HOW TO PREPARE YOUR MAST FOR TUNING

Get
to know your mast stiffness

Etchells masts vary in stiffness. They are all
the same section, extruded from alloy of the same specification and cut to the
same taper. However, variations in the alloy stock, the manufacturing process
and the age of the spar lead to differences among manufacturers and between
masts from the same manufacturer.

It is helpful to measure the stiffness of your mast, as this
gives a baseline for setting up your rig, and allows us to cut your Main to match your particular mast.

We classify spars according to the table.

Mast Stiffness

Spreaders

headstay

Stiff

less than 1¼"

less than 1"

medium

1¼" to 1¾"

1" to 1½"

Soft

1¾" plus

1½" plus

How
to measure your mast stiffness

The standard system for measuring mast stiffness is easy to do.

Lay the fully rigged mast
horizontally on trestles, luff track up, so it
is supported at the upper black band and at the position of the partners
where the mast goes through the deck. Take care that the fore and aft axis
is truly vertical.

Tie all rigging along the
mast so it doesn't touch the ground. Shackle the halyards to the spinnaker
pole ring.

Stretch a thread or light
string tight from the upper black band to the lower black band, so it
touches the aft edge of the mast at each band.

Measure
from the aft edge of the luff track up to the
string both at the spreaders and at the headstay
intersection.

Mast straightness

Many Etchells masts
are not straight; sideways, fore and aft, or both. The
most common bend is a curve to one side in the tapered section above the
hounds. As this area is not controlled by the shrouds, a mast with this fault
is hard to tune well.

We have had some success in straightening masts with sideways curve by
supporting them on a padded sawhorse in the region of the bend, wedging the tip
under something heavy, like a trailer, and pushing down hard on the butt. If
you try this, have a spreader installed so you can restrain the mast from
turning as you torture it.

It helps to have two people for this job and to proceed cautiously, as
overdoing it can fatigue the metal and leave the spar with no liveliness. Do this at your own risk!

Fore and aft bend is rarely correctable. Some masts have a permanent aft set
above the hounds and in others the track kicks forward in this area. These
faults affect the stiffness measurements and may require a change from our
recommended shroud positions. If you have a mast like this, you should let us
know before we make your main, so we can adjust the luff curve.

Spreader
angle

The most important factors in setting spreader
angle fore and aft are:

raking the spreaders back equally
on each side

choosing the correct angle
for your mast stiffness

We
measure how far forward

the aft edge of the spreader tip is from the aft face of the mast. When you
lay a long straight edge across the aft side of the mast, how far forward is
the spreader tip on each side?

Remember to pull aft on the spreader tips, as you want to measure the furthest
aft the spreaders will go. The easy way to do this, when the mast is lying
down, is to support the weight of the mast with blocks of wood under the
spreader tips. If the mast is in the boat, be sure to have your stays adjusted
and the backstay tensioned firmly.

Setting spreader angle

Kenyon spreaders. There are two techniques for setting the angle:
glue them in with thickened epoxy, or wrap the end of the spreader with glass fibre tape. We like the second method, as it is easier to
fine tune the angle. The plastic inserts that come with the mast are useless.

Recommended
Spreader Angles

(distance forward from aft face of mast)

stiff mast

1 ¼""

medium mast

1 ¼"

soft mast

2"

(spreaders are straight across)

First, check your spreaders are the same length. Then, wet-out
some 2" fiberglass tape with polyester or epoxy resin and wrap it around
the end of the spreader until it is too thick to fit into the spreader base.

Let the resin cure. Then grind it until the spreader fits into the spreader
base at the appropriate angle. Re-drill the holes for the retaining bolts and
re-make the cut-outs for the lower shroud tangs.

Spreader tip heights: most spreader brackets angle upwards slightly. This is
correct. The spreader should bisect the angle between the stay above and below
the spreader tip.

To set the spreader angle, it helps to level the mast on blocks, luff track up, and place supports under the spreader tips.
Masts with extruded grooves in each side can be leveled by using the grooves as
a reference. Masts without grooves can be leveled by using a level against the
side of the heel plate, but make sure the bolts are tight.

Initially, aim to set the spreaders a little forward of your target position,
as it is easier to grind away material than to add it!

