I have a confession to make: I've run boats aground on several occasions. Granted, it's always been at dead-idle speed when poking up shallow rivers. And the damage, thankfully, has so far been limited to a few nicked propeller blades and shredded rubber hubs. But, despite all precautions, it happens. If we were to rank groundings and collisions on the scale of skippers' worst fears, I suspect they'd fall somewhere between an engine room fire and the pirates' scene from Captain Ron.
Hitting something in a well-built boat is usually survivable, but is still a scary and potentially life-threatening situation. In this chapter, we will take a look at how some common hull materials respond to impacts.
I thought we were talking about cruising boats here, so your comment: “It is for this reason that aluminum is the material of choice in the uncharted, rock-strewn lakes of Northern Ontario” leaves me a bit bewildered.
You see, I happen to come from Northern Ontario – and I can assure you, the cruising boats I see in the 30,000 Islands, Georgian Bay or in the North Channel of Lake Huron, are just about 100% fiberglass. Just like the cruising boats on the Hudson River and all the way down the US east coast in fact.
Now if you’re talking small boats, yes, there are lots of aluminum boats – 12 – 20 foot recreational fishing boats, and they are everywhere. That’s because about 90% plus of the boats made for this market are made out of aluminum due to the economies of scale and the fact they can be built cheaply, like the one in your photo – not because they are tougher. I tow a 12 foot aluminum as a dinghy, because of its durability and because I cruise some pretty remote places.
France, which has NO rock strewn lakes with cruising boats on it, is known for aluminum cruising boats however. For whatever reason, Europeans and especially the French, have accepted aluminum as a material for cruising boats.
No edit function, so I’ll add to my post here – the problem with aluminum is that it is very costly, especially in comparison to fiberglass. In part, that’s due to the availability of fg boats – there’s simply an awful lot of them.
Additionally, while accidents do happen, the likelihood of being holed is fairly low – and can certainly be made less possible with proper training and care while cruising. Does that nullify the advantages of aluminum? No, of course not, but essentially, the availability of aluminum cruising boats along with their cost, puts them out of consideration for most voyagers.
Hi Wally,
Many of the parts of Northern Ontario that I spend time in are more remote and farther inland than Georgian Bay. Most of these lakes and rivers are uncharted and unmarked, and hard groundings are routine. The materials mix on these waterways, in all sizes, is about 60% aluminum, 30% composite, 10% steel.
On the more popular, better-charted waters, such as the upper Great Lakes, we do see the same mix of materials as in any other area.
It’s a different environment than offshore cruisers, yes, but I think it illustrates the point; in areas where you know you’re going to be running aground on a regular basis, there’s a strong bias in favour of metal. That bias disappears if we consider more “normal” operation, where the boat isn’t bumping into rocks every week or two (or being dragged over them as part of routine use).
I grew up in Sudbury, worked as far north as Wawa region – so I’m familiar with the areas you’re talking about. Generally, locals are familiar enough with where they boat to avoid a lot of problems even on the unmarked lakes. A lot of the damage one sees on the bottom of these aluminum boats is from beaching them, or dragging them ashore across a rock bottom. Which, of course, makes aluminum a good choice.
Hi Matt,
as a steelboat owner I’m well aware that she has certain disadvantages when compared to the same boat in aluminium, the main and only worth mentioning for me being the weight issue. But I always thought I had an advantage when it comes to impact resistance, and I’m a bit shocked about this statement of yours: “Mild steel is somewhat more fracture-prone in impacts than marine aluminum, …” Isn’t it the other way round? Steel has a considerably wider range of flexibility than aluminium, so that it can absorb more energy by deforming itself before being fractured. I just assured myself that this is still the case at http://www.kastenmarine.com/alumVSsteel.htm
Hans, good catch; that section got switched around in the final edit and I evidently didn’t proof-read it well enough. (Original post has now been edited.) New, corrosion-free mild steel, of the grades commonly used for boatbuilding, is indeed somewhat more fracture resistant than 5000-series aluminum.
