Good plan for first build

Discussion in 'Metal Boat Building' started by yaplej, Jun 19, 2007.

  1. yaplej
    Joined: Jun 2007
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    yaplej Junior Member

    So if I wanted to build a steel boat I would have to use 1/16" sheet? I found this artical on welding thin sheet, but it has a lot of terms that I just dont know. Ill keep it around it will probably make more sense after I take the welding class.
  2. timgoz
    Joined: Jul 2006
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    timgoz Senior Member

    If they teach, and you show a proficiency in, aluminun welding, I'd go that way for a dinghy/skiff sized boat. That is if you are set on a small metal boat.

    Only the smallest steel boats would use 1/16'. You are contemplateing one of these small (12") boats. If you do succesfully weld one up, you will have to be extra careful with your coating system and attention to detail. Sheet that thin can corrode in a hurry. For small skiffs aluminum is hard to beat.

    Check out Wynands steel boat site and Kanstens (sp?) Marines web site on aluminum construction.

  3. yaplej
    Joined: Jun 2007
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    yaplej Junior Member

    Iv pretty much been stump-wooped away from the idea of making a small steel boat. I just thought it would be difficult to start welding aluminum right off the bat, but it seems like with all the complications of building a small boat from steel learning to weld aluminum would probably be the better route.
  4. Gilbert
    Joined: Aug 2004
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    Gilbert Senior Member

    Steel's ok, just learn to weld first

    With steel there is nothing wrong with your first boat being a big one. You just need to learn how to weld before starting. You can learn on scrap steel, it may take a lot of scrap steel and a lot of time too. While learning you should cut your beads to find out how good your weld was. Unless you have sofisticated weld inspection equipment and know how to use it, that is the only way to tell how good your welds are.
    But you have arrived at a good approach to use aluminum if your immediate goal is to build a small boat. Aluminum is better suited to small boats than steel.
  5. SkipperSki
    Joined: Sep 2007
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    SkipperSki Junior Member

    I think a better hobby both for time and money, would be fishing in a slightly larger Aluminum 12 to 16 foot already built BASS boat or Vee-hull skiff.

    While you take classes in welding and blueprint reading at the local C.C., and loan out boat building books from the Library.

    IMHO, your first boat should be a Plywood Skiff, or Dory 14' or larger. Go to a local boat store and sit in a 10'-0" row boat, and you will see just how much room you have to fish in, let alone room for a fishing buddy, tackle boxes, coolers, fishing poles, landing net, outboard/gas can, or trolling motor and 12-Volt Batt. etc. etc.

    Check out; or

    And post what you think of them.
    Last edited: Sep 9, 2007
  6. Geoh
    Joined: Jan 2007
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    Geoh Junior Member Good site for beginning builders stitch and glue not metal but looks like an easier place to "get your feet wet"

  7. tevhit
    Joined: Sep 2007
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    tevhit Junior Member

    1/8' or 3mm.of steel thickness.isn't it to much.?
  8. marshmat
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    marshmat Senior Member

    I gather that the hobby is as much about the fun of learning new skills and building something, as it is about being out on the water.
    I'll be honest with you- I can only think of two welded steel boats under 17 feet long, that I've seen around here. Both designs are heavy, working boats (one's pointy-bow, one's square-bow) designed to carry a whole lot of rock/lumber/concrete/gear out to do maintenance on docks, etc. The vast majority of small metal boats these days are sheet aluminum, fastened with rivets in a mass-production factory.
    It was mentioned earlier that the boat was to be handled by one person. Does this mean that one person has to be able to lift it out of the water and manhandle it around the landing? Or that one person can comfortably handle it on the water? If it's the latter, I'd suggest thinking slightly bigger and more seaworthy- which, interestingly, will probably be easier and less frustrating to build (because of more gentle bends and curves, thicker metal, etc). Aluminum is somewhat harder to weld than steel (I haven't learned how yet, but from what I've been told one of the biggest problems is learning how to select the right wire and gun types for the particular variety of aluminum being welded), but I think it'd be the better choice here- a thin steel plate will burn through before you know it; if not, it'll rust through instead.
  9. PAR
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    PAR Yacht Designer/Builder

