toy boats

Guus Flogel demonstrates one of his wooden shoe pop-pop boats.
How to make a pop-pop boat

Simple toy submarine. Attach motor and battery holder to bit of styrofoam using rubber bands; break off bits of styrofoam to neutralise buoyancy. Small and cheap enough to introduce to a public swimming pool clandestinely.

Propellor quite easy to make using small bits of plastic packaging glued to a plastic bush. Shape and dimensions surprisingly un-critical. Make it about 15mm diameter. If done in a school play 'sub hunt': line everyone up along the edge of the pool, throw submarines into pool with motors running, shout "go", when anyone catches one they bring it to you whereupon you throw it into an empty area of the pool.

If two batteries are used, the sub goes much faster but stability becomes a problem. This design is stable even though it only has one propellor.

foil surfing
hydrofoil sailing

This is a toy airboat, it uses the submarine ideas.

This is another radio controlled version, the fan can be rotated through 360 degrees, this makes it very manouverable, also nothing essential goes below the water line, so it doesn't get caught on weeds.
Link to movie of airboat

This is a version of the toy submarine that automatically avoids obstacles.

This is a very simple radio controlled boat, it uses the radio from a single channel car; it has the disadvantage that you have to reverse in order to steer.

how to make a putt-putt boat; difficult but very highly recommended

Here we see a potentially dangerous impasse between a duck & a putt-putt boat

This one has two engines side-by-side, boat just made from bit of styrofoam; foil insulation on top of boiler. Each engine has 2 straws, one half the length of the other.

simplified pop-pop design

This is slater harrison's design, simplified to use less glue & dexterity.
Cut ends off coke can, fold round ruler

trim off excess

bead of araldite

sellotape while glue sets

araldite in end

crimp with pliers or vice

fold over & crimp again

straws in other end

link to instructions for simpler pop-pop engine
pop-pop engine pumping water
some very elaborate examples
movie of orca immitating outboard motor sound

how a pop-pop engine works

by jeff bindon
A PopPop engine is a water pulse jet. To function there must be air and water inside. It starts to gently pulse because as water nears the boiling point, a bubble of steam forms explosively and nudges the water in the tubes into motion. But the steam immediately condenses and the water flows back again. The water columns in the tubes act like "pistons" and their momentum causes the pressure to fluctuate above and below the atmosphere and the membrane to flex in and out.
As the pressure drops inside the engine, the water finds itself above the boiling point and steam forms rapidly ('flashing') and this drives the water "pistons" outwards and the explosive formation of steam is swamped. Steam condenses on the cold wet surfaces exposed by the retreating water "pistons" and the pressure falls. Soon it is below the atmosphere which then drives the "water pistons" inwards to compress the steam and air inside. The air acts as a spring to bounce the water "pistons" outwards again.. Warm water is expelled from the engine and cold water is taken in. When it eventually reaches the boiler, its dissolved air is released.
Gradually air builds up and will be pushed further and further down the tubes until small bubbles are expelled. To satisfy the Second Law of Thermodynamics, heat is expelled from the engine via the ejected pulses.

boat I made up from one of jeff's kits

detail of boiler & burner

James Rumsey's steamboat with beamless Newcomen engine

Early development of steamboat
more ambitious pop-pop engine
DIY submarine

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bishop wilkins on the advantages of submarines (1648)

1. ‘Tis private ; a man may thus go to any coast of the world invisibly, without being discovered or prevented in his journey.
2. ‘Tis safe; from the uncertainty of Tides, and the violence of Tempests . . . from Pirates and Robbers .. . from ice and great frosts which doe so much endanger the passage towards the Poles.
3. It may be of very great advantage against a Navy of enemies, who by this means may be undermined in the water and blown up.
4. It may be of a special use for the relief of any place that is besieged by water, to convey unto them invisible supplies....
5. It may be of unspeakable benefit for submarine experiments and discoveries: as,
The deep caverns and subterraneous passages where the seawater in the course of its circulation doth vent itself into other places and the like. The nature and kinds of fishes, the severall arts of catching them, by alluring them with lights, by placing nets around the sides of this Vessell, shooting the greater sort of them with guns. ... These fish may serve not only for food, but for fewell likewise, in respect of that oyl which may be extracted from them.
The many fresh springs that may probably be met with in the bottom of the sea will serve for the supply of drink and other occasions.
But above all, the discovery of submarine treasures is more especially considerable, not only in regard of what hath been drowned by wrecks, but the several precious things that grow there, as Pearl, Coral Mines, with innumerable other things of great value.
All kinds of arts and manufactures may be exercised in this Vessell. The observations made by it, may be both written and (if need were) printed here likewise. Severall Colonies may thus inhabit, having their children born and bred up without the knowledge of land, who could not chuse but be amazed ... upon the discovery of this upper world.
Mathematical Magick, Vol. II