Mobo hull construction - balsa core sandwich

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AHoy2

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To date I have avoided boats with balsa core hull construction as I have been concerned about long term integrity and consequences of any damage. Now I find myself seriously interested in a couple of mobos from established builders which use this method of hull construction. I am aware of the benefits of sandwich construction, but still concerned about the use of an absorbent material such as balsa. With modern build methods and materials is durability and repair not an issue?

TIA.
 
jimg said:
Which ones are you thinking of?
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That may well depend on the responses here :>)

I didn't want to get model specific just yet, unless you are suggesting that construction /durability varies significantly across builders and within their models - worrying!

Do certain builders have "suspect" design/quality and consequent reduced resale value?
 
I think it very muh depens on the vintage of the boat. coring is widely used throught modern boats because it greatly increases strength without adding much weight.

Now, there coring materials are also foam based and in use by manufactuers from Bavaria to Windy. Isoplasmic Resins greatly improve (in fact almost eliminate) water ingress into GRP hulls, assuming that the resin and fibres have been laid correctly. Again, modern manufacturing techiniquesgreatly improve the success of this process.

It is import then, to understand what vintage and origin the boats are. No doubt someone (Oldgit maybe?) will no doubt be along to post a ream of links to the very outdated David Pascoe site which will do much to make you never want to consider a cored boat - despite the fact that all the boats he consider were built at the end of the 80s and early 90s when resi technology and the American build ethic were less than perfect.

There are so many variables, at least give us a clue to the age and origin of the boats you are considering, otherwise your question id pretty pointless.
 
Whitelighter said:
.....

Now, there coring materials are also foam based and in use by manufactuers from Bavaria to Windy. Isoplasmic Resins greatly improve (in fact almost eliminate) water ingress into GRP hulls, assuming that the resin and fibres have been laid correctly. Again, modern manufacturing techiniquesgreatly improve the success of this process.

......

There are so many variables, at least give us a clue to the age and origin of the boats you are considering, otherwise your question id pretty pointless.
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Sorry, I should have given some idea of vintage.

Boats being considered are from 2000 onwards (not just for hull reasons) and of N. european origin.
 
By 2000 most manufacturers developing planing hulls were using some form of coring as it leads to a lighter and therefor more efficient boat. Its the same reason that vacuum resin infusion is now becoming widely used - you only need the right amount of resin as you get it in the right place.

I would expect most boats of this era to be using the modern isoplathic resis, as well as other anti-osmosis treatments on there hulls, so in a welll made, well looked after vessel water ingress directly through the hull to the core should be unlikely.

Most EU builders I would expect to have been using foam or a specific marine PVC injested foam product such as Divinycell as a coring product. If the boats you are looking at genuinly have a Balsa core (as oppoosed to being cored with any other material) I would expect them to be of US manfucature? Even so, I wouldnt consider the core to be at risk on avessel of this age so long as the survey doest show signs of water penetration with a moisture test.
 
balso core is widely used since the eighties
you have to consider 2 things if balsa or foam coring is used for the sides and decks you dont have to worry about it, unless a foolish owner does not some sort of holes in the sides and deck where water can find its way trough
if it is for hull bottom you need to make a deep check
a difference can also be if the builder is using normal balsa versus end grain too...
as for Isphotalic gel coat, yes this is less water repellant to polyester but does not make miracles but it does reduce
some builders today are also using vinilester resins for the bottom which in term is less water solubile versus conventional polyester
if you send me a PM with the name of the builders I can tell you if there is a bad history in there construction methods
 
AHoy2 said:
To date I have avoided boats with balsa core hull construction as I have been concerned about long term integrity and consequences of any damage. Now I find myself seriously interested in a couple of mobos from established builders which use this method of hull construction. I am aware of the benefits of sandwich construction, but still concerned about the use of an absorbent material such as balsa. With modern build methods and materials is durability and repair not an issue?

TIA.
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You say modern materials, but balsa isn't. Modern would mean a plastic core, like airex or divinycell (sp?). Do you mean balsa or something else?

