Adding stringers to reinforce mast step and trunk.

Discussion in 'Fiberglass and Composite Boat Building' started by Canracer, Dec 2, 2014.

  1. Canracer
    Joined: Aug 2009
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    Canracer Senior Member

    I'm about to cut into the cockpit floor. I want to add stringers alongside the centerboard trunk and the mast step.

    I removed most of the hardware, and have some tools ready. There are many ideas in my head, but I'd like to hear from other people on this project.

    Under that red box is a panel I want to remove (and a smaller panel aft.) This has to be done for access.

    [​IMG][/URL][/IMG]

    [​IMG][/URL][/IMG]
     
  2. gonzo
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    gonzo Senior Member

    What is the problem with the structure?
     
  3. Canracer
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    Canracer Senior Member

    I think that compression from the mast step, the weight of the crew, and the stress from the centerboard have finally started to weaken the hull.

    I had water in the hull last time I went sailing, that's never happened before. It looks like there might be some fine cracks at the forward end of the centerboard slot.
     
  4. SukiSolo
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    SukiSolo Senior Member

    How is the C/board pivoted?. If not a drop in stirrup, it (water) is more likely to be weeping in along the glassed in pin. Had this with a double floor GP14 recently and was a pain to trace down, as it had self bailers in wells and buoyancy hatches as well as other possible entry points including the bond at the top of the C/board case to internal moulding. If it has a pin, remember it is most likely to be below the waterline in a static scenario so you can test simply by floating on a calm day, leaving for say 30 mins tied up and pulling out and opening the bung. Don't forget the bung seal itself though. A pressure test may well be worth trying as this can often locate the weep.

    If the panel itself has gone soft, the only real solution is to replace it with new foam or a timber core. I've known a few Cadet dinghies get this on the floor as the foam compresses after some years of use and then becomes soft. Easily felt with the palm of your hand just pushing down.

    One nasty trait of a leaking hull with your configuration is IF there are timber or ply reinforcements they can often rot undetected. The mast kingpost could be one of these areas. I have before now cut out bits of packing crate and odds and sods glassed in hidden from view and well sub standard for small boat construction. What the eye does not see..... etc. However equally there are really good builders who seal timber and put in sufficient good quality reinforcement.
     
  5. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    Before slicing the boat open,why not try to identify the source of the leak?All you need is the type of footpump used to inflate an airbed and some soapy water.Arrange a bung with a tube to the pump and lightly pressurise the tanks.Use a paintbrush and lots of soapy water to see where bubbles are forming.Once you have identified the source of the leak it will be easier to direct your attention to the problem.It may be as simple as a loose screw on a rudder fitting.Attacking the boat with a saw is best left until you are certain that the piece you are cutting is in some way related to the leak.
     
  6. Canracer
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    Canracer Senior Member

    Thanks wet feet. I've had the saw ready for a few days now. So "the attack" is hereby postponed, at least until I work through a few ideas.

    There are no tanks; the interior of the hull is all one piece.
     
  7. Canracer
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    Canracer Senior Member

    The centerboard bracket. The pin has a male and female side, welded onto the inside faces. SukiSolo, I think this is what you'd call a stirrup?
    [​IMG]

    The bracket positioned in the slot.
    [​IMG]

    Here's looking inside, at the suspected problem area. At left is the compression post, the middle is an insert (probably meant to add stiffness,) at right is the bottom corner of the trunk (the location of the leak.) I think I see some evidence of weeping and also what might be rotten wood.
    [​IMG]
     
  8. SukiSolo
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    SukiSolo Senior Member

    Well there maybe no tanks, but there is a tank! the whole deck/hull joint creating one large tank. Pretty rare in the UK unless positive buoyancy usually expanded polystyrene is added, in case of rupture in a collision. Hence a lot of stuff certainly from mid 70s' have separate tanks, as a failsafe option.

    Yes, that arrangement for the C/board pin is usually called a stirrup at least this side of the Pond.

    I'm not quite sure where the lower photo is taken if there is no entry into the internal part of the hull/deck. Is it through a hatch? or after cutting open?
    Worth ensuring the kingpost is solid and that the area that supports the stirrup is sound too. Often the only way to check if the wood inside is good is poke it with a small chisel. On really bad stuff your fingers can peel it away.....;)
    If it is soft, hack it out until sound dry stuff is found then replace. Worth pre-sealing any new timber cores though. Epoxy and fillers help a lot when renovating this type of build. Also do not be afraid to use generous fillets to help spread the loadings.
     
