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Aluminium, Fiberglass, Steel or Wooden Hulls?

Updated: Mar 28, 2023

So we have a yacht design or two and are contemplating building your dream explorer yacht.  Now just what are you going to use to build it? Always assuming that is not already decided by the naval architect.

Wooden Hull

Let’s get the easy one out of the way.  I’ve owned a wooden boat, 25-foot carvel built, larch on steamed green oak frames, lug rigged of 1919 vintage.  Romantic but an actual pain. Scrape paint, scrape paint, leak, caulk repeat —no more wooden boats for me though there are those more patient types who will go this route. It’s a very forgiving and pleasant material to work with.

Fiberglass Hull

How about glass fiber or its derivatives?  It is frankly quite hard to beat for series boat production, especially if the yard knows their business and uses decent polymers.  True, they can suffer from issues, but there again, some of the best mid-sized motor yachts on the market (Fleming, Hatteras, Cheoy Lee, Ocean Reef, Nordhavn…) are glass fiber of superb quality.  It would help if you had a mold for the big boats; it’s of little use as a one-off.   Unless you like wood substructures, but I think you already know my feelings on that score.

Steel Hull

Steel – that is truly wonderful stuff. Cheap as chips, weldable and available worldwide.  In my years in the UK Merchant Navy, everything I sailed on was made of steel.  Mostly welded, some riveted, but that’s another story.    On ocean-going merchant vessels, you can get a little clever with steel.  They use high tensile variants to reduce the scantling thicknesses, cost, and weight.  What kills it for the smaller craft is corrosion or, better said, corrosion allowances.  It’s not the overall deterioration that takes a slow toll. It’s the crevice corrosion caused by pools of stagnant water and gatherings of anaerobic bacteria.  Those sulfur-reducing beasties can drill holes in your vessel in a matter of months.  Think bilge and the bottom of fuel tanks. Enough of a hole to be a nuisance and to cause a drydocking or two in its lifetime.  Steel has its supporters; it’s tough, cheap, malleable, forgiving, takes knocks, and scrapes like no other material.  Some builders use a combination of steel hull for cost and strength then aluminum superstructure to increase stability. Less weight up top, increases the metacentric height. See two 24m explorer yachts from designed Knud Hansen and built in 2018.  In our search, we looked at steel yachts from the Turkish yard, Bering. They make a beautiful product once faired and painted. Many Dutch yards also go this route – think Steeler and the likes for good seaworthy vessels.

Aluminium Hull

Now for the finale.  Aluminium.  Yes, I spelled it right, it’s the Americans who can’t.  It’s a lot more expensive than cheap old steel, but there are some superb mitigating factors.  Price is based on weight, but it’s about ⅓ of the density.   Balance this with its strength, meaning 1.25 to 1.5 times the thickness results in the same strength as steel. This goes a long way to balance the cost.   Some additional benefits go further towards mitigating the costs.  It’s easier to form, bend and persuade into shape.  Welding, even at increased thickness, is much faster.  It is less resistant to abrasion though I’m not sure how important this is unless you are a very poor navigator. Its none magnetic so does not interfere with Navigation equipment though you need to be vigilant for anodic corrosion from dissimilar metals.  It is more malleable than steel, so more likely to bend and deform than crack or rip.  It does not need painting if you appreciate the workboat look (my wife does not, its a bone of contention right now). There are also more Yards with the skill set to create in aluminium than to build in steel successfully.

I’m not inclined to form an opinion without attempting to understand the basic theory behind the position.  If you are similar, I’d recommend you purchase a copy of Dave Gerr’s book, “Boat Strength for Builders and Designers” – McGraw Hill – ISBN 0-07-023159.  It goes a long way in explaining why most explorer yachts of our proportions, FPB, Circa, Arksen …. are made of marine-grade aluminium with over-specified scantlings. The end result being the crew has a less worrisome night.  Happy reading! 

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