CigDaze

Quiet Storm,

Frankly, I have no idea what resins Cig used in the early 90's but by then most manufacturers were using element resistant, toughened resins. I wouldn't worry about that hull.

CigDaze

Additionally, for comparisson, below are some property values for the three materials. Keep in mind these values are at optimum resin ratios.

Modulus of elasticity(stiffness)
Glass: 2,600,000psi
Kevlar: 3,100,000psi
Carbon: 8,700,000psi

You can see how much stiffer Carbin is than the other two.

Here are ultimate strengths for bi-directional woven fabrics:

Glass: 25,000psi
Kevlar: 51,900psi
Carbon: 87,900psi

Now, here's how they compare in terms of weight:
Glass: 0.072 lb/in^3
Kevlar: 0.061 lb/in^3
Carbon: 0.054 lb/in^3

Here are the strength to weight ratios:
Glass: 333,333
Kevlar: 850,819
Carbon: 1,627,777

You can see that Kevlar is about 2.5 times as strong per pound of glass and Carbon is about 5 times as strong per pound.

MrCIG

iTrader: (1)

Roger,
Jimmy's Cig is Kevlar and mine is fiber glass there is a significant weight difference between the two. Cigarette says 1000 lbs. Jimmy's is a 86 and there doesn't seem to be any brittleness problems.

You can see the difference the way they sit in the water.

There was a cost difference between the 2 but i don't remember what it was. Jimmy may have that info.

Also neither one of them my 85 and his 86 have stress cracks in the hull.

Mark

The Menace

I had a glass CIG and now have a Kevlar TG. The Kevlar does not flex like the glass. Two different rides. No stress cracks and very solid. If you had a boat of each material described above side by side and hit the hull with your palm like a bongo, each would resonante significantly different.

Baja Daze, those numbers are impressive.

chromecat

baja daze...

isn't it true though that kevlar stiffness factor isn't that high but that is why it was used. i thought they used it because of its ability to bounce back and not break down as fiberglass and other more rigid fabrics do.

Don

mcollinstn

Early Kevlar bassboats delaminated cause they sopped resin on too heavy cause that was easier than getting the cloth to lay properly otherwise (from a friend who worked at HydroSports). They got to where they only let a few good glass men do the layups on the Kevlar boats after that and had no more problems with them. They charged a pretty good upcharge for theKevlar cause it cost more AND they had to use the experienced (and more expensive) labor. The grunts still layed up all the glass boats.

Bulldog

Kevlar is stronger even with a lighter layup. The only concern I know of is that epoxies have very low UV resistance, and some if not many Kevlar hulls used epoxy on the layup. The gelcoat is polyester based, and acts as a barrier, protecting the epoxy underneath.

My hull is Kevlar/epoxy, and it basically booms like a big subwoofer when you beat on the sides or deck. There are 8 bulkheads, with black carbon fiber tape reinforcement in the sides and under the hatches. 3 person standup, 38 footer, roughly 8000 lbs ready to go.

Good topic!

puder

i know of the fomula cars we wear areas in kevlar. Like the bottoms are sidepods. Its ie much mor eresistant to abrasion than fiber aand the carboin fiber. The CF is more rigid and stonger and used in structural elements like carbon monococques.

CigDaze

Kevlar's stiffness is slightly more than glass, about 20% as shown in the above numbers. HOwever, glass fibers have a crystaline molecular structure, while Kevlar is a polymer. Though Kevlar may be stiffer, when you examine the modulus curves(load vs deflection plots), glass will flex very little at the onset and all the way up to the point where it's about to let go. Kevlar will flex much more gradually throughout it's entire load curve until breakage. There's the advantage! In other words, glass will suddenly and violently fracture(because of it's crystalin structure); hence the brittleness. Kevlar will stretch gradually and fail slowly. This is also one of the reasons it's successful in bulletproof vests. It can dissipate energy more gradually.

CigDaze

Absolutely right, Puder. Additionally, Carbon parts must usually be well protected, otherwise they usually have some kind of protective layer, because it is so sensitive to scratches and abrasion.