1970's Reinell floating stringers

Discussion in 'Fiberglass and Composite Boat Building' started by KootenayTroller, Jan 22, 2015.

  1. Ike
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    Ike Senior Member

    The structure in the first photo looks exactly like my 1972 Sea Ray 18 foot with a mercruiser I/O. One thing not yet mentioned is that Fiberglass construction was still relatively new and they still did not understand it's structural properties. So they built it a lot thicker and heavier than it need to be or would be today. This meant stiffer hulls which need less interior structure to reduce twisting and flexing. If you bond the stringers to the hull they eventually just break loose. Tabbing keeps them in place. The whole structure kind of floats in the hull (what's that old quote about hundreds of parts moving in close formation at high speed) Any way it works well. My boat is 42 years old and still strong.

    The below image shows the rebuilt stringers but I just duplicated what was there with a few slight mods but nothing that would change the basic structural design. I bedded it in epoxy putty.

    [​IMG]
     
  2. nczimm
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    nczimm New Member

    It was commented that the stringers float on foam. The person doing the refurb mentioned using something he called "peanut butter" to replace the foam under the new stringers. My understanding is that "peanut butter" is a mixture of resin and fiberglass. This would be hard and not allow the stringer to float but I heard no comment about that choice. At the same time foam does not seem durable enough for the place between the hull and the stringer. Thanks in advance for informing me on this subject. My boat is identical to the one being worked on and I am about to embark on the same adventure.
     
  3. Ike
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    Ike Senior Member

    The peanut butter reference is to the consistency. The material is epoxy putty. You can buy epoxy putty or simply make your own with epoxy resin and a filler. I used crushed walnuts that I bought at the local fiberglass supplier. You mix it until it has about the same consistency as peanut butter, and if you use the right color filler it even looks like peanut butter.

    It doesn't get rock hard like fiberglass. Even when it's fully cured it can be carved and sanded and ground. I used it because it takes a lot of the work out of getting the curve on the bottom of the strings to exactly fit the curve of the hull. Close enough is fine and then you fill the gaps with the putty. After that you tab the stringers into the hull so that they won't move around. As was said, you don't want to bond them to the hull because it forms a hard spot where stress is concentrated.
     
  4. nczimm
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    nczimm New Member

    thanks
     
  5. SamSam
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    SamSam Senior Member

    I doubt it was actual parquet flooring, but we took apart a deck that was made from 6" squares of plywood glassed on both sides. It was like a crude balsa core and allowed the plywood to conform to curved surfaces. These folks here do it also...

     
  6. Easy Rider
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    Easy Rider Senior Member

    This epoxy used to make the "peanut butter" doesn't cure hard? Can one push a phillips screwdriver into it 1/8" to 1/4" leaving a "dent" or hole? What is this flexible and compressible epoxy called? What does one ask for "in the store"? Just epoxy putty?

    "Tabbing" is attaching the stringers to the hull with "epoxy putty"? Dosn't sound as it could be interchangeable (stiffness wise) with foam. The foam sounds crazy to me. Seems to me it would just shear off if it's adhesive held.
     
  7. Ike
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    Ike Senior Member

    Hard is relative. It cures hard compared to foam, but not compared to FRP. it can be carved but I doubt you could push a screwdriver into it. it's called Epoxy Putty and that's what you would ask for. But it's just as easy to buy some microballons ore ground up shells, or wood powder and make your own. That's what i have always used, wood powder or ground up walnut shells. I prefer the wood powder. You can actually use sanding dust if you can get enough. These newer sanders all have little bags on them to catch the sanding dust. That makes it easy to save it.
     
  8. PAR
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    PAR Yacht Designer/Builder

    Wood flour is what Peter is referring and though I used to advocate it's use, I don't any more, unless is very fine flour and hardwood only. Sanding dust (regardless of the sander or grit paper on it) makes too big of particles. What happens is these larger particles, particularly softwoods suck up resin initially, but once the exotherm starts up, the resin tends to run out of the wood chips (thins with the heat increase), pooling at the bottom of the fillet. The end result is a resin rich bottom, with loosely held together wooden particles higher up in the fillet. Well ground wood flour is a much finer product and though it too can suffer this same fate, is less troublesome in this regard.

    For a bulkhead or partition standoff (as described above), just about anything will do, so long as it holds the piece off the hull shell and more importantly makes a neat radius for the tabbing to land on. The tabbing does the work and the standoff is just preventing a hard spot. Now, you're thinking, well if it's epoxy, shouldn't it be pretty hard, even with a filler? Yep, you'd be correct, but it's the tapering fillet that eases the load transmission through the opposing planes.

    Think of it this way, if you measure the density of the hull side (bottom, whatever) and inch along with your magic density meter, you'll have consistent readings, until you meet a structural element, where the density will dramatically jump up, because a perpendicular element is on the other side. This dramatic rise in density is where the loads will concentrate and cause a problem. If the perpendicular element is sitting in a tapered bed of fillet and tabbing, the density meter will see the density gradually rise, maxing out at the perpendicular element and then gradually decrease, as you move the meter farther down the panel. It's this gradual rise and fall of panel density, that will permit the loads to mitigate through, without undue spikes in load path choices, hence less issues. There will still be spikes in panel density, but they'll ramp up and down, instead of just suddenly appearing and disappearing.

    The sketch below shows the density changes. A dramatic change in density, will cause the part/element to break, just before or just after the huge density change.
     

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  9. Ike
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    Ike Senior Member

    Great description PAR.
     
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