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Old 28-01-2007, 23:50   #1
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Nidaplast in crossbeam repair

I am at a stage in my rebuild where it is time to redo the main crossbeam that supports the mast. The original was a 55cm x 55cm box structure of 12mm nidacore sides and bottom with 25mm pressboard top with fibrerglass/polyester skins. Termites ate the pressboard and camped in the honeycomb (it was scored) so it has to be redone. The repaired beam will be 55cm x 85cm. I would like to use Corecell or Airex but none is available on short notice in Thailand. Nidaplast is, however so I am thinking of using this.

Anybody have any opinions on the suitability of this material in this application? I would use 25cm with unidirectional/biaxial fibreglass/epoxy skins with bulkheads every 60cm. The boat is 45' long with a 28' beam.

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Old 29-01-2007, 00:14   #2
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What the hell is Pressboard, and termite's, Wow.

I would have thought Nidaplast would work, but put a solid insert around the mast base area to avoid compression, and then maybe a pile of uni's going across the boat for good measure.

Before covering in a D/B or Triax or Quad, whichever you are using in the rest of the job. Please don't say choppy and roving's.

Without seeing the boat or the job, I am of course, making this up as I go.

Dave
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Old 29-01-2007, 02:57   #3
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NIDAPLAST POLYPROPYLENE HONEYCOMB CORE
Nidaplast has similar values for compression strength, slightly lower values for shear and tensile strengths, and lower stiffness (moulus) properties; when compared to typical PVC foam cores.
In turn, foams have much lower properties than end grain balsa cores.
Compare specific products by:
Tensile Strength
Shear Strength
Shear Modulus
Compressive Strength
Compressive Modulus

I suspect that any variations in final “quality” may be more due to the builder’s skill, particularly in achieving a proper wet-out and good bond-line, than to core material properties.

“Pressboard” is a reconstituted-wood product (compressed wood fiber), roughly analogous to particle board, chip board, or composition board.
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Old 29-01-2007, 03:01   #4
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Dave,I would think that pressboard is solid wood chipped up and/or ground to a powder like substence and ,wait for it,"Pressed together"with some sort of super duper adhesive.Don't really know what was wrong with solid wood in the first place,but ya do have ta glass it to make it stronger,they dont fix em like they use to.Mudnut.
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Old 29-01-2007, 03:36   #5
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Dave,I would think that pressboard is solid wood chipped up and/or ground to a powder like substence and ,wait for it,"Pressed together"with some sort of super duper adhesive.Don't really know what was wrong with solid wood in the first place,but ya do have ta glass it to make it stronger,they dont fix em like they use to.Mudnut.
What, like Weet-Bix [chipboard, MDF, Craftwood] surely not, say it aint so.

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Old 29-01-2007, 04:03   #6
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What, like Weet-Bix [chipboard, MDF, Craftwood] surely not, say it aint so.

Dave
Nup!Aint got a clue.If it hasn't got anything to do with wood.Why?would ya call it Pressed wood.My whole thought was to advocate "solid wood".I personly have never repared boats of any discription,except our old corro iron and two 4x4's we used on a dam over the next paddock from our place,but the seeing that little boat sink and knowing the only two things on it that were solid,was the two 4x4's attatched at either end.Solid wood. Mudnut.
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Old 29-01-2007, 12:31   #7
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Pressboard is probably someone's trademark, but in the US these days it is a generic term for what Gord says, a mixture of wood scraps pressed together with resins to make a sheet of "woodish" material. Often used as a floor underlayment, because screws don't hold well in it. And it's heavier than all hell, not very rigid, not much of a structural material but a cheap way to reuse whatever parts of the forest fell on the milling room floor.

