Fibreglass vs Aluminium Impact Strength

[europaflyer]

Originally Posted by minaret

I wasn't gonna say it, but I sure wanted to. That is one rich layup!

A rather moderate way of putting it! Really sorry for what I am about to say, Mr B, if that's your boat - but is seems to be made of resin, weird dribbly goo and plastic bags. I've heard stories of Tiwanese boats laid up with old newspaper, but frankly a bit of good newspaper would reinforce that stuff. What boat is it??!!

[silverp40]

Hey Minaret

Very curious as to what use you have for the (seeming) allthread taped (to a thru hulll) of your boat.

BTW, there also seems to be a bit of adhesion issues on Mr B's hull...?

[minaret]

Originally Posted by silverp40

Hey Minaret

Very curious as to what use you have for the (seeming) allthread taped (to a thru hulll) of your boat.

BTW, there also seems to be a bit of adhesion issues on Mr B's hull...?

Lol! That is a vacuum hose. I am installing G10 backing plates for the new thru hulls and seacocks, was grinding off the gelcoat on the interior of the hull around each one to prep for bonding. Taping a vacuum hose to the hole you are grinding on helps.

[silverp40]

Ha ha , that vacuum hose certainly works better when grinding inside than an all thread!!

[Mr B]

Originally Posted by europaflyer

A rather moderate way of putting it! Really sorry for what I am about to say, Mr B, if that's your boat - but is seems to be made of resin, weird dribbly goo and plastic bags. I've heard stories of Tiwanese boats laid up with old newspaper, but frankly a bit of good newspaper would reinforce that stuff. What boat is it??!!

My boat is a 2002 34 foot Gemini, Made by Performance cruising of Annapolis MD in the USA,

You dont drill a hole thru the hulls when you buy a boat to find out how thick it is,

But go for it, Feel free to give your opinions, I am past getting upset about it,

I was very surprised on how thin it was, and the lack of stiffeners,
It is being beefed up and stiffeners added as part of the repairs,
My repair man is very good at what he does, He does repairs to F/B boats all the time, and he is very qualified to do it,

Fibreglass is not my forte, So all opinions are appreciated at this point in time, Good and bad, Probably more bad than good,

And you dont have to say your sorry either before canning it,

Leaving my home port, I travel firstly through Bass Straight and the top end of the Southern Ocean and the The Tasman sea to go any where, so my boat has to be capable, and will be before I leave,

Cheers,
Brian,

[europaflyer]

Originally Posted by Mr B

My boat is a 2002 34 foot Gemini, Made by Performance cruising of Annapolis MD in the USA,

You dont drill a hole thru the hulls when you buy a boat to find out how thick it is,

But go for it, Feel free to give your opinions, I am past getting upset about it,

I was very surprised on how thin it was, and the lack of stiffeners,
It is being beefed up and stiffeners added as part of the repairs,
My repair man is very good at what he does, He does repairs to F/B boats all the time, and he is very qualified to do it,

Fibreglass is not my forte, So all opinions are appreciated at this point in time, Good and bad, Probably more bad than good,

And you dont have to say your sorry either before canning it,

Leaving my home port, I travel firstly through Bass Straight and the top end of the Southern Ocean and the The Tasman sea to go any where, so my boat has to be capable, and will be before I leave,

Cheers,
Brian,

Hi Brian,

My comments were slightly tongue in cheek - I'm sure there's absolutely nothing wrong with your boat that can't be fixed by someone who's really competent with fibreglass. It looks like the photos of the resin rich parts are right at the bottom of the hull. It's not unusual for excess resin to run to the bottom of the mould if the builder gets a bit too enthusiastic when laying the hull up.

It looks like one of your problems may be layers of resin on the outside cracking and delaminating from each other at the crack in the hull. If I was repairing it, I would consider either grinding away the excess resin to get to some actual fibreglass (which I assume there is in there somewhere ) or taking the easier route of just sheathing the hull in a layer of fibreglass to hold it together. If the hull really is too thin, adding a few more layers to it won't hurt anyway. Hard to tell exactly what is happening from the photos though.

There really is no excuse for any builder, big or small, not using vacuum infusion in this day and age. I hope you don't take it too badly is I say your boat proves this quite well...

Cheers!

P.S. - I think the problem could be one of semantics. Are you sure they used resin rather than rosin?

[minaret]

I find it interesting that anyone would build a cat in a solid laminate instead of cored. Of course it's too thin, if it wasn't it would be a terrible performer due to weight. I hope Mr. B's glass man is planning on reinforcing this hull with something strong but light, like a nice carbon lam. Of course that would cost as much as the boat is worth...

