|
Building components with Kevlar™ braid
By Hugh Horton

Braided Kevlar, or composites with Kevlar and carbon braid, are used for joints and many
components of my sailing canoes. These include the hull/deck joint, cockpit
coaming and spray deck rims, the leeboard bracket and retaining pin, the
attachment of the mast step to the hull, the gunter’s yard heel fitting, and
the seat and its major parts. My source
for Kevlar braid is A&P Technology, 4595 East Tech Drive, Cincinnati, Ohio
45245-1055, phone 513-688-3200. Their website is www.braider.com. The
techniques shown here can be adapted to many other projects.
Because
of the variety of Kevlar and carbon braids available, forming intricate shapes
is easy. However, after Kevlar has cured, shaping is difficult because of its
toughness. Tools and abrasives must be
kept sharp. Here’s how I did it.
Building the cockpit rim

Figure
1—A
hose is used as a mold. I pick a hose that is smooth, 1-1/8" to 1-1/4"
diameter and capable of bending fairly. I precisely lay out the cockpit opening
and fair the cutout as perfectly as I can. I round over the underside edge of
the deck, although this is difficult because of the layer of Kevlar. It is very
important to align the hose precisely, getting it exactly at the edge. I lace
the hose in position with marline, a fine thread that is strong enough to pull
tightly.
Figure
2—Notice the fairness of the hose layout. The joint at the aft end is
connected and aligned by a piece of heavy copper electrical wire bent as needed
for a fair joint. Before gluing, remember that it is easier to be too cautious
with masking rather than clean up later, especially after the epoxy has cured.
Figure 3—The
first layer of Kevlar tape overlaps the underside of the deck. I keep checking
the hose to be certain of its position. After this first tape cures, I cut and
remove the marline so subsequent layers don’t show the marline bulge. I apply
a second thin tape, overlapping the first, carefully positioning the tape’s
outside edge. It will be the determining edge for the next layer, a heavy Kevlar
braid. After this tape has cured, I remove the hose/mold and fill and fair the
marline grooves inside the curve before proceeding.
Figure
4—I apply a 3-1/2" diameter braided Kevlar hose over the cured tape
layers. This is the primary structure of the rim. The aluminum roof gutter to
the right is used to wet out the Kevlar hose. When it’s thoroughly wet out, I
wrestle the heavy, warm, very slippery snake into position, rather than trying
to wet it out in place. The shiny black material under the rim is foam pipe
insulation wrapped in plastic film, which I use to clamp the edge of the hose
where it tucks under the rim. It’s important to not deform the first tapes by
forcing the insulation under too tightly.
Figure
5—After this cures, I apply a final thin tape under the rim, overlapping
from inside the rim curve to the deck.
Building the leeboard bracket
The
leeboard bracket is designed to transfer all of the side loads of the board
through the hub and into the hull without being permanently attached to the
hull. I used the hull as a mold to get perfect alignment of the attachment
points.
Figure
1—I
built a permanent lip on the sheer, which will be grasped by the bracket.
Figure
2—I
formed the deck piece of the bracket by molding a layer of carbon fiber fabric
to the deck, which was protected with plastic. The upper edge is molded into the
curve of the rim and the lower edge is wrapped over and below the lip at the
sheer.
Figure
3—A
carbon plate, the vertical face upon which the leeboard pivots, is attached to
the deck piece. The laminated plate is clamped to a piece of stiff plywood,
which is aligned plumb and parallel to the centerline of the boat and holds the
plate to the deck piece. I use every trick I can to assure alignment
accuracy—note the string centerline, a level, and the plywood. I first glue
the plate to the deck piece with a fillet, then apply tape to reinforce it.
Figure
4—The
upper piece will act as a brace between the vertical and deck pieces. I mold the
upper piece, on a thin plastic sheet bent around the upper edge of the vertical
face and taped temporarily in place.
Figure
5—After
I remove the cured upper piece from the mold, I then bond it back in place with
fillets and tape the joints and edges with Kevlar tape.
Figure
6—I
drilled a hole for the axle bolt through the board and bracket. Large rubber
washers between the board and bracket provide plenty of bearing surface,
allowing the board to be raised and lowered easily, but held firmly.
Figure
7—The
lower edge of the bracket locks under the lip that was bonded to the hull in
Figure 1.
Figure
8—The upper edge of the bracket slips
under the cockpit rim. Once in place, I determine position of eyestraps attached
to the hull on either side of the bracket. A single pin through the eyestraps
traps the inboard joint of the bracket and holds the bracket firmly in place on
the hull.
Epoxyworks 16 / Fall 2000
Copyright © 2002, Gougeon Brothers, Inc. All rights reserved.
This page is maintained by Gougeon Brothers, Inc. Last Modified on 10/28/02.
Reproduction in any form, in whole or in part, is expressly forbidden without the consent of the publisher. EPOXYWORKS, Gougeon Brothers, WEST SYSTEM, Episize, Scarffer and Microlight as used throughout this publication, are trademarks of Gougeon Brothers, Inc., Bay City, Michigan, USA.
|