Plastic vs. Composite vs. Thermoform Kayaks

I’ve been in similar considerations but from my understanding rotomolded plastic is as durable and indestructible and inexpensive as it is heavy and flexible. So you strain more to carry it, and it takes a greater effort to move it at the same speed. Plastic kayaks are also much harder to fix in the event of catastrophic damage, which is what is needed to break them though they almost never need it.

Composite can be quite light, fiberglass/soric designs like Stellar are getting as light as wood/composites, down well into sub 40lb range for singles. They are very stiff, take way less effort to carry and paddle fast thanks to their light weight and stiffness. Unfortunately as weight goes down and stiffness goes up, so does cost, and durability goes DOWN. Composite is very fragile and doesn’t like rocks at all. You can improve durability somewhat with a straight fiberglass design which is significantly heavier but still reasonably stiff performance wise. You still can’t launch it or drag it on rocks though like you can plastic.

What I was told is that with thermoform is the stiffness and durability are in between composite and rotomolded. So is the weight and so is the cost. They won’t stand up to being dragged on rocks nearly as well as rotomold, but they aren’t as easy to carry as composite. I was attracted to the somewhat lighter weight of rotomold but to me what stood out from the various dealers I spoke to is that rotomolded is the most difficult and expensive of all the designs to fix and the damage might not be repairable to the point where it will handle like new or “close enough”. So if your kayak is fed a steady diet of rocks like we do constantly launching from a rocky beach it will still wear out in a short enough time that very expensive repairs will be necessary in short order and you’ll curse yourself for not getting rotomolded.

What I mean is that if you are turned off from the composites because you are needing the durability of plastic, you’re not going to be happy with thermoform as it’s nowhere near as resilient. If durability is not an issue then there’s no reason to go for the higher performance of composite which in the end will save you money in the long run as it’s far less expensive to repair and more likely to be fixed successfully should any major damage occur.

1 Like

@CA139 said:

What I was told is that with thermoform is the stiffness and durability are in between composite and rotomolded. So is the weight and so is the cost. They won’t stand up to being dragged on rocks nearly as well as rotomold, but they aren’t as easy to carry as composite.

Why would a thermoform kayak not be as easy to carry as a composite?

Some composites can be very light…

@grayhawk said:
Some composites can be very light…

As are thermoforms. My thermorform is 47# and my composite is 48#. Thermoform boat is easier to carry because it’s a foot shorter than the 17-ft composite.

My carbon/kevlar Nordkapp was in the high 30’s and most good wood composites come in around 40.
But those do cost a bunch more than thermoforms.
The best Epic 18X is advertised @39 lbs.
Having had kayaks in all the materials CA139 is spot on.

@grayhawk
Wow, didn’t know such a lightweight Nordkapp existed. That’s pretty amazing.

@Rookie said:

@CA139 said:

What I was told is that with thermoform is the stiffness and durability are in between composite and rotomolded. So is the weight and so is the cost. They won’t stand up to being dragged on rocks nearly as well as rotomold, but they aren’t as easy to carry as composite.

Why would a thermoform kayak not be as easy to carry as a composite?

I am pretty sure CA139 is referring to weight. On average, thermoform is lighter than rotomolded, but heavier than composite.

@Rookie said:
@grayhawk
Wow, didn’t know such a lightweight Nordkapp existed. That’s pretty amazing.
Mine was a carbon/kevlar LV and max weight limit was specified when I ordered it…
And I did weigh it before I took delivery.
$$$$$$$
All was a big waste of time and money as I didn’t like it and sold it…

@Peter-CA said:

@Rookie said:

@CA139 said:

What I was told is that with thermoform is the stiffness and durability are in between composite and rotomolded. So is the weight and so is the cost. They won’t stand up to being dragged on rocks nearly as well as rotomold, but they aren’t as easy to carry as composite.

Why would a thermoform kayak not be as easy to carry as a composite?

I am pretty sure CA139 is referring to weight. On average, thermoform is lighter than rotomolded, but heavier than composite.

That’s what tripped me up as when I was looking for a 15-16 foot LV, the fiberglass composites were heavier than thermoform. Never considered lighter layups such as carbon fiber/kevlar because of price.

My 16’ Epic 16X is 40lbs. My wife’s 16’ Epic V6 is 40 lbs. My 13’ Current Designs Vision 130 is 40 lbs.

My 16’ Eddyline Nighthawk was 50 lbs and the Fathom LV was about the same.

I’ve seen some thermoformed models really abused on shallow, rocky streams and not be nearly as scratched up as rotomolded poly boats of reasonably similar design and purpose.

My observation is that composites can be either heavier or lighter than thermoformed boats of similar dimensions, depending on which composite layup is used.

Thermoform won’t scratch as much as plastic will but it will fatigue faster and eventually crack when subjected to repeated flexing against hard objects like rocks. And when it does fail it’s the most difficult layup of all to repair in terms of effort and expense.

What I mean is that OP should either go for the durability and low cost of plastic or pay a bit more for a lighter composite like Stellar’s advantage layup of fiberglass/soric which weighs as much as a wood kayak but is a bit tougher. This is still a lot cheaper than kevlar/carbon and the least expensive layup type to repair thanks to the fiberglass and gelcoat. 36lbs for a 14’ boat is pretty equivalent to wood and quite lovely to handle and carry around and it costs about $2800 or $300 more than their straight fiberglass layup but saves a lot of weight.