Steel does, however, lose any such advantage if you let it rust.
which of course I don’t. Thank you for the clarification. Otherwise it would have robbed me of my main argument in favour of steel. Its hard enough to drag around all that weight of a steel hull only 33ft. long, but being without argument is harder I suppose.
But tell you the truth: even the weight doesn’t bother me much. And the rust issue is almost non existing, provided there is good construction, proper insulation, a good paint system and some vigilance involved. It surely is as you say: Every material has its strenghts and weaknesses and , John, I didn’t accuse Matt of putting one material above the other. Thanks for sharing your knowledge.
Hi Hans and Wally,
I’m sure Matt will answer your questions and concerns, but I just wanted to step in here and point out that Matt has never said that one material is better than another.
In fact, in his last post in this Online Book his base hypothesis was that all the common boatbuilding materials have advantages and disadvantages and that any attempt to pick a “best” material is futile.
Matt is simply sharing his engineering training to explain what the trade offs of each material are.
Thanks for emphasizing that, John.
I do not have a preferred material and I do not think that any one common hull material is generally superior to the others.
The point of this little series is to better understand the trade-offs between the popular options and the factors that go into deciding what materials to use. I’m not trying to evangelize one system or technology over the others, only to point out that your own choices may be different depending on what qualities you consider important.
Hi this is interesting, i hava a quistion. What is the best material for a cruising boat if i want too go realy north and ice can bee suspekted (alminium?)
Trond
Where ice is involved, abrasion becomes a concern. This doesn’t completely rule out wood and composites, but it does put them much farther down the list than they’d otherwise be. Softer materials are more easily gouged and abraded by ice and debris.
Ice classed ships are almost universally steel-hulled; there are a few aluminum ones around, but steel’s hardness and resistance to abrasion make it the default choice for ice work.
Matt, of abrasion is a concern for using composites in ice-infested area’s, could this not be solved by using an outer layer of kevlar in the composite?
Regards,
Erik
Hi Trond,
I can jump in here. Having spent years in the north, much of it around ice, my thinking would be that aluminium (as long as only the bottom is painted) wins over steel for a high latitude sailboat that might push a bit of loose ice around but won’t be ice breaking, due to the fact that it does not corrode when the paint is abraded and that maintenance of an aluminium boat is much cheaper and easier than steel.
(It is interesting to note that both Skip Novak and Hamish Laird went with aluminium for their later boats after years of maintaining the first Pelagic that is built of steel.)
If you are going to break ice, then steel is the winner due to the abrasion resistance (as Matt points out), but very few yachts (none?) actually break ice, if for no other reason than that activity takes tremendous weight and size.
My personal preference for operating in ice infested waters is steel. If you were to build a vessel officially ice-classed and certified, aluminium would not even be allowed, and in my opinion for a good reason.
Both Mild Steel and 5000 series Alu will get bridle when exposed to sub zero temperatures, but for steel, there are special alloys available to make it “sub zero proof”, something that is much harder to achieve with aluminium.
Opposite to what John mentioned, I do not feel that steel is more expensive to maintain IF the proper paint was applied when the boat was built. There are special paints for steel boats in ice waters, and is generally sold under the name “ice-breaker paint”. I have sailed on Steel boats in icy waters since 1989, and own my own, specially designed and built, steel “polar boat” since 2008.
I personally would not consider any other boats but steel for serious cruising in the (Ant-)Arctic, especially if you consider spending some off-seasons there as well. Although this opinion is contradicted by a lot of highly respected sailors, including the people mentioned by John, and John himself.
Hi Erik,
All good points. Probably what I should have added to my comment is that its a close run thing between steel and aluminium. For me, it would be aluminium, for you steel.
