Design of an unmanned surface vehicle for water quality examination of a harbour

I am currently engaged in developing an Unmanned Surface Vehicle (USV), focused on environmental monitoring, specifically focused on assessing the water quality of a harbour. In a nutshell, the USV will use a random motion and obstacle avoidance algorithm to randomly cover a large area of water and take readings.

I’m looking for some guidance in terms of the design of the hull. Firstly, I’m trying to figure out how big the vehicle should actually be. I would like to keep it as compact as possible, but I understand that it has to be a certain size in order to be stable in the strong ocean currents. I also understand that there is a calculation I can do to determine the speed of the vehicle in relation to hull length. Could you help me with a logical path that I could follow in order to determine the minimum size of the vehicle.

Secondly, I’m stuck between HDPE and fibre glass for the material. I’m trying to gauge how much it would cost to build a boat out of fibreglass vs HDPE. I’ve got the whole year to work on the project so time isn’t really an issue.

I’m also trying to figure out how to determine if my design will actual be buoyant and hydrodynamically sound. Is there any software that you know of that I could use for conducting such tests?

Hi Sappi -

One thing we struggle with when integrating USVs is the lack of provisioning or hull design to optimize or enable sensor mounting and performance. It seems it is always an afterthought. That is task one, figure out the sensors and work backwards. Be careful of dedicated wells or pockets in the hull (use the Xylem / YSI HyCat as an example). The fixed dimension and provisioning don’t allow much forward integration or future-proofing. And, debris piles up against the probes, and we see weird vortices and cavitation.

Also try to pay attention to draft, drag, and how sensor position may affect navigational stability. Mounting a sensor on one side of a catamaran leads to offset drag or list, and the control system expends energy to drive straight.

Another aspect we study carefully is the period and amplitude of the waves in the operational area. Not all hull designs are optimal in certain conditions, and most vessels are too small or equal to a wavelength, which puts a lot of demand on the sensors and nav systems to compensate heave, etc. We try to pick a hull length at 1.5 times the average wavelength. This may not follow your ‘length of waterline vs optimal design’ marine architectural standards, but you will also most likely be a displacement hull and not much matters anyway. Not many USVs are really designed well for a certain condition, because we mimic the traditional boat designs.

One last concept is if you care if the hull is wet on the top. We built an aluminum hull catamaran, with a sort of wave penetrating bow, and what we call a wet deck. It is 2.2m long, and the freeboard is only a couple of inches. We designed it for transportability and stability in high wind generated wave ‘chop’ vs open ocean swell. The insides of the hull are flat, to enable straighter tracking and ease manufacture. It works really well, and is partially submerged to stay out of the wind. If I had to do it over, I don’t know that I would change the design much…

I’d love to see other feedback on this topic!


As someone who’s never designed a boat or hull before I’m struggling to find a place to start and a methodology to follow, do you have any advice?