LVL for Stringers & best Method to secure?

Discussion in 'Fiberglass and Composite Boat Building' started by MAD JAX, Feb 1, 2011.

  1. MAD JAX
    Joined: Jun 2008
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    MAD JAX Junior Member

    I searched the forum and reviewed what has been posted...has anyone actually completed a Twin-Screw to Single Re-rig/Retro-fit?

    I'm using an Arneson Surface Drive (Borg Warner 1721/ASD-6s type) with -- eventually -- a 450+ H.P. Turbo-Diesel/Multi-speed Transmission, but for now, a Marinized "Pro-Jected" 454 (w/Thru-Transom CMI Elbow-Tops) into a Velvet-Drive is the Mock-Up...the Boat is a retired-from-racing '80 Formula 302 Runabout that's pretty stout for how much Glass 'n Resin it was both originally fabricated with AND repaired from...some of which appears to be Kevlar, and it's to become a dedicated Volunteer Safety/Rescue Tow-Boat.

    The transom has been blanked-out, keel cut-down & re-glassed to accomodate an Oil Pan, and the Outdrive is mounted (see attached pic.), now I need to install Stringers spaced to accomodate the Single Powertrain...If/when the Turbo-Diesel/Transmission makes it in it'll weigh-in at +/-1500 lbs., so that, A/C, a Gen-Set, additional Fuel tanks, Batteries, etc. will more than make-up for C.G. weight lost in the Twin-to-Single conversion.

    I have an 4" x 10" x 8' LVL I'm lookin' to carve-into Powertrain Support Stringers that will mount in-board of the originals...I'll Tow/Salvage disabled boats with this boat, so I think I want it bullet-proof strong.

    Then too, I've read everywhere that "Flex" in the Hull is important...I'm assuming that adding another pair of Stringers will make that portion of the hull somewhat more rigid.

    Should I simply fit them in tight with epoxy and Glass-in versus (that AND?) pre-drill, counter-sink, and anchor the Stringers with 6" x 3/16" anodized Lags (where they'll meet at the bulk-head, Hull, and Transom) before glassing everything back in?

    All knowledgable Experience/Opinion(s) shared would be greatly appreciated, Thank You!
     

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    Last edited: Feb 1, 2011
  2. tunnels

    tunnels Previous Member

    I've read everywhere that "Flex" in the Hull is important...I'm assuming that adding another pair of Stringers will make that portion of the hull somewhat more rigid.

    Depend how you interprate" Flex "! .
    Flex as in twist or flex as in up and down of the bottom ??:confused:
    Flex of the bottom going up and down can soften you ride and act like shock absorbers and help to prevent the hull from breaking up before it should .A panel that bend will absorb shock loading !! one that wont bend (flex) can damage very quickly not only its self but other parts of the boat !.
    Flex as in twist can be a bit hard on deck joins and corners of the deck if its not built strong . Can also be a bit un-nerving to get used to in a rough water situation , but will hold together better in that one in a million freak scary situations .
    Combine the both and you really have a boat that can take a wealth of punishment and come out the other end smiling ready for the next lot!!!.
     
  3. MAD JAX
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    MAD JAX Junior Member

    That would be both as I interpret it!

    This boat was originally designed and built as a "Runabout", then modified and raced a few years (I have a picture of it from that era where it's about 15 feet in the air for jumping a wave), and there's been some additional structure added forward of the Cockpit in the form of bench-seating that's been closed-in and filled with closed-cell floatation, so it's built "Strong" for rough water situations...enough to hold-up to that "one-in-a-million freaky-scary" situation is where I want to take it, and therein lies that balance of "Flex" just as you've described it!

    I'm inclined to proceed using the lags as I've described...there's been a few views, so if it was a grossly stupid idea hopefully someone would've pointed it out by now.

    I need to make progress, and from My perspective the last third of the Hull is where most of the weight will be located, and not the place (I think) that I'd want any "Flex"...I'm sure doing so will produce a boat such as you describe, and that's what I want, Thanks.
     
  4. tunnels

    tunnels Previous Member

    Carefull if you have panels that flex and absorb shock and then add stringers that are ridged and unforgiving you have lost the plot and changed the whole structure that is likely to fracture just at a time when you really dont want it to . :confused:
     
  5. MAD JAX
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    MAD JAX Junior Member

    I hear You loud 'n clear...the last thing I want is a catastrophc hull-failure right when I'm trying to "Do My Thing", such as salvage a swamped/sinking boat or punch through a Breaking Wave trying to get to a rescue!

