1708 Bi-axle over Balsa

lots if if's and but's Flooding balsa you will end up with a heavy panel and defeating the excise of light . roll a generous amount over each side ,let it completely go hard ,Balsa absorbs resin by its very nature .
i have done some absorbtion testing to see how well it soaks .
A 25 mm thick block ,water will penetrate and soak right through in 30 seconds .
standard polyester resin uncatalysed i have at work, over night it completely soaked from bottom to top .
So the differance between using fast and slow resins the penetration could be significantly differant . But because of its penetration is the whole key to the shear strength of balsa and the reason we use it .
you want light use foam core ! BUT do some searching . Not all foams are made equal! .Its cost more but corecell seems to be the flaver of the month !check that out as well
Glass fabrics with chopped strand ! the chopped strand layer becomes a sandwich layer used to glass reinforce the resin between the core and the main fabric . most people are completely againt csm and poo poo its existance but its there for a reason . if you use peel ply you will never even notice the csm's existance .theres always a reason for some thing that most people dont take notice of !!all they see is chopped strand glass and go into a tizz !! so unless you are using a high grade of epoxy i would not hesitate to use the chopped strand thats on the cloth . on a job such as the bulkhead you could possibly use 1 cup of resin more and if you peel ply couls save 50 % of that so unless you are laying a whole roll of glass its a no brainer . you want to save weight you should not be using balsa and not using glass either , so where you want to draw the line ??

 

Weight saving is a totall package deal , glass and resin and cores etc is only a very small part, what about all the other junk that boat gets fill with , you can throw 2/3 of it away and hardly ever miss it as most is just comforts of home!!, so whats the point skimping on the eccentuals . Air conditioners , gensets big enough to power a small city just to run all the electronics and power the lights and gadgets etc etc , just to impress the neighbours in the marina , LOOK WHAT IV GOT !!!!!

 

i would use only epoxy with balsa, more waterproof to protect against rot, osmosis and no CSM required to tie it to the core as the matrix is stronger...

seal the balsa core by scraping a thin layer of very thick epoxy / silica mixture, otherwise it will drink up gallons of resin if used neat... once this sealer coat has "set up" or gone tacky, go ahead and start laminating your biax in the normal fashion ie. wet on wet.

 

Thickening resin for any job is partually defeating the purpose of using it !!! if it dosent penetrate a short way into the balsa you may as well just use pva glue to stick you glass on with !!!. ,
Thicked resin will just sit on top and the balsa and will draw a small amount of the resin out of your thickened exspensive best you can buy epoxy ! its not much better than using a good general purpose polyester resin that will have penetrated a good way into the cells of the balsa .
If you play with and add things to resins and the like you are playing with fire so to speak and if you have a failure some where down the track, you can stand in front of a mirror and point the finger at yourself .
You want to seal the balsa! simply roll a coat of resin over it and let it go hard , then resincoat and lay your glass , the old and new resins will bond and you will have a much better adhesion .
Like i said earlyer the csm on most cloths is usually just a sprinkiling of 300 grams or less and because it is stitched there no binder used , or if there is a binder its a hot melted power binder reguardless if it disolves or not its still doing its job of glass reinforcing the resin layer between the balsa core the the glass fabric .
In more than 25 years i never seen any polyester laminate of any sort come off balsa !!,never !! seen the glass above the balsa rip to shreads but the glass never came off the balsa at all .
You want to see what workes and what dosent go and do boat repair work for a while specially boats that hit things and get smashed badly !!. then you will get a greater appresiation and understanding of materials !!
Foam on the other hand is real scary how easy it peels off from end to end in one good pull ,its not the resin letting go its the foam letting go from its self !!.as far as density goes think of what you should be using and take another couple of steps

 

Not wanting to fence you anyway but as you said it yourself "it's not much better" so it's better.. We can allways discuss how much but I believe it's made clear in this thread what's recommended for poly and what's for epoxy so no reason to scream your opinion ad nauseam. If there's something new to the subject please feel free...
BR Teddy

 

Peeling glass from core material is a sign of improper glass lamination specs, not a problems with adhesion. Each foam sheet is made up of small particles, not strands - so it can never resist peeling.

