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The Mumm 30's carbon fiber rig with swept spreader and no
runners has simplified sailing and boat handling but requires some
different techniques in rig tuning. To fully understand how to
tune the rig, first take a step back and look at what the goal of
rig tuning is. The main objective with tuning is to insure that
the rig fits the sails and that the sails work together. The mast
bend and headstay sag should fit the sails as they were designed.
(I'll assume the rig is centered side to side and that it has
similar bending characteristics tack to tack, which could be an
article in itself).
The basic concepts of setting up the Mumm 30 rig is not that
different from many other modern boats today. The basic philosophy
is to match headstay sag and mastbend to fit the sails and then
adjust the rig and sails to keep this relationship similar as
conditions change. The key factor in accomplishing this balance is
headstay length. The headstay length should decrease as wind
increases.
This may seem backwards but the reasoning here is simple. It
has to do with rig tension and sail shape not the location of the
center of area of the sail plan. Changing the fullness/shape of
the sails has a much greater effect on how the boat is balanced
than a small movement of the center of area of the sail plan. A
longer headstay reduces rig tension and pre-bends the mast. The
looser rig allows headstay sag, fitting the jib's design
parameters which allows it to set fully. The pre-bent mast allows
the mainsail luff curve to fit the mast without using backstay
tension to bend the mast. However, as the wind increases, the
headstay will sag more. To reduce the sag, the headstay should be
shortened. This will flatten the jib, straighten the mast and
allow backstay tension to be applied. Doing this will maintain the
same relationship between the headstay sag and mastbend.
Let's look at the sails individually. The jib is a tall and
narrow sail which is greatly effected by headstay sag. As the
headstay sags the jib gets fuller and has more power. This is fine
as long as the conditions warrant it. As the wind increases the
sail rotates back into the mainsail and starts to spill air into
the main causing the main to luff. When the jib sag is greater
than it is designed for, the sail acts more like flaps on an
airplane wing. The resultant air foil is a high lift but also high
drag air foil. To reduce the drag you have two options:
1. Move the jib lead back and pull the sheet in to flatten out the
foot .
2. Tighten the headstay to reduce the sag.
The mainsail responds to the mast bend the way the jib responds
to headstay sag except in the opposite direction. A full mainsail
is similar to an airplane wing that has its flaps down, thus
creating high lift and drag. To reduce this drag you need to add
bend to the mast thus pulling material from the center of the sail
and reducing the depth of the sail. This is accomplished by either
tightening the backstay in heavy wind or loosening the headstay
and the lowers/D1 in light air.
The goal is the same, get the perfect relationship between the
mastbend and headstay sag and have that relationship fit the sail
design so they work together.
The approach we use in the Mumm 30 is to set up the rig with
some prebend. A prebent mast is one that has some fore and aft
bend mainly focused in the lower portion of the mast. This occurs
without any backstay tension. Prebend is accomplished by the
location of the mast butt and the mast chocks. Moving the mast
butt aft and the mast chock forward increases prebend. Prebending
the mast is a critical aspect of rig tuning for light air
performance. Easing the headstay results in lower mastbend (with
the mast butt and mast chocks properly positioned) and counter
acts the shroud load. This balancing act loosens the headstay with
small adjustments of headstay length. A looser headstay fits the
jib's designed shape better in light air. As the wind increases
the headstay length is shortened thus tightening the rig by
pulling the rig forward, removing prebend and adding rig tension.
Now with less prebend the mast needs to bend more to fit the
mainsail. This is accomplished through backstay tension. Backstay
tension bends the mast and adds headstay tension which is
desirable as the wind increases.
Now that you understand why we change the rig tuning for
varying conditions, let's explore some of the critical controls to
play with in the Mumm 30 rig. Lets rank the controls in two
separate areas. First will be the on the water controls and second
will be the on the land controls.
On the water controls:
1. Headstay length, vary + - 1 ¼" total about 2 ½"
2. Backstay, full on to full off
3. Lowers or D1, hand tight to + 5 turns
On land controls:
1. Mast butt and mast chock location HSM=6'
2. Cap Shroud tension, about + 15 turns (32 On Rod Guadge) D1
Tension 17 On Wire Guadge
3. Diagonal or D2 tension, hand tight +3 turns
With this basic understanding of what to look for while tuning
your rig, making the critical decisions of where to put the rig
should be easier. Some key items that will help you decide what to
do would be as follows:
From the helmsman position look up at the top spreader and
estimate where the headstay intersects the mast if you can see the
luff tape of the jib the sag is correct. If the luff tape cannot
be seen you'll need to reduce the headstay sag. If you see a lot
of sail behind the luff tape you should add headstay sag.
While trimming the jib on the leeward side of the boat looking up
at the jib the leech should come straight back. If you see the
leeward side of the jib the headstay has too much sag. If you do
not see any of the leeward side the headstay may be too tight.
For the mainsail in light med air, if the top batten is stalling a
lot you will probably need to add some mastbend.
Fine-tuning the Mumm 30 rig:
This two step process that consists of at the dock measurements
and sailing tune. At the dock you will want to measure the mast
position side to side (athwart ships) insuring the hounds are in
the center of the boat and then adjust the mast chocks to keep the
mast at the deck is in the center of the boat. Step 2 is completed
while sailing, and you will want to look at side bend on each
tack.
At the dock tuning:
To complete step 1; Step the mast with the mast but in the
position recommended to fit your sails.
For Doyle sails measure from the
center of the lifting ring to the aft face of the mast step to be
4'. A double check for this measurement is from the front edge of
the mast to the center of the forward head stay bolt (see
reference photos below).
