Foam cores - opinions

[extravert]

Anyone who has read David Pascoe's Yacht Survey web site will know that he has a low opinion of foam core boat building methods. Does anyone know if his opinions are right and they are a recipe for disaster, or does he just have a thing against this building method and exagerates his views.

Has anyone here had particular problems with foam cored hulls, especially where they are used below the waterline?

 

[david_e]

Re: Foam cores - mixed views

Haven't seen the site.

ETAP's have a foam core and they seem to be OK. Don't many other builders use foam in their deck structures?

There was a photo in a mag recently showing a foam cored boat, from the 'gone bust Bowman yard' being re-skinned. Whether this had anything to do with the foam, not sure. When I was researching older boats, the Sadler 32 was one, and I learnt that on some of the older models the foam had turned to dust with age.

Brother, who has a boat on 12a, is a foam expert and has done specialist applications in many marine situations, the foam they use is stronger than the stuff they stick it to in many cases. With modern manufacturing techniques and application methods it should be OK, just look at the amount of foam filled aircraft parts there are. But the problem with specialist boat builders is their tendency to cut corners, or possibly lack of investment in the right equipment, which could be a concern.

Get the feeling that out of sight, out of mind scenario comes into play.#

Is this on the Cat?

 

[extravert]

Re: Foam cores - mixed views

Yacht survey is here...

http://www.yachtsurvey.com/articleslist.htm

The type of foam cores I am interested in is not the kind where void spaces are filled with foam to provide bouyancy in case of a hull pirecing, but where foam is used to seprate to layers of GRP laminate to provide a truss structure to add strength and reduce weight of the structure. This method is used widely in decks, often with balsa cores.

It seems to me that foam cores like this below the waterline are frequently used in multihulls, and are used by both the current trimaran manufacturers marketed in the UK, ie Corsair and Dragonfly. They both use a technique called 'Vacuum bagging', supposedly to improve the foam to GRP bond.

David Pascoe talks mainly about large American motor boats, which sound like many of them are built by small short lived outfits that lack knowledge and care, and cut corners like you suggest. However, both Corsair and Quorning (Dragonfly manufacturer) seem to me so far to be high quality and long established outfits, despite being relatively small and specialized compared to BenJenBav. They don't however seem to be cut price manufacturers, both charging highly for the relatively small boats they produce. But the high price just adds to my concern that it may be too high a price to pay for a troublesome and maybe short lived construction technique.

 

[Twister_Ken]

It\'s good enough for Hallberg Rassy

from its website...

"The gelcoat is based on isophtalic resin. The isophtalic resin is very resistant to water penetration. The white gelcoat is sprayed on. White for the hull and blue gelcoat for the HR stripe. The outer skin is then laminated layer by layer. Also here we use the isophtalic resin in order to get a resistant laminate against water penetration.

The dimensions are very much the same as in older constructions with single laminate, but a single laminate is not as stiff as the boats we build today. Today we add an insulation that improves the comfort in the boat and the torsional strength of the hull.

 
The material used is a PVC-foam made by Divinycell. It is fitted when the laminate is still wet, and then covered by laminate. The Divinycell is a superior material for a cruising boat, compared to balsa. The PVC foam has closed cells, which means that the material does not absorb water. The different colours of the Divinycell are an indication that different density of Divinycell is used. There is higher density around the chainplates. The Divinycell will finally be covered with more laminate. "

 

[davel]

Re: Foam cores - mixed views

You may have seen a brief news item in last months PBO about a problem with a batch of Bowman Starlight 35s that use this construction method.

It's believed that a failure in the manufacturing process caused the outer hull to separate from the foam lining resulting in distortion of the hull. The boats were so badly damaged that they were declared unseaworthy by the insurance companies. Subsequently the owners have had to undertake extensive repairs (basically have new outer hulls remoulded and have the original inner hull and fittings reinserted) at tremendous expense.

This seems to illustrate that the process is far from fool proof and even the biggest names can still foul up.

Dave L.

 

[snowleopard]

years of experience

derek kelsall has been designing boats with pvc foam core for 30 years and many of his earliest offerings are still afloat and working well. i have built 2 myself and have had no problems.
the pvc core (airex or herex in my case) is closed-cell and thus doesn't fail if moisture gets in where balsa cores would rapidly rot.

there is a risk with the sandwich construction that the skins fail to bond to the core which was what caused the hull failures in team philips. correct construction techniques prevent this, i.e. vacuum-bagging or applying the laminate to the foam.

bad design can cause problems, in a different context i have experienced failures where the core is subject to excessive/unfair loads. i have also heard of core failure as a result of 'oilcanning' on a whitbread racer. this is caused by insufficient stiffening of an almost-flat panel.

