I came across the site of Roeivereeniging "Nautilus".
The Nautilus rowing-club was founded 1 januari 1886 by a group of 10
Rotterdam youngsters. It is located in the center of Rotterdam, and the
successes of its members, were responsible for a growth in its first 25
years to a memberschip of over 100. All male, since it wasn't until 1917
that the club decided to allow female members as well. In 1924 the club
moved to Kralingen and Hillegersberg, as the Maas was getting too busy
for rowing. On the waters of the Rotte the club continued to grow, and
members still gains successes, including, shortly after its centennial,
three world championships.
The flag of Nautilus is a blue cross on a white field.
Source: the club's website.
Peter Hans van den Muijzenberg, 1 Jan 1998
"Nautilus", Rotterdam - This club has a flag which is identical to that
of Finland. The burgee follows this design. Ergo: a shifted cross. That
flag is older than the one of Finland!
Jeroen van Leeuwen, 24 Apr 2005
by Jarig Bakker, 9 Aug 2003
The Yearbook of the "Rotterdamsch Nieuwsblad" - Wie, Wat, Waar 1941
has two pages with burgees. For Nautilus it has a burgee white with a Scandinavian
blue cross. The width of the arms of the cross is 1/5 of flagheight.
Jarig Bakker, 9 Aug 2003