When used correctly...it is an economical material. SImilar products and names in the US: Masonite, Beaverboard, and "Pegboard" which is the same thing but with holes drilled in it every inch, so you can stick pegs in them and hang up tools and things. About the only use for it where the lack of strength doesn't matter.<G>
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Old 29-01-2007, 19:45   #8
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I'm not sure how they make pressboard but I do know that it makes crappy boatbuilding material but ideal termite food.
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Old 29-01-2007, 20:54   #9
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It may well be a dumb question, but have you considered using timber? It is readily available & cheap (it is one of the few things that does actually grow on trees!) and has been used in structural applications on boats since our ancestors first ventured onto the water! Of course there are materials that are stronger and materials that are lighter, and even a few that are stronger and lighter, but timber is reasonably strong, light, cheap and easy to work with. If your boat is a lightweight flyer, perhaps a more exotic material choice might be better, but given that the boat is, presumably, a crusing boat, so that weight is probably not quite so crucial (plus it sounds as though the additional weight will be low, so "good" weight), the extra weight may not be an issue.

Timber will also take fibreglass well, rendering it almost termite proof!
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Old 29-01-2007, 21:24   #10
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Mike, it sounds like you had some kind of box beam that was skinned with FRP. If the pressboard was just used to give the FRP something flat to form over, that would be fine. Often a boxed beam doesn't need a strong center filling, the skin (the FRP) is the structural part.

But what I find curious is how termites got into a fiberglass sealed beam. How did they breach the outer skin?
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Old 29-01-2007, 22:40   #11
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Quote:
Originally Posted by hellosailor
Mike, it sounds like you had some kind of box beam that was skinned with FRP. If the pressboard was just used to give the FRP something flat to form over, that would be fine. Often a boxed beam doesn't need a strong center filling, the skin (the FRP) is the structural part.
Don't know how you can say that, the nidaplast was there to seperate the skin, like on all sandwich construction, thereby having a thin skin either side of a core giving it stiffeness,

If you took the core away you would have a skin probably around 1 to 2 mm thick that would'nt support a box of tissues, let alone a mast.

Every box beam , or drum bulkhead i've seen or worked on has a solid section inserted where the mast sit's to stop crushing. On a forty footer the compression load's when powered up can be several ton's.

A lot just use a solid timber top section out of Kauri, Oregon or similar, obviously given a big drink of epoxy and epoxied and glassed into place.

Mike, these guy's may be able to help with a choice of local timber's in your area

NUSA DUA CUSTOM BUILD YACHTS | Power Boats | NUSA DUA MARINE | BALI | INDONESIA

or

Phithak Shipyard and Services

There are plenty of places on the modern Multi to save weight, and this area is not realy one of them.

My opinion of course.

Dave
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Old 30-01-2007, 00:28   #12
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Thank you all,I had a punt at solid wood for the fix,never been there but chipboard or any other smashed together bits of wood just couldn't be that strong.Just for Hellowsailor,85% of wood chip comes from whole trees ripped out and raped from the land to fill some ecconomic need for the people of the world.Not to say that its better to use solid wood.Apparently it's the people born in 20yrs time that are gonna have to worry about the lack of air.Opps,sorry OT.err,umm,"Keep it solid!!".Mudnut.
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Old 30-01-2007, 08:31   #13
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Catman-
To some extent a boxed beam can be considered akin to a pipe. Making it solid, rather than just a skin, does not buy you a lot of anything in most applications. That's why we use pipes (tubes) instead of solid rods for masts and poles on the boat, right?
I've seen keel ribs that are glass over foam, and the foam was just there to give the glass it's shape. A box beam, akin to a tube, and the foam inside really had no strength to it. Without knowing what kind of beam mudnut had or what it was doing, I can't guess how/if the filling makes a difference but I'd think pressboard (at least what we call pressboard in the US) would only be suitable to spread a compressed load, like it does in floor underlayment. Under a mast...maybe, but I wouldn't trust it for point loading like that either. I'm not big on the words "trust me" when they're on a structural part.<G>

Mudnut-
At least here in the US, it is somewhat apalling to see the teens and college kids now, totally sucked into the material void and carrying on almost none of the activism that was happening in the 60's (antiwar) and 70's (environmentalism). Darfur, global warming...all less interesting than wearing the right logos, and that's upsetting. Instead of conserving plastic, they all want to buy bottled water and carry that around. Despite the fact that we've generally got great tap water in the US, and bottled water and juices have no bottle deposits (unlike beer & soda) so the ground underfoot is littered with the water bottles. Hmmmm....

