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In the BB10m Newsletter from September 1997
Flemming Sørensen (Danish Champion in 1993 and again in 1997) wrote:
1. Mast slope
Hoist a yardstick to the top using the
mainsail halyard and measure the distance to the point where the stern stay cut
the deck. We use as a starting point 12800 mm. Then this measure is adjusted
according to wind speed and the size of the waves The aim is to steer the boat
with only very little pressure on the rudder.
2. Longitudinal stiffness (DEN-80)
In order to obtain a large pressure
on the forestay by using the stern stay we have changed the angle of the
spreaders and the mast foot. On DEN-80 we used 13 degrees angle and max. length
of the spreaders. The placement of the chains at the deck (the fittings which
holds the shrouds) were changed such that the distance measured in a straight
line from the forestay for the top shroud was 2960 mm and for the sub shroud was
3160 mm. In order to make the bottom part of the mast more stiff (rigid) we
placed an aluminum wedge (12 mm thickness where it is thickest) under the mast
foot. In this way the column pressure was moved forward to the fore edge of the
mast tube which then was forced aft. With this tuning we obtained a very stiff
mast which did not "loose" the top in windy weather and had a large
pressure on the forestay under all wind conditions. The mast was now so rigid
that the sub shroud essentially only was used to prevent the mid part of the
mast to move to leeward. But now the old main sail was too hollow at the front
due to too much curvature in this part of the sail. Together with North Sails,
Denmark, we developed a new main sail which has lees curvature and larger cuts,
flatter bottom and larger cap (due to less curvature in the fore of the main
sail). The result was a rig type which clearly was fast in wind speeds over 14
knots but which according to our opinion was not flexible enough in the very
light wind and when we had some small and steep waves.
3. Forestay has to be able to fall
out to leeward in calm weather and steep waves (DEN-83)
When I in winter '95/96 got the
opportunity to fulfill a big dream, namely to build a whole new BB10m I also got
the opportunity to test a completely new rig tuning. In order to control the
depth and the entrance angle on the staysails it was necessary to be able to let
the forestay fall to leeward. This meant that the mast could move forward when
the stern stay was released. The placement of the chains at the deck was changed
to the following: top shroud 2940 mm and sub shroud 3040 mm (from forestay). The
angle of the spreaders was changed to 11,5 degrees. The result is a rig type
which is very moveable longitudinal but at the same time extremely rigid sideward.
With the stern stay it is now possible to control the staysails, e.g. in light
winds with some steep waves as we experienced during Danish Championship in 1997.
As an extra bonus it is now also possible to move the mast top 700 mm forward
during spinnaker legs. This has the effect that the sail center is moved forward
over the pressure center of the keel and thereby the boat is becoming easier to
steer with the rudder. However, we have not yet been able to test this tuning
type in wind speeds over 20 knob. I can, however, assure you that this rig type
requires that the crew is concentrating 100% and that you know exactly what you
are doing and why.
4. General
Put marks
When you have found how the sails
should be trimmed you should put marks on the sheet rails where the sails are
trimmed. You can e.g. put a piece of tape on the deck where the sheet traveler
are and on this tape write which sail was used and under which wind speed it was
used. As a trim manual you can also put tape on the sheets and halyards.
Use logbook
Do you want to make the tuning
perfect on your BB10m you write all information into a logbook. Here you note
wind speed and direction, the height of the waves, type of sails used and the
position of the halyards and sheets, etc. and do this for every sail race. By
using the logbook you can any time look up and check how you should tune when
the wind has a specific speed.
(translated from Danish by B.S.
Clausen. Please excuse me for not knowing all the English words for the marine
expressions)
Polar diagram for
BB10m
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