Steel vs Fiberglass

[MicHughV]

What about hull thickness?

Interesting question.

I had the option of building the hull out of 1/8" thick plate or 3/16" thick mild steel plate.

Seeing as I had never welded before, I was advised by experienced welders to go for the 3/16" plate as it would be more forgiving regarding welding distortion, etc.

So 3/16" is what I used. I also had the advantage of having the guidance of some pro welders that taught me a variety of things I never learned in the welding class I attended.

The keel was formed from 1/4" plate and the keel shoe was 1/2"

All the ribs, etc were also 3/16". but I removed several as being unnecessary. I am a structural marine engineer by profession, so this was not done willy nilly, but I wanted to remove weight where not needed.

Nonetheless, despite the heavier plate thickness, the boat floated pretty close to the design lwl at time of launch.

Both the interior and exterior of the hull was sand blasted to white metal standards.

I had the exterior hull painted with a propriety paint "system"...zinc....base coats, etc...5 coats in all.

The interior I slathered in coal tar epoxy paint.

I also insulated the interior hull and deck with 1" styrofoam panels which I glued on.

I never had any issues with being too hot inside, never any condensation problems, etc and never had any rust issues either.

Sometime after I launched the boat, I covered the deck and cabin top with a "decktread" material which was glued on. Loved it, as it provided secure footing when wet.

I had that boat for 12 years or so, and it's now on it's third owner, and still going strong. 43 years old now.
When I sold my boat, the next owner had the hull " sounded" by the marine surveyor.
Nowhere was the hull any less thick than the original thickness.

If in doubt, a metal thickness sounder can be bought online for a few $100.

While building my boat, I came to know several other people building steel boats. Not sure that they took the level of care I did, but the finished product looked good.

For sure, a metal thickness sounder is a good tool at time of survey. There will be parts of the hull behind stoves, fridges, etc which can't be seen from inside, but the metal sounder will let you know if there is an "unseen" problem anywhere.

I enclose a pic for your viewing pleasure.

[sailorboy1]

fiberglass doesn't rust!

[Threemonkeys]

Oh man, there's a lot of great info these posts. All I have to say is, this is not getting easier as I'd hoped...

[Threemonkeys]

I read the FAQ's about Corten steel and it strongly advised against using dissimilar metals especially zinc. So how would one battle electrolysis if zinc's are not an option? Mild steel?

[dannc]

Originally Posted by Threemonkeys

Oh man, there's a lot of great info these posts. All I have to say is, this is not getting easier as I'd hoped...

For more information, go read the articles on Kasten's website. This is a good one to start with, Metal Boats For Blue Water - Kasten Marine Design.

Later,
Dan

[dannc]

Originally Posted by Threemonkeys

I read the FAQ's about Corten steel and it strongly advised against using dissimilar metals especially zinc. So how would one battle electrolysis if zinc's are not an option? Mild steel?

I suspect the FAQ from the previously posted link, is concerned with using Corten and zinc in buildings where the zinc would eventually disappear and cause problems They mentioned galvanized not touching Corten which I assume they mean having a Corten structure touching say galvanized steel panels. In that case the zinc in the galvanized panel might be consumed which would be a bad thing but that is what one wants to happen on a boat.

Plenty of boats have been built with Corten and used zincs. One could use aluminum in place of zincs.

Colvin was a ship and boat build builder as well as a designer back in the 60's-80's. Hundreds of steel boats were built from his designs.

I just looked real quick through Colvin's two volumes on steel boat building and he did not mention a problem with zinc and Corten. He recommended Corten and mentioned that one really good rust prevention method was to flame spray zinc or aluminum on the interior of the hull along with epoxy.

Kasten also recommends using Corten or it's equivalent.

Later,
Dan

[Cheechako]

Nothing is stronger and tougher than steel really. But do you need that? Are you planning a trip over Niagara Falls? NO.
A well layed fiberglass hull is lighter, looks much better, and far far easier to maintain.

[Bowdrie]

Probably dated, but many of the steel boats, (yachts,) I've seen that used rolled plating without having a ton of "filler" for fairing were built in the Netherlands.
With access to high quality steel from Germany and Sweden, they seemed to have developed a "knack" for shaping a good-looking hull, one that didn't look "homebuilt/commercial".
In contrast, many, (most?,) of the US boats tend to be hard-chine/multi-chine, or rolled in only one plane, (developable surface,) even if built by "pro" builders.
Exceptions of course, Palmer-Johnson earned a good reputation for shaping metal and using good technique.
As others have mentioned, eliminating any area where water can stand is a key feature for longevity, that and access to all the interior.
Edit; Just for trivia, the Electric Boat Co,. (submarines,) built a few good-looking compound-rolled steel yachts back before WWII.

