BOATSBOATS
Sizing up for
seaworthiness
Small yachts are cheap and easy to handle but are
they seaworthy enough offshore? Bjorn Haraldsson,
Jack Gifford and David Harding share their views
R
eading the article in PBO
January 2019 about how
Roger Hughes built a
beautiful model of a
Norwegian Colin Archer boat,
got me thinking about the natural laws of
size. Roger not only wanted the model to
look identical with the original, but also
wanted it to be a sailing model. Since I
enjoy building both full size yachts and
model boats, I have often had to ponder
over the physical and mathematical laws
concerning the size of boats.
The way your boat looks has a lot to do
with the size of the planet you plan to sail it
on. The size of the earth gives us a fi xedamount of gravity, which affects how
everything around us is constructed, not
least yachts. On a planet twice the size of
the earth everything would look different,
including humans and boats.
Things have a certain size, and if you
change this size they won’t work as
originally designed.
For instance, if you shrink a sailing boat to
a tenth of her size you will get a boat with
ten times more sail area in relation to its
stability, compared with the original boat
and, consequently, can only sail in very
light winds.
I will try to explain why this is so and what
happens when you modify the size of a boat.