  9. Canracer
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    Canracer Senior Member

    Here's the hatch. I'm just able to get my head, and arms, into the hull. There's a limited amount of work that can be done with this sort of access. Two long blocks of Styrofoam used to run along each side of the centerboard trunk (6.5" square and 4' 2" long.) I removed the floatation, and have been sailing without it.
    [​IMG]
     
  10. wet feet
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    wet feet Senior Member

    Did that hatch ever have a rubber gasket?I also notice that your c/b stirrup appears to have been bolted in place with no sealant around the bolt holes.Both of these factors can mean leaks will be present.
     
  11. JosephT
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    JosephT Senior Member

    Hello Canracer, by the looks of the problem area it appears you'll have no choice but to open up the deck. If you're very good with it you can slice through the deck very neatly with a diamond or good fiber wheel (much smoother than a saw). Once you have the area opened up beef up the area really well. Rotten wood will have to be cut out & replaced. Build it up like Fort Knox & fair in the deck openings nicely (sand smooth, apply matching gel coat, buff, etc.).

    A company out of Ohio by the name of Abrasive Technologies makes some good diamond wheels. I have one that is still going strong after 10+ years. Worth the money if you're doing composite work a few times a year.
     
  12. Canracer
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    Canracer Senior Member

    Maybe the water entered through the hatch (it does have a gasket that I don't use.) The stirrup bolts might leak a drop, but last time out a few gallons collected. Probably not from a small leak.

    Did I mention,,, that I was sailing downwind with the centerboard fixed in cleats (no shock cord) and hit a sand bar? I don't know how I might have left that part out. ;)

    It was a hard hit, and I'm confident that it caused small cracks where the lower front corner of the trunk meets the hull (that's how the whole assembly would rotate.) I should take the hull over to the Bay and try to absolutely verify the leak's location, but how can you look at that mess (from the factory) and not rebuild?

    It looks worse in real life.

    [​IMG]

    And so the cockpit starts to come apart. I have a cutting wheel and a grinder, but that thing is a beast. The jig saw did a nice job and there was very little fine dust.
    [​IMG]

    The cockpit sole is sturdy. A quarter inch of good looking plywood and 1/8th" of fiberglass.
    [​IMG]
     
  13. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    Now you can visually see everything inside, maybe you should just float her and look for the tell tale water ingress? Often you will see it visually or at least a quick pass with a finger will let you feel it.

    It looks to me as if she was actually very sound, maybe a small local repair would have been fine. The king post (mast compression) looks dry, not sure what the piece behind is, and maybe the front edge of the box has a very minor pin hole. It is unlikely that hitting the sand bar has done any damage to the box, the board just pivots, more likely to put load on the stirrup and mounting screws. Check any through points under water at rest ie keelband screw holes, bungs (on launch/recovery), normally I'd say self bailers but you don't have any!. One tip is you can isolate things like keelband screw holes fast by just taping from the outside when dry ie duck tape. If it still leaks you can eliminate those.

    Worth checking where the box meets the top moulding ie front top lap of box and also along the rear 'joint' as sometimes these 'pop' after many years of use. When the boat is on the move a certain ammount of water can swirl up a bit higher than the static level.
     
  14. JosephT
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    JosephT Senior Member

    Yes, I would cut out any bad wood. The fiberglass that encapsulated it was obviously porous. When you make the repair, be sure to re-glass the area to ensure it's 100% water tight. Keep an eye on the area in the future. The slightest discoloration of underlying wood means moisture has entered. Dry it out and re-glass as necessary.

    Signing out
     

  15. Canracer
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    Canracer Senior Member

    Everything checks out level and plumb.
    [​IMG]

    Bought a sheet of 3/8" Okoume. Thank you to the guy at Atlantis Boatworks. He told me that 1/4" would be a little flimsy for the bulkheads, and he was right. http://www.atlantisboatworks.com/index.html If you need marine plywood in the Sarasota / Bradenton area, You can find it at The Teak Hut. They have a teak decking business out back, and a small retail shop in front. It's a small inventory, but everything a boat builder could need. http://www.teakdecking.com/
    [​IMG]
     
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