Wet transom wood, 1982 Glasply

Discussion in 'Fiberglass and Composite Boat Building' started by Akgramps, Oct 22, 2012.

  1. Akgramps
    Joined: Aug 2008
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    Akgramps Junior Member

    How many threads start, “We were getting ready to do blah, blah, blah and discovered this.....”...?

    And so it goes with our 1982 Glasply, prepping the transom to fill some abandoned holes and discovered wet wood under the glass.

    I milled out a section with a router to get a better feel for things and discovered the wood is wet but sound.......probably been wet for a while. I would imagine there are a lot of boats this age and size (24') that have a this condition and many owners are not aware until the boat changes hands or a repair is needed. This boat is new to me and I suspect it has spent at least part of its life moored, we plan to trailer this boat.

    In any case I machined this slot yesterday, the wood when pressed with a tool would bleed water around the tool. I went home to contemplate and today that wood is dry, at least if I push on it with a tool it doesn’t show water, I know internally it is still wet and that brings be to my question.

    How can I dry it out? Is it possible given time this will dry enough? Rather than just tearing the inner skin off I decided to see if I can dry it out, today I drilled a series of 1/2” holes on 4” centers, angled slightly downward and tried to not penetrate the inner glass skin.

    A few were very wet, some moist and those close to the water line were dry. I also drilled a ½ dozen 2” holes through the fiberglass on the inside of the transom, just enough so I could pop the glass off, which was still bonded to the wet wood.

    I covered 3 of the holes on the outside for a ½ hour with a piece of clear plastic (taped and sealed to the fiberglass) so I could see moisture form on the inside, and to give me a baseline so to speak. Sure enough, some fog formed on the wet hole, and none on the dry hole. I also sanded the stern-drive opening to give the water another pathway out.

    I plan to try to drive out as much moisture as possible using halogen lamp and a fan, the boat is a warm dry shop, for now anyway....

    I have two questions, other than will this work...?
    What kind of epoxy resin should I pour in the holes once I have decided its a dry as its going to get?
    I angled the holes to facilitate this step later.

    Is there some thing I can pour in now that will help drive the moisture out and not affect the or weaken fiberglass? I am thinking some type of a isopropyl alcohol, maybe like Heet or what is used in airlines to keep them from freezing on semis.......

    Any thoughts...........? Am I kidding myself here.....the wood is solid enough, just wet, seems a shame to tear the transom apart......!
     

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  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I've done too many transoms to count and one of the things I consistently see is they are a lot worse they they seem when examined. Simply put, if you have a wet core in some place, you're only seeing 10% of the actual damage within the core.

    No there's no magic goo in a can that can be poured into the wet core to make it unwet and restore the integrity of the rotten wood fibers. Some products suggest this on the can, but trust me, there's no such thing.

    The core can't be dried either, mostly because it's all enclosed, between the 'glass skins. From a technical stand point you could stick the boat in an autoclave and suck it down a few atmospheres and the water will boil off, but most of us don't have vacuum booths as big as a UPS truck.

    The bottom line is you need a new core. Yeah, it sucks, but it's quite common for a boat of this vintage. You may also have stringer and sole issues to contend with as well, for this era boat. When you open the transom up, you'll find it's much worse than you thought, though many places will still have solid wood, the important places will be water soaked and rotten.
     
  3. Akgramps
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    Akgramps Junior Member

    I understand the diffuculty in drying out something encased in fiberglass, the reality is the core is still solid even though the wood is wet. The stringers are glass in these old Glasplys, so I am not concerned about transfer to the stringers.
    The condition of the wood is testimony to the materials and methods they used 30 years ago, how long has it been wet? If its not rotten now, why not?
    It is solid enough I am wondering how diffucult it will be to seperate the plywood from the outer skin once I start cutting....? The holes I drilled on the inside still had a bond between the wet wood and the glass.......
     
  4. PAR
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    PAR Yacht Designer/Builder

    I'll tell you what you'll find, if you remove the inner or outer 'glass skin. Around each hole will be wet and rotten, along grain lines and voids will be wet and rotten and these will all lead down to the base of the transom, where the moisture collects (it's a gravity thing) and the base of the transom, where the loads are transmitted to the bottom, will be wet and rotten. On an outdrive boat, these issue take much longer to appear, than on an outboard powered boat, mostly because the engine beds carry much of the loading, so the transom is "torqued" nearly as much. I've done many a transom, including old Glasply's and the story rarely changes. Maybe you're lucky, but more often then not, the 3rd of century old core is done.

    You're not going to dry it out without an autoclave or a vacuum chamber of some sort. You could vacuum bag it for a few days, which might dry it out, but you'll have no true way of insuring it's dry, but more importantly be able to restore the rotten core in the places it is bad.

