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How to tune your mast training - Nockamixon Sailing School

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Basic Mast Tuning for Sailboats
typically found on Lake Nockamixon.
Captain Mike Brown
How to Tune your Mast
• Thick books have been written on mast tuning.
This presentation is focused on the bare basics of
mast tuning and not an advanced tuning guide
for all vessels.
• This document provides some mast tuning
common sense recommendations and rules of
thumb for the type of sailboats typically sailed on
Lake Nockamixon.
• These include sailboats with a single mast,
forestay, backstay, one spreader, and 1-3 shrouds
on each side.
For most of us Mast Tuning is a bit of an art.
• Unless you are a mechanically inclined, you
may not be able to intuitively understand the
complex relationship of all your stays, shrouds,
and spreader on your sailboat.
• By understanding the function of each
component and being methodical in your
approach you can make more intelligent
choices.
What is wrong if your rig is too loose?
• When sailing close hauled, a loose rig will
cause the mast to tip off to leeward,
increasing the wind force downward and
therefore increasing heel. As the heel
increases, the weather helm increases. In the
end, you have a boat that doesn't want to
point and heels excessively.
• Having loose rigging can cause shock loading
of members and rig failure.
What is wrong if your rig is too tight?
• Too much tension can result in permanent
bend in your mast, pulling out chain plates,
excess stress on stays and shrouds, tangs, etc.
and rigging failure.
What are Major Concepts and Terms
Involved with Mast Tuning?
•
•
•
•
•
•
•
•
•
Standing Rigging
Weather Helm
Mast Rake
Fore and Aft Tuning
Canted Mast
Mast Lean Athwartships
Mast Bend Athwartships
Static Mast Bend
Turnbuckles and Shroud Adjusters
What is Standing Rigging?
• The term 'standing rigging' refers to fixed pieces
of stainless steel wire or rod which support the
mast.
• Stays offer principally fore and aft support.
– Backstay
– Forestay
• If the support is principally from side to side, they
are called 'shrouds'.
– Lower shrouds
– Upper shrouds
Standing Rigging
What is the purpose of the spreader?
1. If there was no spreader, then the angle
of support from the chainplate to the top
of the mast would be too low and would
cause extremely large tensile forces in
the shroud and equally large compressive
forces in the mast.
2. The spreader becomes a compressive
member and when properly loaded by
the upper shroud, the spreader pulls the
top of the mast to windward and pushes
the middle of the mast to leeward.
3. If your mast is swept back it moves the
upper shroud aft of the mast so the
upper shroud supplies some force in the
aft direction on the masthead.
What is the purpose of the lowers?
• To avoid the resulting
leeward bow caused by
spreader compression, a
lower shroud is installed
both port and starboard
running from the mast at the
spreader to the deck near
the upper shroud chainplate.
• The purpose of the lower is
to provide athwartships
support for the center of the
mast.
Why have two lowers on each side?
• If you have two lowers on each side, one will
typically run forward and the other aft of the
mast so in addition to the lowers providing
athwartships support for the center of the
mast, some fore and aft support is also
achieved depending on how far forward or aft
the lowers are located.
What is the purpose of the Forestay?
• Forestay holds mast
up so it cannot fall
back.
• Forestay length
determines mask
rake.
• The forestay should
be tight as you can
safely make it
without overloading
the stay. This helps
to reduce forestay
sag and maintain
proper sail shape.
What is the purpose of the Backstay?
• The backstay holds the mast up
so it cannot lean forward.
• The backstay counters the
forces from the forestay and
creates enough pressure on the
mast in an aft direction to allow
for a couple degrees of static
bend of the mast.
• If your backstay is adjustable the
backstay allows your mast to be
bent aft to tighten the forestay
or bend the mast aft.
Weather Helm verses Lee Helm verses
Neutral Helm
How much weather helm is good?
What is Mast Rake?
• On most sailboats, the
mast is not supposed to be
perfectly straight fore and
aft. Instead the mast
should be tilted slightly
back.
• The angle of the mast to
the surface of the water is
called mast rake.
• The length of the forestay
controls mast rake.
What is Mast Lean Athwartships?
This mast is canted
or tilted to the left.
What is Mast Bend Athwartships?
This mast is out of column.
Mast Static Bend
• Static mast bend is
desirable because
without it your mast
can pant fore and aft
causing shock
loading and rigging
failure.
Turnbuckles and Shroud/Stay
Adjusters
Tangs and Chainplates
What are the objectives of mast
tuning?
– Your mast should be raked back enough to cause a
slight degree of weather helm.
– Eliminate any mast leaning from side to side so it
is straight athwartships both in the slip and while
sailing in moderate winds.
– Eliminate mast bending athwartships so the mast
remains straight athwartships both in the slip and
while sailing in moderate winds.
– Optimize stay and shroud tension to improve sail
shape and minimize risk of rigging failure.
