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Old 19-02-2013, 20:56   #76
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Re: Opinions about Cored Hulls ...

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Originally Posted by s/v Jedi View Post
Sorry, but that does not sound like anything to brag about imo... whenever water ingress can occur, problems follow. Put a little piece of PVC closed cell foam in a jar of seawater for a week. Next drain the seawater out the jar and close the lid with the foam inside for another week... you will find that things are rotting in there and many chemical substances have entered with the water or are the result of the organic decomposition, some of which will deteriorate the PVC foam.

Nope. I've opened up boats that were foam cored below the waterline and had been saturated for many years. No sign of rot or delam of any sort in any of them. One weighed five hundred pounds less after we dried the core with the Hotvac. I had to cut out big sections of it to properly repair the crappy repair that was responsible for the saturation. Core was just fine. Owner said the boat got on a plane much easier afterwards. Foam beats the holy living hell out of balsa.
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Old 19-02-2013, 21:13   #77
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Nope. I've opened up boats that were foam cored below the waterline and had been saturated for many years. No sign of rot or delam of any sort in any of them. One weighed five hundred pounds less after we dried the core with the Hotvac. I had to cut out big sections of it to properly repair the crappy repair that was responsible for the saturation. Core was just fine. Owner said the boat got on a plane much easier afterwards. Foam beats the holy living hell out of balsa.
Nope? What nope? you mean that organic life does not rot after death?
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Old 19-02-2013, 21:27   #78
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Re: Opinions about Cored Hulls ...

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Originally Posted by s/v Jedi View Post
Sorry, but that does not sound like anything to brag about imo... whenever water ingress can occur, problems follow. Put a little piece of PVC closed cell foam in a jar of seawater for a week. Next drain the seawater out the jar and close the lid with the foam inside for another week... you will find that things are rotting in there and many chemical substances have entered with the water or are the result of the organic decomposition, some of which will deteriorate the PVC foam.

No, I mean there are no chemical substances in seawater, decomposed organisms or not, that will deteriorate PVC foam. Thought that was pretty clear. It will, however, thoroughly deteriorate an organic substance like balsa in a hurry. Especially if you throw in some dead organisms....
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Old 19-02-2013, 21:59   #79
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Re: Opinions about Cored Hulls ...

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A cored deck is much riskier than a cored hull because there are many more potential points of water ingress. But we can't do without cored decks -- there just isn't any other practical way to do a strong deck on a GRP boat.
Does any one know of a boat that utilizes an aluminum deck on fiberglass hull? In my (humble and untrained) opinion this would be the ultimate boat - No deck leaks, No deck cores or deck fastenings (weld everything you can). No Aluminum in water - No bottom paint problems (for now), No stray current worries,


When I first saw what these guys are doing (Futuna) my first thought was that it is a nice mix of materials but they got it bass ackwards!


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Old 19-02-2013, 22:36   #80
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Re: Opinions about Cored Hulls ...

Jdi,
Sorry I didnt mean to 'brag' if thats what it sounded like. What I was trying to show was that some cores are instant disaster when wet, and some (PVC at least) can survive a decent dunking. And getting wet somewhere is bound to happen on a boat.

Certainly PVC wont last forever, but IMHO its better than the ply, wood and glass boats Ive had. The wood/ply rots if you dont protect it, glass blisters and its heavy for the same strength, balsa we heard about, steel rusts, and you cant build a cat from it, aluminium is best in batteries....:-)

Rob
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Old 19-02-2013, 23:08   #81
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Re: Opinions about Cored Hulls ...

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Does any one know of a boat that utilizes an aluminum deck on fiberglass hull? In my (humble and untrained) opinion this would be the ultimate boat - No deck leaks, No deck cores or deck fastenings (weld everything you can). No Aluminum in water - No bottom paint problems (for now), No stray current worries,


When I first saw what these guys are doing (Futuna) my first thought was that it is a nice mix of materials but they got it bass ackwards!


