Fibreglass vs Aluminium Impact Strength

[Mr B]

Originally Posted by goboatingnow

please show me the yachts tests showing that , or is it just your "belief"




The RNLI builds all its hulls from composite.



No large displacement ferries are built from Aluminium, Fast Cats are , purely to minimise weight for the needed speed The Cunard QM2 was built from steel due to issues with her predessor the QE2.

Of course Aluminum in theory is a good material, but in a lesiure yacht it has major drawbacks. ( Cosmetic repair, skills neeeded, paint adhesion , impressed corrosion)

Steel is actually a better material, but needs more care.

Dave

sorry I didnt get back to this, I have had other personal problems that needed my time,

Yes, this is my belief,
After 50 years of Forging, Moulding Bending, Twisting, Forming, destructive testing, Welding, including Forge welding, In steel, brass, copper, aluminium, Monel, Tungsten, Molybdenum, and more materials that you know even exist,

working in all facets of Engineering manufacturing shipping, mining, aircraft equiptment, I do know what it takes to rip most materials apart, This is from personal experience, But they did teach me my trade very thoroughly to start with,

I just loved demolison, I could load up beams till they literaly tore off the beams holding them up,
It was very good experience tearing structures and other equiptment apart to find out whether the so called laboratorys and other airconditioned testing facilitys were any where near what it actually took to destroy some thing in the real world,

Thankfully my knowledge that came out of my head from experience, saved an Engineers arse because the tower crane he designed would have collapsed killing a lot of people, if he failed to listen to me and my advice,

over those 50 years of hands on experience does give me a little bit of belief in my own capability,
If I say some thing will collapse it will,
There are very few people left with the qualifications and knowledge I hold and was taught, Most are all dead now, or in their 70 and 80's,

I designed it, then I actually made it, then tested it, then I wrote the certificate for it, all in my own name,

So, Yes, it is my belief. The bit that pisses most theoretical Engineers off, Is I do know, and I dont need a computer or Cad system or refer to a book to tell them so, It comes out of my head,

Did I mention that I am a fully Qualified Practising Engineer, Not a Theoretical Engineer,

Cheers,
Brian,
Engineering Blacksmith, VRTC,

[minaret]

Originally Posted by noelex 77

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.

"Deformed and damaged" is not failure. We are discussing failure modes here. Face it, it's a fact. The two failure modes are completely different. Stress an alloy to the failure point and it will crack or hole. Not true of a laminate.

[noelex 77]

Originally Posted by minaret

"Deformed and damaged" is not failure. We are discussing failure modes here. Face it, it's a fact. The two failure modes are completely different. Stress an alloy to the failure point and it will crack or hole. Not true of a laminate.

I really think you have this entirely the wrong way around. I strongly believe that metal boats can survive impact with rocks, containers etc and maintain their water integrity better than a fibreglass boat. The metal boat will be dented, but watertight in conditions that will puncture the more brittle fibreglass.

As we not about attack to each others boat with a sledge hammer.
I hope.
Besides I have got my own secret weapon, (note the metal rollers )


I guess we have to agree to disagree.

[minaret]

Originally Posted by noelex 77

I really think you have this entirely the wrong way around. I strongly believe that metal boats can survive impact with rocks, containers etc and maintain their water integrity better than a fibreglass boat. The metal boat will be dented, but watertight in conditions that will puncture the more brittle fibreglass.

As we not about attack to each others boat with a sledge hammer.
I hope.
Besides I have got my own secret weapon, (note the metal rollers )


I guess we have to agree to disagree.

Of course. But note that ONE of us is a professional shipwright who has actually repaired hundreds of heavily damaged glass hulls. I have repaired almost no heavily damaged alloy hulls, because they tend to sink when heavily damaged. If you believe fiberglass is brittle, try taking a fiberglass fishing pole and a piece of alloy rod of the same diameter (though the same weight would be a better indicator, however this would leave you with wire for this test). Bend them until failure. Which one bent further? Which one sprung back to shape? How did they fail, clean break or still attached by fibers? How many load cycles did it take to achieve fatigue and failure? This test would be much better if you compared 1" glass rod to 1/4" alloy rod. You will need a big hydraulic press to bend the 1" glass rod. The alloy you can do by hand.

