Fibreglass vs Aluminium Impact Strength

[carstenb]

Originally Posted by chala

By writing

This may suggest that the protective coating of a steel boat should be replaced after 12 years and also that a GRP boat should be replaced after 12 years.
It makes me wonder which will be cheaper to replace?

I must admit that to her benefit the boat in the picture does not show ugly rust mark.

Wow, now I know why I sold my first boat. It was 30 years old. the guy who bought it is probably at the bottom of the ocean looking up, after the boat dissolved......
well, not really, just saw him last summer sailing along fine.

if 12 years is the case, why is scrapping a fiberglass boat such PITA?

[silverp40]

Quote:
why is scrapping a fiberglass boat such PITA?

Quote:
there are no junkyards full of FRP boats

Getting rid of a boat is shockingly quick and not fun to watch -

A backhoe with a reasonaby skilled operator will reduce a 35' glass boat to small pieces in about 1/2 hour. A medium size backhoe will also take apart an aluminum boat relatively quick.

Another hour to load up 2-3 dump trucks and it's off to the dumpsite. The keels take longer but usually are cut up and the lead/iron pigs separated (and most of the time recycled).

Steel is usually harder and gets cut up with a torch/plasma cutter, depending on size of boat.

ever try to get rid of one?

Unfortunately yes, Pearson Triton 8 hours with skillsaw.

[daddle]

Okay. Good. That must be why they make bullet proof vests out of aluminum rather than Kevlar. The same Kevlar which boatbuilders use to protect the bows of FRP yachts ... Oh wait ...0

[Andrew Troup]

Interesting that they don't bother using kevlar to protect the bows of aluminium yachts...

[noelex 77]

Ned Kelly used steel pretty effectivly

Kevlar does have very good impact resistance and is light weight and can be made slightly flexible all of which are great properties in body armour.

I do think the the very minimal Kevlar layup with polyester resin that is frequently used is more of a nominal token, designed by the marketing department.

It is possible to make an excellent, strong, light impact resistant hull with a layup consisting predominatly of Kevlar and epoxy. It's a pity no one does it.
Aramid cloths are horrible to work and very hard to get right, without delamination problems etc, which might be part of the reason.

[goboatingnow]

Originally Posted by noelex 77

Ned Kelly used steel pretty effectivly

I do think the the very minimal Kevlar layup with polyester resin that is frequently used is more of a nominal token, designed by the marketing department.

.

Have you specific knowledge here. I'd be interested to hear it.

Dave

[minaret]

Originally Posted by noelex 77

Ned Kelly used steel pretty effectivly

Kevlar does have very good impact resistance and is light weight and can be made slightly flexible all of which are great properties in body armour.

I do think the the very minimal Kevlar layup with polyester resin that is frequently used is more of a nominal token, designed by the marketing department.

It is possible to make an excellent, strong, light impact resistant hull with a layup consisting predominatly of Kevlar and epoxy. It's a pity no one does it.
Aramid cloths are horrible to work and very hard to get right, without delamination problems etc, which might be part of the reason.

Ever actually work with aramids? I have, a lot. And believe me, even a minimal Kevlar layup will dramatically increase penetration resistance. Ever try to grind Kevlar? Or cut it with shears? Special tools are required. We just finished a large job that came to us from another yard. When they started grinding on it they just gave up. It had a layer of Kevlar over the bottom, right at the surface where it should be. It is absolutely impossible to" make an excellent, strong, light impact resistant hull with a layup consisting predominantly of Kevlar and epoxy". A Kevlar lam has very little panel stiffness. That's why it's almost always paired with carbon fiber in a layup, the two materials are almost totally opposite in their properties and thus compliment each other quite well. Carbon is extremely stiff and strong, but slightly brittle. Kevlar is not strong at all, very flexible, but incredibly resistant to point loading. Body armor is a terrible thing to compare to, it has very specific needs. The aramid fibers in body armor are dry, not in a resin matrix, which is why armor is light and flexible. And the new gen of body armor is no longer aramid, now they make it out of spun UHMW fibers-Starboard! If you made a boat with nothing but Kevlar in the layup, it would flex like a noodle.

[noelex 77]

Originally Posted by goboatingnow

Have you specific knowledge here. I'd be interested to hear it.

