# cored vs solid fiberglass hulls



## MarkMiner (Oct 10, 2006)

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?


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## Newport41 (Jun 30, 2006)

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


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## Valiente (Jun 16, 2006)

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.


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## sailingdog (Mar 19, 2006)

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.


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## sailingfool (Apr 17, 2000)

*Religious War*



MarkMiner said:


> 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...".


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## Giulietta (Nov 14, 2006)

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


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## sailingfool (Apr 17, 2000)

*Not a Problem*



Giulietta said:


> 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.


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## sailingdog (Mar 19, 2006)

Hey, Giu-

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


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## Giulietta (Nov 14, 2006)

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?


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## sailingfool (Apr 17, 2000)

*Giu's Tax*



sailingdog said:


> 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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## Giulietta (Nov 14, 2006)

SF that was funny....Carbon tax....ehehehehe

However, you know there's a shortage of raw CF materials here??

We had to import from US, for a project that is going on here....

Al Gore hasn't found that there are Countries on the other side of the water....


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## sailingdog (Mar 19, 2006)

Giulietta said:


> 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?


Yes, we're both picking on you and joking...  Boy, he's awfully defensive about his hull.... must be compensating for something...maybe it was built by the French, like his boom...


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## Giulietta (Nov 14, 2006)

Nahhh...built by a "less smart boat builder" as the whole boat is cored, except a 1' wide line on the center bottom of the hull where its not cored (where the keel goes).

By the way..only 3 thru hulls..all thru uncored parts.

I'm not defensive..I'm just kidding...I don't really care what you guys say


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## sailingdog (Mar 19, 2006)

Giulietta said:


> Nahhh...built by a "less smart boat builder" as the whole boat is cored, except a 1' wide line on the center bottom of the hull where its not cored (where the keel goes).
> 
> By the way..only 3 thru hulls..all thru uncored parts.
> 
> I'm not defensive..I'm just kidding...I don't really care what you guys say


Well, he was smart enough to leave a bit solid laminate and then to put the throughhulls through the solid bits...rather than the cored bits... so it must have been a Portugese builder...rather than a French one.


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## sailingfool (Apr 17, 2000)

*Bad news!!*



Giulietta said:


> ....However, you know there's a shortage of raw CF materials here??
> 
> We had to import from US, for a project that is going on here....


WOW, bad news! President Bush just used the War Powers Act to ban the export of carbon fiber materials - US needs all CF and more for production of the new F22 F-22 Raptor Team Web Site. This weapon system is being rushed into use so the US will be ready for war with France.

He also recalled all exported material, assigning the CIA to collect any boats build with US CF, by any means necessary.


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## Giulietta (Nov 14, 2006)

SD...this guy and his 2 sons and employees spent a year and almost half building it...what do you think they were doing?? all was done with special attention..everywhere there is a thru deck or thru hull was not cored, and the places where stress is expected is not divinycell its either wood or metal..

I think I have ir covered...


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## Giulietta (Nov 14, 2006)

eheheheh SF you're loosing it..

the US CF was for another thing we have "going" on here...not my boat...we bought it in Early march, at a place recommended by you guys...

For my boat all was aquired in Europe....some time ago..try again

Portugal is helping the US in Iraq, so the CIA will bring some more, if we need!!


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## sailingfool (Apr 17, 2000)

*Generalizations*



Giulietta said:


> Nahhh...built by a "less smart boat builder" as the whole boat is cored, except a 1' wide line on the center bottom of the hull where its not cored (where the keel goes).
> 
> By the way..only 3 thru hulls..all thru uncored parts.
> 
> I'm not defensive..I'm just kidding...I don't really care what you guys say


Giu,
Obviously my comments are generalizations, sounds like your builder was on top of the subject - just don't do too much drilling on your own - I'd take your boat in a minute, just the way it is (broken boom OK).