Steve

Could be a good idea. A lot of the newer core materials use aluminum honeycomb, and some new methods are using aluminum plate in a fiberglass sandwich, even for aerospace. This method is incredibly light and strong.
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Old 20-02-2013, 08:10   #82
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Re: Opinions about Cored Hulls ...

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Certainly PVC wont last forever, but IMHO its better than the ply, wood and glass boats Ive had. The wood/ply rots if you dont protect it, glass blisters and its heavy for the same strength, balsa we heard about, steel rusts, and you cant build a cat from it, aluminium is best in batteries....:-)
I don't share your POV and with me many thousands others. In fact, many boatbuilders and naval architects will tell you that steel and aluminium are probably the best materials for boats.

I also see no problem with protecting materials from the environment. That has been the way to build things like boats for ages and is a proven technology. And the wood-epoxy hull that you dislike so much will make short work of your preferred plastic hull when racing as it will be even stiffer.

I have a plastic hull so I got nothing against it at all, but I also have nothing against other materials and would even switch to metal if I wouldn't prefer the tropics as my primary sailing area.

ciao!
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Old 20-02-2013, 08:14   #83
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Re: Opinions about Cored Hulls ...

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Originally Posted by minaret View Post
No, I mean there are no chemical substances in seawater, decomposed organisms or not, that will deteriorate PVC foam. Thought that was pretty clear. It will, however, thoroughly deteriorate an organic substance like balsa in a hurry. Especially if you throw in some dead organisms....
Oh, well then, I must have been in another dimension of the universe when I found PVC foam that had been exposed to the environment and crumbled apart in my hands.
I guess it would lead to discussing brands and types of PVC foam, which I don't remember, so I'll just let it go.

I do agree that balsa will rot if exposed to the environment long enough. I never thought anybody would think otherwise, I mean, you know I am an engineer with adequate grey matter, right? The kind that tend to understand such things about wood

cheers,
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Old 20-02-2013, 13:28   #84
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Re: Opinions about Cored Hulls ...

Jedi,

You read too much into my post. Obviously ply/wood/alu and steel are common boat materials. We DONT write them off because of their disadvantages, instead we deal with them by proper construction and protection.

But the general theme of hating cored boats seems to run along the lines that all cores are the same, and all cores are always bad, and that proper materials, construction and protection of the core is irrelevant.

I dont write off steel/alu/wood/glass as materials. I just prefer PVC foam/glass from my personal experience.

I see you sail a sundeer 64 - aluminium? You must be well aware of galvanic current, and I'm sure you take the usual precautions against problems. I'm also sure that there will be small areas of corrosion somewhere on the boat, and that you deal with those. It doesnt make a sundeer any less admirable.

There is a beautiful 17m charter boat here (aluminium) that was given a berth tied to an old barge for a year or so. Rumour has it they had to replate the bottom. But I still like the boat, and I dont write off aluminium on that basis.

Foam core boats are no different, they need maintenance, and proper care too. BTW I'm in NZ, we know a little about racing here. I havent checked but I think it would be difficult to find a top racing boat here that wasnt built with a cored hull in the last 10 years
Rob
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Old 23-02-2013, 03:14   #85
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Re: Opinions about Cored Hulls ...

Actually the newest Oysters are cored above the waterline and solid below. That seems the best compromise to me. Mine is older and solid up to the deck. I was attracted to a heavy thick single skin boat because I believe it would be a lot stronger if I hit a rock. Not as stiff maybe, but much more resilient to that sort of nasty accident. Also, if the sealing to the core around through hulls goes bad and a little water gets in, or small pinhole leak or crack in the skin allows a bit of water in then you are likely to be in trouble with a cored boat. One less maintenance/safety worry with a solid hull.
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Old 23-02-2013, 05:03   #86
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Actually the newest Oysters are cored above the waterline and solid below. That seems the best compromise to me. Mine is older and solid up to the deck. I was attracted to a heavy thick single skin boat because I believe it would be a lot stronger if I hit a rock. Not as stiff maybe, but much more resilient to that sort of nasty accident. Also, if the sealing to the core around through hulls goes bad and a little water gets in, or small pinhole leak or crack in the skin allows a bit of water in then you are likely to be in trouble with a cored boat. One less maintenance/safety worry with a solid hull.
That's the thing: cored hulls have no core where things like thru-hull fittings are. What you write above is a myth afaik.

