Here is a simple mast tuning
guide that will give you a good basic trim for an IF-boat mast. No gauges
are needed for this procedure.
- Adjust the mast rake to 0.25 - 0.35 metres (10 - 14 inches), measured
horizontally at the lower mast spar band (along the boom). To determine
this vertical line, hang a small anchor weight or similar heavy object
from the mainsail halyard.
When measuring the rake, heavy items such as batteries, filled water
tanks, outboard motors, etc., should be removed from the boat. As an
alternative, all the heavy items may be placed on the cabin floor, just
aft of the hanging locker(s).
Only one person should be on board and he or she should stand on the
cabin roof just aft of the mast. (see Figure
1)
- After the proper rake has been established, connect the mainsail
halyard shackle to the boom fitting as close as possible to the aft
side of the mast. You will use the mainsail halyard as the straight
reference line between the mast top and the lower spar band. Do not
keep the halyard tightened during adjustment, but only when determining
the mast bend as per (3.) and (4.) below.
- Bend the mast by tightening the upper shrouds so the bend at spreader
height is about equal to the mast spar longitudinal dimension (about
0.13 metres or 5 inches).
- Tighten the lower shrouds so that the bent mast is going back to
only about 0.03 - 0.05 metres (1 to 2 inches). Be sure to check the
straightness of your mast by frequently eyeing up the sail track. (see
Figure 2) The shroud tension measured
by a tension gauge, should now be something like 300-450 kp (660 to
990 lbs.) for the upper shrouds and 130-200 kp (290-440 lbs.) for the
lower shrouds (regardless of shroud diameter).
updated: 04/27/1999
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