Solar powered boat

Hello, I will be making a solar powered boat as a project, it will be made from PVC, and I am trying to calculate the power that will be needed to push the boat, any tips?

 

Welcome to the Forum H72

What are the dimensions, weight and target speed?
These will largely dictate how much power you need.

 

It is a modular design, catamaran hull, 0.75m length, 0.5m width, 0.6 height. A quick design was done for demonstration, the weight is shown in the image as well. I am still in the proposal phase so I haven't done a lot of research on the concepts of boats and power

 

Design is 100% going to change, very initial things for now, roof pipes are for PV panel installation

 

Are these the overall dimensions that you have to work with, and I presume that you cannot deviate from them, even slightly?
Is this a project for school or college?
What speed is your catamaran required to achieve?

Have you identified some suitable small solar panels which you could use?
These solar panels are going to form a substantial proportion of the weight of the boat, so the hulls need to have enough volume / buoyancy to support them at the designed waterline.
Re the roof pipes for the structure supporting the solar panel(s), are you planning on using standard 1/2" diameter (or similar metric) white pvc pipe?

And what about propulsion - can you perhaps use a standard model boat electric outboard motor?
Some typical examples here -
Outboards & Outdrives | Rc Boats by OffshoreElectrics https://www.offshoreelectrics.com/products.php?cat=Outboards+%26+Outdrives

Or do you have to have a shaft driven propeller and motor in each hull?
I presume that you do not have a requirement for a remote control unit for steering and speed control - that starts to get very complicated and expensive.

 

Yes, everything is initial, deviating is possible. It is a college project. It is needed only for showcasing purposes, 5km/h is enough. PV panels will be most probably thin film, and will be the same size as the roof so 0.75m. The structure will most probably made from the same pipe, the design was made by 1.5inch PVC rigid pipe. The propulsion and power needed is the part that I have no idea in. Single motor in the middle and no remote control needed.

 

That size panel isn't going to make 100 watts.
So a 100 watt motor will work.
You could wire it direct without a battery, just a switch.

Matching a prop to that will be guessing.
A two bladed, 75mm diameter, 50-75mm pitch, low aspect-ratio blades might work.
Small airplane props work best.
Germany produces some that have adjustable pitch which may be helpful in tuning.

 

Based on simple calculations done for the solar energy to be harvested, it was calculated that in my country for a PV panel that is 0.4m2, it’ll generate around 19 watts. I need to know the power needed to push the boat to see whether the project is viable. But if the case is that I wire the panel directly to the motor, can I turn on the motor at all times since the is no energy storage? Do you think the project is viable? Thanks for the input you’re saving me a lot of time, really appreciate it.

 

19 Watts from 0.4 m2 of panel?
That's awfully low.
Should be more like 60-75 Watts
Are they really old panels?

You said the solar panel will match the roof at 0.75m2

You have too many balls in the air.

Yes the project is viable.

 

Power needed for any solar powered vehicle is always "all of it"

There's a reason you don't see solar cars on the street. The solar race cars that are made, are all about maximizing solar area while minimizing weight and drag to make what little power they have turn into speed. That's probably where you'll end up.

A catamaran is a good choice for hull. It allows for maximum deck area for minim weight and drag. Long skinny hulls are the answer. Only thick enough to support the weight required. Skinny to offer as little frontal area as possible. Weight is going to play a role as more weight is more wetted area, more water to push making more drag requiring more power to overcome, along with f=ma

Your height seems a little high. It might be a bit of a sailboat. Of course, sailboats are ultimately solar powered too, just not directly. If you're outside in the sun, there is often wind, and that wind is going to blow the thing around unless you have copious amounts of power to overcome that, which you don't have because solar. If you control how it is blowing around, then you're back to sailing.

Without looking real close, for the approximate dimensions you give, I'd estimate a walking speed is the best you can hope for. Using the most efficient panels, and covering all the area you can with panels is the way. Maybe bifacial panels to get reflections off the water? Once you have an idea of how much area you can cover with whatever panels you can manage, then you'll have your power number. With that it is simply a matter of sizing the drive to handle or optimize the power available.

