Still Using Balsa Core..Why?

[Warren Kaplan]

I was just passing the time of day today reading a new issue of Blue Water Sailing (I can dream can't I) that came in the mail. It has an article about the new Saga 35. When they got to the construction specs, they said the hull is balsa cored. I got to thinking that my boat is balsa cored and its 22 years old. I know that balsa is light and end grain balsa is pretty strong. All attributes of this building material. But how many of us have had to replace major sections of the deck due to rot from water getting through the surface into the balsa core. I had to replace a good size sagging section of Sine Qua Non's foredeck when I bought her 2 years ago. Hardly an uncommon problem. I am a little bewildered that something hasn't come along to replace balsa as a "core material" that is strong, light and unlike balsa, won't rot. I remember even way back about 20 years ago, they had something called AIREX. I remember airex cored boats. I don't know much about that stuff but do they still use it? With all the space age technology that has given us kevlar, carbon fiber and god knows how many other synthetic wonder products, why are they still using balsa with that huge rotting problem. Is it just cost? Would using other suitable or superior products make new boats prohibitively more expensive? Or maybe I'm misinformed. Maybe boatbuilders are using alot of other core materials and I just never realized it. But if they are still using balsa by and large as the core material...how come?

Warren Kaplan
Sine Qua Non
CD27 #166



Setsail728@aol.com

[Don Carr]

Warren;
I'm probably incorrect but my CD hull is solid laid up fibreglass as I believe is the CD27. Where coring was used was on the decks. BTW..the real racing boats are translucent laid up Kevlar/Carbon Fibre no core (on the hull any way) very eery to be below and see the glow of sunlight in the V-berth (aka sail locker).

FWIW.



carrds@us.ibm.com

[Fred]

I was just passing the time of day today reading a new issue of Blue Water Sailing (I can dream can't I) that came in the mail. It has an article about the new Saga 35. When they got to the construction specs, they said the hull is balsa cored. I got to thinking that my boat is balsa cored and its 22 years old. I know that balsa is light and end grain balsa is pretty strong. All attributes of this building material. But how many of us have had to replace major sections of the deck due to rot from water getting through the surface into the balsa core. I had to replace a good size sagging section of Sine Qua Non's foredeck when I bought her 2 years ago. Hardly an uncommon problem. I am a little bewildered that something hasn't come along to replace balsa as a "core material" that is strong, light and unlike balsa, won't rot. I remember even way back about 20 years ago, they had something called AIREX. I remember airex cored boats. I don't know much about that stuff but do they still use it? With all the space age technology that has given us kevlar, carbon fiber and god knows how many other synthetic wonder products, why are they still using balsa with that huge rotting problem. Is it just cost? Would using other suitable or superior products make new boats prohibitively more expensive? Or maybe I'm misinformed. Maybe boatbuilders are using alot of other core materials and I just never realized it. But if they are still using balsa by and large as the core material...how come?

Warren Kaplan
Sine Qua Non
CD27 #166

1 It's cheap

2 It's proven technology

3 Easier to work with

4 Doesn't change shape when it gets hot, ie. gets painted a dark color.

It really is preferable in a lot of applications. FWIW foam can get pretty wet as well, though it doesn't rot.

Properly built, balsa core works very well. The problem is that builders bolt hardware, or though hulls, into it. Then its just a matter of time until it gets wet.



fred@hotsheet.com

[John]

Warren:
Some manufacturers (ie Hunter) use short pieces of balsa plywood laid end to end, this allows the epoxy to flow in between the pieces, they still get the stiffness, but any rot goes only as far as the individual piece. I know Hunter isn't considered the Cadillac, but it is an interesting way to keep the stiffness, loss of weight up high and avoid the rot.
John

I was just passing the time of day today reading a new issue of Blue Water Sailing (I can dream can't I) that came in the mail. It has an article about the new Saga 35. When they got to the construction specs, they said the hull is balsa cored. I got to thinking that my boat is balsa cored and its 22 years old. I know that balsa is light and end grain balsa is pretty strong. All attributes of this building material. But how many of us have had to replace major sections of the deck due to rot from water getting through the surface into the balsa core. I had to replace a good size sagging section of Sine Qua Non's foredeck when I bought her 2 years ago. Hardly an uncommon problem. I am a little bewildered that something hasn't come along to replace balsa as a "core material" that is strong, light and unlike balsa, won't rot. I remember even way back about 20 years ago, they had something called AIREX. I remember airex cored boats. I don't know much about that stuff but do they still use it? With all the space age technology that has given us kevlar, carbon fiber and god knows how many other synthetic wonder products, why are they still using balsa with that huge rotting problem. Is it just cost? Would using other suitable or superior products make new boats prohibitively more expensive? Or maybe I'm misinformed. Maybe boatbuilders are using alot of other core materials and I just never realized it. But if they are still using balsa by and large as the core material...how come?