If the glass layer is so lightweight that you can peel it, then it wasnt heavy enough in the first place. The glass layup should be so rigid, that it wouldnt bend enough to peel. Adhesion only has to be adequate to prevent moisture ingress and collection.

Foam is only for compression ! Shear strength, torsion, etc are all required from the glass layers - the core material is only there to be "squashed"

The sheer strength of balsa is touted as significant, but considering that balsa sheet is made up of small blocks - how much sheer is there between the blocks ? Stuff all ! It would be different it we were talking about planks of balsa on edge, but that has little compressive ability. Even if the blocks were glued together with epoxy, how much sheer is there within the 20-30mm vertical block of lightweight wood? Stuff all - the fibres on balsa split vertically very easily. You can do it with your fingers.

From what I can read, the biggest benefit of balsa is its ability to withstand high temperatures, that can deform other types of cores.

 

even if there was 10mm thick layer of glass each side of an sheet of foam core it would simply shear apart really easy the foam is the weak link !! Balsa on the other hand you would have to tear the layers of glass apart to part the panels and it would be the glass letting go not the balsa . , i would trust my life unquestionably with a balsa laminate !!, LIKE i already said i have never in more that 25 years of being in the glass industry ever seen a glass balsa lay up ever part off the balsa its just dosent happen !
Dont believe me try and find on the net where Balsa has sheared !!

Let me ask you have you ever used balsa core in any of what ever work you do ?? you have used a load of foam i would say
The only foam i have not had the pleasure of being introduced to yet is core cell . Steve from s&f has been a advocate for core cell for some time and i value his honest opinion that its good stuff

 

Tunnels - what you are forgetting to say, is that there is always sides and bottom layer of fibreglass over every core. You never, ever have just one layer - as you well know.

Its up to all these outer layers to resist all the outer forces. You cannot tear glass off a core if it is of sufficient strength.

100's of boats are running around the ocean successfully built out of foam and/or balsa. All of the foam cores have this low adhesion you observe - all of them ! Its all in the engineering of the surrounding glass.

 

You cannot tear glass off a core if it is of sufficient strength.

And most foams are not of sufficent strength . !!
think of what has been specified and up the density!!spescs have a habit of being the minimum requirement to build to in critical areas always exceed the specs provided .
A designer in nz found out the hard way with core shear ! the foam sheared !! it was the same as what has been used in lots and lots of other boats but this one time the boat got caught in a sudden storm . just about cost the designer his house and is lively hood when the courts had finished . Foam for slower vessels ok cores for most yachts ok but when the speed get up !!,never !! balsa dosent shear !
i have never seem,found or heard of evidance ever to say it does !!
The next best is core cell so i am lead to believe !
Race boats is the best testing ground for any materials !!
Small races boats and go fasts always use Balsa !! always !!

 

Tunnels me ol' mate, you are a big one for making the broad statement,

This is utter B^&(Sh^%t Tunnels. Sure, there are failures, but we are talking about a small percentage.

Next time you take a trip in your high performance sailplane, or pay a million to take the commercial space flight with Virgin Space, or just fly to London in one of Boeings new planes, you better hope you are talking rubbish.

Back on the water, take a stroll down to the local marina, and count up the number of foam hulls visiting from all over the world. See any large cracks or delaminations happening ? No you dont.

You cant possibly think that the thousands of qualified NA's, supported by huge professional liability insurance policies, that design hundred of foam cored boats are all pushing underspecced craft onto the oceans of the world.

And who is this person - can you quote me the link please ?. While you are at it, you can also look up the yard foreman that was sued when the steel keel on that canting keel yacht that broke and drowned several people. Oh, and One-Australia, the Carbon Fibre yacht that sank in the Amercias Cup.

