G'day again fogie (or: back to the thread drift),I had a good look through the reference books for the different varieties of flageolet. Like any instrument that has been around for a long time, in a number of countries, the flageolet did come in a variety of shapes and fingerings (quite apart from the 2 and 3 barrel versions that allowed various degrees of harmony playing for the nimble-fingered). The most common national reference is to "the French Flageolet" with 4 finger-holes on the front and 2 thumb-holes at the back- and the "English Flageolet" with all 6 finger-holes placed frontally. Either way, these basic forms have only 6 holes - just like the fife and the penny whistle - and so have a basic diatonic (7-note scale) form.
Whether the fingers - or the thumbs - cover some of those holes doesn't really give any more fingering options for accidentals but, just as we see today, skilled players can get any accidental from a 6-holed instrument by careful fingering. This usually means lowering one or more fingers below an open hole to flatten a note ... or else "half-holing" - slightly raising one end of a finger pad to sharpen a note.
By the 19th century, it was becoming common for better quality flageolets to come with additional, normally closed, keyed valves ... anywhere from 3 to 7, depending on the skill and ambition of the player. (Actually, I suspect that there would have been the odd instrument with just one or two keys ... as in the first steps from fife to "school flute", but these are not usually seen in the collections or illustrations.) There may be slightly more room on the front for finger keys of a "French Flageolet" where both thumbs are used for fingering (but a raised risk of dropping the damned thing). The holes covered by the keyed valves can be placed anywhere convenient since the lateral positions of these holes or keys don't affect their intonation, which is a product of their distance from the ends and relative size.
As well, by the 19th century, most English flageolets had moved to the full 8-hole fingering pattern still seen today on the recorder: 7 finger-holes in front and one thumb hole at the back, nearest the fipple. As any recorder player will tell you, this pattern (and a good memory for fingering charts) allows you to play fully chromatically. Throw in a bit of 'half-holing' and you can even play microtonically (or out of tune ...!).
So, in the end, I'm not sure of the peculiar advantage to ship's captains of "French Flageolets". They existed ... but were supplanted by more complex fingerings or valve patterns. The great attraction of 6-hole fingering (6 fingers or 4 fingers and 2 thumbs) has always been the rugged simplicity and vigour of playing in the home key ... and (mostly) its closest related key. This is normally a fourth above (eg: the Irish habit of playing a 'D' whistle mostly in 'D' and 'G').
Maybe some Liverpool ship's chandler with a good line of patter just came across a large job lot of older style "French Flageolets"!
Regards,
Bob Bolton