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## sailingdog (Mar 19, 2006)

SF-

Giu just sails his boat and breaks his boat... he doesn't actually work on his boat... he has people for that...


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## sailingfool (Apr 17, 2000)

*Duck*



sailingdog said:


> SF-
> 
> Giu just sails his boat and breaks his boat... he doesn't actually work on his boat... he has people for that...


SD
think Cam will kick some butt when he reads this tread?


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## sailingdog (Mar 19, 2006)

SF-

Nah, we answered the question asked by the OP.. or I tried to anyways.. and it's not like Giu can't hold his own...we're just picking on him—much like he does to us...


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## Giulietta (Nov 14, 2006)

not true...not true..I do a lot of things... not as many as I wanted, because of work and being away some times, but I do a lot..

I installed the dodger, the mast steps, I repaired several things that broke...I do a lot actually...if I can't do it then someone else does it...but not normally


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## sailingdog (Mar 19, 2006)

Alex-

You do know that I'm joking... right??? 

BTW, have you gotten the boom yet??? Huh... or did it get held up in customs... I know...they shipped it air freight via Continental airlines...


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## southerncross31 (Sep 16, 2006)

Someday G, i'm going to sail over there and race you. I know i could win. Hull/displacment ratios won't matter....i am putting this special paint on the hull thats going to make my boat way faster!  I have created a revolutionary electric/garden hose drive that runs on AAA batteries and completely recharges itself whenever i fart!


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## sailingfool (Apr 17, 2000)

*No drilling*



Giulietta said:


> not true...not true......I installed the dodger, the mast steps, I repaired several things that broke...I do a lot actually...if I can't do it then someone else does it...but not normally


That's cool, we'll have to call you Giu the Tool Man (here's a reference in case this joke is too parochial Tim Taylor (fictional character) - Wikipedia, the free encyclopedia ) , but no drilling in the hull, and definitely no hammers...
by the way, what's with a French boom? Would you buy a Citroen? The guys at Selden Seldén Mast AB could have taken care of you...A French boom - that will be slow - it'll only work 32 hours a week..


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## Giulietta (Nov 14, 2006)

southerncross31 said:


> have created a revolutionary electric/garden hose drive that runs on AAA batteries and completely recharges itself whenever i fart!


SC...you already won...I give up...I'm not racing against a guy that has an electric garden hose in his rectal cavity!!


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## sailingdog (Mar 19, 2006)

Giu-

Thanks for that... I really didn't need to have that image stuck in my imagination... UGH...


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## southerncross31 (Sep 16, 2006)

I guess i set myself up for that one huh? let's see...it recharges whenever i ah..uh....  A guy in my boatyard said the only other thing that would handle like my boat on BBay is a barge.....and he has a Catalina G....a Catalina. What an insult .


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## sailingdog (Mar 19, 2006)

Oh, great...now CD is gonna come charging in here... foaming at the mouth as usual.


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## sailingfool (Apr 17, 2000)

*SA versus Disp*



southerncross31 said:


> I guess i set myself up for that one huh? let's see...it recharges whenever i ah..uh....  A guy in my boatyard said the only other thing that would handle like my boat on BBay is a barge.....and he has a Catalina G....a Catalina. What an insult .


Hey its all sail area versus displacement, while Catalinas have some beef, they also usually have some mast...I would think that Buzzards bay is a good venue for your SC 31, you must enjoy the afternoon South-Westerlies that blow so often, with gusto.


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## sailingdog (Mar 19, 2006)

I know I do... Haven't been down to the marina because of the Nor'easter and traffic today... Conditions were like this:


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## Giulietta (Nov 14, 2006)

southerncross31 said:


> .....and he has a Catalina G....a Catalina. What an insult .


SC.. just ignore him (he has a Catalina   God will forgive him...he allways does....)...tell him you have a close relative that is an extraordinaire good looking sailor, that has a very very good looking exquisite fast boat but he is in Europe now with his boat...and you can have a ride anytime you want....

