Fibreglass vs Aluminium Impact Strength

[minaret]

Originally Posted by Jim Cate

g'Day 55 North,

Welcome to the forum. and thanks for your well written post. It's always good to have some objective information to salt the conjecture, and you did a good job of objectifying some of the issues that we've been babbling about.

But, as to the concern of fibreglass vs steel... the appended picture of the bow of a Beneteau Oceanus 47 which contested right of way with a steel trawler is self explanatory.

I look forward to your further contributions to CF.

Cheers,

Jim

What was the difference in size and scantlings between the trawler and the sailboat? If the trawler has twice the displacement and hence twice the hull thickness it's hardly a fair test. And even that severe looking damage can be repaired like new fairly easily on a glass hull. The trawlers minor damage may have actually been more difficult and expensive to repair. And the layup on a Beneteau is hardly high tech either, it would be hard to pick a more easily damaged sail boat.

[minaret]

I'll just say again, the point of the video isn't necessarily that glass has a higher impact resistance than aluminum. It's about failure modes. Both materials failed, but the aluminum failed by cracking or getting a hole in it. The glass laminate shattered, which means the resin matrix has failed and the laminate has lost almost all it's strength, but it is still there. No holes, just a big area of shattered and delaminated glass. I have seen this in the boat yard a great many times, as I said at the beginning of the thread. Glass boats that by all rights should have sunk come in leaking heavily, with saturated cores, etc. Like this trawler that came in after a major impact. The owner sprayed foam all over the shattered glass and brought her in leaking. An alloy boat would have sunk for certain. The pic is of the section of shattered bow I cut out. Note how she is repaired like new in the after photo (better than new really).

[atoll]

doubtful this would have happened to a metal boat..............

[minaret]

Originally Posted by atoll

doubtful this would have happened to a metal boat..............

Why? That would happen to any boat you managed to balance on top of a piling, lol! That one looks like a crane may have dropped it.

[Mr B]

Originally Posted by atoll

doubtful this would have happened to a metal boat..............

Going by the barnacles on the pole its sitting on, it would not have had to have too much high tide to sit it on the pole, once its started to bang on the top of the pole and being tied up, soon pokes a hole in the boat, Tide goes out. leaving it high and dry,
Steel boat would have been dented,

[minaret]

Originally Posted by Mr B

Going by the barnacles on the pole its sitting on, it would not have had to have too much high tide to sit it on the pole, once its started to bang on the top of the pole and being tied up, soon pokes a hole in the boat, Tide goes out. leaving it high and dry,
Steel boat would have been dented,

Maybe a steel destroyer. A steel sailboat exactly the same size as this one would have exactly the same hole in it. But it would be harder to fix. Those barnacles look like they stop 8'-10' short of the top of the piling to me. Which would of course be normal for any piling, a piling that is submerged at high tide is no good to anyone.

[Jim Cate]

Originally Posted by minaret

What was the difference in size and scantlings between the trawler and the sailboat? If the trawler has twice the displacement and hence twice the hull thickness it's hardly a fair test. And even that severe looking damage can be repaired like new fairly easily on a glass hull. The trawlers minor damage may have actually been more difficult and expensive to repair. And the layup on a Beneteau is hardly high tech either, it would be hard to pick a more easily damaged sail boat.

G'Day mate,

I didn't actually say that this was a fair test! At any rate, the trawler was said to have little but cosmetic damage (I didn't see it myself). And truthfully, it might well be hard to define "cosmetic damage" on the typical Clarence River trawler, they not being noted for beauty or glossiness.

The Bennie was indeed repaired by the local shipwrights, but perhaps not in the way that you would have done it, Minaret. They had Beneteau supply a new bow moulding from France and grafted it onto the hull aft of the damaged area. I didn't see the finished job. Oh... a new mast was also required as it went by the board when the stem fitting disintegrated.

Having said all that, my point in posting the pic was to illustrate one example of steel vs FRP. My own suspicion is that in the size of vessels that we tend to have, most such collisions would end up with glass loosing the war.

Finally, I was pretty well shocked at the thin layup in this highly stressed area. All of the folks here on CF who trumpet the idea that some modern techniques used by FRP boat manufacturers make substantial layups obsolete should have a close look at this photo, or better, a similarly exposed shell on some other boat.

Cheers,

Jim

[Mr B]

Originally Posted by minaret

Maybe a steel destroyer. A steel sailboat exactly the same size as this one would have exactly the same hole in it. But it would be harder to fix. Those barnacles look like they stop 8'-10' short of the top of the piling to me. Which would of course be normal for any piling, a piling that is submerged at high tide is no good to anyone.

I would say that it was an abnormal tide that did that damage, Hurricane surge,

Steel would have just ground up and down on it, with out puncturing the hull.

