Fabric decks,
spray shields, and cockpit tents are comfortable, space saving, and lightweight.
They can significantly increase your living space, make a rough passage
a bit safer and dryer, or turn sleeping aboard on a cold, wet night into
a pleasant experience.
Fabric structures should be as low as possible to keep windage to a minimum.
Well designed fabric foredecks and small shelters may sometimes be left
in place when under way. If you want to, you can sew plastic windows,
vent flaps, and mosquito netting into the fabric.
A wide variety of fabric types, weights, and colors is available. Quality
is related to price — you get what you pay for. Some fabrics stretch,
fade, or wear more than others, and even shock cords may not be able to
take up the slack of cheap fabric or wet, untreated canvas. We’ve
found heavy-weight fabric advantageous in building these structures. And
when in doubt as to the best fabric weight for a specific application,
we call our supplier and ask his opinion.
No matter how it’s designed or which fabric is used, a structure
that flaps, sags, or leaks is as bad as none at all. A good support system
is the key to success. Every boat offers different options for se- curing
and supporting fabric structures. Battens, ridgepoles, upright poles,
and shock cords can provide tension and support. Fabric also needs slope
to effectively shed moisture. Even a heavy dew will fill pockets in a
flat and loose-fitting piece of fabric. And a bit of flex is necessary
because a stiff and unyielding fabric structure will strain lines, bend
supports, and stretch fabric.
Narrow boats with small spray shields don’t usually pose difficult
design problems, but wide hulls often require a more complex structure
to provide proper support.
Simple Supports
Options for framing and support of a fabric structure are limited only
by the imagination. A ridgepole is the simplest support and does a creditable
job (Fig 1). Ridgepoles usually run fore and aft down the centerline,
although they can also be positioned on one side of a hull for a “lean-to”
shelter. A boom is the classic ridgepole, but we’ve also used a
10-foot sculling oar supported by a forward tripod and a notch in the
transom.
Halyards attached to sewn-in D-rings provide prime, adjustable overhead
support (Fig 2). However, they offer such strong leverage that you must
be careful not to tear the whole affair off the hull and hoist it to the
masthead. When using halyards, you may have to snub the line to the mast
to quiet flapping in a breeze.
Telescoping supports may also be situated inside the structure, braced
up from thwarts or the sole (Fig 3). I made three good aluminum supports
from an old tripod. I adjust them by tightening two knurled knobs on each
leg. These sup- ports can be placed in a grommet or rein- forced patch
in the fabric.
Battens & Beams
Support battens may be rigged under or above the fabric or sewn in between
layers (Fig 4). One method for supporting fabric is an external batten
much like a mountain tent (Fig 5). All you need is a pocket at either
end for the batten and small loops or ties along the rest of the batten
length. If these ties are small diameter shock cord, they can be adjusted
to keep the fabric at exactly the correct tension to shed water and wind.
This structure only requires tie-downs at corners and along the edges
to be self supporting.
You may find fiberglass, plastic, or aluminum battens that work well and
do not require any finishing, but wood battens are the best looking. They
finish nicely and bend to a uniform curve. Hardwoods like ash or mahogany
or straight-grained softwoods like spruce and fir make fine battens. All
wood bat- tens should be well sealed to keep their strength, since soaked
wood will lose much of its stiffness and may snap in response to a gust
of wind or a sudden load. Three coats of epoxy, followed by varnish if
exposed to sunlight, are best for sealing.
Wood battens made for supporting a fabric structure usually need to be
wider than thick to prevent twisting and make rigging easier. A successful
size for us has been ¼-inch by 1½-inches, but each application
seems to require some experimentation as to best size and shape. Start
big and keep shaving the batten with a block plane until it bends easily
to the shape you want. Keep in mind that laminated and epoxy-sealed battens
will be stiffer than plain, unfinished battens, but they will also retain
uniform strength under all weather conditions.
You may wish to drill small holes in the ends of the battens to provide
a tie off point. Straight battens may be slipped out of the batten pockets
and rolled in the fabric, allowing a large assembly to be stored easily
in a small place. In many fabric structures, the battens are different
lengths, and having each batten labeled makes it easier to rig. If the
batten pockets start to wear, consider wrapping the batten ends in duct
tape.
Fabric decks can be supported with beams that fit into sockets
or notches in the gunwale or deck structure (Fig. 6). Sometimes these
beams can be permanent and the fabric covering removed or left in place
according to the weather. By laminating, you can make the beams to almost
any shape for a small boat.
These beams are best lofted and laminated right on the lofting board.
Make the lofting board of ¾-inch ply and do all the layout right
on the board, then screw down short sections of aluminum angle and use
the lofting board for laminating the beams. We build ours out of 1/8 inch
veneer.
Tie-Downs
The outboard ends of decks, tents, and spray shields can be held in place
with snaps or loops and hooks (Figs. 8-10). They can be attached to the
outwale, under the outwale, or in the case of hooks even inside the boat
if you drill a small hole under the gunwale to provide access for a small
hook.
We favor shock cord loops and hooks over snaps as a means of attachment.
Shock cord stretches in response to pres- sure on slack and will keep
a fabric panel at about the same tautness whether wet, dry, hot, or cold.
Using cords of various size and length also allows a degree of fine tuning.
Be sure to get the quality cord that comes in rolls in various diameters
a few inches.
If hooks are permanently attached to the boat, the fabric structure, once
adjusted, can be set up easily, even late at night or in wind or rain.
With any fabric structure, you may need to rig additional lines fore and
aft to provide proper sup- port tension. We always throw a few small C-clamps
in the boat for overnight trips, since you can easily clamp a structure
together in an emergency. Small ply pads protect the hull from marring.
A couple of words of caution. Anchor your boat so it can weathercock into
the wind. If the wind blows into the tent from the backside, your ears
will pop every time the thing flaps.
Also, test everything before your first night aboard. For some reason,
nothing ever seems to happen to fabric decks or tents till late at night
or miserable weather, when you least want to get up and deal with it.
Originally published in Small Boat Journal,
Issue 53, March 1987.
Reprinted with permission of Paul Butler.
Illustrations are by Marya Bulter.
If you would like to review other projects by
Paul Butler,
please take a look at his web site—
Back Yard Yacht Builders
A non-commercial association of amateur boat-builder enthusiasts.
All our wooden boats are Stevenson designs.