    I designed a small metal boat a couple of years ago (21' on deck, 18' LWL) and these issues came up. In the size range you're looking at, riveted construction with "braked" reinforcement is the logical choice. The client insisted on welding as his son was an expert. We selected aluminum, because the weight penalty after you account for corrosion, made steel too much of a burden for this small craft. After some discussion about distortion and the thinnest that could be reliably welded, 12 gauge plate was used, which is just a tad thinner then 1/8". Because of the thin plate, stringer and framing spacing was rather tight, but it's a light and sound structure.

    Frankly, you need to develop a well burdened hull form (fat) for steel construction, especially in the thicknesses you're wondering about and the size you're looking to build. Typical steel hulls for this size vessel would be 16 (.0625") gauge, which is very difficult to weld without considerable distortion, closely spaced internal structural elements and a carefully designed welding schedule. In this gauge material you'd have limited puncture and little corrosion resistance. Aluminum would have similar difficulties, with less puncture and more corrosion resistance. It would be much wiser to rivet these thin sheet metal hulls then weld. Riveted construction is well established and proven, with many tens of thousands of examples around the world.

    Your first course of action should be to study the design of boats much more intently. Next up would be the general construction practices used in the boat building industry. For a metal hull, you should have some experience engineering around the common pit fails and trouble spots inherent with metals. Once you've absorbed the information necessary, then you can begin to tinker with a design of your own and expect good, safe results. Pick up the book, "Elements of Boat Strength" to get yourself started understanding what goes into a metal boat.
  10. theoldwizard
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    theoldwizard Junior Member

    The problem with aluminum is that the initial cost of the equipment is high and poor technique will give you poor results.

    Someday :rolleyes: I would like to build an AL alloy power catamaran. I know I need to take to take a couple of classes in metal fab and welding first and it will take many hours of practice to do a good job.

    Many aluminum boats are now built similar to "stitch and glue" plywood methods. Large pieces of AL are laid out and cut following precise templates. After joining at the keel, the bow is pulled together and welded. This works with AL because even at .125 it is much more flexible than steel.
  11. kmorin
    Joined: Apr 2005
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    kmorin Senior Member

    First Boat- Metal or Wood?


    I agree with the posts here about building a first boat of welded aluminum being more difficult than wood. Not only is the cost of solid MIG & TIG equipment high compared to wood working tools, the learning curve is pretty steep as you've heard.

    Learning to weld AND build at the same time can be expensive. A stitch and glue wood project could be used to help understand sheet built boat methods even if you're not using a 'hot' glue gun.

    While a welding course is a good way to get some arc time in the hood, you're still along way from boat building quality when you get out of the usual level of instruction in Vo-tech classes. So you'd want to budget several hundred hours and a few rolls of MIG wire, and several bottles of Argon to post-weldclass practice.

    If you do decide to build in welded aluminum after getting some experience with aluminum welding, you'll find out about the difficulty of welding thinner material usually associated with smaller boats; say under 16' LOA.

    So there is a rock and a hard place in beginning to build in aluminum- small affordable projects are best built in materials that are thinner than larger boats- but..... these thinner materials are much more difficult to weld- well.

    That means while the new builder is least experienced in overall building - but specifically in welding lighter materials: you'd be called upon to have a HIGHER level of skill. So if folks recommend you build an 18'er or larger skiff for an initial project, that's really pretty sound advice since that skiff will usually have 0.125" material as the lightest part. This can be welded with good results using 0.035" or smaller wire and is very controllable for distortion.

