stringers

Discussion in 'Powerboats' started by shane blower, Apr 16, 2008.

  1. shane blower
    Joined: Apr 2008
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    Location: lake orion michigan

    shane blower Junior Member

    :mad: i just tested my stringers on my 21.5 88 glasstron these stringers run from the transom up under the motor and stop at rib where the floor starts. then another stringer steps out and runs the rest of the way up .where they caped off that back stringer is where the water got in, not good.this is a very nice boat 350 merc nice cuddy for its size,shuld i fix it or pull motor & drive and count my loss.think i would have to pull the motor or could i just do one side at a time by pulling off the mount. its not something i want to do this year so do you think it will be alright on the small inland lakes and taking it easy i dont see sings of weakness no cracking or stress anywhere but stringers are wet from the rib to the transom. sorry i got ahead of myself
     

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  2. dragonjbynight
    Joined: Apr 2008
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    Location: Indiana

    dragonjbynight Senior Member

    I have an older smaller glastron, and I have some major problems with the transom being rotted out. If your stringers are wet all the way through, It's probably a safe bet your transom's got the same issue. As for giving advice any further, ill leave it to the gentlemen who have been helping me along, but seeing if that rot has made it further up would be something I would check into before you make any other decisions. My thread dealing with that can be found at: http://www.boatdesign.net/forums/showthread.php?t=22113
    hope that might help.
     
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Unlike Dragon's outboard powered boat, Shane's boat is an outdrive, which doesn't stress the transom nearly as much. This means it's quite possible you don't have issues there.

    Stringer replacement is a back yard doable job, though not the most enjoyable thing you'll ever do.

    As to scrapping the boat instead of repairs, I couldn't address this without an up close inspection, but if it's just stringers, it'll be cheaper to fix them, then yank all the equipment and install it in another boat.

    You could remove the stringer with the engine in place, but frankly it's a lot more trouble. You want as much room as you can get to grind on things, plus the hull will be weakened once it's removed. The weight of the engine and drive can distort the hull during the process, so they should come out. It makes it so much easier to have free space around things to swing a reciprocating saw or grinder, trust me.

    While you're at it, the tank and other stuff (like the water soaked foam) can get removed. You needed to install new hoses anyway right?

    There are several threads on the subject, use the search tool and read up on the process. You're not alone, we share your pain, but it's not as bad as it could be.

    A good tip to prevent future issues is to not install carpet. Carpet traps moisture under it, which finds it way into the sole (the decking you stand on, inside the boat), usually through a screw hole or other unprotected area. Rot starts and eats up the wooden elements.
     
  4. missinginaction
    Joined: Aug 2007
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    Location: New York

    missinginaction Senior Member

    As usual PAR's on the money with his advise. I'm currently replacing the stringers in a 1973 Silverton. This boat at 25.5' is larger than your Glastron. Even so, I'm very pleased that the engine and running gear are out of the way and in my shop. It is sooooo much more pleasant to work in an uncluttered environment, especially when grinding old polyester resin and glass.

    You might want to take a look at Dave Gerr's book "The Elements of Boat Strength". He makes an interesting observation. The wood, or foam or whatever is inside of your engine stringers is in reality just providing a form for the fiberglass and resin to be draped over. You DO need some structural wood is the area where the engine mounts are actually bolted to the stringers. Other than that area though, the material that supports the fiberglass is not structural, in other words it does no work, so the fiberglass/resin actually supports the engine and carries the loads not the form material.

    I've done extensive research on line and in print regarding materials used to construct stringers. Advise runs the spectrum from marine plywood to various "marine grade" foams, high density foams and even douglas fir boards.

    Based on Mr. Gerrs observations the strength of the former material is not critical. What is important is the quality of the fiberglass layup that covers the former.

    With that in mind I've researched various types of extruded polystyrene foams such as Dow Styrofoam (commonly called blue board in the construction industry) some extruded ploystyrene foams available through on line retailers and a product called Formular 250 made by Owens Corning. These materials are inexpensive, will not absorb water and are reasonably strong, meaning they will certainly hold up the fiberglass until the resin sets up.

    I've decided to construct my new stringers using 4 to 5 layers of DBM 1708 • Wt: 25.3 oz/sq yd 17 oz double bias fabric • ±45° + 3/4 oz mat over 2 inch thick Owens Corning Formular 250 formers with the top 1/3 of the former made of solid Douglas Fir in the areas where the engine mounts are bolted. These formers are about 8 inches high and roughly 8 feet in length.

