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    • B.J. Porter

      Moderation Team Change   06/16/2017

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Spin Echo

Longevity of foam cores

40 posts in this topic

A lot of new boats (X-yachts, Riptides, Blue Jackets and many more) are being built with foam core (Divinycell, Corecell, etc). Im just wondering how well foam core holds up over time and what are some of the issues with them since they started being used in the 1980's. Are they really superior to the good old Balsa, except for the rotting, of course, but then i've read they also deteriorate with water ingress.

 

Some marine surveyors have really seen a lot of problems with the foam cores, eg: http://marinesurvey.com/yacht/material.htm

 

So just wondering what the great minds here think about the topic. Thank you for the info in advance.

 

 

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A local boat - Porpoise - a Discovery 47' "racer at the time" was reputedly the first foam core boat built - Airex in about 1968. It is still going strong. I looked at it with a view to buying it about 12 years ago and while scruffy, it was totally solid, unlike many of the balsa cores I've seen.

 

I'd take foam over balsa any day.

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Foam any time, great long lasting material, easier to repair in far away places.. now wheres my zip cutter.....

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well done foam hulls have a potential longevity that is no different than solid hulls. Many of the worlds finest builders choose to build foam cored hulls. They wouldn't if the longterm resale of their boats was compromised.

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That surveyor has a huge problem with foam cores. I agree with him if not vacuum bagged to the outer skin, cores can be a problem. Just bedding in bonding putty is usually a mistake.

 

But I'd take a foam core over balsa any day. My 29 year old catamaran has Klegecell core and is holdiing up just fine thank you. And we don't baby the boat when we sail.

 

And that surveyor's web site shows how a hull holds up to catastrophic conditions - hurricanes. I don't think that it is reasonable to expect any hull construction to prove entirely fool proof in 'extreme' conditions. Real world damage with foam cores generally seems that they do quite well in collisions and local impacts. The foam does a good job of spreading the load and the inside skin often remains intact.

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My 1985 Airex cored Hinckley is doing just fine. I expect to leave her to my children.

 

Whether a core works well or is a problem depends on both the builder and the owner. To make core work, it need to be isolated from water, so the good builders don't put penetrations in the core. Where there will be thru-hulls, the core should be deleted and replaced with solid glass. The owner should refrain from stupid stuff, like just sticking a screw thru the inner laminate in or near the bilge where it's likely to be submerged.

 

You have to take groundings seriously. If the outer laminate is compromised, deal with it sooner rather than later. Just because the boat isn't leaking doesn't mean the outer skin isn't letting water into the core.

 

A lot of reputable builders core because it offers significant mechanical advantages in term of stiffness/weight and thermal/sound insulation. If the builder is coring to try and save money on glass and resin, it will probably be a sad boat. If he uses core to build a better boat, and is willing to expend the effort to do it right, the result can be very, very good indeed.

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What CL said. And I'll take foam over balsa anytime.

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I agree with Mr. Loser as well, but regarding balsa v. foam can someone be more specific about why they prefer foam any day. My understanding is that both foam and balsa are (equally?) vulnerable to water ingress and that balsa is stiffer, lighter and more impact resistant. I know that there are some horror stories out there regarding older J boats with wet decks but J boats is still using balsa, and presumably not to save money. In any event, I think great boats can be built with either material, if done properly with attention to detail.

 

Frede

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I agree with Mr. Loser as well, but regarding balsa v. foam can someone be more specific about why they prefer foam any day. My understanding is that both foam and balsa are (equally?) vulnerable to water ingress and that balsa is stiffer, lighter and more impact resistant. I know that there are some horror stories out there regarding older J boats with wet decks but J boats is still using balsa, and presumably not to save money. In any event, I think great boats can be built with either material, if done properly with attention to detail.

 

Frede

 

Balsa has some advantages in it's properties. It's easier to get a good surface bond, it's less expensive than an equivalent foam, and it's better at localizing damage. However I would say that balsa, like any wood, has a finite life span no matter how well it's built into the laminate or how well it's taken care of, and once it gets wet the fuse is lit. Foam is not that vulnerable.

 

Personally I think foam cores are easier to repair too.

