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floor stringers just aft of the forward bulkhead - CS 17


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8 replies to this topic

  #1 Chris Stone

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Posted 04 July 2012 - 10:40 AM

We are putting in the stringers in the forward bulkhead on the hull and on the floor just aft of the bulkhead itself.
The ones in the bulkhead fit no problem i.e, it is easy to orient them so they lay flat.
We are assuming that these stringers are screwed in to insure tight fit while epoxy dries.Screws removed after drying. That seems straightforward.

The floor stringers aft of the bulkhead do not lie flat at all. To get they to lay flush with the floor, something is going to to have bend: the stringers, the hull or both.
Should I be worried about that? Or find an alternative?


While I am at it, what specifications should be used for the Bow eye?

thanks in advance for any helpful advice.
Chris from VT.

  #2 Jim Stumpf

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Posted 04 July 2012 - 11:03 AM

Pics of my stringers, I don't recall any stressful bends or twist.
Hope that helps,
Jim

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  #3 Chris Stone

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Posted 04 July 2012 - 12:52 PM

Jim, that is helpful. Thanks. Chris

  #4 Peter HK

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Posted 04 July 2012 - 06:16 PM

From memory the floor stringers aft of the bulkhead did not lie completely flat and had to be screwed in a few spots to hold them in place... also the aft ends extended past the scarf where the 6mm and 9mm ply was joined (and thus forming a small step) so I trimmed 3mm off the end of the stringer to accommodate the change to the 9mm.

Cheers
Peter HK
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  #5 Joe Antin

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Posted 05 July 2012 - 11:11 AM

I bent them to match the hull and used thickened epoxy where the fit was not tight. this is more or less like bedding the keel stringer.

  #6 PAR

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Posted 06 July 2012 - 02:28 AM

My understanding of these stringers (CS-17 build) is they replace the stiffness lost, because of the bottom panel thickness reduction, to accommodate the twist in the forward sections. Rather then fuss with fitting more pieces, I elected to use two layers of 12 ounce, 45/45 biax over the whole area. In fact, instead of taping the inside of the seams, the biax was used as a single piece, covering the seams in the process (over fillets). This replaced the lost stiffness and also added some puncture resistance too. It's quite likely the 24 ounces of biax sheath is lighter than the stringers as well and weight savings, with no strength or stiffness loses is always a good thing. Of course, the draw back to this approach (there's always something) is you'll have more fairing to do. My logic was, this wasn't an area where I needed a really sweet surface, so if I just got the weave filled, I could call it a done deal. Lastly, yes, a couple of layers of 12 ounce biax on 1/4" plywood, makes it as stiff and strong as 3/8" which is what the rest of the bottom is made from. This assumes good contact and resin/fiber ratios. Probably no help for you now, but food for thought to other builders.

  #7 Peter HK

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Posted 07 July 2012 - 03:36 AM

I actually find the stringers a bit helpful. I keep the anchor/'chain/rode in a plastic box in that area. With a couple of stringers screwed under the box it keeps it aligned and easy to pull in and out whereas when I didn't have the stringers under the box it would fall to the lowest point i.e. in front of the the centerboard case and then be hard to pull out.
I suppose there is always a plus and minus.
Cheers
Peter HK
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to hell for a pastime."

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  #8 Ray Frechette Jr

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Posted 08 July 2012 - 06:24 AM

I never mess with stringers in this area. A hassle in my estimation finishing them off with fillets to make cleaning easier and still a dirt catcher.

When gluing up the panels I have the exterior hull flush. In the interior after the hull is glued up and taped I fit in sections of 1208 Biax cloth and theat pretty much brings the floor up flush. Skim over with thickened epoxy to final fair and smooth and once sanded is indistinguishable formt he floor.

Per Graham it gives requisite stiffness and as an added plus it give a fair increase in impact strength and makes a smooth floor without the stringers..

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  #9 PAR

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Posted 08 July 2012 - 08:53 PM

Yep, that's my approach too Ray, except I don't like to waste resin with combo fabrics, as the mat is essentially useless in an epoxy laminate, just increasing resin/fabric ratios, which makes the laminate heavier and weaker then necessary. My tests have shown that 2 layers of 12 ounce 45/45 on 1/4" meranti is just as stiff and slightly (very slightly) stronger then 3/8" meranti of the same dimensions. I've also tested a single layer of 17 ounce, but it wasn't quite as strong (again very slight differences), though did have the same penetration resistance as 3/8". I find it easier to fair 12 ounce then 17 so the two layer choice on 1/4" is my usual route. This said, it is a lot easier to make a stitch mat fabric fair, if the mat is up and I do use mat for this occasionally, but it's always a really light layer of mat, 1.5 ounce being as heavy as I go. On larger projects, this isn't as big a concern, but on small, preformance oriented craft, weight is often critical, so good resin/'glass ratios and no mat are my goals.

As an example, a buddy just finished a multi chine tripper style canoe, of some length (18' I think). He weighed it just after assembly and got 45 pounds, before fairing and paint. After fairing and paint it was nearly 55 pounds. Paint does weigh something, but I'll bet 8 of those 10 pounds is fairing filler and epoxy. That's a 15% increase in the boat's weight, just from goo and filler!