Engine mounts and stringers

Discussion in 'Powerboats' started by grady, Apr 23, 2007.

  1. grady
    Joined: Oct 2006
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    Location: Scituate, Ma

    grady Novice

    Deeper and deeper we go, After pulling the powerplant and sterndrive. And after pulling up the sections of cockpit sole, (access hatches) to gain access to the fuel tanks to ready them for removal. I noticed some small cracks around the stringer where the engine posts attach.


    Let me better describe my boat. It's a 1986 24' grady white I/O it appears to have two stringers (at least aft of amid ships) of about 2"x4" in size.

    In the engine compartment there are two post that rise in toward the centerline from the stringers. they are about 4"x6"x 12" tall. where my motor mounts sit on top.

    The cracks are in the glass around the base of the post where they meet the stringers.


    Now my question is this a sign that too much torque has been applied. Or just normal wear and tear.

    Is this serious enough to grind down the area and reinforce the post then reglass.

    Note: I repowered the boat twice in recent past with a 350 ci increasing both the hp and the torq of the original engine 230 omc. by about 20%.

    So am I in trouble here? I'll try to post some pics tonite.

    thanks guys

    Grady
     
  2. TerryKing
    Joined: Feb 2007
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    TerryKing On The Water SOON

    Cracks ain't good....

    Grady I'm sure you'll get more answers from the group, but sounds like something you'll want to deal with! Are the 'cracks' just in the topmost layer of resin, or can you see any fibres??

    4"x6"x 12" tall with a 500 Lb 350 weight on the top, in a roll, chop, slam etc. sounds like a lot of force, as least occasionally.

    Does the engine have resilient mounts, I assume?? Are their any diagonal or cross braces on those pedestals? Is there stuff like plumbing and wiring in the area between the pedestals? Or could you add some bracing like 3/4" ply fore and aft of the pedestals/posts??

    Anyone familiar with this particular boat??
     
  3. grady
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    grady Novice

    Engine compartment pics

    Here are those shots of the damaged areas
     

    Attached Files:

  4. charmc
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    charmc Senior Member

    There will be better and more specific recommendations from others, I'm sure, but to me it looks like a serious problem. I see a void inside that last picture, i.e. a wide crack showing dry fiber inside, "dry" meaning no sign of resin ever being there. The fiber looks like coarse chopped fiber, rather than cloth or mat. If it is chopped fiber, then there might have been a bubble or similar defect in construction, creating a weak spot and leading to the crack. The cracks are big enough and deep enough that I would be concerned about moisture in the wood of the stringer. I would grind away all the loose material until you get down to solid glass resin, or to the wood stringers. Test the wood for soundness in several places. Any soft spots (rot), I would rip the stringer out. Whether you have to replace the stringer or not, build up with lots of resin on the stringer, then glass mat, then resin, for at least 3-4 layers. Using mat for the repair will make the area stronger than the original. You'll need the extra strength for your bigger engine, and to improve on the original construction, which doesn't look up to G-W's reputed quality.
     
  5. marshmat
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    marshmat Senior Member

    From the looks of the photos, the engine bearers simply aren't beefy enough and are built too weakly for a motor that size. I think you'll have to get all the broken material out and see what's left- I doubt much will have survived. You'll find out what the stringer's like in the process.
    When you build the new engine bearers, use woven cloth. Production builders use the chopped fibre crap because they can spray-gun it in with minimal labour. The short random strands are not that effective at increasing strength though. Sheets of mat are fine for building up thickness but are not very strong- fibreglass gets its strength from the long, straight, continuous fibres of a woven cloth. Use cloth, lots of it, with little pieces of mat where you want more thickness.
    If you intend to keep the boat a while, I'd suggest you consider a better way of mounting your engine; maybe through-bolted aluminum L-brackets, maybe a full cradle. Lag bolting the mounts directly to the engine bearers is common practice, yes, but there are stronger and more reliable ways of mounting a motor.
     
  6. grady
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    grady Novice

    Boy I've been considering the task of tearing those engine bearers and stringers out , daunting. But I guess if you just put your head down and have at it, it might move along alright.
    My concerns are the mounting dimentions. So if I document the height I just may be able to improve on the design of the bearers with the help of near by bulkheads and alum braces then cap it with a piece of L stock weld it all up and down the road we go.
    Next question. How does one go about tearing out this stringer? The bearers seam straight forward enough, but with the stringer glassed to the hull bottom, I'm a little apprehensive.
    By the way is it possible that these stringers go only as far as the bulkhead that boarders the engine compartment?
    I'll try to post more pics later today.

    Thanks Grady
     
  7. charmc
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    charmc Senior Member

    Grady,

    Circular cutting wheel held parallel to the inside of the hull so it cuts only into the stringer should work without damaging the hull. If the stringer was resin bedded, you'll have to cut through it, then go back and grind away to good glass inside the hull. When you glass in your new stringers you'll be reinforcing the hull again. It's possible the engine stringers only go to the first bulkhead, only way to tell is to measure centers first. If they're different, obviously no problem. If they are on the same line, you could make a small cut at the bulkhead-stringer junction, which will tell you if it's one piece or two. If the original was one stringer going full hull length, I have some ideas on reinforcing a new stringer section, but I'll wait for someone with more experience redoing stringers; there might be a proven and generally accepted repair method that I don't know.
     
