To balsa core or not to balsa core?

[BigCat]

CompositesWorld.com - Composites Technology -
Basalt Fibers: Alternative To Glass? - August 2006

Basaltex - The thread of stone

[cat man do]

Originally Posted by BigCat

Looks like amazing stuff- 2 times stronger than e-glass. It seems like you'd be hard put to use a small enough amount-one light layer of quad would do almost any job in a shell laminate.

Surely then (like kevlar) you would have to put a layer of 400gsm biax or DB over the top (on the outside) to get some impact and abrasion resistance.

Dave

[Robertcateran]

More abrasion resistance than impact,
Rbert

[fastcat435]

Send me your E mail address Alan and I will mail you much more info on basalt Fiber
we have used it for well over one year and are very happy with it,the strenght, adhesion to epoxy, elasticity are all better than e glass and in some ways better than carbon.

Greetings\

[Aac]

My first post; thanks all for a great forum

My question? Why not use Kevlar cloth below the water line (I think Gunboat has an option of using Kevlar) of a Balsar wood core. It would make punture mor difficult and it also seems inexpensive, see

http://www.infinitycomposites.com/cg...b.pl?catcarkev

My estimate is around $2000 USD on a 48' cat. I dont have experiece with kevlar, or any other type of resin for that matter, but is it that difficult to use. I also read an article of someone describing building a canoe with kevlar cloth.

[Nordic cat]

This use of Kevlar/Aramid/Twaron is growing in high end boats. I will be using it up to about 50 cms above the waterline as part of the inner skin. Kevlar has different characteristics than say e-glass or s- glass so it will be used together with a glass layer, and not alone.

As you say, a few thousand dollars more in a larger boat is probably less tha ½ a percent of the price. But it all adds up, weight and price!!

Regards

Alan

[fastcat435]

Originally Posted by Nordic cat

This use of Kevlar/Aramid/Twaron is growing in high end boats. I will be using it up to about 50 cms above the waterline as part of the inner skin. Kevlar has different characteristics than say e-glass or s- glass so it will be used together with a glass layer, and not alone.

As you say, a few thousand dollars more in a larger boat is probably less tha ½ a percent of the price. But it all adds up, weight and price!!

Regards

Alan

Hallo Alan

you do not have to use a combination of glass and Kevlar . using 500 grams of kevlar up to 600 mm over the waterline on the inner laminates side is plenty saves weight and money. We have had our boat calculated thru and that was the result.
Adding glass over your kevlar just ads weight but no extra strenght.
The cost of quadraxial Kevlar of the highest quality Yarn type 2200 in 500 grams per meter costs 66,00 euro per kilo or 33.00 per squire meter
x 104 meters in our case ads 3.432,00 euro or 5422 usd to the cost of the boat, the resin absorption is slightly lower than glass so a bit of savings can be reached here I estimate that for a 45 ft cat the total added cost is around 5000,00 usd and the impact resistancy is up by a factor 5 or 5 times as tough. Adding Basalt on the outer laminate makes it even stronger by 30 % and gives another weight saving.
That is the reason for using it standard on all our boats including the lightweight rigid inflatable.

Greetings

Gideon

[Howard N]

using 500 grams of kevlar up to 600 mm over the waterline on the inner laminates side

I'm probably making my first post a dumb one.

Why would you put the kevlar layer on the inside? Seems to me that if you hit a log or a rock it'll be the outside you want protected.

[Aac]

Good novice article on E-glass, S-glass, Kevlar, Nomex etc... is at

boats.com - News: Shifts in Fiberglass

[fastcat435]

Originally Posted by Howard N

I'm probably making my first post a dumb one.

Why would you put the kevlar layer on the inside? Seems to me that if you hit a log or a rock it'll be the outside you want protected.

Not a dumb but a logical one
Kevlar works better on the inside of the laminate to prevent damage thru out the hull , the elongation and stretch it can take is enourmous and having the foam barrier increases the resistancy to damage.

Greetings
Gideon

[BigCat]

Kevlar is strong in tension but weak in compression, and so it is put inside for strength. When it is put outside, it is usually for abrasion resistance, but, some don't like it outside, because it gets frizzy and soaks up water if it is exposed by scraping.

