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The
current SUNDOG setup and "tips"
There have
been quite a few postings to the Gemini ListServe since its' inception
concerning the tuning and set-up of Gemini rigging. While I think
there are some substantial differences between the older "Classic"
models and the current 105s in that regard, I'm going to present
here what works well for us with our 105. The "Classics" are another
case entirely and the suggested methods and values given here
are intended for reference for 105 owners only.
The values
and methods herein presented were derived from the Gemini manual
that came with the boat, "book learning" from a number of respected
sources, three seasons of club racing SUNDOG, input from other
owners and my own thirty years or so of racing and cruising both
monohulls and cats. This is what currently works for us on our
boat with our sails…I certainly don't present it as "gospel",
but it is offered as an empirical place to start as you derive
your own tuning for your 105.
The
Shrouds…
The "Owners Manual" that came with our boat (#551) called for
all the side shrouds to be set with equal tension and giving a
value for that tension as a defection of 2" horizontally when
a 40 lb. pull was exerted on them at a point about 6" above the
deck. We first set this value with a digital "fish scale" and
a ruler. This value expressed as pounds of tension on a Loos professional
tension gauge turns out to be 1,100 pounds on our boat.
Initially,
we started with a lower value, having read that a cats' rig should
be a bit slacker than a monohulls'. At the lower values, we discovered
that the lee shrouds on our boat went "floppy" slack when the
boat was pressed to weather up to the reefing limit of about 18kts
apparent with full genny and main. I was concerned that "too slack"
might allow the mast to move out of column and flex in a head
sea, so we slowly began to tighten them up to the point that under
the sailing conditions mentioned above, the lee ones now go to
almost "0" tension, but remain taut enough to "catch" any flexing
in the mast before it can move out of column. As it turned out
on our boat, the initial factory setting proved to be correct,
and the Loos gauge shows it to be around 1,100 pounds, which is
well within the designed load for the cables involved.
There are three cables involved  :
an "upper" a "middle" and a "lower" on each side. These cables
take most of the side loading of the mast and are anchored to
chain plates that
transmit the loading to the main bulkhead inside the boat. It
is a good idea (on older 105s) to reinforce the center section
of this bulkhead under the mast step with an additional thickness
of plywood (see picture at right). Later models now come with
this extra thickness under the mast. As another "tip", we find
that thin-wall PVC plumbing pipe makes great turnbuckle covers
as shown in the photos.
The interior
bolts on the chain plates should be tightened down evenly with
a torque wrench to a value of about 40 ft-lbs…and checked at least
once a year. The deck penetrations can be made more waterproof
if the 5200 is removed from under the deck trim plates and replaced
with marine silicone caulk which will adhere better to stainless
and withstand movement and flexing without the bond separating.
It is important to keep these deck penetrations dry, as water
leaks there could, over time, seriously compromise the strength
of the main plywood bulkhead with potentially disastrous results.
The Forestay…
On a 105, the forestay should be "tacked" to the forward hole
in the bow chainplate. The tension on the forestay is controlled
by the tension on the backstays, but there is a turnbuckle up
inside the roller furling mechanism that can be accessed if needed,
to set the "pitch" of the mast on a fore and aft axis. The 105
is designed to have a vertical mast to the water plane when the
boat is in trim and the stock sails are cut with that in mind.
If your boat is in "trim" and floating on its' lines…not bow or
stern heavy, the mast, when viewed from the side of the boat,
should appear completely vertical and straight, with no center
bow or top bending either aft or forward…just straight up and
down, top to bottom. If ever necessary, only adjust the forestay
turnbuckle to achieve this.
We thought it prudent to install an inspection port in the "bowsprit"
just behind the anchor roller to be able to access the mounting
area for the forestay and to be able to service the bow roller
and bow-boarding ladder bolts. The inspection port is stainless
steel throughout and has a rubber "o" ring for watertight security
(from Hood Yacht Systems). The bolts that hold the forestay chainplate
go through a solid chuck of the same plywood the centerboards
are made from and are secured with nylock nuts and washers on
the underside of the bridge deck. We noted some stress crazing
around the washers, so we added a plate of 3/8" thick stainless
steel there to contain all four bolts within a rigid backing plate.
No more crazing has been noted since. The original bolts were
long enough to include the plate and did not need to be replaced.
The
Inner Forestay…
The inner forestay is "tacked" to the bridge deck on a "U" bolt
just forward of the window into the main stateroom. It has only
one purpose…to keep the mast straight and "in column". It is too
close to the mast to be used to fly any staysail on it and the
tack is not strong enough for this anyway, so don't do it.
Adjust the tension on this stay by sighting up the mast. If you
pull on it with your hand while sighting up along the mast to
the top, you will see what it does. Just adjust it with enough
tension so that your mast is straight and has no center bow or
tip deflections forward or aft. On our boat, the Loos gauge indicates
a tension of 410 pounds when it is adjusted properly. The adjustment
is made with the aft lower stays slack, the backstay tensioned
and the shrouds tensioned.
