Waterprothing all under waterlevel seams/rivets from inside Aluminum hull

Discussion in 'Boat Design' started by the brain, Nov 13, 2017.

  1. the brain
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    the brain Senior Member

    I was planning on smearing goop over G2 covering revits so two differnt layers of glue.

    however goop maynot be needed, G2 alone a few new closed revits is all she needs.

    nice illustration however goop is blobed on inside and outside thats two layers of glue.

    the heatgun heats the revits so the blob of goop oozes around revit shaft.
     
  2. PAR
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    PAR Yacht Designer/Builder

    All "tinnys" that I've worked, on have bedding (sealant) under the seams. G2 is a lower modulus epoxy and though fairly effective in some aspects, not something you can trust to seal these rivets. They'll just "circle out" in time, especially on a powerboat, causing a leak. This is common with riveted construction and the only good repairs are to braze the area with a low temperature, special alloy silver solder or drill it out and replace the rivet. Both of these repair options have good and bad things to consider. Brazing is very effective and I do it all the time, but panel distortion and contamination is a real issue. Re-riveting works, but the seam edges need to "mate" within the range of the bedding elongation. Since the aluminum is quite thin and you only have say 300% elongation in the bedding, it doesn't take much of a ripple or dent to move the seam well past this dimension. Then as you pound on a seam to get it to "lay down" within the range of the bedding, distortion and panel stretch become issues. These are controllable issues, but you need to know how to work metal.

    The short of it is, you can play with this puppy, using all sorts of home brewed techniques and misunderstood goo beliefs, or you can do it right or you can just coat the entire bottom, with something that will seal everything down, call it a day, knowing you'll do it again when the coating wears through in a few years. It's your call.
     
    Last edited: Nov 18, 2017
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  3. fallguy
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    fallguy Senior Member

    I didn't realize you were gooping the outside. I can't see that ending well or looking good.

    PAR knows this business. I am a casual lover of boats, so I defer to him.
     
  4. Barry
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    Barry Senior Member

    I would never apply heat to a riveted seam with a bedding tape/compound between the seams. The rivets hold the seam together and the mastic makes the seal between rivets.
    The mastic will just bubble out and you lose a larger area of the sealed area.

    Years ago, when we were building welded boats a friend came in to see if we could repair a few seam leaks in a riveted boat. . We at the time, rookies in riveted construction, tried to tig the joint, the mastic bubbled, the bubbles dropped the aluminum out, and we were left with a one inch hole. The only fix was a riveted patch on the outside with a mastic sealant under the whole thing across the seam. Ugly as sin.
     
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  5. PAR
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    PAR Yacht Designer/Builder

    We've all learned this lesson, though (again) a low temperature braze is possible with out boiling out the bedding. The stuff I use melts at around 325 - 350 (F) degrees. These seams can't be TIG'd. It does require some practice and welding skills, which is why I recommend a polyurea or polyurethane coating over the whole bottom. These have become tough enough in the last decade to be a viable alternative, that can be over coated if repairs are needed and also can be painted. I braze with an oxyacetylene torch, a #2 tip and just keep it moving.
     
  6. the brain
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    the brain Senior Member

    Update

    The revets I say are loose aren’t completely loose just a tad enough for a fingernail to be inserted in mushroom of revet (always the outside of revit and just half is loose).


    G2 oozs around open piece of revet. I’ve only applied heat w/ gun to freeboard never to seams and there mastic.

    The tramsome seams mastic was exposed to welders heat for my trim tabs mount.

    I would have preferred to braze this seam however pressed for time I decided to glue

    Mainly because I just ran out of fall temps.winter first freeze begins today glad I started gluing Thursday.


    The missing revets fill be 3/16 Closed End (Sealed) Blind Pop Rivets - Aluminum #68, 3/16" Diameter (.376 - .500 Grip) - 25 Pieces - Walmart.com https://www.walmart.com/ip/Closed-End-Sealed-Blind-Pop-Rivets-Aluminum-68-3-16-Diameter-376-500-Grip-25-Pieces/129679075


    Yes the outside freeboard looks terriable.


    The lower seam on each side is weak I’d like to reinforce before I poured in foam.
     

