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Old 27-08-2009, 07:05   #1
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Balsa vs Foam Core

Im looking at a few boats, but two in particular. One is foam core, one balsa core. Excerpt from a website posted below. Is this of concern, or is this marketing material for someone who happens to sell foam cored cats?

-----------

Feature: How they're built...

The Wrong way: Some builders are incorporating the old monohull construction techniques incorporating balsa core in the hull--including below the water line. While at first glance, this might seem to be a good idea because of the high initial strength of the cored panel- balsa has two potentially devastating properties in this application.
1. When the panel receives a hard impact, (such as whacking an underwater obstruction or even a piling) the stiffness of the balsa that gives the panel it's stiffness, also transfers the impact load directly to the inner skin, often separating the inner skin from the core, and totally eliminating the strength of the panel, and opening the core up to water that eventually causes rot and further damage.
2. Any intrusion of water, and if the core is used below the waterline--this is a major concern--will cause delamination and rot and greatly reduce the strength of the hull.

Even if you do not encounter these problems, your vessel is likely to suffer at resale because American surveyors have seen so many problems that they assume the worst and instruct buyers to be wary.
Here's a typical discussion by one surveyor about a well known power boat manufacturer that certainly outlines the discourse.
What’s better...
A foam core hull, using injection or infusion molding techniques to insure the strongest, lightest structure possible.
It takes experience to get this right. You don't want to use foam that is too stiff, or you get back to the same impact resistance problem. Fountaine Pajot uses a foam and engineers the design so that the resulting structure is more forgiving. If you should impact a piling, or anything else, the hull will take advantage of fibreglasses unique ability to flex without deforming--and then return to its original shape. In the event of a really severe impact, instead of the damage being transmitted to the inner laminate (like with balsa core) the damage will occur to the outer skin where it can be readily seen and repaired. And, as a bonus, any water that might get in, will not do core damage like with wood.
Experienced builders of cruising cats create modern designs that are light, strong AND forgiving!
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Old 27-08-2009, 07:49   #2
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Excellent boats can be built from both Balsa and foam and terrible boats can be built from both.

Point #1 is pretty bogus. That can happen to panels of either core material, and in fact foam core is more likely to fracture in the foam than balsa.
Point #2 is slightly less bogus, water in the laminate is potentially more damaging to balsa, but it is not great for either material and should be avoided/fixed in either type of panel.

Consider boats of either material, but get them all well surveyed.
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Old 27-08-2009, 09:13   #3
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There are plenty of folks posting on the internet; boatbuilders, surveyors, naval architects and people who know nothing at all (I fit seamlessly into the last category) who will state categorically that core material "X" is patently unsafe at any speed, whether it is foam, balsa or honeycomb. I think it is far more usefull to look carefully at the builder and the construction techniques used, in conjunction with a carefull survey to decide which boat is more suitable for your needs. For the record, I believe Leopard has something like 600 balsa-cored hulls built to date.

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Old 27-08-2009, 12:27   #4
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I agree that good or bad hulls can be made with either balsa or foam cores; that being said, foam typically is more resistant to rot/delamination than balsa and, if nothing else, it allows one a little more time to repair leaks on deck before suffering from the dreaded problem of delamination. Further, I have been led to believe that the insulation properties of balsa is a bit less than for foam.

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Old 27-08-2009, 13:00   #5
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Both have plusses and minuses, get a good survey. If the foam core has failed in shear it can be repaired. If the balsa has gotten wet and rotted it can be repaired.
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Old 27-08-2009, 13:32   #6
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i stay away from cored boats....each is bad ..... i prefer solidity and antiquity....i did once have a slop with a honeycomb cored deck--was goood--no sag in 26 yrs...if one must choose--seems honeycomb is strongest.....my eroicson 35mII ha s a deck cored with end grain balsa---it has ben strengthened post water intrusion and has not shown any further signs of deterioration....
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Old 27-08-2009, 15:14   #7
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Same = same. Both good. If water penetrates both terrible.

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Old 27-08-2009, 16:35   #8
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Originally Posted by zeehag View Post
i stay away from cored boats....each is bad ..... i prefer solidity and antiquity..
In reality a solid laminate is not possible on a multihull.

While it has been done, load carrying and performance are seriously compromised.
Quote:
I did once have a sloop with a honeycomb cored deck--was good--no sag in 26 yrs...if one must choose--seems honeycomb is strongest....
Based on your single experience?

I would disagree.
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Old 27-08-2009, 16:47   #9
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Originally Posted by estarzinger View Post
Excellent boats can be built from both Balsa and foam and terrible boats can be built from both.
Agreed

Quote:
Point #1 is pretty bogus. That can happen to panels of either core material, and in fact foam core is more likely to fracture in the foam than balsa.
I Disagree.
Both Balsa and foam have no inherent longitudinal strength and are pretty close to being equally as weak as a core relying on the outer skin for panel stiffness.