The failures are not restricted to the building material used ..
IT IS THE ENGINEERING ERRORS .

If you under-engineer the glass around Balsa - it breaks just like any other material.

Read about about the court case of a badly designed balsa core fishing boat at

http://openjurist.org/839/f2d/1085/snyder-v-whittaker-corporation-allen

"Whittaker's decision to build its shrimp boat hulls of two materials--balsacore material above the waterline and fiberglass laminate below .... that allowed a small impact to cause a large hole. ... the TEXAS LADY had been defectively designed and that this design had caused the accident. "

Google 'Balsa Core Testing' and read all the research being done to prevent Balsa failure. They talk about the importance of grain orientation, layout of the balsa blocks, best methods of laminate etc etc. Preventing failures in Balsa cores is big business .... because failures can occur.

Race boats are NOT the best test for materials. They are the indication of the cheapest, easiest hull builds, and most hulls in power or sail, that are designed to win, are not designed to last. Very few race hulls are expected to last more than a few years - they get replaced constantly, like their engines or sails.



I am not saying that Balsa cannot last if properly engineered, but the other core materials can perform just as well if they are designed properly.

 

And who is this person - can you quote me the link please ?.

Mr Max Carter is the designers name and it cost him more than $400.000 nz dollars . Hi modulas was also involved as well with specing the materials used .

The biggest boat i built a very high percentage of was 147 feet long my crew and myself built all the internal framing ,including tanks ,and floors all had glass foam glass cores all built to DNV specifications , 6000 hp with twin catapillar motors !
Maritani !built by Sensation yachts is still on the web last time i looked about 3 months ago , had 50 mm thick foam cored hull top sides but the bottom was solid glass !!.


Quote from the hull truth ! Grady has used balsa successfully for decades. !

Some of the testing cycled at 900 times per minute and the count was as high as 35 milliom plus times !

some were quite low at 2300 but was the adhesive that was stated to be at fault for what ever reason was the wording .

During my early years of making power boats we used foam cores mostly divinicel contured in small blocks on scrim sheets and set it in on a slurry mix that we formulated our selves ,This was before core bond was on the morket the mix came up between the blocks and we were very particular about the installations . Never to this day has one of the boats we made ever have any kind of any sort of a problem . We made our own hole saws for the skin fittings and routed out the core between the skins so its had 9 mm of solid epoxy filler between the fitting in the hole and the foam core .

Next week i intend to do some testing of my own to do with the peelability and bonding of polyester resin /csm glass and 25 mm balsa all bagged !!
The small test i done so far showed that our resin will penetrate 3 to 5 mm into the balsa during its gel time depending on the hardness of the individual blocks i tested . A 25 mm block sitting in a pool of uncatalysed resin for 12 hours will penetrate the full 25 mm bottom to top so its does get in !! I have always been a firm believer of resin coating balsa before its glassed and never using high catalysed resin with a short gel time , the better the penetration the better the bond ,the less problems .
i will stick to what i know is to be true and advise other on the facts as i know them from my own working exsperiances having been there done that for many years !!

The 90 foot boat i have been posting pictures of here on Boatdesign has 25 mm thick Balsa vac bagged onto 900 grams of wet csm the top sides and the transom . all the decks forward and aft plus side decks and cabin sides will be balsa cored incuding the small fly bridge on top of the cabin , everything has 25 mm balsa core !!
Do i have any worries about the balsa?? never !!!i get a good nights sleep as far as materials are concerned !! only thing i think about is the workmanship !!.
All the materials and the methods have done this countless times and will keep doing it same way for as long as i can still get inside the hulls to work on them

Like i have said many times on boatdesign 90% of glassing problems and failures are from bad workmanship and 10 % from bad choice of materials because people dont know what they are doing !!
If you fully understand the materials your working with you will make a better job of the products your making .

 

Core bond !!! or csm and resin !!!