 

[Chris_Robb]

Re: Foam cores - mixed views

I think that they were Balsa core to the waterline

 

[Chris_Robb]

Re:Balsa

Another well known quality Swedish yatch uses Balsa core below the waterline, I saw an early one (3 years ago) where a core sample had been taken and the inner core was total mush. - the company settled on the steps of the high court I believe. - Boat belonged to a barister.

I think the hydraulic pounding effect described on powerboats may be more exclusive to stinkies than slower yachts.

Balsa is a stronger material in the short term but I would not have it. Nor would I have the floor grid structure used by most of the AWBs where it is not actually glassed into the hull but stuck. First bash on the bottom and you have a progressive breakdown of the bond over several years - ending up in a complete bottom rebuild - if you can afford it - or provided your still with the same insurance company.

 

[kingfisher]

Better than balsa

Mine is solid hull, but balsa laminate for the deck mould. Where water has ingressed (cable throughruns for example) the balsa has rotten. Result : black tears in the heads where the cables come in the boat= purely aesthetical problem. But: she's starting to suffer from a soggy deck: the deck starts to get sponge-like as the balsa rots away. Apparently there's little I can do. Even if I plug the holes, the moisture inside will continue to cause rot. The only option would be to completely remove the deck. No thank you.

I wish I had closed cell foam instead of balsa. And I guess there will have been instances where, due to a failed production process, boats with balsa cores have delaminated as well.

Group of people on the pontoon: skipper is the one with the toolbox.
http://sirocco31.tripod.com

 

[Chris_Robb]

Re: It\'s good enough for Hallberg Rassy

Ken - having now read the reports on any type of core - it appears that foam - even closed cell is considered to be considerably worse than balsa.

Considering that you are paying top buck for a Halberg - sorry I would buy an Oyster - who avoid the use of coring in the hull for the very reasons stated in the yatchsurvey.com web sight.

 

[Chris_Robb]

Re: No its not

Go and read Yachtsurveys.com and the section on core types - he favours balsa over foam - although non absorbant it is just not strong enough, and does not bond as well. This is a very good article explaing all the plusses and minuses.

Wont help with your existing deck however - good luck with a solution.

 

[pandroid]

Re: It\'s good enough for Hallberg Rassy

There's a difference in using foam as an insulator or a structural component. HR claim that its not structural. The final inner layer of glass is merely to keep the foam in position.

Interestingly Najad claim that it they do the same and that it isnt structural either, but that they have the same thickness of laminate on both sides of the foam. The rationale being that 'it makes the hull bounce back in the event of an impact' (?)

Either way, all these hulls are phenomenally stiff.

Both have a third layer of insulation made up of wooden slats and an air gap on the inside

 

[pandroid]

Re: Better than balsa

A surveyor on my last boat said one way to rescue this is to inject resin with a syringe into the void (thus substituting resin for core) Obviously this wouldnt work if the whole thing was shot

 

[castaway]

Re: No its not

I had a Pacesetter 29 that I fitted out from hull and superstructure moldings. This boat was balsa core thoughout, right down to within about 12 inches if the keel (deep fin) When I started cutting the various holes in the hull for fitting /seacocks etc. I kept some and chucked then in a bucket of water where I left en for about 5 years. None showed any signs of deterioration or rot and I still have section on a key ring.

I remember being told that the qualities of balsa were far superior to any of the foam cores available then (15 yrs back) and so long as the balsa endgrain tiles are correctly applies and sufficient resin is used to isolate each tile from its neighbour there would be no problems, and certainly I has none whatso ever.

I agree that the problem of core breakdown comes when a flatish area is subject to constant deflection; I'm sure that foam./balsa cores where never intended to work in those areas,(with out suitable support) which tends to put the problem with the designer rather than the material.

Regds Nick

<A target="_blank" HREF=http://www.yachtsite.co.uk/fairweather>http://www.yachtsite.co.uk/fairweather</A>

 

[Chris_Robb]

Re: No its not

The survey site said that Balsa has natural anti fungal properties- untill they wash out. Then the black gunge develops. Perhaps a standing bucket of water will not get the fungal spores washed down by the rain???

