Turbo-Charging your Catamaran

Note: this article appeared in September 2004 in Multihulls Magazine

Even the ardent cruising multihull owner has to admit that somewhere in the
hidden recesses of his mind is the desire for more speed. This is usually one
of many reasons people switch to a multihull. Why sail at 5 to 6 kts when you
can go 8 to 12!

For the first two years on our 28-foot Richard Woods-designed Gypsy cat, Light
Wave, we sailed with the basic arrangement of main, working jib, and spinnaker.
We bought a used spinnaker and sock which my wife and I used a couple of times
on the 80-mile run from Vancouver to Desolation Sound when the wind happened
to be behind us (about one in four trips!). Surfing along at 10 to 15 kts, racing
Pacific White-Sided Dolphins was exhilarating, and the speeds were our best
yet.

The drawback to traditional spinnaker flying in in-shore waters (with its
variable winds) is that it is a lot of work using one when shorthanded sailing.
From in-the-sail-locker to flying takes a minimum 20 minutes — setting
up lines in their respective blocks and stoppers, checking to ensure all lines
will run properly, etc. Sure enough, you just get it flying when the light wind
dies down to nothing and you have to start motoring. Then comes another twenty
minutes to stuff it and carefully pack the lines so that the next time you want
to fly it, it takes only 20 minutes not 40 when everything gets tangled up.
Another limitation of a regular spinnaker on a multihull is that you can only
use it on a run or very, very broad reach because the apparent wind quickly
moves forward if you head up from those points of sail due to the multihull’s
speed. An asymmetrical spinnaker gives more heading options as you can get closer
to a beam reach, but there still is a limitation.

Given the reality that most people sail in relatively light winds (many ocean
veterans say that 60 to 80% of their sailing is in winds from 5 to 15 kts),
what is the alternative to a spinnaker, especially for catamarans with their
reputation of sluggishness in light winds? Answer: the screecher! It is the
perfect sail-power system to turbocharge your cat into a tiger. It gives you
the ability to sail on a close, beam, or broad reach in 5 to 10 kts of wind.
Screechers are now standard equipment on virtually all the newer designs (Farrier,
Schionning, amongst others, and even some production cats).

Planning a 900-mile trip around Vancouver Island, we took the jump and sold
our spinnaker and retrofitted a screecher system onto our cat. As a general
rule, the screecher adds about 2 kts to our sailing speed on most points of
sail. We use it upwind in up to 12 kts of true wind and downwind in up to 25
kts of true wind. We use the screecher with both main and jib on anything from
a broad to close reach, and with the main alone when on a very broad reach.
When running, we use it wing-on-wing with the main (a conventional spinnaker
would still be very useful when running during longer ocean passages with more
consistent winds). The chart in Figure 1 shows our screecher speed improvements
on a beam reach for various wind strengths.
Even in just 8 kts of wind, we can now sail at 5 kts which is as fast as our
normal motoring speed. We are sailing while every monohull (or “monoslug”
as we like to call them) is still motoring.

The following are some technical installation details and setup and operation
tips you will need to rig your catamaran with a screecher.

Bowsprit

We had a metal shop fabricate a 5-foot A-frame bowsprit out of medium-wall
2-inch stainless tubing. It swings up (Photos 1 and 2). When we come into a
dock, we slacken the guy lines that hold it down in position and fold it up
out of the way so some over-zealous marina manager doesn’t charge us for
the extra 5 feet. This is also reduces the risk of damaging other boats when
you have a bad day docking or the wind is up, resulting in using the A-frame
as some kind of Roman battering ram.
It is important that the eye plates on the inside of each bow be mounted as
low as possible, just above the water line (Photo 3 — Leeward bow damage
is from hitting a 1-foot diameter, 30-foot log at 8 kts. I guess I should be
keeping a better a lookout—the only drawback in sailing in beautiful British
Columbia, land of a kadzillion trees!). This gives the guy lines, that keep
the bowsprit down, the best angle for the downward pull.

