Vacuum Bagging vs. Hand Lay up

I was curious what the real advantages/disadvantges are of vacuum bagging vs. hand laid glass. I own a Nimus Telkwa and I think it’s a nicely done lay up, but I do notice a certain “give” or flex in both the deck and parts of the hull. A friend of mine has a Valley boat and the thing is like a rock in comparison. I suppose the real issue here is weight, but I’m wondering if there is a certain advantage to a beefier lay up that is hand laid and not vacuum bagged. Also, it seems the gel coating on certain boats (i.e. Valley, NDK, etc.) is fairly thick compared to my Telkwa. A boat designer told me recently that he feels a certain (but small) amount of overall flex is a good thing and that vacumm bagging allows for that flex - but I’ve also heard the opposite. Just curious to get your thoughts on this.

isn’t the valley kayak a handlayup too?
various types of vacuum bagging can standardize the amount of resin used as well as control air pollution in curing resins compared to hand lay-ups but the physical characteristics of the final product are more a function of the materials and design than how it’s put together. For example you could have two identical designs made with any construction technique,but one is made with woven roving and one is made with a corematerial between lighter glass. The one with thick roving ‘might’ be more flexible and might be more durable,but then again it might not depending on the shape or weight of the materials.

A great question…
and response by LeeG…something I have always wondered about. Although there are a number of folks on this site who will be able to respond like LeeG…you might also want to raise this question on where most of the very talented builders hide…



– Last Updated: Feb-09-05 8:36 AM EST –

is simply a way to evenly squeeze the composite layers together and squeeze out excess resin. There's no magic about it.

For equal layup schedules, the bagged version should have a higher glass-to-resin ratio, be lighter, and possibly thinner. Since stiffness goes as the cube of depth, that might account for some variation in stiffness. Adding bulky layers like chopped-strand mat adds stiffness because it adds thickness. Extra resin adds a lot of weight without a significant increase in strength.

But there's no point in comparing bagged boat A to hand-laid boat B. There are too many variables. The only meaningful comparison would be same boat, same layup schedule, same mold.

Probably the stiffness difference you
noted was more due to the cloths used and the number of layers than to the difference between hand layup and vacuum bagging. One of my vacuum bagged boats, a 17’ canoe, is a bit flexy in the sides, though stiff in its foam core bottom. The other, an S-glass/carbon slalom hull, is incredibly stiff, which was desirable for the Olympic paddler who designed the boat and raced in it.

Both VCP and NDK use chopped strand matt in their boats, which makes for a stiff, heavy and not especially strong layup, especially since they’re not vacuum bagged. The matt tends to soak up much more resin than woven cloth. A vacuum bagged layup with all woven cloth would be thinner, lighter, more flexible and stronger.

I’m doing a chine repair on my Anas Acuta currently and the layup is suprisingly thin at only .100". It’s a bit hard to tell, but it appears to be simply one layer of coarse woven Diolene on the inside, one layer of matt and gelcoat. I’m not impressed.

From your posts, it appears the flex I feel is not necessarily a bad thing. My Telkwa uses non-crimped fabrics and have a polyester thread woven around the fibers for impact resistance. There are also Kevlar reinforcement strips in the bow and stern, which I assume is fairly standard these days. I know the seam is glassed on both sides. Also, I’m assuming most boats now use vinyl ester resins as my Telkwa does??

they do.
the only manufacturers who use polyester resin are the super cheapos. it is a bit surprising that while many elite paddlers prefer British boats, many would also argue that NAmerican (and many renowned Canadian) boats use more sophisicated, and higher quality constructions. very few of the Brit boats i’ve seen have the same consistency or overall build quality that Cdn boats in particular show.

a question about Diolene. is this the same as chemically activated polyester fabric? it seems like a trade name and i remain fuzzy about it’s difference and characteristics…

No, Diolen is not the same as CAP.
Diolen is peculiar stuff. Slides well, wears smooth. CAP will fuzz when it wears because of the toughness of the polyester. The advantage of CAP when used with vinylester is that the resin literally eats into the surface of the cloth fibers, making an unusually strong bond. Vladimir Vanha of Noah was one of the first to use CAP with vinylester, and his laminate could be literally bent double without cracking or getting floppy. I know it from folding pieces of a Noah CAP kayak I have when I installed a keyhole cockpit.

There would be nor reason to use CAP with an epoxy boat, except as a cheap alternative to Kevlar to add toughness. But if vinylester is used, CAP may have some advantages over Kevlar, because it bonds better to the resin than Kevlar.