Warren Kaplan
Sine Qua Non
CD27 #166

1 It's cheap

2 It's proven technology

3 Easier to work with

4 Doesn't change shape when it gets hot, ie. gets painted a dark color.

It really is preferable in a lot of applications. FWIW foam can get pretty wet as well, though it doesn't rot.

Properly built, balsa core works very well. The problem is that builders bolt hardware, or though hulls, into it. Then its just a matter of time until it gets wet.

branchedoakmarina@alltel.net

[Hobbster]

Warren:

I have boaters ask me this question a lot. Over the past year I have been getting ready to layup the 300MS. We will be using Balsa for the core material on this boat. We will use it in the decks and in the hull from the water line up. We are going to core the hull for insulation reasons, both thermal and sound. Some reasons are;

1. Balsa core has a proven track record when installed properly. As far as being cheep, not so. There are other core materials we could use and save money.

2. Easier to work with? Not so. Foam is much easier to work with. I use foam core in several products we make that are not marine related.

3. Balsa will keep it's physical properities when hot, ie, dark colors in the sun. This is very important.

4. Great tech. support and engineering from the companies. You also get this from other core suppliers.

5. When properly installed, water into the core is not a problem.

6. The problem with your decks was not rot but water getting into the core material. Rot was a result of the problem. Will water damage other core materials? Yes. The cure is to install the core material and hardware properly.

7. Balsa (all balsa used as a core material is end grain) has very good shear and compressive properties. If you build several like items out of several core materials and then distroy them (hammer and chisel) you will walk away with a good feeling about balsa.

I am starting to sound like a commerical for balsa. I have been working in fiberglass for over 20 years. Most of my time has been spent building industrial products. Yes, I build boats also. We always do the engineering and the products work well. What I have yet to figure out is that in the industrial field, our customers first ask "Where is the engineering information" and then "What will it look like". With boats they only ask "What will it look like" I am never asked "Who did the engineering"

I hope I have answered some of your questions.

Glen



glen@hobbymarine.com

[Warren Kaplan]

Warren:

I have boaters ask me this question a lot. Over the past year I have been getting ready to layup the 300MS. We will be using Balsa for the core material on this boat. We will use it in the decks and in the hull from the water line up. We are going to core the hull for insulation reasons, both thermal and sound. Some reasons are;

1. Balsa core has a proven track record when installed properly. As far as being cheep, not so. There are other core materials we could use and save money.

2. Easier to work with? Not so. Foam is much easier to work with. I use foam core in several products we make that are not marine related.

3. Balsa will keep it's physical properities when hot, ie, dark colors in the sun. This is very important.

4. Great tech. support and engineering from the companies. You also get this from other core suppliers.

5. When properly installed, water into the core is not a problem.

6. The problem with your decks was not rot but water getting into the core material. Rot was a result of the problem. Will water damage other core materials? Yes. The cure is to install the core material and hardware properly.

7. Balsa (all balsa used as a core material is end grain) has very good shear and compressive properties. If you build several like items out of several core materials and then distroy them (hammer and chisel) you will walk away with a good feeling about balsa.

I am starting to sound like a commerical for balsa. I have been working in fiberglass for over 20 years. Most of my time has been spent building industrial products. Yes, I build boats also. We always do the engineering and the products work well. What I have yet to figure out is that in the industrial field, our customers first ask "Where is the engineering information" and then "What will it look like". With boats they only ask "What will it look like" I am never asked "Who did the engineering"

I hope I have answered some of your questions.

Glen

Glen,
Thanks so very much for that detailed answer. And to everyone else who provided information. You CERTAINLY DID answer my questions. That's why I always come to this board! There's always a bunch of people who know what they are talkin' about.

