J/70 Owner Guide
Page
© Copyright 2012, J Boats, Inc. All Rights Reserved
29
Tuning the Rig
Your sailmaker will have specific shroud tensions recommended for different conditions. The following
is a general tuning guideline that will work well for most sails and conditions. Before tuning, be sure the
headstay turnbuckle is pinned to the recommended length and the shrouds are connected.
Center the mast: Establish reference points on the toe-‐rail abeam of the mast, by measuring aft from the
bow equidistant to both rails. Then hoist a metal tape measure up the main halyard. Measure from rail
to rail and adjust the upper shrouds hand-‐tight until the top of the mast is centered. The lowers should
be slack.
Tighten the uppers two turns per side until you reach a shroud tension of approx. 800 lb. as measured by
a LOOS gauge. Then hand-‐tighten the lowers so that the mast is straight side to side while sitting up the
mast track.
Once the mast is straight, tighten the lowers two turns per side up to 700 lb.
Tighten the backstay lashing/adjustment so that with the backstay line released, the backstay bridle rests
approximately 12-‐14 inches below the intersection with the upper backstay.
This shroud setting is a good all-‐around starting point. In sea-‐trialing the J/70 with several sailmakers,
we arrived at the following general “grid” using a LOOS PT-‐2 tension gauge:
Loos Gauge Settings:
Wind Speed (kts)
Upper Shrouds
Lower Shrouds
0-‐6
18
12
6-‐10
20
18
10-‐14
25
23
14-‐17
28
26
18+
30
30
New wire rigging tends to stretch a little. Be prepared to go through this same tuning procedure after
your first day of breezy sailing and thereafter to check it periodically.
Sail Handling Tips
Sheeting the Main
The mainsheet is a simple 5:1 system that cleats on a swivel base in the center of the cockpit. The 2:1
traveler allows a large degree of flexibility to power up or depower the mainsail. In general it is good to
depower with a vang sheet technique by attempting to twist off the top of the mainsail and depower with
the backstay, while flattening the sail with the outhaul and Cunningham.
Sheeting the Jib
For most day sailing, as well as racing in light to moderate winds, you can trim the 2:1 jib sheet directly
from the ratchet turning block and then to its local Harken cam cleat. You also have the option to lead
the sheet aft to the leeward winch and this is quite handy when single-‐handing. In windy conditions, you
have a third option of trimming the jib sheet across the cockpit to the windward winch (cross sheeting).