Timber Strip planking on the other hand has superior longitudinal strength to both, and if using the same outer laminate is considerably stiffer and stronger than both foam or balsa.

Of course you could also use a lighter laminate (less resin and glass) and still get a high performance panel for less cost.

None of my comment is meant to detract from any of these core material choices

Quote:
Consider boats of either material, but get them all well surveyed................
.................by someone familiar with multihulls and their construction methods
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Old 27-08-2009, 17:02   #10
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My preference is for a solid hull- I don't see the need for a cored hull on a cruising boat. Racing, on the other hand, is a different story.
Still, if I had to choose a boat with a cored hull, my preference would be for the foam. Either way, a survey is paramount!
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Old 27-08-2009, 17:07   #11
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Originally Posted by PyotrBee View Post
Im looking at a few boats, but two in particular. One is foam core, one balsa core. Excerpt from a website posted below. Is this of concern, or is this marketing material for someone who happens to sell foam cored cats?

-----------

Feature: How they're built...

The Wrong way: Some builders are incorporating the old monohull construction techniques incorporating balsa core in the hull--including below the water line. While at first glance, this might seem to be a good idea because of the high initial strength of the cored panel- balsa has two potentially devastating properties in this application.
1. When the panel receives a hard impact, (such as whacking an underwater obstruction or even a piling) the stiffness of the balsa that gives the panel it's stiffness, also transfers the impact load directly to the inner skin, often separating the inner skin from the core, and totally eliminating the strength of the panel, and opening the core up to water that eventually causes rot and further damage.
2. Any intrusion of water, and if the core is used below the waterline--this is a major concern--will cause delamination and rot and greatly reduce the strength of the hull.

Even if you do not encounter these problems, your vessel is likely to suffer at resale because American surveyors have seen so many problems that they assume the worst and instruct buyers to be wary.
Here's a typical discussion by one surveyor about a well known power boat manufacturer that certainly outlines the discourse.
What’s better...
A foam core hull, using injection or infusion molding techniques to insure the strongest, lightest structure possible.
It takes experience to get this right. You don't want to use foam that is too stiff, or you get back to the same impact resistance problem. Fountaine Pajot uses a foam and engineers the design so that the resulting structure is more forgiving. If you should impact a piling, or anything else, the hull will take advantage of fibreglasses unique ability to flex without deforming--and then return to its original shape. In the event of a really severe impact, instead of the damage being transmitted to the inner laminate (like with balsa core) the damage will occur to the outer skin where it can be readily seen and repaired. And, as a bonus, any water that might get in, will not do core damage like with wood.
Experienced builders of cruising cats create modern designs that are light, strong AND forgiving!
Point 1] Yes a cored hull that is damaged CAN suck up water

Point 2] In theory and practice, the water should only travel as far as the next cell. The cell strucure on end grain balsa is like a straw with the ends sealed by resin and the glass laminate.


You can clearly see the grain (tubes) running up and down to the top and bottom face, where the glass and resin would be. Water ingress would be considerably restricted by the cell (tube) walls left to right.

Point 3] This is not to say that you cant get water damage over a larger area, contour balsa (scored) will allow water travel if the voids are not properly filled during construction.

BUT MOST IMPORTANTLY
an owner who is slack and does not address underwater damage will cause what may have initially been minor damage, to worsen.

It is easy enough to dry the boat out between tides, dry the core out and do a quick resin, glue, glass repair, preventing any further water ingress, which can then be addressed properly during a later regular lift for antifouling etc.

Saying that, I have seen some damage on a cat that had that had broken the skin and had been left in the water for at least 6 months, and the affected area was very small, hardly any larger than the initial damage. It is worth noting that this was a duflex boat, so all epoxy construction and no contour cuts.

4] The ONLY truly successful resin for a balsa core (or any timber core) is epoxy with vinylester to a lesser extent.

The use of polyester resins, which the above article would have used, is in my and many opinions a very poor choice and is based on cost cutting, not laminate performance.
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Old 27-08-2009, 17:47   #12
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AFAIK the majority of production catamarans are balsa cored. Despite all the dire predictions these seem to be holding up well, even though a huge number of them are in charter use (abuse).
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Old 27-08-2009, 18:50   #13
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Just a thought here....Aren't Catalacs solid laminate? Those hulls seem to have held up well through the years and load capacity (due to shape) seems as good as other catamarans of similar size.
Any other boats solid fiberglass?
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Old 27-08-2009, 19:00   #14
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Old 27-08-2009, 20:44   #15
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Just a thought here....Aren't Catalacs solid laminate?
Performance?
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