1970's Reinell floating stringers

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

  1. KootenayTroller
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    KootenayTroller Junior Member

    Hello everyone. I've started a rebuild on this boat 3 weeks ago and been documenting the rebuild on another forum. I have some questions regarding how this boat is built and it seems that its not constructed like most boats are! I figured the questions were better aimed at a design forum....so here we go

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    It only has two stringers, and some long dimensional boards fiberglassed flat on the hull to reinforce it.

    The boat appears to rely heavily on the foam pressure under the floor to support the hull.

    Stringers are 2x10 fir and are largely intact but need work or replacing. They are not fiberglassed to the hull rather they are floating and a small amount of foam underneath. They are not wrapped in glass nor do they appear to have resin on them......and lasted 33+ years!

    The boat will be used on a large inland lake
    There are A LOT of these old Reinells on our lake and seem to handle the rough water well and offer a comfortable and stable ride.

    I know little about boat design but am very handy and learn quick,

    Can anyone comment on these floating stringers, should I add support? keep it all the same?

    Are the boards fiberglassed flat a common design?

    The floor is only supported by the stringers down the middle and the outer chine flat, I can't get to the outer edge of the plywood without cutting out something that I'm gonna call a torque box that is fiberglassed to the floor and side of the boat above the level of the floor approx 6"x6"

    The floor with the foam underneath was very solid to walk on......is there an acceptable way to butt the new floor into the old floor, maybe using PL and some biscuits or??

    Thank you for any help!,

    Jeff
     
  2. KootenayTroller
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    KootenayTroller Junior Member

    After further demo, it appears the stringer is glassed to the hull on one side only
     
  3. PAR
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    PAR Yacht Designer/Builder

    Yep, this construction method is proper and appropriate for several reasons, the details of which aren't all that important, though continuing the engineering approach sure is.

    There are a few different engineering principles at play here, but this build method is quite sound. The stringers do float, usually on foam, though you can use other stuff like a bead of polyurethane. The idea is to get the hard stringer off the hull shell, having only the "tabbing" hold it in place. In production boats like this, roving is the usual choice, because it bulks up quickly. If the stringer is allowed to touch the hull shell, you create a hard point which will cause untold strains on the hull shell along their length.

    The foam filled cavity and perimeter bonded plywood sole (floor) work in a similar fashion, though offer more stiffness athwartship, rather than longitudinally. The foam acts likes as a compression element in the various compartments, also deadens sounds, offers floatation, dampens vibrations and prevents more of the point loaded previously mentioned.

    Don't be tempted to add a little here and a little there, as this is a performance and durability killer, without some serious understanding of the forces involved. You got a 1/3rd of a century out of the original structure - how much better do you think you can do . . . Make it the same, but pay attention to the stuff they kind of short cutted on. These would be the amount of and completeness of the tabbing under the sole plate and and hardware and equipment attachment. If done well, it'll last a 1/2 a century.
     
  4. KootenayTroller
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    KootenayTroller Junior Member

    PAR...thanks very much for the input.

    I have dug the foam out from under the stringers because it was wet and the stringers were in pretty decent shape but are wicking up moisture from the foam.

    It has been suggested for me to use thickened resin(peanut butter) or PL Adhesive and fill the gap left from removing the foam, create fillets and tab the stringer into the hull on the side that was left untabbed from the factory.

    Because the stringer has a few spot repairs I wanna make I was going to sister a full length 3/4" marine plywood on the side of the stringer before bedding and tabbing it to the hull.....Is this acceptable ?




    Also there was what looked like structural members laid flat against the hull to reinforce some of the chines, they looked rotten but after cutting one open it was waterlogged parquet panels, and a mesh screen between that and the hull that appeared to allow movement and flexibility! This mesh screen is not bonded to anything!

    It has been suggested to cut these open, dig out the parquet and replace it with plywood and to bed and fiberglass them to the hull!!

    I'll post a pic soon!

    Thx again

    Jeff
     
  5. KootenayTroller
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    KootenayTroller Junior Member

  6. PAR
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    PAR Yacht Designer/Builder

    Yes, to everything you've mentioned, except, don't use PL Premium, as it's great for hold fake wood paneling on your family room wall, but truly sucks in a boat. Also, instead of plywood sisters on the stringers, use solid wood, which is 30% stiffer longitudinally than plywood and this is the direction they need to be stiff. Lastly make sure to bond to good, solid material. No amount of tabbing will fix a mushy hunk of something and a bond can't be trusted if it's contact surface is questionable.
     