 

Pascoe's web site should be considered comedy rather than informative. Yes there is some crappy "marine composite" employed in the cheaper range of mass-produced boats, but what do you expect? There's a reason why Hinckleys, Swans, Oysters, etc etc cost more. Pascoe seems to think that the existence of crap proves there is no such thing as non-crap QED. It's shame... but it's on the internet so it must be true!

 

FB- Doug

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I've seen plenty of soggy balsa cores. Wet balsa has the mechanical properties of wet cardboard. Useless. I wouldn't buy a boat with balsa. I've seen lots of wet foam cores. Nothing scary, unless you plan to be in freezing temps.

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Foam is well proven, on some boats with relatively thin laminates it'll show, which is fine because that's for a reason, on conservatively built it's great, I looked over a 35 year old Klegecell boat just before Christmas... raced most it's life & in regards to structure excellent but built by a top end Aussie yard. I'm comfortable with balsa & using it in my own boat but for hulls only with minimum penetrations & appropriate close outs, for the deck it's foam core, not for me but the future when stuff gets added by new owners, trimmers etc who might not fully understand consequences of their actions in attaching "stuff" & not casting anulus close outs & countersunk sealing & the like.

Foam is good,

Balsa is good,

But gotta be done good.

Jeff.

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So... on an older boat, where some re-coring work is needed, can the average DIY guy buy these foams in smaller quantities?

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I agree with Mr. Loser as well, but regarding balsa v. foam can someone be more specific about why they prefer foam any day. My understanding is that both foam and balsa are (equally?) vulnerable to water ingress and that balsa is stiffer, lighter and more impact resistant. I know that there are some horror stories out there regarding older J boats with wet decks but J boats is still using balsa, and presumably not to save money. In any event, I think great boats can be built with either material, if done properly with attention to detail.

 

Frede

Just a couple of points

 

Modern PVC and SAN foam cores don't have an issue with moisture, the only issue is if they haven't been bonded to the laminate skins properly or if the engineer has taken into account the shear loadings.

 

Standard balsa has a density of 155 kg/m3, foam cores are available from 38 kg/m3 up to 250 kg/m3.

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So... on an older boat, where some re-coring work is needed, can the average DIY guy buy these foams in smaller quantities?

Chat to your local boat yard, they'll may have small left over sections that can be exchanged for a pack of beer. ;)

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I've had no problem scrounging foam at boatyards as well. Generally dumpster diving with permission:-)

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Foam is well proven, on some boats with relatively thin laminates it'll show, which is fine because that's for a reason, on conservatively built it's great, I looked over a 35 year old Klegecell boat just before Christmas... raced most it's life & in regards to structure excellent but built by a top end Aussie yard. I'm comfortable with balsa & using it in my own boat but for hulls only with minimum penetrations & appropriate close outs, for the deck it's foam core, not for me but the future when stuff gets added by new owners, trimmers etc who might not fully understand consequences of their actions in attaching "stuff" & not casting anulus close outs & countersunk sealing & the like.

Foam is good,

Balsa is good,

But gotta be done good.

Jeff.

I agree with jeff. When done properly either balsa or foam is good, with balsa having generally superior structural properties especially in compression and sheer. Problems in balsa or foam can occur because it of poor construction by the builder and/or poorly done modifications by subsequent owners. No matter what core you have it is best to "pot" or cast anulus close outs etc any holes through the core in order to tie the inner and outer skins together and to prevent crushing the core when fasteners are tightened. Water can damage foam core lay-ups when it finds its way between the core and the skin and then freezes, but this is less frequent than damage to balsa from water.

 

Here is a good source of information on composite materials by Gurit who provide all types of core and fabrics (including both balsa and foam) to composite builders:

http://issuu.com/gurit/docs/guide_to_composites_2011/1?e=1086841/1088243

 

Edit: PDF version:

http://www.gurit.com/files/documents/guide-to-composites-v5pdf.pdf

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Balsa rots when it gets wet, foam doesn't - pretty simple. I've also dealt with lots of badly or partially bonded balsa so I question if there's much difference there

 

I am able to buy small pieces of various types of foam, either either solid or scored, at local fiberglass suppliers - it's a standard product for them. I've had good luck with Q-Cell.