[Orion Jim]

Originally Posted by Liminal

My two cents as a trained fiberglass technician, competent multi-material welder, and who self-surveys "cheaper" boats as my hobby:

Would never touch a used steel vessel with what I have seen personally and the nightmares I have seen other folks end up with even after very careful surveys: the tales of discovering "structural paint" while at sea are extremely real. Any steel vessel is going to require a hull-up total interior removal refit after a few decades with at least some replating during that, no matter how thorough the original interior coating was. Significant costs involved there.

If you want a used metal boat, buy aluminum, it will be much easier to determine if it has been damaged by electrolysis. If it hasn't, and you take care of it - it will outlast the sun with minimal maintenance.

Aluminum and Cold-Molded are, in my opinion, the two best choices to pursue for used market vessels. Well worth the additional hassle of carefully surveying and finicky maintenance.

Fiberglass is fine and dandy, easy to repair once you have the skills and mostly indestructible by time, but it has material fatigue limits(as do metal boats) which you don't often hear about - and many vessels over the 40 year mark are almost certainly starting to approach these no matter how tight the owners have been with upkeep. An older foam-cored hull would, in my opinion, be a suicidal choice - wave action induced delamination of the skin to foam bond is a real and serious consideration for those vessels.

While the common logic in the 90's to 00's was to buy a cheap 70's/80's boat and refit it for modest cost, that was over twenty years ago. Broadly speaking in 2023 I would not set to serious offshore passages on a boat older than the late 1980's (of any construction) without accepting that my hull is approaching the end of its materially useful lifespan and there are risks stemming from that which go above those usually found offshore.

Folks will chime in with "poppycock, there's thousands of 60's & 70's boats sailing around out there just fine to this day!" and they're correct. One can, of course, ride a time bomb for what is perceived as indefinitely - if you don't know when the timer is going to run out.

Are you referring only to cored hulls or do you feel this is applicable to solid fiberglass hulls?

[mako]

Originally Posted by Jim Cate

With respect, no, it did not need those efforts. Had you not made them the boat would have still performed as new... just not as shiny. Your desire for appearance drove the work ethic, not the material's needs.

Jim, I would say your statement is correct. However, in reality we like to care for our boats and keep them looking pretty, which requires maintenance man-hours.

[Liminal]

Originally Posted by Orion Jim

Are you referring only to cored hulls or do you feel this is applicable to solid fiberglass hulls?

Solid fiberglass is no exception to material fatigue, everything has cycle limits and for fiberglass UV exposure is busily breaking down the polymer bonds holding all these boats together. On top of that, hand-laid fiberglass as we saw in the 60's & 70's is prone to uneven wetting of the mats (leading to resin rich/dry regions) and lots of air trapped in the layup. Chop-strand is a joke compared to engineered directional layers, and usually comprises 50% of the layers in these hulls.

The belief that fiberglass boats are "indestructible" by age alone is poppycock. Yes, many of them will limp along as coastal cruisers for many decades yet, but for serious heavy ocean passages they are hitting a wall. Catastrophic hull delamination while half way across the pacific is a risk which should be on everyone's minds - especially for the super-heavily laid up early hulls which so many people still think are more "bombproof" than a modern infusion lamination. Totally the opposite, the thickness of some of those hulls is becoming a massive liability as the resin ages.

Plenty of young folks buying boats which have been cooking on the hard in La Paz / Panama / Faro for the past twenty years while the owner was on life support, with grand dreams of Tahiti and further, not considering that it's probably less structurally sound than your average Ferro after soaking up that much sunshine.

[wyb2]

Originally Posted by Liminal

…

Fiberglass is fine and dandy, easy to repair once you have the skills and mostly indestructible by time, but it has material fatigue limits (as do metal boats) which you don't often hear about - and many vessels over the 40 year mark are almost certainly starting to approach these no matter how tight the owners have been with upkeep. An older foam-cored hull would, in my opinion, be a suicidal choice - wave action induced delamination of the skin to foam bond is a real and serious consideration for those vessels.

While the common logic in the 90's to 00's was to buy a cheap 70's/80's boat and refit it for modest cost, that was over twenty years ago. Broadly speaking in 2023 I would not set to serious offshore passages on a boat older than the late 1980's (of any construction) without accepting that my hull is approaching the end of its materially useful lifespan and there are risks stemming from that which go above those usually found offshore.

