Aluminum alloys for small boat

Discussion in 'Metal Boat Building' started by sal's Dad, Apr 5, 2006.

  1. sal's Dad
    Joined: Apr 2005
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    Location: New England

    sal's Dad Atkin/Bolger fan

    Hello -

    I am getting ready to order aluminum for a 19' W Atkin "Rescue Minor".
    http://www.boat-links.com/Atkinco/Utilities/RescueMinor.html

    This 1940's design was for heavy plywood construction; I hope to create a rugged, low-power, no-maintenance workboat for year-round use in New England. I have minimal experience with metal, but a few years ago did a trial Bolger Teal dory, of 1/8 aluminum, welded by a local guy.

    This time, I have signed up a first-rate welder, whose day job is building big boats - twice the speed, 10,000 times the displacement, and 100,000 times the cost of my little project. He has offered some general guidance, but I am buying materials, building a construction frame, and cutting/fitting the panels, and figuring out power.

    As I price out the 800 pounds of materials, it appears there is a BIG difference between 5052 and 5086 alloys, and some shapes and tubes are extraordinarily expensive. The 26" wide bottom will be 0.250", and everything else 0.125", with treadplate decks, if they only add a couple hundred dollars.

    For rails and deck edging, I would like to use the lightest, most bendable pipe/tubing that can be welded; one quote from a big national supplier was over $20/foot, $60+/lb for 5086 1.25 o.d. pipe!

    Pollard indicates that 5052 is appropriate for lower-strength applications, Gerr refers to 5054, but doesn't discuss 5052. Is 5052 a "fresh-water" alloy?

    Resale value and appearance are not major considerations, but maintenance is! I am trying to sort out the pros and cons of various alloys, while working through the byznatine pricing of suppliers. What areas are appropriate for economizing? If I beefed up the framing, would a lower-grade alloy be appropriate? Any thoughts for additional information, resources, or suppliers would be apprecuiated.

    Sal's Dad
     
  2. Baywatch Towers
    Joined: Apr 2006
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    Location: Cantonment

    Baywatch Towers Junior Member

    Sal's Dad

    I use 6463 grade anodized sch 40 pipe when building all of my towers for boats. This is generally the same as 6063 but made with a little bit more copper added to the mix. This creates a better finish when anodized. And still very bendable material. And stronger than 6063. If you were ever to bend a piece of each by hand, you can fill the difference. I buy all of my anodized products from eastern metal supply. http://www.easternmetal.com/ Give them a call and see if they can help you.
     
  3. antonfourie
    Joined: Oct 2005
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    Location: London

    antonfourie Senior Member

    5083 is marine grade Ali sheet and plate, 6063 is fine for topside tubes / shapes.
     
  4. sal's Dad
    Joined: Apr 2005
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    Location: New England

    sal's Dad Atkin/Bolger fan

    Thanks, A bit of digging, and I found a supplier of 5086-H116 at $2.55/lb for their stock sheets. Tubes and other special shapes are still expensive, but it looks like there will be ways of dealing with this through cut-offs, surplus etc.

    Also, I got a very helpful response from David over on the Metal Boat Society forum! http://www.metalboatsociety.org/phpbb2/viewforum.php?f=4

    Sal's Dad
     
  5. Tom Wroe
    Joined: Apr 2006
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    Location: Kingston, Ontario

    Tom Wroe New Member

    Aluminum alloys for small boats

    Hello Sal's Dad:

    I have just downloaded the Atkin's Plan Order form to get myself a copy of the "Rescue Minor" drawings. I would build the boat in aluminum, as well - assuming that doesn't violate anything proprietary that Atkin & Co. may stipulate.

    I am an aluminum boatbuilder in Ontario (see www.metalcraftmarine.com). My experience when converting scantlings from plywood to aluminum is that it is very difficult to keep the weight down. I don't know enough about "Rescue Minor" at this point, but her aluminum scantlings (like all boats) can essentially be a) thick plating with minimal framing or b) thin plating with lots of framing (think Starcraft). I am interested to learn more about your scantlings for the design. A good weight survey of the metal package would be my the first step.

    We use mostly 5083 H32 or H116 for everything below the maindeck with 5052 for superstructure, non structural and non-immersed parts. When bending pipe we use 6063-T5.

    Regarding price; 5083-H32 costs us around $2.00USD/lb. for 20,000 lbs at a time, so your 5086 at $2.55 is reasonable given the small volume. Don't forget the scrap factor, though; you should expect 25% to 40% into the recycling bin - good thing that scrap prices are high, too. The 6063-T5 will be about $2.00/lb. as well.

