A sure way to start a fight on a boating forum is to ask what the best boatbuilding material is. If you do, you’ll likely be rewarded with a drawn-out battle between the metal-heads, the wood lovers and the plastic addicts, running to hundreds of posts before getting either modded or Godwinned to oblivion.
The reason nobody ever gets a clear win in these fights is because there is no generally applicable right answer. Most private vessels in the 20 to 100 foot range fall very near the balancing point where you could get excellent results in aluminum, fibreglass or wood composite, and a significant fraction of those boats could be built equally well in steel or in traditional wood methods. What really matters is whether it’s designed and built correctly—it’s quite possible to build a modern ultralight ocean racer out of wood, and it’s quite possible to spend a few million dollars on a wallowing pig made from the finest aerospace composites.
That being said, there are quantitative ways to compare the structural properties of different materials, and we’ll look at a few of them today.
Great post, Matt.
And proof yet again (as you point out) that it’s the design and build process that makes all the difference.
I’m looking forward to the future posts already!
Best wishes
Colin
Matt, Nice analysis, well presented, and it is a help to have the comments about different materials side by side. I am continually impressed by how often these discussions come down to the skill of execution rather than outright choice of material and I suspect most of the bar-room controversy stems from this source rather than materials. As you say, materials reveal themselves clearly while construction skill is often masked.
Dick Stevenson, s/v Alchemy, St. Petersburg, Russia
Dick & Colin – Thanks for the supportive comments. One thing I do see over and over again is that there are both great boats and terrible boats to be found in any given material; the deciding factor is whether the designer and builder understand that material.
A century ago, we wouldn’t have dreamed of making a 40+ knot powerboat out of nothing more than rubberized fabric, yet now we have the Zodiac Futura. Even twenty years ago, cross-linked polyethylene was something you used for tanks, not for complete hulls, yet today the Hobie Mirage Island trimaran is selling as fast as they can make it. You wouldn’t be able to duplicate either boat at home- it’s the hard-earned knowledge of how to design and work with these odd materials that makes these weird but wonderful boats possible.
Matt, thank you for the very interesting post… and putting your cards on the table. It may have been posted elsewhere, and I’ve missed it, but to see that you’re building a strip-planked wood/epoxy trimaran is most interesting. I think you’re daft[1], but it’s very interesting.
Justin C, by the sea.
1. If it’s just another Dragonfly then what’s the point, if it’s another B&Q then, Wow! WTF, good luck, and you kick ass! … but you’re still daft[2].
2. …’cos I can’t see the appeal – but what do I know, I want a moderate to heavy displacement cutter/ketch, and I don’t care what it’s made from (within reason).
Hi Justin,
Yes, the boat my wife and I are building is a wood/epoxy composite trimaran. Details here and build blog here. As much as I enjoy big boats and sail power, most of our favourite cruising grounds have low bridges, shallow rivers and long stretches of over-land travel to get there, so a trailerable powerboat is the way to go.
We chose wood/epoxy because that’s the method that Katy and I have the most skill in; the boat would work just as well in aluminum but I have yet to figure out how to weld aluminum without blasting giant holes through it. The boat could also be done in fibreglass and work just as well, but the tooling cost isn’t justifiable for a production run of one hull.
Bonjour
Cet article généralise la plupart des matériaux utilises dans la construction navale, a l exception du ferro- ciment ( qui a été abandonne)
C ‘est difficile a comparer sans inclure les techniques de fabrication qui doivent être appliquées dans les règles de l art
En fait je rejoins l analyse de l auteur de cet article , il n y a pas de meilleur matériaux mais du savoir faire dans chacun d eux ?…. D Faivet
Mon français est quelque peu défaut, ça vous dérange si je réponds en anglais?
It is interesting that you mention ferro-cement. Of all the possible materials, this one- more than any other- depends on the skill of the builders. Ferro done properly is virtually invincible; ferro done badly self-destructs in a few months. The difference is so great that attempting to quantify and publish the properties of the raw material is an almost pointless endeavour.