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A lot of new boats (X-yachts, Riptides, Blue Jackets and many more) are being built with foam core (Divinycell, Corecell, etc). Im just wondering how well foam core holds up over time and what are some of the issues with them since they started being used in the 1980's....

 

 

The when?

 

I remember seeing Boston Whalers that were "foam sandwich" construction long before then.

 

If you want to know what happens to old Whaler foam, go ask on continuouswave.com. Short answer: it crumbles if exposed to air or sun and soaks up water if water is available. If those things don't happen, it seems to last a very long time.

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A lot of new boats (X-yachts, Riptides, Blue Jackets and many more) are being built with foam core (Divinycell, Corecell, etc). Im just wondering how well foam core holds up over time and what are some of the issues with them since they started being used in the 1980's....

 

 

The when?

 

I remember seeing Boston Whalers that were "foam sandwich" construction long before then.

 

If you want to know what happens to old Whaler foam, go ask on continuouswave.com. Short answer: it crumbles if exposed to air or sun and soaks up water if water is available. If those things don't happen, it seems to last a very long time.

 

Water? In a boat? Chance in a million.

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Balsa rots when it gets wet, foam doesn't - pretty simple. I've also dealt with lots of badly or partially bonded balsa so I question if there's much difference there

 

I am able to buy small pieces of various types of foam, either either solid or scored, at local fiberglass suppliers - it's a standard product for them. I've had good luck with Q-Cell.

 

That is true, but, foam core also gets installed poorly. I have been to several presentations at IBEX discussing this subject and there are plenty of instances of poorly bonded foam cores. Bruce Pfund has plenty of pictures of both foam and balsa disasters. The one I remember most was a high speed powerboat which developed a crack in the outer skin forward of amidship which let water in and when at speed hydraulically blew the outer skin off the foam core for the length of the boat. I assume (because I do not know for sure) that there are a lot of boats out there with foam cores which have become debonded due to poor adhesion caused by faulty construction.

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Was looking for a boat a few years ago, came across a 40 footer with a foam core, ad said new bottom job.

It turns out they stripped the outer skin and core, and replaced both with the boat upright.

Just left the solid strip along the centerline intact.

I found the builder who did the job, and asked why they did it. He said the boat had osmosis in the inner skin.

So I asked him if he would ever do the job again, he said no without hesitation.

Apparently these boats had a problem with water ingress, usually through through hulls leaking. The builder said "usually we put them on the hard and drill drain holes in the low part of the skin, when the water stops coming out we plug the holes and they are right for a few years".

So we ended up with a boat with a solid hull.

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I helped a guy once with a Canadian built 47'er with a foam core. It was a Cooper boat. He had some delamination. Turned out he had more delamination than he had lamination. I estimated about 70% of the hull was delaminated.

That was just the outer skin.

 

I helped another guy with a bigger Cooper boat, 65' as I recall, foam core. The boat was delaminating before it was launched. I gave the job to Gary Mull. I'm alergic to expert witness work. Some builders preferred to work with Balsa. Easier to get a good bond.

 

I think that either core type can be well done or poorly done. I would have no problem goling with balsa today if I had a good builder. But I'd probably go foam.

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Wasn't there a thread here a few years ago where the IP had a euro boat that basically had no bond between the core and the outer skin? One of the reasons Hinckley went to Awlgrip instead of gelcoat, as I understand it, was so they could inspect the laminate after it came out of the mold, to confirm resin penetration into the kerfs in the core. Alden was doing the same on their later boats.

 

Morris replaced a bunch of core and outer skin on a big custom Hinckley a couple of years ago, with the boat upright. IIRC the water had found it's way in as a result of a grounding.

 

Holy shit Jose! That's freaky. That may be what Pascoe is complaining about.

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I agree both foam and balsa are fine if properly constructed and maintained. Our balsa hull is 40 years old this year and still going strong, we've owned it 14 years and have had it surveyed twice now. One funny thing, when we had the deck repainted we contracted to pay by the square foot for all wet deck repair. They went up and down that deck with a moisture meter and tapping. The repair bill for wet core was $0.

