Characteristics of Boat Building Materials

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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.

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  2. Is It a Need or a Want?
  3. Buying a Boat—A Different Way To Think About Price
  4. Buying a Cruising Boat—Five Tips for The Half-Assed Option
  5. Are Refits Worth It?
  6. Buying a Boat—Never Say Never
  7. Five Ways That Bad Boats Happen
  8. The Two Biggest Lies Yacht Brokers Tell
  9. Learn From The Designers
  10. You May Need a Bigger Boat Than You Think
  11. Sail Area: Overlap, Multihulls, And Racing Rules
  12. 8 Tips For a Great Cruising Boat Interior Arrangement
  13. Of Cockpits, Wheelhouses And Engine Rooms
  14. Cockpits—Part 1, Safe and Seamanlike
  15. Cockpits—Part 2, Visibility and Ergonomics
  16. Offshore Sailboat Winches, Selection and Positioning
  17. Choosing a Cruising Boat—Shelter
  18. Choosing A Cruising Boat—Shade and Ventilation
  19. Pitfalls to Avoid When Buying a New Voyaging Boat
  20. Cyclical Loading: Why Offshore Sailing Is So Hard On A Boat
  21. Cycle Loading—8 Tips for Boat and Gear Purchases
  22. Characteristics of Boat Building Materials
  23. Impact Resistance—How Hull Materials Respond to Impacts
  24. Impact Resistance—Two Collision Scenarios
  25. Hull Materials, Which Is Best?
  26. The Five Things We Need to Check When Buying a Boat
  27. Six Warnings About Buying Fibreglass Boats
  28. Buying a Fibreglass Boat—Hiring a Surveyor and Managing the Survey
  29. What We Need to Know About Moisture Meters and Wet Fibreglass Laminate
  30. Offshore Sailboat Keel Types
  31. US$30,000 Starter Cruiser—Part 1, How We Shopped For Our First Cruising Sailboat
  32. US$30,000 Starter Cruiser—Part 2, The Boat We Bought
  33. US$30,000 Starter Cruiser—How It’s Working Out
  34. Q&A, What’s the Maximum Sailboat Size For a Couple?
  35. At What Age should You Stop Sailing And Buy a Motorboat?
  36. A Motorsailer For Offshore Voyaging?

Matt, Engineering Correspondent, is a Professional Engineer and true renaissance man, with a wide range of expertise including photography and all things boat design. He has a unique ability to make complex subjects easy to understand and he keeps an eye on the rest of us to make sure that we don’t make any technical mistakes. Working as M. B. Marsh Marine Design, Matt designs innovative powerboats of all shapes and sizes.

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Colin Speedie

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

Dick Stevenson

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

Justin Catterall

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).

FAIVET DANIEL

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

Ken Page

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.

Eric Klem

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

RDE

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.

Erik de Jong

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

John Harries

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.

RDE

In the spirit of never ending debate and casting stones into the den of aluminum true believers, (LOL) here is an example of long term success using steel to produce a structurally efficient mid-sized yacht that you can paint any color you wish.

http://www.gilana.org/ (the “boat” section)

RDE

Hi Matt,
There was a French-built Corten 45 footer abandoned at a storage yard for back fees here a while back. Had more than one rusted out plate section. So “better” materials are no substitute for proper construction methods. That said if I were building in steel I’d give serious consideration to using Corten, not only for its corrosion resistance characteristics.

The Waterlines method of keeping the stringers proud of the frames and only welding to the stringers is well worth consideration, whether the material is steel or aluminum. It is this technique that allowed them to build a very fair hull out of thin(er) high tensile steel.

Here is a photo of the owner’s personal 50 footer at the Seattle boat show a couple of years ago. It was ten years old at the time, and the adjoining boat is a brand new Oyster 56. Given the choice there is no question which one I’d take as a gift! http://www.flickr.com/photos/gsprangle/4513145333/in/photostream/

Marc Dacey

I don’t want to give the impression that I just want to garner hits here, but one of the reasons I like steel, despite its admitted shortcomings, is its ability to flex under impact.

Right after we bought the boat, the boatyard had a preventable accident and dropped out cradle with our boat in it off the trailer:

http://alchemy2009.blogspot.ca/2007/05/its-not-great-day-when.html

I hope not to hear that sound…like the lunch bell of Hades…again in our sailing career.