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    Last edited: Nov 19, 2017
  7. fallguy
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    fallguy Senior Member

    I could be way off here, but that hull doesn't look like it is rated for 175hp. What boat is it?
     
  8. the brain
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    the brain Senior Member

    boat has 2" thick transome that alone according to Armstronge will hold 200hp.

    additionale knee brace I built/installed will hold a new Merc.400hp 175hp is plently for this boat
     

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  9. fallguy
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    fallguy Senior Member

    Sorry, I thought you wanted to reinforce transom bottom.

    I like the knee if you don't trip on it.
     
  10. gonzo
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    gonzo Senior Member

    Knees like that are likely to make the boat porpoise. When the transom flexes, it will bend the bottom which will act like a trim tab moving up and down.
     
  11. fallguy
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    fallguy Senior Member

    is it due to the knee being too short? What would be a solution?
     
  12. gonzo
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    gonzo Senior Member

    No, Ideally the force of the motor gets transferred to the sides and bottom through the transom. Using a knee, we found skiffs would tend to porpoise. The solution was to make a horizontal plate from side to side. The original skiffs with that problem were wooden. Most modern boats have an outboard well that acts as a stiffener.
     
  13. the brain
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    the brain Senior Member

    update
    found three missing revitos all at port midship this is the most stresseded part of hull when offshore.

    in the process of elevating hull off trailer so I can redrill missing revitos w/closed end blind inserted from outside.
     
  14. fallguy
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    fallguy Senior Member

    I think if you get the rivets fixed up nice; you'll not need to bother with the goop. Then you can monitor the failures easier. But I think you could also listen to PARs advice and use a different coating and paint it and it'd look great.

    A question though. Was that vessel really intended for use on the ocean? I'm taking a guess here that intended use is on lakes and the Great Lakes issue sc advisories rather quickly on 2-4 foot waves even sometimes. I think a part of your repair is understanding the limitations of the vessel and that she is meant to be babied in certain conditions that she wasn't intended for....kind regards and congrats on finding the leakers.

    I once found a boat problem by filling the bilge with water until my trailer started to creak. At just the moment I turned the water off, I realized the problem as the livewell drain started to run water. The hose of the livewell had detached and was not accessible without major work. I had not leaking rivets. It is a little risky to the trailer, but it worked to help me solve my unknown leak source and it might help you find leaking rivets with a bit less water than I risked.
     
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  15. the brain
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    the brain Senior Member

    I have been in ruffer seas than I like to admit to, especially at the entrance/exit to GOM.I’m testing the limits of the vessel and have to say I’m impressed w/ the results.


    Been on about 15 cruises (over last year /half) majority where ruff seas where the vessel took a good beating.


    Yes you are absolutely correct being a good idea to baby more in ruff seas, like when approaching taller than 5’ waves outbound approach at 45* angle to minimize the slamming.


    However it’s unavoidable eventually the vessel will get repeadatally pounded w/

    Majority of impact at midship outer port seam.


    I want to reinforce from inside heres the plan so far.

    1.5200 latituale hump stringer to lower freeboard

    2.then revit angle formed around

    Hump and flat on freeboard basically extending length of latituale hump stringer

    And glueing to freeboard.

    3.tilt hull then G2 seam.


    Airplane pilots visually inspect prior to every flight, I do a quick observation

    Unfortchantley the seam where missing revits where it’s view is obstructed by the trailers bunk. I believe the bunk needs to be at this seam for surport correct?


    I want my hull to be stronge as possible because I’m upping the power to etec 225-250ish

    since the batteries sulferric acid leaked it has started a light layer of Roy I will clean aluimiun w/ my new rubber brisol brush which I use to clean auto cylinder heads gasket leftover.https://www.amazon.com/gp/product/B06WVJ4166/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

    I then what to use sharkhind to coat the exposed alumimin.


    Edit2 not sure if the starcraft was designed for saltwater however I do know it was designed for great Lakes which have been know to have ruff seas.

    I know the poured in foam will stiffen/strenghten the seam would like it to be as stronge as possiable.
     
    Last edited: Dec 8, 2017
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