Thanks again!
Warren Kaplan
Sine Qua Non
CD27 #166 (1980)



Setsail728@aol.com

[Tom]

Airex foam is still in use however it has two drawbacks. First of all it has a tendency to delaminate with time. Secondly, it is hugely expensive and relatively hard to work with. (Like plywood airex doesn't like to bend in two directions at once) Cape Dory hulls are laid up with unidirectional roving which is stronger than traditional roving. Traditional roving was woven like clothing fabric, i.e., over and under strands. The problem with this is that it leaves little pockets of resin between the voids where the strands go over and under. Resin by itself has little strength and needs the glass fiber to give it strength. The study of boat hulls that broke apart on rocks or whatever showed that they tended to fracture along the line of these little resin pockets that were devoid of glass fiber.

A superior type of roving was developed that they call "uni-directional" roving. This is not woven over and under like fabric, but all the fibers run in one direction parallel to each other and side by side close together so that no resin pockets are formed. The fibers are held in place by a thin layer of angel hair mat until they are wetted out. This makes a denser and stronger hull that does not fracture down the seam of resin pockets which is kind of like tearing a dishcloth by cutting a little slit and then tearing it along the seam. Uni-directional roving is harder to work with (runs the cost of manufacture up) and is more expensive to buy than traditional roving, but produces a much stronger hull. Only top quality builders bothered with uni-directional roving in their layups.

As far as I know all the Cape Dorys were laid up with uni-directional roving. You can see this if you find a place where the hull is unpainted and study the weave of the roving through the resin. You'll notice there isn't any over and under weave to the roving. In additon to this Cape Dory made their hulls about twice as thick as, for example, Island Packet hulls. It's these little unseen and costly things that that give Cape Dory their reputation as a quality boat. You wouldn't put balsa or airex into a hull that you are hand laying up with uni-directional roving where you're striving for density and strength. I don't now anything about the Saga boats, but would you want a balsa core in your hull with it's known problems of wet spots and rotting etc?

In the areas where you're striving for lightness with strength such as decks and cabin tops, and where you'd want some heat insulation to keep below decks cool in summer and warm in winter is where they often use balsa or foam cores - not in the hull where you want weight and density down low. You can lay up solid decks and cabin tops, but they raise the center of gravity and are more flexible unless laid up very thick. That's why decks and cabin tops are often cored in quality boats. We live with the cracks and wet spots and things that cored decks bring with them because of the very real advantages they also bring. I'm not a big fan of balsa cored decks and cabins, but the fact that they are still making them this way shows you that there are some advantages for doing it this way. To some extent we have to trust that Carl Alberg knew what he was doing when he designed our boats this way. Airex has been around for 30 plus years and few builders use it so that says something as well.

Just what are you suggesting is the correct material and method to use and what is your evidence? It sounds like you are questioning Alberg and Cape Dory, but you aren't giving us any contrary evidence. You seem to just be saying why not this and why not that? We can respond better if you tell us what you recommend and what your experience has been. Are you saying that the way Saga builds their boats is a better method than Cape Dory used? Personally, I don't think I would want a balsa cored hull and I think it's just a way to make a light weight hull cheaply, but maybe you can convince me otherwise. Why do you recommend a balsa cored hull? Do you know people who have had good experiences with Saga hulls?

I was just passing the time of day today reading a new issue of Blue Water Sailing (I can dream can't I) that came in the mail. It has an article about the new Saga 35. When they got to the construction specs, they said the hull is balsa cored. I got to thinking that my boat is balsa cored and its 22 years old. I know that balsa is light and end grain balsa is pretty strong. All attributes of this building material. But how many of us have had to replace major sections of the deck due to rot from water getting through the surface into the balsa core. I had to replace a good size sagging section of Sine Qua Non's foredeck when I bought her 2 years ago. Hardly an uncommon problem. I am a little bewildered that something hasn't come along to replace balsa as a "core material" that is strong, light and unlike balsa, won't rot. I remember even way back about 20 years ago, they had something called AIREX. I remember airex cored boats. I don't know much about that stuff but do they still use it? With all the space age technology that has given us kevlar, carbon fiber and god knows how many other synthetic wonder products, why are they still using balsa with that huge rotting problem. Is it just cost? Would using other suitable or superior products make new boats prohibitively more expensive? Or maybe I'm misinformed. Maybe boatbuilders are using alot of other core materials and I just never realized it. But if they are still using balsa by and large as the core material...how come?

