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Lee Mulholland

A Pop Pop Boat Made of Glass

An Article by Lee Mulholland, University of Southampton Faculty of Chemistry Email:

It is not the first time that we are visiting one of our neighboring countries in the north with our trade journal. You may remember how we reported in our 02/2020 issue about Jens Christian Kondrup, who we all know to be an excellent colleague and who works at Denmark's second largest university, Aarhus University. Now we can travel to the Netherlands, to Adriaan Hendrik van der Weel. He is a glass apparatus builder from the bottom of his heart. What does training for this profession look like in the Netherlands, how in demand are you as a specialist there and how can you continue your education in our neighboring country if you want to achieve more, much more than many others?

VDGN 2/2023

A pop pop boat is a toy that runs via water propulsion. The simple motor requires no moving parts like pistons, valves, or gears. A simple candle or similar heat source is the only source of Energy. There are plenty of pop pop boats made of metal, but as we learn from an article by our colleague Lee Mulholland, they can also be made of glass. Here, art and technology go hand in hand once again. Creativity is boundless. 
Metal pop pop boat
Glass pop pop boat (battery for weight only, not for power)



The Manual

The first step is to fill the two pipes that poke out of the back of the boat, including the tank, with water. Once the boat is floating, the openings of the pipes will be under the surface of the water. Then a heat source is placed under the tank (e.g. a tea candle) and the boat moves forward immediately, with the typical putting noise.

The exciting question:

How is the invisible propulsion force achieved?

The tank remains full of water, until this reaches boiling point. As water turns into steam, the water further down in the pipes is pushed out. As the steam keeps spreading, it follows the water through the pipes. The pipes are much colder than the tank, so the steam condenses in the pipes and turns back into water. This reduces the pressure in the tank and the water flows back into it. The thus refilled tank reaches boiling point again and the cycle continues.  




Background for the idea to make a glass pop pop boat

Lee Mulholland and his team at the glassblowing workshop at the University of Southampton were approached by science YouTuber Steve Mould with the request to make a glass pop pop boat. He wanted to make a video that shows clearly how the propulsion of these little boats works. This was a challenge that wasn’t all that easy to meet. In this article, Lee describes his approach to the production of the boat.; Film about the operation of the boat in English

Creating a Pop Pop Boat Made of Glass by Lee Mulholland

The design of the hull of the boat was to be super simple. This required us to pull some square profile tubing. We did this by creating a simple “down draw” setup. We shaped a piece of square graphite with a slight taper on one end, drilled a hole down the centre and hung it onto a piece of straight metal rod.
We then attached a weight to the bottom and used a large hand torch to apply an even, gentle heat and let gravity do the work. (The same can be achieved by pulling tubing on the lathe, as demonstrated during the 2007 and 2019 VDG Symposium workshops.)


Shaping the bow

We shaped the bow of the hull on the lathe. By attaching a glass rod, we created a blowtube/holder that allowed us to do a flat bottom for the stern and blow two holes, so we could attach two GL 14 screw threads that would give us a water tight seal for the two exhaust tubes due to their plastic fittings and seals.
Once this was done we took the entire section to the saw and cut it in half, leaving us with a completed hull.
The bow is shaped on the lathe
The holder and the two holes fort he GL14
The watertight GL 14 threaded caps connected to the exhaust pipes

The water tank as a real challenge

We had to go through several designs for the water tank, as we would get wildly different results even when we were trying to repeat a test with everything seemingly the same as the previous test.
We had our best results using a very flat, round tank, but could not repeat that success again for unknown reasons. 
The flat, square quartz tank
We had issues with the tanks cracking on second or third use so tried a flat, square tank made of quartz.
The flat, round tank with – initially – the best test results
This still cracked on second use, so we ended up using a simple round, closed end tube made of quartz and this seemed to give the most repeatable results without cracking.                     
The water tank made of quartz glass. The water was coloured red for better visibility of the tank and pipes (also quartz)
P. Frampton
P. Tryc
The boat was built by Mr P.Frampton and Mr P. Tryc.

The article was translated by Julia Schweifel.

Read the article in german