[silverp40]

. I hope Mr. B's glass man is planning on reinforcing this hull with something strong but light, like a nice carbon lam.


Minaret, sorry to diverge from the topic a bit, but what is your opinion on the different flex rates between carbon fibre and regular woven/biaxial?

When I redid our rudder, complete reglass and all, I wanted to add 6" carbon tape in a fwe places for stiffening purposes but opted not to.

I was concerned that the differrent glass material flex rates might cause micro delamination.

[55north]

I said in my first post that I couldn't find any data comparing the impact strengths of various boatbuilding materials. I have dug a little deeper, and found this, which seems to cover this thread perfectly.

http://www.vtt.fi/inf/pdf/publications/1997/P317.pdf

Briefly, the results state that aluminium has between 2.5 and 10 times greater specific impact strength than FRP, depending on the layup and the alloy.

It also demonstrates the difference between various FRP laminates. 22% CSM absorbs 2.8 J/kgm^-2, against 7.8 for a 44% layup with mostly woven roving. A 2.8 times impact strength difference is a strong argument against a cheap hull.

The different aluminium alloys (AlMg3/5754 and AlMg4.5/5082) show less variation, 25 against 28 J/kgm^-2. The 2mm aluminium exhibits poorer specific impact strength than the 4mm, with only 18 J/kgm^-2 absorbed (note that this is specific impact strength, ie. takes the halved mass in to account - the difference is presumably due to greater deformation in the thinner sample producing greater stresses).

The conclusion? An aluminium hull (5082 alloy) will have 3.8 times more impact strength than a FRP hull of the same weight (44% fibre content WR layup, typical for yacht hulls). The improved impact strength is due to the higher ductility of aluminium versus FRP (see my earlier post).

Resin infused layups (optimal 75% fibre content) with exotic fibres may exhibit better impact strength, but I think it is unlikely that they will equal aluminium. In the original video, we are seeing probably the best resin-infused layup possible with current technology (which I suspect may incorporate kevlar) being pitted against very thin aluminium indeed, which as the test proves will exhibit poorer specific impact strength than a typical plate thickness for a sailing yacht. This is how they manage to conclude that aluminium comes off worse.

Apologies for the rather wordy post!

Oh, and is there anyone out there with a plywood yacht? You might want to avoid reading the report...

[goboatingnow]

Plywood reinforced with GRP is almost as good as GRP.


Dave

[Andrew Troup]

Thanks for posting that, 55north

I have reservations about the test method used, although it's obvious that the comparison between different materials is a lot more scientific than others discussed in this thread.

Firstly, to my way of thinking, the sample should be larger and the edges flanged and clamped, to keep the relationship between elastic and plastic strain realistically similar to a panel on a boat hull. I mentioned this in an earlier post in relation to the test linked by the OP .


I also think that the way the load is applied is not very realistic: there's a big difference between a mass free falling (which hits hard, but the force drops away quickly to zero) to a mass being moved by an inexorable force.

An example of the latter is when a massive boat is carried by a high-volume swell against an immovable rocky pinnacle: the force doesn't go away immediately on contact.

... but it's interesting that a similar method to the one forming the initial basis for this thread results in such a different conclusion. It would be good to see the same brief given to a number of scientifically competent researchers, who would then come up with their own methods based on their own assumptions. I suspect their results would show startling variation.

[hpeer]

55north, thanks for the report. Useful.

[chala]

By writing

Originally Posted by 55north

the three major disadvantages of steel (rust, rust and rust!)

the poster demonstrates that he knows little about steel protective coatings. Interestingly, for reason of warranty claims on GRP boats, a European country, some time ago, came to the finding that GRP should be free from defect for the first 3 years and that both GRP and Epoxy will start to deteriorate after 12 years. 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.

[europaflyer]

Originally Posted by chala

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?

So GRP yachts fall apart after 12 years? Really, I never knew that.

Originally Posted by chala

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

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

[sailr69]

Originally Posted by chala

By writing


the poster demonstrates that he knows little about steel protective coatings. Interestingly, for reason of warranty claims on GRP boats, a European country, some time ago, came to the finding that GRP should be free from defect for the first 3 years and that both GRP and Epoxy will start to deteriorate after 12 years. 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.

how is it, the first FRP boats after the war (ww 2)are still around today? most FRP boats are on their second, third and more owners. there are no junkyards full of FRP boats. ever try to get rid of one? how many steel CC roamers are still with us? I know of a few that were sold for scrap.