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Spray HPK – Carbon Fiber Cockpit Coaming

Posted By Dan Caouette

Pretty much my standard cockpit coamings has been cast carbon fiber.  I’ve done a few solid wood ones but customers really like the look and feel of the carbon ones.  Why not?  They’re thin, light weight, very strong and look great.  The carbon one-off construction is built on the deck  and allows some very smooth and organic shapes that can be of virtually any size and/or shape.  There is no post-bonding after construction.

They’re VERY hard to make (tongue firmly in cheek). 😉

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First trace the cockpit opening onto the deck.  I make a half-pattern out of thin board. This assures that both sides are symmetric.  The deck doesn’t need to be flat or have a flat recess.  It does make it easier.

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Cut out the opening and sand it smooth.  Do not round over any of the edges.  Mask off the deck.  The area nearest the opening is clear packing tape.  The rest can be paper.

This method uses a simple, single-use Styrofoam form that is attached to the deck.  Cut out and bond some 3/4″ (19 mm) builder’s foam to the deck opening.  Use the half-pattern as a template for the inside opening.  Cut outside the line by 1/16″ to 1/8″ (1.5 to 3 mm) so you can sand the foam to the inside opening. Make sure the foam is wide enough.  2″ (50mm) should be adequate for most coaming lips.  The foam is attached to the deck with spray adhesive.  The tape will release before the spray glue.  Bits of masking tape hold the foam in place while the glue sets.

If you have a curved deck the foam will conform to a slight radius.

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Remove the tape used to temporarily hold the foam and sand the foam even with the deck opening.  A sanding drum chucked in a cordless drill works great for this.  The orange lines help define the round over at the interior edge of the coaming.

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Slightly round over the interior edge to about a 3/8″ (9mm) radius with sandpaper.  By hand, sand the entire coaming smooth.  Flip the deck over and sand the interior surface of the deck where the coaming will overlap.  It should be at least an inch (25mm).  To keep a clean interior you can mask off the perimeter of what you’ve sanded.

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Cover the foam with a release.  I’ve tried things as paint and PVA release materials but pieces of packing tape seem to be the easiest and release the cleanest.  Cover just the foam.   Flip over the deck and sand a 3/16″ (4.5mm)  radius into the deck edge.  Fiberglass and carbon fiber do not like sharp edges.   Trim the tape at the joint between the deck and the foam so the coaming can bond to the deck edge.

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Now the fun part: laminating the layers of fiberglass and carbon fiber.  I use the following schedule on my coamings, starting from the form up: one coat of neat epoxy, two layers of 3K carbon fiber, three layers of 9.0 oz tightweave E-glass, finished by two more layers of carbon.  I used to use only one layer of carbon on each face but lost some of the depth in final look of the carbon.  In other words I could see some of the fiberglass in the gaps between the carbon tows. The layers of carbon fiber and fiberglass are then laminated directly to the form.  The finished thickness is just under 1/8″ (3mm).

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Now brush on at least two fill coats of neat, clear epoxy.  You want to bury the weave of the carbon.  When cured the foam is removed and the coaming is marked for width, trimmed and sanded smooth.  You definitely want to have enough epoxy on the surface so you don’t sand through to the carbon.  If you start to hit the carbon while sanding, lightly scuff sand the rest and apply another fill coat.

Next up: steering components.

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