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SAIL SETTING and BASIC
TUNING WITH AN INTERNATIONAL ONE METRE YACHT
I am
indebted to many people for the information which
follows because it is a compilation of things I have
learnt from them, either through personal contact or
from publications, together with a few things I have
discovered for myself over the past seven or so years of
experience. Among those who have been good enough to
encourage me with my radio sailing and share their
knowledge are; Graham Bantock, Brad Gibson, Lester
Gilbert, Peter Stollery, Martin Roberts, Geoff Byerley
and numerous other contacts within the radio sailing
fraternity. By following these recommendations you
should be able to put together a boat that sails well.
However, nothing is set in stone and I encourage you to
experiment and try things for yourself, read and
research more and talk about boat set up, sail trimming
and tuning with others in order to expand your knowledge
and optimise the performance of your boat.
First
– you need to attach the rig to the boat:
1.
Keep the jib
sail attached to the mast whilst the sails are stored
off the boat, (preferably in a sail box) then provided
you don’t change the backstay or forestay settings it
will need no adjustment or only minor tweaking to get
the boat going well again next time you sail.
2.
Fit the fin,
complete with ballast, to the boat and place the boat in
a stand (be careful it doesn’t blow over in the breeze)
or lay it on the ground.
3.
If you are
right handed and rig your boat from its left hand side;
take the rig from its box or bag, holding the bottom of
the mast and main boom/kicker in your right hand, and
the jib boom in your left so that you keep control of
both sails and they don’t flap in the breeze. Allowing
the sails to flap uncontrollably could damage and crease
them badly.
4.
Place the
mast heel in the mast tube making sure it is properly
located.
5.
Locate the
mast in the mast gate and/or let it rest against the
ram.
6.
Check that
the headsail leech line and forestay are not twisted and
then attach the head sail to the appropriate deck eye.
7.
Attach the
backstay to the hook or eye at the stern of the boat and
if necessary adjust the tension in it until the mast
bend matches, approximately, the mainsail luff curve. If
the top seam of the main sail begins to flatten or if
creases run from the clew diagonally upwards the mast is
over bent and the tension in the backstay should be
reduced until the sail sets correctly. It may be
necessary to revisit back stay tension later in the
tuning cycle.
8.
Attach the
side stays to the appropriate deck eyes. The wire and
bottle screw can be permanently attached to the deck
eye. The threaded eye should be fitted with a self
locking, nylon lined nut and permanently attached to the
side stay. A a rough guide, put just enough tension in
the side stays, so that when the boat is laid on its
side, the side stay nearer the ground doesn’t become
slack. Later you may need to change this slightly in
order to obtain the desired rig tension and boat
performance. When you have done this lay the boat on the
ground, propped up by a sail box or tool box, or put it
in the sort of stand that holds the boat near
horizontal, and sight down the mast to ensure that it is
vertical and not pulled off to the left or right. If the
mast is, for example, pulled off to the right, relax the
tension on the right hand side stay and increase the
tension on the left hand stay until the mast is
vertical. Check that the side stays are still at the
correct tension and if necessary go through the
procedure again until the mast is vertical and the
tension in the side stays is correct. The side stays
should be tight enough to avoid the slackening as
described above but not so tight that they twang like
guitar strings. If you want to temporarily reduce the
tension in the side stays, for light airs or for some
other reason, simply insert one or two washers between
the bottle screw and lock nut before assembly. It is
often worth experimenting with side stay tension,
especially when the deck mounting points are aft of the
mast, because of the effect it has on rig tension, mast
bend and the way the main sail sets. If doubtful about
just how tight to have them, I suggest that it is better
to have them a little bit too loose rather than too
tight. Once the correct setting is achieved the rig can
be detached from the boat after sailing, leaving the
locking nuts undisturbed, so the same settings can be
used again next time. It is essential that the side
stays are evenly tensioned and the mast vertical (left
and right) if the mainsail is to have the same amount of
twist on both tacks. Side stays - especially new ones -
will stretch and become loose and/or unevenly tensioned
with use, so it is important to check them from time to
time.
9.
Attach the
sheets to the main and jib booms.
10.
If your
mainsail has a luff wire be sure not to over tension it
because this will cause strange wrinkles to appear in
the sail and interfere with the movement of the main
sail when changing tack.