    I've seen cores completely rotten, but most of the time it's just localized rot, again around the penetrations and collected at the bottom of the transom. The core is Douglas fir and this species has widely different densities between winter and summer growth wood, so the soft grain lines rot out right away, leaving trails through the core, providing a neat passageway for more moisture to infiltrate the core.

    You could just fill the holes with epoxy and hope for the best, maybe getting a season or two out of her before having to change out the core. If taking this route, use an epoxy that setups up under water.
     
  5. CDK
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    CDK retired engineer

    You can surely dry the core with heat and ventilation. Or inject methanol or ethanol, these liquids mix with water in any ratio, so what drips out contains a lot of water shortening the drying time by a couple of days.

    Of course that does not cure any wood rot, but it gives you the satisfaction that you at least made the effort. PAR has a lot of experience and is probably correct this time also, but you may be lucky and get more than just two seasons....
     
  6. Akgramps
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    Akgramps Junior Member

    Decied to remove the wet woot

    last weekend we decided to go ahead and remove the wet wood, as mentioned here it would have never dried out.......

    We removed the lower 2/3 of the transom, so to speak. Above that point that point the wood was sound and dry and as if cutting into a new sheet of plywood.

    Amazingly what we did remove still had a lot of integreity, it was delaminating in a few spots and I suspect it would have lasted for a while yet.

    There were no cracks in the outer gel-coat and the wood was still well bonded to the fiberglass. If we had not bought a project and the boat was functional we would have got several years out of it before this needed to be done. Once discovered, it was hard to ignore especially considering the transom was stripped on both sides.....

    I can only imagine how amny boats are out there getting used with wet transoms, sometimes ignorance is bliss.

    We bought a sheet of hydrotek to make the repair, we breifly considered coosa, but decided the plywood would probably out last us and since we did not remove all the wood it seemed logical to go back in with wood. The GP is a good hull but still its a a 30 year old production fiberglass boat.

    We plan to mill a lap joint at the top, hard to see in the photo, but there are 2 layers of 3/4" plywood. We plan to overlap 3-4 inches.

    This is where it gets interesting as I want to make sure of the sequence and material before we start.

    We have planned to use some 1708 biax mat and some 1.5 oz chopped strand mat (CSM).
    Between the new wood and outer fiberglass skin we would use a layer of csm/1708/csm. Then the wood. on the inside we would use a total of 5 layers, csm/1708/csm/1708/csm. On the inside we would tab the layers onto the sides of the hull and the bottom, starting with 2" on the first layer and each suceeding layer would overlap for a total of ~6".

    Finally we have decided to use polyester resin to make the repair, we had intially planned to use epoxy, however I recieved advice from several suppliers that said using epoxy will make for a diffucult job as epoxy does not wet out mat very well and the boat is built out of polyester.......

    His exact words were "you will repent"......

    I just finished reading a 2004 article written by the Gougeon Brothers and of course the point made is epoxy is superior to polyester and can be used to make repairs to polyester.

    I know epxoy is stronger and shrinks less but can it be used with mat? Or just cloth? Rather confusing and contradicating information......

    Lastly we are concerned as to whether we can complete this job 100% in a day, so plan to get the new wood in and then do the inside glassing the following day. We would plan to pva over the first step and then remove before we went on......

    Any advice here would be appreciated.......J

    [​IMG]
     
  7. PAR
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    PAR Yacht Designer/Builder

    Who ever is giving you the "you will repent" advise should be ignored from now on, as they literally haven't a clue what they're talking about. There's absolutely nothing that polyester can do, better then epoxy. Polyester is harder for the novice to work with, the end result is weaker, less waterproof and it stinks to high hell too. Epoxy easily wets out mat, but if the bonehead that you talked to had a clue, he'd know this and would have suggested you don't even need mat with epoxy. In fact, using mat with epoxy, just wastes resin and weakens the laminate.

    This sort of repair is covered many times in previous threads on this site, some searches are in order (I'm sure you have already). The lap joint idea you have, isn't the best approach, you'll want a scarf joint as a minimum (I'd never scarf a transom core, especially with polyester), having a 8:1 or better taper. The lap joint will just project a stress riser through the new laminate and core (read, it'll crack) once the transom has seen some engine torque. You also appear to be making this lap joint right where the most "cantilever" on the transom will occur., Consider moving the joint up at least a half a foot (or more). 6" overlap on the tabbing to the hull shell would be a minimum, try to get more if practical. With an epoxy job, you don't need a fabric layer between the plywood cores either, just thickened epoxy on all mating surfaces.

    If using polyester, you do need the mat, because its lack of elongation modulus needs this extra reinforcement. You'll also need to bulk up the tabbing so it rivals the thickness of the hull shell (not the liner, the hull shell). Use alternating layers of 1708 and roving for best results.Lastly, give the inner skins (inside the hull shell and the now removed liner piece) a really good scratch with 40 to 60 grit. You should see nothing but clean, well scuffed laminate, not remnants of stained wood. Especially with a polyester bond, which is limited, you'll need a heavily scratched surface for good results. If the "you will repent" guy would like, have him call me and I'll straighten him out on the realities of epoxy, it's physical attributes and how it works within a laminate.
     
