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Old 29-11-2012, 13:09   #61
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Re: Fibreglass vs Aluminium Impact Strength

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That's the same boat?
Yes, it is the same boat. I made some changes that make her better suited for cruising the inside passage.

Steve
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Old 29-11-2012, 13:39   #62
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Re: Fibreglass vs Aluminium Impact Strength

Dave

You seem to be asserting that the wisdom of crowds can be a reliable indicator of engineering excellence.

All I can say is that it took the public a long time to demonstrate this wisdom in the case of your single example, Apple. Three decades, in fact.

It's not because Apple Computer have suddenly embraced engineering excellence in the last few years; it was a hallmark since almost day one.

You might equally well have instanced Toyota, and I would have to concede this is a strong example.

However once again it took decades for the US public to come to their eventual senses, and for Toyota's quality to supplant the woefully poorly designed and engineered domestic offerings.

I think it's significant that you wanted to restrict the field to engineered products, when I had instanced entertainment products. One could argue that for many years, many US auto buyers bought for entertainment and prestige rather than fitness for purpose.

I would certainly argue that boats which almost never venture away from their marina slot are essentially entertainment products, whose primary purpose is to satisfy pride of ownership and impress social and business contacts.
 
That's where I think the essential weakness lies, in your arguments both on hull material and on the use of brass for underwater fittings. You are inferring a fitness for purpose from popularity. I think that's fair enough, but I'd say you're misinterpreting the 'purpose'.

- - - - -

In the hull material case (as your contortions on the criteria demonstrate) the real reason metal is not popular as a hull material has nothing to do with engineering merits:

It's simply not economically viable for series production, unless (as in the case of automobiles) you are talking tens or hundreds of thousands of repeats of individual panels.
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Old 29-11-2012, 13:55   #63
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Re: Fibreglass vs Aluminium Impact Strength

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...
As to impact strength , I reserve my opinions Until I see specific facts about specific boats. Anything else is faith

...
Well I guess your opinions will have to stay reserved in perpetuity.
Unless you can persuade someone with deep pockets to do realistic destructive testing under controlled conditions of identical boats made of different materials.

In broad terms, that's how knowledge used to be advanced a hundred years ago, when they knew a lot about past failures.

Unfortunately, because they didn't understand the 'why' of those failures in any detail, they had virtually no ability to predict failures under future circumstances, like the Liberty ships or the Comet airliner.

Landing men on the moon, and deploying a sky-crane above Mars, were not achieved by looking in the rear-view mirror. I suppose you might call it faith, what those teams did. I prefer to save that term for instances of wishful thinking.
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Old 29-11-2012, 15:17   #64
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Re: Fibreglass vs Aluminium Impact Strength

This is beginning to get as good as the anchor/gun threads.
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Old 29-11-2012, 15:26   #65
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Re: Fibreglass vs Aluminium Impact Strength

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This is beginning to get as good as the anchor/gun threads.
I think it falls into the same category as religion LOL .
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Old 29-11-2012, 15:52   #66
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Re: Fibreglass vs Aluminium Impact Strength

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I think it falls into the same category as religion LOL .
You maybe right! It seems to have to do with what one believes.
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Old 29-11-2012, 17:18   #67
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Re: Fibreglass vs Aluminium Impact Strength

I base my opinions on some fine builders that build boats in steel, aluminum and FG.

Also on the opinions of some fine nautical architects/engineers.

I have some experience with FG and aluminum but not in cruising boats. Well, some small experience in a cruiser that was single skin FG and it was noisy and hot and I spent much of my time in the bilge trying to fix things. That was in the Key West, Cuba, Mexico and Belize in the winter. I'm sure glad I didn't spend the summer in it in Columbia. Oh, did I mention that it did a lot of pounding? Of course pounding isn't because of the material.
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Old 29-11-2012, 17:57   #68
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Re: Fibreglass vs Aluminium Impact Strength

They are all good materials for boat building, just depends on what you want and who builds it! Each material has it's issues... blisters, rust, corrosion, weight and manufacturing compromises.
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Old 29-11-2012, 19:01   #69
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Re: Fibreglass vs Aluminium Impact Strength

I have always wanted an aluminum boat (Garcia) but never was even close to being able to afford one. So, got a composite fiberglass boat, cored deck to keel thinking it will be relatively strong what with cored hulls and decks being stiff...


