Multihull sails for the
modern cruising catamaran
I would like to focus on performance sails for cruising catamarans.
As most of these boats are purchased with intentions of coastal cruising and offshore
voyaging, the sails for these boats need to be designed and constructed accordingly.
The modern cruising catamaran has been intentionally designed with a conservative
rig and sail plan.
Yacht designers have done this to build in certain safety factors. This reduces
the risk of being overpowered in sudden squalls and large seas found in offshore
With most cats cruising shorthanded, often with a husband and wife crew using
auto pilot, response time from increasing winds is reduced. Forgiving sail plans
In addition to conservative sail plans, other safety features include, mainsails
with 3 reefs, single line reefing, and furling headsails that can be reefed from
The risk of capsizing has been greatly reduced with modern boat designs and rigs,
to the point that this is a very rare occurrence indeed. Monohull advocates are
losing their main arguments as capsizes become more rare. The downside to all
this is, less power under sail.
I have been researching used catamarans while looking for our next cruising cat.
One thing I have noticed is, diesel engines with high hours. This is true even
on boats that have not been chartered. Often the sail inventories for these boats
only include a main and a jib, or genoa.
I have to assume these boats are motoring more than sailing.
The performance of an average production cat, with basic mains and jibs, will
suffer upwind in light air and on reaches and downwind, even when there is a breeze.
These boats will only sail well in moderate winds upwind and close reaching. To
achieve good top end speeds on low sailing angles, strong breezes are required..
A large part of job as a sail designer is to maximize a boat's performance. In
addition to providing the optimal sail shape, choosing correct material and construction
for the intended sailing, is of equal importance. This is the case with cruisers
as well as racers.
For racers, I look for loop holes in the rules to maximize sail area, as well
as optimizing shapes, and reducing weight, to get that extra speed to win a race.
For cruisers, I look for ways to improve durability, ease of handling, and sailing
performance to minimize the motoring time. After all, we did but a SAIL BOAT!
The first part of my discussion will be dedicated on ways to make the sails easier
to handle with a minimum crew. Then, I will go to options for increasing performance
under sail to reduce engine time.
The following are key points for ease of handling on the main and headsail.
Attributes for ease of handling and safety, what features do you want in your
LIGHT WEIGHT. Sail construction, sail material,and battens.
These are main contributors to the weight of a sail. The cloth must be chosen
to be up to the job but, without excess weight. Sail construction, well done,
minimizes unneeded weight. The number of battens are dependent on the amount of
roach and the stiffness of the battens. These full battens should be engineered
to support the sail's profile efficiently with minimal weight.
GOOD DESIGN. Too full will increase effort to raise, weather helm, and be inefficient
upwind. Too flat will reduce power. Sails should be designed for each boat's predicted
windward ability and intended areas of sailing.
MODERATE ROACH. This allows for less battens. 5 to 6 stiff battens are best for
cruising. More roach increases batten compression and friction raising and lowering.
Although, often production mainsails, are made with very little roach. This leaves
room for improvement.
BATTENS PARALLEL TO BOOM FOR GOOD STACKING. This is important to have the main
stack compactly for ease of installing a sail cover. Less batten and intermediate
slides also reduce stack height.
GOOD TRACK AND CAR COMBINATION. Roller bearing cars offer less friction, but there
are many good options for sail luff hardware. This depends on boat size, sail
size, and sail loads. Ask your sailmaker for recommendations.
LAZY JACKS AND BUILT IN SAIL COVER several good choices on zipper covers. I feel
that this is the next best thing to a boom furler.The sail covers that are supported
by lazy jacks and battens and use a zipper on top, seem to be the most conveyance
3 REEFS WITH 2 SINGLE LINE REEFING In these cases, the first and second reefs
can be put in with the use of a single line run to the helm station. This effectively
brings both the new tack and clew down to the top of the boom very easily. I recommend
a third reef that is much higher, proportionately, than the first two. This is
the "Storm Sail". The height of this third reef is too high to have
lines run thru it. Best to simply drop the main, tie in the third reef, and re
tighten the halyard, for this storm reef.
ELECTRIC HALYARD WINCH. This is especially nice on boats with large mainsails
over 600 sq. ft. and short handed crews. The weight of large mains make raising
them a real chore, even with good luff hardware.
Attributes for jibs and genoas, what to look for in efficiency and ease of handling.
FURLING JIBS, Furling systems are great to deploy and douse a self tacking jib
or genoa. Genoas can be reefed to reduce sail area from the cockpit.
SELF TACKING JIBS, Prevents 2 steps when tacking. No easing and trimming on sheets.
Usually too small with tall thin profiles to reef, Best to use all or nothing.
Although a self tacking jib is very convenient, it often is less efficient than
a jib or genoa with sheet track on each side.
