12
J/35
Tuning Guide
SPEED TIPS FOR HEAVY AIR
RUNNER & VANG
The use of boom vang in heavy air
(over 18 true) comes very naturally to
some sailors and raises objections
among others. Here is why it works
on a J/35. The downforce generated
on the leech allows mainsheet play
with less resistance. When you use
the vang, you bend the spar forward.
In breeze over 18, we suggest you
shorten the headstay to 48’-10” or
9.5m. This eliminates prebend and
creates the impression the main has
too much low luff curve. The vang
adds just enough mastbend to fair
the mastbend curve back to the
original design.
North 3DL Mainsail 12600 dpi in 24k True (29k approx.) This sail is handling
the loads nicely. The top is flat, open and twisted. The draft is located forward in
the bottom half of the sail, and not too far aft up top. Cunningham is loaded to
position the draft. The vang is aggressively loaded with 100 lbs. (with feet
braced, use both hands!) on the tail of the purchase system. The most
critical element is sheet tension.
A good rule of thumb is to sheet the sail harder until the boat heels too much,
or has too much helm. When this occurs, flatten the sail and move the draft for-
ward. The old rule of when in doubt, let it out may be O.K. Since this makes the
sail less powerful, you may want to adjust other shape controls first, then ease
the sheet as little as necessary.
Small speed gains generate big wins,
especially when sailing in heavy air.
The 3DL mainsail (at left) is nicely
powered up, showing a clean leech
with linear twist from the boom to
the head. Tensioning the checkstay or
runner on the J/35 produces exactly
the opposite sail adjustment com-
pared to a fractional rig. When you
tighten the runner, the mast becomes
straighter. Mastbend flattens the
main, added runner deepens it.
The best way to get this right is to
bend the mast with the hydraulic
backstay, then add checkstay/runner
until the sail is shaped right for the
conditions. The desired sail shape has
the draft ahead of center. Do this by
juggling cunningham and checkstay
load. Don‘t forget to pull the outhaul
to the black band. In wind speeds
above 18 true, take-up 3 turns on the
D2s, and 2 turns on the D1s.
Using Vang in Heavy Air