Now that the mast butt is properly located, set the headstay to
5'11 ¾" then attach the backstay and pull some tension on
it. Attach the uppers and lowers, hand tightening the uppers but
leave the lowers loose. Then release the tension off of the
backstay. This is now the starting point, use the topping lift
(centerline haylard), as a tape measure and measure the mast
position from side to side. This is accomplished by easing the
topping lift off until the snap shackle touches the chain plate on
one side, then cleat it off. Applying the same tension on the
topping lift measure the other side. Adjust the shroud turnbuckles
to get the hounds centered in the boat by easing one and
tightening the other. Now the mast in centered in the boat the key
points to look at are; The D2 or the second diagonals, should be
sufficiently slack to allow the center point to move about 1"
off the straight line.
By sighting along the luff grove from deck level check that the
masthead is directly over the hounds and that the middle of the
mast is straight. At the deck place the mast chocks in making sure
the lower portion of the mast is straight side to side. Place the
fore and aft chocks in at the recommended position to fit your
sails. (Doyle Sails like the mast 1/2cm Forward of center) The
most important item at this point is to keep the mast in column
side to side. You may need to shim the mast more on one side than
the other to accomplish this. Now take up 11 turns on each shroud,
your D2 should just come taught. You should be able to adjust them
by hand still and if they are not even you should adjust them at
this point to even the tension out. The lowers or D1 should now
have the slack taken out of them to be hand tight. Sight up the
mast, it should still be straight from side to side with a little
fore and aft bend.
Take up 5 additional turns on the uppers (Bringing the Caps to
32 on the Rod Guadge) the diagonals D2 should just become tight.
And the mast should be straight side to side. Take up 6 turns on
the lowers D1 making sure the mast is straight side to side. You
may need to take up one side more than the other to keep the mast
straight side to side (17 on the Wire Loose Guadge). Now you can
tighten the forestay to position correct for the conditions and
the cut of the sails. Now your set to tune the rig undersail.
Mast Chocks:
With the mast tuned the mast chocks can be place in the mast
partners. The for and aft position of the mast should measure 10'
10" from the front edge of the mast to the headstay pin
(Generally its 1/2cm forward of centered in the partners). Add
chocks to the side of the mast to keep the section in colume.
Sailing at Max J is not important.
Forestay Length:
Place the topping lift shackle to the top of the mast band at the
gooseneck. Then swing the topping lift to the forestay and mark
its intersection. This mark will be your referance point to
measure from. Measure from this mark to the center of the headstay
pin. Heavy air min 5' 9 ¾", light air max length 6'
¼".
For most headstays the light air setting will have the turn
buckel backed off allmost all the way 2 - 3 threads showing, as
shown in this photo.
Tuning under sail.
Before we look at the mast side to side profile keep in mind the
following.
1. The leeward side cap shroud should never become loose while
sailing. If it is loose or dangling the rig is too loose, thus
causing poor stability side to side and inadequate headstay
tension.
2. While sailing the objective of adjusting the diagonal shroud
(D1 & D2) is to keep the masthead, hounds, spreader positions
in a straight line, when the boat is heeled at least 20 degrees.
While sailing it's very important to check the mast at regular
intervals to insure the mast is kept straight, as the tune of the
rig can change over time. To accurately test the straightness of
the rig you will need wind conditions strong enough to heel the
Mumm 30 over approximately 20 degrees.
Sailing in upwind trim, with the sails trimmed in and crew hiking.
Have one person go up to the mast and sight it two ways. First
look up the mast from behind focusing on side bend at each
spreader (not fore and aft). Then go in front of the mast and
sight up the leading edge of the mast and see if you see the same
deflection. Then tack the boat and look up the rig the same way as
the other tack. Noting the side to side bend. Diagonal shroud
adjustments at this point are simple, but do require some time and
fine tuning.
Focus your attention to the rig at the spreaders, if the mast
is straight sideways nice job you have followed the instruction
perfectly. But most of the time you will need slight adjustments
to the rig. If the mast at the spreaders is sagging to leeward the
diagonal's at that point needs to be tightened and on the other
hand if it is bending to windward the diagonal should be eased.
The adjustments should be small ½ to 1 turn and then check the
rig tack to tack. Start adjusting the D2's first and then the
D1's.
Once you get the rig tune straight make sure you mark the shrouds
and the diagonal position with tape or marker and port or
starboard if you remove the lowers from the mast. This will help
you insure proper tune when you set up the rig again. I hope these
hints are useful.
Sail trimming:
The mainsail has two different modes of tune, powered up and
de-powered. The powered up condition is up to about 10 knots (all
the crew hiking). In this condition you have a fairly tight leech
with the telltales just flying. As the wind increases you start
pulling on the backstay to keep the boat on its feet. The
mainsheet stays in relatively the same position. As you start to
get overpowered, use enough backstay to allow the upper luff
portion of the mainsail to luff, freeing up the leech and keeping
the boat flat (rail 6" + out of the water).
The photos above show the Mumm 30 main in a powered up condition,
light backstay and a small amount of mast bend. 3-12 knots.
The photos above show the Mumm 30 main in a moderatly depowered
setting with moderte backstay bending the mast thus flating the
mainsail, starting in 14 knots.
JIB TRIM:
The jib should be trimmed with the aid of leech telltales, marks
on the spreaders can be misleading. Put some telltales on the
leech of the sail at the top spreader. Trim the jib in until these
telltales stall, then let the jib out slightly, allowing the
telltales to fly. Make sure you check the jib trim as the wind
velocity changes. The code 1 jib should be trimmed with the use of
the in hauler (2-3") in air under 7 knts. The photos below
show our light air jib (code 1) left & med air jib (code2)
right.
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