Re: [pop-pop-steamboats] Re: World's fastest putt putt engine?
From: "darylcanada73" <darylcanada73@...>
Sent: Thursday, July 01, 2010 8:51 AM
> Hull design is a problem. The design I use is close to a planeing hull.There are three things that slow a boat down, and the one that is most
> It's pluses are light weight, easy and inexpensive build, good stability
> for the high C of G, fireproof and easy engine fitting. It's big weakness
> is high drag unless planeing which probably won't happen. The "best"
> design for speed might look like something 8 guys would be rowing on the
> Thames but it is not so good in other areas like stability.
> Hull design ideas are welcome here,
important varies with size, with shape and with speed.
= shearing the water - viscosity
= displacing the water - inertia
= wave effects in the water.
Historically, people found that long narrow boats were best for speed, like
a naval Destroyer. They didn't push much water out sideways.
There were two problems with that - one was stability, and the other was
that the bow wave would flood the stern of the boat. We are not EVER going
to get that fast!
There's an interesting detail in that a streamlined ram below the waterline
is faster than a Vee bow. People found that out when they removed
militarily obsolete rams from the bows of warships and found that there was
a loss in speed. So the way in which the water is displaced is important as
well as the volume.
The planing hull was designed to get past the bow wave problem. It is
brilliant because there very little water is displaced or sheared and the
surface area of contact is tiny. However those only apply when planing and
we aren't EVER going to get that fast!
I have coxed (steered) a racing eight on the Thames and can confirm the
stability issue: 'Stroke' (the guy sitting right in front of me) kept
shouting "Don't let us sink, Cox, I can't swim!" Indeed a racing eight is
stabilised by the way the crew handle the inertia of the blades (oars)
while they are out of the water. Neat.
To overcome the stability issue, Polynesians developed Outriggers - in the
West these became Catamarans and Trimarans.
The latest fast hulls could be just what we need - two long narrow hulls
with a space in between them and a deck over the top of them. We could put
the exit pipes down between the two hulls, channelling the outflow better,
while perching the fire and 'boiler' between them. Daryl's type of motor
seems ideal for this type of hull.
My concern about it is that the wetted area is quite large - too much
shearing of water, but all we can do is make practical comparisons and be
creative with materials. The lighter the boat the less is in the water, and
only the engine room needs to be flameproof.
- Hi Slater.
I agree with Daryl. It is a nice page on your great site.
I would comment only one sentence. it is "All these friends I've quoted, and dozens more, are members of an informal e-mail group of pop pop enthusiasts scattered around the world.". There are dozens of pop-pop enthousiasts to talk and write on forums... but I think we are a very few (one dozen?) real amateurs spending time to develop pop-pop engines or/and pop-pop boats.
--- In email@example.com, "darylcanada73" <darylcanada73@...> wrote:
> Nice page Slater and a good addition to your great site. I wish I had been able to read a page like it when I first started building. And thanks for the link.
> --- In firstname.lastname@example.org, Slater Harrison <Sharrison@> wrote:
> > Hi Gang,
> > I have added a new page, http://www.sciencetoymaker.org/boat/BigPopPopBoat.htm just about scaling up. My apologies to David, Jean-Yves and Daryl for cutting and pasting stuff shamefully-under a bit of time pressure. Where I've goofed, let me know and I'll get it worked out. Understand that it's not supposed to be a comprehensive study of scaling, rather it's to let them know I don't have the answers. And if they want to know more they really need to get connected with the group.
> > I've reprinted the gist of what's in the page below: Titles, Daryl's embedded page did not transfer.
> > Slater
> > So You Want to Build a Giant Pop Pop / Putt Putt Boat?
> > Before delving into scaling up the engines, I insist that you learn a new word: serendipity. Serendipity means we go looking for one thing, and perhaps we don't find exactly that thing. But-if our minds are flexible enough to be open to it-we find something as good or better in the process of looking.
> > OK, many intelligent, curious people have wondered, "If pop pop boats are this cool, how cool would it be to make a person-sized pop pop boat?!" In fact, the idea has even seeped into popular culture. In the children's animated movie Ponyo, the young heroes use magic to transform a toy putt putt boat into a big boat and ride in it.
> > Alas, those of us who are lacking in magical powers have to grapple with the persnickety laws of nature.
> > My friend David Halfpenny from England has some interesting things to say about the difficulty and hope of scaling up in general: I quote,
> > "There's a critical size for everything in nature. That's why you'll never see a moth as big as a dog - the insect respiration system just can't get enough oxygen."
> > "There's an old joke that goes:'According the laws of aerodynamics, a bumblebee cannot fly. Fortunately nobody has told the bee.'Well actually, bees cannotfly, not like a bird or a plane - they 'swim' through the air, which, at their small size and low weight, is much stickier than it is to us. Or a bird. Or a dog. So that means there must be a crossover between Insect Size 'lungs' and Dog Size lungs, and sure enough you can get a beetle as big as a mouse."
> > "In a wind tunnel (used to simulate aircraft flight), the airspeed isn't scaled in the same ratio as the aircraft model size. In an oil tunnel (used to understand insect-sized flight), the fact that oil has to be used instead of air speaks volumes about what it's like to be an insect."
> > "It means there must be a crossover between Gnat Flight and The Flight of the Condor, and sure enough there is the Humming Bird - a bird so small it can swim though air as well as glide, and so skilled it can hover."
> > Then my friend Jean-Yves Renaud from France adds some specifics:
> > Building a half meter engine should not be a problem. My bigger one (just to check that there is no limit) was approx 3m long. However, I must warn you about the performances. When the size of the engine increases, its thrust/weight or power/volume ratios decrease. In other words, for the same weight two small engines are better than a big one. The thrust doesn't increase much with the pipe ID though the weight does as well as the volume. The velocity of the jet decreases when the size of the engine increases. Multiple pipe engines and or multiple engines are to be preferred if performances (speed and thrust) are expected.
> > Jean-Yves has also measured the efficiency of pop pop engines and found them wanting. And he notes that pop pops do not reverse, and questions how long the appeal of being shaken back and forth several times a second will remain amusing.
> > From Canada, my friend Daryl Foster has created some extraordinary boats with many pipes. Look half a minute into this video and see the new world record holder for speed. Even vetran pop pop builders are amazed http://www.youtube.com/watch?v=9rt1l-zmCug
> > So, at top of the page, what was all that about serendipity-discovering things while looking for something else? All these friends I've quoted, and dozens more, are members of an informal e-mail group of pop pop enthusiasts scattered around the world. Despite the fact that I have only met one of the members in person, I do mean friends. We share a common bond. These charming boats have tickled our imagination we're all and curious about what are the possibilities? There's the serendipity. If you've come to this page you might not have found an easy answer the question of scale, but you have discovered a community of people who are finding out.
> > I rarely participate, but I get the e-mails automatically and I stay abreast of what's going on. Sometimes the chatter is about a new discovery, sometimes there's a contentious issue, sometimes there's humor, sometimes the group goes into hibernation, sometimes the topics go careening delightfully off topic, and sometimes we welcome new members. So consider joining. It's a Yahoo group that you have to join, but it's free, and-other than being hosted by Yahoo for administrative convenience-non-commercial. As you might expect, there's great archived threads and pictures.
> > http://groups.yahoo.com/group/pop-pop-steamboats/
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