Warren Kaplan
Sine Qua Non
CD27 #166

TomCambria@mindspring.com

[Larry DeMers]

First of all Tom, this was an excelllent review of the differences between Airex foam cored decks and balsa cored decks. Airex foam IS expensive, I believe it's crushability rating is lower than end-grain balsa, so it is a less qualified substitute for compression prone areas.
As to Warrens question..I think you got it backwards. He was asking why balsa coring is still used..when it was used in his older Cape Dory. Surely something better has come along in the intervening time, heh? He also did not seem to advocate the cored hull concept..but merely questioned why balsa is still being used in the market today.

One reason I would not consider a foam or balsa cored hull is the lack of strength from puncture. Both products are good for loads spred over an area, but point pressure..like from a log encountered as you come off a wave surfing down a following sea, will be more likely to puncture a hull than the equivalent layup in solid fiberglass.

By the way, my 1983 CD30 has traditional roving for the last layer on the inside. You can see the basket weave effect quite easily in the galley, under the sink, where I plugged up a thru-hull hole not needed anymore (depth sounder thruhull hole..sounder was moved to under the head to give a more timely warning of impending skinny-water).

Cheers,

Larry DeMers
s/v DeLaMer
Cape Dory 30

Airex foam is still in use however it has two drawbacks. First of all it has a tendency to delaminate with time. Secondly, it is hugely expensive and relatively hard to work with. (Like plywood airex doesn't like to bend in two directions at once) Cape Dory hulls are laid up with unidirectional roving which is stronger than traditional roving. Traditional roving was woven like clothing fabric, i.e., over and under strands. The problem with this is that it leaves little pockets of resin between the voids where the strands go over and under. Resin by itself has little strength and needs the glass fiber to give it strength. The study of boat hulls that broke apart on rocks or whatever showed that they tended to fracture along the line of these little resin pockets that were devoid of glass fiber.

A superior type of roving was developed that they call "uni-directional" roving. This is not woven over and under like fabric, but all the fibers run in one direction parallel to each other and side by side close together so that no resin pockets are formed. The fibers are held in place by a thin layer of angel hair mat until they are wetted out. This makes a denser and stronger hull that does not fracture down the seam of resin pockets which is kind of like tearing a dishcloth by cutting a little slit and then tearing it along the seam. Uni-directional roving is harder to work with (runs the cost of manufacture up) and is more expensive to buy than traditional roving, but produces a much stronger hull. Only top quality builders bothered with uni-directional roving in their layups.

As far as I know all the Cape Dorys were laid up with uni-directional roving. You can see this if you find a place where the hull is unpainted and study the weave of the roving through the resin. You'll notice there isn't any over and under weave to the roving. In additon to this Cape Dory made their hulls about twice as thick as, for example, Island Packet hulls. It's these little unseen and costly things that that give Cape Dory their reputation as a quality boat. You wouldn't put balsa or airex into a hull that you are hand laying up with uni-directional roving where you're striving for density and strength. I don't now anything about the Saga boats, but would you want a balsa core in your hull with it's known problems of wet spots and rotting etc?

In the areas where you're striving for lightness with strength such as decks and cabin tops, and where you'd want some heat insulation to keep below decks cool in summer and warm in winter is where they often use balsa or foam cores - not in the hull where you want weight and density down low. You can lay up solid decks and cabin tops, but they raise the center of gravity and are more flexible unless laid up very thick. That's why decks and cabin tops are often cored in quality boats. We live with the cracks and wet spots and things that cored decks bring with them because of the very real advantages they also bring. I'm not a big fan of balsa cored decks and cabins, but the fact that they are still making them this way shows you that there are some advantages for doing it this way. To some extent we have to trust that Carl Alberg knew what he was doing when he designed our boats this way. Airex has been around for 30 plus years and few builders use it so that says something as well.

Just what are you suggesting is the correct material and method to use and what is your evidence? It sounds like you are questioning Alberg and Cape Dory, but you aren't giving us any contrary evidence. You seem to just be saying why not this and why not that? We can respond better if you tell us what you recommend and what your experience has been. Are you saying that the way Saga builds their boats is a better method than Cape Dory used? Personally, I don't think I would want a balsa cored hull and I think it's just a way to make a light weight hull cheaply, but maybe you can convince me otherwise. Why do you recommend a balsa cored hull? Do you know people who have had good experiences with Saga hulls?