Dave

Is that knowledge of Ned Kelly, body armour, or fibreglass layup

Wandering around boatyards is very illuminating. There are always lots of damaged sailboats and their failure mode says a lot.
It's easy to pick the yellow fibres of Kevlar in the laminate. it really is just a token effort in all the production boats I have seen. (the only exception that has ever looked a little more substantial, in a production boat, was the plywood RM series)
For example a Jeanneau I saw last year, with bow damage, had a thinner layer of Kevlar in it than a model boat that I built out of Kevlar many years ago. It was a Marblehead yacht about 3 foot long!
I think these strategies are driven by the marketing department. The boat can legitimately add "Kevlar reinforced" even if it is small section of the laminate over a small area.

Given the problems using Kevlar, and the difficulty repairing it, further reinforces this is a token effort to attract buyers, rather than a serious effort to build a superior laminate.

It is a pity because there are some wonderful materials available, but the cheapest polyester resin and chop strand mat comprise most of the layup of many boats.

[noelex 77]

Originally Posted by minaret

Ever A Kevlar lam has very little panel stiffness. That's why it's almost always paired with carbon fiber in a layup, the two materials are almost totally opposite in their properties and thus compliment each other quite well. Carbon is extremely stiff and strong, but slightly brittle. Kevlar is not strong at all, very flexible, but incredibly resistant to point loading. .

It is difficult to know the ideal layup for a cruising boat, because it is rarely done. The sudden failure mode of carbon fiber and its brittle nature would concern me in a cruising boat and I would be inclined to use it sparingly.
Carbon fibre and kevlar is commonly used in racing boats, but their goals or slightly different.
I would favour a solid laminate of predominatly Kevlar and E- glass with epoxy resin for an ideal cruising yacht.
This would need to be professional engineered, but the goals would be a strong, puncture resistant and osmosis free Without the concerns of water penetration and delamination that accompany cored structures.
This is very different to the goals of race boat (light and stiff), or a production boat (low cost).

[chala]

Originally Posted by europaflyer

And a steel yacht would not have suffered similarly catastrophic damage?

Do not know. I have seen a lot off crumpled one but never one sliced like this.

Originally Posted by carstenb

Wow, now I know why I sold my first boat. It was 30 years old. the guy who bought it is probably at the bottom of the ocean looking up, after the boat dissolved......
well, not really, just saw him last summer sailing along fine.

Great news. So you reckon that the protective coatings on my boat should last 30 years + without showing sign of deterioration?

Originally Posted by minaret

Ever try to grind Kevlar? Or cut it with shears? Special tools are required.

Must be different types of Kevlar. The one I bought to reinforce the leading edge of the rudder was easily cut with scissor and Stanley knife.

Originally Posted by silverp40

Getting rid of a boat is shockingly quick and not fun to watch -

Steel is usually harder and gets cut up with a torch/plasma cutter, depending on size of boat.

A 230mm angle grinder with a thin inox cutting wheel is much faster, will cut SS, less heat, less chance for the paint to catch fire (does not affect the steel but protective coatings do burn the same than GRP boats) but make a lot of noise.

[minaret]

Originally Posted by chala

Must be different types of Kevlar. The one I bought to reinforce the leading edge of the rudder was easily cut with scissor and Stanley knife.

Helps if you do more than an amateur amount of work with it. Sure, regular shears will cut kevlar cloth-for a few feet- before they are dull. If you actually build things with these materials, special tools are required.


Kevlar: Woven - Scissors | Cutters | Trimmers | Cutting Tools - Wolff Industries, Inc.

[chala]

Originally Posted by Panope

If I wanted to lie naked on my decks, I would not want a metal boat.
Steve

Why?
Steel is a good heat conductor and dissipates it well. The submerged surface of a boat sinks the heat well. By comparison it is nearly 12 degree C colder than plywood.

Originally Posted by simonmd

It's not great in really hot climates, teak can hold heat very well and in summer certainly, its impossible to walk on in bare feet!

And I would agree with the above.

[55north]

Originally Posted by noelex 77

It is a pity because there are some wonderful materials available, but the cheapest polyester resin and chop strand mat comprise most of the layup of many boats.