Barnacles will take the side out of fibreglass very promtly, Its like hitting a reef,

[Hirophant]

Originally Posted by europaflyer

According to this guy, an aluminium yacht is 'stronger' by at least 50% kilo for kilo.

What about $ for $ though? Surely a more appropriate measure!

[minaret]

Originally Posted by Mr B

I would say that it was an abnormal tide that did that damage, Hurricane surge,

Steel would have just ground up and down on it, with out puncturing the hull.

Barnacles will take the side out of fibreglass very promtly, Its like hitting a reef,

If that was caused by surge, where's all the other damaged boats? Or the signs of any storm damage in the background? Not to mention I'm pretty sure that's England, or thereabouts. Don't think they have too many hurricanes there. That said, sure steel is more abrasion resistant. So is aluminum (the topic of this thread). That would be an alloy hulls one strong suit in my mind. And it has absolutely nothing to do with impact strength (also the topic of this thread).

[minaret]

Originally Posted by Jim Cate

G'Day mate,

I didn't actually say that this was a fair test! At any rate, the trawler was said to have little but cosmetic damage (I didn't see it myself). And truthfully, it might well be hard to define "cosmetic damage" on the typical Clarence River trawler, they not being noted for beauty or glossiness.

The Bennie was indeed repaired by the local shipwrights, but perhaps not in the way that you would have done it, Minaret. They had Beneteau supply a new bow moulding from France and grafted it onto the hull aft of the damaged area. I didn't see the finished job. Oh... a new mast was also required as it went by the board when the stem fitting disintegrated.

Having said all that, my point in posting the pic was to illustrate one example of steel vs FRP. My own suspicion is that in the size of vessels that we tend to have, most such collisions would end up with glass loosing the war.

Finally, I was pretty well shocked at the thin layup in this highly stressed area. All of the folks here on CF who trumpet the idea that some modern techniques used by FRP boat manufacturers make substantial layups obsolete should have a close look at this photo, or better, a similarly exposed shell on some other boat.

Cheers,

Jim

Lets just take a more extreme example of what I'm talking about. This bulbous bow protuberance on a Nordhavn 65 is close to a foot thick of solid glass laminate. The boat hit a submerged shipping container when doing ten knots well offshore. Damage was severe. You can see in these pics of the turbo shear work that the laminate is completely shattered all the way through. But there are no holes whatsoever. This boat didn't even leak coming back in. She traveled over 2000 miles in this state to reach our yard from the North Pacific. An alloy boat would have been in Davy Jones'. Not because the alloy boat's not stronger, it IS stronger. But because when tested past the failure point the failure modes are completely different. Shattered but still mostly watertight, or a big hole. Big difference.

[DeepFrz]

An alloy boat would have been in Davy Jones'.

A steel sailboat exactly the same size as this one would have exactly the same hole in it.

An alloy boat would have sunk for certain.

This is all just pure speculation with no facts at all to back up your claims.

[minaret]

Originally Posted by DeepFrz

This is all just pure speculation with no facts at all to back up your claims.

Still haven't seen any of you alloy fans take up the question of failure modes. And I'm far from the only one speculating without facts based on my personal experience on this thread-that would include everyone.

Do you honestly think you could balance an alloy boat on it's side on a piling without poking a hole in it? That would be putting the whole weight of the boat on about one square foot of surface area on the side of the hull. No boat could withstand that (except maybe a dinghy). And how about the submerged container? A submerged container holds thousands of tons of water, you might as well hit a big steel armored rock. Most alloy hulls would crack open like a tin can. The Titanic did. I admit a Nordy is hardly a fair comparison, I just used it to make my point. Few boats can survive such a collision. But glass really can take shocking impact damage without actually holing, as long as it's not hit by something sharp and pointy.

[K_V_B]

Originally Posted by europaflyer

Great mentality. The throwaway culture.

That's not what I mean.
I don't think of a boat as disposable. I just don't think of it as irreplaceable.

[noelex 77]

Originally Posted by minaret

Still haven't seen any of you alloy fans take up the question of failure modes.

The better failure mode is one one of the great assets of a metal boat.
Metal can be deformed and damaged to much greater degree than fiberglass and maintain its watertight integrity.
Both materials will need repair, but by staying watertight, metal boats have a much greater chance of being saved and saving their owners. Fiberglass is more brittle and will shatter and crack.
Even the actual video showed this. The aluminium the used was much weaker than fiberglass, but note how it had to incredibly deformed before it developed a hole. The fiberglass was a much stronger sheet, but it almost lost its watertight integrity with minimal deformation.

You don't even need to look at boats to see this. Look at car after an accident. Even when severely bent and distorted the surface is often still intact and would remain waterproof.
Have a look at the boat "Gringo" in post 17 for a more nautical example.