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Old 10-01-2017, 17:57   #151
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Re: Foam Core Hull

Interesting read about the various issues of core. As someone who has just spent the last 9 years being on the building crew and then building the interior of my 40' Pescot catamaran out of composite materials I think we are confusing a few of the issues. Firstly my boat is not high tech--the shell was built by a damn good builder but there was no vacuum bagging etc, just wet lay up. I learnt to laminate pretty quickly--its not hard, just very repetitive... and there are many great examples of boats built using these materials by amateurs like me.

I do think there is a difference with production boats, clearly they are built to a budget, from the materials they use through to the type of fittings they put on--I'm appalled at the type of through hull fittings some of the supposedly high end manufacturers use on their boats for example.

To start with there are a range of different cores, Western Red Cedar, balsa, foam and some form of honeycomb. Foam is great as long as it is something like airex (as someone mentioned as it is totally inert to water). However it 'dents' and so if you are beaching your boat, WRC is a better core to use on the very bottom of the boat where it sits on the sand--(that bit is for the multi people mad enough to beach their boats like I do). The other cores are all prone to rot if water gets in.

Then of course you have the resin type, epoxy, polyester and vinylester. Epoxy is amazing stuff, and for WRC and Balsa I think it is the only way to go to keep water out and eliminate any risk of blisters. Derek Kelsal has over 50 years of experience with foam and polyester and swears by it and has boats still going to prove it.

The ability to vary the thickness of the core with different lay ups provides a huge range of ways to build a strong long lasting boat--from memory, increase the thickness of the core and you increase the strength by a factor of 3. The strength is amazing (especially with selected use of carbon--2mm of carbon layup has the same strength as 40mm wood stringers).

For furniture I used a cheaper foam and lay it up with 200gsm cloth and epoxy--it is wonderful stuff, cut it up like plywood and make any shape you like--all up, my furniture added maybe 80kg of weight to the boat and it has lasted years of tough offshore use (we are regularly going to windward offshore in 30--40 knot winds (with the boat doing 9-12 knots) so the boat gets a workout--it's much easier to break ply of the same thickness than my foam panels

Not sure I trust balsa without epoxy under the water, the idea of water getting in and rotting the balsa, and there are many examples is terrifying--My boat is WRC and epoxy in the hulls and decks and foam/epoxy on the bridgedeck areas and flat areas. Effectively it is a wood boat so ANY hole (screw or bolt) has a six step method to seal it with three coats of epoxy and sealant. As someone said there is a hell of lot of holes in a deck and fresh water on wood is a real killer.

So in summary, cored built stuff is amazing, strong light and ridiculously tough if it is properly built.....--I just saw a 14 year old 60' cat (made of balsa duflex panels) slammed beam on into the point of a metal jetty (caught in cross winds) and there was nothing but a small graze... (the owner damn near had a heart attack)....and if there had been a hole, it's easy to fix with the right epoxy and glass.

I have seen the photos of a Pescot Firefly cat having been T boned by another cat doing 12-15 knots (racing in Thailand), the prodder speared through the hull but the hull retained it's integrity where the bow impacted it and was able to sail back --it was a big repair job though. In contrast my brother had his beautiful 34' Logon sloop (made out of NZ Kauri planking) T boned by a boat in a race in NZ and it sank within 3 minutes--he and his partner only just got out in time.

As mentioned above, it is horses for courses, for me, cored hulls, especially for the type of boats I like to sail are the only way to go. It is also pretty easy to repair as long as you have epoxy and fibreglass there is not much you can't fix. But the there are distinct down sides (installing fittings into a foam or balsa deck is a long process to do it properly) it is more expensive--especially if you are using epoxy and it has to be done well by people who know what they are doing when being built. This is probably the key thing, even production boats have issues, was just reading on another thread about a number of French production cats having issues with blisters...