    I have never seen engine stringers done exactly this way, but I'm willing to give it a try and see. A 2' x 8' piece of Formular was about $15.00 at Home Depot, I found beautiful clear, knot free 4"x4"x8' Douglas Fir posts at the same store for $9.99. I had to hunt through a rack of posts, but I found a great one! Looks like the cost of my engine stringers will be $25.00 plus the double bias mat and the epoxy resin, which is always the expensive part.

    As the spring progresses I'll post in the Wooden Boat Forum with photos of the work. I did some experimental layups over the winter and the polystyrene foam seemed to work just fine.

    PAR, if your reading this, I just noticed you have 2,345 posts over the past 4 1/2 years. That's gotta be some kind of record. Wow!

    Hope this helps Shane,

    MIA
     
  5. shane blower
    Joined: Apr 2008
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    Location: lake orion michigan

    shane blower Junior Member

    thanks m.i.a. that helps alot i would like to see some photos when things start to come together.what ever is in my motor stringers is very wet & rotting but the glass is good and strong is that why i dont see any stress?Think it will make it for one more season.I would like to fix it next winter .nothing like working on a boat when its 80 outside
     
  6. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The post count may seem like a lot, but it's really not, averaging out at less the one and a half posts per day, across the time I've been a member. I don't post every day and usually make several posts (on different threads) when I'm here. I'm not the person with the most posts, nor the longest member, so there appears to be those worse then me.

    In newer boat construction the stringer core serves a few functions, one is to be a mold for the laminate, but another is the compressive strength of the core in "sandwich" construction. The core has to keep the 'glass skins separated and not permit movement. It does this by having a natural high compressive resistance (like wood does) and being bonded well to the 'glass skin (this bond is very important is this type of engineered structure).

    In older boats like yours Shane, the stringer cores may be actually contributing to the longitudinal stiffness of the hull and the 'glass skin is just a protective coating to prevent moisture ingress. You can check this by seeing how thick the 'glass is over the stringers. If the glass is a light, thin skin, then the stringer core was the bulk of the longitudinal strength. If the 'glass skin is thick and heavy, the wooden element of the stringer is just a core, though it still needs to be well bonded and resist compression.

    I'm not sure if Glastron used southern yellow pine or Douglas fur in it's stringers. It would be wise to error on the side of strength and use the SYP, which is much stronger then fur. SYP can be found at the local Lowe's/Depot, but make sure you buy wide boards (1" x 12" or 2" x 12") because these have to be cut from older, bigger trees, which means they'll have straighter, denser grain with less knots and defects.

    Getting back to posts, much depends on how long you've been a member. For example, there are about a dozen that have more posts then I do. Most of these folks are long standing members, having been here for 4 or 5 years, accumulating a sizable post count.

    But there are exceptions, such as "Masalai" who has made almost 2,555 different posts in the 7 months they've been a member, which amounts to 12.1 posts per day (compared to my 1.4). I'm not sure, but I think the grand prize winner is "Safewalrus", who since becoming a member in early 2005, has posted 3,775 times, which translates to be almost 3.6 posts per day. For what it's worth.
     
  7. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    Ahhh, coffee before a session with the angle grinder later this morning. Spring air....with the slight smell of hot polyester through a respirator, not quite a peaceful day on the water, but I'll get there. It was a long winter here in the Northeast.

    Shane, PAR's forgotten more than I know about this stringer subject so I'd heed his advise.

    Looking at your original post, you said that you don't see signs of stress or cracking anywhere, but the stringers are wet. Based on that comment I'd wager that the fiberglass is carrying the load, not the core stringer material. I'm sure someone will correct me if I'm wrong but my understanding is that if the gelcoat is not cracked in the areas adjacent to the stringers then the underlying fiberglass layup is stable ie. not moving. That's good.

    PAR's right when he addresses the fact that the stringer core needs to be able to absorb "compressive" forces even if the fiberglass layup is doing the work. This is why I need to use wood in the area of the former where the engine beds are mounted.

    PAR, if your looking.....Gerr makes mention of some manufacturers that have actually constructed hollow box stringers (I'm assuming they must use something in the engine mount area to clamp the beds to). He states that they work, but he's not crazy about the idea because if water finds it's way into the hollow "core" you end up with long water tanks in the bottom of your boat. Clearly a problem in the cold north if they freeze. He says that this method will work though. Have you ever come across this type of construction in your work?

