Balsa cored hulls
 

Are a lot of hulls cored w/ end grain balsa? If the outer layer of glass is compromised, wouldn't the balsa get waterlogged and if so is the boat junk or just heavier?

Compromised?

Only in the affected area, it would not migrate at all !! THAT is unless there was a "Shop related problem" with the core bonding/bedding.

One of my military boats a (balsa cored) 12 M Cat ran up a rock breakwater in the fog and was completely out of the water at that, it was pulled off by a tug and towed back to the base where I picked it up later that day.

The only water to be found was under the missing outside laminate ; we simply removed/replaced those small areas and reglassed the bottom.

Easy repair BTW

the boat will be hevier, but the more important issue is the integrity of the hull itself. depending on how much water and how large an area it may in fact be junk. also depends on how long the core has been saturated, because the water will spread and attract moisture especially if the boat has a full cover or remains dormant for lengths of time.
a good way to check is with a moisture meter and then try covering the boat completely and leave a dehumidifier in it for a week or two. after a couple days check to see how much water it colected.

Water will not spread across balsa. Do a test! Take a piece of balsa about 12 inches long and submerse about 3 inches in water and it will not travel up.

Some of the core in the deck of my challenger was rotten from where they didnt seal the bolts for the lifeline. It was all in a 6 inch radius of the wholes and i cut the first layer of glass out with a die-grinder then dug the balsa out.Replacing it was a few layers of mat.

By compromised I mean that if you got say a pinhole (or more) through the outer layer of glass and water could get into the core would the balsa act as a sponge and soak up water to saturation thereby ruining the integrity of the hull. I thought the water would migrate through all the wood. There must be many different manufacturers that core with balsa and a boat that was maybe 20 years old would see its share of dock rash/bottom scrapings that could allow water intrusion.

No, it barely gets bigger than the damaged area.

If it is in an area that saw high water pressure from being at a planing speed, then the core can get "hydrauliced" and lose it's bond and seperate from the hull.

I've taken soaked, rotten balsa out of more than a few boats. Not just small spots either.

Go down to the Skater forum and read about their balsa woes. From what I understand, their problem is that the insides of the hulls aren't painted and laying water soaks into the coring thru the inside layup.

Balsa is one of a few woods with a closed cellular structure. So is white oak- that's why it was used for years as structural members in wooden boats. Most woods cave a cellular structure that looks like lots of miniature straws. Closed-cell woods have a similar structure but each cell is short and the "straw" tapers to a closed end. This keeps them from absorbing water through the "straws"

These woods resist rot, they're not rot-proof.

Isn't all balsa these days used in boats treated to resist rot?
It's not like early 90's stuff used I'm sure.

Like I said before problems with water in the balsa core would be shop related issues! Now to qualify above statement that’s assuming the resin and laminate schedule were even halfway in touch with reality.

We had a lot of gunboats on the gulf all of them with balsa core I never found a core related problem, That whole experience changed my outlook on balsa core.

Water intrusion from the inside then look to see if the last lamination was top coated with an inhibitor.

I have heard the weight gain/age thing before and it was traceable to the two-part foam around the tanks

Bottom pressure ??? What are you talking about in psi? , In “testing” I have cut thru the outside laminate exposing bare core making changes in the bottom geometry and never had a hydraulic/delaminating problem in those days we ran 115-120 these were Airex boats but water pressure is water pressure , That said on return to the shop for modification/race prep no evidence of any damage was to be found and that is pushing the point!

Personal experience.

In the old days balsa came in blocks that you placed one by one into the wet glass one of Harry Schoells guys figured out the scrim system as legend has it..

Its all in the name "End grain Balsa". Water intrusion if it spreads is going to follow the grain.Planks of balsa are likely to spread water intrusion but end grain blocks are vertical to the outer laminate so the water tends to stay in the area of the damage.:p

essentially the answer is yes.

especially when considering YOU, will be paying for the rxpense.

I would think Skater of all companies would be at the leading edge on this.

Baltek has been claiming their product won't wick water since the late 70's.

You have two issues, rot and water absorbtion. If it fills up with water, your light layup hull can gain alot of weight.

I would think the people who build large yachts and commercial boats (ABS specifications, Lloyds standards) would be "Leading edge" also the point being if the material is installed --- Properly (Key word) moisture is a NON issue.

I don't know what products are available what I do know is that my boat is loaded with this product. http://www.baltek.com/alcan/acsites....&m=3&type=.htm

It looks like a checker board and was explained to me if one square gets wet it can't migrate since the end grain is going in a different direction.

You mean like Bertram, Hatteras, Broward and such? That's funny because rotten cored decks are really common in those boats.

How can so many people be doing it wrong?

The grain doesn't alternate. The grain is oriented at a right angle to the sheet. The face of the sheet is the end grain. Balsa (supposedly) won't absorb water because if its cellular structure. Here's a pic-

http://i38.photobucket.com/albums/e1...d_drawing3.gif

good stuff!

Airex? What is it? Who makes it? Does it absorb moisture?

Thanks

So why "Checker Board" effect? I know this stuff is manufactured or should I say harvested,cut and put back together guessing for construction purpose it conforms to shape easier?

I'm not saying because it's in my boat it has to be the best, I can say the hull side and deck integrity is impressive. I have this thing about smacking the side of hull's at boat shows and can notice interesting differences in builds.

Baltek makes Airex. Foam is usually used in hull sides where the forces aren't as great.

It allows it to be laid across contours. It has a material bonded to only one side. That's the top. The bottom squares will open from each other to allow them to go over the curves and contours.

Baltek is truly impressive structurally. It provides a high rigidity to weight ratio. It used to be boats like Cigarette were laid up with lots and lots of fiberglass layers to get the strength and rigidity. Composite core construction came from the areospace industry. The theory is best explained in an example- Take two pieces of steel... they're both the same length and weight. One is a solid bar, one is an "I" beam. The bar will be equally rigid in all directions of force whereas the "I" beam will be much stronger in the one direction it's intended to be loaded in, the flange face. On an equal-strength basis, the "I" beam will be substantially lighter. Coring a composite provides the same effect. The top and bottom skins are the flanges of the "I" beam and the core is that center rib.

I guess they installed the self-rotting brand. Look one has to ask how the water was allowed to saturate the core in the first place and these same people should then avoid Plywood/ply rot like the plague for scantlings since the grain orientation as we know would allow the entire member to be water logged.



Hatteras??? http://www.yachtsurvey.com/boatrevie...terasINTRO.htm

Viking also has no problem with Balsa.

I thought Browards were Aluminium.

Bertram’s problems were from the engineering and installation.

Swamp if you have a Harley then it has an Airex core.

No it does not absorb water in any measurable amount.

It has the highest Peel strength of any cores I have used.

The cell structure can be deformed 60-80% without damage.

It is PVC Foam and a great one at that.

BUT there is a thermal issue that one should be aware of like DO not use in a Dark deck in the sub tropic summer sun.

However I have built race boats from it in the ME where it gets to a comfortable 135 F in July and august.

And it is not cheap.

Best stuff I ever worked with
 

I've worked with Airex, Klegcell, Baltek and lots of other core materials. But my hands down favorite is Nida Core. Its light weight, doesn't rot, good tensile strength and good stiffness. Only down side is you have to be real good at your bonding skills. Your laminates will delaminate from it if you do a trashy job.:p

Just went to their website they have a nice selection of material nowadays and it seem's they are up on infusion also.

If your covering a concave surface the scrim goes outward towards you. If its a convex surface the scrim goes inward away from you.:p