Phil
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Old 18-02-2021, 08:16   #152
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Re: Foam Core Hull

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Originally Posted by Bleemus View Post
Wow, I guess I am lucky to be alive. Sailed across the Pacific three times on a boat with a balsa cored hull. Also saw a few Tartan 37s doing the same thing. Surely they are dead by now.
Simply because you have got away with it does not mean it is a good idea. that is just philosophical illiteracy. The man who wins the lottery cannot be said to have made a good investment decision - and that is what the poster wants to know. Not whether other people have got away with it, but whether is is a sensible decision v a solid hull.

Remember, for every 80 year old who has smoked 2 packs of cigarettes every day his whole life, there are a hundred who died in their 50s - only we don't hear from them in forums.

The plural of personal anecdote is not 'data'.
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Old 18-02-2021, 09:17   #153
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Re: Foam Core Hull

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Originally Posted by Marutji View Post
Simply because you have got away with it does not mean it is a good idea. that is just philosophical illiteracy. The man who wins the lottery cannot be said to have made a good investment decision - and that is what the poster wants to know. Not whether other people have got away with it, but whether is is a sensible decision v a solid hull.

Remember, for every 80 year old who has smoked 2 packs of cigarettes every day his whole life, there are a hundred who died in their 50s - only we don't hear from them in forums.

The plural of personal anecdote is not 'data'.

You realize you are responding to a 4 year old thread?


The only uncored hulls you will find any more (like in the last 30 years) are on the cheapest mass produced boats. Cored hulls done the modern way (vacuum bagging, encapsulated balsa blocks, etc.) are much more expensive than solid ones, and with dramatically increased stiffness and strength to weight. It's the only way to build a boat which you want to be strong, stiff, and reasonably light -- so, good sailing yet durable.


Swan, Hallberg Rassy, Discovery, Contest, X-Yachts, Najad -- have any of these EVER built an uncored hull? Not that I am aware, and they certainly haven't in the last 30 years. Do they ever have core problems? The fact that I've never heard of one doesn't prove that they never happen, but has anyone ever heard of a core problem on one of these boats? Data?



The only solid hulls you can buy in Europe are the cheapest production boats, so the lower end Beneteaus and Bavarias. The lack of coring is why Beneteaus are sometimes referred to as "Bendy Toys".


You are sneering at someone giving his own experience as an example, but in fact it's not just his experience -- all the world's high end sailing yachts have cored hulls, because with modern techniques it is simply a superior way to build a boat; just about the only reason NOT to do it would be because cored hulls are too expensive. The actual philosophical illiteracy is to assume that some badly done cored hulls from the 1970's necessarily represents all cored hulls today. That logical fallacy is called "faulty generalization".
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Old 18-02-2021, 10:00   #154
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Re: Foam Core Hull

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Originally Posted by Marutji View Post
Simply because you have got away with it does not mean it is a good idea...
... The plural of personal anecdote is not 'data'.
Often, anecdotal evidence focuses on subjective individual results (as distinct from probabilistic evidence, that gives estimates of how likely something is to occur, based on experience with large numbers of people), is driven by emotion, and presented by individuals who are not subject area experts.
However, as anecdotal evidence accumulates, it begins to somewhat resemble objective statistical data.
If enough anecdotal evidence is collected, and objectively analyzed, doesn't it begin to become probabilistic evidence, or data?
Or, is it forever tainted by it's subjective origins?
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Old 18-02-2021, 10:08   #155
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Re: Foam Core Hull

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Originally Posted by Dockhead View Post
The only solid hulls you can buy in Europe are the cheapest production boats, so the lower end Beneteaus and Bavarias. The lack of coring is why Beneteaus are sometimes referred to as "Bendy Toys".


You are sneering at someone giving his own experience as an example, but in fact it's not just his experience -- all the world's high end sailing yachts have cored hulls, because with modern techniques it is simply a superior way to build a boat; just about the only reason NOT to do it would be because cored hulls are too expensive. The actual philosophical illiteracy is to assume that some badly done cored hulls from the 1970's necessarily represents all cored hulls today. That logical fallacy is called "faulty generalization".
Geez, Dockhead, without commenting on the merit or lack thereof with cored hulls, your comments quoted above are TOTALLY wrong, and you are yourself totally guilty of "faulty generalization."