I'd guess about a 380 size motor, maybe smaller. You'd want the slowest winding you can get your hands on. Slower spinning prop is going to be more efficient that faster. Even so, you'll probably looking at something really low pitched. Bigger might be better. After maximizing deck area, and minimizing wetted area and drag, the next interesting part of this is going to be the propeller.

RCtestflight on youtube has been playing with different props and solar power, but he is maybe not the best source for aquadymanics, his hulls seem inefficient, and it seems like he can do a bit better in the propellers, but he has drawn a number of propellers and other bits that you might be able to gank.

 

If you have wind, and an effective sail, you don’t need electricity.

But you can regen and store energy you can use later with

-a hydro prop (if the drag isn’t too much)
-Windmill of some sort (being able to deploy or out of wind drag)
-Solar

Wind and hydro drag (as well as weight, mentioned above). are paramount, just like with solar cars. Sail/wind incidence might need to be adjustable

there are some boat design programs, such as Vacanti, that, for example will compute some of the drag of a hull measured in pounds, and while figuring thrust in pounds can be a bit tricky, at least that’s a start.

A nice example of the low drag car above that might point the way to boat design, if solar was molded to the skin, low drag wing, light weight, prop regen, a wind turbine that can be hidden from the wind when not is use.

 

Some real numbers, approximate but with accuracy OK for your original question. This data is fundamental, and works for all size hulls.

Solar power implies displacement speed, which is limited as follows:

SpeedMaximum(knots) = 1.34 x SQRT Waterline Length (feet)

Power required for maximum speed is about 1.5 shaft horsepower per ton of displacement. This assumes a fairly efficient propeller, with a diameter about 8 to 10 percent of hull waterline length, and a pitch/diameter ratio slightly larger than unity. The most efficient setup would be with a single propeller between the two hulls if a catamaran.

For speeds less than maximum, the power required is a cubic function of speed. For example, 80% of maximum hull speed will require only 50% of the 1.5 hp per ton.

Outboard motor practice, typically more appropriate for planing high speed hulls, use propellers far too small for proper displacement speed hulls. Therefore they might need double the power that would be required with a properly sized propeller. At times even more than double!

 

I'm afraid the "car" shown in post #11 is a no-hoper.It is no more than an artist's impression and was almost certainly devised without reference to anybody with vehicle experience.The successful solar challenge cars use as much surface as possible to mount solar panels and also have a means of stopping and steering.The absence of any form of rigging to hold up the rig is also a bit of a giveaway.We may imagine that there is some carefully considered flexural movement of the axles to provide rudimentary suspension,what we won't be able to do is imagine any form of practical spray suppression and that is a bit of a problem for most of the world.It does show that somebody felt the topic was worth considering and it may be that there will be a more practical evolution under consideration.

 

“that might point the way”:tires become very slender catamaran hulls, etc. The Mercedes is a, IMO, a necessary stretch goal…

However, is there a market beyond enthusiasts? This is where medium tech build coupled with high tech design comes into play. And if we keep burning higher tech raw material for transportation, we’ll be lucky to use wood for lightweight construction.

 

I wonder how those rules scale. OP's boat seems like it will be <10lbs, or about 0.005 tons, times 1.5hp/ton, yields 0.0075 hp, converting to electric at 750 watts per hp, is 5watts. That seems fairly slim. OP is saying 0.75m by 0.5 meter, for 0.375 square meters of potential area. That'd be 75 watts of power on a good day, which is way more than 5 watts.

This looks to be about a 5watt panel, and scoots pretty good, albeit it is smaller than what OP is talking about:



Op is talking about a catamaran, where if each hull is more than 10 times longer than it is wide, so no more than 7.5cm wide for his 75cm length, OP won't be constrained by the square root of the waterline times 1.34. You're not going to get sucked into the trough of your bow wave if you can cut it. OP says 75cm, which is 2.46ft, plugging into the formula yields 2kts.


These guys have 60watt panels, and scoot quite nicely. They also have batteries, although there is a claim the batteries stay fully charged. They are also using air props, which I wonder if those are less efficient than water, on account of air being compressible.



They also look to be doing a little better than the 2.3kts their waterline would indicate, but it is hard to say for sure. I wasn't able to find much speed/power data for things this size.