    My intention is to put the lines or developed plate shapes of "Rescue Minor" into Rhino Marine and have the parts CNC cut. Do you have any interest in that?

    Tom Wroe
     
  6. sal's Dad
    Joined: Apr 2005
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    Location: New England

    sal's Dad Atkin/Bolger fan

    Tom,

    I have almost no experience in building in aluminum; what I am looking for is a solid workboat for hard use, with zero-to-minimal maintenance. Minimal draft, protected prop and rudder, economy, comfort, and reasonable speed. I have followed Robb White’s project since the beginning in MAIB, and watched Alex Hadden build a 34’ Atkin Tunnel Stern; both boats exceeded expectations.

    I am working from the published plans, from the Motor Boating Ideal Series #41 http://www.boat-links.com/Ideal/XLI.html ; Mrs Atkin declined to be involved in this project after I informed her I was planning a rough workboat finish. This is for my own use, with nobody but my wife to answer to, so I will improvise a bit, doing the cutting and fitting myself, and hiring a competent welder. I may build the whole boat over temporary frames, out of luaun, to get the panels just right.

    Scantlings: Atkin called for a 1” ply bottom and ¾” ply elsewhere, with oak framing. Since 1/8” aluminum weighs about the same as ¾ ply, and Gerr recommends that 1/8” have framing every 6” or so, I am figuring:

    - ¼” aluminum on the bottom
    - 1/8” elsewhere;
    - Stem of ½” plate
    - Two bulkheads, at stations 3 and 10; Station 3 probably only 16” high, for continuous seating
    - Fore-and aft seats/air chambers port and starboard as a big box beam (it would be nice to go lighter than 1/8 on the interior, if my welder is comfortable with it)
    - Two 1x4 channels lengthwise on the inside bottom, continuously welded to serve as a keel cooler; (cedar floorboards on these)
    - 1x1 (or so) angle stringers approximately midway down the chine panel, near the waterline
    - Seats welded to gunwale panel approx halfway up (maybe a more-complex, but easier to fit detail here)
    - Decks of 1/8” aluminum; side decks extending outboard approx 2” , capped with a split pipe, inboard extending approx 6”, ending in a 1/8 x 2” coaming (to be “sheathed” with cedar). Occasional bracing from coaming to outboard edge of seats, to provide a continuous “box beam”.
    - Deck beams, other framing and stiffeners of 1x1 angle, improvising.
    - No deck hardware; detail stem and rails…

    Material: Any reason to prefer 5083? It is a bit stronger, but that wouldn’t seem significant in a boat of this scale. Waste: I am counting my pennies carefully, and laying out panels based on my supplier’s standard 6’x20’ stock; I think it will work out with very little waste.

    I’m not familiar with RhinoMarine, but have just downloaded the demo; Yes, it would be great to have parts cut (assuming that they’ll fit ;-) but I am not sure about the economics. Perhaps we can chat.

    Thanks for your comments, and I look forward to hearing more about your progress.

    Curtis Betts
    aka Sal's Dad
     
  7. wingsails
    Joined: Jan 2004
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    Location: Warialda Australia

    wingsails Kim Prentis

    I have built a couple of 16ft tris and a cat with aluminium and learned thru trial and error with a mig then took a tech course. The main problem of trying to use marine grade is that theoretically you have to use the same grade all over, including the wire/ filler rod for the mig /tig. Also the 25mm tubing and other sections that I wanted were not available in marine grade.
    However my tri was built before I had knowledge of such things and over the last 4 years has seen a lot of salt and inland waterways with no signs of corrosion at all, and I don't wash it down after use either.
    I pay Au $30 (about $22 US) for 25mm 3mm (about 1" 1/8th) wall tube which bends very nicely and is extremely strong. 25mm x 1.6mm doesn't bend so well but folds.
    Cutting is done with a 4" angle grinder with a new type of thin disc, check local hardware store.
    You seem to be overdoing thicknesses though. You would be amazed at how thin commercially produced boats are though. I was told 3mm to 6mm on the bottom but after repairing a few small runabouts for locals found 1.0 to 1.2 to be the norm. I used 1.6mm on mine and they have found large rocks etc with zero damage.
    Hope this helps, Kim
     

  8. wingsails
    Joined: Jan 2004
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    Location: Warialda Australia

    wingsails Kim Prentis

    This tube price was for a full 6.5 meter length (around 20 ft)
     
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