I am a moderately experienced kayaker and have used both plastic and fiberglass kayaks in the ocean and plastic kayaks in whitewater. I recently had my ocean kayak stolen, so I’m back in the market for one. The old kayak was plastic (cheaper) but I am open to paying the extra money for a fiberglass kayak. However, I am not sure that I see the value of double the cost. I have always been told that fiberglass kayaks are lighter and looking at the weights of similar kayaks, thatis true but not by much - e.g., 60 vs. 53 lbs. Plastic kayaks are more forgiving with being dropped and hitting rocks but scratch easier - true? But it would seem to take a long time to dig a scratch copmpletely through a kayak - at least, with my level of use. Fiberglass kayaks are more scratch resistant and, being stiffer, will be more efficient to paddle - true? But how noticeable is it and is it worth twice the price? What is the advice of more experienced paddlers?
Boredom factor - if you have a plastic kayak, you may be more likely to keep it for a few years and then sell it to someone else and get something different - the latest and greatest design. A fibreglass boat you’re more likely to keep for the long haul.
I’m still a beginner but I’ve already bought and sold a number of boats. On the used market I’ve found older composite boats can often be had for not much more than newer plastic ones. In fact I purchased a used composite boat for the same as I paid for our other plastic boat. I would buy either, the hard thing for me has been finding low volume ones. The plastic boat weighs about 7-8 lbs more, which is very significant to me when car-topping. The composite one also feels a bit nicer on the water, but not super noticeable for me at my stage.
Tooling for composite kayaks (and canoes) can be less expensive that that needed for plastic ones. This allows more experimentation in hull design and also finer lines. The older layups, especially Brit boats tended to be quite heavy. Some of the newer ones if you can stand the price get the weight down while retaining strength. That said, it looks like weights for some of the RM boats like the P&H Corelite X hulls are getting better. My new Delphin is listed at 55 lbs & seems to be close.
Digging further into the differences in regards to repairability.
As you said, plastic gets scratches somewhat easily, but it takes a lot to scratch all the way through. Or otherwise punch a hole in one. They are rugged. But once you do scrape a hole in one or punch a hole in one, they are difficult to repair well. Plastic welds are much weaker than the original plastic. And if the boat is older, the aged plastic is even harder to weld.
Composite boats often feel more fragile (though most aren’t, unless they are a very light layup). But if you do damage a composite kayak, the kayak can be easily repaired, even on expeditions. This makes them the material of choice for most long expeditions.
I have plastic, fiberglass, and kevlar boats. If crashing into rocks is in your future, then there is a good argument to be made for plastic. If you want to lend the boat to friends, plastic might be good. If you want to put your kids in the boat, again with plastic.
If the above do not apply, there is no argument to be made for a plastic touring boat. Plastic boats are heavier, they have leakier hatches, their bulkheads are not as watertight, and their hulls fuzz up over time and develop dents. The weight differential alone will mean that you will paddle it less.
Do what was recommended above: shop used composite boats.
Plastic has its places, well listed by Acadia.
The models I want tend to be mostly available composite. Plus plastic hatch covers have a much bigger tendency to leak than those on a composite kayak in my experience. You can always put on a keel strip, and gel coat is pretty easy to replace if you need to.
Fiberglass canoes and kayaks are stiffer and as you said a little lighter than plastic. I love the stiffness. I hate to see the flex in the hull with each forward stroke in a plastic boat. That flex is wasted energy. Also a 10 lb difference means a lot when the boat gets in an awkward carrying position such as removing the boat from a cartop and a sudden breeze hits you. Then your back may wish the boat was lighter.
If you’re not doing whitewater then rocks shouldn’t be a problem. Anyway scratches show you’re paddling and not just storing the boat in your backyard.
I wanted to find a lighter kayak. My 20 year old plastic Necky Kayook weighs 63 lbs. at 15’ 3". It’s still a great boat, but putting it on the truck in the wind kept getting harder. I bought a slightly used Eddyline Journey, made of carbonlite (still a plastic) weighs only 49 lbs. at 15’6". It’s been a terrific boat, and the weight difference really makes transporting easier.
For whitewater, plastic is generally the way to go. There are a lot of stories of plastic kayaks coming off of racks at highway speeds with just a few superficial scratches. It takes a lot of damage to put a hole in a plastic kayak. Fiberglass and carbon fiber kayaks, under the same conditions, will often shatter and Kevlar kayaks will still generally be watertight, but essentially totaled unless to want to spend a lot of time and money, as well as add a lot of weight with the repair.
The primary difference with a composite kayak compared to plastic is weight. For the same model or general shape of a plastic vs a composite boat, there will be a bit of difference in acceleration, but very little in general handling characteristics. Weight is a significant issue as far as getting the boat on and off of the car, to and from the water, and if you are portaging the boat. If I were often paddling on rocky rivers, performing surf landings on rocky shores, or enjoyed grinding my boat up concrete boat ramps, I would have gotten a plastic boat, However, I usually paddle on open water with sandy shores. I have paddled in less forgiving areas like the Adirondacks, Maine, and the upper Potomac, but I just paddle a little more carefully there. Composite boats are fairly tough and repair is not that difficult unless exact color matching is desired. I consider my boat to be just that, not a work of art. Other than this spring when I reinforced the interior of my 21 year old boat where my heel were wearing though the epoxy, I have only needed a handful or minor gel coat repairs for deeper scratches.
The next most important difference, of course is cost. I have done a lot of solo kayaking with an 18’ boat with a rack on my truck that was 81" tall. So weight was important to me. I chose Kevlar, carbon fiber was not an option back then. For lighter weight new composite boats, they will usually start at around $2800 for fiberglass, $3600 for Kevlar, and $4200- 5000+ for carbon Kevlar. Each step up will generally save 5-7lbs each. A new plastic touring kayak can be as little as $1600, but will often weigh in excess or 60lbs.
All boats are a compromise. You need to consider how you will be using the boat and determine how important the weight is compared to the cost.