11.
Tighten the
downhauls on the jib sail and main sail just enough to
remove any wrinkles or bubbles in the luff of each sail.
For very light airs try leaving the downhauls slightly
slack.
12.
Start with
the mast ram just supporting the mast. You may need to
come back to the ram later when doing the fine tune and
adjustment.
13.
When
dismantling your boat at the end of the day simply
reverse the above procedure and be sure to take all of
the tension out of the rig by slackening off both down
hauls, the luff wire tensioner in the main sail if your
boat has one, and most importantly the kicker. Failure
to do this will have the sails stored under tension with
the strong likelihood that they will become permanently
distorted and pulled out of shape. If after use the
sails are wet, the sail box should be opened on your
return home and the sails allowed to hang free so that
they can dry out. If a bag is used the sails must be
removed from it and allowed to dry. It is better not to
store sails in a bag.
Now that you’ve got the rig
safely on the boat you need to set the amount of camber
in the foot of each sail, the amount each boom is out
from the centre of the boat in the close hauled position
and the degree of twist in each sail.
1.
The main boom
should be about 10mm (+ or- 5mm) from the centre of the
sheeting post in the close hauled position.
2.
The end of
the jib boom should be about 65mm away from the centre
of the mast in the close hauled position (+ or – 5mm).
3.
The gap
measured between the mid point of the boom and the foot
of the sail should be about 20mm for both the jib sail
and main sail (+ or - 5mm).
4.
To set the
twist in the sails: Let the sails fully out and hold the
boat in the wind so the sails fill as if the boat were
on a run. Adjust the kicker so that the middle seam on
the mainsail is at approximately 90 degrees to the mast.
This is the correct setting for running before the wind.
Keep in mind that the wind strength may not be the same
on shore as it will be out on the water and that the
boat is stationery, this means that a little more twist
may need to be set than seems correct. The final check
must be done on the water with the boat sailing. Lay the
boat down and check that the mast head fitting is
straight fore and aft and not twisted off to one side.
This ensures the same amount of twist in the mainsail on
both tacks. With the boat still lying on its side, sheet
in to the close hauled position and hold the main boom
on the centre line of the boat without loading the
kicker. Measure the distance between the middle seam of
the mainsail and the backstay. It should be somewhere
between 35mm and 60mm. Twist can be increased by
tightening the backstay slightly (be careful not to over
bend the mast) and/or reducing the amount of ram
pressure on the mast. Twist can be reduced by slackening
the backstay slightly and/or increasing the ram
pressure. It isn’t good practice to alter twist in the
close hauled position by adjusting the kicker because
this will probably result in the amount of twist being
wrong for running before the wind. For this method of
setting and controlling twist to work well it may be
necessary to introduce some packing between the bottom
end of the gooseneck body and the mast at the time the
rig is built (a couple of layers of tape or deck patch
material about 5mm wide will usually do the job). As a
general rule, in flat water and steady winds less twist
can be used. As the wind becomes more gusty and/or the
water rougher the amount of twist should be increased.
Sailing in very light or flukey air will also usually
benefit from more twist. Try setting the gap between the
centre seam and the backstay at 50mm for a start and see
how the boat sails. If in doubt set more rather than
less twist.
5.
With the boat
still lying on the ground, adjust the jib leach line
until the gap between the mid point of the jib sail
leech and the leech line is 20mm to 40mm. Less in flat
water and steady breeze, more in choppy water or strong
winds. When viewed from the front or back of the boat,
both sails should show a similar degree of twist.
6.
After a good
days sailing when your boat has performed well, record
in a little note book the weather and water conditions
and the basic settings: - wind strength, choppy or
smooth water, the gap at the foot of the main sail and
jib sail, the distance between the centre of the
sheeting post and the main boom, between the centre of
the mast and the jib boom and the amount of twist in
each sail. After a time you will build up a picture of
how to set your boat up for the various conditions you
will encounter and this will help you to quickly achieve
a good setting each time you are on the water.
There
are a few other things you should know about which
affect the way a boat sails and handles.
1.
Bulb Cant.
This is the amount the nose of the lead ballast is
tilted upwards in order to minimise drag and it is
generally agreed that about 2 degrees is right.
