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Thread: 24" diameter Alu tube - pontoons

  1. #1
    Join Date
    Oct 2001
    Location
    Central Calif
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    424

    Post 24" diameter Alu tube - pontoons

    After fishing last year in our smallish boat, my buddies and I are looking at building a pontoon boat. So all eight of us heavy weights can get out on the water at the same time.

    All of the commercial boats I've found are using 23-25" dia, 0.080" to 0.090" wall thickness aluminum tube in 4-5' sections joined with bulkheads to make 16-24' long pontoons. We would need 32-40' of this tube.

    Do any of you know offhand if this is a stock alu. extrusion/drawn tube? If so - any idea on costs?
    or would you roll the tube sections from sheet?

    If stock - any know off hand of a supplier? I know I can check in the Thompson guide but if someone has already dealt with it, so much the faster.

    Thanks,
    Kevin

  2. #2

    Post

    Kevin:
    As I recall the standard size for sheet metal is 4'x12'. If you cut a sheet in half and slip roll it you would have 22.9" dia x 48" tubes you could weld 1 seam and then the bulkheads for each section. I think Tig would be better than Mig but that is because when I worked in a sheet metal shop while going to college they only used Tig for aluminum. I use my Mig for steel but have not tried aluminum (that is because my welding sucks). I need a lot more practice on steel before I try aluminum.

    ------------------
    Dick
    Dick

  3. #3
    Join Date
    Oct 2002
    Location
    Pass Christian, MS
    Posts
    978

    Post

    Kevin,

    When I worked in an aluminum rolling mill we supplied sheet in rolls to one of the manufactures of the pontoon boats. The surface quality of the sheet was critical. I don't remember the manufacturer(something craft I think) or the alloy. The alloy was corrosive resistant, maybe a 5XXX series. With the length you are talking about the design needs to be looked at closely.

    Joe

  4. #4

    Post

    Kevin
    You can order the Aluminum in width up to 5' length can be cut to order off of a coil. Go with a 10AWG as this is fairly easy to weld, the supplier can also roll it for you if you ask.

    Another possibility fo you to consider is the purchase of 30 gallon stainless steel drums. This would most likely cost about the same to fab as the aluminum, would never corrode, and always look "shiney". These can be welded together as they already have a "bulkhead" and would only require a light gauge pontoon nose and tail made in stainless or fibreglass.

    Another alternative that comes to mind is large diameter sewage pipe such as that produced by Ipex. Get a length and cap both ends - instant pontoon.

    New, unused drums can be purchased from the drum makers (search the net) or use www.thomasregister.com

  5. #5
    Join Date
    May 2002
    Posts
    156

    Post

    Hi again Kevin, see my reply to your other post as I answered it first.

    The round logs are made from rolled sheet, a PITA to build right, even in a production setting.

    Most pontoon manufactureres actually use a simpler, easier to manufacture pontoon design than the Harris/Tracker round sealed design.

    Most build a "U" shaped pontoon log filled with expanding foam. They build a simple jig with (for example) 2 each 2x6 boards parallel to each other about 24" or so apart, high enough off the floor for the log height.

    They then break a 90 deg. bend (about 2-3" wide) on each side of the alum. sheet (they all use 5052 alloy .080-.090 thick), then lay the sheet on top the jig w/ the bends down (hanging over the 2x6's), then 2 or 3 guys start jumping down the center (really)until the 90 deg. breaks are hanging off the 2x6's...viola! a U-shaped pontoon! Then weld in some U shaped bulkheads and a nose-cone, fill the logs w/ foam and weld a flat sheet on top to seal everything up.

    The advantage to this system is (other than ease of assembly, cheap jigs, critical welds are done flat, etc) is now you also have a flat surface to start your decking braces from, the round logs have to have a bunch of angle braces welded to the top surface to give you a flat to mount everything to.

    Just some ideas I would use if I was gonna build one at home.

    HB

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  6. #6
    Join Date
    May 2002
    Posts
    157

    Post

    Having owned a pontoon boat for two years, there are several things to consider.

    1. Length. Mine was a 20 footer and I consider that the shortest that it should be. Why, pitchpoling. (bow digging in at speed).

    2. You say you want 8 people on board..Make sure that 20 feet is enough, remember about three feet out the back (for motor support) and at least 4 feet in front for bow/front deck area. (use it only when stopped.)

    3. Now that leaves a relatively small area in the center for all 8 of you to travel on.

    4. Load placement is critical on pontoon boats...cannot have more than about 40 percent of weight forward or it can pitchpole. Ask the family that bought mine one Friday eve and tried to force me to take it back on Saturday afternoon,....after getting out of hospital!! I told the idiots NOT to run at speed with anyone on front deck...they still did and it pitchpoled!!!! Almost went end over end!

    5. Each compartment MUST have a 'pressure relief valve' in it. That is just a simple 1/8 inch tube that goes from the top all the way to the bottom of the compartment so no air pressure difference is experienced. Just put an upside down "J" in the top so it can equalize. My boat dealer had one come to him with a 'hole' from the trailer that hauled it. He didn't notice it, but the new owner brought it back after about 2 months complaining about 'water running out of the left pontoon when the boat was just pulled out of the water. What was happening was it was getting some water, apparently about 1 inch inside the pontoon when underway, but not filling up due to the tube going straight down to the bottom of the tube and air pressure keeping it from filling. He noticed it after getting home or at the loading ramp area..don't remember...1978.

    Just make sure that boat/load/etc can be supported by 1/2 of one of the pontoons for safety sake. Any more, and it may be unstable.

    I once rescued a party of 12 when the one boat motor they had quit about 5 miles from nowhere, late in the afternoon. They had 4 large tents, 14 people, 4 large dogs and only one 18 foot runabout. We made it out with one trip, but I was sitting low. Any good large wake would have been a problem sideways. I kept a sharp eye on the water surface.

    Hope this helps.

  7. #7
    Join Date
    Oct 2001
    Location
    Central Calif
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    Thank for the feedback.

    I have been reading the "war" between the tube and "U" pontoon makers on the company websites. I read a fair number of claims that I'll believe when I see. A few things make sense, like the flat top of the "U" for attaching the crosspieces. Plus it's bouyancy doesn't start rapidly reducing after it's halfway submerged as a tube does.

    Hellbender: I read your other post and if ya don't mind I may be asking you some more questions before I'm through.

    -Kevin

  8. #8
    Join Date
    May 2002
    Posts
    156

    Post

    Glad to help if I can.

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