The damage amounted to a paint job. Close inspection and measurements revealed no cracking or deformation of the hull plate in question:

http://alchemy2009.blogspot.ca/2007/08/damage-report.html

I pass this on not to make a case for steel, but to illustrate that each hull material has its upside, and sometimes you get to experience this even when you’re not in the water! If I had the money, I would love to sail either an OVNI or Boreal or have built an “expedition grade” beauty like Peter Smith’s Kiwi Roa:

http://www.petersmith.net.nz/about/kiwiroa.php

I do think that a properly welded and maintained aluminum sailboat meets my personal needs for offshore cruising, with steel right behind it thanks the ability of even a novice welder being able to do temporary fixes in distant harbours, whereas aluminum welding repair is more complex a skill to master if one is not actually trained for it.

Fibreglass is great, of course, and is certainly popular, but I do not have confidence in the general quality of construction, having found voids and missing tabbing and insufficient or otherwise deficit layup in many modern production boats. Think of the reactive armour on modern tanks held to the chassis with a couple of tack welds, and you’ll find when I part with the marketing arm of modern boat building when it comes to carbon fibre this and bidirectional-glass that.

Marc Dacey

As someone who tries to indulge in illusions only on a recreational basis, I concur entirely. Steel must be properly prepared, and properly maintained, and the only way I know of, short of bashing holes in it, is to have it sounded for plate thickness and “wastage” by someone proficient in that skill.

I had a steel boat surveyor go over it very carefully when we bought the boat, and the comment at the time was “it’s amazing how well steel keeps out of salt and out of marinas”. Now I know what will dictate our maintenance regimen.

I look forward to your hull deformation post, Matt. All I have ever contended is that steel can buy you time if you hit a reef or a container or a larger sort of bergy bit: not that you’ll necessarily be able to save the boat.

RDE

Hi Matt,
Just speculating here, but I’d venture that the limiting factor for plate thinness in 4o—50′ yachts is not allowance for rust, but rather panel stiffness. You have to make a trade off between frame and stringer spacing and panel size, and with reasonable framing layout thin skins that are “strong” enough are not stiff enough to resist oil caning and are difficult to weld without distortion. It is for this reason that plate that is thicker than “strictly necessary” is chosen. The rust depletion factor as a controlling design metric is more appropriate for large ship construction where the level of paint and corrosion maintenance is typically much lower and plating thickness much greater.

Marc Dacey

Because I’m currently measuring for water tanks and because this is an unusually engineering-centric website, I’ll mention some measurements:

3 x ¼ inch flatbar hoop frames with floors – on 37 inch centres
1 x ¼ inch flatbar longitudinal stringers on 12 inch centres
¾ inch plate keel bottom
9/32 inch plate keel sides
10 gauge 1st bottom plate
12 gauge 2nd bottom plate
14 gauge topside plate
14 gauge deck plate
1 ¼ inch solid rod chine bars and transom edge
1 ½ inch tubing caprail
½ x 3 inch stembar
1 ¼ inch pipe rails and stanchions

This makes for a “half-load” weight of 29,500 lbs. in the slings. I expect a full load of 32-33,000 lbs. A lot for fibreglass, but actually “middle-middle” for a 41 foot steel cutter. I have a friend with a beautiful Goderich 40 ketch, designed by Bob Wallstrom when he worked with Ted Brewer, and it’s a 36,000 lb. beast…and yet sails very respectively.

It would be interesting, perhaps, to discuss the role of displacement in modern boat design. Lightness equals speed, but there’s often a trade-off in seakindliness. We were interested in independence from shore resources and less interested in making 200 NM days, so we went for steel. Others go for very lightweight boats as that is the fashion, as is the logic of “running off from the bad weather”. I got a boat that can heave to properly, because if I’m in a hurry, I should have bought a plane.

John Harries

Hi Marc,

Just one point on your lightness=speed equation. Yes, but only if the crew can take the strain. Our boat is mid to heavy displacement but we still regularly get to port well ahead of lighter boats simply because we can keep driving when the conditions get gnarly while the crew on the lighter boat is getting beaten up and is therefore slowing down.

Carina, three time winner of the Newport-Bermuda race, is no lightweight either.

Most amature crews will make faster passages in well designed moderate displacement boats than they will in light weight “flyers”.