But denuding forests is an old and respected tradition. The Brits did it, the Italians did it, most of the "Old World" did it. The US certainly got a good start on it, heck we still sell forests below replacement cost to the Japanese and diesel fuel is still cheap enough that we can sell our old paper to the Chinese, who recycle it and make gobs of money using our paper waste instead of harvesting their own forests. Says something about the relative values of petro and paper I suppose, perhaps we need to take a lesson from OPEC. (sigh) Knowing the way people think...I certainly wouldn't buy any retirement property in warm places located by the existing sea shores.
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Old 30-01-2007, 16:32   #14
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Quote:
Originally Posted by hellosailor
Catman-
To some extent a boxed beam can be considered akin to a pipe. Making it solid, rather than just a skin, does not buy you a lot of anything in most applications. That's why we use pipes (tubes) instead of solid rods for masts and poles on the boat, right?
I've seen keel ribs that are glass over foam, and the foam was just there to give the glass it's shape. A box beam, akin to a tube, and the foam inside really had no strength to it. Without knowing what kind of beam mudnut had or what it was doing, I can't guess how/if the filling makes a difference but I'd think pressboard (at least what we call pressboard in the US) would only be suitable to spread a compressed load, like it does in floor underlayment. Under a mast...maybe, but I wouldn't trust it for point loading like that either. I'm not big on the words "trust me" when they're on a structural part.<G>

.
Hellosailor .

To achieve the strength and stiffness to support a mast in a box beam using no core, the structure would have an excessivly heavy and thick glass layup.

Quality Plywood as a replacment to the core is one way of achieving a relatively stiff strong and light structure with only light glass required to seal.

Without a centre filling the glass would flop around in the breeze and have no strength/stiffness, unless of course one was to use excessive amounts of glass.

While foam/nidaplast in itself has no strength it does keep the skin's seperated and in column providing stiffness/strength. Once the skin's get out of column, the structure colapses. Shear strength of foam, nidaplast and light timber is very important to the calculation required.

In strip plank Kiri/Cedar timber composite construction,a lighter skin can be used as the timber core should be used as part of the overall deflection/stiffness/strength calculation

Notes on Sandwich contruction and how lightweight structures get their strength.


Dave
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Old 30-01-2007, 17:21   #15
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Quote:
Originally Posted by hellosailor
Catman-
To some extent a boxed beam can be considered akin to a pipe. Making it solid, rather than just a skin, does not buy you a lot of anything in most applications. That's why we use pipes (tubes) instead of solid rods for masts and poles on the boat, right?
I've seen keel ribs that are glass over foam, and the foam was just there to give the glass it's shape. A box beam, akin to a tube, and the foam inside really had no strength to it. Without knowing what kind of beam mudnut had or what it was doing, I can't guess how/if the filling makes a difference but I'd think pressboard (at least what we call pressboard in the US) would only be suitable to spread a compressed load, like it does in floor underlayment. Under a mast...maybe, but I wouldn't trust it for point loading like that either. I'm not big on the words "trust me" when they're on a structural part.<G>

.
Thats not really true. In fact a solid mast would be much stiffer than a hollow one of the same section, but it would be unacceptably heavy. A simple experiment you can try is to get some 100mm PVC downpipe and see how easy it is to bend till it kinks, then fill a length with that aerosol polyurethane foam, then try it (after the foam hardens obviously). The foam, by resisting compression, holds the section in shape and makes it much more rigid. This is what cores do in boat building. However, chipboard, particle board, fibreboard, or hardboard are not suitable core materials. For a start, they would offer practically no weight advantage over solid glass construction, and they will turn to mush as soon as they get damp.
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