Many high end boats are built with solid laminate hulls TODAY, and many more are FULL laminate below the water line and cored above. Why would they do that???
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Old 18-02-2021, 11:13   #156
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Re: Foam Core Hull

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Many high end boats are built with solid laminate hulls TODAY, and many more are FULL laminate below the water line and cored above. Why would they do that???
They do that to prevent the possibility of water intrusion into the core due to poor workmanship during construction when installing thru-hulls, or owners doing stupid things like improperly installing underwater lights without removing the coring material.

They use foam coring above the waterline because it provides a greater strength to weight ratio compared to full laminate.

Foam coring also provides insulation, and sound dampening qualities.

There is also the reduced cost factor in manufacturing.
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Old 19-02-2021, 01:01   #157
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Re: Foam Core Hull

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Originally Posted by BillKny View Post
Geez, Dockhead, without commenting on the merit or lack thereof with cored hulls, your comments quoted above are TOTALLY wrong, and you are yourself totally guilty of "faulty generalization."

Many high end boats are built with solid laminate hulls TODAY, and many more are FULL laminate below the water line and cored above. Why would they do that???
I beg to differ. Name one please.

I don't know American boats very well, but I do know that Hinckleys and Morrisses are fully cored.

I do know European boats, and I know that ALL high end European boats are cored. Only one - Oyster - have uncored hulls and only below the waterline, and only the smaller models. As I correctly stated, the only uncored hulls you will find in European boats are in the cheapest mass produced boats. My statement was correct.
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Old 19-02-2021, 01:32   #158
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Re: Foam Core Hull

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Originally Posted by GordMay View Post
Often, anecdotal evidence focuses on subjective individual results (as distinct from probabilistic evidence, that gives estimates of how likely something is to occur, based on experience with large numbers of people), is driven by emotion, and presented by individuals who are not subject area experts.
However, as anecdotal evidence accumulates, it begins to somewhat resemble objective statistical data.
If enough anecdotal evidence is collected, and objectively analyzed, doesn't it begin to become probabilistic evidence, or data?
Or, is it forever tainted by it's subjective origins?
Though I think your questions may be mostly rhetorical, I'll have a go...

It might, depending on how objective the accuracy of the the analysis is.

If the subjectiveness of it's origin is verified it no longer is 'subjective'; it 'crosses the Rubicon' into objectivity; it's tainted provenance is just a curiosity.


Of course, I'm assuming you don't have immediate British ancestry...
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Old 19-02-2021, 18:52   #159
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Re: Foam Core Hull

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Originally Posted by Dockhead View Post
I beg to differ. Name one please.

I don't know American boats very well, but I do know that Hinckleys and Morrisses are fully cored.

I do know European boats, and I know that ALL high end European boats are cored. Only one - Oyster - have uncored hulls and only below the waterline, and only the smaller models. As I correctly stated, the only uncored hulls you will find in European boats are in the cheapest mass produced boats. My statement was correct.


Tartans also. My vintage T40 is fully cored except at every through hull and midline
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Old 19-02-2021, 19:42   #160
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Re: Foam Core Hull

This whole core/no core deal was a much greater issue in the days when Balsa was the primary core material. The problem is that once water got in the core would degrade very fast and over very large areas and the boat would quickly be scrap.

Using rigid PVC or any of the other unreactive core means that damage to the core does not follow the same mechanism. PVC does not break down if exposed to water. It may lose some of its insulation properties. Its also unlikely to conduct water with the same rapidity as balsa.

Finally, the resins used are better in quality than used back in the day. The premium for using epoxy vs polyester is not so significant on a foam cored hull and there will be less in the layup since there will be less weight of higher modulus laminate. Epoxy vs polyester means entirely different risks of having water penetration in the first place. All the polyester hulls will eventually have to be fixed of their blisters and then coated on the outside with epoxy as a barrier coat to keep water out the laminate long term anyway. If your laminate starts off with epoxy in the first place you avoid that problem entirely and also have a stronger boat.

