Why is Balsa coring used anywhere on a boat instead of all closed cell foam?

[Simi 60]

Originally Posted by JimsCAL

With end grain balsa, if you get a leak, the damage is localized. With foam, the water can easily travel and you can get delamination over a wide area. Each has its pluses and minuses.

How does water travel through closed cell foam?

[Jim Cate]

Originally Posted by Scorpius

I do like my all steel boat!

No one has ever needed a needle gun on a cored FRP boat...

Jim

[model 10]

Honeycomb might be a better core material. Tricky to use but very light.

[44'cruisingcat]

Originally Posted by Simi 60

How does water travel through closed cell foam?

It travels between the foam and the glass.

[DerekKelsall]

PVC foam has been available since about 1960. In 1965 I built trimaran Toria of PVC Foam and unidirectional fiber glass skins (polyester). We won RBR 1966. Sister ships are still sailing. The same year I introduced my rule to never spec. anything in the structure that can rot. - had seen the results of balsa in decks. There is no way to justify balsa in a boat structure.
Happy boating, Derek Kelsall.

[44'cruisingcat]

Originally Posted by Chotu

You guys have hull deck joints?

I don't even have one. The topsides just curve in a tight C shape at the top which starts the deck. It's all one piece.

I brought foam up around the curve and switched to balsa on the flat deck so I can mount hardware anywhere I want. With substantial backing plates of course.

Well, there's hull and there's deck, and they are joined together.... but yeah, pretty much the same.

Balsa's a good option for the deck, because it will resist denting from dropped winch handles, shoes etc.

But you have to be aware of it's vulnerability to fresh water ingress when fitting hardware, which some owners aren't, and that's where problems arise.

[Montanan]

Originally Posted by thinwater

I've had foam fail without getting wet.


I've had balsa fail, but it got wet first.


My pet peeve is fender washers that bend and allow crushing followed by movement. You need to use extra thick fender washers. Standard fender washers are too weak and flexible to distribute force.

Ditto as to recommendations for extra thickness so as to avoid bending / cupping of the washer under the compression load of a bolt head or nut, and suggest to be made of stainless steel for marine or corrosion prone applications along with the same grade of metal for the bolt, nut and the item which is being fastened so as avoid galvanic corrosion potential between variant metal types.

Fender washers with backing plates makes for excellent load distribution, fender washers without backing plates can be sketch as to tearing up the composite layer that the through hole is made. Best to not put any fasteners through cored deckings, instead have cored materials where there will not be compression or any through holes as the holes allow for water intrusion which is especially problematic for causing rotting of wood core materials.

A fender washer, though similar in shape to a standard washer, differs in that the outside diameter is traditionally MUCH larger in proportion to the center hole. With this design, a fender washer can be placed under the head of a bolt or nut to help distribute forces applied when tightening. Its oversized outside diameter also provides more bearing surface for the load of the fastener—distributing the load further on soft or thin materials, such as composite decks. Fender washers are commonly used in automotive, marine, sheet metal, plumbing and electrical applications. And they were used to bolt on fenders of cars and trucks, hence the name.

[a64pilot]

Originally Posted by Ecos

Honeycomb might be a better core material. Tricky to use but very light.

Depending of course what the honeycomb is made of.
I would have expected it on high end carbon fiber racing boats as opposed to say balsa, but I have no experience with them.
On aircraft honeycomb isn’t used as much as you would think, it has serious shortcomings like voids, delamination and moisture intrusion to name a few.
It’s one of those things that looks great on the books, but when faced with the reality of being in service, it often fails and requires work, often making it heavier than if it hadn’t been used to begin with.
There is / was honeycomb all over the OH-58 scout helicopter, but I can’t remember any on an Apache.
OH-58 was a much older design.

[stnick]

last boat show I saw some builders using a Poly vinyl Cardboard like sheet Looks like plastic cardboard. Totally water proof , very light I was impressed with that construction of that sail boat, I think it was a dickerson the guy who purchased Hunter yachts.

[jimbunyard]

Seems to be lots of myth, fantasy and inexperience showing up here; suffice it to say that substandard construction techniques can lead to premature failures using either/any core.

