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-   -   cored vs solid fiberglass hulls (http://www.sailnet.com/forums/general-discussion-sailing-related/31457-cored-vs-solid-fiberglass-hulls.html)

MarkMiner 04-16-2007 03:59 PM

cored vs solid fiberglass hulls
 
Aside from the obvious benefit of cored hulls being lighter, are there other drawbacks to having a cored hull vs a solid fiberglass hull? Are there different techniques for constructing a cored hull which minimize any potential negatives?

Newport41 04-16-2007 04:03 PM

I would say that the material used for the core is one of the big issues. But even there there are pros and cons.

Valiente 04-16-2007 04:49 PM

Cored hulls are stronger, being a "sandwich", but only to a point. I personally prefer a solid hull (at minimum below the waterline) and a cored deck, with the coring being Airex or some equivalent non-spongy material. I also believe that ALL deck gear should go through solid glassed-in pads, not only to distribute the load, but to discourage ANY kind of water intrusion. Here in Toronto, we have hordes of balsa-cored decks and the freeze-thaw cycles imposed by hauling out and storing boats in yards is horrendous. Very few escape nasty, expensive "recorings".

I know that for all the advantages of cored hulls (and they are many), I wouldn't want one if I grounded the hull on coral or something sharp. Not all of us can afford Kevlar outer skins.

sailingdog 04-16-2007 05:32 PM

Cored Hull Pros

Stronger and stiffer deck or hull for the same weight
Better insulated, reduced condensation problems inside boat

Cored Hull Cons

If deck hardware or thru-hulls not installed properly, water can migrate into the laminate and cause the core to delaminate.

More difficult to lay up laminate properly IMHO... so more prone to lamination failures.

There are three materials normally used as core materials: foam, plywood and end-grain balsa. Some other things can be used, but they aren't proper core materials IMHO.

End-grain balsa is in many ways the best of the three, since it reduces water migration through the laminate core, which can cause larger areas of the deck to delaminate fairly quickly. Balsa also generally has better adhesion and bonding characteristics than the foams do, and greater compressive strength and sheer strength than most foams. Finally, end-grain balsa has the highest temperature resistance to softening.

Some of the foams, when exposed to higher temperatures can soften, causing the hull or deck to deform. However, foam tends not to rot, and as such.

Plywood's only major advantage is that it is far more resistant to crushing damage than foam or balsa.

Hardware installation on a cored deck needs to be done properly, which means removing the core and potting the area with thickened epoxy to protect the laminate core from any water leaks.

Properly designed, a cored hull can be much stronger and lighter than a non-cored hull. However, all the through hulls should be through areas of solid glass. Potting is only a second-best measure below the waterline IMHO.

Solid glass is far easier to repair and less subject to problems of delamination. It's major problem is weight.

Vacuum infusion, properly done, is going to yield a very high-strength, low-resin, laminate. However, it is also pretty easy to screw up vacuum infusion—which can lead to voids that were never properly wet out and have very little strength.

That's it in a nutshell. The strength of a cored laminate is very dependent on the quality of the lamination as well as the choice of material for the core. Early laminates used foams that had lower sheer strengths, and in certain situations, the laminates would fail as the foam material itself sheered, allowing the laminate to separate.

Personally, I believe that the hulls should be solid laminate, and that the only place for cored laminates is the deck and cabin top of the boat.

sailingfool 04-16-2007 05:34 PM

Religious War
 
Quote:

Originally Posted by MarkMiner
Aside from the obvious benefit of cored hulls being lighter, are there other drawbacks to having a cored hull vs a solid fiberglass hull? Are there different techniques for constructing a cored hull which minimize any potential negatives?

The subject of hull coring is a religous war amongst many sailors. I believe it a fundamental design consideration deserving careful thought. I do not believe the type of coring material matters relative to the risk of water intrusion, although some powerboat builders became infamous for junk filler.

The better bulders use solid glass sections around the keel and all thru hulls, i.e. nothing is cut thru the core sections (at least nothing by the builder...). IMHO the smarter builders use coring only above the waterline, and the smartest builders build all glass hulls.

If you want the skinny as to one side of the debate read the articles about cored hulls on Boat Hulls - Cores and Structural Issues: Online Articles by David Pascoe, Marine Surveyor. One of them relates the story as to how a single set screw installed inside a wet bilge area lead led to a soaked core...

A lot of posters will say "not a problem..." and of course, it isn't until major hull damage happens to you... A friend of mine with a gold plated 42 from a big name Maine builder just replaced all the Airex hull core...otherwise "not a problem...".

Giulietta 04-16-2007 05:56 PM

OHHHH My!!!! Jaysus, Mary, and Joseph, the Saints and Our Lady Of Fatima!!!!!!!! (All together at least 4 times)........

sailingfool 04-16-2007 06:05 PM

Not a Problem
 
Quote:

Originally Posted by Giulietta
OHHHH My!!!! Jaysus, Mary, and Joseph, the Saints and Our Lady Of Fatima!!!!!!!! (All together at least 4 times)........

Hey Giu,

Break anything this week?...How about some pictures of the busted gear...most of us here don't even have our boats in the water yet (May 8 for me).

As to water intrusion into hull core, not to worry, let the saints rest a bit, I read the EU Commision on Marine Matters passed an ordance outlawing wet hulls, so you guys over there are all set. Portugal is part of the EU right..so you're covered.

sailingdog 04-16-2007 06:07 PM

Hey, Giu-

Isn't your boat's hull Carbon Fiber??? I hope you have a good life raft on board.... ;)

Giulietta 04-16-2007 06:23 PM

SD, my "weak cored", "prone to water infiltration", "poor construction" hull, will resist more than you can possibly imagine...simply...beacuse I don't have holes...and the ones I have are thru solid sections and dully protected..

SF..what do you mean outlawing wet hulls? Are you joking?

sailingfool 04-16-2007 06:24 PM

Giu's Tax
 
Quote:

Originally Posted by sailingdog
Hey, Giu-

Isn't your boat's hull Carbon Fiber??? I hope you have a good life raft on board.... ;)

Oh right, forgot to mention, I heard that same group, EU Commission on Marine Matters, also passed a new annual tax on carbon fiber hulls, 200 euros/foot, some form of carbon tax I guess, those guys are really green. Giu can handle it, he'll just buy one less new spinnaker this year.


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