Exactly. Even the OPs video only shows E-glass woven roving in polyester resin, and that withstands a good knock purely due to the high fibre density of the resin infused laminate. The report I linked to a few pages back claims that fibreglass will have about four times less impact strength than a good aluminium alloy, but rereading my previous post I don't think I made enough of the fact that they weren't testing a sophisticated laminate, at all; we're talking 40% glass and polyester resin. Had they been testing a 70% S-glass roving laminate, the results would have been very different. 75% more glass, 35% greater tensile strength glass, that's at least 2.4 times stronger straight away. Factor in the greatly improved properties of epoxy and the 30% greater strain to breaking of S-glass, and I think the laminate would quite probably be a match for aluminium for impact strength, and have greatly improved fatigue life and very much greater tensile strength.

Minaret, I'd be interested to hear your opinion on Kevlar vs S-glass reinforcement. By the basic numbers their properties seem fairly similar, but I keep hearing Kevlar touted as a miracle material. I'm no expert on fancy layups, but surely it will still experience brittle failure, so tensile strength is king here. Kevlar seems broadly similar to S-glass in that respect, IE. about 35% improvement on standard E-glass. What property makes it so good, and just how much would you have to put in a laminate to produce any meaningful improvement?

[tspeed]

I have found this thread to be a interesting read. Me personally sold my FP boat and ordered a aluminum but it was based on what I plan on doing with my sailing and not based on hull strengths but I thought I would share a short out take of a article I had read. People can make their own assumptions as I feel the marketing machines of each builder can spin the material they use to benefit the products they sale.

HOW STRONG IS ALUMINUM?
Strength. Several knowledgeable authors have written about the strength of aluminum verses steel. Their discussions focus on yachts being designed to the “same standards”, such as IMO, ABS, Lloyds or other similar classification societies. They discuss the strength, rigidity or deflection of the structure, the yield point, the flexure or plastic range of the material. For aluminum yachts, structure rigidity is usually the controlling design criteria, resulting in greater overall flexural and tensile strength than would otherwise be necessary.
Steel designs, on the other hand, are developed around the tensile yield point of the material because flexure and rigidity are not limiting factors. The following table from Bruce Roberts-Goodson’s book The Complete Guide to Metal Boats compares the yield
strength, tensile strength and plastic (flexure) range of steel, aluminum and fiberglass. A
measure of material rigidity, the elastic modulus, has been added to this table:
COMPARATIVE STRENGTHS OF DIFFERENT MATERIALS
Steel Aluminum Fiberglass
Yield strength 36,000-42,000 PSI 18,000-40,000 PSI 10,000-15,000 PSI
Tensile Strength 60,000-72,000 PSI 23,000-47,000 PSI 15,000-34,000 PSI
Plastic Range 40% 24% Fair
Elastic Modulus
(Rigidity or
Stiffing)
30 x 106
PSI 10 x 106 PSI
The over strength of the aluminum yacht is a favorable consequence of its rigidity-based design. “Scantlings”, or hull plate thickness, will be about 1.5 times greater for aluminum versus steel. For example, if a steel yacht were designed to use �� inch bottom plate, then an aluminum yacht built to the same strength standard would use 3/8-inch bottom plate. According to Michael Kasten, in his website article on Strength of Aluminum vs. Strength of Steel, this increase in plate thickness yields about 29% greater strength than the equivalent steel plate and will have a 12.5% higher tensile capability. He concludes, therefore, “… That a boat built in aluminum will be far less easy to dent by running into stuff (roughly 29% higher regional yield strength), and will have a slightly higher resistance to ultimate failure (around 12.5%).”

If one wishes, they can read the article them self at http://www.arcturosyachts.com/docs/whyAluminum.pdf

[tspeed]

I also wanted to add that to me it appears that the way the hull is designed and engineered has much to do with how it will fail. No matter the hull material, a boat is only as good as the people that crew the vessel. We all have our own opinions of which material is best, which sail plan to go with, what looks good and what does not. etc etc Long as the owner is happy with the boat they choose, then all is good in my mind.




These are images from a Allures 51 during hull construction, can clearly see the ribbing which is a Sealium extrusion which is covered with a aluminum sheeting with water tight crash boxes. Which is why I personally choose this brand. Sorry for the ramble, just wanted to add my thoughts to the thread.