Karl,
I'm not sure what happened here. There no stringers in this board, and the
whole thing was layed up all at once. Heat is probably a factor, maybe an
autopsy will show something.
Mark
On Thu, Nov 20, 2008 at 12:50 AM, karl Schulmeisters <karlsch@xxxxxxxxxxx>wrote:
> That bulge looks like an offgassing bulge to me. That would be caused by
> chemical breakdown of the foam itself which can happen under heat and
> especially if there is an incomplete cure of the epoxy holding the stringers
> in, or on the interior layer of the layup.
>
>
>
> But a bubble that big would not be caused by stress load failures. I've
> broken rudders, skegs and daggerboards before. They don't fail gradually
> when loaded, they snap. Bubbles are gradual delams.
>
>
>
> So as much as I hate to point the finger at the builder, that's where I
> think the problem lies.
>
>
>
> An easy way to do the I-Beam CF stringers is to run the core on the table
> saw and then glue the pieces back together under vertical pressure after
> wrapping a strip of CF on each side of the "I-Beam". To get alignment you
> can either put it back into the outer shell, or you can prefit 2 pegs
> longitudinally and let those align the merge.
>
>
> ------------------------------
>
> *From:* Mark White [mailto:mwhite4459@xxxxxxxxx]
> *Sent:* Thursday, November 13, 2008 4:37 PM
> *To:* bdally6107@xxxxxxx
> *Cc:* cbull@xxxxxxxxxxxxxxxxx; swiftsolo@xxxxxxxxxxxx
> *Subject:* Re: failing centerboard
>
>
>
> It was Greg Ryan's idea for carbon stringers, not mine. I was going with
> wood origionaly, and thinking about it, my say with wood. The carbon
> stringers will be more work than the wooden counterparts.
>
>
>
> I don't think point loading is a factor here, the bulge is 4" or so lower
> than where it exits the bottom block.
>
>
>
> Another possibility why Bram's have lasted longer, may be because he
> handles the boat better putting less stress on everything, unlike myself.
>
>
>
> Mark
>
> On Thu, Nov 13, 2008 at 4:42 PM, <bdally6107@xxxxxxx> wrote:
>
>
> Mark,
> This is a good topic for discussion.
>
> Let me start by saying that neither the original CB or rudder that I made
> with foam core have failed to date (4 or 5 years now). The rudder was an
> experiment in which I used an even lighter layup than the pdf. That having
> been said, enough of these things have failed that it has become fairly
> clear that there are issues.
>
> I've been concerned from the beginning that we should use spartite gaskets
> to reduce point loading to a minimum but even that has not eliminated some
> of the failures. The newer CB's were 1/8" thinner which makes them 19%
> weaker (all other things being equal) than the originals like mine.
>
> Marks solution should be a good one. Using carbon ribs will make the blade
> substantially stronger because it will keep the two skins in column and an
> equal distance apart. I would reccomend carving a 1/8" V groove in the foam
> on each side of each rib at the surface. You will then fill that grove with
> epoxy/silica when you coat the foam blank immediately prior to lay-up. Make
> certain that the carbon ribs were layed up with peel ply or at least
> rough up and clean the surface prior to insertion and lay-up of the blade.
> On the bottom of the ribs (well short of the bottom of the blade) cut a deep
> V-goove in each rib. This will eliminate the hard spot and point load at
> the end. Since the rib is about 1" wide, I'd suggest a V about 2" up.
>
> I am very surprised that Mark's blade did not fail immediately once it
> bubbled. When that happened it lost well over half its' strength.
>
> Keep the discussion going if you have new or different ideas.
>
> Best regards,
>
> Bram
>
>
>
> -----Original Message-----
> From: Mark White <mwhite4459@xxxxxxxxx>
> To: Chris Bull <cbull@xxxxxxxxxxxxxxxxx>; swiftsolo@xxxxxxxxxxxx <
> swiftsolo@xxxxxxxxxxxx>
> Sent: Thu, 13 Nov 2008 12:57 pm
> Subject: failing centerboard
>
> Chris wanted to see some pictures of a failing centerboard, so I
>
> thought an open discussion might be in order, (since I am going to
>
> make another).
>
>
>
> This centerboard was made as per the instructions from Bram and or
>
> Greg, to the best of my ability. I started using it in the 06 regatta
>
> in FL, so it has seen 3 seasons. Before going to FL in 08, I removed
>
> some surface scratches by filling and sanding back to a smooth and
>
> fair finish. The first blister appeared 2 days before the 08 regatta,
>
> and every time I sail, it gets larger, and now is on both sides. It
>
> still works, but has become increasingly difficult to lower and raise.
>
> You can see 1 large bulge on the starboard side, and 2 on the port
>
> side. The origional rudder broke under heavy air just after the 07
>
> regatta. The pictures of the foam core are the new rudder made just
>
> before the 08 regatta, with wood strips inserted to help handle the
>
> loads it incurs, (which I believe are enormous)
>
>
>
> I'm not an engineer, but it seems hybrid and carbon cannot handle
>
> compression very well, or maybe it's just a limited number of cycles
>
> it can handle. I don't know if altitude has anything to do with it,
>
> but these boards were made at 4500' msl. The fact that they are black
>
> probably has a lot to do with failure, although I tried my best to
>
> keep them out of direct sunlight. If you add heat to epoxy resin it
>
> will soften.
>
>
>
> I will build another centerboard with a foam core, but it will have
>
> stringers (4 or 5) to help with the loads the skins incure. Hopefuly
>
> it will last indefinitly, or at least longer than the first.
>
>
>
> If anyone has any ideas on making foam cored boards last longer,
>
> please chime in.
>
>
>
> Mark
>
>
>
>
>
> IMG_7404.JPG
>
> IMG_7405.JPG
>
> 002.JPG
>
> 003.JPG
>
> 013.JPG
>
> 014.JPG
>
>
>
> These pictures were sent with Picasa, from Google.
>
> Try it out here: http://picasa.google.com/
>
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