    I'm off to the yard........Now where did I put that Tyvek suit?

    Regards,

    MIA
     
  8. PAR
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    PAR Yacht Designer/Builder

    Yep, I've seen hollow stringer and other structural elements, but don't like them for Geer's and other reasons, not to mention it makes a heavier laminate then necessary. In production work, it makes some sense to increase the amount of laminate, because the actual effort is such a small part of the total build effort, making it cost effective (if a little heavier).

    That era Glastron was heavily chopped, with hand laid fabric where they felt necessary, also usually quite thick.

    Shane, bond in some pretty SYP or Douglas fur stringers. Insure good contact and plenty of goo, then repair the tabbing where you gained access. This will prevent the stringers from buckling or collapsing under load.

    You'll do fine and post some more pictures.

    I half expected to see Masalai, Safewalrus and even Frosty biting my head off for posting their "figures" while visiting here. I guess all us big mouths can't have too thin a skin.
     
  9. shane blower
    Joined: Apr 2008
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    Location: lake orion michigan

    shane blower Junior Member

    par im not sure what you are saying , remove all the old and start fresh or sister the SYP next to the old and bond them together.
     
  10. tuantom
    Joined: Jan 2005
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    Location: Chicago

    tuantom Senior Member

    How much are you planning on replacing? It seems to me, your plan is to only replace the two 3' or so sections under the motor. If that is the case, it's a very productive weekend project - and you would remove the old and start fresh. The main stringers, which run the length of the boat from the transom, frame the sides of the engine well - the two you're looking at are more or less the motor mounts. Did they pass through the transverse framing? it's hard to tell from the pictures.

    What is the condition of the floor and the rest of the boat? Transom? Was it in the water during summers or stored dry? Always covered? The reason I ask is, it's may indicate if you have further problems or not - The rot may be isolated to the engine well because they didn't glass it up properly there.
     
  11. shane blower
    Joined: Apr 2008
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    Location: lake orion michigan

    shane blower Junior Member

    tuantom ,no they dont pass through the frame , the floor is in great shape,so is the transom i think , the only thing i can see wrong with the transom is there was a lose bolt it the end of the swim platform i went to tighten it down and it would not grab, so i took it out and filled the hole and put the bolt back in. Then i put a bolt next to it and it grab real good. there has been a few holes in the transom where someone has removed old fish finders and stuff like that and just put the screws back in place. i have pulled filled and replaced so water shouldnt get in now. dont think it ever did, but cant be sure.dont see sings of bad transom it looks and feels strong. the bottom of this boat is very stright not one stress crack,but on the gel coat at the back of the boat where the water line is there are some small blisters should i sand them down and fill or leave alone?
     
  12. shane blower
    Joined: Apr 2008
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    Location: lake orion michigan

    shane blower Junior Member

    blisters

    here's my boat ,its a nice boat and i think its worth fixing dont you?i have some blisters and some chips in the gelcoat, think i can get a gel mix to match this blue ,or can i use auto paint to touch up? see all the screws, not all had filler in them ,think this could be a problem? see this motor mounts should i make one taller ,wider stringer or should i patch one togeter like they did ? im thinking one it will be stronger. then should i rap in glass or keep open so it can dry out i thank rapping its half the problem,one more thing ,what lays under the stringerto give it alittle give. hope you can understand what im tring to say im new at this e mail stuff.
     

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  13. dragonjbynight
    Joined: Apr 2008
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    Location: Indiana

    dragonjbynight Senior Member

    I would say its worth the fix, its a nice boat!
     
  14. tuantom
    Joined: Jan 2005
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    Location: Chicago

    tuantom Senior Member

    Upon looking again, I can't tell if the engine well stringers/motor mounts were ever bonded to the transverse framing. They weren't on an old boat of mine - mine were just free standing (wider though). Wet doesn't mean it's rotted - yet. Are they solid?
    Maybe all the oil in the bilge preserved them ;)
    Either way, being that they're wet, you should replace them eventually; and sooner is probably better than later - But sometimes circumstances dictate the timing.
    Whenever you replace them, you'll have to wrap them in glass and preferably epoxy.
     

  15. shane blower
    Joined: Apr 2008
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    Location: lake orion michigan

    shane blower Junior Member

    no they stop 18" in front of the motor,thats where they were caped off ,and the water got in.So should i make them wide tall one peice stringer/motor mount?
     
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