Fibreglass vs Aluminium Impact Strength

[minaret]

Originally Posted by noelex 77

The bottom plating is 12mm. The keelson is 20mm.

Impressive. But more in the realm of the custom expedition yacht than anything production. Expense wise we could certainly compare it to a carbon Kevlar hybrid pre-preg epoxy vacuum layup. Neither can be afforded by 99% of boaters. Hardly a typical example.

[Mr B]

I can teach any one to weld in ten minutes, But every thing is set up for them to do so.

Knowing what your doing when welding, and all the things that can go wrong with a weld on any material, takes years, and you need very good teachers.

Ive seen welds by people who think they can weld, Nice bead, looks good from all angles, welded one side only,
Then I pick it up and snap it in half, with my bare hands, The look on their faces is priceless,

I thought you said you could weld, Hahahahahahhahahahaha
And your going to trust your life to those welds,

A little bit of knowledge is down right dangerous at times,

Fibreglass will take a hell of an impact, but grinding away on a reef with wave action, it soon reduces to confetti, The holes just keep getting bigger,

Aluminium, not as much, it will dent badly before tearing, but you can pack it out for the next tide,

Plus it all depends on the thickness of hull materials in what ever is sitting on the reef, Thicker will take longer to destruct,

Very Thin materials will just tear to pieces, No matter what it s,

[Panope]

Originally Posted by minaret

I agree with your suspicion. And again I will say, the video was not about ultimate impact strength, but failure modes. If you HAD been able to penetrate the panel with your serial killer maul attack, it would have made a hole, no? If you did the same to a glass panel it wouldn't, instead it would shatter and fracture but still remain mostly watertight. Though high point loading like a maul instead of a sledge hammer might be the exception to that rule, unless there's some Kevlar in the lam. I'll try to make an equivalent video with some hand laminated 3/4" polyester flat stock I have kicking around. It doesn't have enough rovings for it to be an accurate test, but I bet I will need the shop hydraulic press to break it. And 3/4" is a small boat layup.

Before I made my "killer maul attack" video I had little idea what was going to happen to that piece of metal. I think it is safe to assume that we also have little idea what is going to happen to a piece of FG when I get my savage hands on it.

Is 3/4" what I should be looking for as a similar weight to 3/16 aluminum? I will head down to the boat yard tomorrow and see if they are scrapping any FG boats.

Steve

[Panope]

[QUOTE=daddle;1099544]As a test - not very convincing. It shows the lawn is durable as that is where all the energy is absorbed.

Yes, I wish I could weld up a section of plate complete with my framing and stingers in place - would make a better test. It as been raining here for a month and my lawn is very moist. At the end of my "attack" the panel had created a 6' hole in the ground - not very durable.

Steve

[minaret]

Originally Posted by Panope

Before I made my "killer maul attack" video I had little idea what was going to happen to that piece of metal. I think it is safe to assume that we also have little idea what is going to happen to a piece of FG when I get my savage hands on it.

Is 3/4" what I should be looking for as a similar weight to 3/16 aluminum? I will head down to the boat yard tomorrow and see if they are scrapping any FG boats.

Steve

Definitely not, 1/4" plate is quite common on production boats in the mid size range (say 40'). In the same size range a solid glass lam will usually be as thin as 3/4" at the top of the sheer, most of the hull will be 1" and the keel much more. I just mentioned 3/4" because we happen to have lots kicking around right now that we hand laminated ourselves, much like a production boat. Try your test on a piece of G-10 1" plate for a real eye opener. Using this math to match your 3/16 th plate you would have to go up to an 1 1/2" laminate. Good luck!

[DeepFrz]

3/4 in. at the shear? Gerr suggests 0.30" at the topsides of a 40' boat except in high stress points, ie: chainplate area.

[silverp40]

Quote

Unless you were told, You would not know what that boat was built from,


Steel sailboat lost power and stuck on the reef | Parker Marine
Steel.

[DeepFrz]

North Shore boat torn open on land | Parker Marine

Lets see now, is this a FG boat?

And how about this one?
http://parkermarinecorp.com/img/manu...-on-rocks.html

[minaret]

Originally Posted by DeepFrz

3/4 in. at the shear? Gerr suggests 0.30" at the topsides of a 40' boat except in high stress points, ie: chainplate area.