I do stick by my assertion that an unpainted aluminium boat is the easiest and cheapest to take care of. Painting metal boats is very labour intensive, as I know all too well having lived with a painted aluminium boat for 22 years. And even with the best paint system in the world, you will be repainting every ten years or so.
I would also question the brittle from the cold assertion in that the water will be around zero until it turns to ice, and as far as I know aluminium does not experience any substantial brittleness at that temp. Matt?
We’ve been making commercial aircraft out of aluminum for decades, and they operate at -55 Celsius. The cold-weather properties of all common materials are pretty well understood; I think that’s a solved problem.
I can think of no fundamental reason why you couldn’t build an ice-capable vessel in aluminum. Steel is used because it’s known to work in this application, therefore there are very good design codes for ice-rated ships built of steel. An ice-rated boat will necessarily be quite heavy and so aluminum’s weight advantage is somewhat negated. So there’s been relatively little incentive to develop ice-class design codes in anything other than steel. I think that will change as the Arctic thaws out and the oil & gas guys move in.
There are already many successful mid-size yachts, built in aluminum, doing Arctic cruises; as long as the designer knows what to expect, it can be made to work.
Hi All,
For those that are thinking about the steel or aluminium decision, you may wish to read Colin’s excellent Online Book Why Not Steel, which clearly details what it takes to properly paint a steel boat.
For me at least, its a daunting prospect, particularly when you take into account that a paint failure on an aluminium or fiberglass boat is a cosmetic issue, on a steel boat it is, at least potentially, a structural issue—the stakes are high when painting steel.
Hi John, and thanks too all of the answers. I hope that i not will need too break ice, but too sail in to small ice that can bee poosh away, whith no damish on the boat, is what i want.
In my mind a sailing cruiser abaut 40 – 45ft, whith engine power only 50-75 hp is no icebreaker.
Do you, or anybody else have a tips for the best boat? Rigt now am i looking at some of the france boats. And i like too sail as fast as possible whith a cruiser (the normal thing).
Hi Trond,
If I were looking today for a boat to make the voyages we have made over the last 20 years the Boreal 47 would be at the top of my list.
there was an article in ocean navigator magazine at least 20 years ago that recounted the experience of a typical blue-water fg sloop about halfway between bermuda and virgin gorda barreling along one night and suddenly crashing into something unseen that brought everything to a screeching grinding halt as if hitting a brick wall…the crew had barely enough time to escape with their liferaft before their main life raft (sloop) sank…they never saw any trace of whatever they hit…the skipper’s later research revealed there was a navy sub in that area at that time but never could pin down whether or not that was the object possibly cruising close to the surface…sobering article…talk about hitting something hard ! doubtful any sloop could have survived that
Submarines scare me. (Thankfully, I’m Canadian, and Canadian submarines can’t dive….)
A full-speed collision is very much a “roll of the dice” situation, but there are some things you can do at the design stage to improve the odds of coming out of it afloat. More on that in the next post.
