Headsail Trim 101
DRAFT 13/06/13
Evan Walker 3 June 2013
Step 1:
Sit down to leeward (on the side of the boat away from the
wind, also known as the low side of the boat) and while on an upwind course,
trim to an obviously under-trimmed position (top of the jib flapping while the
bottom is filled).
Step 2:
The skipper will use the bottom tell-tales (See figure 1) as
a steering guide so those will fly parallel. Now notice that the middle and/or
top windward tell-tales are breaking (not flying parallel). This shows that the
top of the jib is sheeted out too much compared to the bottom of the jib and
the jib is described as having too much twist.
Step 3:
It is helpful to think of the jib sheet as controlling the
headsail twist. If you sheet on more the twist will decrease. Slowly sheet on
(with the skipper maintaining an upwind course according to the bottom
tell-tales) and only stop when the middle tell-tales stop breaking. Now the
middle (and top) of the jib are working properly along with the bottom. The
twist is correct.
Step 4:
As the skipper slowly steers up above this course, the
middle tell-tales should break slightly before the bottom ones (If they break
at the same time it will be difficult for the skipper to steer). If the top
breaks too early relative to the bottom, correct the twist by sheeting on a bit
more.
Step 5:
Now that the twist is correct, pay attention to the depth in
the foot (bottom) of the jib. You may need to be shown a few times what is an
appropriate depth for underpowered conditions (when you want max power) and
what the foot should look like when you want it fully depowered (flat). This
can be controlled by adjusting the jib carr.
(Most jibs like the Sydney38 Medium have a ‘shelf’
foot. This means the gap between the
depth of the foot and the straight line between the tack and the clew is filled
in with material. When you want full power this shelf should look like it was
meant to, with the edge of the sail pulled almost straight from tack to clew.)
Step 6:
If once you have sheeted the jib for the correct amount of
twist, the foot is too deep, you need to move the jib carr back (away from the
bow, so that the sheet is effectively pulling more along the foot instead of
down the leech) and vice versa. As the wind increases and you get more and more
over powered, you will need to flatten the foot by moving the carr further back
incrementally (If you move the carr too far back you risk tearing the foot
apart).
Step 7:
Moving the carr also affects the twist so now re-adjust the
jib sheet to achieve optimum twist. If you still aren’t happy with the foot
depth repeat steps 6 and 7.
Step 8:
Now while you are getting used to this process it might take
a long time and you don’t want to have to repeat it every time you tack, so pay
attention to the carr position and where the leech of the jib is compared to
the bands on the bottom spreader. An alternative (or additional) method to
using the spreader bands to replicate sheet settings is to put a mark on the
sheets near the winch when they are fully sheeted.
Advanced step 9: Barber
haulers
Once the twist and the depth have been set, the barber
hauler can be used to sheet the whole sail in closer to the centre line of the boat.
This will help the boat sail closer to the wind but might cost some speed. The easiest way to use them is to keep an eye
on the boat speed instrument. If the boat is faster than the target boat speed
when the skipper steers to the tell tales then you can probably pull on more
barber hauler.
Another thing to notice is the leech tales (Figure 1). These
are the tell-tales extending off the back of the leech. If the leech returns too much towards the centreline
(is too hooked), either because of too much barber hauler or too much jib sheet,
these leech tales will suck in behind the sail and not fly freely. Similarly,
if they are flying all the time then you can potentially pull on more barber
hauler (or sheet), so make adjustments until you see them start to suck behind
occasionally.
A sure sign that you have too much barber hauler is that the
bottom of the mainsail luff will suffer from ‘blow-back’ (bubbles). See diagram
2. If there is blow-back and the barber hauler is already fully eased you need
to either ease the sheet a bit, or if you also think the foot is too deep, just
move the jib carr back (flattening the foot while also increasing twist). The
middle tell-tales will now break early but that’s ok because the boat is
overpowered.
Barber hauler can have an affect on both jib depth and
twist, so after any adjustments to barber hauler re-adjust sheet and carr to
return to desired depth and twist.
Advanced step 10:
Backstay
As the wind increases you will notice the forestay will tend
to ‘sag’ more to leeward and sometimes you will see it move around a lot in
waves. It is never good for parts of the sail to move around a lot and it is
also not good for the forestay to sag excessively. Changes in sag affect the
shape of the sail according to Figure 3.
To maintain an acceptable amount of sag ask the main trimmer to adjust
the backstay. More backstay means less sag. You will have to accommodate the
main trimmer however because the backstay also affects the depth of the
mainsail by bending the mast.