    The boat is also to be somewhat of a "Test-Mule" for a variety of Single Engine/Alternatively-Fueled applications, so I'm looking to make My spacing the next size-out from what the BBC normally requires -- in case I wind-up installing something such as a single MANN/MTI, etc., ???

    As such now, the BBC/Velvet-Drive (cum Duramax/Powerglide) will install as a drop-in rail-mounted component-system Powertrain that -- when need extracted for maintainence, etc. -- simply un-couples/un-plugs, etc., and is hoisted out...otherwise testable outside the boat, with fuel supplied and simple connections made.

    Once I've got the spacing figured/marked (using specs. from a MANN applications chart) for the "SINGLE" spaced stringers, I figured to install them parallel to those original stringers that supported the out-board side of the original "twins" (454 Chevys), and I would really appreciate your opinion of how the Stringers installation will go-down:

    1. Use of the Anodized Lags I've discribed...into that LVL material used as Stringer/Eng. Supports?

    2. I was lookin' to notch the new stringers vs. notch those existing strips (?) running diagonally from the center of the (Forward) Engine Compartment Bulk-head out-ward (and aft) into that lower portion of the Transom...is that prudent?

    3. Just how "Tight" need I prep the stringers "FIT" into the interior hull surfaces...loose for accomodating fabric between the components and allowing resin-flow or hewn-flat and tightly screwed & bonded?

    4. I've got a myriad of fiberglass matierials, including quite a variety of cloths to use...how would YOU glass it in?

    Because I don't want the boat to sit outside as a rain-collection basin (at the fill-in-the-blank Boat Repair Shop) waiting for the work to proceed "When I can get to it...", and for having made several contacts over years now -- even offering $$ for their time to just evaluate it and QUOTE Me! -- I've never been able to get any true "professional" to show-up...now I've got a guy that's "done a lot of glass-work on boats...", but he admits the knows little regarding Structure & Design, and -- not to put too fine a point on it -- THAT is where I really don't want to blow-it.

    FWIW I read several of Your posts, including that thread where you discribed finding solutions to those "Surf-Rescue Boats" (also had that attachment showing failure analysis, though I was more a pig-lookin' at a wrist-watch for it... ; ) and it's evident to Me that Your just the person I was hoping would share some knowledge and experience...please bear with My "Newby" ignorance, and know that Your consideration shared is greatly appreciated, Thank You.
     
  6. MAD JAX
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    MAD JAX Junior Member

    Correction...

    That "LVL" is actually 12" (tall) x 3 3/4" (thick) x 8' 1/2" (long)...measureably just enough to divide it in half @ the center with an angle cut to accomodate the pitch (?) of the Transom...I'll then need to cut it length-wise at the pitch of the Hull so that it installs vertically parallel to the sides of the Boat while otherwise fully contacting the Sole of the Hull.

    "Tunnels", I've re-read Your replys several times now, and FWIW am thinkin' I won't want to use those Lag Screws to pull the LVL Stringer into place prior Bonding/Glassing it in...they'd just tear things up if/when the Hull does "Flex" under stress.
     

  7. Petros
    Joined: Oct 2007
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    Petros Senior Member

    The stronger you make the hull the less rigid it will be, because you are building it as rescue boat ride comfort is less important than strength.

    There is a lot opinions posted here that are not relevant for your needs. Make it strong, make it stiff, and you will have less trouble with the hull than if it is allowed to flex. Flexing will cause a lot of problems at all the structural connections, if part of the structure is stiff and part allowed to flex you will get cracks and failed connections. I have built flexing hulls for skin-on-frame kayaks you find every connection works and wears when it flexes. That is okay for a light weight hull, but that is not what you have nor desire. Since your hull was already made stiff for racing anyway, and you are going to add a major structural stinger that will carry all the thrust loading, make the whole aft hull stiff. You might consider adding a few ribs as well at the new stringer locations to help spread the new loads out better.

    Your plan if adding LVL stringers is a good one. special order a pressure treated one if possible, if not soak it well with "end cut solution" (several coats) and allow to dry before installing it. I like the idea of bolting through the hull, it distributes the string loads into the skin in a positive way. But there are a couple of warnings; You want to spread the load out among the fasteners so you do not damage the skin around the fasteners, so more in number of smaller fasteners are better than a few large ones. You want to force the stringer into the shape of the hull before you install the fasteners, that is; do not attempt to "suck-up" any gaps with the screws, they may pull through the hull before the gap is closed. So rig up a way to clamp up the stringer tight to the hull (apply epoxy of course first), and than install the fasteners. Pre-drill the holes and install screws "wet" (fill holes with epoxy first).

    Be careful that you don't distort the shape of the hull too much during this alteration.

    Good luck and have fun with it.
     
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