Procter spreaders. These have an aluminum
sleeve around the inboard end which can be filed carefully to adjust the angle.
setting the spreader angle

Australian spreaders. These are a pretty tight fit. You may not be able to rake
them back, in which case you can compensate by moving the shrouds forward on
the chain plate.

Final tuning of
spreader angle

To fine tune and equalize spreader angle, we
measure and adjust it when we have the mast fully set-up in the boat. The boat
should be in the water with the shrouds tightened correctly, and the backstay
tensioned. The next section discusses stepping the mast and initial shroud
set-up.

Final spreader tuning is best done with two people. The measurements are taken
from a ladder with its top securely lashed to the mast and to the deck near the
front of the cuddy.

Please always use appropriate safety precautions when working aloft!

The spreader tips have to be at equal height above the deck.

Measure to each spreader tip from the center of the front
face of the mast at the deck. Push the tips up or down the stay until
they are equal.

Now compare the fore-and-aft position of the port and starboard spreader tips
by measuring carefully from each tip to the point where the backstay intersects
the deck. Make sure the backstay is tensioned to bend the mast at least 3
inches.

If the tip positions measure equally within 3/8" (6 mm) and are also the
correct distance forward of the aft face of the mast, have a beer!

If one or both of the tip positions are too far forward, you can slack off the
upper, take the spreader out of the socket, slide it down the shroud to the
deck, grind down the fiberglass and then re-assemble the whole thing.
Re-tighten the upper shroud. It really saves time to note or mark the
turnbuckle setting before you slack it off. Now remeasure.
Repeat the process until both spreaders are correctly angled. In practice, this
procedure goes quite quickly.

If the tips are too far back, the quick fix is to shape a ½" length
of hose clamp around the back edge of the spreader and slide it into the
spreader socket so it pushes the spreader forward. Be sure to tape around the
outside to keep it in place. The real fix is to refiberglass
the spreader, which is why it is smart to grind down to the correct angle
gradually!

Old-style Kenyon spreader bases are useless! They have an oval base plate, and
are attached to the mast by four pop rivets. The best thing to do is replace
them. The alternative is to connect them together by a stainless strap around
the front of the mast, welded to each base plate. The objective is firm control
of the aft swing of the spreader.

Shrouds and
turnbuckles

The right equipment is really helpful.

Use Dyform
wire for the lowers. Dyform is a special low stretch
version of 1 x 19 wire. As the wind increases,
the uppers, made of regular 1 x 19 wire, will
stretch more than these Dyform lowers. This is
good because it automatically re-tunes the mast for you! The result is
improved performance in gusty winds and fewer adjustments to lower-shroud
tension while racing.

Use calibrated
turnbuckles and write the settings on the deck, or use some other
system to allow you to repeat settings, such as tape on the threads.

The
turnbuckles should be easy to adjust with a minimum of tools. Our favorite
for the lowers are the flat strip style made by Staymaster,
type 532 or 632. They can be adjusted by hand on the lee side, will fit
in> the next hole to the uppers and are relatively cheap. There are
several other good options.

Marking
the spreaders

Before you step the mast, mark the spreaders with
a white band at the knuckle, as a jib trim reference. Not all spreaders are
equal! Check that your mark is 19½" from the mast on both the port
and starboard side. You should write port and starboard on the spreaders to
prevent mix-ups later.

Spinnaker halyard
size and sheaves

Make sure you have the thinnest legal spinnaker
halyard. The rules call for 7.9 mm. Some brands of ¼" Spectra line,
such as Samson Ultra Lite, are just big enough. Also,
be sure to use Harken #160's for all three of the
spinnaker halyard sheaves.

Check
backstay length

We have sailed many Etchells
on which the backstay was too long. The result is that the swage hits the deck
in heavy air. This prevents the use of adequate mast bend and guarantees you
will be slow. We use a backstay length of 36' 6" pin-to-pin. This will
never hit the deck.

While you have the mast out of the boat, it is simple to have a rigger shorten
the wire and swage on a new eye. We usually replace both ends.

You will have to change the wire lengths inside the boat so you can let the
backstay off enough downwind. The objective for downwind is that the front face
of the mast will go forward all the way to the front of the mast partner with a
little slack left in the backstay.