RE: Kevlar/carbon versus fiberglass

[Lbeale]

Yesterday while Karen G and I were paddling near Hog's Island, Essex, we had a "lively" debate. Is the extra $$$ for a kevlar/carbon boat worth it? Of course, we didn't know what we were talking about because neither of us has a kevlar boat. So, for those who have some legimate opinion or insight, is it worth putting out the extra $$$ for kevlar? Does kevlar boats go faster or handle better than their fiberglass counterpart? What were specific factors that helped you decide to go with kevlar instead of fiberglass? Knowing that it is more difficult and costly to repair kevlar, why would you? Was the final decision based just on weight, kevlar being lighter than fiberglass?

Perplexed,

les

[Gcosloy]

Kevlar is much stronger than fiberglass and will result in a lighter boat if used in combination with glass. However Kevlar alone is not stiff enough and is seldom used alone. Boats that are largely Kevlar are very flexible and may just bounce off submerged rocks while a fiberglass boat being more stiff could be damaged more easily. All boats have a gel coat exterior which is less flexible than Kevlar. If you sit on the deck or stern of a Kevlar boat while on land, you may very well cause cracks in the gel coat. The irony is that while a Kevlar boat is more resilient to real damage, you might have to baby it more if you want to preserve it's unblemished gel coat exterior. I briefly owned a Kevlar Ellesmere which while it weighed only 45 lbs. had no other performance advantage over it's heavier bretheren. It was a joy to launch and carry.

[shewhorn]

To add to that in the event of damage it's my understanding that Kevlar is a bit more difficult to repair and that it also soaks up water at a faster rate than glass if you get an area that's rubbed through (like under your heals, etc.).

From my own research the most common advice I've heard as an argument for getting Kevlar is if you must cartop the boat your self and have physical difficulty lifting up a glass boat.

Cheers, Joe

[Kevin B (RPS Coach)]

>From my own research the most common advice I've heard as an

>argument for getting Kevlar is if you must cartop the boat

>your self and have physical difficulty lifting up a glass

>boat.

Agree. Furthermore, if you have difficulty getting the boat on the top of the car, investing in something like Thule's automatic loading system would be much cheaper than the difference in cost between the glass and kevlar boats.

[bob budd]

As an owner of a used kevlar boat the cost is not always significantly more than a comparable glass boat.

I don't know what the "autoloader" costs. Is someone willing to reveal their purchase price?

[PeterB]

You might get a wide range of opinions re: the strength and general soundness of fiberglass vs. carbon/kevlar. Also, layups may vary in quality from boat to boat and manufacturer to manufacturer.

The one thing that all agree on is that carbon kevlar is lighter, so if weight is of prime importance to you, (e.g. if you must handle and cartop your boat alone, much or all of the time) and is worth the extra $$ it would be a good choice, and I wouldn't worry about the layup being better or worse than fiberglass. If weight is not as big a concern , the differences in strength , hull speed etc. are arguable and probably not significant enough to warrant the extra money.

Personally, I see fiberglass as a tried and true product, repairs are straightworward and I can handle the extra weight, so I would choose fiberglass unless I saw a really good deal for a c/k boat somewhere.

If you always paddle with others and handle your boat with the someone's help ( both are generally advised anyway) , I would say; go with fiberglass.

[Deb Millar]

My first boat was a kevlar Slipstream. The weight issues aside, I was not happy with the lightness of the boat which, in turn, affected the kayak's performance. I paddle low volumn boats -- a Vela, a RomanyLV, my husband's Pintail and an ExplorerLV -- and my weight wasn't enough (truthfully, I don't consider myself small, weight or height wise) to keep the Slipstream down in the water unless I carried full kit all the time -- or loaded water bags/bottles when I wasn't stuffing dry bags into all the hatches. I still have to load my boats to optimize my performance, but not as much as I did when in a kevlar kayak. I also found the boat's lightness was affected by wind and current, but then this could have been me at the time, and not the material.

The price differential is essentially $500 between glass and kevlar. The Thule Loading system is, I believe, priced between $350 - $400+. There are a few paddlers who post here who could give you a better figure as they own these, which are a pretty nifty user-friendly invention.