GENOAS, These sails can add more sail area for light air conditions than, be reefed
to predetermined locations. The best reefing arrangements will include a foam
or multi rope luff along with reefing strips at pre determined locations. The
foam luff helps to remove shape in the genoa's mid section by rolling up more
material in the mid luff. Without this, the partially furled sail would become
much fuller when reefed. This is the opposite of the desired shape in stronger
LARGE SELF TAILING JIB WINCHES. These should be large enough for the smallest
crew to handle. This is especially important for husband and wife teams. Too often,
genoa sheet winches are undersized on production boats. This is something to make
note of when shopping for a cat. I have been on mid sized catamarans and found
it a real workout to trim the jibs for upwind in moderate winds. This would be
even more difficult for smaller people.
WINCH LOCATION, It is best to have both main sheet and jib sheet close to the
helm station. With this arrangement, the sails will be trimmed more often and
the boat sailed more efficiently. Having the single line reef controls close to
the helm, is a big plus as well.
IMPROVING SAILING EFFICENCY IN THE MODERN CATAMARAN.
Here are some ways to increase sailing efficiently over the production main and
jib rigs. I often am asked when it is time for sail replacements, "What can
be done to improve performance on the next set of sails? What can be added to
the sail inventory to improve light air and downwind performance?"
Here are some key features and sail options to consider.
Custom sail designs for the boat can be a big improvement. Some production sails
are basic designs and can often be either too full or too flat. Draft location
is also critical. There is a misconception with monohull sail makers that the
draft on all catamaran mainsails should be forward like beach cats.
In reality, because the great majority of cruisers use non rotating masts, this
is not the case. Turbulence from the fixed mast, results in bad air in the forward
parts of the mainsail's leading edge. This causes the attached flow, on the mainsail,
to be farther aft. Because of this, mainsails should have the maximum draft closer
to the center. Non tapered battens will actually perform better in most cases
than tapered battens, on sails with fixed rigs.
Adding area with more roach is a typical improvement.
This is a good way to improve light air performance. I see several production
main sails with very little roach. Increased roach up high will improve twist
in the upper leach as well as add area. This will help in the light and moderate
conditions. The trade off is, sails that are a bit heavier with increased batten
compression on the luff slides. I feel that a moderate, "performance"
roach will be a good compromise in performance and ease of handling. (see diagram
Reducing weight and stretch are areas where large improvements can be made. A
very important consideration in choosing sailcloth and sail construction options
is maintaining the designed shape over wide range. There are two lifes of a sail.
The life of the sailcloth, and the performance life. The performance life relates
to how long a sail will maintain it's designed shape. The best designed sail will
still not be a good one if inadequate cloth or construction is used. In the larger
size multihull sails, dacron may not be up to the job. In these cases, other material
and construction options should be considered.
Some of these other options include, triradial cut cruise laminates, D4, FST,
3DL, Load Path, and other "string sails" with taffeta.
Furling self tacking jibs and genoas;
The small self tacking jibs often have no battens. This results in a hollow leech,
to reduce leech flutter. When these tall, thin, sails have hollow leaches, the
upper sections are too thin to generate much power.
Adding vertical leech battens with some roach (convex shape instead of concave),
can enhance performance. This improves the tip effect, adds more sail area, keeps
the exit flat on the leech, and reduces leech flutter. These vertical battens
must be parallel to the luff for the sail to furl tightly.
Use of a multi hole clew board can improve fine tuning and reduce twist. The jib
sheet can be changed to the various hole locations, to improve trim.
Problems with self tacking jibs include too much twist in the top, on all but
close hulled settings. Once the boat is on a reach the lower section, of the jib,will
have to be over trimmed to obtain correct upper trim. With an athwartship track
only, it is difficult to get good all over trim while sheets are eased out.
Innovations like camber spars help here but, loss of furling is the trade off.
EXTRA SAILS, AFTER MARKET OPTIONS
As I mentioned before, the average cruising cat, with stock main and jib, will
suffer from being under powered in light air and off the wind.
The most effective way to increase sailing performance in these conditions is
to add specialty sails to the inventory. By doing this, much time can be saved
on passages and motoring time can be greatly reduced. These are some of the options
on additional sails for a cruiser's inventory.
SCREACHERS, REACHERS, AND GENNAKERS
These large headsail's names are typically descriptions for the same sail. The
terms may be different throughout various parts of the world. In the US the old
loose luff reachers made of nylon, have been replaced by "screachers".
These are large, loose luff sails, set on short bow sprits, typically with a furler.
Europeans sometimes refer to this as a gennaker.
The term "Screacher" was coined in the early days of the Corsair F 27
racing in South Florida.
It was in an attempt to get a reacher classified as a small spinnaker to avoid
a handicap hit for an over sized headsail. This didn't last long as race committees
saw it for what it is.
The evolution of the screacher, has produced a low stretch sail that can be used
effectively upwind in light air. For effective upwind use, it will need to be
designed to be sheeted inside the cap shrouds and trimmed to an inboard position
at 10 to 12 degrees off centerline.