Some boats will continue to be built with solid fiberglass laminate but the ones that justify that will be enduring extreme service with routine groundings and impact, like shallow water fishing boats and the like or where they are just constantly going to be banging into things. Even then, these can be made of heavy layers of stitched fabric, bonded with either Vinyl ester or epoxy and still be totally different from the old boats made from CSM or even the chopper gun loose roving applied robotically with polyester.
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Old 20-02-2021, 14:39   #161
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Re: Foam Core Hull

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Originally Posted by Westcliffe01 View Post
This whole core/no core deal was a much greater issue in the days when Balsa was the primary core material. The problem is that once water got in the core would degrade very fast and over very large areas and the boat would quickly be scrap.

Using rigid PVC or any of the other unreactive core means that damage to the core does not follow the same mechanism. PVC does not break down if exposed to water. It may lose some of its insulation properties. Its also unlikely to conduct water with the same rapidity as balsa.

Finally, the resins used are better in quality than used back in the day. The premium for using epoxy vs polyester is not so significant on a foam cored hull and there will be less in the layup since there will be less weight of higher modulus laminate. Epoxy vs polyester means entirely different risks of having water penetration in the first place. All the polyester hulls will eventually have to be fixed of their blisters and then coated on the outside with epoxy as a barrier coat to keep water out the laminate long term anyway. If your laminate starts off with epoxy in the first place you avoid that problem entirely and also have a stronger boat.

Some boats will continue to be built with solid fiberglass laminate but the ones that justify that will be enduring extreme service with routine groundings and impact, like shallow water fishing boats and the like or where they are just constantly going to be banging into things. Even then, these can be made of heavy layers of stitched fabric, bonded with either Vinyl ester or epoxy and still be totally different from the old boats made from CSM or even the chopper gun loose roving applied robotically with polyester.
Balsa has some advantages and is still used.

Balsa wood is stronger than titanium by weight, so makes an immensely strong composite panel with GRP.

Both balsa and foam will degrade quickly if water gets in -- foam is not indeed less "reactive" than balsa -- but that problem has been solved (unbeknownst to some people with bombastic opinions out of date by at least three decades) with vacuum bagging/vacuum infusion of resin. Another level of protection for balsa, which makes it basically fail-proof, is to build it up in encapsulated blocks. All this adds still more to the cost, making cored construction far more expensive than solid glass, but the advantages of strength, stiffness, and weight are irresistable for sailing yachts.

But it is true that foam is becoming more and more common. It is somewhat more expensive than balsa but it is more consistent and easier to engineer, as it comes in a great variety of different qualities.
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Old 12-03-2021, 10:41   #162
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Re: Foam Core Hull

The idea of a sailboat is not monolithic; all sailboat lines of production are different and are designed to accomplish different things. It is impossible to say hull coring is good or bad until you know what the sailboat is intended to do. A racer will love cores because they save weight. A liveaboard will love foam cores for the insulation they provide. A cruiser exploring rocky inlets and bays or coral reefs will hate cores because they are often crushed in a collision with hard/sharp objects and require a hull repair. For myself, I prefer solid hulls but will tolerate Airex cores in the decks as long as there are full depth fiberglass pads at every deck penetration. But it is just a preference because I cruise, not race. My boat has to endure a knock or two.
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Old 14-03-2021, 09:30   #163
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Re: Foam Core Hull

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. . . A cruiser exploring rocky inlets and bays or coral reefs will hate cores because they are often crushed in a collision with hard/sharp objects and require a hull repair. .

Not necessarily. I would prefer a cored Hallberg-Rassey to a solid Beneteau, for encounters with hard/sharp objects. Cored hulls are "often" crushed in collisions wiht hard/sharp objects? Do you have data on that?


Cored hulls are generally much stronger than any solid hull with realistic weight for a sailing vessel (motor sailer might be different). Better quality boats add even more strength and penetration resistance with Kevlar outer skins (my boat has this). I do not think that cored hulls are an issue for this. I certainly never worried about my cored (and Kevlar-skinned) hull when exploring the rocky, uncharted waters of Northeastern Greenland. The main drawback of modern cored hulls is high cost.
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