Sledge hammering each others boats would be a great test. I bet I can hole most alloy boats in a single stroke (I can really swing a hammer). I bet you couldn't hole my 1 1/4" lam with a dozen strokes. And then I could fix the damage in a couple of days, like new. You would take weeks to remove interior for welding and then painting the whole hull.

[minaret]

When I attended boat building school, we had to run the numbers on all sorts of materials. We also built planks and panels in all sorts of materials and then destructively tested them. I'll have to look up some numbers in my old textbooks. But believe me, the reason most quality boats are built in fiberglass these days is not just economy. If it was, you would never see a one off fiberglass hull. But I have built a number of those. The second to the last one finished out at 12.8 million dollars. The owner could have built in any material he chose, the designer was probably the worlds most famous and successful designer. The boat was built in hybrid carbon lam, not alloy. Because its a better boat construction material. Or at least the architect thought so. I'll look up some destructive testing numbers and post them here for posterity.

[noelex 77]

The most common boat building material for the worlds "super yachts " Is aluminium.
An epoxy resin, carbon, cored structure is,however, much lighter and more suited to the high performance boats and is a common alternative.
This sort of exotic structure has very little in common with the polyester resin, CSM layup, (with or without core) that is used in the typical fibreglass boat.

[Mr B]

I can weld aluminium or steel from the out side only, and have a fully guaranteed weld,

As for the finish on aluminium or steel, I can finish it off so you would not know what the material underneath was after it was painted, unless you tapped on it,

Weld doesnt have to look like crap, Thats just cost, A bit of a buff after welding, you would not know it was welded, Removing distortion is only procedure during welding,

Even HAZ can be eliminated, Heat Affected Zone, thats the bit beside the weld that gets affected by the heat of welding,

[minaret]

Originally Posted by Mr B

I can weld aluminium or steel from the out side only, and have a fully guaranteed weld,

As for the finish on aluminium or steel, I can finish it off so you would not know what the material underneath was after it was painted, unless you tapped on it,

Weld doesnt have to look like crap, Thats just cost, A bit of a buff after welding, you would not know it was welded, Removing distortion is only procedure during welding,

Even HAZ can be eliminated, Heat Affected Zone, thats the bit beside the weld that gets affected by the heat of welding,

Of course, any decent marine welder can do it. But if there is any cabinetry or other wood interior structure at or near the weld it needs to be removed before welding or it will get burns. And then instead of doing a localized gelcoat repair, as on a glass hull, you have to paint the entire hull.

[Mr B]

Just slide a bit of plate down behind the cabinetry, it doesnt have to be removed, If its removed you can weld inside as well,

[silverp40]

Originally Posted by Mr B

Just slide a bit of plate down behind the cabinetry, it doesnt have to be removed, If its removed you can weld inside as well,

I never saw interior cabinetry that one could "slide a plate behind"....It is all attached to the hull and firing up a welder and beginning inside or outside will set the cabinetry on fire in short order (unless the cabinetry is also alloy). Then there are the frames/ribs that one needs to contend with also, so it's not that simple.

Quote:

I bet you couldn't hole my 1 1/4" lam with a dozen strokes.

I can also swing a sledgehammer and cannot go through 3/8" fiberglass the hammer keeps bouncing back and tries hitting me - I tried with 1/4" non cored glass and I could not do it even in 20 strikes. .. 12 Strokes for 1 1/4"? 200 sounds more like it but I think it will be much more...

It is also shocking how difficult it is to go through a FG hull with pickaxe...it took me Many blows to go through a 1/2" hull.

DISCLAIMER: I am not a boat demolisher/vandal, just my own testing on completely ruined, ready-for-final-crushing hulls after hurricane IKE.

[minaret]

Originally Posted by silverp40

I never saw interior cabinetry that one could "slide a plate behind"....It is all attached to the hull and firing up a welder and beginning inside or outside will set the cabinetry on fire in short order (unless the cabinetry is also alloy). Then there are the frames/ribs that one needs to contend with also, so it's not that simple.

Quote:

I bet you couldn't hole my 1 1/4" lam with a dozen strokes.

