From the Drawing
(occasional ramblings of a Small Craft
Mr. Bolger would laugh
his socks off...
As a New Zealander with a passionate interest in sailing,
I drive through Auckland with one eye on the road and one on the sea, and
of late I even make detours and sit on the clifftops of North Shore City
where the parks and beaches overlook the Hauraki Gulf where the Americas
Cup contenders will be racing in a few weeks time.
Yesterday there were five pairs of the distinctive sails
with their attendant fizzboat wakes out there, and when later in the day I
pulled into Halsey St. where the challengers bases are, the activity was
like an anthill that had been well stirred with a stick. The pressure is
on, Team New Zealand has launched the first of their two boats, and will
be sailing her very soon. The rumours are flying as to a new breakthrough
in design, possibly a new type of rig, odd shapes underwater, strange
keels and odd winglets and fins. All top secret, all big bucks, and so far
beyond the aspirations of the likes of us that it hardly seems related to
reality at all.
But while sitting chatting to one of the senior members in
a challenger compound that has to remain nameless ( I'm on good enough
terms with the troops to get into some of these places, but the boss had
better not know I'm there) I noted that the shapes of most of the boats is
actually very simple. The odd bumps and hollows of years past seem to have
disappeared in this generation of boats, while the keels, ballast bulbs
and rudders are sprouting odd little fins and wings the hulls actually
have a very strong resemblance to some of our simple plywood hulls. Mr.
Bolger would laugh his socks off and drag out the plans for the old "Black
Many point to the excesses of The Americas Cup and witter
on about the "waste" of money ( we have a name for this sort of thing
here, we call it a "Woftam" - this means a "Waste Of F (you know the word)
Time And Money). But there are some interesting things to be gained from
the research and development. Even our simple plywood sharpie shapes are
able to be improved, and tank testing is not something most of us have
access to so a few minutes spent carefully eyeballing a shape that has
cost millions to develop, and half an hour with binoculars watching a boat
sailing can give a designer like me a years worth of experiments to do.
Now I don't have a test tank, but do have one of the best
tow testing sites I know of. Lake Rotorua about 10 minutes walk from home
discharges through a weir about 12 meters wide and a meter deep. The water
speed through there is around five knots and the lake bottom for several
hundred yards out into the lake shelves very slowly into deeper water and
the bottom is almost perfectly smooth giving a waterflow with very little
turbulence. I trial hull models in there with a video camera, a big
surfcasters fishing rod, a very delicate spring balance and a long rod
marked off in tenths of a meter in the same scale as the hull model.
How I go about this is I build a model, some would call it
crude, I call it appropriately simple, all is has to do is give me an
accurate scale representation of the underwater shape, and it has to have
a consistent surface finish so that a series of models will not have their
results skewed by one having a surface finish with more drag than another.
The model is then fitted with the scale marked rod along the centreline
and ballasted to its design waterline.
Next, I get out my fishermans waders and head off down to
the lake exit very early in the morning or last thing on a calm night,
wander around in thigh deep water with my hand held boat speedo until I
find the speed range I want, then go about 20 paces upstream and drive a
spike with a fishing rod holder into the lake floor.
The rod is perfectly ordinary, it has 20lb monofilament
nylon line on the reel, but I have a very delicate spring balance in
between the reel and the first guide. The idea being that by taping the
line to the balance I can measure the pull. By undoing the tape and
letting out more line I can let the model back into faster water closer to
the weir and take another reading.
I puzzled over speed reading for a while, messing about
with means of measuring speeds and movement, but came to the conclusion
that it was Speed / Length Ratios (S/L) that I wanted, and by putting the
marked rod along the centreline of the boat and noting the spacing of the
peaks of the wave train in the wake, I could determine the S/L ratio and
compare them with the balance readings. An hour or so in the soft light of
a summer dawn can give me twenty or more readings over S/L ratios from 0.5
to 1.5 and I can go home to breakfast with enough data to keep me puzzling
for a day or two while I run the videos and compare the results with
graphs made on other days with other models.
I am also a bit of a petrol head, having raced motorcycles
and cars in the past. There is a very true saying that "you can take the
boy out of the racer, but not the racer out of the boy" . Throughout the 7
or 8 months of the season I sit up every second Sunday night watching the
Formula One racing cars shriek around circuits on the other side of the
Now what on earth is this turkey on about I hear the
voices say! This emag is about us amateurs building little boats not mega
million dollar racecars and even more expensive boats.
I am old enough to remember driving cars with cable
brakes, cars that would slide off the road and fall or roll over at the
slightest provocation. The car I drive today has four wheel hydraulic disk
brakes with an antilock system, fully independent suspension, amazingly
grippy radial ply tyres. It uses half the fuel at much faster cruising
speeds than I could have achieved with my first car, and is hugely safer
in an accident than the old one. Many of these improvements were pioneered
in racing cars, cars that at the time seemed to have no relevance to our
day to day reality, and so with the boats.
The IACC ( International Americas Cup Class) boats are
magnificent, their speed upwind and their ability to manoeuvre, to
maintain speed through a tack or gybe, their resistance to pitching, and
their use of high tech materials is a testing arena similar in relevance
to our pottering about on lakes and bays as the Formula One racing car is
to our commuting in to work each day.
As a designer, I have to believe that I can produce
something a little better today than yesterday. If not, then I may as well
just tell people to go buy a copy of John Gardners Dory Book. So I
actively pursue improvements both to the boats and to my knowledge of how
they work, and for me one of the many challenges I face is to adapt and to
make relevant to "our world" some of the information being generated by
the many millions of dollars being spent on those incredible boats now
sailing Aucklands outer harbour.
John Welsford Small Craft Design.