Yikes Matt, do we Canadians—well, I’m almost one—really want to let on about that one. If for no other reason than it’s an admission of how badly we got took by the Brits! 🙂
Bonjour
Cet article est exceptionnel, par son analyse technique sur la déformation des matériaux : acier, allu, composites et bois
Les echouages bien évidement font partie des accidents, impondérables de la vie de marins confirmes, il convient donc d attacher une importance particulières au choix du matériaux
J ai bien note l anecdote du vendeur vantant la ” dureté ‘ de son bateau et sa technique de démonstration , qui s est avérée fausse, cette histoire me rappelle un grand constructeur de bateau connu actuellement et que nous connaissons bien qui pour vanter la solidité de son bateau en exposition avait mis un MARTEAU qui cognait sur le rouf et coque il y a de nombreuses années ? c etait impressionnant ce qui lui a permis de réaliser de nombreuses ventes
En matieres d’ échouages talonnages ( la photo est remarquable de réalité) nous connaissons bien puisque nous avons echouer 2 fois directement sur les rochers pour cause de pannes moteur ( voir article blog HANSE échouages) et une autre fois il y a des années sur un Beneteau qui fut reparé en Martinique
J ai lu attentivement l analyse de l auteur sur l acier et son pouvoir déformant lié a son élasticité, c est très juste évidement, j ajouterai la facilite de réparation et la sécurité pour les grandes traversées ou l on risque de rencontrer des OFNIS ( engins flottants non identifies)
Pour terminer, cet articles fait la synthèse du choix des matériaux de fabrication qui doit etre associer a la conception du bateau qui a fait l objet d un précédent article dans ce forum pour exemple simplifié les epaisseurs des parois de coque le varangage , raidissage etc qui modifie la capacité de résistance a l impact des coques, l ensemble construit doit etre cohérent et fonctionnel et c est tout l art et la compétence de l architecte naval concepteur …….choix des materiaux, calculs de resistance des materiaux, statique des forces mecanique des fluides etc
Cordialement Ulysse
No doubt some have been waiting for my response, well here goes. Somewhat of a long read. Firstly Matt – my apologies if my comments have caused you hurt. My original statement was about you needing to be careful about how other people represent you, I had omitted the words “by others” so my mistake for thinking these implied words were apparent to other readers (Paul’s posting is very true). I wish you well to attain your professional status and receive the “iron ring”. John –It was my view you were not accurately portraying Matt’s background by omitting which discipline his engineering training related to and hence left the implied suggestion that his engineering training related to the subjects being discussed on this site. I accept you have sort of acknowledged this and that it was not intentional. So I am making the effort to be conciliatory and suggest we now all move on. Moving onto to my issues about Matt’s article on “Impact resistance” and my view that it lacked balance. I think this article might have better been titled “Puncture Resistance” because that was the subject being discussed, at least until the reader reached the section about cored hulls where it seemed to turn into a general condemnation of cored hulls by the generalisation about engineers and other selective examples quoted without qualification. To me this is a bit like taking the following selective facts: 1. Richard Branson’s aluminium Virgin Atlantic I (the cat) hit something near the end of its run and sank off the English coast; 2. A 30m aluminium yacht being built in Thailand was relocated to New Zealand, inspection of the hull in NZ found the welding totally deficient and all welds had to be ground out and re-welded; and 3. The bad batch of 5083 Aluminium from Alcan which was faulty, due to a change in the heat treatment process, and drawing the conclusion that aluminium is a bad material to use in construction of boats. Not true of course, but this is much the same logic path Matt has used. I do not have a particular axe to grind about cored construction, only believing it to be a good form of construction when properly executed, just like any other medium. My experience ranges from assisting in the build of, I believe, the second only foam sandwich boat of any size built in NZ in the 70’s, using Airex foam, polyester resin and woven rovings/CSM (those were the days when you washed your hands in acetone, horrifying to think about that now) – this boat is still sound in spite of being somewhat neglected and having been washed ashore several times due to mooring failure. Since then I have owned a balsa cored power boat and now a foam (Klegecell) cored yacht. I have also been involved in quite a lot of industrial fibreglass applications including project managing the construction of possibly the tallest (120m) fibreglass chimney flue in the Southern Hemisphere. This… Read more »
Hi Alan,
Just to clarify, nowhere in his three part series on hull materials did Matt express any preference for aluminium over GRP. All he said was that he did not like or approve of cored laminates under the waterline on voyaging boats–an opinion I agree with.
You might want to re-read the first part of the series in which his whole premise was that there was no best material for sailboat hulls.
Hi Alan,
I do agree with you that cored construction can and should play a role in many applications. I don’t think this technology should be categorically dismissed; foam- or balsa-cored fibreglass is often an ideal choice for decks, topsides and bulkheads, and one would be hard pressed to build a competitive modern raceboat without cored composites.
