I think the reduction in capacity of a battery with increasing load can be explained if we consider the battery to consist of an 'ideal' voltage source in series with an internal resistance.

Lead-acid batteries have a high internal resistance. Therefore, as the discharge current is increased, there is a greater voltage drop across the internal resistance. More of the battery's energy is being dissipated as heat inside the battery and less is available for the load. Hence the available ampere-hour capacity reduces.

Other battery types have a much lower internal resistance, so the effect is much less to the point where the battery, within large discharge limits, can be considered to have a known fixed capacity.

Thanks all for the info. Some experimentation called for methinks.

Good discussion. I agree with AlessandroSPQR that Lithium Ion or Polymer batteries are overkill for most model boats, I see so many scale tugs and submarines powered by them and they just need more ballast as a result. I am disappointed by the poor characteristics of lead-acid batteries though and have been very happy to use NiMHs whilst keeping a watchful eye on the progress of LiFePO4 batteries.

The DREAMDASH types illustrated in Alessandro's posting appear to be suitable candidates for scale boats. Much safer than standard lithium types, much better electrical characteristics than SLA, and cheaper in the long run because you won't be replacing them as often. But one thing bothers me - the maximum continuous discharge current is only 1C - 6 amps in the case of the 6v SLA equivalent. This would rule them out for some applications.

I wonder it any modellers have had experience with them, and whether or not they live up to their claimed specifications.

https://www.aliexpress.com/item/1005008380732622.html?spm=a2g0o.productlist.main

Interesting to compare the different smoke effects. The fog machine produces lighter 'smoke' that appears to rise naturally, whereas the water vapour provided by a nebulizer is naturally heavy and tends to sink more rapidly. Is the fog fluid expensive and readily available? Any further details?

Lew, I use 24v because the tug has a 24v drive motor and battery. But I have tested the smoker on 12v via a 5A XL6019 booster module. The current draw was 1.6 Amps (19W), a slightly higher power consumption because of the losses in the booster.

I can assure everyone that there is nothing innovative or special about "my" smoker, it is a conventional arrangement of parts as used by some commercial units of the past, with minor improvements. I provided full details in the August 2025 edition of Model Boats magazine (UK) and I think I would get in trouble with the editor if I repeated them here! However this diagram should explain the basics; it can be built quite cheaply if you are handy sourcing parts.

An interesting point is that the fan must always run forwards, even if the boat is reversing. Otherwise the smoke will be sucked back down the funnel and blown out of all the ventilators and openings on your model! Quite an interesting spectacle. I am assuming here that you have the fan slaved to the motor speed controller; the issue can be avoided by feeding the fan motor via a full-wave bridge rectifier.

Nebuliser:

https://www.aliexpress.com/item/1005006906832202.html?spm=a2g0o.productlist.main

Just to add to this discussion, I have been making my own misting smokers from room nebulizers. I find they are great in the cooler months, but less so in the warm months because the 'smoke' dissipates too quickly. Their fan is slaved to the throttle.

For comparison, they have a 200ml water tank which lasts about 30 minutes. That works out at about 7ml per minute. They consume 650mA on 24 volts (16 Watts) but can be run at lower voltages via a step-up voltage converter.

Shown fitted to my 1:24 scale tug Wattle.

No Ron, I have never thought of doing that. It would be worth doing a simple experiment to see if you can capture worthwhile energy. The extra panels would need to be connected in such a way that they don't effect the power of the main panel when they are not capturing much reflected energy. Perhaps they could be wired independently to just put some charge into the receiver battery only.

Yabbie1

The point is, you need to consider the type, number (and configuration) of solar panels you are going to use BEFORE deciding on the scale of the model, otherwise the chances are you will not have a good fit on the available area and the performance will be poor.

In your case, I looked at the overhead photo and saw there were eight roughly square solar panels. My first thought was that 150mm x 150mm panels looked a good candidate for a model, hence the 600mm x 300mm roof area for the eight panels. But there are many different sizes available and if you can find a size that can be arrayed to fit your roof area nicely then go for it, but more likely you will need to vary the size of your model to get an optimum fit.

I see there is a 136mm x 110mm size, eight would need a roof area 544mm x 220mm, that might suit your model better. The other thing you will need to bear in mind is the electrical configuration. These panels are rated at 6v 0.33A each, so 8 of them could wired to give 12V at 1.3A or 6V at 2.66A in series/parallel (16W) for which you would get a suitable motor. Note that in this case, even if you had room for one more solar panel, it would be unusable without another one or three panels to pair it up with.

See:

https://www.aliexpress.com/item/32905776528.html?spm=a2g0o.productlist.main.42.1

Here's a LARC-V model built by a modeller in our club, Gordon.

Yabbie1

I hope you build that little fishing boat Ron, I found its story quite inspiring. I think the solar array would need to be something like 600mm x 300mm in size to make it worthwhile.

With enough interest there could be solar boat races and solar vs sailing boat races, where the solar boat would make up lost ground during the upwind part of the course. Different classes could be defined based on power generated or size of solar array etc.

Yabbie1

To return to the topic...

A trimaran layout would be a logical one, with the central hull providing propulsion via a conventional motor and prop without the need for the complicated gearbox or twin motors of a catamaran. The outriggers could be attached by struts running underneath the overhead solar array. A 750mm x 300mm solar array of ten 150mm x 150mm solar panels would provide around 30 watts for a really good performance.

Yabbie1

Thanks for the welcome, I only hope I will have the time to participate properly.

It seems to me a catamaran configuration is best for a solar boat - good stability while providing maximum surface area for the solar cells without the drag of a wide hull. Many full-size types are like this, but it raises the problem of propulsion in a model. You wouldn't want the power loss and complexity of a long drive shaft or outboard arrangement, so perhaps a slim brushless motor in each hull would be best.

I felt my ears burning so I thought I'd better join your forum and post a public reply.

As Roy has mentioned, my name is John Parker and I write a regular column for Model Boats magazine called Flotsam and Jetsam.

The solar powered RC boat I designed for the magazine took the form of an old wooden ferry with solar panels on its roof. It was designed above all with efficiency in mind - long slim hull for low drag, large propeller, 300 kV brushless motor. There are 15 solar panels on the roof, each rated at 2v 0.25A connected in series-parallel to give 10v at 0.75A (i.e. 7.5W). Scale is 1:25, size about 854 mm x 152mm and weight about 3.25 kg.

It has two modes of operation, solar powered only or solar with battery back-up. There is no problem in mixing with other boats on sailing days - the power is enough to drive it at 'hull speed'. On solar only I believe it would be able to keep moving slowly in light overcast, but be stopped dead in heavy overcast. Of course, the sun always shines in Australia so I haven't been able to test that out!

John