    Even if it may seem that it makes no sense for someone to suggest you start with an 18' or 22'er- the welding conditions there are more forgiving, by ten times, than on 0.100" or less. It may seem logical to build an 8' dinghy or pram to start, but I'd suggest that isn't the case.

    On the other hand....

    If you were to learn to weld then bought some scrap 5052, 5086, & 6061 (extrusion drops) you could train yourself to weld as thin as 0.040" using 0.025" wire with today's pulse welding MIG power supplies.

    I'd suggest a flat bottom power skiff as a first boat. I'd base the chine to chine width on the existing sheets regularly milled so the bottom becomes 4', 5', 6' or 7' wide as all these are "sheet sizes". This material can be 1/8" thick or heavier for a beaching work boat.

    Then, using a pair of 4' wide x 20' long side sheets you'd be able to cut the shape of the sides of 1/8" with plenty of flare in the bow 1/3 of the hull shape. The transom can be the same thickness with stiffeners to hold an outboard.

    This simple flat bottom shape skiff will go together easily, and you can weld it with 0.035" wire with a minimum of practice. The chine weld's parent material are at enough of an angle to support each other in contraction so the skiff will most likely be fair when you're finished helping to keep your interest, and allowing you to sell the skiff.

    While there are some matters of caution like spending the time to learn to use relatively expensive MIG equipment- with reasonable research and practice; I'm confident this class of skiff would be the best 'first boat' in welded aluminum.

  12. tevhit
    Joined: Sep 2007
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    tevhit Junior Member

    Thank You Sir...

    THIS BOAT WILL BE 12/14 BY 6.5 meter.AROUND 4000Kg.
  13. DanishBagger
    Joined: Feb 2006
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    DanishBagger Never Again

    First off, there's no need to SHOUT! So please remove the caps lock. If for nothing else (disregarding it reads as if you're shouting), writing in all-capital makes it very hard to read - not least for people that have a hard time reading to begin with, be it dyslexics or others.

    Chloride? I didn't know you were to drop the boat into a swimming pool?

    Aluminium will do fine in a salty environment. Why would it not?

    If you want to see something corrode very fast, try having 316-steel constantly submerged in salt water.

    You're wrong, but by all means try it. If not, then try looking up (on google, teoma or another search engine): "Crevice corrosion" and "oxygen starvation". You'll be surprised.

    From one non-native english speaker to another: There's nothing wrong with your english – However, the SHOUTING GETS TO ME!!
  14. theoldwizard
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    theoldwizard Junior Member

    With the proper anodes ! :D

  15. marshmat
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    marshmat Senior Member

    The chloride that gives us trouble in the ocean is sodium chloride, which forms about 80 to 90 percent of the salt content of the ocean. (Most of the rest is magnesium sulphate and calcium/potassium salts.) Hence, a concrete suitable for maritime use is rated for "C-1 chloride exposure".
    Swimming pool chlorine is usually some combination of sodium hypochlorite, trichloro-s-triazinetrione, and trichloroisocyanuric acid. In these, the chloride ion is locked into a compound ion structure containing oxygen. They can be quite vicious in attacking metals, but the concentrations are vastly lower than the concentration of salt in the ocean (pool chlorine is kept around 1-2 parts per million, or about 0.0002% active chlorine, seawater is anywhere from 3.5% to 5.5% sodium chloride).

    Aluminum, anodically protected by a piece of magnesium or zinc, does just fine in high-chloride environments. Aluminum boats are often left unpainted apart from an (aluminum-compatible) antifouling coat; they require virtually no hull maintenance in this condition. Hauling and repainting is only required when the topsides are painted for aesthetic reasons, or when the antifouling craps out.

    Stainless steel is not, in fact, corrosion proof. It gets its low-rust properties from the film of chromium oxide that automatically forms on its surface when exposed to oxygen, and protects the metal below from electrochemical attack. Deprive it of oxygen, ie. in a crevice or crack, and this oxide does not form. It is then just as vulnerable to rust as plain, uncoated mild steel.
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