This dial is a favorite because of its charming shape. This
in spite of the fact that it is fundamentally flawed as a time
keeping device. But hey, who uses a sundial anymore for accurate
time?
The ship's dial may be readily fabricated of brass etc. The
main decision to be made by the maker is whether to layout the
dial via calculation or to simply copy the scales etc. from a
printed model or photograph. If you want to do the "proper
job" and calculate your layout get a copy of Fine's Second
Book of Solar Horology as interpreted by Peter Drinkwater(references).
Drinkwater's translation/interpretation not only gives the information
to layout this and other dials, it also tells you their problems.
Alternatively you can copy the layout from a known example.
The most readily available is from Gentleman's Magazine, on
pg 49 of the January 1787 issue. As this magazine was very important
in literary circles it is available on microfilm at many libraries.
For convenience I have included scans of the note
and the illustrations of both the front
and the back of the instrument. You
may want to obtain hardcopy due to the better resolution available.
Photographs of two example navicula are available on Epact
the on-line catalog of Medieval and Renaiance instruments held
by four of the World's great museums of the history of science,
one
at the Instituto e Museo di Storia della Scienza, Firenze, the
second
at the Museum of the History of Science, Oxford.
Medieval Science & Scientific
Instruments