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Wasn't there a thread here a few years ago where the IP had a euro boat that basically had no bond between the core and the outer skin? One of the reasons Hinckley went to Awlgrip instead of gelcoat, as I understand it, was so they could inspect the laminate after it came out of the mold, to confirm resin penetration into the kerfs in the core. Alden was doing the same on their later boats.

 

Morris replaced a bunch of core and outer skin on a big custom Hinckley a couple of years ago, with the boat upright. IIRC the water had found it's way in as a result of a grounding.

 

Holy shit Jose! That's freaky. That may be what Pascoe is complaining about.

 

Seems to be a tricky problem. This may be the best argument in favor of vacuum bagging or infusing; sometimes even experienced builder intending to do a good job have bonding issues.

 

I wonder if part of it isn't working conditions; for example I have had work space in a boat shop (some years ago) that was very dusty. They did have a negative-pressure anti dust system, but still everything in the shop including stored cloth acquired a layer of fluffy sanding dust. This was at a business that had built (and was still building at much reduced volume, hence renting out shop space) well-regarded boats. The shop supervisor shrugged off the dust problem, obviously feeling that the only real problem was that I was complaining about it. And I had some laminating work that I did personally in that shop come unzipped all of a sudden. Bad stuff.

 

FB- Doug

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Yep, vacuum bagging or better yet infusion is the way to go, but you have to make sure you place the bag correctly to avoid bridging in any tight inside corners etc. Kerfing the core so it conforms to tight radii is important too, as is tapering the core where it transitions to different thickness core or to solid laminate.

 

Dirty working conditions from dust to dripping sweat contribute as well.

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When I use core in small amounts - 4 sq' or so, I open all the kerfs and brush epoxy in them, then I roll epoxy over the surface, THEN i press it against the wet glass. I've never had a failure.

 

Of course, doing it with full sheets in a mould might present some problems. ^_^

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A lot of new boats (X-yachts, Riptides, Blue Jackets and many more) are being built with foam core (Divinycell, Corecell, etc). Im just wondering how well foam core holds up over time and what are some of the issues with them since they started being used in the 1980's....

 

 

The when?

 

I remember seeing Boston Whalers that were "foam sandwich" construction long before then.

 

If you want to know what happens to old Whaler foam, go ask on continuouswave.com. Short answer: it crumbles if exposed to air or sun and soaks up water if water is available. If those things don't happen, it seems to last a very long time.

 

 

Our yacht club had some vvvvvveeerrrryyy heavy 13' whalers that seemed to consist of 50% retained water. Functioned fine, but a bit slow to get on a plane.

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A lot of new boats (X-yachts, Riptides, Blue Jackets and many more) are being built with foam core (Divinycell, Corecell, etc). Im just wondering how well foam core holds up over time and what are some of the issues with them since they started being used in the 1980's....

 

 

The when?

 

I remember seeing Boston Whalers that were "foam sandwich" construction long before then.

 

If you want to know what happens to old Whaler foam, go ask on continuouswave.com. Short answer: it crumbles if exposed to air or sun and soaks up water if water is available. If those things don't happen, it seems to last a very long time.

 

 

Our yacht club had some vvvvvveeerrrryyy heavy 13' whalers that seemed to consist of 50% retained water. Functioned fine, but a bit slow to get on a plane.

 

Good job you weren't stowing them in the overhead.

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IIRC Whalers were filled between the mouldings with some kind of injectable foam, not core type foam.

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One thing that people never seem to notice is that different foam cores have VERY DIFFERENT bonding strength. You can't lump them all togather. The reason we use Corecell is because one day we took all the different foam cores we had around the shop and infused a piece of each one. The green stuff from vendor X, kinda' like a inexpensive Arex, bonded no better than peel ply. Just worthelss. The best were Divinalcell(sp?) and Corecell with Corecell being slightly better.

 

-jim lee

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One thing that people never seem to notice is that different foam cores have VERY DIFFERENT bonding strength. You can't lump them all togather. The reason we use Corecell is because one day we took all the different foam cores we had around the shop and infused a piece of each one. The green stuff from vendor X, kinda' like a inexpensive Arex, bonded no better than peel ply. Just worthelss. The best were Divinalcell(sp?) and Corecell with Corecell being slightly better.