Mast Tuning is a two or more stage
process
• Tuning involves adjusting the tension in the
shrouds and stays so that the mast will remain
properly positioned under most sailing
conditions with the desired amount of rake for
comfortable helm balance. Tuning involves
two phases.
– Tuning at the dock.
– Tuning while under sail.
Raising your Mast
When your mast is raised the shrouds and stays are
fastened but loose and in need of proper tuning.
Step number one: Make sure your
spreader is straight
• A crooked spreader
is not only
unsightly but
unseamanlike and
dangerous.
• The spreader may
be forced to slip
further down the
shroud resulting in
the loss of the
spreader and
resultant collapse
of the mast.
Fore and Aft Tuning
• After spreader is straight adjust tension of
shrouds so they are all loose.
• Adjust mast rake by tightening the backstay
and loosening the forestay or loosening the
backstay and tightening the forestay until
proper amount of rake is achieved.
How to Measure Mast Rake and How much
should your mast be Raked?
• Try to get specifications from manufacturer for
your vessel. Many manuals have little available
in terms of mast tuning. If none available start
with 30:1 (20 feet mast X 12 = 240 inches.
240/30 = 8 inches).
• Measure rake by hanging a weight to your main
halyard and measuring the distance it hangs
from your mast when suspended just above the
deck. Vessel must be floating level and there
should be little or no wind when you do this.
• Only way to measure weather helm is to sail in
moderate winds (10-12 knots).
Getting your mast straight Athwartships
• This mast is straight
athwartships and there is no
canting.
• No Mast lean.
• No Mast bend.
Getting your mast straight Athwartships
• Start with the lower shrouds fully loosened and the
uppers tightened as much as you can tighten them
by hand.
• Adjust tension on the port and starboard upper until
the mast appears straight athwartships when you
look at the mast track or groove on the aft side.
• First check by eye.
• Then check by using a halyard as a guide.
How to use a halyard as a guide?
• Take the main halyard and lead the shackle
end to a point on the rail or chainplate. Adjust
the tension in the halyard so that the shackle
just touches the rail or chainplate with a given
tension, and then cleat the halyard.
• The particular part of the rail or deck you
choose as your reference point is not
important as long as it is the same point on
each side.
Getting your mast straight Athwartships
• Then without adjusting the halyard take to the
port side.
• Adjust upper shrouds until the halyard
measurement shows the mast is straight and not
canted. Confirm by looking at the mast by eye.
• If not, let off one upper shroud's turnbuckle and
take up on the other to bring the masthead closer
to centerline until the halyard shackle touches
both sides under the same tension.
Getting your mast straight Athwartships
• After the mast is centered athwartships, tighten
both upper shroud turnbuckles uniformly, one
full turn on one side, then one full turn on the
other. Repeat until the turnbuckles become
difficult to turn. Cotter pin the turnbuckles.
• Tighten up the lower shroud turnbuckles so that
almost all of the slack is removed. Sight up the
trailing edge of the mast to make sure that it is
still straight.
Next tune your mast based upon
sailing performance
• Now that your mast is tuned in the slip you
are ready to tune your mast based upon
sailing performance.
• Before heading out to the water please note
the following guidelines and rules of thumb.
Balance of forces
• The lower shrouds always pull the mast to
weather at the spreader where they terminate.
• The spreaders, on the other hand, due to the
compression from the wires going over their tips,
push the mast to leeward.
• In order to tune a mast athwartships, you need to
establish a dynamic balance between "pull" of
the lower shrouds and the "push" of the spreader
and upper shroud.
Shroud Tension
• The back lower
shrouds should be
looser than the
forward lower
shrouds. The back
lower shrouds
need to be just
tight enough to
prevent any fore
and aft panting in
the midsection of
the mast.
Shroud Tension
• The forward lower shrouds control mast bend
athwartships and generally need to be tighter
than the back lower shrouds; tight enough to
keep the mast from bending athwartships while
under sail and to provide a small amount of
static mast bend from backstay tension.
Shroud Tension (Continued)
• The upper shrouds hold the top of the mast
straight so it does not lean athwartships.
They should be tight enough to keep the
mast straight in moderate winds.
• The upper shrouds should be tighter than
the forward lowers to allow for the greater
distance and angle.
Forestay Tension
• The forestay should be as tight as
you can make it without
compromising the integrity of the
stay. Can go up to 15% of the
break strength of the cable. Can
use a gauge to determine this.
• To determine the break strength
you will need to determine the
diameter of the cable with a
caliper and look up the break
strength of the cable and then use
a rigging gauge to set at up to 15%
of the break strength.
Rig Tension Gauges
• If you have a tuning guide or if
you have tuned your mast using
the principles described in this
document you can measure and
record how tight your stays and
shrouds are and tighten or
loosen them using a rig tension
gauge. Once you know the
correct tension required on your
stays and shrouds it is relatively
easy to tune your mast in the
future.