Sometimes this is fixed by the boat builder and no
adjustment is possible. However if the ballast is
attached to the fin by a single central stud and nut,
the amount of bulb cant can be adjusted by inserting
shims, such as flattened crimps, between the bottom of
the fin and the bulb. At the rear end to tip the nose
upwards and at the front to tip the nose downwards.
2.
Mast Rake.
The position of the mast is usually determined and fixed
by the designer but the amount the mast is raked back is
also very important because it is the primary factor
governing the ‘balance’ of the boat and the amount of
weather helm/lee helm it displays. Raking the mast back
moves the centre of effort of the sails back. The more
the mast is raked back, the more the boat will tend to
turn up into the wind, this is called ‘weather helm’. If
the mast is not raked back far enough then the boat will
fall off or bear away from the wind, this is called ‘lee
helm’. A certain amount of weather helm is usually
considered desirable because it means that when
small
amounts (no more than 5 degrees) of corrective rudder
are used it produces lift in the same direction as the
fin – to windward. Lee helm means that corrective rudder
increases the load on the fin and consequently the
leeway. Change mast rake by taking all the ram off the
mast and then adjusting the forestay and backstay to
increase or decrease the amount the mast is raked back.
Some boat designers will supply measurements - usually
taken between some point on the mast and the transom -
and this takes the guess work out of the process.
Alternatively and as a rough guide you can apply the
following: Rig No.1, – 1degree to 2 degrees of rake; Rig
No.2, – 2 degrees of rake; Rig No.3, - 4 degrees of
rake. Finish rigging the boat, setting it up as above
and then set it on a close hauled course to windward and
see how it sails; if she bears off, falling away from
the wind, then the mast needs to be raked further back.
If she turns strongly up into the wind and the sails
flap (luff) then the mast needs less rake, if she sails
steadily to windward without showing any signs of
weather or lee helm then the boat is ‘balanced’ and will
be easy to sail, however she may not be travelling to
windward at her maximum speed. For this to be achieved
the boat may need to display a
small
amount of weather helm, so the mast will need to be
raked back just a little more. You need to establish
mast rake for each of the 3 suits of sails allowed and
once these positions are determined measure the distance
from the headsail stay limit mark to the rear most edge
of the boat and record it for future reference. Don’t
disturb the forestay and backstay bowsies when
de-rigging, and you can easily reproduce the settings
each time you sail. Once a basic mast rake setting is
established for each rig I would suggest leaving it
alone and not fiddling with it on a day to day basis.
Minor adjustments to the balance of the boat can be made
to account for stronger or lighter winds by changing the
amount of twist in the sails and the relative sheeting
angle of the main and jib. Sheeting the main sail in and
the jib out will increase the amount of weather helm;
sheeting the main out and the jib in will have the
opposite effect. Similarly, less twist in the mainsail
will increase weather helm and more twist will decrease
it.
3.
Mast pre-bend and mast bend.
Masts are usually given a certain amount of permanent
forward bend or set (prebend) so that when the back stay
is adjusted to set the main sail correctly, there is
more tension between the backstay and forestay than
would be possible with a straight mast. Tension in the
forestay prevents it sagging, and this enables the boat
to point higher than it otherwise would (pointing high
means the boat will sail very close to the wind when on
a beat to windward). The curve in the mast, rigged and
under tension, should match the curve in the luff of the
main sail. This allows the sail to set properly and fall
easily into its designed shape. The shape of the mast is
controlled by the tension in the forestay, backstay and
side stays, the angle of the spreaders and the amount of
pressure exerted by the mast ram. The side stays will
have more effect on mast bend if the side stay anchor
points on the boat, are set aft of the mast,
transferring some of their tension to the forestay,
which reduces or even eliminates the need for pre-bend
in the mast. The ram is used to control the bend in the
lower part of the mast, the amount of twist in the
mainsail and the fullness in its lower part. It is
important to follow the directions of the sail maker
concerning mast pre-bend; some sail makers cut their
sails for straight masts, some require a small amount of
pre- bend and others specify a quite significant amount
of pre-bend. Usually the No.1 rig will require more
pre-bend than the No.2 rig and the No.3 rig probably non
at all. This is because the shorter masts of the 2 and 3
rigs are inherently much stiffer than the mast of the
No.1 rig.
