composite kayak construction

Submitted byZoltan Sasadi onSat, 06/06/2020 - 13:25

Dear All,

Firstly thank you for having me on the forum, and i hope that all members are doing well considering this world wide crisis..

I have composite industry background however i started my career as a wooden boat builder. I have built wooden power boats as well as composite sailing and motor yachts, but my main field is composite tooling.

I am currently in the R&D phase of building a kayak for mainly flat water use. The intention is to create a fast, lightweight yet sturdy enough kayak for a single paddler with some cargo allowance for few days trips, by combining the best characteristics of wood and composite.

I have already built a male mould which is suitable for vacuum infusion. My intention is to build the kayak from the inside out to have both inner and outer surfaces smooth.

The kayaks main dimensions are: LOA: 5.2m (17 foot), LWL: 5.29 (17.3 ft) due to reverse bow, Beam: 56 cm (22 inch)

I've been researching on the web for specific layup plans for different kayaks but very rarely find detailed layup plans as manufacturers tend to keep the details for obvious reasons (or i am just not good enough to use Google :D ), but with the information i have found so far i came up with a layup sequence and i was wondering if i could discuss it with you guys as i assume some of you have great experience already in building kayaks with different techniques. 

The inspiration behind the layup is cold moulding technique of wooden veneers.

The below sequence is based on a male mould (building from the inside out), where zero direction is along the chine:

 

-clear gel coat

-100 gsm (3.5 oz) 2x2 twill glass fiber ( 0-90 direction along chine)

-0.6mm straight grain spruce veneer (o direction along chine)

-320 gsm (11 oz) bi-axial glass or carbon fiber (+/-45 degree direction along chine)

-3mm 3D PET core

 -320 gsm (11 oz) bi-axial glass or carbon fiber (+/-45 degree direction along chine)

-400 gsm (14 oz) 2x2 twilll carbon fiber reinforcement on the deck at the cockpit area only (0-90 direction)

-0.6mm straight grain African mahogany veneer (0 direction along chine)

-200 gsm (7 oz) 2x2 twill glass fiber (0-90 direction along chine) on the hull and 100 gsm (3.5 oz) 2x2 twill glass fiber on the deck.

 

I will try to get all the layers up and infuse epoxy resin under vacuum pressure. As per my initial calculations the kayak would measure around 16-17kg  (35-37 pounds) without seat, footbrace, skeg.

I have mentioned glass fiber or carbon fiber as i am not sure whether one has a huge advantage over the other at this specific layup...

I would love to have some feedback whether the above layup would suit structurally for a kayak construction with the above mentioned intention of use?

Thank you

Regards

 

 

JohnAbercrombie

Sat, 06/06/2020 - 15:05

Why did yo decide on this style of construction?

How do you plan to keep the veneer layers aligned before infusion? And infuse through veneer?

It looks like it will be very heavy?

How did you make the male mold? Do you have pictures to share?

Hi John,

Initially the mould was made for building a cold molded kayak using out of autoclave, low temperature cure, epoxy resin film  as adhesive with additional carbon reinforcements on key areas such as cockpit, bulkheads etc, that it why it is a male mould and is being built from the inside out. Currently I have put that project on the side for several reasons, and i am looking for some alternative built method.

The veneer is only 0.6 mm thick and i am hoping that it will stick enough with the normal spray glue used in infusion process, but that is still subject for testing. This is plan "A"

 In case it won't i will leave the last layer of glass out from the initial infusion (which would be over the veneer layer) so i can just use tapes to hold the veneers on its place until the vacuum is applied. This is plan "B".

As for the infusion, it is again needs some testing, theoretically the resin should be able to penetrate through the joints of the veneer and get into the reinforcement, or else i can start the infusion from one end putting the feed line on the reinforcement (just need to leave it a bit longer than the veneer, which can be trimmed later) and have the suction point the other end therefore I can control the direction of the resin flow.

If neither of this would work as plan "C", i will do the infusion without the veneer and apply as a second stage process.

 

As for the weight i would be very happy to get some feedback which layers/ materials i should remove or replace, which are the ones i can sacrifice and still get a safe kayak, which can perform.

the mould was built as a traditional strip plank kayak with an aluminum strong back, marine grade plywood stations, meranti planks, and has 3 layers of wet laminated 300gsm CSM matt, i used high temp resistant epoxy resin and finally coated with Duratech paint.

sorry i ve been trying to upload pictures but for some reason i cant i reduced file size as well...any idea ?

cheers

 

Zoli

 

 

Now take this as a grain of salt as I know little about wood or building kayaks save what a sorry experience it was for me to try, especially in light of how inexpensive, stiff, light and well built composite boats are, especially 2nd hand. This goes 150 (as in one-hundred fifty) times if you're building your own boat from scratch rather than buying the kit as there's a learning curve. Like I said I know very little but from what you are posting I am not sure that you have much experience with building KAYAKS as what works in the boating world does not work with kayaks.