While my ExplorerLV is a hefty gal-- they must have done a high calorie gelcoat load the day she was made -- my Vela and my RomanyLV are lighter and I can load both of them onto standard Thule stackers/cradles without much trouble. True, I have to stand on a step stool to do so and I have an Audi A4 wagon (which might be shorter than the average), but the boats get up there securely without me killing my back and arms.

There are also FG boats whose layup isn't as seemingly heavy as the British-made ones. My husband's Wilderness Systems Tempest165Pro is lighter than either the Romany or Vela, and I've hefted a few in the Impex line that feel lighter also.

I'd go with Fiberglass for all the reasons mentioned here. To me a $500 price differential for about 5lbs of weight isn't worth it.

Deb M

[EEL]

>

>I don't know what the "autoloader" costs. Is someone

>willing to reveal their purchase price?

A Glock 17 9mm runs around $500.

Oh, kayak rack.

The Thule Hull A Port runs around $140

Ed Lawson

[hopefloats]

Thule Hullavator was about $450. Definately an investment but It was a lifesaver when I was loading a plastic boat on top of a high-up jeep by myself. Now that I am using a glass boat, its more of a luxury, but still makes for a quick get-away strapping onto the same high-up jeep.

[eneumeier]

My 7-year old kevlar Gulfstream has never, until now, needed a repair. I am ruthless with it and I routinely launch by sliding off rocks and drag it back in across rocks when I land on my "beach." (I had to learn the hard way not to treat my light-layup glass KS Vivian Avalon the same way.)

So, ALL the gelcoat is gone from a patch on the bottom and I need to epoxy/gelcoat it over. Water seeps in, in tiny amounts. No big deal. The only deck gelcoat cracks are under the coaming rim behind the cockpit, where I put my paddle to brace on entry and exit. (No BCU form for me.)

The bottom has softened up a bit. When I paddle across rocks (just drawn to them I guess) I can feel the hull flex under me. I can't say if it is soaking up water.

The new 2000 Gulfstream cost $600 more in kevlar and weighs 6 lbs. less than the glass version.

I wanted to save the weight and did not want to have to worry about damage to glass when launching alone from my home rocks. I am pleased with my choice for both reasons.

Liz N.

[Gcosloy]

>

>>

>>I don't know what the "autoloader" costs. Is someone

>>willing to reveal their purchase price?

>

>A Glock 17 9mm runs around $500.

>

>Oh, kayak rack.

>

>The Thule Hull A Port runs around $140

>

>Ed Lawson

Remember what Woodie Allen had Alan Alda intone in one of his better flicks, "Comedy is tragedy plus time." Your atempt to amuse falls short because not enough time has passed since the massacre at Virginia Tech. Try again in 5 years!

[risingsn]

I think a lot of the consideration depends on who is the manufacturer. I had a Falcon 18 in Kevlar for about 6 years, basicly a bullet proof boat. Currently I have an Avocet Ultra Carbon boat (Carbon/Kev hull & deck). I have used it for my Canoe Saftey recert, 4* assesment, L3 training & surf work. No cracks , no holes, no errors (or something like that). During L3 training I had an Impex Assatuage (60+/- lbs) & a 200 lb paddle sitting on my bow deck, no problem other than the fact that I almost became a submarine. It also depends on how you treat your boat. I don't baby my boat but I do take care of it. On the other hand I have a freind who can turn a new boat into a 7 year old boat in about 6 months. I have also seen some glass boats that are just to thin to be up to the task. Depending on the boat flex should not be an issue. The hull of my Avocet is very stiff, but the deck has some flex yet I have had no problems sitting on it or standing on it in the water (OK, trying). Yes, if you are to light for your boat (I was for my Falcon) than their will be control issues but I would rather add weight as needed that to lug it all of the time. Personally I would always go with a lighter boat assuming it was up to the task.

[Lbeale]

Thanks everyone for your helpful responses. I asked the people at Impex and their response was also helpful. It seems that for the Impex Force 3 at least, yup--it does make a difference--stiffer hull, more acceleration (i.e., slightly faster) and supposedly more extension or follow through with lower body paddling movement--not to mention 6lbs difference at the end of the day--so as someone stated in the thread, maybe it does just depend on the boat and the paddler--the question now, does carbon/kevlar require or is it strongly recommended keel strip (yet another cost factor)--Les

[EEL]

> Your

>atempt to amuse falls short because not enough time has

>passed since the massacre at Virginia Tech. Try again in 5

>years!

Point well made and taken.