Advanced step 11:
Headsail halyard
Similar to forestay sag, headsail halyard tension can have a
big effect on sail shape. A tighter halyard will move the shape towards the
front of the sail (Figure 4). This might be beneficial in choppy water or in
stronger winds. It can also help correct the effect of age. As sails get older
the shape moves further aft (back).
A good starting point is to tighten the halyard until there
is only a hint of horizontal creases in the luff. This will vary as the wind
strength changes.
It is important to be able to replicate the halyard setting
every time the jib is hoisted, and if you have changed headsails on the last
run you need to have a starting point for the new sail’s halyard tension.
The easiest way to keep track of this is to have an area of
stickyback on the sliding hatch. On it draw a table with wind strength down the
side, and sail selection across the top (Light Medium Heavy). It is then the
pitperson’s responsibility to record the setting whenever the trimmer is happy
with it. Within a couple of sessions the table should be close to complete.
Mechanics of headsail
trim
Only use the self-tailer on the winch if the load is too
heavy to wind with one hand and it is inconvenient to give the tail to the
offside trimmer. For any big trim moments like the wind up at the start or the
bottom mark, or after a big dip, the offside trimmer should make themself
available (just turn your shoulders in and reach your hand out).
Always take the handle out of the winch once you have
reached target trim, and cleat the sheet on the inside of the cockpit. Putting
it in the tailer means you need more time to leeward going into a tack.
When you need to add a wrap, always try to have the handle aiming
towards you so you don’t have to reach over it.
Upon exiting the tack (immediately after tacking), the
trimmer should pay close attention to the jib tell-tales and only trim the jib
to match the angle steered by the skipper. There are a number of reasons why
the skipper might steer higher or lower than usual out of a tack. If they come
out too low, trim to that angle, and then wait til they steer up before
trimming in any more (But be careful not to undertrim when easing to the
skipper’s course. Can can lead to the skipper steering further away from the
wind).
It’s also important to have a slightly softer (looser) trim
while the boat is building speed, then wind up to your target trim only once
the boat has reached the target boat speed.
When tacking, the offside trimmer should move across the
front of the cockpit while the trimmer steps behind.
At all times both trimmers should be conscious of their
weight. Offside should tail as far across the boat (to windward) as possible
(unless the weight needs to be to leeward out of the tack such as in light
winds). After turning legs in the trimmer should stay to windward til the last
second before the tack and then after trimming to the tack exit/speed build
setting, should move to windward with the tail where you can see the jib
tell-tales from the windward side of the mast, here you can ease more sheet if
necessary during the speed build before returning to leeward to wind in the
last bit once the boat approaches target speed (In strong winds you might take a
long time to get the sheet in. In this case don’t worry about moving to the
windward side for the speed build).
Recording Settings:
It is important to keep track of what carr/spreader
band/barber haul combination you used for each wind strength. The optimum
setting will change across the wind range and might be completely different for
each jib used. Get in the habit of carrying a notepad to record quick notes
while sailing and then consolidating these along with the halyard settings at
the end of the day.
Super Advanced Sail
Shape and the influence of mast bend and forestay tension:
There are two ways that sail makers build shape into any
upwind sail. These are known as broadseam shape and luff curve shape.
o
Broadseam shape is built into a sail in the way
that the various panels in the sail are joined together. On any seam, shape is
introduced to the sail when one edge is cut in a slight convex curve and the
adjacent panel is cut straight. This type of shape accounts for most of the
shape in the sail.
o
Luff curve shape is the same technique on a much
larger scale along the luff of the sale. When the luff, which is prominently
convex curved, is forced onto a straight mast, shape is introduced to the sail.
The benefit of luff curve shape is that we can easily influence it by bending
the mast for a mainsail, or changing forestay sag for a jib.
The mast can be bent by pulling on the backstay. The more backstay you pull on the more the mast bends and
the more closely the bend of the mast matches the luff curve, producing a
flatter sail. This reaches a limit when the mast bend matches the luff curve. Over
bend creases will occur if the mast is bent any more (Figure 5).
The backstay also affects the tension in the forestay. This combined
with the load in the sail determines the amount the forestay sags. Forestay sag
affects a jib in a similar way that mast bend affects a mainsail. The more the
forestay sags, the more luff curve shape the sail will have. More accurately it
affects the ‘angle of entry’. This is the angle between the wind coming into
the sail and the front of the sail. Forestay sag affects the ‘angle of entry’
in the middle of the jib luff more than it does the top and the bottom.
Therefore, excessive forestay sag might result in a middle tell-tale that
breaks before both the top and bottom tell-tales.
No comments:
Post a Comment