I was just passing the time of day today reading a new issue of Blue Water Sailing (I can dream can't I) that came in the mail. It has an article about the new Saga 35. When they got to the construction specs, they said the hull is balsa cored. I got to thinking that my boat is balsa cored and its 22 years old. I know that balsa is light and end grain balsa is pretty strong. All attributes of this building material. But how many of us have had to replace major sections of the deck due to rot from water getting through the surface into the balsa core. I had to replace a good size sagging section of Sine Qua Non's foredeck when I bought her 2 years ago. Hardly an uncommon problem. I am a little bewildered that something hasn't come along to replace balsa as a "core material" that is strong, light and unlike balsa, won't rot. I remember even way back about 20 years ago, they had something called AIREX. I remember airex cored boats. I don't know much about that stuff but do they still use it? With all the space age technology that has given us kevlar, carbon fiber and god knows how many other synthetic wonder products, why are they still using balsa with that huge rotting problem. Is it just cost? Would using other suitable or superior products make new boats prohibitively more expensive? Or maybe I'm misinformed. Maybe boatbuilders are using alot of other core materials and I just never realized it. But if they are still using balsa by and large as the core material...how come?

Warren Kaplan
Sine Qua Non
CD27 #166

demers@sgi.com

[Warren Kaplan]

Just what are you suggesting is the correct material and method to use and what is your evidence? It sounds like you are questioning Alberg and Cape Dory, but you aren't giving us any contrary evidence. You seem to just be saying why not this and why not that? We can respond better if you tell us what you recommend and what your experience has been. Are you saying that the way Saga builds their boats is a better method than Cape Dory used? Personally, I don't think I would want a balsa cored hull and I think it's just a way to make a light weight hull cheaply, but maybe you can convince me otherwise. Why do you recommend a balsa cored hull? Do you know people who have had good experiences with Saga hulls?

Tom,
Thanks for the education! I asked the question because I really know nothing technically about this subject. I was just wondering why, in all this time, balsa was still used as a core when the problem of "water getting into the core" seems relatively common and can require extensive work, in some cases, to fix. The only reason I mentioned Saga Yachts (which I know nothing about) was because the article I was reading was a review of a new Saga 35, and they mentioned that it had a balsa cored hull. That's what started the whole process. I was just wondering, in this day and age of all kinds of synthetic "wonder materials" (just look at all the different types of sailcloth these days), why some other material hasn't been used that would have all the attributes of balsa but wouldn't rot if water got into it. Evidently, nothing that could be used on a practical or profitable basis for boat building has come along.
Doubt Carl Alberg!!! I wouldn't presume! My first boat was a Sea Sprite 23 (Alberg design). Before I owned that boat I rented boats on weekends to go sailing. Pearson Ensigns...GREAT boat (Alberg Design). Now I own a CD27. Marvelous boat! Construction is first rate. I still have a great deal to learn about all aspects of sailboats. Here's where I come for part of my education. You wouldn't want me to pass on any wrong information to my grandchildren (if I ever have any) would you? (HA!)

Warren Kaplan
Sine Qua Non
CD27 #166 1980



Setsail728@aol.com

[Hanalei]

Captain Kaplan,

A Trivia note: Balsa is used as an insulator in the construction of Liquid Natural Gas tankers. It is end grain, and strong, and has a good R value. So, next time you see an LNG tanker, you will know what keeps that liquid cool! Cool, Huh? ? ?

Hanalei

[Tod Mills]

I can think of three reasons for little squares:

1. end-grain balsa is probably only available in comparatively small sizes anyway since it's a natural product.
2. easier conformation to curved shapes.
3. damage control with water ingress....providing there was thorough joint wet-out with resin.

Some other foams besides Airex are Divinycell and Klegecell. They are available in differing densities (and correspondingly, strengths) and thicknesses and in either solid sheet form or in sheets cut into little squares with a scrim backing to hold it together. Divinycell (and I would guess the others too) also offers a special resin called Divillette that you put on the diced sheets....If I recall, it's a contrasting color so you can see if you have it sqeezed into all the cracks between the squares.

However, there's nothing quite like nature's wonder of engineering...good old wood. Just gotta not neglect it.



htmills@bright.net

[John Nuttall]

here is a link to some data on balsa cores. the data is supplied by Balteck, I don't know if it is skewed......

If you look at the rest of the website you will see many applications for balsa cored laminates....autos, jet fighters, trains, superyachts, etc., etc., etc,

very interesting site / info.

John
s/v Aimless
CD31 #28