Ed Lawson

[risingsn]

Les, I do have a keel strip on my Ulta Carbon Avocet. I did it more for protection than because on the material the boat is made of. I estimate that it adds between 2 & 3#. I think you will be very happy with an Impex Force boat, I have paddled the 3 & 4...very nice. Also Impex is a great company to deal with. Enjoy!

[Brian Nystrom]

"-stiffer hull, more acceleration (i.e., slightly faster) and supposedly more extension or follow through with lower body paddling movement-"

None of this makes any sense at all, unless the boat is a different shape from the fiberglass version.

"-not to mention 6lbs difference at the end of the day-"

This is the real difference.

[jason]

Brian,

When they say Carbon/Kevlar has less flex that is compared to just a normal Kevlar boat. I know that when I carry my Kevlar boat it flexes where I grab it.

-Jason

[subaruguru]

I've made successful repairs in a cracked/frayed Kevlar layup simply with epoxy. The woven Kevlar fabric imparts enormous strength AND flexibility, while staying light (note its use in some loudspeaker cones, where its lightweight results in speed, but its compliance reduces resonance ("ringing" overtones).

Kevlar hulls' stiffness is provided ONLY by the liquid substrate and gelcoat surface. Hence they can crack easily, as Gene points out.

But 100% carbon hulls are VERY brittle and thus fragile upon impact. I haven't seen many fractured hulls, but have seen several smashed Trek OCLV (all carbon) bike frames. Quite the mess, and extremely difficult to repair.

Lightweight stiffness, but no compliance or forgiveness.

Thus the Kevlar-Carbon matrix: carbon fiber for stiffness, Kevlar for resilience.

Cracks/fractures tend NOT to migrate (unlike fibreglass), as the weave acts like a "ripstop" in woven nylon, for example.

Re Impex, It's interesting that they use C/K for the hull, but because it IS difficult to lay in the nooks and crannies of the deck contours, still use glass up top. Hence the weight savings isn't as much as other manufacturs who use 100% C/K. My Force 5 weighs 52.5lbs in C/K, rather than the 49-50 expected by its dimensions. It's STILL a bear to load solo broadside to an Outback, as I don't unload it, so net is about 60lbs with paddle, float, pump, etc.

If you're getting an Impex Force and you don't like the seat hangers pinching you let me know, as there's a recourse for the wide-hipped.

[Brian Nystrom]

"When they say Carbon/Kevlar has less flex that is compared to just a normal Kevlar boat. I know that when I carry my Kevlar boat it flexes where I grab it."

Jason, I don't doubt that at all. However, the claim that the boat is faster is simply wrong, as speed is not a function of boat weight or hull stiffness, it's a function of the various drag components and the power of the paddler. Yes, there will be a minor difference in acceleration with a lighter boat, but when you consider that the combined weight of the boat, paddler and gear is going to be between 200 and 300+ pounds, a 6 pound difference isn't going to affect acceleration much.

The claim that the MATERIAL affects your stroke follow-through is just plain ludicrous.

I'm not trying to discourage anyone from buying a Kevlar/carbon boat, I'm just not buying the rationale that was given to Les by the dealer or manufacturer. The bottom line is that you get a better stiffness-weight ratio, which means the boat can be either lighter or stiffer than a similar fiberglass model, but most companies choose to make their boats lighter, since that's what consumers want and expect in a high-end layup. The main benefit is ease of carrying, plain and simple.

[scamlin]

Brian:

I think the theory is that a stiffer hull has speed benefits for both acceleration AND once at cruising speed. In both cases, flexing of the hull is asorbing the paddler's energy instead of transmitting it to forward motion. I could also imagine that flexing could create more distortions in hull shape and therefore more turbulence and drag. In these senses, kevlar and glass hulls that come out of the same mold may not act the same in the water.

Granted the differences are small (as both Impex and Leslie pointed out) but over the long haul, may add up. One practical demonstration of the effects is that racing boats are not only very light, they are very stiff. Same theory as for for bike frames, which are also very stiff.

Rather than dismiss out of hand the effect on stroke follow through, I'd be curious what the rationale is.

Scott

[Brian Nystrom]

...but if you really think about it, it doesn't stand up to scrutiny.

1- Where is hull flex robbing power from the paddler?

