There isn’t much in there Jeff . Couple coils, a trans former, a switch to change polarity
and a button to energize. Mumbles built one. I’ve heard a car battery can be used as a
power source. As far as the amount of magnetism a coil need to make a spark, I can
best describe it as being like the volume on a radio. You can turn it up to make it louder
but what is being transmitted is the same. However the speed that the magnet passes
over the coil does increase the intensity of the spark. Often people check a flywheel
magnet by dragging something over just 1 pole. To real get a indication of a magnets
strength you need to bridge both poles.
Video Link. https://youtu.be/PZ0uPBfUD7E?si=_YNzCI2rWB9BYx06
Tubs
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.