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post #41 of 59 Old 12-28-2010
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Quote:
Originally Posted by Hartley18 View Post
This isn't directly relevant to your purchase, TD - but on the subject of cored hulls:

I still remember wandering around the CYC marina after we withdrew from the 1985 Sydney-Hobart race marvelling at the damage to the many other boats that withdrew. You could see which tack they'd been on at the time the front moved in, because on more than a few of them the high-side windows were smashed in and the low-side hull rippled like corrugated-iron with the rib/bulkhead positions clearly showing outside - basically the core had been crushed by the impact of the boat launching off the waves for hours on end.

OK, that's pretty extreme conditions and it shows there is a definite limit to how far a hull core can be pushed before irrepairable damage occurs - but it seems to me this limit is set by the designer/builder and is NOT going to be all that evident to the yacht's owner.
Unless the boat is incredibly heavy cored hulls are stronger. You have boats like some Open 60's that have circumnavigated 4 times and made a lot more transatlantic races in very rough seas and were pushed to the limit and that are ready for more of the same. That is more stress that any sailor will gonna to give to its boat.

Yes , you need to have more care in the maintenance on a cored hull, but that is not a big deal. You have just to recoat the under water part of the hull each 7 years with three coats of epoxy primer. Anyway, you shoud do the same in a fiberglass boat if you don't want to have osmosis issues.

Yes you will also need to have more care when choosing a used old cored boat, but that is nothing that a good surveyor would not detect.

Regards

Paulo
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post #42 of 59 Old 12-28-2010
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Originally Posted by PCP View Post
Unless the boat is incredibly heavy cored hulls are stronger. You have boats like some Open 60's that have circumnavigated 4 times and made a lot more transatlantic races in very rough seas and were pushed to the limit and that are ready for more of the same. That is more stress that any sailor will gonna to give to its boat.

Yes , you need to have more care in the maintenance on a cored hull, but that is not a big deal. You have just to recoat the under water part of the hull each 7 years with three coats of epoxy primer. Anyway, you shoud do the same in a fiberglass boat if you don't want to have osmosis issues.

Yes you will also need to have more care when choosing a used old cored boat, but that is nothing that a good surveyor would not detect.

Regards

Paulo
This advice about bottom coating has no relevance the the reasons cored hulls get wet. For readers who would like to better appreciate the issues related to cored hulls, read what a surveyor actually has to say here Boat Hulls - Cores and Structural Issues: Online Articles by David Pascoe, Marine Surveyor

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post #43 of 59 Old 12-28-2010
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This advice about bottom coating has no relevance the the reasons cored hulls get wet. ..
Can you explain that better?

From the article you have posted:

"How About Cored Hull Sides?
No problem. Hull sides are not submerged and are far less likely to become water saturated."


It seems to me that if you coat the bottom with epoxy you have an impermeable water barrier and the water cannot go to the core.

Regarding what is called "hydraulic erosion", well, the article is about motorboats and I don't know much about motorboats. Probably with fast motorboats the continuous pounding can have an effect that you just don't find in sailboats.

As I have said, there are sail racing boats that have circumnavigated several times, boats that have endured huge seas and were pushed to the limit and they are in such good conditions that it was made a race just to take advantage of them. I mean inexpensive seaworthy and sound boats that are still fast but not a match for recent boats. The race is on at this time, it is the Velux five oceans and the boats are:

Operon Racing (19 years old): 6 racing circumnavigations (not counting the transats)

Active House (11 years old): 4 racing circumnavigations

Five Oceans of Smiles (18 years old) : 3 racing circumnavigations

Le Pinguin (12 years old) : 3 racing circumnavigations

Spartan (13 years old) : 3 racing circumnavigations

These boats that had many names and raced an incredible number of ocean races have been subjected to more stress more wave impact (more hydraulic erosion) that any normal sailing boat during all its life time and they are doing just fine, still racing.

If that article was right in what regards sailboats, these ones would be just dust

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Quote:
Originally Posted by PCP View Post
....

If that article was right in what regards sailboats, these ones would be just dust

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Paulo
Not at all. The article observes that the risks of cored construction can be managed with careful construction techniques, the issue being that few production boat builders willl bear the costs of such techniques, as their buyers don't know to demand them.

The classic example I recall from the article, of a builders' error were the set screws securing a pump in a wet bilge, that subsequent wet the entire hull core.

I don't think the boats you mention are representative of the production boats most of us might buy.

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post #45 of 59 Old 12-29-2010
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Quote:
Originally Posted by PCP View Post
Can you explain that better?

From the article you have posted:

"How About Cored Hull Sides?
No problem. Hull sides are not submerged and are far less likely to become water saturated."


It seems to me that if you coat the bottom with epoxy you have an impermeable water barrier and the water cannot go to the core.

Regarding what is called "hydraulic erosion", well, the article is about motorboats and I don't know much about motorboats. Probably with fast motorboats the continuous pounding can have an effect that you just don't find in sailboats.