  7. KootenayTroller
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    KootenayTroller Junior Member

    PAR...it is very refreshing to receive feedback from someone who has an intimate knowledge of the topic, thank you.

    Do you also agree with replacing the parquet with plywood or is there another method I should look at?

    I'm not sure what the intention of he parquet was! Was it to just used as a filler to shape fiberglass over or did it offer something more?
    If the goal was more for the fiberglass and not the core, should I try and dry it out as much as possible and just beef up the fiberglass surrounding it, the fiberglass is thin and weak, could use a bit more heft in my opinion?

    Thx

    Jeff
     
  8. PAR
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    PAR Yacht Designer/Builder

    Oh please, I'm just making it up as I go along. In reality, some of us actually do this sort of thing, mostly because we're not bright enough to get job with a living wage or develop enough ambition to move up the social/employment ladder.

    Sometimes factories used whatever was handy (especially in certain eras), including the remnants of the owner's family room remodel, where a sudden windfall of used parquet flooring was available. Who knows why they used this stuff, but it was likely a local reinforcement, to save laminate or core material. Plywood will do in this area, but it's tough to tell. If the flooring remnants (my assumption) are solid hardwood, I'd consider something stiffer than plywood, like white oak, though the little pieces of flooring suggests it was just a reinforcement, so plywood will likely do just fine.

    The real failure with factory built boats is they cut corners to save labor and materials, often leaving the innards vulnerable to moisture. Since you're not paying for labor, you can do a much better job, insuring things are actually sealed in good and sufficient tabbing is in place too. So, concentrate on getting all the wood well sealed and all attachments well tabbed and you'll do much better than the factory.
     
  9. SukiSolo
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    SukiSolo Senior Member

    To make it more 'exciting' for you to dig it out!

    New one on me though, packing crate timber, newspaper rolls etc I've come across but no parquet ...yet.....;) something to look forward to...
    Just follow PAR's excellent advice and you'll get a good job done.
     
  10. KootenayTroller
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    KootenayTroller Junior Member

    With this info it makes moving forward much more comfortable now.

    It has been suggested that that stuff inthe last two pics is balsa core.... It's all end grain, in its current state it is VERY soft, so I doubt it's hardwood. I have seen a few restorations on other forums were balsa core was used......this stuff certainly looks looser than even that stuff, I seriously question, even in its dry and original state, how much support it offered.

    One comment was made that end grain balsa is actually very strong on compression and being patches of end grain squares is easily formed to the hull. I fear with the curve of the hull I won't be able to properly fit a stiff board in place.... Time will tell.


    Thanks again guys...
     
  11. KootenayTroller
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    KootenayTroller Junior Member

    [​IMG]


    Here's a picture that shows both of the parquet core members, in all they cover a substantial portion of the hull
     
  12. PAR
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    PAR Yacht Designer/Builder

    I don't see parquet flooring stuff, but balsa is a common core material and it is a good way to make a stiff hull. If it is balsa, it's likely serving a structural purpose, so its replacement should as well, or you'll have to bulk up the laminate in the area to compensate for the lose of the core. I don't like balsa in powerboat hull shells, especially on the bottom, but it's not uncommon. How thick is the balsa (depth from inner skin to outer)?
     
  13. KootenayTroller
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    KootenayTroller Junior Member

    The balsa core is 1/2"

    How many layers of fiberglass would I need to lay if I wanted to get rid of he balsa all together?
     
  14. PAR
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    PAR Yacht Designer/Builder

    The reason balsa and other cores are used is because, 'glass isn't especially stiff, so you have to really bulk it up to get some, which adds weight, materials and labor. Without knowing the boat (make, model and year) and the locations of the core, plus other items, it's tough to say how much laminate to add, though if you put in more than enough, you can't go wrong, except in the weight and materials columns. Obviously there's a potential for problems if you're to skinny on this extra laminate. If it was me, I'd just install some 1/2" plywood and bond this down with the same amount of laminate as used previously.
     

  15. KootenayTroller
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    KootenayTroller Junior Member

    Sorry I missed the details from the start, it's an early 1970's Reinell 21ft Alaskan hardtop



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