Closing the Gap- How Your Kayak is Made, Gelcoat

As we continue to expand the business and our reach is getting larger, I have become aware that there is a "veil of secrecy" about how these boats are made. Another frequent topic of conversation is the weight of kayaks. The comment I hear and read all too often, "I love my boat, but it's heavy". Why is that? It comes down to the materials and process, plain and simple. Small changes can have a dramatic effect on the ACTUAL weight of a kayak. I capitalized "actual", because there can be a large discrepancy between finished and advertised weight. Kayakers are a smart bunch, and they are getting smarter. So, the marketing needs to match the finished product, or people are going to notice.

So the idea was hatched. I want to pull back the curtain and dissect all of the different parts that go into the construction of a modern composite kayak. More importantly, how all of these components and processes affect the weight. I am going to try to divide this all up into sections that will build up to give a comprehensive explanation of what goes into our boats. To illustrate the effect of material/process changes, I will use the surface area of 5.5 sqyds or 4.59 sqm as the "control" in each of the illustrations. This is equivalent to a 16' touring kayak with a 22" beam. So, lets dive in and get started with Gelcoat.....

Gelcoat

There is much to talk about the hard candy shell that gives our kayaks character. Truth be told, it is a sort of necessary evil in the composites world. Why do I say evil? You'll know the minute your buddy cracks the lid on the can, it's nasty stuff. It is a modified resin, polyester or vinylester, with tint and thixotropic additives. The additives are what help it to stay put on vertical surfaces without sagging. These additives also keep gelcoat from leveling out like a high quality paint. So brush marks don't magically disappear with gelcoat. It also contains a nasty chemical called Styrene. Environmentally and medically speaking, Styrene is really, really bad for us and the environment. As time passes, more and more restrictions and monitoring are put in place on Styrene emissions. To date, the alternatives are still a work in progress and lack the durability of Gelcoat.

How is is used? A kayak is made in the mold. The Gelcoat is applied into the mold first. It can be sprayed, rolled or brushed into the mold. Each method is perfectly acceptable, but can affect the weight of the boat. A sprayed finish will be smoother than a brushed or rolled  application. Why does that matter? Think of it like this. If you look at your walls, you'll see a texture on the surface. This resembles a sprayed application of gelcoat. Brushed/rolled will have a more prominent texture.  This is important because the texture increases surface area and will need to be filled with resin. The more texture, the more resin will be required when the laminating process begins. So, a smoother gelcoat application is the foundation to keeping weight in check.

This is going to ruffle a few feathers because it goes against everything we sea kayakers have been told. If gelcoat is thick, it will make it more durable, right? Not exactly. Gelcoat is brittle, just like unsupported resin. It will crack and fracture if stressed. The thixotropic additives (fillers) actually make it more brittle than resin. They give it a hard surface that resists scratching, but at the expense of flexibility. Every single Technical Data Sheet I have read, gives the specification of 22-26 mils as the proper thickness of gelcoat. It is the Composite Industry Standard, developed by Composites Engineers. The thicker it is, the less flexible it becomes and from my experience, the more likely that it will crack. (I know...I've just committed a mortal sin by stating that). Here is what I base my opinion on. I repair boats for a living and I will get a 20 year old kayak with the standard 22-26mil gelcoat and it has NO CRACKS anywhere. A three or four year old kayak with 40+ mils of gelcoat is having multiple stress cracks repaired. I've even had one that had 80mils of gelcoat! So, contrary to what we have been told, more gelcoat does not make a boat more durable and is likely to contribute to the need of future repairs. 

Pictured below are two test samples of White Gelcoat that were sprayed onto a glass plate. each one was built up to the desired thickness and a final coat was applied with the wax additive to ensure a complete cure. The final thickness measured 22mils and 40 mils. From the photos, you can see the 22mil sample is quite flexible. Much more flexible than the 40mil sample. The final two photos illustrate the difference in flexibility. The 22mil sample was able to be loosely folded without failing. The 40mil sample failed and cracked. Although this isn't all that scientific, but it does illustrate the importance of a proper gelcoat application. Of all the cracks that get fixed at Turning Point 90% have an excess of 50mils of gelcoat. When the substrate is more flexible, the gelcoat will fail by cracking. The other 10% are kevlar layups which are inherently flexible and frequently crack the gelcoat.

So how does gelcoat factor in to the kayaks final weight? The color of the gelcoat will be a factor. Three gallons of gelcoat, three different colors, three different weights. The more tint that is required for a color, the heavier that gallon will be. 

• The average weight of a Gallon of Gelcoat is about 9.5lbs or 4.3 kg. 
• Coverage for that same gallon is 70 sqft at 22mils thick. 
• The control value is 5.5 sqyds or 49.5 sqft

Now how will it effect the final weight? Lets do the math. The gelcoat on the control will weigh approximately 6.7lbs at 22mils thick. At 44mils the gelcoat will weigh 13.4 lbs! Adding unnecessary  weight and is more likely to crack. 

Now that I have committed blasphemy, let me share my findings with our prototype kayak. Gelcoat was applied at 24mils to the hull. Over the past year, I got over my feelings about having a pretty boat and started beating the hell out of it. The bottom of the boat looked like it was dragged down the road. I wasn't shy about interactions with rocks and other boats. The more I ran into and over stuff, the more data I was able to collect. We lent the boat out as a demo mule and I got a message about hitting a rock. The person paddling is said she hit a rock and the sound was awful and the boat only suffered some superficial scratches. The person following her wasn't as lucky and the damage was more apparent. Once the boat was back home, I gave it a thorough inspection. Scratches were the extent of it. No cracks, no cuts only the expected scratches. Would it have been more durable with more gelcoat? Heavier but not more durable.

So, that is the truth about gelcoat. The technology in marine in-mold coatings is advancing rapidly due to increasing styrene emissions restrictions. There are low styrene Vinylester Gelcoats available, but the supply is limited at present. We are looking forward to the advancement at Turning Point as we aim to reduce or eliminate styrene emissions. The days of mopping gelcoat into a mold are coming to an end and the composites industry is moving to a more environmentally friendly process.