Martin 242 Mast Tuning Clinic
Sunday, March 18, 2007
courtesy of Fleet Three - MdR
Introduction This document is a guideline for basic mast tuning on the Martin 242.
Any references to numbers are based on the cut of the Ullman Sail but the technique will be the same for any mainsail.
A. Boat Preparation – Before starting make sure of the following.
All halyards are loose
Boomvang is loose
Backstay is loose
Boom is resting on deck
Shrouds are loose Turnbuckles should be almost fully unscrewed.
Note: Depending on the type of turnbuckle you use, this is a good opportunity to make sure the threads are
evenly fed into the turnbuckle. We suggest you completely undo turnbuckles and start at zero turns.
Tip: paint one side of all turnbuckles black. This will help you keep your place when tightening or
loosing the shrouds.
Tools Needed:
1. Wooden mast wedges and something to trim the wood with such as a hack saw
2. Power drill with counter sink and 5/32 bit
3. #10 x 5/8 Flat head wood or sheet metal screw
4. Mast boot material
5. Adjustable wrench
6. Screw Driver
7. 12’ Tape Measure
8. 50’ Tape Measure (optional)
9. Loose Gauge
B.Mast Preparation:
1. Centering The Mast At Deck Level
The first step in tuning your rig is to center the mast at the deck. Do not expect the mast to look centered in the
collar.
Note: Not centering the mast properly will result in an incorrect mast shape and will only get worse when
tension is applied to the shrouds. You will notice this incorrect balance first when you cannot achieve
consistent starboard versus port shroud tension. The result can be inconsistency in sail shape, speed and point
from tack to tack.
Make sure to have wood blocks or any other preferred method of locking the mast at the deck handy.
a. Apply enough tension so the shrouds are not dangling but not tight in any way. To do this, once the
turnbuckles are evenly threaded, make sure that the same amount of threads are showing for the uppers and
lowers on each side. Start applying the same amount ofhalfturns to the corresponding turnbuckles on each
side. Do this until there is consistent (light) tension on all four shrouds.
b. Using a 12’ tape measure, measure from each lower shroud to the center of the back of the mast.
Note: Make sure to measure f rom the same shroud height on each side.
Tip: A good place is just above the vang lug on the mast.
c. Continue to measure from the shrouds as you place blocks around the mast holding it at the same distance
from both shrouds.
d. Once the mast is centered and the blocks are securely in place, mark the posit ion of each block around the
mast. This will great ly facilitate t his procedure next time the mast is removed.
Tip: It is good to minimize mast prebend so the sail is not too flat. To accomplish this, the mast should
be positioned (blocked) as far aft as possible on the deck opening.
2. Centering The Mast At The Top
The second step is to center the top of the mast. If the above procedure has been done correctly the top of the
mast should be close t o center.
Note: Not having the mast topcentered before staring the tuneup procedure can also cause inconsistent
starboard versus port shroud tension as well as inconsistency in sail shape, speed and pointing ability from
tack to tack. This is usually noticed by differences in the shape at the top of the mainsail from tack to tack.
a. Attach a tape measure to the main halyard and pull up enough to take a reading on both sides. The reading
should be taken using the same t ension to the halyard at the aft most U bolts on both sides.
b. Adjust the upper shrouds to bring the mast to center. This is accomplished by t ightening one and loosening
the ot her.
Tip: Half turns on the turnbuckles usually work best. Marking the outside of the turnbuckles black will
help you keep track of the ½ turns
c. Once the mast is topcentered, look up the back of the mast. The mast should be straight. Any curvature is
usually caused by uneven tension on the lower shrouds and should be minimal. If an abnormal curvature is
observed, check the lower shrouds and make sure one side is not over tightened.
Adjust the lower shrouds appropriately to remove the curvature. Make sure to adjust both sides by t ightening
one and loosening the ot her. Half turns on the turnbuckles usually work best.
d. Once the mast is visually straight, take tension gauge readings of all the shrouds.
If the tension is too loose for readings apply four (4) half turns to each turnbuckle until a reading is possible.
The tension between corresponding shrouds should be similar. Any differences can be corrected by adjust ing
the corresponding shrouds. Make sure to adjust both sides by t ightening one and loosening the other. Half
turns on the turnbuckles usually work best.
Goal:
Mast centered at the deck and top
Consistent shroud tension on the corresponding shrouds
C. Base Setting
A base setting is a combinat ion of upper and lower shroud tension that optimizes sail shape for given average
regional condit ions.
For example, a base setting in San Francisco will not be the same as one in Marina del Rey. (at least not during
the summer)
Base settings in the same region will differ based on sailing st yles, weight on the boat and sail manufacturer.
It is important to develop a feel for a base setting that will suit your sailing st yle.
1. Getting to Base Setting
For a Martin 242 in Marina del Rey, a starting point for a base setting can be 44 on the upper shrouds and 38
on the lower shrouds using the inexpensive Loose Tension Gauge.
When your rig is centered and you have consistent tension on the shrouds. You are ready to set your base
tension.
a. Put eight (8) half turns on the uppers and four (4) on the lowers.
b. Take a tension reading and cont inue applying and even number of half turns on uppers/lowers unt il you
have reached t he desired setting for your region.
Goal:
Rig is centered
Shrouds have even tension
Desired base setting on Tension Gauge
D. On the Water Tuning Advanced Rig Tune
Check your fleet rules regarding adjust ment on the race course.
The goal of adjust ing the r ig on the water is to power or depower the sail plan as condit ions change.
Knowing how much to go one way or the ot her when adjust ing the rig takes practice, observat ion and most ly,
time on the water.
Decide on what change in condit ions would cause to make an adjust ment in your rig tension. For some sailors it
may be 2 knots for you it may be 5 knots increase or decrease.
1. When adjusting the rig on the water:
Always apply the same number of (half) turns to the corresponding shroud on both sides.
A minimum adjust ment is four (4) half turns on the uppers and two (2) on the lowers. Any less in eit her direct ion
will not likely create any change in the shape of the sails
Following are important things to look at when making rig adjust ments:
a. Sail shape
Frequent ly look at the mainsail while sailing so you get a feeling for the shape. This way you’ll be able to
notice the changes in sail shape after adjust ing the shrouds.
Effects of adjusting the upper and lower shrouds:
b. Leeward shrouds (while sailing upwind)
There are different schools of thought on how these should look while sailing upwind. (Dangling or tight)
c. Speed, power and point
Speed test with other boats to get a feel for you speed, power through waves and pointing abilit y.
If the groove is too wide or too narrow:
1. Adjust main halyard
2. Adjust main sheet
3. Adjust jib halyard
4. Adjust jib sheet
5. Adjust rig tension
E. Every race day morning before leaving the dock …
Take a tension reading to get a feeling as to what the previous day’s changes were.
Set the rig back to base setting.
Make sure the top of the mast is centered.
Look up the back of the mast for unusual curvature. Adjust appropriately.
Take a tension reading and readjust as necessary.
Tips: It is also helpful to have the same person always adjusting the rig.
Tip: Write down the adjustments as they are made. This can be done on deck and then transferred to a
notebook.
