How do all these principles apply to
model boat racing? The model hydro
pictures above are a clue. Keeping
everything out of the water is the goal.
Understanding how wings in ground
effect work is key. The next part will
describe ways to take advantage of
wings in ground effect and why too
much lift can be bad. We will also look
at some recent innovations in planing
surfaces, as well as foil drag issues in
both air and water.
PROPWASH
18
October 2016
and can work well for medium size boats
at moderate speeds.
The America’s Cup sailboats
completely revolutionized sailboat
racing using hydrofoils. Before that,
watching a sailboat race was as exciting
as watching grass grow. Cavitation
limits the speed on conventional foil
sections and supercavitating foils don’t
offer enough advantage in drag
reduction.
However, wings in the air, especially
close to a solid surface, have very good
lift to drag ratios. The three point
hydroplane takes advantage of this
effect. Chip Hanauer once described a
modern unlimited hydroplane as a “wing
with training wheels”. The wing carries a
large percentage of the hull weight
leaving only half of the propeller, the
turn fin, and the rudder in the water to
cause drag. The planing surfaces on the
sponsons mostly stabilize the wing and
carry little load at speed. Of course the
ultimate solution would be to completely
lift the “boat” out of the water. This is
called a wing in ground effect (WIG)
craft.
High Speed Boat Design
-
Part 1
(Continued from page 17)
window of your car at the same speed.
However, the lift that air flow over a
boat creates can materially reduce the
total drag. This happens because the
airflow lifts the boat out of the water
more than planing alone. Even normal
monohulls experience this. In more
extreme designs wings on the rear of the
hull will lift the hull out. The Northwind
monos used this effect. Wings on the
bow can be used to adjust the planing
angle.
The real gains come when the hull
gets lifted even more out of the water.
Hydrofoils have been used for this.
They are basically wings in the water
Oracle America’s Cup sailboat
A Russian hydrofoil boat
The Caspian Sea Monster wing in
ground effect craft
A model of the classic round nose hydro
$ Bill setting a two lap record
A Mark Anderson Sport 40 flying
Wings on river racers
Northwind model boat bottoms with
central flat planing surface
Batwing mono, note the modern
multistep design with strakes