As I have said, there are sail racing boats that have circumnavigated several times, boats that have endured huge seas and were pushed to the limit and they are in such good conditions that it was made a race just to take advantage of them. I mean inexpensive seaworthy and sound boats that are still fast but not a match for recent boats. The race is on at this time, it is the Velux five oceans and the boats are:

Operon Racing (19 years old): 6 racing circumnavigations (not counting the transats)

Active House (11 years old): 4 racing circumnavigations

Five Oceans of Smiles (18 years old) : 3 racing circumnavigations

Le Pinguin (12 years old) : 3 racing circumnavigations

Spartan (13 years old) : 3 racing circumnavigations

These boats that had many names and raced an incredible number of ocean races have been subjected to more stress more wave impact (more hydraulic erosion) that any normal sailing boat during all its life time and they are doing just fine, still racing.

If that article was right in what regards sailboats, these ones would be just dust

Regards

Paulo
The article you mention using the term "hydraulic erosion" is referring specifically to balsa core. I don't believe any of the boats you mention are balsa cored.

Epoxy is not impermeable. It is hygroscopic....but less so than polyester.

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post #46 of 59 Old 12-29-2010
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The article you mention using the term "hydraulic erosion" is referring specifically to balsa core. I don't believe any of the boats you mention are balsa cored.

Epoxy is not impermeable. It is hygroscopic....but less so than polyester.
No, neither balsa is used to core modern hulls.

Epoxy is not impermeable? this is news to me. There are several types of Epoxy but the one that is used to do a waterproof barrier on the hull, known as "sealant" is, or at least is advertised as such by all the companies that commercialize the product.

Please post a link with information regarding the permeability of an epoxy barrier.

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No, neither balsa is used to core modern hulls.

Epoxy is not impermeable? this is news to me. There are several types of Epoxy but the one that is used to do a waterproof barrier on the hull, known as "sealant" is, or at least is advertised as such by all the companies that commercialize the product.

Please post a link with information regarding the permeability of an epoxy barrier.

Regards

Paulo
Balsa coring is currently used in the hulls of J-boats, Farr 40's, Sea Ray, Doral, Cruisers inc. and a host of others.

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Sorry Paulo, I missed the first part of your response. Just google Hygroscopic epoxy" and you will turn up hundreds of articles and papers similar to this ......

Abstract
In this study, various hygroscopic effects of such parameters as hygrothermal temperature, matrix volume ratio (Vm), void volume ratio (Vv), specimen thickness, lay-up sequence and internal stress were investigated for epoxy/carbon fiber composite laminates. The specimen thickness and lay-up sequence had little effect on the through-the-thickness water absorption behavior of composite laminates, but the other parameters affected the moisture absorption rate and equilibrium water uptake in different ways and intensities. The glass transition temperature of composite laminates was strongly affected and linearly decreased by the quantity of equilibrium water uptake. A characteristic length of moisture migration through the unidirectional laminates was proposed as a function of fiber angle to the exposed laminate surface. In this approach, the fibers imbedded in the matrix were assumed to act as a barrier to the penetrating water molecules, and the developed model was well compared with the experimental results.

Author Keywords: A. Polymer–matrix composites (PMCs); Lay-up; E. Prepreg

Article Outline
1. Introduction
2. Theoretical background
2.1. Fick's second law of diffusion
2.2. Modeling of diffusion path of water molecules into unidirectional composite
3. Experimental

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post #49 of 59 Old 12-29-2010
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Sorry about the ignorance regarding the US market. In Europe all the boat builders I know of use Divinycell, Airex or a similar product for hull coring.

Regarding hygroscopic epoxy, well google non-hygroscopic epoxy. You will find almost as many entries

It seems that there are a lot of epoxies, some are hygroscopic others not:

"This clear, very pale, light amber, low viscosity resin is the basic resin used for all coating, encapsulating, laminating, and sheathing applications....POXY-SHIELDŽ Hardeners at a 5:1 ratio (5 parts resin to 1 part hardener, either by weight or volume). It's suitable for bonding all types of woods, most metals, and some plastics. It's waterproof upon curing, and cures without shrinkage. "


Epoxy Manual - Poxy-Grip adhesive and Poxy-Shield epoxy resin

Regards

Paulo

Last edited by PCP; 12-29-2010 at 11:16 AM.
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Sorry about the ignorance regarding the US market. In Europe all the boat builders I know of use Divinycell, Airex or a similar product for hull coring.

Regarding hygroscopic epoxy, well google non-hygroscopic epoxy. You will find almost as many entries

It seems that there are a lot of epoxies, some are hygroscopic others not:

"This clear, very pale, light amber, low viscosity resin is the basic resin used for all coating, encapsulating, laminating, and sheathing applications....POXY-SHIELDŽ Hardeners at a 5:1 ratio (5 parts resin to 1 part hardener, either by weight or volume). It's suitable for bonding all types of woods, most metals, and some plastics. It's waterproof upon curing, and cures without shrinkage. "


Epoxy Manual - Poxy-Grip adhesive and Poxy-Shield epoxy resin

Regards

Paulo
Paulo : I think I would believe studies done by independent labs and Standards Societies rather than sales blurbs from the manufacturers of these products

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