Over the next 7 years I was very surprised at just how strong the composite built really is:


-first sail we took, ran the boat aground under full sail , almost hull speed on a bed of oysters and rocks. After a day of hypotermic hauling off, I dove the boat but could not see any damage. After hauling off the next month, the damage were a few small gauges, deepest one about 1/4" deep.


- a few years ago we were caught by very large cat 2 hurricane IKE, in a marina in Texas, with the eye passing right over us. We were well prepared but most of the other boats were not . As a result, for about 12 hours we had many 30-50 foot boats pound us from all sides, including landing on top of us (I almost got a Hatteras on my head!), cars and floating vans, telephone poles, even the roof of a house that somehow landed on top of the cockpit, I think it was from a tornado (we were on board). The surge was over 20' and the whole marina was afloat with big and small debree. Waves were big as the winds were sustained over 100mph so everything was crashing around.


In the last 5-6 hours when it "moderated" to about 60-70kts, I realized that we were entagled with another boat, a 34' boat. After I cut the stanchions and wire off, I realized it was a steel boat. Then, after 2-3 months, I got the job to repair the hull and cabin of the steel boat. Result: the area where we were entangled, our boat bend the 3/16" Cor-Ten steel hull back almost 1' in, bend the fwd steel bulhead and crushed the port side of the stern area (Hard to fix that one!). Our damage was also great but not to the hull or deck : no hull or deck penetration, just up to 3/8" deep gouges (never got past the outer skin). We could see our hull flexing in as much as 4" when getting hit by the big boats and other debree, really scary!


So, I have a lot faith in the strength of FG.
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Old 29-11-2012, 19:09   #70
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Re: Fibreglass vs Aluminium Impact Strength

Oh, almost forgot. The previous owner got hit by a 200' barge (glancing blow) and never penetrated the outer skin or delaminated bulkhead tabs.
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Old 30-11-2012, 04:11   #71
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Re: Fibreglass vs Aluminium Impact Strength

I am glad boat designers don't use anecdotal information when deciding on construction ... all these materials are (obviously) good for building boats. It can be done heavy or light, made well or poorly. What is worse, getting hit by a 200' barge or the 40,000,000' earth? That would be my balsa cored FRP boat and a coral reef. Just a scratch.
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Old 30-11-2012, 05:46   #72
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Re: Fibreglass vs Aluminium Impact Strength

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i have seen a few metal boats safely anchored inside lagoons after they have been washed over the reef,but dived on many fiberglass boats that never made it beyound the breakers................
But most boats never end up on reefs. The boat I dream of at night is build from plywood...
In the end I think it's better to spend money on a good insurance rather than on aluminium.
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Old 30-11-2012, 06:08   #73
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Re: Fibreglass vs Aluminium Impact Strength

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You seem to be asserting that the wisdom of crowds can be a reliable indicator of engineering excellence.
I don't think that is what Dave is telling. I read in his posts more that good engineering doesn't involve trying to maximize one particular property (hull strength) a the expense of everything else.
Engineering is about compromises. It is not necessary to build a boat as strong as possible. It only needs to be as strong as needed for it's purpose.
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Old 30-11-2012, 06:10   #74
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Re: Fibreglass vs Aluminium Impact Strength

Thinking of definitions. From this thread I get these definitions that work for me.

BLUE WATER....when my sail takes me beyond a modern highly reliable weather window where I may not be able to make a port of refuge. Be it five days or five hours.

BLUE WATER CAPABLE....a boat that will give the crew a good chance of survival. This means a tough boat around shore but for off shore it must also have relative comfort so the crew can get some rest to stay sufficiently engaged.

Both definitions are relative. Blue water is that which can get you caught out. When I sail in Newfoundland almost any time I cross a headland I'm in blue water. Even with modern forecasting you may get an unexpected gale.

A blue water boat for a couple crossing an ocean is not the same as a young deck ape racing crew on an overnight passage. The former boat needs to keep the crew warm, rested, and alert.

All that being said, it is the crew and their heart that makes it possible.

I met this most wonderful young couple this summer, they have had a remarkable voyage so far, 14 days Newport to Newfoundland engineless, Greenland, Iceland and now Spain. The name of the boat says it all.

http://www.svramshackle.com/
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Old 30-11-2012, 06:12   #75
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Re: Fibreglass vs Aluminium Impact Strength

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Originally Posted by K_V_B View Post
But most boats never end up on reefs. The boat I dream of at night is build from plywood...
In the end I think it's better to spend money on a good insurance rather than on aluminium.
personally i would rather spend my money on a good boat,good anchors,good tender,and a semi auto rifle
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