The forces on this inner forestay are taken on the bridge deck
just forward of the window. We found it necessary to reinforce
the fiberglass "strut" dividing the big window over the "queen"
bunk to keep it from buckling as it transmits this force on up
and into the coach roof. We did this by installing a 3/8" thick
x 2" wide teak batten into a very tight fit in the center of this
strut on the inside between the upper and lower teak trim pieces
above and below the window. The inner forestay was slacked and
the piece of wood carefully cut so that it took a bit of force
to snug it into a tight fit between the two  upper
and lower teak battens above and below the window…where it was
secured with teak butt dowels and West system epoxy. You can see
this new piece in place in the photo. The inner forestay was then
re-tensioned and the buckling problem has not re-occurred. Note:
I've seen these same phenomena in several early 105s, but the
factory may well have noted it and corrected it in later models…just
check yours and see if it needs the additional teak strut.
The Aft Lower Stays…
These stays are there to keep the mast from "pumping"…flexing
excessively when going to weather. They do not need much tension
at all to do the job intended for them. We keep about 200 pounds
each on them according to the Loos gauge. This is not a lot, but
it counters the 410 on the inner forestay, and allows them to
easily be slacked off, disconnected and moved forward on a run
so the main will not chaff on them.
If you use 3/8" Aerofast lower clevis pins to serve as quick disconnects,
you will not be able to remove the pins under any kind of load
(unless you have a grip like Superman!), so if you use these pins,
just leave these stays just slack enough to get the pins out.
The "Sliphook", shown here as another disconnect alternative,
is better…but more costly and a bit more work to install. It does
allow you to carry a little balance tension against the inner
forestay and still be easy to disconnect and remove under light
loads. The install requires that you shorten the stays a little
by cutting the swaged threaded end off the stay and replacing
it with a new one and a Sta-Lok connector. As you can see in the
picture, the turnbuckle is still there for adjustment, but you
can't use the PVC cover on it…just tape.
The
Backstays…
We depart considerably from "stock" with our backstay rig; so
consider yourself warned that the factory has not blessed what
we did! Having presented the proper disclaimer, I can tell you
that what we did was a simple modification to give us a little
bit of a "pointing" edge by taking some of the sag out of the
forestay. It required no rig cutting or alterations to the boat,
so if you decide to try this, you can easily go back to the stock
configuration whenever you wish.
 If
you will look closely at the picture to the left, you will see
that SUNDOG's twin backstays can be "pinched" together by the
bridle and line rig you see in the photo. This "pinching" tackle
method is a very common method to increase and decrease backstay
(and hence, forestay) tension.
What I think is a bit unique, is our decision to place the pinch
rig down low, so that it can only work in a fairly narrow range.
The geometry of this setup is such that the rig simply cannot
be over tensioned by an inexperienced crew member…no matter how
hard he (or she!) hauls in on the trim line. The maximum tension
that can be exerted on the backstays is about 600 pounds on each…giving
a maximum forestay tension of a little more than the shrouds,
or around 1,200 pounds.
In the fully slacked off mode, the tension is eased to 400 pounds
on each one with a forestay load of 800 pounds, which is fine
for normal day-sailing and much safer in storm conditions. Additionally,
I don't think it wise to leave the backstay tension set up high
all the time in a Gemini, as the light "monococque" construction
employed to keep a cat as light as possible also makes it even
more vulnerable to a condition that effects race boats over time…called
"hogging", where high rig tensions have "bent" the structure of
the boat.
SUNDOG's backstay system actually allows the boat to be under
less continuous stress that the stock rig imposes…with the option
of easy application of upper-limited tension when desired, with
the upper limit being only modestly more than "stock", which we
think is a nice little edge to have in an occasional club race.
To do this, you move the stock turnbuckles to the inboard of the
two chainplate holes. You then use one of the outboard holes to
"dead-end" the pinch line and the other to secure a turning block
for the line on up to a cam cleat assembly mounted on the aft
deck below the life-lines as shown in the picture.
The actual tackle is made up of stock parts you can get at any
West Marine store. The triangle plate has a lower sheave in it
to pass the tensioning line and the two legs are made up of vinyl-coated
lifeline cable with adjusting turnbuckles and a pair of wire blocks
to ride on the backstays. You adjust the pinch tackle to keep
the backstays just inboard of the inboard push-pit railings instead
just outboard of it. In use, the backstays will move in and out
in a range of about 4" to 6", so you have to be careful that they
don't hit anything in this range of "pinching" movement, but on
our boat that wasn't a problem. It might be if you carry a dink
or solar panels there and the existing backstay clearance is close
to begin with.
Click
here for parts list and detailed instructions on how to
set this up!
One last tip…if you use an insulated backstay for a SSB antenna
as we do, make sure the upper insulator is at least 4' down from
the masthead and the lower one is just above the crew's "reaching
height" at deck level.
-
Rob Hoffman, SUNDOG #551
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