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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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  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

  7. #7
    Join Date
    Mar 2007
    Location
    Oahu, Hawaii
    Posts
    2,469

    Default

    One of the kids brought in a jonboat to the class to fix. teacher with years of experience at Pearl Harbor, said it wouldn't be worth it to fix. Too old with too much salt water. Even if you tried to burn it out with the TIG, still, too much crap/junk in it. Personally, I would re-rivit it, but put in a whole bunch of 5200 (it's something like a 1 part epoxy, GREAT for salt water). Although, I would probably try to TIG or MIG it just for the experience!!!!!!!
    good luck
    I'm not late...
    I'm just on Hawaiian Time

  8. #8
    Join Date
    Nov 2006
    Location
    Lake of the Ozarks MO
    Posts
    3,583

    Default

    I don't know if anybody even cares about this post anymore but i'll go for it anyhow!
    Firstoff ...1448 is just a fancy way of saying it's a 14 1/2' long boat!
    You can bet it's already 5052.
    If it's a fresh water craft and you got lots of time you could do a fun project out of it.
    One thing I will say is I would do as that shop said and just carefully grind loose the entire bottom. On a boat that small it would be nothing more than dead weight and lightness is one of the main advantages to that little jon!
    Heck you are already going to be twice as thick anyhow!
    Just grind all the rivets from the outside or if yer really good then just drill 'em out from the git go. When you weld back in your bottom you can simply "plug weld" the rivet holes along with a few skip welds as well.
    Carefull fitting would make all the difference in how this project turns out. just leave plenty of the sides so you can have plenty of fusion effect as .060 is fairly thin for mig but still within the realm of possibility. It will be easier welded from the inside on the corners but outside is all you can do at the crossmembers. The hardest part is getting it all cleaned and ground nice enuff.....take yer time heare cause there are no shortcuts.
    You can just set it on the floor on 2x4's and step on it to tack parts together.
    At my shop I would simply call this just another day at the office altho I would use tig instead to weld the sides to the bottom.
    I used to build jons one time in the off season and they were smooth bottom and had angle runners welded to the outside made from 1" x 1/8th angle. would work great for you as well.
    I would bring the bottom past the transom a couple inches like you was saying BTDT and it works great. Brace the bottom like you were saying also.
    I wish I could reccomend wire sizes and feeds and speeds and all but I don't run a 210. I will say you will have to flat get a move on tho and keep yer heat on the 1/8th part! Also lay a tack about every inch on the entire thing before you weld ANYTHING or it will turn into junk real fast!! Weld an inch or two then maybe peck the parts together a little and then weld a little more but don't get in a big hurry. You want a good burnthru on that weld anyhow.
    I simply love fixing up old boats and it is 90% of my income these days...I do more pontoons nowadays tho.
    To test it throw it up on sawhorses and fill 'er up with water....mark the leaks with a lead pencil...they work while wet unlike sharpies. then weld over the leaks after re-cleaning them first with a stainless brush on your 4 1/2" grinder.
    FWIW I wouldn't rivet a single piece..... All they are is a leak waiting to happen!
    I'd do that job in a heartbeat but nobodies gonna give me a 100 bucks an hour but on your own it's unlimited man!! Go for it ...I would...HTH!!

  9. #9
    Join Date
    Mar 2006
    Location
    Ocean City, Maryland
    Posts
    951

    Thumbs up

    Thats some pretty good advice Fusion King. You said some interesting things. For me, the biggest concern would be the age and salt its got in it. Aluminum in salt for a long time seems like it crumbles and sometimes, even with the tig, its hard to get all the crap burned off. I swear the salt is actually "in" the aluminum. And since its so thin you can't sand or wire brush much off.But if you made a whole new bottom that would be much better probably. I think thats what I would do, just replace the whole bottom.




    good luck
    Scott
    HMW [Heavy Metal welding]

  10. #10
    Join Date
    Oct 2006
    Location
    DFW area
    Posts
    180

    Default

    I'd slap patchs on the leaks with a 2 part epoxy resin & cloth/mat while I was saving up for a new hull.

    Keep in mind (for budget considerations) the old hull is worth about 60 cents a pound.

    .
    "Gone are the days of wooden ships, and Iron men.
    I doubt we'll see either of their likes again".

    Circa 1920.
    Author:
    Unknown US Coast Guard unit Commander.

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