Marc Dacey

I concur entirely, John, but if I hadn’t bought a bordering-on-heavy steel boat fit for purpose in 2006, we’d still be saving for a medium FG or “other” in 2013.

I’ve been in rough stuff on modern medium-displacement (Catalina 47) and heavy-displacement (Bristol 45.5) boats…I could actually sleep on the Bristol, even in 12-15 foot seas. The squalls woke everybody up, though. Seakindliness is in my view almost ignored in current boat design which is obsessed with speed in fair-weather conditions…meaning slamming in short seas and a very rolly downwind ride….errrp!

By contrast, our steel full keeler is very comfortable in rough stuff and we can heave to if needed with more alacrity than most current designs. If I was racing, I would have a different boat. If I was richer, I’d have an OVNI or a Swan 53 or even a Sundeer 64. But I wouldn’t mind a Waterline 50 if the lotto paid off…that’s very near my sweet spot of immaculate design in steel that’s still a go-fast, ocean-capable cruiser that’s just within the range of what a reasonably fit cruising couple can handle. Still, I’m happy with the cutter-rigged Land Rover at about one-eighth the price.

RDE

Hi John,
My turn for dyslexia. I read “amature” as armature and thought for a minute that you’d secretly become a fan of electric propulsion.
Richard

John doe

You should compare carbon fibre aswell.

It wins, hands down.

You can make a dtructure that withstand the needed strains and even flexibility in certain areas, by using CAD software and the component would be much lighter than any other material. If you just take a chunk of each material the same size, maybe not. Carbon fibre needs to be arranged to fit its purpose. Whereas a solid metal is uniform throughout, fibres run only in the directions you lay them.
Thats why they make race yachts from carbon and not steel. Faster and stronger.

John Doe
Composite boatbuilder

Homero

Dear Matt, John and Colin.
The subscription of your site was the best investment I made in the “sailing expenses” so far.
Because I can only dock a maximum of a 38 ft in front of my house, and because there are no affordable Boreals at 36-38 ft, I am thinking of building a Kiribati 36 from the Brazilian B&G Yacht Design.
Could you guys indicate some shipyards best suitable to building something like this in the USA or Canada : http://www.yachtdesign.com.br/ingles/projetos/ki36/desc34-1.php

The second question is: do you think it would compensate to built it in another country where the us$ exchange rate is more favorable (maybe NZ) and ship it back to Fort Lauderdale, FL (where I live) to be equipped? I am hoping this boat would be strong enough to sail from Florida to Brazil and then to Australia, and yet simple and affordable.
I apologize if this is not the right place to ask these questions. I could not find another place to pose my questions.
Thanks for the help.
Homero

John Harries

Hi Homero,

Wow, big question. I don’t know of any yards in North America that I could recommend for a one-off aluminium construction based on first hand experence. I have heard good things about Kantor in Ontario.

As to building in NZ and shipping back, I doubt you would save any money. Having said that, Kiwi boat builders have a great reputation so it might be worth considering it from that point of view.

Perhaps a bigger question is why do you want to take on a one-off build with all the attendant risks? How about just buying a second hand Ovni? The point being that one-off builds are very, very difficult to do well, even if the owner has years of boat ownership and voyaging experience. Correct me if I’m wrong, but I think this maybe your first offshore boat?

Homero

Hey John, Thanks for the tips.
Yes my first offshore boat…I could not find any Ovni with less than 10 years old, for my budget of 250 K in the USA. I found one in Italy , year 2000 for 252 K.
That is what motivated me to investigate one like the Kiribati 36, which should be much less than 250 K and new. If you compare the specs, the Kiribati has much more tankage then the Ovni.
Other than a new Ovni for $300 K+ I could find no other manufacture that build strong small ( less than 38 ft) aluminum boat.
I will keep investigating.
Thanks, John.

Wyn Folsome

I am surprised that I this blog that no mention of Ferro Boats are made.
A properly built Ferro boat is way stronger than fiberglass, doesn’t delaminate, blister. Doesn’t rust like steel. Doesn’t have any problem’s that are part of a wood boat. No issues that occur with aluminum boats.
And is very easy to do repairs due to the frame, structure.
But as brought up they must be properly built to start with. Our Samson C Lord was built in Vancouver Canada in there yard, and has always been a great boat. Very stable and quite fast ( 13.8 kts )and we weren’t even trying.
Point being……. Ferro Boats have been around longer than glass boats and should be in included in your material type of construction.

