To balsa core or not to balsa core?

[Robertcateran]

Originally Posted by DGK

End grain balso has two advantages over foam, The first being the price is less, and secondly as stated before it is stronger/stiffer than foam of equivalent weight. If the hull is done using vacuum infusion and and all penetrations are epoxy cored, you have a great boat.

Not cheaper than polyprop honeycomb, but I agree about the stiffness and the quality if done well, especially the factory made panels, and is pretty fire resistant. Then again stiffness is not all, as this can bring about failure of the inner skin in the case of collision. Polyprop honeycomb is stiff enough to do the job if designed properly and is more forgiving of bonding problems, water intrusion, and collision. Sheer stiffness is not the same as sheer deformation to failure. If the later is compared, the honeycomb comes out well
Robert

[Joli]

Fixing wet balsa is not really a hard or expensive job. To avoid the problem of getting wet core the balsa must be removed and replaced by epoxy. Filling holes is easy but time consuming.

[ssullivan]

Originally Posted by Joli

Fixing wet balsa is not really a hard or expensive job. To avoid the problem of getting wet core the balsa must be removed and replaced by epoxy. Filling holes is easy but time consuming.

It's pretty hard and expensive, in my experience.

You have to use a skil saw and cut away the outer layers of glass to get to a rotten core (from the inside if possibe, to it looks nice at the end), then tear out the old balsa, fix and re-glass. This has to be done in a dry environment if you can't access it from the inside of the boat. I've seen a single walk-around on the side of a deck done professionally for $10K+

[jzk]

I am told that the Leopards are cored in small squares such that if water gets into one square, it won't go to the next square over.

But, they do have balsa in the hull. So, a really good survey is a must. I would stand right next to the surveyor as they pound their little hammer over every square inch of the hull. Then perhaps a nice epoxy barrier coat regardless of whether you are getting blisters.

[Joli]

I guess I've done so much of it I don't think of it as big deal.

We re-cored the transom (~8 foot by 4 foot) on our current boat from the outside (too much structure onthe inside to allow the work to be done there) for about $400 over three weekends while the boat was outdoors in Mchigan. I will admit I am getting to old to do long boarding, maybe a nice Hutchins Air file is in my future?

Originally Posted by ssullivan

It's pretty hard and expensive, in my experience.

You have to use a skil saw and cut away the outer layers of glass to get to a rotten core (from the inside if possibe, to it looks nice at the end), then tear out the old balsa, fix and re-glass. This has to be done in a dry environment if you can't access it from the inside of the boat. I've seen a single walk-around on the side of a deck done professionally for $10K+

[mikereed100]

I would like to echo Robert's comments on honeycomb. The hulls of my current project are scored honeycomb with kevlar/epoxy skins. The PO "bedded" all the ports, deck and underwater fittings with silicon without excluding the core in way of screws. Naturally water intruded everywhere and, due to the scoring of the core, was free to travel throughout the hull. There was no delamination, however, and after a thorough drying out the laminate shows no signs of trouble. Pretty forgiving stuff.
I think balsa got a bad rap in the early days before end grain was used and water could wick through the core easily. Some well respected designers such as Bob Oram have enough confidence in the stuff to use it below the waterline. As with any cored structure the skins need to be well bonded and thick enough to resist water intrusion, but I certainly wouldn't balk at a well constructed and maintained balsa cored boat.

Mike

[Thenaz007]

Solid fiberglass is not a cure. All reputable surveys now use a meter to check for moisture content, and all boats are difficult to finance without one. Moisture intrusion eventually rots fiberglass, and it is not unusual for boats newer than 2000 to already have unacceptable moisture levels around windlasses, etc. An epoxy, rather than a polyester or vinylester, hull is technically more moisture resistant when correctly applied. Epoxy is more difficult to work with, and expensive, but if someone was conscientious enough to use it in the first place, they MAY have also been conscientious about sealing when drilling down into the core for attachments.

[delmarrey]

Originally Posted by Joli

I guess I've done so much of it I don't think of it as big deal.

We re-cored the transom (~8 foot by 4 foot) on our current boat from the outside (too much structure onthe inside to allow the work to be done there) for about $400 over three weekends while the boat was outdoors in Mchigan. I will admit I am getting to old to do long boarding, maybe a nice Hutchins Air file is in my future?

Ditto!

The picture I posted above took only two days and less then $20 worth of materials (minus new gelcoat, I don't have one). A thin 4" grinding disk is what was used to cut out the one layer.

Another point, re-coring upside down is near impossible. Trying to keep wet FG in place is an attempt to defy gravity. Even horizontal is a challenge.

[Tropic Cat]

Originally Posted by jzk

But, they do have balsa in the hull. .

Balsa cores look great in the magazines, but in day to day living, it's just asking for expensive repairs.

Owning a boat these days is expensive enough. The idea is to minimize ownership costs and your own labor.

[ssullivan]

Originally Posted by Joli

I guess I've done so much of it I don't think of it as big deal.

We re-cored the transom (~8 foot by 4 foot) on our current boat from the outside (too much structure onthe inside to allow the work to be done there) for about $400 over three weekends while the boat was outdoors in Mchigan. I will admit I am getting to old to do long boarding, maybe a nice Hutchins Air file is in my future?

In a way, that was a response that had me laughing (not at you having to do it). I suppose if you're used to it, it is no big deal.

[44'cruisingcat]

Originally Posted by mikereed100

I think balsa got a bad rap in the early days before end grain was used and water could wick through the core easily. Some well respected designers such as Bob Oram have enough confidence in the stuff to use it below the waterline. As with any cored structure the skins need to be well bonded and thick enough to resist water intrusion, but I certainly wouldn't balk at a well constructed and maintained balsa cored boat.

Mike

Obviously I went through this thouroughly with Bob. As it happens we were talking about this again just a couple of days ago (he lives less than 5 minutes away) and I asked if there had been any problems with the balsa in his boats.

There was one instance - where the builder had failed to follow the plans and had left the balsa core in place in the deck UNDER THE MAST STEP. (The plans specify replacing the balsa with ply, heavily epoxied in and glassed over)

After 20,000 miles the balsa had started to give a little, but still not enough to damage the (800 gsm) laminate. The fix was simple and straightforward, after unstepping the mast.

[mikereed100]

After 20,000 miles the balsa had started to give a little, but still not enough to damage the (800 gsm) laminate. The fix was simple and straightforward, after unstepping the mast.

It's pretty amazing stuff...and I'm told it grows on trees!

[Maren]

Originally Posted by mikereed100

It's pretty amazing stuff...and I'm told it grows on trees!

Miracle Fiber 'W'

I recommend reading this link. The article is by a marine surveyor and it covers understanding a moisture meter's results, plus a good deal on Balsa and Fiberglass hulls

[Maren]

Originally Posted by mikereed100

... Some well respected designers such as Bob Oram have enough confidence in the stuff to use it below the waterline.

If I were using Coremat over it on the exterior, I certainly wouldn't have a problem using it under the waterline either. Just as long as the thickness of hull was under a certain size. As I recall, there is a problem with shear loads when the balsa is too thick but I don't remember at what point it becomes a factor.

There is a lot to say about a material that is renewable, lower cost, relatively eco-friendly, non-toxic, buoyant, repairable, stiff, and has good insulation properties.

[BigCat]

I finished out a boat with a balsa deck, and over 30 years and 50,000 NM later, it's in great shape-so mileage may vary.