Real size boat propelled by a pop-pop engine
You are not the first to come with the project to propel a real size boat by a pop-pop (or putt-putt) engine. This is interesting in the principle, but I'm afraid you will be disappointed. We have to warn you about many "negative" aspects. If we don't do it now, you will be much more disappointed later, after spending time and money for nothing.
As many pop-pop enthusiasts I would have liked to sail on a boat propelled by a pop-pop engine. Though that was not my first goal, I started to study and build small engines (pipes of internal diameter approx 3mm) and progressively I increased the size. In August 2007 my biggest engine had a pipe diameter of 23.5mm, and I'm ready to believe that in theory there is no upper limit. However, for those who expect to propel a real size (small) boat, I would like to draw the attention on what follows:
· To deliver an acceptable thrust would require a gigantic pop-pop engine. According to our today's knowledge it is evident that we cannot get the same thrust as with classic propulsion for less weight. If we extrapolate what we know, to get a thrust corresponding to the one delivered by a 4HP engine at a few knots would require a single pipe pop-pop engine with a pipe diameter of more than 100 m (> one hundred meters!). And its weight, including water, would be more than 15 000t (> fifteen thousand tons!). Though theoretically it could be lighter with multiple engines, I let you imagine for instance (for the same thrust) how to locate on the stern of the small boat 10 000 pipes of internal diameter 10mm.
· Enormous amount of fuel. The efficiency of a pop-pop engine is pathetic. It could increase with the size of the engine, but it is so minute on a toy (between 0.001% and 0.1%) that it cannot be "acceptable" on a real size boat. Even if some weight could be saved on the engine itself, think about the enormous amount of fuel (whatever it is) that the boat will have to carry.
Any of the two above mentioned reason should suffice to stop immediately the project. Nevertheless, if you don't trust these figures, we can list other reasons:
· What about using raw water (worse would be sea water) inside the engine? When you know the water treatment and water quality that are required in a water/steam process...
· What about reversing to maneuver?
· What about burn out phenomenon?
· Would you like being shaken? The pop-pop engine is reciprocating engine acting on a pulsed jet. Would you be happy to live on a boat that is shaking day and night?
Nevertheless, the pop-pop engine is fascinating. Hope you will enjoy it.
In my previous message I forgot to mention what follows:
· The attainable speed is very slow. I have never built (or seen, or read from others) a pop-pop engine and a hull whatever their sizes- able to exceed 0.3m/s (1.0 ft/s), which is very slow. Less than 0.6 knot. If somebody succeeds to reach a higher speed, don't expect several knots.
0.3m/s is good for a toy or a small replica; not for a real size boat.
- Hi,I had heard that several years ago someone made a Pop-Pop engine from the lids of 30 or 55 gallon drums. Supposedly used 8 to 12 one-inch copper pipes. Mounted it in a small row boat, used a charcoal grill as the heat source. The story says the boat actually moved with him in it.Of course such a boat would be noisy, slow, hot, and could not back up. So what? I think the point is to have some fun and build and play with something unique. It does not have to be practical to be fun. Actually, the more useless it is, the more fun you can have.Hopefully someone out there will try to build such a beast and then post a video of them pop-popping across the water a a blazing speed approaching 1 mph.BTW the 4 hp comaprison seems high. I saw one electric trolling motor that draws 7 amps at 12 volts for boats up to 12 feet. This is 0.084 kW, which equates to about 0.10 hp Jean, it looks like the pop-pop engine could be at least 40 times smaller than your calculations and still move a small boat with a person in it.Carl S.
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Thank you for your comments. I would like to know more on the big pop-pop engine you heard about. If you could follow the track and post photos and characteristics of this engine on the forum, I'm sure many people would be interested.
I agree with you concerning the fact we can have fun with the "useless" pop-pop engine. As a proof, I spent hundreds and hundreds of hours to study it and play with it. And it is only for my pleasure. Nobody is requesting me to do that. What follows is not pedantic. It is just to let you imagine that today pop-pop engines are toys for me. I'm curious and want to know more about these engines. I have a rather good knowledge of big propulsion plants because I was involved in many projects. The last one was Queen Mary 2 with a propelling power of approximately one million times the one you are referring to i.e. 84MW instead of 84W. I also worked on high speed crafts propelled by big waterjets. Up to 25MW per jet. It was fun to make it work and then to sail 47 knots for a couple of hours during the sea trials, but it is more fun and mysterious for me to see a pop-pop boat sailing at 0.1m/s with a pop-pop engine delivering 84 microwatts. 1000.000.000.000 times less than QM2!!!
You wrote that "The story says the boat actually moved with him in it". I have no doubt about the feasibility to propel a boat with somebody in it, but what about the speed? At slow speed, the power evolves as the cube of the speed. Therefore, in steady state conditions, at any power corresponds one cruising speed. Using your figures (84W and a 12 foot boat with one person in it) I can guess that the speed could be approx 1.5m/s but I don't know how to get as much as 84W from a pop-pop engine. If only we could get 1W the speed would be 0.34m/s. With 0.1W it would be 0.16m/s Test to be performed indoor because the least wind would have more propulsive effect than the engine itself.
My message is longer than expected. Don't forget the second sentence which is the most important.
Thanks in advance.
- Jean-Yves,I always enjoy your posts. Sounds like you are an engineer and were involved in some interesting projects. I am a chemical engineer and have spent 40 years mostly in research and development. My career has allowed me to see many things most people never get to see. The traveling also gave me a chance to browse in antique shops all over the world looking for toy and model engines.The barrel head pop-pop engine was a story told to me about 10 years ago. I have done several Internet searches but never found anything. I will try asking the person that told me the story to see if he has any more details. It may be a myth or it may be true.Carl S.
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Ditto on Jean-Yves....
I'm not sure that this the "Barrel Head" type boiler that you mention. Check with member Dan Noyes. This is his sketch. He may have more details for you.
He has a series of photos of his 4' pop-pop dory in the photos section. I believe that he has also posted a couple of messages on his boat and engine.
--- In firstname.lastname@example.org, SWANEE0523@... wrote:
> I always enjoy your posts. Sounds like you are an engineer and were involved
> in some interesting projects. I am a chemical engineer and have spent 40
> years mostly in research and development. My career has allowed me to see many
> things most people never get to see. The traveling also gave me a chance to
> browse in antique shops all over the world looking for toy and model engines.
> The barrel head pop-pop engine was a story told to me about 10 years ago. I
> have done several Internet searches but never found anything. I will try
> asking the person that told me the story to see if he has any more details. It may
> be a myth or it may be true.
> Carl S.
> ************************************** Get a sneak peek of the all-new AOL at