Marc Dacey

Wyn, I considered ferro early on. I have seen good examples. But, as with home-built steel of the Roberts design type, I have seen absolute disasters fit only for making seawall bases. So much depends on the skill and preparation of the builder, and this has been lacking in so many cases that they are just about uninsurable, and today are a niche boat-building material, much like the copper-alloy boat I’ve read of from the Sixties that is “self-anti-fouling”. I can only assume that the alloy or the welding of it was too daunting for such an otherwise worthy material to pursue in production building.

John Harries

Hi Wyn,

Actually, we have discussed ferro boats here.

Andre

Environmental update. We have 2 boats to get rid of at our local marina:
-One ferro ciment that is no longer insurable and since our policy is that all boat have at least 2 M$ civil responsibility, the poor owner has to get rid of this boat. (38 feet)
-Another small 25 feet polyester boat (fiberglass) that the owner has disapeared without paying is account.

Guess which one is easier to get rid of ? Well it is the ferrociment. It will be demolished by an excavator in about 1 hour and put in a container. Cost for getting rid of it 200$

Now the polyester boat. The local (city ran) incinerator doesn’t have the right to burn it. The city garbage disposal doesn’t want it. The recyclers don’t want it. Officially we have no place to get rid of it locally. We don’t have a solution and it is more and more embarassing.

The point is, with environmental requirement getting more and more stringent, do not be surprised to see one day either a carbon tax or an environmental tax appearing on GRP or any plastic, kevlar,carbon related new boat.

(wood, aluminum, steel and ferrociment) are fully recyclable…

Marc Dacey

Take off the deck, remove the keel for lead scrap, cut out the stern for a door, and strap the upside-down hull to a cinder block base (called breeze blocks in the U.K.). You now have a useful, six metre shed.

Paul

Hard on rocks means hard on the crew. I spent a few days with a professional fisherman who, on turning 50 got rid of his steel long-liner and bought a 30 ton, 46′, 80 year old wooden boat. His first specification for the new boat was that it be wooden. He was fed up with how hard steel is on the body. I expect aluminium would be the same. Something to add to the material decision matrix.

John Harries

Hi Paul,

I too have heard Maine Lobstermen say the same about wood over GRP. That said, I think it’s a matter of hull form. For example I have never found a boat that is easier on the crew than our own aluminium M&R cutter. And the reason M&R boats do so well in ocean races is that the crew can keep driving hard long after crews on boats with hull forms that produce worse motion have had to ease up.

Paul

Doubtless hullform is vital to comfort. However virtually any hullform can be built in any material so it scarcely informs the material decision (although the uncomfortable beamy lightweights you mention would be difficult to achieve with steel.)
What my fisherman friend spoke of seemed to have more to do with the deck and interior. The things you brace yourself against and bump into are more forgiving and less cold if made of wood. They edges also tend to be more generously radiused in wood construction.

John Harries

Hi Paul,

Hum, most metal boats have wood interiors, so I’m not sure that makes a lot of difference. The Maine lobsterman I talked to said he liked the way wood flexed when slamming into waves, which softened the shocks on him, I can see that in his case, but on an offshore sailboat the last thing we want is hull flex.

Paul

And, while in the mood to provoke a known curmudgeon:
James Wharram insists on flexibility in offshore craft. ?

John Harries

Hi Paul,

For Wharram’s boats that makes sense. But having sailed offshore in an old soft fibreglass boat and a super stiff aluminium one I know which I prefer. Got more than a little tired of living on a boat that leaked through the deck like a sieve due to flexing making impossible to keep things watertight. Also lying in your bunk listening to the hull flex and wondering what is fatiguing is a lot less than fun—flexing leads to failures.

Paul

I guess an expensive cruising boat might be better lined than a commercial fishing boat inside. But outside where’ you’re already a bit cold and buffetted? Coamings, bulwarks, cabin top-side joints, companionways, hard dodger edges, toe rails, window overhangs, etc… all harder, sharper and colder on a metal boat.

Not saying wood’s good, metal’s bad. Just adding another factor to consider.

Paul

Yeah, good point about hull flex. My new friend’s 80 year old fishing boat had had it’s decks polyester/dynel sheethed at some point. But the sheething has cracked in a few places and there are deck leaks. And wharram’s hulls don’t flex, just the platform. Each hull itself is very stiff and tight.