  8. grady
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    grady Novice

    The tank compartment forward of the bulkhead is inboard of the stringer centerline. With no access to view, at least by a full grown adult. My guess would be that these stringers go further than the next bulkhead.

    I got in there and poked and proded some areas with much longer exposure than these cracks and found no soft wood.

    This damage can only be one season (maybe two) old because I had the motor out twice in the the last 4 years and as recently as late in the season two seasons ago and noticed no damage. And I did exstensive work around and on these bearers 4years ago. So I am hopful that the damage is just to the glass and I will be able to grind away my problems and reglass the stingers. I am still considering replacing the engine bearers and assisting them with a alum cross brace and certainly capping with a large piece of L stock thru bolted to the bearers from the side. Then bolting to the alum without penetrating the bearer from the top


    thanks Grady
     
    Last edited: Apr 26, 2007
  9. marshmat
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    marshmat Senior Member

    Hi Grady,
    If you've been poking an awl into the stringers and finding no soft wood, that's a good sign. You'll find out for sure when the damaged glass is gone, of course....
    If you want a longer-lived stringer this time around, I'd suggest you go easy on the chopped-mat crap and use a lot of layers of a flexible, easy-draping glass cloth. The extra labour will be well worth the vastly higher strength and integrity.
    The aluminum engine bearing structure you describe sounds good, definitely better than lag-bolting the mounts directly into the bearers (which will lead to the exact same rot/deterioration problem all over again). Through-bolting an L-angle, with a big beefy backing plate on the other side, should be a fair bit more durable in the long term.
     
  10. grady
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    grady Novice

    Hey Matt, Yeah I've got my fingers crossed.

    What material makes for the best engine bearers, I would think clear fir but I have litte or no knowledge on how various woods behave in this enviorment.
    What with all the stress and potential exposure to moisture.

    Thanks Grady
     
  11. PAR
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    PAR Yacht Designer/Builder

    Those cracks are classic stress risers, which have delaminated the sheathing. You have no choice but to grind it all out of there and replace the laminate with new stuff (Matt's right, cloth is a much better product)

    Once you've stripped the sheathing away, the stringer condition can be accessed. If they too, need replacement (you're probably okay given the short amount of time) then Douglas fur could be a good choice (SYP is another). Make sure the wood is straight grained, clear and dry. Scrub the surface with acetone and let dry, just prior to wetting out with unthickened epoxy, to remove the oils and resin seen in fur.

    Removing the stringers isn't particularly pleasant, but you can hack at it with one of several tools. The stringers on your boat do pass through the bulkhead. Making the stringers thicker in the sided dimension wouldn't hurt and provides more "meat" for engine mounts.
     
  12. charmc
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    charmc Senior Member

  13. grady
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    grady Novice

    WELL today was enlightening!!
    I took a 4.5" angle grinder to the bearers and the stringers as well as the areas around the bearers on the hull bottom. some not all glass was adhered
    to the wood. And where it wasn't there was some moisture, I can't tell to what extent the moisture has done damage. But It doesn't look bad at all.

    What I was surprized to find are voids under the stringers on the inboard side
    and void or bubbles on the hull bottom in the tabbing that brings the stringers and the bearers to the hull. Some of these had water not moisture in them.

    I would have thought that the low side of the stringer would have been filled with epoxy or puddy or something.

    Overall I was happy with the condition of the wood But disappointed with the quality of the workmenship.

    any thoughts?

    Grady
     
  14. charmc
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    charmc Senior Member

    Grady,

    I've ceased being surprised at the stuff that gets past "quality control" at boat and engine manufacturers. I once almost lost a transmission and got a bilge full of oil because a line running outside the bottom of the transmission housing of a 31' sportfisherman was made of steel tubing instead of brass, and rusted through. The boat and engine suppliers were both big names, known for quality.

    Look like you'll be doing more work, but at least you'll know it's done right.
     

  15. PAR
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    PAR Yacht Designer/Builder

    You're correct, there should have been a putty/grout mixture under the stringers. If you found pools of trapped water, then you've likely got some rot. A scratch awl can be a very handy tool to find "soft" spots. These isolated pockets of rot will need to be removed and repairs made to the stringer.

    It may be easier to remove and replace wholesale sections of stringer(s), rather then little bits and pieces along its length. It's likely that there will be other air pockets and voids under the stringers, as well as failed sheathing bonds under the 'glass on the stringers and tabbing. Most times you can find larger sections of sheered or delaminated 'glass with a mallet (I use a home made leather one, but most use a deadblow or rubber hammer), using the sound as a key to yank out the grinder for a look see. This will not find voids under the stringers, so maybe it's better to just hack the skins off and have a look for yourself. A chisel you don't especially care for, is also a handy tool in this kind of work.
     
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