What core?

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whingeingpom
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Joined: Sat Jun 27, 2009 12:32 pm
Location: Caribbean

What core?

Post by whingeingpom » Sat Jun 27, 2009 12:41 pm

Hi everybody. I'm a new user of this forum, came across it while trawling the net looking for boat building info, certainly looks like it's all here!

My question: I'm considering building my own catamaran, although am really at the dreaming stage at the moment. I've been looking at Schionning designs, specifically the Wilderness 1320 or 1500 (when feeling particularly ambitious and/or drunk) who make a good case for using balsa cored Duflex rather than foam cored, does anyone have any opinions one way or the other - I'm a bit concerned with what might happen to balsa if (when?) water gets into the core.

Thanks!

44c
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Location: Hervey Bay, Qld

What core?

Post by 44c » Sat Jun 27, 2009 5:23 pm

It shouldn't be a matter of "when". Always use proper building techniques and water won't get in, full stop.



There are hundreds, if not thousands of old balsa cored polyester boats still going strong. You never hear about them, you only hear about the occassional disaster, which is almost always the result of an owner drilling holes all over his deck, without taking the proper measures to seal the core.



And if you do that, foam cores can suffer problems too.



An epoxy/glass balsa cored boat should last forever, as long as you use proper techniques.

madaz
Posts: 527
Joined: Thu Apr 26, 2007 7:47 am
Location: Hobart, Tasmania

What core?

Post by madaz » Sat Jun 27, 2009 7:32 pm

If I could afford my top choice would be foam.

puremajek
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What core?

Post by puremajek » Sun Jun 28, 2009 6:32 am

I am another for Foam. Started a 'Poll' for you too, hope you don't mind Whingeingpom
James
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http://www.diycatamaran.com
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whingeingpom
Posts: 5
Joined: Sat Jun 27, 2009 12:32 pm
Location: Caribbean

What core?

Post by whingeingpom » Sun Jun 28, 2009 8:23 am

Thanks for the feedback. OK, so foam gets the vote so far, although apparently it's more costly - what are the advantages over balsa and how much more expensive would you estimate it to be? Are there different types of foam used for this purpose?

madaz
Posts: 527
Joined: Thu Apr 26, 2007 7:47 am
Location: Hobart, Tasmania

What core?

Post by madaz » Sun Jun 28, 2009 8:40 am

You would have to price the faom in your area. Cost comparisons in Australia would be irrelevant.



I beleive the foam used is closed cell not sure of the chemical composition though, come from places like DIAB, Kledgecell etc, you can do some searchs and start gathering info that way.



The main advantage would be IF water ever gets into the core the foam wont rot and the water wont spread through the thickness of the core. with basla it will do both and in some cases quite quickly.



As Alan rightly states if a duflex boat is built properly you shouldnt have any trouble anyway however if anything out of the ordinary happens or flexs or impacts etc etc or it develops a harline crack somewhere that you dont know the water gets in and then there are problems.



start googling the various cores you are considering for exapmle type "rotten balsa core" in a google search and see what you get. do the same for foam and ply and weigh up the benefits. I am building in ply as thats what i can afford, my boat will be heavier for its length than duflex or foam boat and have straighter lines but I can build a boat for less than half the price.

darwincat
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Location: a bit south of Darwin

What core?

Post by darwincat » Sun Jun 28, 2009 10:08 am

Good Day All,



There are two very important points that have not been considered in this interesting discussion and all other discussions about cored materials.



The first is that balsa is not just balsa. A factory made material such as Duflex, by its very nature is highly resistant to the spread of moisture for one simple fact.

Duflex is made up of slices across the tree growth after the timber has been ripped into a rectangular shape. These slices are then laid up (parquet style) on one laminate with another on top, this lay up is then infused.



The process therefore forms large 1mm to 3mm barrier walls between each slice or parquet block piece. I am well aware of these little epoxy walls, as they are are hard to remove when one de-cores and replaces for secondary fit out. It is therefore it is virtually impossible for moisture to travel through more than one of these, (100mmX 70mm on average), blocks between the laminate.

One could also acquire the non-laminated end grain balsa. Then use this balsa as a core, with out a very professional vacuum process, then one could get water traveling throughout the core. This particularly the case with unsound core management during secondary fit out.



The second matter here is that a properly made end grain laminate is STIFF when compared to other materials, particularly foam. This means so very much when building, that is, one does not have to build a second boat (sophisticated framing) first, and or then bog out all the bumps and hollows caused by wobbly material.
Last edited by darwincat on Mon Jun 29, 2009 12:54 am, edited 1 time in total.

whingeingpom
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Joined: Sat Jun 27, 2009 12:32 pm
Location: Caribbean

What core?

Post by whingeingpom » Sun Jun 28, 2009 5:30 pm

Schionning make the point that balsa cored Duflex is somewhat stronger than foam cored, both in impact resistance and shear strength. Although foam is almost half the weight of balsa this benefit is largely reduced since the build has to be that much heavier, i.e. thicker panels, more glass and epoxy. If all the above is true, it leads to the question: why would you choose foam over balsa? :?

44c
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Location: Hervey Bay, Qld

What core?

Post by 44c » Sun Jun 28, 2009 6:40 pm

You could still build a slightly lighter boat from foam. And you may feel better using a foam core.



But the boat will be nowhere near as light as the difference in density would suggest, because, as you say, you need to use more foam, and more glass/resin to achieve the same structural result. It's up to you to decide if the cost/benefit is worth it.



Simply googling rotten balsa core will give you absolutely no information about Duflex. Because no Duflex cores have rotted.



Foam cores also have their problems. The claims that water won't penetrate foam cores have proven to be false. If water gets in to a foam core it too can break down, just by a different process, hydraulic erosion.



It turns the foam to mush, much like rotten balsa.



http://www.yachtsurvey.com/HiTech.htm



Probably the best option is to contact either ATL or Schionnings, and ask them what the price comparison for a foam cored vs balsa cored kit would be. Then it's up to you.

madaz
Posts: 527
Joined: Thu Apr 26, 2007 7:47 am
Location: Hobart, Tasmania

What core?

Post by madaz » Sun Jun 28, 2009 7:49 pm

you can tell who is building duflex boats..... :P

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