Core bond i have used truck loads of 20 litre pails over the years , all tins when they are recieved i always make sure the date is written on the tin not the lid as they can get taken off and changed .
It has a bad habbit of separating as the light filler materials float and the resin ends up as straight resin in the bottom so of with the lid and get a poweful stirer and mix for at lease 20 minutes each tin and chack the consistany is the same from each pail . Core bond on foam i dont question , but core bond for balsa !!!! a big red sign goes up !!!
Because of the nature of balsa is to draw resin into the pores of each individual block, the balsa needs a generous roll over with catalyzed resin !! , once before you trowl on the core bond to the skin and another generous coat just before you lay the balsa onto the core bond !!. Apart from the soaking the resin will also make the core bond flow better up into the spaces and holes in the blocks when Vacuum is applied the resin should and will draw up even further and almost completely saturate the complete top surface of the balsa blocks as well . Like all resins and mixes know there gel time of each!!, the core bond could be in a thickness between the balsa and the skin and the resin used should be way up inside the balsa so core bonds warmth could trigger all the mixes to go off at the same time or very close .
Never release the vacuum to soon , resin and core bond has a crumbly stage !!! leave for longer and dont be in a hurry . laid over an uneven surface the sheets could and would have tension and want to spring out off hollows and sit on top of humps.
All the core bond i have used ,has a stick like nothing else !!there is a slight amount of flex with core bond so the bond is almost impossible to get apart even with a sharp chisel .

Cores stuck on csm glass also has a excillent stick and the glass reinforced resin is really good . The surface being bonded onto needs to be as flat as possible ,again always prime the core surface ,let it soak for a while and roll another coat of resin before you lay NEVER SKIMP ON RESIN the core and the job in general will only use the resin it requires to do the job the rest will come to the surface and be bleed off , it takes long hours of practice and skill to know exactly how much is just right !!!
Again have never had a core failure on any job because i am methodical and have a system so nothings gets forgotten any where during the installation .
Its all in the preperation and every one knowing exactly what has to be done where everything is and why we are doing what we are doing !!
I have a countdown on my watch that i set when the catalyst is poured and mixed , i set the alarm 5 minutes before the gel time so have a small window of oppotunity in case some thing happens ,always have tools and spare materials open and just a hands reach away . also safety is a part of the whole excise ,not dropping anything on the floor no matter how small !!, not throwing things to anyone ,you take it and hand it to them !!, the final minutes we all count down the seconds together in harmony !! its called team work !!
Be there 2 people or 10 people in the team the system never changes !!.

 

here I am Tunnels - sorry to keep you waiting, no need for personal messages to grab my attention.

..and he is a well respected boat designer. Where is the link to the court case with the details ? I couldn't find it.

Yeah, but you also said "And most foams are not of sufficent strength . !!", which is much, much higher than 10%

I still say that the number of 'below spec' foam boats is very small, and not "MOST". You havn't done anything to support your assertion.

 

Find another sand pit !! we are here to help people best way possible !!

DO YOU WANT ME TO BOW TO YOU WITH YES SIR ,NO SIR SORRY I DONT THINK SO YOU HAVE TO EARN RESPECT !!
You sound just like BOTH my 2 ex wives when they started to argy over pointless silly things i got up and left them to it !! you want some one to nit pick with i will give you there addresses one is a kiwi and the other is Japanese so take you pick ! Mind you i never keep in contact with eiether of them because they never earned respect either !!
So why fill the airwaves with meaningless jibber jabber !! lets get on with what this sight is all about !! helping people the best way we can !!!be a good chap !!!

 

Great response Tunnels. You throw a lot of grand statements around to confuse any puzzled newbies, and then just casually accuse me of nit picking jibber-jabber.

The best way I can help is to keep people who make unsupported statements honest. Please do stick to your areas of excellent expertise - and don't catch the apex disease ( you know what I mean )

Heaven help that anything on the internet is wrong Hi-Ho Silver Awaaaaaay