Steel Sail Hull - Hidden Costs?

Discussion in 'Metal Boat Building' started by metalsailer, Jan 20, 2022.

  1. metalsailer
    Joined: Mar 2019
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    Location: East Coast, USA

    metalsailer Junior Member

    Price of steel plate (5 mm) for something like a Tom Thumb 24 seems to cost much less than marine grade plywood. However, I know there are other costs such as surface prep and proper coatings for steel. Anyone have experience with cost comparisons between steel vs ply hull?

    I would assume from hull to full boat would be about the same cost for either.
  2. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    If you are also capable of welding aluminium, I think that I would be looking at building the boat in ally rather than steel.
    I do not have any comparisons between steel and plywood, but I was able to compare steel and aluminium re two power cats that we built 20 years ago.
    The aluminium was more than twice as expensive as the steel to build, but the difference was reduced substantially once I had taken into account the cost of blasting the steel, and multiple coats of good quality paint applied (not to mention the need for regular maintenance re more painting).
    Do you really want to use 5 mm thick steel for your Tom Thumb?
    That is going to be a relatively heavy boat for sure.
    I think that if I was working out scantlings in ally, I would be looking at 4 mm deck, cabin and topsides, 5 mm bottom, and perhaps 6 mm keel.

    But if I may backtrack a bit, once you build this boat what do you want to use it for?
    rwatson and Will Gilmore like this.
  3. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    It's very hard to make general statements since local prices and building systems vary to much. Comparisons should be made for a unit of surface area in finished state. For example one square foot of steel hull consists of: outside paint, primer, steel plate, steel frame/stringer/floor, primer, inside paint, insulation, ceiling. The plywood hull could be: paint/varnish, fiberglass (optional), plywood, wood frame/stringer/floor, epoxy (optional), inside paint/varnish.

    Beside basic material prices there are other factors involved. Plywood is noiseless construction compared to steel, this can express itself in money for a suitable building space. Lifting equipment or a crew are usually needed. Steel plate must be degreased and sandblasted, money if you have to tent the boat and hire a pro. Priming must be done immediately after blasting, if necessary the blasting must stop for priming, the pro must come two days instead of one. Alternatively one can use wheel blasted and preprimed plates (weld trough primer must be compatible with later topcoat and be protected during the build). Insulation can be mineral wool, sprayed foam, Armaflex. The ceiling can be solid wood, plywood, fiberglass, etc. each with its own finish demands.
    With ply you have a wide price range all sapelli with certification is much more expensive then domestic fir or indonesian meranti. Epoxy and fiberglass coatings can be required or not, and there is a range of prices for epoxy.
    Consumables and tools must be added for both methods, and steel additionally requires one to learn how to weld and grind properly.

    The only way to make an informed decision is by comparing two actual designs with your specific location, materials and skills. That beeing said, amateurs don't usually build in steel or alloy unless they also work with it professionally.
    rwatson and bajansailor like this.

  4. Will Gilmore
    Joined: Aug 2017
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    Will Gilmore Senior Member

    5mm does seem heavy for a 24 foot steel boat. I read an article about using 2mm, which seems too light, but I have no experience with steel, just a fondness for the idea of it. I struggle, conceptually, with the galvanic corrosion issues it includes.

    Most plywood construction today, includes a glass layer, although not strictly necessary. If you're thinking about steel vs wood, you are likely going to be in the glass sheath camp too.
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