The
end result of this setting-up should be a boat that is
well ‘balanced’ and has good speed on all points of
sailing. Further refinements and tuning adjustments
should be made as necessary following on the water
testing and by seeing how your boat performs against
others. Further important points are listed below.
1.
Luff ties.
It is important that the
ties securing the luff of the mainsail to the mast are
not too tight. A good way to achieve this is to ensure
that a 2mm or 3mm drill bit can be inserted between the
luff of the sail and the mast at the position of the
tie. Be aware that dyneema and other tie materials will
have to be replaced from time to time as they shrink and
become too tight.
2.
The mast head crane.
The mast head crane should
always be as short as possible - only just long enough
that the back stay clears the leach of the main sail
with the main boom on the centre line of the boat. This
ensures maximum rig tension fore and aft.
3.
Spreaders.
The length of the spreaders should be around 55% - 60%
of the beam of the boat. With the side stay mounting
points aft of the mast, the degree to which the
spreaders are angled back affects the amount of bend in
the middle of the mast, so it is worth experimenting
with this to get the sail to set nicely. Take care that
the spreaders are angled the same each side.
4.
The sheeting radius.
The sheeting radius is the
distance from the boom pivot point to the sheet
fairlead. The sheeting radius of the jib boom should be
about 10% more than that of the main boom. This is
because at close hauled the jib is further out than the
main, thus to maintain the balance between jib and main,
the jib should travel in and out more slowly. Most IOM’s
have a main boom sheeting radius of about 200mm and in
this case the jib boom sheeting radius would need to be
about 220mm.
5.
The jib boom pivot point.
The jib boom pivot point is
usually in the range of 20% - 25% back from the front of
the jib boom. This helps achieve high forestay tension
as the tension from the back stay and side stays feeds
into it. More tension in the forestay also puts more
tension in the leech of the jib sail preventing the clew
of the jib lifting too much in strong winds.
6.
Flattening the sails.
When the wind strength is
near the top of the range for the rig in use it can be
helpful to de-power the rig by flattening the sails and
increasing the amount of twist. Both the main and jib
can be flattened to some degree by using the outhaul
adjustment at the end of each boom. The mainsail can be
further flattened by increasing the tension in the
backstay. Look at the top seam of the mainsail as you
increase the tension in the backstay and you will see
the point at which it begins to flatten off. Easing the
pressure exerted by the ram on the lower part of the
mast will allow it to bend forward causing the bottom of
the sail to flatten off slightly, but be careful not to
relax the pressure on the ram so much that it is no
longer controlling the mast at all. Increasing the
tension in the backstay and relaxing the pressure
exerted by the ram will also increase the amount of
twist in the mainsail. Twist in the jib sail should be
set to match that in the mainsail. This is just a quick
fix and if the wind strength increases significantly the
correct and sensible thing to do, in order to remain in
proper control of your boat at all times, is change down
to a smaller rig.
7.
Placing and fixing corrector weights in
your boat.
Most one metre boats need extra weight fixed in the hull
to bring them up to the minimum weight allowed by the
class rules. This weight is usually best placed low down
in the bottom of the hull, either side of the fin box.
Strips of lead flashing make suitable weights and these
strips should be covered in deck patch material and then
stuck in the boat using clear silicone sealant. Don’t
stick the weights in with epoxy or similar glue because
it may be necessary to remove them at some time in the
future if a different rig, mast, winch or battery is
used. Follow the recommendations of the designer/builder
of your boat regarding the positioning of any corrector
weight if it is different to the above. Ideally the
fully rigged boat, complete with batteries, should be
checked in a tank of water to ensure that it floats
correctly on the designed waterline - this can be
critical. Your measurer should be able to do this for
you if you don’t have a suitable floatation tank.
More
useful information on sail setting and tuning can be
found here:
SAILSetc
website;
http://www.sailsetc.com
Lester
Gilberts Radio Sailing website;
http://onemetre.net/index.htm
and in
the following books;
The
Physics of Sailing Explained by Bryon D Anderson,
Sail
Trim Theory and Practice by Peter Hahne
Sail
and Rig Tuning by Ivar Dedekam.
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