Vacuum Bagging vs Vacuum Infusion

A good explanation of vacuum infusion.

chopped/blown carbon/epoxy
I was chatting with a fellow who said that’s how some high strength low cost production is done. Kind of a updated version of chop strand glass like cheap old fiberglass canoes.

That you really don’t need long fibers for a strong laminate. Sounded neat

What gets me is that while the infusion method that Necky uses should be better you still need core materials for rigidity or be careful were flexible sections meet rigid sections without developing stress risers. In the big picture it seems like a conducive way to reduce assembly labor as well as making a higher glass/resin ratio laminate but I wonder, regular vacuum bagged roving works.

Until reading this I didn’t understand what the difference between bagging and infusion was or if there was a difference in the two processes.

In my Valley Ultra layup (infused) it looks very dry and the only resin to be found (seen) is on the deck seems and bulkhead seals. Quite amazing.

I had a Chatham 18 and it was a trip to look around the inside, absolutely no shiny wet areas.

Big difference in the WS boats too

and QCCs garden variety vacuum bag layup makes for a light boat. My old Express wasn’t light, but it was sturdy.

Just out of curiosity what is the Tempest layup like? Is it all glass, does it have a full core like Current Designs boats or does it have partial core like Neckys?

What do mean by core? I don’t fully understand yak construction.

easy peasy eh?
think i’ll go vacuum infuse me a home made kayak…

fiberglass reinforced plastic, frp
1. fiberglass cloth, or any cloth. It’s flexible and strong in tension. If you tried to make a kayak out of it it would be as solid as a big sock, fill up with water and sink.

2. plastic or resin that hardens after formed into shape. It’s good in compression. Imagine a block of plastic, you could stand on it. If you made a kayak out of it it would have to be thick or it would break like hard glue or bend like flexible plastic sheet. Or you can make it out of plastic that’s good all by itself and make rotomolded polyethelene plastic,but is a bit heavy.

3. so combine the two, glass cloth and resin/plastic(different than polyethelene). But to make it light you don’t want it too thick and heavy so you make it thin as needed to hold a shape and handle impacts. But some shapes are inherenly flexible. A flat sheet of material is more flexible that a ball of material, imagine an egg compared to a flat thin sheet of ceramic material. The same material but one is strong and one will break easily.

4. Back to the combination of cloth soaked with a stiff resin matrix. Now the floppy cloth material is pretty rigid and waterproof. But some areas are not as rigid as other. Small curved areas are stiffer than large curved or flat sections. Instead of simply making the glass/resin laminate thicker and heavier you make it with a core material with cloth on both sides. A core material could be made with something light and traps air within it to give the laminate some thickness without adding much weight. Think of a thin felt like material about 2mm thick.

Once you do that you make the laminate stiffer. Kind of like how it’s harder to bend a 2x4 through the 4" thickness than the 2" thickness.

5. Ok,so some kayaks are built with just cloth and heavier amounts where rigidity is needed, some are built with cloth and core material in selected places, some are built with less cloth and more core material.

Vacuum infusion
Pretty good explaination of vacuum infusion, with several hard parts left out.

Vacuum bagging, by the way, is wet laminating a boat, then sealing it under a nylom film and applying vacuum to compress the laminate and remove excess resin. It has the disadvantage of combining the mess of contact or hand lamination, with the expense of bagging = all done at a frenetic pace. Bagged hulls have fewer voids and are thinner and lighter than contact laminated ones, even after adding extra material layers to maintain hull thickness and stiffness. Catch traps are always needed because excess resin is placed in the laminae, then drawn out.

Vacuum Infusion is cleaner, in that the hull is layed in the mold dry, yielding more precise partial placement. One can stop and answer the phone because resin has not been catalyzed. The trick with infusion is to get the resin to completely wet out the part.

Infusions where weight is not an issue can use porous core materials to build thickness and promote resin transfer. Foam cores can also be punched and scored to aid in resin transfer.

