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  1. #1
    Join Date
    May 2007
    Location
    Fairbanks, Alaska
    Posts
    3

    Default replacing the bottom in a jonboat?

    Looking for some opinions on replacing the bottom in my jon boat.

    It's a rivited 1448, 0.060" hull.

    I plan on putting a 4'x8'x0.125" 5052 on the bottom. I'm not sure on the best way to do it. I talked with a local shop and they want to cut the old bottom out. I don't see a reason to do that, other than it might save a bit on labor. I think that cutting the old bottom completly out would cause you to loose alot of structure that is already there.

    Here are some pics of what I was thinking of doing.

    Cut out the runners (represented by the black), grind the outside rivits flush with the bottom, weld the new bottom to the stringer (i think that's what you call it), weld the stringer to the origional bottom just because. Also put a weld from the new bottom to the old in the middle of the runners I removed (forgot to put that one in the picture) The welds are the grey areas (kinda hard to see).



    On the back of the boat I was thinking of leaving the new bottom sticking out 3/8-1/2" and putting a 4-5" plate on the back of the transom the whole width of the boat.



    I would drill a few holes in the stringers so water can get back to the bilge.

    I am going to be using a MM210. What wire/size would you reccomend? Right now it is setup with .035 5356. Should I go with 4043?

    I don't have much experience with welding aluminum, but I've been reading all I can find and practicing alot.

    I think the hardest thing is going to be making that first cut! I do have another boat incase this one is in the shop for a while, lol.

    Thanks!

    Kevin

  2. #2
    Join Date
    May 2007
    Posts
    539

    Default

    Hi Kevin,

    I am by no means an expert, but I do have some boating experience. Seems to me that boat is going to flex, a lot. There was a reason they used rivits originally.

    My opinion, be carefull where you replace rivits with welds.

    The only thin aluminum I have welded was with a tig. It is difficult to do well. Can't offer much help there.

    Good luck.
    Tom

  3. #3
    Join Date
    Dec 2005
    Location
    wisconsin
    Posts
    836

    Default

    Kevin,
    I too question the welding. I would consider riveting (solid rivets)the patch on using a metal filled epoxy as a sealer between. Im not familiar with 1448, and could not find it in any literature of mine, perhaps a typo? In any event riveting is simple and straight forward, or you can always find a local aircraft mechanic to do it for a few bucks. I wouldnt "grind" down any rivet heads, drill them out and re-rivet through your patch if you have to.

    -Aaron
    "Better Metalworking Through Research"

    Miller Dynasty 300DX
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    Smith, Meco, Oxweld , Cronatron, Harris, Victor, National, Prest-o-weld, Prest-o-lite, Marquette, Century Aircraft, Craftsman, Goss, Uniweld, Purox, Linde, Eutectic, and Dillon welding torches from 1909 to Present. (58 total)

  4. #4
    Join Date
    Mar 2006
    Location
    Ocean City, Maryland
    Posts
    951

    Default

    They do make aluminum John boats all welded but I'm not sure I've seen one that has been changed over from rivets. I have welded some stern repair spots, brackets and made some compartments in them. Most sterns are welded anyway it seems. The rivets are easy. Takes 2 people and an air hammer with blunt chisel. Person inside holds the dolly [auto body] Give it a shot with impact, all done.
    As far as welding with the mig. The boat is probably .063-.080 and I have a pulsed mig with spool gun and I have a time with it. The TIG works much better in my case. Also the aluminum your working on [at least what I work on] has been in the salt water and it gets "into" the aluminum. That makes it even harder to weld
    Just my 2 cents worth, good luck
    Scott
    HMW [Heavy Metal welding]

  5. #5
    Join Date
    May 2007
    Posts
    100

    Default

    I think you should consider selling it to someone with more ambition than money and use the money you were going to spend on that 4x8 sheet of aluminum and trade up !!! Unless you are very experianced you will not get that aged .060 aluminum welded sucessfully with the above mentioned equipment and even then I am not sure. I have a MM251 with a spoolgun and a good bit of experiance with it and I would fully expect to scrap the boat and waste a good sheet of aluminum by trying.

  6. #6
    Join Date
    May 2007
    Location
    Fairbanks, Alaska
    Posts
    3

    Default

    I'm going to can the project till winter. Buttoned her up enough today to use for the summer. Getting tired of looking at the new motor sitting in the corner.

    Thanks for the ideas

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