When Contest built solid glass boats they boasted about it as much better too, until they finally managed to built a cored hull. Here, now I kick a Dutch product too
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Old 23-02-2013, 08:26   #87
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Re: Opinions about Cored Hulls ...

I suppose that when a thread asks for opinions you get folks forgetting science, data and history and offering opinion.

Have there been problems with cored materials below the waterline? Yes. Is it common? Arguable. I have seen many deck core issues in most builders (mostly due to poor install or maintenance issues), but rarely have seen a problem in cored hulls that was not caused by a poorly installed or botched repair work done after manufacture. I don't think there is an argument that a well built cored hull is stronger and lighter than a solid hull. I would rather have two layers of hull with a core if I encountered a log than one of brittle glass. This could be tested and I would bet with core over solid in weight to area in any test of absolute or impact strength.

If I was a boat buyer I would carefully survey the deck of any boat as these are almost always cored by all manufacturers with some material and this is where most core problems occur. It is a routine for a survey to inspect the hull and any problem. I would be willing to bet, if we had data, that the incidence of delamination of solid hulls is more common than leaky cored hulls. Without data, it's just my opinion based on years of boatyard work.
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Old 23-02-2013, 09:05   #88
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Re: Opinions about Cored Hulls ...

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I would be willing to bet, if we had data, that the incidence of delamination of solid hulls is more common than leaky cored hulls. Without data, it's just my opinion based on years of boatyard work.
I completed my 2,804th survey yesterday. My records show you have it backwards.
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Old 23-02-2013, 09:59   #89
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Re: Opinions about Cored Hulls ...

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I completed my 2,804th survey yesterday. My records show you have it backwards.


I agree with you. Never seen a solid hull delam that was not caused by hydrolysis or an impact. But I've seen a whole lot of rotten balsa, most of it in boats that used the "isolation" technique mentioned here. Only works in a vacuum bag, which many builders still refuse to do because it would hurt their bottom line. The majority has certainly been deck core, but I've seen more than one cored hull repair. Totaled a few boats out and wrecked them due to saturated hull core too. In the case of Cascadia, a 16.8 million build, the boat was vacuum cored below the waterline as well as above with balsa, because its lighter and it was a Schumacher design. She hit a rock on her first summer of trials and the entire bottom became saturated. Cost a million dollars to fix. And this in an extremely high end boat designed by the worlds most renowned designer, with vacuum bagged balsa core set in epoxy. It makes sense in an America's Cup race boat that will be raced a few times and then get broken or abondoned, having served its purpose. But for a boat you want to actually last? I would never even consider balsa core. Foam is a whole different bag of feed. If Cascadia had had a foam bottom, she would have weighed about 200# more, on a 77' boat. But we would have been able to dry her out and fix her for 50k instead of a million bucks. 200# ain't much on a 77' race boat.
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Old 23-02-2013, 10:03   #90
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Re: Opinions about Cored Hulls ...

I prefer to have any of the coring to be above the water line.

Balsa or Foam in the hull side walls or bridge deck on cats should not ever be a problem.

When you have Balsa core in the deck, then you just have to be real careful with any sealings and deck fittings. Over time these joints need to be looked at or re-sealed

If any new hardware is drilled it should be done properly to seal the balsa core.

Sealing Deck Penetrations to Prevent Core Rot Photo Gallery by Compass Marine at pbase.com

Here is a picture of a foam cored hull. You can clearly see that the core stops at the water line. Each little squire has epoxy on all side, so its like a strong bridge in effect with none of the expense of adding weight.

Balsa is stronger, but has the down side of absorbing water.
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