See the problem is I went in with a friend of mine who like you had experience in building boats and yachts but *NOT* kayaks. The two are very different. You might want the extra layers for a real deal boat but the performance difference if you add all your layers will be detrimental to the kayak. You can feel a difference of about 4lbs in terms of acceleration and maneuverability in a kayak so you will be loading it up so much that whatever extra stiffness will be cancelled by the extra weight. It was significantly overweight, like the boat weighed 180lbs heavy, it was so big and massive that it prooved IMPOSSIBLE to move and couldn't get out of its own way. 

From everything I have read in a wood kayak you just use varnish/epoxy&fiberglass/wood/epoxy&fiberglass and that's it. That's the layup, basically the fiberglass surrounds the wood and nothing else. This layup for the same weight is stiffer and more impact resistant than a store bought fiberglass composite layup which is really the only advantage in going to wood. Long term you can repair the boat to exactly the same weight whereas a fiberglass hull gets a smidgen heavier every time you patch it up. That said my experience with fiberglass composite boats has been so overwhelmingly positive as I am careful with them that at this rate they might need repairs so infrequently this will never amount to much. In the end the wood/fiberglass already gives you more durability and stiffness than a fiberglass composite, you're more in the fiberglass/kevlar territory in terms of weight/performance but more durable.

Your layup just has too many layers. There's no need for carbon. If you're using carbon I definitely don't think your boat will weigh only 35-37lbs at all. Carbon is super light by itself and can make for some real featherweight boats (look up the OC's for example), like 16-20lbs for a 20ish foot boat with the outrigger and tubes for it. Once you start to mix the carbon with other materials you're going to need epoxy to secure it and seeing as how it's so porous it will take a LOT of epoxy. So in the end the carbon is basically like another layer of fiberglass. Look at Stellar's Ultra layup which is a composite (as opposed to straight) carbon with some Kevlar and fiberglass to give it a teeny bit of impact resistance. The weight difference is only about 15% or so for this reason. So the wood boat is already plenty stiff for paddling and slapping on carbon will be like slapping on another layer of fiberglass weight wise. Slapping on two layers you won't get a boat that weighs 35-37lbs for a 17 foot boat, more like double that.

Like I said I am not an expert on this at all and probably the least knowledgeable forum member. I found this post on a web search actually but thought I would share my tale of woe. If you'd like to ask my dumb, not knowledgeable at all self any questions let me know I will share contact info.

Here's a good read on why carbon doesn't work on wood kayaks. Stick with wood & fiberglass only!

https://metakrome.com/kayak/carbon.html

Brian Nystrom

Sun, 08/23/2020 - 08:19

CA139 - First let's dispense with the 180# "kayak", which is a bizarre anomaly built by someone who obviously had no idea what they were doing. It bears no resemblance to anything people here would build and it's ridiculous to even bring it up.

Second, it's well-known that to get the best results with carbon fiber and Kevlar, you have to use vacuum bagging or resin infusion. If you do so, you can produce lighter, stronger layups than you can with fiberglass. Otherwise, why would other industries spend so much on building with carbon fiber if fiberglass was just as good? If you read Zoltan's posts, he's planning on using one of these techniques, so he should be able to take advantage of the properties of carbon fiber.

Zoltan - I'm not sure what the point of using the thin wood veneers is, beyond cosmetics. From a strength, stiffness and weight perspective, wouldn't you be better off just using a thicker PET core to increase the separation between the reinforcing layers? It would also greatly simply the layup process and insure better resin flow and bonding of the layup, wouldn't it?

Exactly! The 180lb monstrosity was indeed built by someone who didn't know what they were doing and part of that was using carbon on wood and fiberglass and kevlar but I think it's VERY relevant to the OP  because the OP wants to build a boat in a very similar way, and the OP has boatbuilding (as in power/sail not paddle stuff like Kayaks) experience just like the person I knew who built the "monster". What I am trying to communicate is that what works in regular boats doesn't in Kayaks and using my experience as an example.

So to take it from the top, what you are talking about is a Carbon Kevlar layup. That is practical. Weighs slightly less than fiberglass composite, is stiffer, fine it works. But you either do a carbon based layup or a fiberglass based one, not mixing both, then you have the worst of both worlds. I am not saying Carbon is bad, I am saying Carbon with a wood/fiberglass construction doesn't work. Please reference the above link I provided and let me explain

Fiberglass/carbon/wood/carbon/fiberglass in the OP is very similar to the "monster" boat I had except ours had kevlar on the outside too. Carbon and wood or carbon and fiberglass don't go together that well because the carbon soaks up a lot of epoxy so you don't really get much if any weight savings. Only fiberglass really works well with wood. You can build a space age composite with Carbon, Fiberglass and Kevlar (look up Stellar's Ultra layup) along with say a nomex layer but you need to make everything really thin and in the end a wood boat is going to be stiff and durable enough you don't need to go through all that trouble to get that expensive, laborious layup in the first place. In other words the Carbon doesn't help a wooden boat much if at all stiffness wise but greatly increases the weight and cost.

So what I am trying to say is that OP from his boat building experience came to the same flawed idea as the person whose idea it was for our franken-boat from the non-kayak world, mixing carbon on fiberglass layers. It's not needed and just adds a lot of extra weight!