Performance And Characteristics - Per Brohall Albin 25 Handbook

stock. The wheel turns two full revolutions from side to side giving a rudder angle of
35" each side. If the flexible cable is loosened from the rudder,arm a spare tiller can
be mounted directly into the rudder arm.
Fuel tank is made of Argon welded stainless steel plate with a capacity of 75 litres
(16.5 Imp. gal., 20
Water tank is made of Polithene with a capacity of 65 litres (14 Imp. gal., 17 US. gal.).

Performance and characteristics

Stability
If the power and length
the weight (displacement) is increased, there is a loss of speed. The Albin 25 has
been designed around its engine t o produce the most efficient boat, obtaining the
best speed with available power. This means that the boat must b e light. Therefore
the necessary stability is achieved b y means of a suitable hull shape
stability. Fig. 4 shows just how the force of gravity
gravity and how in a heeled position a similar force works vertically up from the
centre of displacement. If we multiply displacement (P) (in this case 1680 kilograms)
times the length
get the stability moment which is the "power" which will bring the boat back to an
Fig. 4.
Section showing stability moment.
Us.
gal.).
of
a motorboat are increased the speed is increased, but if
of
the moment arm (distance 0.25 metre between the two forces) we
upright position. Heeling an Albin 25 up to 50
degrees (empty boat with mast and boom and
one person on the cabin top) the accompa-
nying stability curve was measured a (fig. 5).
For heeling angles larger than 50 degrees the
stability moment has been calculated as
shown. As a comparison the sailboat Vega
has about twice as large a stability moment
up to heeling angles of 50 degrees. A normally
loaded Albin 25 weighs more than the test
boat and also has a lower center of gravity.
Because of this the loaded boat gains even
better stability than the curve shows.
that the Albin 25 is as good as uncapsizable
and that you can use rig and sail without any
risk of capsizing. It also shows that ballast is
not necessary from a stability point of view.
Ballast decreases speed through increased
weight and if the ballast is put deep into the
boat
ment to the boat.
Period of roll
The results of such good stability give the
Albin 25 a comparatively quick natural period
of roll (time of swing from one side to the
other and back). A longer period of roll gives
a more comfortable athwarthship movement
in a seaway. The formula for calculating the
period of roll
Radius of inertia means the distance from the
axis of rotation to a theoretical point where
the mass of the boat i s concentrated when
rolling around this axis. The radius of inertia
can be considered about the same as the
length of a pendulum. The meaning of the
meta-centric height is shown in fig. 4 which
also shows that this height is a measure of
stability. A n increase or a decrease of the
meta-centric height gives an increase or de-
crease of stability. Seemingly it is possible to
lengthen the period of roll through decreasing
the meta-centric height (the same as raising
the center of gravity of the boat which is the
-
(P)
works from the centre of
can also give a less comfortable move-
it
is:
(t)
1.108xradius of inertia
t =
metacentric height
giving form
It
shows
5