Papierschnitzel - good question!
At first, I thought these were "scuppers", but they are not, as they are high off the deck. Suppers are used to drain water from the decks, and as a result, are placed below deck level - sometimes with a drain connection.
Looking at the number, and the height and positioning of these openings, and bearing in mind this is a very small vessel, these look like "sweep ports" - openings to allow the vessel to be rowed if necessary in certain situations. They are also the right dimensions for this
Sweep posts were adopted by the Royal Navy for smaller vessels (up to 46 gun frigates in some cases!) in the 17th century onwards - and were used to manoeuvre the vessel in port, as well as to enable quick manoeuvres during battle. They were used as well to assist the oarsmen in the boats when the ship was being towed in calm weather, or they could be used for steering from the stern ports. they were also used to get a ship out of port in calm weather.
Given the size and role of the ship, these would be at home on a cutter the size of HMS Fly......
In size the "seeps" were large - average length was 45 feet long +/-. The blade was 12" + wide, and they were stowed when not in use with the spars. They were also used for steering if needs be, via the stern ports which this vessel also has.
I attach a drawing of the set-up for a sweep below.
A good reference on sweeps is the
1816 2nd edition of The Art of Making Masts, Yards, Gaffs, Booms, Blocks ad Oars as practiced in the Royal Navy and According to the Most Approved Methods in the Merchant Service