Alu or steel construction for small SY?

Discussion in 'Materials' started by Sim Phil, Nov 26, 2018.

  1. Sim Phil
    Joined: Nov 2018
    Posts: 1
    Likes: 0, Points: 1
    Location: Stocholm

    Sim Phil New Member

    I have built a few small wooden boats and repaired bigger, and I do not know steel or aluminum very well. My purpose is to buy about 28-30 feet of steel / alu boat hull and finish it by myself. I have not received enough information about the advantages and disadvantages of aluminum and steel, and I try to ask about this. Boat manufacturers praise their own material but I have not received any objective information.

    I'm interested in alu hull, but material is here in Scandinavia is a bit more unknown than steel. I do not know what word it is in English, but aluminum becomes weak when it is Stressed (fatigue of alu?). Is this a problem with sailboats?

    The aim is to sail with higher latitudes.

    This whole case and question is very wide and the question is short, but it's good to start somewhere :)
  2. Ad Hoc
    Joined: Oct 2008
    Posts: 7,435
    Likes: 1,317, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Hi Sim Phil

    There are so many inputs into steel v aluminium it is very hard to generalise. However, I shall attempt to provide a quick one for you:

    Steel weight = twice as much as an aluminium hull. That means for the same draft your payload will be less, or if you let the vessel sit on a deeper draft, will go slower.
    This also means the lightship will be less in aluminium = easier to move about on land.
    In scandinavia, aluminium is very well used, so, the skill set is there and availability.
    Steel is much cheaper than aluminium
    Don't need to paint aluminium, steel requires endless maintenance.
    Aluminum corrodes if the detail design features are not taken into consideration at the design/procurement stage.
    Aluminium has very good notch impact energy values, that means down to roughly -200c aluminium bhevaes the same as +20c. Steel is poor and degrades below 0c, unless you get a different grade of steel.
    Aluminium is known for poor fatigue behaviour, but like the corrosion, if understood it can be 'designed' out to the point it is not an issue coupled to good quality fabrication that compliments the fatigue design.

    These are just a few as I said many things to consider.
  3. M&M Ovenden
    Joined: Jan 2006
    Posts: 365
    Likes: 80, Points: 38, Legacy Rep: 527
    Location: Ottawa

    M&M Ovenden Senior Member


    28-30 seems a bit short for steel, unless it's very heavy displacement hull. I think steel starts looking good as a material in 40ft boats or so.

  4. Barry
    Joined: Mar 2002
    Posts: 1,673
    Likes: 387, Points: 83, Legacy Rep: 158

    Barry Senior Member

    For the length of boat you are considering, aluminum would be the best way to go and you will find many articles on the net to support this statement. If you search under
    Aluminum Boat Design, you will find that many of the worldwide aluminum boat manufacturers will discuss this very topic, Steel vs Aluminum to help guide your decision.

    Of extreme importance are two points
    1) proper design to limit future problems
    2) competent fabrication processes to ensure a long lasting boat

    Look at a current thread running right now, "Cracks ion (on) Aluminum Hull: Reinforce or Not" to see an example of a poorly designed and poorly welded/fabricated hull and
    the problems the owner is having now. Had the original boat builder followed proper design and fabrication procedures, the owner would not be looking at a sketchy fix at this time. The actual cost of doing the job correctly, (besides hiring a welder who was capable) in material might have been under $1000.
    Aluminum boat building is strong in the Pacific Northwest area of North America and there are thousands of aluminum boat that are standing the test of time without issues.

    If you decide to purchase a hull, ensure that the hull is of proven design with a high quantity of boats in existence for many years. You risk a higher expense later if you purchase a boat
    hull that is unproven

    A few other considerations are fitting out the boat. Contact with dissimilar metals, you cannot just attach bronze/brass attachments to the hull due to corrosion issues. At high latitudes,
    you will need to insulate the boat and there are ways of doing this properly. As AH mentioned above, twice, the boat has to be designed properly for corrosion issues and fatigue resistance

    A couple of books worth reading Boat Building in Aluminum Stephen Pollard and Aluminum Boat Building Eric Sims. While their focus is design/fabrication they have references to other aspects of finishing and mechanical installations. Additionally there are several fine books on fitting out boats.

    Aluminum and Steel, one designer's view - Ocean Navigator - July/August 2007

    Some links to some discussion on this topic can also be found in this Forum as noted below "Similar Threads"

    A fitting out process on a boat is a complex process. The mechanical systems that we take for granted in our homes, and at comparable low cost, need more elaborate mechanization in a boat. Pumps to provide water for a head, sealed discharge and inlet valves, holding tanks, discharge pumps. Freshwater holding tanks, black water holding tanks, the list goes on.

    The set of regulations or standards for small craft in North America is consolidated in the ABYC manual, that discusses the various components and the proper standards.
    At over 2 inches thick it is thorough but it provides the most comprehensive look at any of the systems . For example the section on even the construction
    and installation of a fuel tank, an important boat component, is several pages long but discusses types of acceptable fittings, fuel line routing standards, grounding, corrosion considerations etc. You might find someone who has a used set to save some bucks

    Certainly in Sweden there will be another set of standards. I would check out a library to at least view either of these books.

    The high price of these books might make you omit purchasing them so consider this:

    1) If you want to insure the boat, you may need a survey. If you have incorrectly installed a system or two or even say used the incorrect type of wire, different in a boat than say an automotive application, you may not meet the requirements to insure your hull or have to redo, at great expense, some aspect of your installation

    2) Without this type of technical information, you might use non-marine techniques in your mechanical systems that could lead to expensive fixes down the road or life threatening failures
    or at the least major trip failures

    3) Having such a set of standards will answer probably 90% of questions that you will need answered and ensure if followed that you will have a reliable boat

    Saving several hundreds of dollars on such a text or set of standards and not buying one, WILL cost you much more money than just writing the cheque. Additionally, they will save you much frustration in trying to figure out the best way to move forward.

    "Pay me now or pay me later"

    PAY 400 plus US dollars equivalent NOW (and maybe in Sweden they are cheaper) or perhaps PAY several thousands of dollars LATER
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.