The sail also requires working around the considerable luff sag from a loose luff
Unlike the nylon reachers of the past, these sails must be designed and built
to take the considerably high apparent wind angles and speeds from upwind sailing
on modern multihulls.
If used upwind in true winds of 10 to 12 kts., it is not unusual to have apparent
winds in the 17 + knots range. A properly designed and trimmed screacher can be
a real work horse upwind and close reaching in the light breezes. This can greatly
reduce motoring time. Other advantages are seen while reaching and even running
in higher winds.
If used on a furler, the screacher furling line can be lead to a position close
to the furling line for the jib. It will than be a simple procedure to simply
roll up the jib, and unroll the screacher, as the wind gets light, or reverse
this, as the breeze increases.
(See diagram 2)
CODE 0 AND ASYMMETRICAL SPINNAKERS
For long downwind passages, often the main, jib, and even screacher, lacks the
horse power to achieve good speed averages. The solution here is either a code
0 or an asymmetrical spinnaker.
This is also a bit of a vague term. The original code 0s were designed for the
Volvo round the world racers, as their flattest spinnaker. These early sails were
heavy nylon. Because of the popularity of this trend, sail cloth manufacturers,
designed and produced fabrics specifically for code 0 sails.
This code 0 cloth, is a laminated fabric with mylar film on one side and a light
woven taffeta on the other. Heavier versions include Aramid (Kevlar) fibers in
the warp for added strength.
The end product is a light, low stretch fabric with a "soft hand." These
sails can be stuffed in a bag, doused with a sleeve, or used with a furler.
We design these, as well as the screachers, with an adjustable Spectra, or Aramid
luff rope that furls well.
The code 0 that we build for multihulls, uses the same attachment points as the
spinnaker, the end of the bow sprint, spinnaker halyard, and sheet blocks in the
back of the hulls. The foots are longer than the screacher and are trimmed outside
Because of this, the highest angles the sail can be used are about 60 to 70 degrees
off the true wind. But, the extra size creates a powerful reaching sail as well
as an easy to use downwind sail.
These code 0 sails are designed with the draft well forward and flat leeches.
This creates good top end speeds for the reaches, often giving much more power
per square foot than the spinnakers.
Because of the light weight cloth typically used, it is not the best candidate
for a UV cover strip. This means that the sail should be deployed than, stowed
in a bag after use.
(See diagram 3)
We design multihull spinnakers with a draft forward camber, and fairly flat leeches.
These designs work well on reaches as well as downwind.
In the case of these "all purpose designs" , the upper girths are less
than those of a downwind spinnaker. Because of the extra area outside of the straight
line leech and luffs, the total sail area can be much more than the comparable
code 0. These sails, with their larger areas, will optimize downwind sailing.
Typically, cruising cats will use the spinnakers tacked to twin lines from the
two bows. This allows a wide range of adjustment. For sailing downwind, the tack
can be brought to the windward bow.
For close reaching, simply ease the windward tack line and trim the leeward one.
This brings the tack to leeward, increasing close reaching performance.
I feel that the best case still, is to use a bow sprint. A bow sprit brings the
tack, of the spinnaker, lower to the deck, allowing for a longer luff and larger
Gibing is easy. Just bear off easing the sheet, than, once the sail is forward
of the forestay, trim in on the new sheet.
The spinnaker on a bowsprit can still be trimmed to the windward bow for downwind
We design the asymmetrical with a full triradial Matrix cut. This along with 1.5
oz. nylon, reduces stretch and helps maintain the draft forward shape. A well
designed and built asymmetrical spinnaker will give a wide range of use. Close
reaching in true winds up to 70 degrees are possible, in lighter breezes.
These sails work well with a dousing sleeve like the ATN product.
So, with all of these extra sail options the question is, "What sail is best
This depends a lot on the sailing in mind. Will you be;
Day sailing and coastal cruising, short offshore runs, or long offshore passages?
For day sailing and coastal cruising, a screacher would be a good first step.
This will improve the light air upwind and close reaching, greatly increasing
sailing pleasure in these conditions. Long downwind runs will not be an issue.
For short and long range passage making, the addition of a good downwind sail
will be well worth the expense. This will greatly reduce hours of motoring time,
as well as time spent offshore on passages.With less time spent on passages the
risk of encountering bad weather is also reduced.
A code 0 can be an alternative to having both a screacher and spinnaker.
The size of a code 0 falls in between the screacher and asymmetrical spinnaker.
It will not sail as close to the wind as a screacher or offer the downwind speed
of a full sized spinnaker. It will be a good all around reaching and running sail
than can be rolled up from the cockpit, making it easy to deploy and douse. (See
Best to evaluate your needs and talk to a multihull sailmaker for a custom evaluation
of what sail inventory will be best for you. Than, go use the sails more and the