Is there to anyone’s knowledge someone who’s tried wood laminate layered with fiberglass mat in epoxy? By that I mean a veneer of wood, a layer of mat, then wood, then mat etc, etc? Maybe I’m missing a major weakness to that method but it seems to me that it can’t be that far fetched. What if a thin layer of mat was woven with veneers and crossed diagonally, would that benefit somehow a cheaper build cost with added strength? I’m just throwing ideas, maybe worthless I know.
Ken,
The trick when combining materials is to get them to carry the share of the load that you want. To carry any load, a material must deflect. Therefore, you generally need materials with similar values for Young’s Modulus if you want to be able to distribute the load between them. If one material is much stiffer than the other, it will carry basically all of the load until it yields.
Another thing is as Matt pointed out, the bigger the structure, the more load it can carry(for example an I beam). Designers generally try to put two strong materials at the extremes then attached them together with something very light and less strong. Balsa cored hulls are a perfect example of this and they work really well provided that no water gets in. My first statement still applies to these hulls as the outer skins carry the vast majority of the load.
I do not know of anyone trying what you describe but someone may have done it. I hope that this makes sense and is helpful.
Eric
Exactly right Eric
Putting matt in between layers of a cold molded hull would simply weaken it on a weight basis by adding excess resin on the neutral axis of the quasi-beam structure where it contributes little to stiffness. At the same weight it would end up being thinner and thus less efficient in bending stiffness.
One point: balsa cored hulls produced by epoxy resin infusion are no more susceptible to damage from water intrusion than foam cored ones because each individual balsa block is isolated by an impermeable epoxy resin barrier that precludes moisture migration. Precisely because of this resin absorption into the core they are substantially heavier than an equally stiff foam core structure.
Excellent point about the balsa, RDE.
End-grain balsa core got a pretty bad rap in its early days. If you just stick it in by hand and glass over it, you leave huge air gaps that are an open invitation for water damage to spread. Now that the industry’s figured out how to infuse the resin under vacuum, the balsa blocks get nicely sealed up in resin with no air voids.
Ken- I like how Eric and RDE summed up the issue with a mixed laminate like that. An alternating wood/glass/wood/glass laminate could be pretty durable, but it’s not an efficient use of the materials. You can get a stronger, stiffer structure for the same weight and cost if you put all the wood in the middle and use the fibreglass for the outer skins.
There is 1 yard in the Netherlands that I know of combining wood and fibers in that way. “Waarschip”, see: http://www.waarschip.com/new/, has been building plywood boats for over 50 years now. I think it was in the early 90’s when they started advertising that they could build their boats with Aramid reinforced plywood. It was a plywood type with a thin aramid sheet between the individual layers of wood.
One of the things you run into when designing a boat, is minimum plate thickness or slenderness of structures. For steel, you can’t go thinner than 3mm in order to weld it properly, that is a lot stronger than you need for a deck plate for example, but you don’t really have a choice. For aluminum, the same story, welding thinner material than 4mm is going to be problematic.
Plywood boats are a lot stiffer than you need for a boat, because you need a minimum thickness for your impact resistance. “Waarschip” introduced the plywood-aramid plates for this specific reason, the plywood only has half or a third of the regular plywood thickness, but due to the aramid fibres, a better impact resistance compared to the regular plywood previously used.
With this method, they successfully reduced the weight of their plywood boats significantly while maintaining a great hull stiffness, and a more than usual impact resistance.
When I was attending university (Naval architecture), I’ve seen some comparative lab tests of this plywood and regular plywood, and it impressed the living h#ll out of me I must say.
Unfortunately, the yard went through several bankruptcies, several restarts and several owner changes in less than a decade, and the aramid-plywood does not seem to have survived these changes.
Too bad, it was a really great yard, my brother still owns one of these boats, very low maintenance, and virtually indestructible. For reference: his Waarschip 1010 is 34ft and weighs only 2100 kg including 1000kg of cast iron keel and has been hard-raced (offshore) since 1983.
Best regards,
Erik de Jong
Hi Ken,
If you would like a more in depth expansion on Eric and RDE’s excellent replies, you might want to read this post by Matt that really helped me understand the issues in mixing materials.