Lightest Building Material

[Mat-C]

Leaving aside the 'exotics', what is likely to be the lightest building material?

There seems to be a number of powerboat projects around 30ft long discussed hereabouts. So, using that as an example - a 30ft powerboat with a top speed of say 25 knots, to be built as a one-off boat - which would be lightest?
Foam-core
Wood-epoxy (glass over ply, strip plank, balsa core)
Aluminium
Soemthing else......

[alan white]

Not getting into exotics, probably glass over balsa core or foam core. this will give a stiff boat hull, though not as tough and puncture resistant as plywood, but stiffer and therefore stronger for the weight if top performance is the desired result.
Then, quality of lay-up and vacuum-bagging count for a lot in terms of weight reduction.

Alan

[Mat-C]

That's what I would have tough too.
In The Nature of Boats, Dave Gerr suggests that a wood core - he talks about strip plank - might actually be the lightest and easiest for a one-off.

[Willallison]

There's a bit more to it than simply the lightest material. A strip plank boat will tend to have greater impact resistance than a balsa cored boat, which will in turn have greater impact resistance than a foam cored boat. And whilst the strip plank core itself is denser than either balso or foam, it requires thinner shins to give it strength and far less in the way of interior supporting structure - frames, bulkheads, stringers etc.

[frosh]

I tend to agree with Will on this one. You are not building a racing yacht so that practical considerations and costs are also important. This is not to say that light weight is not a worthwhile goal. It is, but it isn't the main thing for your project. My take on this is wood strip in cedar with biaxial glass both sides set in epoxy would be probably the best choice. It isn't the cheapest but it is much less than exotics and probably cheaper and more practical than a balsa core as well. Hey, it's your call, but consider all the important factors before deciding.

[Mat-C]

Thanks Alan, Will, Frosh.
I understand the differences between the materials and how they effect the overall structure. And yes - you are correct, the weight is not the only consideration (cost definitley comes into it...perhaps another thread...) But all else aside, I'm interested in the lightest overall structure for this (hypothetical btw) "project".

[alan white]

Strip plank is an excellent all-around one-off method. A balsa or foam core will generally be layed up inside a mold, which eliminates a lot of time gluing and fairing, but such methods require a mold and so favor multiple copies.
I don't know if foam or balsa core require more stringers or frames--- this may be debatable as strip-building might need frames more than stringers and cored may need stringers more than frames, and each design will be unique (for instance, certain furniture in a larger boat will provide both frames in the form of bulkheads and stringers in the form of berths, shelves, etc..
In a small boat, cockpit seats make stringers and so a cored hull might be lighter for its strength, while a kayak usually has full bulkheads and no long interior pieces and so favors strip construction.
Multi-chine plywood is another light and strong method, well suited to one-off. All of the methods mentioned use resin and cloth to achieve tensile strength, water-proofing, and bonding. In that sense, all are cored in principle. The exception would be plywood in cases where only the exterior is fully glassed.
Every one of the methods will produce a light and strong hull if properly designed and carefully built. Barring using exotic materials, I would say that without knowing which particular design was being analyzed, there isn't a very significant difference between any of them that would make one better in every boat.

[Raggi_Thor]

It's also a question of practicality.
I think you can save some weights with lots of frames (cnc cut) and a very thin skin (plywood). But it's time consuming, it's hard to keep clean inside, the skin is so thin it will puncture if you hit a sharp stone or a corner.

[War Whoop]

Originally Posted by Mat-C

Leaving aside the 'exotics', what is likely to be the lightest building material?

There seems to be a number of powerboat projects around 30ft long discussed hereabouts. So, using that as an example - a 30ft powerboat with a top speed of say 25 knots, to be built as a one-off boat - which would be lightest?
Foam-core
Wood-epoxy (glass over ply, strip plank, balsa core)
Aluminium
Soemthing else......

Foam core by a mile!