As Balsa is used in almost every deck (except Victory and probably your Halbadier) on every yatch produced - it is good for a long period. I have problem (well - not my problem) with it being used below the waterline where no one can guarantee that a minor piece of unoticed damage will not occur in 20 - 30 years.

 

[Solstice]

Re: Foam cores - mixed views

As a Starlight owner I naturally made a few enquiries when I read the item in PBO about hull failures on the latest batch of Starlights. It seems that problem dated from a change in the hull moulding subcontractor and changes in the rules about CFCs, and the foam insulation used between the mouldings. The material used previously was no longer available and the replacement foam turned out to be prone to shrinkage which after a few months produced hollow areas in the outer hull where the foam was contracting. The fault was restricted to a small number of identifiable hulls and I assume the foam specification has now been amended and that present and future Starlights will now be as sound as the many previous foam cored Sadlers and Starlights that have been built over the past twenty years or so and are still giving good service.

Having said that it must be acknowledged that nothing is ever perfect and standards of construction can fall from time to time however good the specification is. Where these coincide with above average stress in use, hull failure may occur but I would hazard a guess that foam cored hulls are no more liable to fail in this respect than others, which are more at risk from excessive flexing of unsupported areas etc. Probably the greatest drawback to a foam cored hull is that if failure or damage does occur the cost of repair can be much higher, as the unfortunate owners of the recent Starlights have found to their cost.

 

[castaway]

Re: No its not

Chris

Actualy the Halberdier does have balsa deck and they are totally sound..however I suspect that the laminates on each side are so thick that it is unlikely that I would ever notice if the entire core disappeared!

I think that the problem is that when any core material is used the difference in the skill levels of the laminator, that would never show up with a normal lay up ( until it all starts blistering of course).. becomes very quickly apparent.

Also a lot of probs with cored hulls comes from badly fitted desk ware and skinfittings, the core in the area of a fitting,, if a hard point is not fitted,, should always be removed and the laminates closed.

My experience was very good, but out of choice.
a. I would rather have a solid laminate hull
b. If not, I would definately rather have balsa rather than foam crumbling away and delaminating. Never did like cavity walls on boats!

IMHO.

Regds Nick

<A target="_blank" HREF=http://www.yachtsite.co.uk/fairweather>http://www.yachtsite.co.uk/fairweather</A>

 

[david_e]

Re: Foam cores - mixed views

Have had a brief look at this site, wow! I recall visiting it last year but not reading this particular article. My only reservation with Pascoe is that he stopped talking about Yachts a while back and now concentrates on powerboats so this, imho, needs to be factored in to his views. Firstly from a design and manufacturing aspect and secondly from the type of usage, in particular the comparitive intense pounding that powerboats suffer.

I just wonder if as a user/buyer it is possible to ascertain a full answer to your concerns without going into immense research. I know from my days working with aircraft that foams and their applications are probably far more sophisticated than Pascoe portrays.

If you are buying new then I would have thought that on balance the construction method used should not be a major concern unless there is evidence to the contrary. Is there is an option to have them built in a different way, or is the only alternative to choose a different boat builder?

The point that Pascoe makes about the Lloyds certificate is good and is applicable to all types of boats. If your chosen manufacturer does not have this certification then possibly getting your own survey/inspection done at the critical stages is an answer to partly resolving your concern about the price paid for this process. (Not sure where they are built so no flaming please!)

I like Kens comments about HR's. I think from a simplistic angle I would be comparing what they do and their processes to your preferred builder.

Interesting thread, would be useful to know how it transpires.

 

[AndrewB]

Built-in obsolescence?

No-one knows definitively whether his opinions are right. What we do know is that in some cases there have been problems, but whether this means that in general foam-core yachts will be short-lived is anyone's guess.

Personally though I believe there is sufficient uncertainty that I would never buy a foam cored yacht. It is the same situation as with ferro-cement - except that the experience is shorter.

I'm deeply suspicious that yacht builders have been looking for ways of creating built-in obsolescence in GRP yachts to maintain future demand, and this may well be one of the ways.

 

[Twister_Ken]

Re: Built-in obsolescence?

>Personally though I believe there is sufficient uncertainty that I would never buy a foam cored yacht.<

The problem is, that leaves you with a very small choice of (new) boats to choose from.