The only place where I will unequivocally reject cored construction is from the waterline down on a cruising boat. This is for two reasons: the risk of long-term water damage to the core, and the tremendous difficulty in creating a cored structure that can survive an impact with a hard object. (Once you’ve designed the structure and are confident in the design, there’s still a big gap between being confident in the final product of skilled craftsmen making a one-off under a class surveyor’s eye, and being confident in the final product of $10-an-hour labour laying up a hull a week.)
There has been a point raised about my technical training and qualifications, to which I respond: My formal training is in engineering physics, an R&D-oriented discipline that includes most of what mech eng and physics students would take, a fair chunk of what elec eng and math students take, and a few other random scatterings. My experience in things directly related to the cruising boats discussed here at AAC include 20 years driving and fixing boats and roughly 5,000 hours of academic study and shop time in hull and rig design, fluid dynamics, advanced composite construction, DC power systems, engine and drivetrain, and structural analysis. I do not, and will not, write about topics which are outside my realm of experience and knowledge.
I stumbled upon this interesting photo:
A picture is worth a thousand words as they say!
I presume that this is an aluminum hull looking at the apparent malleability.
Hi Philip,
Yikes, that must have stung! Good advert for aluminium though.
This is a fascinating, and somewhat confounding discussion for someone who is following all of the design, construction, budgeting and planning articles carefully as we research, consider, and inspect various boats in our quest for a relatively affordable cruising boat that we can refit and enjoy for years to come. Without getting too far into the weeds on personal selection criteria, two of the boats on our list for consideration are the Tartan 41 and Ericson 39, there are certainly several others but I want to use these two as an example here because I think they illustrate my question well and relate to topics brought up here. The Tartan generally seems to have a better reputation and by all accounts is built like a tank by a reputable builder who is still in business. I’ve come across no accounts of structural issues in them yet. The Ericson generally seems to be considered more lightly built in more production focused environment, and I’ve read accounts of the hull flexing and tabbed bulkheads breaking loose over time with hard sailing, similar to people’s experiences with Cal 40’s and some other uncored GRP boats. I’ve come across some laminate schedule info on the Ericson that shows 7/16” thick sections at either side of the glassed in keel and 5/16” at the bow. Unfortunatly there is no info about other parts of the hull, or the keel to hull transistion area. The T41s I’ve inspected have full balsa coring, all the way under the waterline, ending somewhere before a very heavy duty over 1” thick keel stub area to accept the bolt on lead keel. Some of the very first boats might not have had this but it sounds like they were trying to lower the weight pretty soon in the build cycle as they came out heavier than intended as designed. Leaving out the obvious possibility of removing both of these boats from consideration, and knowing that they both enjoy a pretty dedicated following and have sailed all over the world, if you (John, Matt, and others with informed opinions) had to choose in this sort of situation, which criteria would you weight higher? I tend to want to favor the repution of Tartan and the generally heavy duty build of the T41 in particular but this discussion on coring has given me pause. Maybe this is just to big, and at the same time too specific of a question but any thoughts are appreciated.
Thanks again for all that you do, Matt
Hi Matthew,
Unlikely that Matt will answer: https://www.morganscloud.com/2013/11/10/aac-comment-guide-lines/ (#5)
I like the Tarten 41 as a boat, although it does have a very funky IOR stern that makes them a bit squirally off the wind.
As I understand it, only some were built with balsa in the core. Given that this was very early days for this technology and that the boats are now 40 years old, I would probably avoid those hulls.
On the other hand as I remember, the Ericsons where not, as you suspect, built to a very high standard, although that did, I think vary a lot. I do remember the keel fell off one being delivered to Bermuda, although admittedly, that was when a tow rope got around it.
Bottom line, the key to all of this is going to be a really good survey, not an opinion you get from me, or anyone else. See our online book for more on how to make sure you get that: https://www.morganscloud.com/category/boat-design-selection/book-how-to-buy-a-cruising-boat/