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valhalla360 · 01-05-2019, 23:29

Quote:

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.

Shouldn't be attaching hardware thru cored sections at all.

Foam can work but as mentioned, takes a thicker cross section to get the same strength and stiffness. Plus it's harder to get good adhesion between the layers.

Keep it dry and balsa is a great material.

jimbunyard · 01-05-2019, 23:55

Quote:

Originally Posted by Stephen2258

I'm NOT a newb when it comes to boats and their construction. But, I still don't know why balsa coring is used at all. Having dealt with having to deal with soft decks on a vintage sailboat I understand that closed cell foam might not have been available as a coring option. But now, in current building situations foam is available at 100% of the time. I haven't done the research on the differene in cost between balsa and foam, but let's say cost wasn't an issue in this case. I'm hoping that a professional designer or engineer might offer an explanation. And any opinions or experience from anyone who has worked replacing coring would also be welcome.

Supposed superior compressive and sheer characteristics aside (foams, and even balsa core, are available in different densities; it is common to compare cores with different densities as if they were the same), I would suspect for most manufacturers the primary reason is cost.

A quick comparison using one supplier.

1/2" balsa core 4' x 8'.................. 64.18

1/2" H80 divinycell pvc 4' x 8'......144.53

Balsa core is fine as long as it's kept dry, which is difficult in the long run. I like it for easily replaceable things like hatch covers or shelves. For decks and bulkheads, if a customer can afford it, I use pvc or, preferably, Coosaboard.

As with most things, there's a cost/benefit tradeoff. A prime example is small (17-25') powerboat transoms. High density foam is available and plenty strong (no compression issues at all) but it is very expensive. Most owners opt for the cost-effective use of properly dried, big-box-store treated 3/4" plywood (36.00/sheet x 2), fully encapsulated with cored penetrations because it represents the best solution as regards cost/performance/longevity...though if they can afford it, coosaboard is available for about 600.00/transom...

44'cruisingcat · 02-05-2019, 00:12

Quote:

Originally Posted by StuM

Big washers used in lieu of a backing plate.

Ah, OK. Not on my boat.

**a64pilot** · 02-05-2019, 04:38

Quote:

Originally Posted by 44'cruisingcat

Ah, OK. Not on my boat.

Yes, but it’s very often based on finances, and in truth they are sometimes the best available option, my deck to hull joint is through bolted every three inches, and fender washers are used on those bolts, not much else is viable.
Balsa is an economical alternative, there are better cores but more expensive.
Plywood is probably the bottom but is often used as it’s less expensive, then you go up from there.

I see the need and use of cores, I just don’t like them, yes solid glass is heavier, and likely more expensive, but doesn’t fail when it gets old.
Cores are in my opinion for those that want new and high tech, and likely won’t own a boat that is over ten years old.

You can in fact make a lightweight, stiff solid glass deck, but it’s going to cost way more than one cored, and won’t help insulate like a core will either.

JimsCAL · 02-05-2019, 05:09

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.

nuvaslacker · 02-05-2019, 09:14

An additional point is that foam tends to soften when heated, as a deck is in the sun. This doesn't appear to be practically a problem as long as the deck is light coloured, but has been raised by those advocating balsa.

Allied39 · 02-05-2019, 09:24

Quote:

Originally Posted by Stephen2258

I'm NOT a newb when it comes to boats and their construction. But, I still don't know why balsa coring is used at all

Thats because you don't know what you are talking about and obviously have very little experience.

That being said I applaud your effort to gain information and knowledge...WELL DONE !!

I am not going to go into all the wonderful properties and uses of end grain balsa or the myriad of times it is far superior to foam core because I think you will get more than enough of that.

Oh, foam core is also an excellent form of construction.

Marine repair/ fabrication is not a "one size fits all " situation.

Once again, well done.

contrail · 02-05-2019, 09:33

Balsa core is also superior for certain types of impact. It resists crushing better than foam.

Scorpius · 02-05-2019, 09:41

I do like my all steel boat!

MikeFergie · 02-05-2019, 10:26

Balsa core also provides truly good insulation properties. My boat is just so cool downstairs which is another big plus

captlloyd · 02-05-2019, 10:48

Quote:

Originally Posted by Allied39

Thats because you don't know what you are talking about and obviously have very little experience.

That being said I applaud your effort to gain information and knowledge...WELL DONE !!

I am not going to go into all the wonderful properties and uses of end grain balsa or the myriad of times it is far superior to foam core because I think you will get more than enough of that.

Oh, foam core is also an excellent form of construction.

Marine repair/ fabrication is not a "one size fits all " situation.

Once again, well done.

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

44'cruisingcat · 02-05-2019, 11:15

Quote:

Originally Posted by a64pilot

Yes, but it’s very often based on finances, and in truth they are sometimes the best available option, my deck to hull joint is through bolted every three inches, and fender washers are used on those bolts, not much else is viable.
Balsa is an economical alternative, there are better cores but more expensive.
Plywood is probably the bottom but is often used as it’s less expensive, then you go up from there.

I see the need and use of cores, I just don’t like them, yes solid glass is heavier, and likely more expensive, but doesn’t fail when it gets old.
Cores are in my opinion for those that want new and high tech, and likely won’t own a boat that is over ten years old.

You can in fact make a lightweight, stiff solid glass deck, but it’s going to cost way more than one cored, and won’t help insulate like a core will either.

You can't make a solid glass structure as stiff as a cored one without making it much heavier.

If the engineering is right a cored boat will last a very long time. There are balsa cored boats over 50 years old still going strong.

When you say "better cores", better in what way? Foam is "better" in that it is light and doesn't rot, but it isn't better in terms of it's ability to take load or impact, or bond to the laminates.

There are multi million dollar carbon fibre boats where balsa core was chosen, for structural not cost reasons. On the big RTW racing trimarans balsa is often used in heavily loaded areas like beams and bulkheads, foam used in less stressed areas. Again, budget isn't the reason.

My hull to deck join is glassed inside and out. Seems a viable option to me.

Chotu · 02-05-2019, 11:57

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.