Diolen should not be viewed as adding much strength to a boat. An outer layer of S-glass or even E-glass will add more stiffness, though it will not wear quite as well. Diolen sleeves are often used on wooden canoe paddle shafts to protect the wood from wear. Glass would not work for that because the glass would irritate the hands while wearing.

Valley layup
My Aquanaut has thicker gel coat than the North American boats I’ve been able to examine. The hull withstands more abraison without exposing the fabric than boats with thinner gel coat.

My boat’s layup is Valley’s ProLite (Carbon/Kevlar). It seems very stiff. Of course being a Brit hand layup with thick gel coat, my ProLite boat is only light by Brit standards - it weighs slightly over 50lbs.

What the hell is an elite paddler?
are you sure you don’t mean emotionally aloof.

Erroneous info about Diolene

– Last Updated: Feb-11-05 12:01 PM EST –

Diolene IS polyester fabric, like Dynel. A quick search on the web will confirm this for you. I'm not familiar with CAP, so I can't say how the two compare.

VCP boats have Diolene in the lay and after doing repairs on several of them, it apppears that the only thing it could be is the innermost layer, since the rest of the layup is chopped strand matt. The Diolene fuzzes badly when abraded. Anyone who's owned a VCP boat for any length of time has probably seen this where their heels rest on the hull.

Why Brit’ boats are popular.
It’s all about the performance. In general, Brit’ boats are outstanding handlers, particularly in demanding conditions. That’s why people - myself included - buy them. Sadly, many of them suffer from inferior materials and quality control. NDK’s absymsal quality is legendary. VCP is significantly better, but still lacking somewhat. P&H seems to be the best of the British sea kayaks commonly available in the US. Still, none of these are up to the quality standards of North American built boats. It’s a real shame and there’s NO excuse for it.

“Elite” vs. "Elitist"
I think what jbv was referring to could be termed “top echelon” paddlers, the best of the best. The term “elite” can be misconstrued, as you apparently did. As with most sports, the people who are truly the elite performers are generally pretty low key about it. This is true of all the best paddlers I’ve been fortunate enough to meet. It’s the “wannabees” that are generally elitist jerks.

best of both
It is ideal if you love a Brit design kayak that is built by Canadian or good American manufacturer. Among such boats are the Nigel Foster boats built by Seaward and the Derek Hutchinson designs built by Current Designs.

Impex makes and is expanding their line of Brit style/influenced boats. Impex boats are well made and tend to perform well.

Can’t bring closure from my end
until I locate my copy of Walbridge’s Boatbuilder’s Manual. The material I am talking about is used for exterior wear, and certainly would not fuzz in the way you describe.

Following is John Sweet’s comment on
Dynel. Obviously I was confusing it with Diolen.

“Dynel fabric has very high abrasion resistance but swells in the resin such that it works better if vacuum bagged or pressure molded. The most common uses of this fabric are for wear patches on boats, edgings on paddles, and the like. It has also been used as a deck covering on wooden sailboats. It seems to be a good choice anywhere that abrasion is a major issue.”

This is not CAP, and it is not the polyester used as an alternative to Nylon and as a cheap sub for Kevlar. Sweet does not say whether it is some other kind of polyester. Dynel does not fuzz, but it is not particularly strong, either.

Gelcoat thickness
What I’ve been told and have observed about gelcoat is that a kayak with a thick gelcoat is more likely to crack and / or chip following impact with a hard object or surface. A thick gelcoat is also more likely to develop cracks if the hull flexes significantly – even when tying the kayak down on your vehicle. A thin gelcoat, while providing less protection to the underlying layup, has more ability to flex and thus is less likely to crack and chip.

It would seem the worse combination would be a thick (think rigid) gelcoat over a thin flexible cloth layup.

I’ve heard of and seen spidering and gel coat cracks on Impex boats and QCC boats. Neither has a thick gel coat.

I am not aware of gel coat cracking being an issue on Valley boats. I know that NDK boats have had a number of issues, but I don’t know if gel coat spidering or cracking is among them. Some NDK boats have thicker gel coats than Valley boats.

Spider cracking
QCC and Impex hulls (and also most American and Canadian boats) are designed with thin, low resin layups that flex under pressure. If pressure is applied and the underlying layup is able to flex more than surface gelcoat, the gelcoat may crack. At one point, someone bumped the bow of my Q400X into the side of concrete pool, knocking out a big piece of gelcoat. (The gelcoat is signficantly thicker on the bow and stern than elsewhere). Other than that, I’ve never had any gelcoat damage to my fleet of QCC boats.

The alternative is a boat with a thick heavy gelcoat and a thick heavy layup. And these boats do not seem immune to spider cracking in the gelcoat either – I’ve seen some older Brit boat hulls that are thoroughly spider cracked.