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until you reach -12 on the headstay.
This will be the base setting. See the
photo to the right on how to measure
the tension of the forestay in nega-
tive numbers with your Loos Gauge.
If you get more than
2 1/4"
move the butt position 1/4" forward.
Conversely, if you get less than the
suggested prebend, move the butt
position 1/4" aft. You will need to
move the base forward or aft until you
get the desired pre-bend.
Pre-bend is measured holding the
main halyard directly to the goose-
neck, and then measuring from the
aft face of the mast to the halyard
at the spreader height.
FINE
Your mainsail is designed to perform in 10 knots of wind with 2 1/4" of pre-bend. In
heavy air, bend can be achieved through backstay tension, which will bend the upper
TUNING
part of the mast, increase headstay tension,which flattens the genoa. Because we don't
THE RIG
want to flatten the genoa in light air, the 2 1/4" of bend must be achieved without add-
ing backstay tension. Once the wind lightens, you will ease shroud tension, which will
increase headstay sag and power up the genoa. As the wind picks up, you will progressively tighten the
lowers more than the uppers. The lowers will reduce pre-bend and stiffen the middle of the mast. Every
time you apply backstay tension, the upper part of the mast will bend, freeing the leech of the main and
flattening the genoa. When you want to gain power, ease the backstay.
SHROUD TENSION CHART
Wind - Knots
0 - 3
4 - 10
10 - 15
15 - 18
18 - 22
22+
**
Distance from the genoa to the spreader. If the sea conditions are smooth (flat seas) in winds from
8 up to 16, you can trim the genoa one inch closer than the numbers on the above chart.
Tip: Write this chart on the deck with the number of turns you need to move from one
tension setting to the next.
pre-bend,
Uppers*
Lowers*
16
10
20
15
24
21
27
26
29
29
29
29
*
Loos Tension Gauge Model B
Stay*
-12
-12
-5
0
+5
Jib (Leech straight)
+5
Jib (Leech twisted)
Genoa**
6 - 8"
3 - 4"
1 - 2"
6"
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