It's not all that difficult to mix up common sayings in the English language, which is rife with sound-alike phrases and confusing idioms. Is it "for all intents and purposes" or "for all intensive purposes"? Is it a "doggy dog world" or a "dog-eat-dog" world? (In the first case, the former is correct; in the second, it's the latter.)
When it comes to the use of the phrases "jury-rigged" or "jerry-rigged," it's easy to say them interchangeably — and you wouldn't necessarily be wrong. Both phrases have come to mean essentially the same thing, although originally "jury-rigged" referred to something that was cleverly but only temporarily repaired, while "jerry-rigged" represented an item that was hastily or poorly built from the start.
While these may seem like obvious distinctions, the phrases "jury-rigged" and "jerry-rigged" have morphed into a similar meaning over their lengthy etymological histories.
The term "jury-rigged" first caught on in the 1700s, where it was recorded in newspaper articles as a strictly nautical term. At that time, the word "jury" meant "improvised for temporary use, especially in an emergency" or "makeshift." The meaning and usage of "jury" was taken from the 1400s, when in the Middle English the word "jory" meant "improvised" and was used exclusively in reference to sailing. At the time, a "jory sail" was synonymous with an "improvised sail" that had been repaired well enough to catch the wind.
The "rigged" in "jury-rigged" is a term that also originated in the 1400s and which referred to the "rigging" of a boat. In this context, a rigging represented the ropes and chains used aboard a ship that worked the sail and supported the masts.
Taken together, the words that form "jury-rigged" — although centuries old and nautical in origin — refer to a temporary solution that repairs or replaces something. And that's not exactly what "jerry-rigged" means.
How does "jury-rigged" differ from "jerry-rigged? It isn't well understood how the term "jerry-rigged" originated, but it is believed to be a variation of "jury-rigged" that refers to something that is "jerry-built" or "cheaply or poorly built," which is an important distinction in meaning.
While "jury-rigged" refers to something that has been temporarily (and often cleverly) repaired, "jerry-rigged" refers to something that wasn't well-constructed in the first place. "Jerry-rigged," therefore, seems to be a mashup between "jury-rigged" and "jerry-built" and reference tomes ranging from The American Heritage Dictionary of the English Language to Merriam-Webster's Collegiate Dictionary accept its usage as an official word of the English language.
Don't get either "jury-rigged" or "jerry-rigged" confused with a "jimmy rig," though. While a jury-rig and a jerry-rig both refer to repairs that aid an object's function, something that is "jimmy-rigged" with a temporary fix isn't likely to work at all.