  8. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    You don't want pva until the last layer of resin. You want to use unwaxed resin for everything so the resin remains tacky and chemically receptive to the next layer. The last layer can have wax or pva to exclude the air and allow a full cure, but it has to be removed for painting if paint is the final finish.
     
  9. tunnels

    tunnels Previous Member

    good luck

    Resins /
    Polyester is the bottom of the barrel so to speak its easy to use , cheap and manufactures love the stuff . its pretty good and lasts quite a long time .
    Next on the scale is Vinylester is a better resin that polyester stronger more chemical resistant and just all round better . it uses the simular catalyst to poly but ratios ar usuall a bit higher . and like all things its more exspensive than poly
    Top of the heap is epoxy its a differant animal all together !! still resin but sticks well onto wood , sticks well onto polyester or vinylester as long as the surfaces are well prepared before hand . is slower to wet out glass so chose wisely which glass you use . with epoxy you dont need to use Chopped strand matt ! but in saying that against the wood i would use a 225gram 0r 300 gram ( use and make sure it P matt you get !!) just as a bedding layer for the 1708 Some 1708 has csm on one side so could put the csm against the wood !! and if you using a second layer then csm outermost and peel ply over !!
    Because it slower to wet you could use a slower hardener to giv yourself longer working time so dont have to panic near the end of the job . Epoxy can be use over poly and vinyl ester bot poly and vinyl should not get used over epoxy as i does not adhere every well !! Do you home work with resins as they are not all the same . ask and get advise . I would also advise to use peelply material over the top of the glass and hard roller it all over . it makes a neat tidy and smooth finish, when the risin is 100% hard you simply rip it off it takes away the surplus resin helps to compress the glass and is good and very little sanding need before you paint the inside of you boat .
    Overlaps of glass onto the hull sides up to 150mm wide . sounds like over kill and its is a little but last thing you need is a weak join take all the glass rond and onto and then step each layer back in steps of about 30 mm or so and peel ply to pin all the ends of the glass down tidy so they wont be sticking up . :):D:p:p.
    End of the job build a small tent and warm up the whole job and cure everything for 6 to 8 hours Remember Warm not hot !!!
     
  10. Akgramps
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    Akgramps Junior Member

    We had planned to use epoxy between the 2 layers of new wood, but against the outer skin and on the inside we had planned to use mat & csm, If not mat, then just cloth?
     
  11. tunnels

    tunnels Previous Member

    to use csm or not to use csm !!

    You are perfectly ok doing what you planned to do .reguardless of what others say there is nothing wrong using Csm !! between layers of wood and or between the old and the new it will be a glass reinforcement for the resin . some people have differing opinions , at the end of the day the choice is yours !! layers of resin without glass to help hold it all together is not so good . :D:p:p
     
  12. PAR
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    PAR Yacht Designer/Builder

    It's not a matter of differing opinions, but simply fact that mat is an unnecessary element, in epoxy laminates. It's also unnecessary to employ fabrics as a bulking agent between wooden laminations. In fact, it's not advantageous to do so, which the exception of preventing print through, in some laminates, in which case you only need a light scrim. Mat just increases resin to fiber ratios, resin usabge and weight, which isn't desirable in any laminate. In the polys, you don't have a lot of options (again) because of the resin's elongation properties. This isn't the case with epoxy.

    This said, Tunnels is correct in that you can employ CSM if you want to, in either application. Naturally, resin use and ratios will rise sharply, but hey, it's only extra goo. All current available mat and combo fabrics, using mat has a sizing, that is compatible with epoxy. You'll have to look hard to find one that isn't. The sizing doesn't melt, like it does in polys, but it does remain in suspension, so a moot point if someone tries to bring it up.
     
  13. tunnels

    tunnels Previous Member

    Taking things to exstremes i remember long long time ago a guy complaining bitterly about all the loose glass strands on the combination fabrics he had bought so he laid it all out on his drive way and set to with a vacumn cleaner to remove the unattached chopped strands . naturally he filled the cleaner bag a few times , my friend and i cracked up laughing!!!! he really wasnt a very happy chappy !!! . :eek::confused:
     
  14. Frosty

    Frosty Previous Member


    I don't the joke!!
     

  15. PAR
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    PAR Yacht Designer/Builder

    That's not surprising Frosty. The directly address Akgramps;

    CSM and mat are the same thing, if you tab the core to the hull shell, CSM (only) isn't the wise choice, as it has no real strength, it's a bulking agent. The typical tabbing laminate would also be alternating layers of CSM and roving or cloth. This is why combo fabrics (1208, 1708, etc) are so popular, as they save a step. This alternating layer process, is the backbone of polyester and vinylester laminates.
     
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