Loos Gauge Initial Tension Setting
Recommendations
Diameter
Breaking Strength Pounds
Forestay Pounds
Shrouds
3/32
1200
180
120
1/8
2100
320
240
5/32
2200
500
350
3/16
4700
750
500
7/32
6300
1000
700
1/4
8200
1300
850
9/32
10300
1600
1000
5/16
12500
2000
1300
3/8
17500
2750
1800
How tight should the backstay be?
• Backstay tension must be sufficient to maintain
proper mast rake with the desired forestay
tension. Since the backstay makes a greater angle
to the mast, backstay tension will be lower than
forestay tension. May not be true on fractional
rigged sailboats.
• The backstay also needs to be tight enough to give
the mast some static bend. This stabilizes the
middle part of the mast. Static mast bend can be
induced by tightening the forward lowers.
• If you do not have forward lowers it may not be
possible to have static bend on mast. In this case,
increased backstay tension affects forestay sag.
How tight should the backstay be if
there is a backstay adjuster?
• If there is a backstay adjuster then backstay
tension should be enough when the backstay
adjuster is loose to maintain proper mast rake
and forestay tension and when the backstay
adjuster is tightened the mast should bent aft
at least 2-3 degrees. Some masts can only be
bent a few inches while some masts may be
bent 16-18 inches. Depends on material mast
is made of and other factors.
How to tune your mast while sailing?
First check if the top of mast falls off to
leeward when under sail. Go sailing in a
moderate wind (10-12 knots). Look up the
mast track on both sides. If the top of the
mast appears to fall off to leeward, try
tightening the windward upper. Sail on both
tacks and tighten or loosen the uppers until
the top of the mast stays straight under sail.
How to adjust your mast based on
sailing performance?
Then check if the middle of the mast stays straight
when under sail. Go sailing in a moderate wind
(10-12 knots). Look up the mast track on both
sides. If the middle of the mast appears to fall off
to leeward, try tightening the windward forward
lower. Sail on both tacks and tighten or loosen
the forward lowers until the middle of the mast
stays straight under sail.
Tighten the aft lower just enough so it remains
tensioned while under sail on the leeward side.
Check both sides and tension accordingly.
How to adjust your mast based on
sailing performance?
• Getting a straight mast athwartships is an
iterative process involving both the uppers
and lowers. After making gross adjustments if
the top of the mast appears to fall off to
leeward you may need to loosen the lower or
tighten the upper.
How to adjust your mast based on
sailing performance?
Don’t adjust shrouds when they’re on the
windward side. Tack so the shroud is loose
and then remove cotter pin (not clevis pin)
and then loosen or tighten 1-2 turns. Then
tack back and look at mast again and adjust
again if necessary.
Shroud Tension
• The back lower shrouds should be looser
than the forward lower shrouds. The back
lower shrouds need to be– Just tight enough to prevent any fore and aft
panting in the midsection of the mast.
– Just tight enough so there is no slack on the
leeward back lower when under sail in moderate
winds.
Shroud Tension
• The forward lower shrouds control mast bend
athwartships and generally need to be tighter
than the back lower shrouds.
– Tight enough to keep the mast from bending
athwartships while under sail.
– Tight enough to provide a small amount of static
mast bend from backstay tension.
Shroud Tension (Continued)
• The upper shrouds hold the top of the mast
straight so it does not lean athwartships.
They should be tight enough to keep the
mast straight in moderate winds.
• The upper shrouds should be tighter than
the forward lowers to allow for the greater
distance and angle.
Other
• Before tuning mast make
sure chain plates not in
rotting deck or corroded
and that shrouds and stays
not chaffed or bent at sharp
angle.
• Check all clevis and cotter
pins and replace any that
are worn.
• Make sure stays and
shrouds line up well with
their fittings in their ideal
positions and angle and
they are not fatigued.
Other (Continued)
• Lubricate turnbuckles before tightening them
to keep them from stripping. Use Sealube or
something similar.
• Lock all turnbuckles with cotter pins. If using
round cotter pins then round cotter pin should
go around turnbuckle body and then through
whole in threaded pin to lock it in place.
How often do you need to tune your
sailboat?
• After initial tuning your rigging will stretch to
the extent that retuning from scratch will be
necessary in a matter of days. However, after
this initial working-in period, you will find that
your boat tends to hold this tune for fairly
long periods of time.
How long will it take to tune your
mast?
• Unless you have a tuning guide that you trust
you will have to test different tensions on your
stays and shrouds until the optimal tensions
are found. This will take many hours or even
days and a lot of trial and error. You may want
to work on your tuning a little bit every time
you go out for a sail.
• Once you have the correct tensions you can
use this in the future and it is much easier.
Resources
• Rigging guides from manufacturer.
• Rigging recommendations from Sail
manufacturers. North Sails One Design has
rigging guides for some vessels.
• Unless you have a one design type vessel
rigging guides may not be available or may not
be suitable for your vessel.
• Ask your fleet captain or other members of
your fleet for advice for your vessel.
The End
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