Power is transmitted to the boat at the butt, thighs and feet. There is no significant flex at the first two points, so that leaves the foot braces as a potential point of lost power. I have yet to paddle a boat that flexed enough there to make any difference. If foot brace flex was a real power-robbing issue, those of us who pad our bulkheads with (flexible) Minicel foam should notice that we're moving slower than we did with foot braces. Has anyone ever reported that?

Keep in mind that the average paddler only applies 8-10 pounds of force to their paddle with each stroke. Even if all of that was transmitted through the foot braces (which it isn't), how much hull flex would it actually cause?

2- The racing boat hulls I've seen are so thin and soft that you can't enter them on land without risking damaging them and they feel like you could push your thumb right through them. Yes, they're relatively stiff along their length, but that's true of touring boats too, probably even more so.

3- If stiffness really made a difference in speed, fiberglass boats would be faster than their Kevlar or carbon/Kevlar counterparts, as manufacturers invariably make their high end layups lighter than their 'glass layups, rather than stiffer, or even as stiff.

4- "Oil-canning" type of flex is not going to occur to any noticeable degree in a touring boat except in really rough water, where it's not likely to make a significant difference in speed.

5- I have yet to see ANY company publish ANY hard data on this subject. The only information available consists of marketing claims and theories, neither of which are reliable indicators of real-world performance.

As for stroke follow through, if you're comparing two boats that are identical except for the hull material, I don't see how there could possibly be any difference. That sounds to me like something you'd hear from a salesman who's grasping at straws for selling points for a product. Frankly, it's rather silly to go to that extreme, since most people who buy boats with high-end layups do so because they're lighter weight and that's all the justification they need.

[Lbeale]

So does the rationale of stiffer boat result is faster boat negate wooden with fiberglass overlay kayaks for speed? My Night Heron @ 17' is light, fast yet I doubt it is as stiff as a C/KV boat--NIck S. may answer this question with more insight than me but I tend to support Brian's logic due to paddling the NH-- Les

[donperry]

Think of the hull as a series of cross sections from bow to stern. They are called stations and are spaced, say, 1 inch or whatever apart. Typically they are mutually symmetrical about a central vertical plane. Each successive section either varies from or is identical to one of its immediately adjacent neighbors.

When the hull is placed in the water static displacement floats your boat. It equals the weight of the loaded boat.

As the hull advances water molecules have to move from one station boundary to the next. Dynamic displacement requires force to move the water molecules and it limits the speed you can paddle.

If the hull flexes there is a change in the relationship between adjacent station sections. So the dynamic forces acting on the hull have to change there also. Wherever the water has to accelerate more to pass the hull there will be more resistance than normal.

I’d agree with Brian that this can’t be noticed in any of the boats we usually paddle. It’s the kind of thing that might show up in an inflatable kayak with low pressure. Yet the manufacturers can claim a stiffer boat is faster than a more flexible one.

[Brian Nystrom]

In order answer your question, it's necessary to do an apples to apples comparison. The majority of commercial boats have curved hulls, which by their nature are stiffer than flat panels of equivalent construction. However, if you could find a commercial boat with similar panel shapes to your Night Heron, you would probably find that your hull is actually much stiffer. Wood core construction separates the inner and outer fiberglass layers, which results in a dramatically stiffer panel. For the same reason, cedar strip/fiberglass boats are MUCH stiffer than commercial composite boats, despite being considerably lighter than most.

It's also important to understand that a stiff hull is not a panacea.

While a stiff hull may be most efficient in flat water, there is evidence that flexible boats (in the size range of typical kayaks) may be more efficient in rougher conditions. Among other things, the Aleut built their baidarkas with joints in the keel specifically to allow them to flex over the waves and swells they dealt with daily. If the boats didn't work better, they wouldn't have gone through the extra trouble to make them flexible. While it's easy to be dismissive of ancient cultures, their boat building was quite sophisticated.

Additionally, a hull that flexes is less likely to be damaged when it hits an obstacle than one that's rigid. A flexible hull distributes impact stresses over a large area as opposed to a rigid hull which tends to concentrate them in a small area, increasing the likelihood of localized damage. Flexible hulls are also more likely to bounce or slide off of obstacles, rather than "sticking" when they hit.

FWIW, I'd rather have a boat with some flex in the hull, as impact resistance makes a substantial difference to me, certainly more than an infinitesimal difference in flatwater speed.