Composites are “strong” because they are stiff but this “strength” translates to fragility and brittleness when you have to deal with sharp, hard objects like rocks, and this liability is multiplied times 10 if dragged upon them. If you never have to launch from rocks or carry long distances on rocky surfaces where you risk dropping your craft (it happens!) it’s not an issue so get composite. In the end you’re not saving money with thermoform because when you eventually need it repaired it will be far cheaper going forward with composite, it will be possible to repair your composite “like new” without much difficulty, and you will enjoy the lower weight and higher performance all the while. But if rocks are in your future then plastic is really the best and only answer, from a long term point of view.

@CA139 said:

Composites are “strong” because they are stiff but this “strength” translates to fragility and brittleness when you have to deal with sharp, hard objects like rocks, and this liability is multiplied times 10 if dragged upon them.

Yes, some boats like NDK/SKUK are built with inferior materials that result in an overly stiff and brittle composite, but that’s certainly not true of the majority of composite kayaks. Well-constructed composite boats have resilient layups that will flex when impacted and generally emerge unscathed, though perhaps with a bit of gelcoat damage that is easily and inexpensively repaired. I’ve beaten the crap out of composite boats in rock gardens and while I have occasionally done damage that required fiberglass repair, most of the time the boats have survived with nothing more than gelcoat scratches.

@bnystrom said:
I have occasionally done damage that required fiberglass repair, most of the time the boats have survived with nothing more than gelcoat scratches.

My experience too. Though I have often thought I might pick up a used rotomolded sea kayak for cheap as you can find them in the $400 to $600 range, but have not done so. As I age every pound adds up, and it is really nice to have boats that are 52 pounds or lighter. I have long thought I might turn my hand to making a skin on frame sea kayak one day.

The only boat I have damaged down to the cloth was my CF Rapid fire when I hit rebar imbedded in a rock on the Withlacoochee River.
That hurt my feelings but was easily repaired by a friend who repairs boats for a living.

@bnystrom said:

@CA139 said:

Composites are “strong” because they are stiff but this “strength” translates to fragility and brittleness when you have to deal with sharp, hard objects like rocks, and this liability is multiplied times 10 if dragged upon them.

Yes, some boats like NDK/SKUK are built with inferior materials that result in an overly stiff and brittle composite, but that’s certainly not true of the majority of composite kayaks. Well-constructed composite boats have resilient layups that will flex when impacted and generally emerge unscathed, though perhaps with a bit of gelcoat damage that is easily and inexpensively repaired. I’ve beaten the crap out of composite boats in rock gardens and while I have occasionally done damage that required fiberglass repair, most of the time the boats have survived with nothing more than gelcoat scratches.

I just have to say about NDK I had a NDK Greenlander Pro 2004 build year. It was the stiffest, strongest kayak I have ever owned. ZERO flex. super tough. I would disagree about inferior build. Could it have been lighhter with some type of vacuum bagging. Sure BUT the way it was made it was super strong. Bounced off rocks a few time with gel coat damage but that was it. Not brittle at all. You don’t want flex in the hull. Just saying.

@castoff said:
I have long thought I might turn my hand to making a skin on frame sea kayak one day.

SOF kayaks are easy to make if you have even rudimentary woodworking skills or the desire to learn them. The list of tools required is really short, too. For a couple of hundred buck and a few relaxing days’ work , you can end up with a fun, high-performance boat that’s uniquely yours. If you decide to take the plunge, let me know and I’ll recommend some good books on the subject.

I’ve been thinking about a SOF myself lately. Really want to do a strip boat, but the time involved is just too much right now and this is where SOF seems to fill the gap. Just starting to research the building technique and a direction to good book sources would be great! Thanks.

@dc9mm said:

I just have to say about NDK I had a NDK Greenlander Pro 2004 build year. It was the stiffest, strongest kayak I have ever owned. ZERO flex. super tough. I would disagree about inferior build. Could it have been lighhter with some type of vacuum bagging. Sure BUT the way it was made it was super strong. Bounced off rocks a few time with gel coat damage but that was it. Not brittle at all. You don’t want flex in the hull. Just saying.

Don’t confuse stiffness with strength or durability. NDK boats are as heavy as they are because the have to seriously over-build them due to the crap materials they use (specifically chopped strand mat and sprayed chopped strand). If you whack one hard enough, you’ll crack or hole it because the chopped strand material cannot distribute and dissipate the impact energy over a large area like woven material can. They also use huge amounts of gelcoat that contribute nothing to the strength of the boat, but add a lot of weight. I’ve even found areas on NDK boats I’ve repaired that had no fiberglass under the gelcoat! Unless things have changed there in recent years, they have the absolute worst quality control in the industry. Its a real shame, because the designs of their boats are excellent and they handle great on the water. That’s the only reason that they’re still in business.

The fact that you haven’t put a hole in yours yet doesn’t mean that it’s well-constructed, it may just be a matter of luck.

You absolutely DO want flex in a kayak hull, as that’s what makes it able to withstand impacts without weighing as much as a Buick. The best hulls are stiff enough to resist the pressure of the water when bouncing over waves, but flexible enough to absorb impacts with hard objects while sustaining little or no structural damage. I’ve owned and repaired enough kayaks to understand the difference and I’ll take a resilient hull over a rigid one any day.

@bnystrom said:

@castoff said:
I have long thought I might turn my hand to making a skin on frame sea kayak one day.

SOF kayaks are easy to make if you have even rudimentary woodworking skills or the desire to learn them. The list of tools required is really short, too. For a couple of hundred buck and a few relaxing days’ work , you can end up with a fun, high-performance boat that’s uniquely yours. If you decide to take the plunge, let me know and I’ll recommend some good books on the subject.

Bryan, I gave him one of the books you recommended back when I built one.

Cool! Another great resource is: http://www.qajaqusa.org
The forum has been pretty dead lately, so having someone new ask questions should perk things up: http://www.qajaqusa.org/cgi-bin/GreenlandTechniqueForum_config.pl