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Editor's Note: Special thanks and credit to Matt Claiborne for ferreting out the details and doing the research on this terminology.

Always looking for distinct definitions and the origins of nautical terms, I could not resist researching an oft-used description of specific areas of Florida’s coast by Ralph Middleton Munroe in his book The Commodore’s Story first published in 1930.

Throughout the text he and co-author Vincent Gilpin refer to “sand bores” in various respects when reminiscing about their adventures transiting the Florida coastline and crossing to the Bahamas in the late 1800s and early 1900s. I could not deduce from the context exactly what sand bores are and how they are to be navigated. I asked for help from one of our expert cruising editors, Matt Claiborne, who was raised in the Florida Keys and is on board their vessel with his wife Lucy plying the same seas as Commodore Munroe.

Here is his report:

First, the best answer I could find comes right out of The Bahamas Explorer chart books, which uses the label "Shifting sand bore" to mark the feature often. Then, they have this note nearby:

"Note: Sand Bores (fluid, shifting, live sand bars) constantly shift and depths change. VPR apply near the Bores." (VPR in Explorer parlance means "visual piloting rules.")

The charts use three terms, often very near one another in the same area. "Shallow shifting sand," "shallow sand bar," and "shifting sand bore" are all used for similar features. I put out a call out on the Explorer user forums and was answered by none other than Mr. Monty Lewis (Publisher). His reply:

"Sand bore is a term given to shifting shoals or sand bars by British surveyors in the nineteenth century."

Another interesting definition I found came out of a research study on Queen Conch fisheries that was conducted in an area near Andros Island, Bahamas known as the Eastern Sand Bores. In describing the geography/hydrography of the place, they provided this explanation:

The bank environment in the study area is characterized by large sand waves (sand bores) with the deep channels and shallow wave crests running approximately southeast to northwest. The troughs of the bores were vegetated with seagrass...and the wave crests can be described primarily as bare coarse sand...Tidal currents, flowing primarily north and south, were particularly strong in the deep channels between sand bores. (Reference: Stoner, Allan W., Davis, Martha H., Booker, Catherine J. 2015, June. Queen Conch Stock Assessment, Eastern Sand Bores, Tongue of the Ocean, The Bahamas. CommunityConch.org report for Bahamas Department of Marine Resources.)

So, like Explorer charts, this implies that the "sand bore" is the entire area, a large bar that is eroded with bars divided by shifting channels. In some cases the bars, or "wave crests" as they put it, are completely dry. 

One last reference is a fun-to-read 1893 survey of The Bahamas. Here is what they had to say about a prominent bore on the Great Bahama Bank to the west of Staniel Cay:

In the shallower parts of the banks this action forms great sand bores, which, exposed to the action of the winds, also tends to increase them in size in the direction of the prevailing winds. To the eastward of Green Cay we could see such a great sand bore, seven feet high, forming as it were a cay consisting of nothing but a constantly shifting tract. In many localities on the banks these great sand bores have assumed quite definite positions, which they retain, merely shifting north or south or advancing eastward or westward within narrow limits. At our anchorage off Green Cay the bottom consisted of fine hard coral sand, fairly well covered with coralline algae. (Reference: Agassiz, Alexander,1894, December.) A Reconnaissance of the Bahamas and of the elevated reefs of Cuba in the Steam Yacht "Wild Duck" January to April 1893.