In an ideal world, manufacturers would use the best core for the application; the problem comes in when the decision is made as to what is 'best'. And different factions within the business have different ideas of that definition as well...

Regarding water damage being 'localized' in balsa core, maybe in the 'ideal world', or, perhaps, in well-executed modern vacuum-infused construction (though I have my doubts), in my experience the opposite is the rule; unchecked water intrusion into balsa core leads to massive failure.

Which is of course a reason that non-rotting foam cores, properly done, are a good solution; they are somewhat 'idiot-proof'.

Regarding fender washers, if you're cupping them then you're doing something wrong. I'm sure this must have been covered dozens of times, but either the core under load or stress bearing fitments should be removed completely under the fitment, or the area around the individual bolts should be de-cored (about 4 times the diameter of the fastener is a good rule of thumb), the area filled with thickened resin, and then the hole should be drilled, thereby isolating the core from the bolt hole and water intrusion, and providing a rigid, non-compressible seat for the nut to clamp the fitment to the deck. Certainly backing plates are better, but as A64 says, sometimes one has to use what fits...

Anyone who thinks they can drill a hole in a balsa cored deck and just bolt down a cleat because of balsa's 'superior compression resistance capacities' 'has another think coming'--- and (eventually) likely a deck core repair as well...

[Chotu]

Originally Posted by jimbunyard

Anyone who thinks they can drill a hole in a balsa cored deck and just bolt down a cleat because of balsa's 'superior compression resistance capacities' 'has another think coming'--- and (eventually) likely a deck core repair as well...

I didn’t see anyone here say anything like that. I’m pretty sure everyone here knows they have to de-core, be it balsa, foam or other.

[Allied39]

Originally Posted by captlloyd

Strange that you would start off an otherwise excellent reply with such a snarky, rude first sentence ?

It's not a snarky rude sentence....it's accurate.

For example, if I were to open a thread with the question " I don't know why my Mac phone won't work with my open CPN network and download my nav points to my garmin chartplotter....why not? "

If I were to do that I dare say I would likely be told that I don't know what I am talking about and lack experience .......WHICH WOULD BE ACCURATE!!!

So maybe before you start throwing labels about...consider thinking whether what you are reading is accurate or you just need to be offended for someone else.

[a64pilot]

Most issues are owner and “Pro” induced. I’ve been amazed at what I’ve seen done by paid “pro’s”
They indeed just drill a hole, slap 5200 on whatever is being installed, and use fender washers on the bottom side.
Assumption is the 5200 will waterproof it, a few may ooze some 5200 into the hole to you know, seal it . I’ve never seen someone fill the hole with epoxy or cast a part into epoxy, I’ve done it, but not seen it done.
I’ve only done it on my bowsprit which is wood encapsulated in glass, I cast the all thread in to mount my chain stopper.

However when boat shopping I saw many fender washers under winches and things like Windlasses, they were factory installed, in fact it seemed to be the norm, not backing plates.
A few boats had backing plates glassed into the hull, but that wasn’t the norm from what I saw.

[DerekKelsall]

Originally Posted by JimsCAL

With end grain balsa, if you get a leak, the damage is localized. With foam, the water can easily travel and you can get delamination over a wide area. Each has its pluses and minuses.

Simply not true - provided you use the right foam, PVC or Corcell, and the right technique, which ensures the resin is filling the cut cells, which then ensures full contact between the skin and the foam.



The whole idea of a sandwich structure is to allow the use of thin skins. Thin fiberglass skins cannot be considered to guarantee no moisture will pass. ie this is a matter of not if but when.



PU foam is brittle and subject to delamination from impacts. Airex is the most elastic of the foams. Cross linked H-80 is the ideal for most purposes. We use for the whole structure - bulkheads etc. The lightest weight boats around are PVC cored and definitely the most durable. 1960"s Kelsall can be expected to survive for a few more decades. My spec is basicly unchanged. Happy boating, Derek.

[Rumbottle]

As a yacht surveyor in Singapore I have inspected boats with balsa core that have severe problems with termites in the hull and decks. Just where the termites have entered is not always found. I have also seen many boats with soft decks resulting from water ingress, generally when fittings have been screwed onto the decks and leaked after a few years. Great stuff - as long as nothing goes wrong.