I can also swing a sledgehammer and cannot go through 3/8" fiberglass the hammer keeps bouncing back and tries hitting me - I tried with 1/4" non cored glass and I could not do it even in 20 strikes. .. 12 Strokes for 1 1/4"? 200 sounds more like it but I think it will be much more...

It is also shocking how difficult it is to go through a FG hull with pickaxe...it took me Many blows to go through a 1/2" hull.

DISCLAIMER: I am not a boat demolisher/vandal, just my own testing on completely ruined, ready-for-final-crushing hulls after hurricane IKE.

I was trying to be charitable. I too have been around a lot of hurricane boats (was a hurricane chaser for a bit). Usually we were fixing them but we demo'd quite a few as well. Destroying a boat that has already been partially destroyed by nature will teach you a lot about boat construction fast.

[Andrew Troup]

Originally Posted by Mr B

....

Even HAZ can be eliminated, Heat Affected Zone, thats the bit beside the weld that gets affected by the heat of welding

I presume you're talking stainless, not aluminium - the subject of this thread.

If you can tell us a practical way to restore the tensile strength of a 50xx series marine aluminium alloy plate back to H14 (or even H32), in the vicinity of the hull plating seam welds, you will have every reason to be considered a true hero.

[silverp40]

Originally Posted by minaret

Destroying a boat that has already been partially destroyed by nature will teach you a lot about boat construction fast.

Agree with that!! Especially some of those Far East yards that steal designs/plans from good architects then "improve" on them.

Here is a test I did on a Pearson 35 (totally destroyed) that has the exact same lazarette lockers as our Pearson: I was wondering if someone could get inside a locked locker by brute force, i.e. sldgehammer and crowbar.

With the crowbar, I immediately realized that with good hardware (hinges and locks - these are adequate on Pearsons)) it is impossible to get in. I chipped a few edges but maybe with a 10' crowbar or so.

Next, 10 lb slegdehammer. After about 30 blows, people in the yard were looking at me thinking I lost my mind. So I stopped, but did not really even Begin to penetrate the locker. I would have needed Many more blows to make a hole.

The thickness of the lid glass was 1/4".

[goboatingnow]

Yes, this is my belief,
After 50 years of Forging, Moulding Bending, Twisting, Forming, destructive testing, Welding, including Forge welding, In steel, brass, copper, aluminium, Monel, Tungsten, Molybdenum, and more materials that you know even exist,

working in all facets of Engineering manufacturing shipping, mining, aircraft equiptment, I do know what it takes to rip most materials apart, This is from personal experience, But they did teach me my trade very thoroughly to start with,

Mr B, Im not arguing that in a ultimate test metal is a very durable material indeed, My comments relate to small leisure made out of it. ( which I am very well familar with), High quality cosmetic standard repair of metal vessels demands great skill, as you obviously have. the same is not true of GRP ( to teh same extent). This is not to mention the inevitable repaint , which is equally trickey if its high quality LPU finish. Equally many classification societies require both side welding as well. And Ive always seen teh interior being removed as well as the insulation ( often PU foam, which makes areal mess).

In summary I remained to be convinced that an average metal boat is significantly more durable then an average modern GRP boat especially with exotic materials in crash areas and/or epoxy/vinylester and resin vacuum systems ( all standard stuff).The metal boat fanboys all say its better, but to my knowledge noones done the testing

[silverp40]

I think that a quick informal survey amongst readers of this post would be interesting for two reasons:

1. Determine in a real life fashion how metal, fiberglass and maybe wood hulls react when impacted by various objects while underway. I am sure a lot of the posters have hit various bits of flotsam while making offshore/inshore trips.

2. Get an idea of the amount of collisions offshore that exist in one's sailing experience in this small cross section of sailors many of whom I think have extensive miles under their belts/keels.

Here is one of ours as a first:

A few years ago, at night, offshore, in heavy air, we hit a semi-submerged object hard with our centerboard. It was hard enough to think that we lost the board for a moment. We were also sailing at hull speed. Upon getting inside an inlet later and examining the board, a small, 1/4" or so dent was visible at the leading edge of the board (which is rounded, not sharp). No other damage to board or mechanism. The board may have swung back a bit but is still weighs 250lbs or so so it had a lot of inertia.
We thought it could have been a log or maybe a turtle.