I can't imagine a 1/4" topside laminate in a boat of that size, even just at the sheer. 1/4" is a standard thickness for hatch lids and companionway sliders and the like. Way too light a scantling. Even the external skin of a cored boat is often well over that. Just ask any of the many owners of such boats here, anyone who's gotten a hull sample by installing a new through hull or the like will agree. I've never seen a solid 1/4" hull lam even in boats less than 30'. With fiberglass providing proper panel stiffness depends on thickness. You can build a very thin hull that is very strong, but it will oil can severely because it has no panel stiffness. This is what cored composites are about, providing panel stiffness without the weight of the extra laminate needed to do this in a solid lam. So in a solid lam by the time you've built in sufficient panel stiffness it is generally much stronger than it needs to be. A 1/4" hull would oil can severely under way. Of course since its fiberglass you could do this, as stress fatigue is not an issue, unlike alloy. But it would be uncomfortable and perform poorly.

[DeepFrz]

Gerr was talking about modern designs and methods in his "Elements of Boat Strength" and of course the hull would have stringers and ring frames. He gives outer laminate thickness for cored hulls of 5.03 mm or 0.198".

Of course you don't install a thru hull at the shear line.

Gerr is quite a conservative designer I believe, judging from some of the beautiful boats he has designed.

[Panope]

Originally Posted by minaret

Definitely not, 1/4" plate is quite common on production boats in the mid size range (say 40'). In the same size range a solid glass lam will usually be as thin as 3/4" at the top of the sheer, most of the hull will be 1" and the keel much more. I just mentioned 3/4" because we happen to have lots kicking around right now that we hand laminated ourselves, much like a production boat. Try your test on a piece of G-10 1" plate for a real eye opener. Using this math to match your 3/16 th plate you would have to go up to an 1 1/2" laminate. Good luck!

Thank you Minaret for the response. I was not able to follow exactly some of your technical words i.e: G-10?. Are you saying that an 1 1/2" laminate weighs the same as 3/16" aluminum per square foot?

I know that a metal boat may have more internal structure than FG but for ballpark figuring we can ignore.

I looked up some specs for a Catalina 34. It has similar displacement and similar ballast as my boat. Do you (or anyone else) know off hand how thick the layup is at the turn of the bilge of a Catalina 34 or similar?

Steve

[K_V_B]

Originally Posted by msponer

Are there any others, like that, for any material?

I must admit that I'm seriously in love with hard chine boats build in plywood.

When I learnt to sail as a kid in 70ies and the 80ies the usual progression was: Optimist first, then Vaurien. The Vauriens were made of plywood. On day when sailing at sea (yes, we did take Vauriens out in the North Sea...) I managed to hole my boat by running in to another one that just had it's mainsail down. We had been practicing sailing on jib alone that day. The boom of the other boat, sticking over the side, made a nice hole in mine.
I actually managed to make it back in to port, where at the school they just slapped a piece of plywood on it, screwed it down, and off I was again...
I ended up sailing more plywood boats. At Les Glenans we sailed in a Herbulot design, that had bunks for 8 on a length of 7.8 m. No engines, no winches, no electricity, electronics or instruments. Just a simple boat with a good rig, centreboards, so it could be beached, and great fun was had by all. Later in the Netherlands I sailed (and raced) in a Valk, a open keelboat designed by Van Der Stadt, in plywood again.
Now I'm eying an RM 1200...

[atoll]

Originally Posted by K_V_B

I must admit that I'm seriously in love with hard chine boats build in plywood.

When I learnt to sail as a kid in 70ies and the 80ies the usual progression was: Optimist first, then Vaurien. The Vauriens were made of plywood. On day when sailing at sea (yes, we did take Vauriens out in the North Sea...) I managed to hole my boat by running in to another one that just had it's mainsail down. We had been practicing sailing on jib alone that day. The boom of the other boat, sticking over the side, made a nice hole in mine.
I actually managed to make it back in to port, where at the school they just slapped a piece of plywood on it, screwed it down, and off I was again...
I ended up sailing more plywood boats. At Les Glenans we sailed in a Herbulot design, that had bunks for 8 on a length of 7.8 m. No engines, no winches, no electricity, electronics or instruments. Just a simple boat with a good rig, centreboards, so it could be beached, and great fun was had by all. Later in the Netherlands I sailed (and raced) in a Valk, a open keelboat designed by Van Der Stadt, in plywood again.
Now I'm eying an RM 1200...

hard chine plywood boats are great,and almost completly biodegradable after about 25years or less if not looked after

[K_V_B]

Originally Posted by atoll

hard chine plywood boats are great,and almost completly biodegradable after about 25years or less if not looked after

That's another plus :-)

[atoll]

Originally Posted by K_V_B

That's another plus :-)

not if you happen to be mid-ocean when the boat bio-degrades