If he asks, I'll confirm.....OK???


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## edwmama (Jun 15, 2008)

Hi fellow boater

It seems to me that wet balsa cored hulls is like wooden homes being
Gobbled up by termites

On the outside the house looks good and strong until one
Day...... OH s...£#%¥@!


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## Victor Lopez (Aug 8, 2021)

sailingdog said:


> Cored Hull Pros
> 
> Stronger and stiffer deck or hull for the same weight
> Better insulated, reduced condensation problems inside boat
> ...


So, you state: "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".

So, that means that in the critical hull you prefer solid fiberglass but on the "less critical" deck you prefer cored material.

In my opinion, unless weight-speed is critical, solid fiberglass is superior because no rot, no water infiltration, no need to use solid epoxy around any hole.

Solid fiberglass has the disadvantage of weight and less insulating power but has superior integrity and, therefore, not deterirating strength. If the fiberglass layout is heavy, with many thin layers, fiberglass is also stronger than cored materials.

My overall conclusion, for people not interesed in racing, for cruising sailors, both coastal and bluewater, solid fiberglass, specially if laid up heavy, is the superior material. This is why I bought with solid fiberglass hull and deck.


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## SanderO (Jul 12, 2007)

Coring has a high strength to weight ratio. Penetrations require "special attention" such as solid lay ups at penetrations or where compressive strength is important.

My hull is end grain balsa cored with solid glass in the lower section where the keel is attached. At those areas the lay up is almost 3" thick solid fiberglass. The deck is cored with solid lay up at chain plates and locations of deck hardware.

Boat is 36 years old and has no blisters, wet core or other problems.


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## Jeff_H (Feb 26, 2000)

Victor Lopez said:


> So, you state: "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".
> 
> Solid fiberglass has the disadvantage of weight and less insulating power but has superior integrity and, therefore, not deterirating strength. If the fiberglass layout is heavy, with many thin layers, fiberglass is also stronger than cored materials.
> 
> My overall conclusion, for people not interesed in racing, for cruising sailors, both coastal and bluewater, solid fiberglass, specially if laid up heavy, is the superior material. This is why I bought with solid fiberglass hull and deck.


Apparently your are not familiar with the science on this. Pound for pound, (depending on the core and laminate engineering) a cored composite has a much higher bending and flexural strength. Cored hulls are less prone to fatigue, so maintain a much greater percentage of their original strength over time. But most importantly to a cruiser. They are far more resistant to both large and small area impact.

Except for the resistance to high velocity small area impact, similar characteristics for the weight can be achieved with a solid glass that has a system of closely spaced frames. But to achieve those strength to weight characteristics, the hull needs to have the framing that is directly glassed in. Constructing a hull with closely spaced in that manner is very labor intensive and requires an extremely high level of quality control.

I know some ill informed cruisers think that weight should not matter to a cruiser and is only important to racers. While it is true that racers strive to minimize weight to achieve performance improvements, unnecessary weight should be more critical to a cruiser since it can minimally become a matter of comfort and more seriously become a matter of life and death to a cruiser.

It is important to understand that in and of itself, weight does nothing good for a boat. It does not make it more seaworthy, it does not improve motion comfort. It does not make the boat stronger. It does not improve carrying capacity. It does not make the boat easier to handle.

In fact unnecessary weight is detrimental to all of those factors. From a yacht design standpoint, weight is a zero sum game. Excess weight in the hull results in some mix of compromises that includes reduced ballast, interior fit-out, and/or carrying capacity, as well as adding drag and the associated need for greater sail area, more fuel consumption.

The net result of reducing ballast is a mix of making a boat harder to handle, less stable, with a poorer motion comfort. The added drag does much of the same, while making the boat more expensive to maintain, and means more motoring at a higher fuel consumption, poorer light to moderate air performance, and greater difficulty in heavy air conditions.

Those are all characteristics that should be of greater importance to a cruiser than a racer.

Jeff


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