Untra light all cloth laminates used in aerospace and some watercraft require low centipois resins and carefully thought out ducting to work. Unidirectional fabrics help.

The benefits are considerable: contact lamination yield ~ 45% fiber content, all cloth infusion about ~55%. Several aerospace products are turning to infusin because the additional fibre content gain available through prepreg materials, 2%, does not justify the price increase of the prepreg, about 100%, and the cost of an autoclave. We’ve been told a used autoclave fitting our 12 to 15 foot boats would cost ~ $500K. Is the world ready for a $20,000 canoe? Doubtful.

Reusable silicone bags with built in ducting save production time, but as they cost ~$1K per hull, some sales volume is indicated. The catch trap is needed only until a precise resin amount is arrived at by trial and error. From that point on, measure, catalyze and let the vacuum draw in the percise amount of resin required to wet the part. Variation in part weight disappears as an issue.

Surface condition of the part has nothing to do with vacuum bagging verse infusion. The mat finish mentioned is a function of covering the innermost cloth layer with peel ply. Use of release film gives a shiney surface. Examples: Bell Canoe wet bags and uses release film; shiney interior. Placid boatworks infuses with peel ply; mat interior finish. Both release products free the interior surface of resin caught in folds in the bag and in delivery ducting. Without a release layer the spiral tube down the hull center would be part of the boat for all time.

There is more concerning resin chemistry that is sfecific to each resin, laminate schedule and hull - pretty closely guarded proprietary information.


Is the structural integrity a …
…product of design, or is it the core material, or both? What is typically used for the core material?


QCC didn’t vacuum bag last I heard…
… but most would swear they do something based on the quality/consistency and minimal resin. Shows what a LOT of composite experience and careful work can do. Notice the initials QCC - Quality Composites Corp. They are composite experts building kayaks - not kayak experts learning to work in composites. For design - they look to Winters and customer feedback.

When I hit LOTTO, I have have some work for them if they have time for OEM.

wow,I guess that explains the raised pattern in the weave instead of smooth with little wrinkles here and there. It looks very clean.

that’s like asking what makes the structural integrity of a wall. It’s the whole package.

Do you mean what gives the flexible panel rigidity? It’s seperating the thin resin soaked fiberglass cloth into two layers, one on either side of the core material. So it’s like a 1/8 thick laminate instead of 1/16’ thick but the middle 1/16 is a relatively dry/airy material that doesn’t soak up resin.

You can have an air core, look at a door or a hollow wall, full of air and very rigid.

You can have a thick foam core like surfboard with a fiberglass skin over foam.

In this case the thin core material has very little structural significance beyond the space it provides for an I-beam effect. If you try and bend an I beam one side is in compression and one side is in tension. Same thing with that little 2mm piece of corematerial.

Earlier Necky kayaks used 1/2 round dowel covered in glass as a hull stiffener. My old Express had a 3" wide strip of core-mat.

Plywood kayaks use plywood as a core material that is already strong and increases it with a relatively thin fiberglass/epoxy skin.

Core materials in and of themselves aren’t anything magic or exciting. It’s like saying your car is made with plastic, it’s neither good nor bad. It’s just a part.

With respect you dont have a clue of what you are talking about here. If ever in the PNW I will introduce you to people who do. OK

That’s good!
People…resin does not equal strength!

I really like you, and so want to educate you. Please email me for my cell #.

Thanks Charlie

I appreciate the kayak sructure 101
I never quite understood what was involved with the layup of a composite boat. Thanks for shedding some light.

LeeG agree w/ Salty here …

– Last Updated: Jan-27-07 2:35 AM EST –

Cores DO have structural importance.

In first post your friend might have been talking about SMC type process. Choped fiber "preform" layed into mold with either a "shot" of resin or sandwiched between upper and lower resin paste or films. Generally used in automotive industry under extreme pressure from matching Nickel ot SS. molds.

Edit, one of the most expensive methods out there .... fast but will never see in kayak industry.