[fastcat435]

Originally Posted by BigCat

Kevlar is strong in tension but weak in compression, and so it is put inside for strength. When it is put outside, it is usually for abrasion resistance, but, some don't like it outside, because it gets frizzy and soaks up water if it is exposed by scraping.

Dont you ever sleep Big Cat ? Must be 01.30 where you are right now

Greetings
Gideon

[BigCat]

Originally Posted by fastcat435

Dont you ever sleep Big Cat ? Must be 01.30 where you are right now

Greetings
Gideon

Hi, Gideon - Not so late as that-I don't recall what time it was, but this came in after I went to bed, and it came in a little after midnight my time. We have daylight savings time, in which we "spring forward and fall back."

[BigCat]

I had an idle hour, so I did a google search to see who uses balsa. I
didn't include limited use of balsa in interiors or just in decks.
I was looking for sailing catamarans, and didn't list builders of
small runabouts. I also didn't look for builders of large powerboats,
but I listed a couple that I tripped over.

-Catamaran Designers using Balsa
Schionning
Oram
Hughes
Lavranos
Hill
Simonis Vogt
Lidgard
Morelli and Melvin
Roberts
Antrim
Grainger

-Stock Sailing Catamarans using Balsa
*Prout
Admiral
*Broadblue
*Leopard (Robertson and Caine) (Moorings)
Tasman
*Lagoon
*Dean
Seawind
C.I.M.s Ocean Voyager 65

-Power Catamarans using Balsa
Afticats
Allura Marine
*Lagoon

(* very well known high volume builders)

[DerekKelsall]

I will jump in here having read part of this thread for the first time. Much of the same comment on balsa is also on the KSSboat Group and the Multihullrequest on Steamradio forums. However, there is a very different outcome to the debate there, with an overwhelming list of experiences, theories etc., which anyone using or considering using balsa should be aware of.
The most powerful argument on these forums in favor of balsa is the long list of users. Many on the list are designers. Designers have a powerful influence on what happens within this industry. You may or may not be aware that there is no requirement for the best qualified designer in the World to have spent one hour in a boat shop or for that matter one hour on a boat on the water.
To make a truly informed choice on such matters it needs extensive all round experience. Experience you get in boatyards when boats come in for repairs, such as cutting into the various materials and seeing with your own eyes which are wet, or already rotting and which are dry and you know will last for decades. Experience of handling all of the options. Knowing how the materials choice affects the boat builders, the tasks in the boat yard, the overall costs and not just the per sq. m. cost. In the above forums we heard of the need for great care to avoid water getting into the balsa core immediately and the consequences when it does. We heard how no laminate is a 100% barrier. Boat repair people told how they love balsa. Google balsa and there are pages of guidance on how to deal with balsa problems. You hear none of this from those promoting. Many are not aware of them. Others clearly are but keep quiet. Many issue no warning of the need for great care.
This is not laying blame. It is the way this industry works. Some strange practices become industry standard for no overall advantage to the end user who pays, but can also become self sustaining. The dominance of strip in custom boat building is a case in point. We were told it was/is simple and quick – which it never ever was. I was never, ever tempted as we were already achieving all the shapes we ever needed starting from full size foam sheets, in a fraction of the build time.
Before my second design in 1966, a 42 foot cat, I had cut into ply and foam sandwich on my first Toria, and found the ply was already wet. I decided that foam sandwich would be simplest and best structure for all parts of the cat. I made a rule for myself which I have never varied – nothing should go into any boat which can rot. 1960’s Kelsall boats are testimony of the value of that rule. I am more than glad to be able to say to new buyers of old Kelsalls - my boats will never rot. PVC foam, with composite skins has never, ever been found wanting on any count, over 44 years of all types from super lightweight racers to around World record holders. There is nothing to gain from balsa. There is no possible way to guarantee no ingress of water into a core. If nothing else, it will attract a big question mark for the rest of the boats shortened lifespan.
I have nothing to gain from taking this stance – except to hopefully see better boats in the hands of owners and less of the disasters like the nice looking 55 foot cat, about 5 yo, with new owner, which came in alongside a KSS new build to have a soft area around a chainplate checked. Two days later, the whole of one side of the hull was stripped of its skin – and no one had yet checked the other side. Another reported on one of the forums of owning tonnes of wet balsa.
Kon Tiki told us all we ever needed to know of balsa.

Happy boating.

Derek.
FRINA.