I set up a 2-to-1 purchase on the guy lines (using low-stretch line) and led
them back to horn cleats on the foredeck (Photo 4). I plan to replace the cleats
with Spinlock jammers to simplify and quicken the lifting and lowering of the
bowsprit.
Attaching the bowsprit to the bow beam can present an interesting challenge.
On our boat, the bow beam is a fiberglass I-beam with a flat top that is relatively
convenient to attach to (Photo 5). Each installation will be unique. The mounting
point and hinge has to be done just right so that when the bowsprit is raised,
it swings just past the vertical position and is supported by the hinge (Photo
6), but not so far back that it touches the headstay.

Furling Unit

Harken makes several models of furlers for staysails and screechers. We used
a Model 3029 Small Screecher Furler that can be used with sails up to 400 square
feet. We had to modify the 3/16-inch furling line they recommended because the
drum would get full, not allowing the sail to be fully furled. On a suggestion
from Blake at Protech Yachting in Vancouver, we removed the core from the part
of line that wraps around the drum. Sure enough, this allows more wraps on the
drum so everything works well, yet it does not significantly weaken the strength
of the line. We then ran the line back to the cockpit to a Spinlock XAS jammer.
Many people use a simple horn or jam cleat, but the Spinlock jammer allows you
to gradually furl the sail in stages without having to cleat it, while still
giving you control when letting out the sail.

Sail

Because of budget limitations (no money after building our boat), we did not
order a custom-made screecher. Instead we bought a used jib with a wire luff
(and hanks removed) from Atlantic Sail Traders for only $100. The wire luff
has to be properly seized to the sail along the full length of the luff for
it to work with the furler. The sail material of this jib was 4.5 oz., which
is quite a bit heavier than what would be used for a custom-designed screecher.
To furl the screecher with the heavier sailcloth, the main and jib must be up
to effectively blanket it. If you try heading into the wind to furl the screecher
like a conventional furling jib, only the lower part of the screecher furls
as the wire in the luff doesn’t transmit the furling forces up the luff
like the extrusion does on a conventional jib furler. You will then run out
of furling line with some of the sail still unfurled, and you will have to let
the halyard off and take the sail right down to douse it. Our dream, custom
screecher will have a Kevlar line luff and be made of 2-oz Mylar with a UV furling
strip. This sail will furl much easier, and we look forward those the days.

Sheet Tracks

We mounted the tracks on the outboard of the hulls (Photo 7). This position
works great on a beam-to-broad reach. When close-reaching, we use the lazy sheet
to pull the screecher in for a better sheeting angle (Photo 8).

Bow Beam

The upward pull by the screecher on the A-frame is offset by the downward
pull of the guy lines, but this also results in a significant compression force
on the bow beam. After we noticed flexing of our less-than-rigid bow beam, we
installed a temporary horizontal spreader aft of the bow beam to stiffen and
strengthen it (Photo 9). This has worked satisfactorily, but when we have the
boat in the yard later this year we plan to install a rigid compression post
or catwalk across the netting from the mast beam to the bow beam.

Anchoring

On Light Wave, the starboard screecher guy line has to be released to allow
the anchor to fall unimpeded. We have devised a simple tieback line (Photo 10)
to do this. When we have retrieved the anchor, we simply release the tie-back
line and tighten the guy line, and off we go.

Storage

When we return to our permanent dock space in Vancouver we take the screecher
off, put it in a locker, and fold up the A-frame, which takes about 10 minutes.
Our total set-up and takedown time is a one-time 20 minutes per trip (at the
dock and not on a pitching foredeck!), as opposed to 40 minutes per use of a
spinnaker.

Cost Benefit Analysis

Our total investment for hardware and a used sail was $1,200 USD. This relatively
simple and inexpensive addition has a made a huge difference to our light-air
sailing enjoyment. Go for it! Turbocharge your catamaran with a screecher!

Comparison of Wind Speed versus Beam Reach Boat Speed

True Wind Speed	Boat Speed in kts with main and jib only	Boat Speed in kts with screecher
8	3	5
12	4	8
16	8	10
20	10	12