologies and guiding systems (AprilTags3D) were designed in this study of latching systems for autonomous robotic boats. The designs were prototyped and test on different swimming pools, the Charles River, Amsterdam canals and Tokyo marina.