Next question is where is it cored. Hull? Above/below w/line? Or just deck and furniture and lockers and stuff?

FWIW, I would avoid a cored hull usually but if a GRP boat didn't have cored deck, furniture, lockers I'd probably avoid that too :-)
 
Whitelighter,
Thanks for the technical insight to modern methods and materials.

jfm/Poweryacht,

The boats in question are current production. Below is an extract from one of the manufacturers spec sheets taken off their website today:

"CONSTRUCTION ______________________________
HULL
Composition: Sandwich (Polyester resin - Glass fibre / Balsa
core) - White gel-coat - Structural hull counter moulding in
monolithic laminate (Polyester resin - Glass fibre)"

Balsa specifically listed, hence my initial query. I too expected to see some other material.
 
hello Ahoy

that is very basic description...
can you ask this builder to be more specific normally they can tell you this too...
even if it is a used boat
no surprise for Polyester
Isoftalic is more used as a Gel coat mix, prime resins remain polyester as they give the best bonding and cure, vinilester in a perfect world is used after the gel. Some builders use Isoftalic after the Gel and then go on with polyester
 
AHoy2 said:
To date I have avoided boats with balsa core hull construction as I have been concerned about long term integrity and consequences of any damage. Now I find myself seriously interested in a couple of mobos from established builders which use this method of hull construction. I am aware of the benefits of sandwich construction, but still concerned about the use of an absorbent material such as balsa. With modern build methods and materials is durability and repair not an issue?

TIA.
Click to expand...

I think jfm has it right. Personally, if a hull was balsa cored below the waterline, I wouldn't touch it. Partially it's not knowing whether the builder has laminated the hull properly but also whether skin fittings have been correctly installed by the builder or subsequent owners. In addition, if the hull has been damaged at some point, you don't know how much moisture has been taken up by the balsa core before a repair was made. Above the waterline, I don't think balsa coring is such an issue so the question you should be asking, IMHO, is whether the hull is balsa cored below the waterline. I see that David Pascoe has been rubbished on this thread but I think this article is fair

http://www.yachtsurvey.com/cored_hull_bottoms.htm
 
Is it a Beneteau?

AHoy2 said:
"CONSTRUCTION ______________________________
HULL
Composition: Sandwich (Polyester resin - Glass fibre / Balsa
core) - White gel-coat - Structural hull counter moulding in
monolithic laminate (Polyester resin - Glass fibre)"
Click to expand...

OK which Beneteau are you looking at? ;) ;)
 
jimg said:
OK which Beneteau are you looking at? ;) ;)
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The spec I quoted was from the Trawler 34 (I can dream) but is common to many of the current Beneteau boats.

I assume from the responses so far that

a) all Beny owners are satisfied with the construction of their boats or
b) most Beny owners don't know what hull construction they have or
c) aren't worried that they might have soggy bottoms :>)
 
Deleted User said:
I think jfm has it right. Personally, if a hull was balsa cored below the waterline, I wouldn't touch it. Partially it's not knowing whether the builder has laminated the hull properly but also whether skin fittings have been correctly installed by the builder or subsequent owners. In addition, if the hull has been damaged at some point, you don't know how much moisture has been taken up by the balsa core before a repair was made. Above the waterline, I don't think balsa coring is such an issue so the question you should be asking, IMHO, is whether the hull is balsa cored below the waterline. I see that David Pascoe has been rubbished on this thread but I think this article is fair

http://www.yachtsurvey.com/cored_hull_bottoms.htm
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I have David Pascoe's book on choosing 35 foot mobos. Its worth reading and I do subscribe to his knowledge. Balsa sandwich is done because its.....cheap! Also look out for "chopped mat" coz that's cheap as well.
 
AHoy2 said:
Interesting point to put to the Beny sales folk at SIBS. Do you think I will get a big enough discount because of this to put my mind at rest ;>)
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Well, it certainly can't do any harm
 
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