Hypercarbon, Kevlar, honeycomb, monocoque, fiberglass, composites, carbon fiber… it all sounds very technical, and maybe it’s Greek to you. You’re not alone, most rowers and coaches really have no clue what all the technical terms really mean, or more importantly how it translates to boat durability, stiffness, or speed. So here it is – our multi-part “give-it-to-me-straight, jargon-free” series: Composite Boats 101. Check out Part 1 here if you missed it.
In last week’s post, we talked a little about racing shell construction, and how the industry moved from wooden boats with internal frames to today’s monocoque hull design. In this week’s post, we’re going to let you in on a dirty little secret of the boat building world:
WE ALL USE THE EXACT SAME MATERIALS.
Every boat builder is benefiting from advances in the aerospace industry, and we’re all experimenting with the composite materials the guys building airplanes are developing and using. (Though at Pocock we are lucky to be geographically advantaged – global leader Boeing is right down the street, and we have at our disposal the same sales reps and suppliers, and hire from the same pool of composite-savvy candidates.)
When you hear about a “shark skin” or “rhino skin” boat, that’s marketing – it’s just the name a boat builder gives to their blend, or “schedule”, of composites. We call ours “Hypercarbon.” All the boat builders are using the same composites. What is different is how those materials are put together and how much of those materials are used, or the “lay-up.”
Lay-up: the way the materials are combined in layers to create the racing shell. The lay-up is done in steps, with time and temperature considerations leading to a partial or full cure in between.
Thanks to the adoption of the monocoque hull, your racing shell gets its structural integrity from its skin. The skin starts with sheets of a composite fabric, like carbon fiber, fiberglass, or Kevlar. All these materials come on rolls, much like fabric does in a fabric store. At this point they’re not stiff or very strong.
Carbon Fiber: a woven fabric made up of extremely thin carbon atom fibers. Carbon fiber gets its strength from the way the atoms bond with microscopic crystals and align themselves along the long axis of the fiber. This provides an extremely strong bond in proportion to the strand’s size. These strands are woven together to form yarn, which is then woven into fabric. The fabric is available in many different patterns depending on the intended use.
Fiberglass: a woven fabric made up of very fine strands of glass. The first composite boats were made with fiberglass, though it’s used less now because it’s heavier than carbon fiber. Fiberglass is significantly less expensive though, so it is still used as the primary component in many lower-end shells.
Kevlar: a woven synthetic fiber that’s commonly used in body armor and tires. It’s very strong, but it’s expensive, extremely difficult to work with, and once damaged, impossible to repair to like-new.
Carbon fiber has become the material of choice for most racing shells, due to its strength-to-weight ratio. Thanks to its microscopic crystals, carbon is strong when the fibers are in one long continuous piece; the longer the continuous piece, the stronger the finished racing shell. As you can see in the photo above, these fabrics come in many different styles. Depending on the materials used, the tightness of the weave, and the orientation of the fiber intersections, different styles are used in different parts of the boat. A very small, tightly knit carbon (like the background swatch in the photo above) is good for tight spots because it’s extremely pliable and can fit into creases – like the very end of the bow or stern. The swatch in the middle has fibers that all run in one direction (uni-directional), making the laminate extremely strong and stiff in any one specific area.
The carbon fiber is laid in the mold similar to how fabric is draped on a form, and then epoxy is applied to harden it. The epoxy flows into the gaps in the carbon, and “cures” (or hardens) the carbon fiber – now it’s considered a “composite”.
Epoxy: a resin that’s mixed with a hardener. Combined in exact proportions, the epoxy is precisely applied to the carbon fiber in the mold. It cures at a specific temperature after a specific period of time.
Once the carbon fiber and epoxy have cured, it’s very strong. To increase the strength and durability of the materials, a core is sandwiched in between two layers of carbon fiber.
Foam: a closed-cell, very strong, very light foam sheet.
Honeycomb: solid sheeting that is made up of many small hexagonal (six-sided) tubes. It looks just like its namesake – a honeybee honeycomb.
This sandwich construction method follows the same mechanical principle that makes I-beams so strong; the core makes the laminate exponentially stronger, and the thicker the core, the stronger the construction. That’s why if you look at the inside of a Pocock shell right by the rigger, you’ll see that the hull is actually thicker. The type and size of core used in this section is different than the type and size that’s used at the seat deck. The rigger and the footboard are both stressing the hull with each stroke, so this position in the boat needs additional reinforcement.
So that’s the basic list of ingredients in a racing shell. How all those materials are combined together is where a boat builder turns mad-scientist. Next week we’ll have a list of FAQ’s to help explain why despite all using the same materials, our boats are all very different.