 

-jim lee

 

Divinycell is nice to work with, crisp. No nasty granules all over the hands and everything else. Generic polyurethane foam is fragile and ends up everywhere, like in underwear you haven't even seen for three years.

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One thing that people never seem to notice is that different foam cores have VERY DIFFERENT bonding strength. You can't lump them all togather. The reason we use Corecell is because one day we took all the different foam cores we had around the shop and infused a piece of each one. The green stuff from vendor X, kinda' like a inexpensive Arex, bonded no better than peel ply. Just worthelss. The best were Divinalcell(sp?) and Corecell with Corecell being slightly better.

 

-jim lee

 

Divinycell is nice to work with, crisp. No nasty granules all over the hands and everything else. Generic polyurethane foam is fragile and ends up everywhere, like in underwear you haven't even seen for three years.

Any underwear I haven't seen in 3 years belongs, by definition, to someone else, so no big deal.

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The one brand of cruising sailboats that I know of with hulls that have foam cores is Southern Cross. Are there any known instances of structural failures due to debonding in those boats?

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One thing that people never seem to notice is that different foam cores have VERY DIFFERENT bonding strength. You can't lump them all togather. The reason we use Corecell is because one day we took all the different foam cores we had around the shop and infused a piece of each one. The green stuff from vendor X, kinda' like a inexpensive Arex, bonded no better than peel ply. Just worthelss. The best were Divinalcell(sp?) and Corecell with Corecell being slightly better.

 

-jim lee

 

Divinycell is nice to work with, crisp. No nasty granules all over the hands and everything else. Generic polyurethane foam is fragile and ends up everywhere, like in underwear you haven't even seen for three years.

Any underwear I haven't seen in 3 years belongs, by definition, to someone else, so no big deal.

 

Just go commando - one less thing to worry about. The girls generally like it too.

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One thing that people never seem to notice is that different foam cores have VERY DIFFERENT bonding strength. You can't lump them all togather. The reason we use Corecell is because one day we took all the different foam cores we had around the shop and infused a piece of each one. The green stuff from vendor X, kinda' like a inexpensive Arex, bonded no better than peel ply. Just worthelss. The best were Divinalcell(sp?) and Corecell with Corecell being slightly better.

 

-jim lee

 

Divinycell is nice to work with, crisp. No nasty granules all over the hands and everything else. Generic polyurethane foam is fragile and ends up everywhere, like in underwear you haven't even seen for three years.

Any underwear I haven't seen in 3 years belongs, by definition, to someone else, so no big deal.

 

Just go commando - one less thing to worry about. The girls generally like it too.

 

Not when it's covered in polyurethane dust.

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Sorry, I thought it said genital polyurethane foam.

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For years Balsa was the least expensive core material. That made it the most used and also the most miss-used core material. There were many poor building practices such as not adequately wetting out the core, walking on the core after it has been put in place, not keeping packaging sealed which allowed moisture content to increase and so on. Moisture in the core retards the time it takes resin to gel and also affects the cure rate. Resin drains from the inner skin leaving pockets of styrene gas. Walking on the core leaves pockets on the outer skin. Not only do you have poor bond, but also the resin around those pockets will not cure.

 

While a lot of people blame water ingress into core on poorly bedded through hulls or unsealed screws, the fact is that if water is present in the bilge, the summer heat will turn the inside of a boat into a high humidity environment. While water may not pass through laminate, water vapor quite easily does. Proper infusion fills all the kerfs in a core, but early infusion attempts often left a dry porous laminate on each side of the core..

 

Polyurethane foam is not a suitable structural material, it is only suitable for flotation. Both linear and cross linked PVC as well as Linear SAN foams are good structural materials provided that a density (sheer strength is directly tied to density) appropriate for the application is chosen. When PVC density approaches that of end grain balsa, so does it's sheer strength.

 

In order to support rot you need moisture, air, and bacteria. Those three elements do not exist together in a properly engineered and built laminate. Rot only exists where the laminate has failed and allows these elements to enter. i had test panels out in the weather for 5 years and checked them every few months. Rot developed along the exposed edges of the panels, but did not ever travel more than a half inch away from the edges.

 

The good thing for people buying used boats is that most problems with core show up within the first couple years. They will have either been fixed or should be easily detected by a competent surveyor.

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