Folks will chime in with "poppycock, there's thousands of 60's & 70's boats sailing around out there just fine to this day!" and they're correct. One can, of course, ride a time bomb for what is perceived as indefinitely - if you don't know when the timer is going to run out.

Do you have any evidence for this?

I understand the logic, I understand fatigue life and the fact the these boats weren’t explicitly designed to last forever. But how did you decide that the true useful life of a fiberglass hull is 40-ish years? Why not 20? Why not 80? And you actually said of any construction, it seems like a pretty big coincidence that the answer would happen to be the same for any construction type.

I think one would need some very good real-world data to decide this. Going purely on theory, the difference between 40 years of cycles and 80, or 200 for that matter, is pretty small. It can be predicted for applications like airframes because it’s been heavily studied, tested, and refined on that specific application for decades. But I’m not sure that rigor has been done in fiberglass boats? Maybe if it’s been done in racing, we could extrapolate to cruising boats for a slightly better answer than pure theory. But it also seems like it could easily be eclipsed by other variables, like seemingly minor design choices, the use case of a specific boat, minor material quality differences, and a dozen other things.

I’ve heard of plenty of hulls being damaged by finite events, like a hard grounding. But I’ve never heard of an actual failure from just fatigue. Again, maybe racing sees this, as they operate so much closer to the limits? (I don’t know, happy to learn if so). But for a recreational cruising boat?

[MicHughV]

Steel boat building has come a long way since the 70's.

These days one can get a "kit" boat, where all the steel bits and pieces arrive in autocad precision precut plates, etc.

Also seen now, are the " soft" chine steel boats, where the traditional hard edged chine is replaced by a rolled piece of metal, arriving on your doorstep as a pre-cut piece.

Lastly, I welded up my boat with a buzz box stick welder, but these days there are a wide array of welding tools available, far too many too detail here.

Paint system have also come a long way since the 70's.

I have come across professional constructed steel boats that looked as flawless as a fiberglass boat.

If you wanted to take the time and effort, a variety of "fillers" are also available to smooth out bumps and humps.

Back in the 70's, there was a big homebuilding "build your own boat" craze going on. Homebuilt boats could be seen on a lot of driveways. Wood, steel, fiberglass, concrete, you name it, it was out there.

These days, it's rare to see anyone tackle a homebuilt project.

Finally, for me, as it was for many, money was an issue...a big issue at that. I simply did not have the wherewithal to purchase a boat ready made. If I wanted one, and I did, I was going to have to build it myself.

A steel boat has one other advantage. it can be built out on the open, as it does not require a large shed to build under. Again, being basically broke as a young 25 year old, this too appealed to me.

There are not that many steel boats around. Could not say with any precision, but probably, 1 in 10,000 boats might be steel. They are far and few between, this is for sure.

I loved my steel boat. It served me well, and I never had any issue with it. For anyone with rtw ambitions, it's tough to beat. Welders can be found in the remotest places.

Without admitting to it, it is tough, and can bounce off reefs with only a scratch to the paint work.

Practically speaking, many people have opinions about steel boats, but to get to core of the matter, talk to people that have built or owned a steel boat for a proper opinion on the subject.

[Pauls]

Seconded on MicHugh5's post above.

The posts about the necessity of Corten are not accurate. Yes, Corten is more rust resistant than mild steel. It was designed for architectural use, unpainted. BUT IN A SALT WATER ENVIRONMENT CORTEN STILL RUSTS BADLY. It still requires a quality paint job. The main reason to use Corten or the other steels available which are similar to it is that it is stronger than mild steel, allowing thinner plating for the same strength. Mild steel has been used in marine construction for boats, ships, bridges, oil rigs, etc for ages. It is a fine material.

Steel, like any other boatbuilding material, makes a good yacht when built properly. And, like any other material, when not built properly it doesn't. That is what you need to take away from this thread. With ANY material, get educated on what it requires for quality construction and then verify whether that was or was not done on the boat you are interested in. This applies to any boatbuilding material, whether steel, fiberglass, aluminum or wood.

[Renegde_Sailor]

Originally Posted by wyb2

Do you have any evidence for this?

I understand the logic, I understand fatigue life and the fact the these boats weren’t explicitly designed to last forever. But how did you decide that the true useful life of a fiberglass hull is 40-ish years? Why not 20? Why not 80? And you actually said of any construction, it seems like a pretty big coincidence that the answer would happen to be the same for any construction type.

I think one would need some very good real-world data to decide this. Going purely on theory, the difference between 40 years of cycles and 80, or 200 for that matter, is pretty small. It can be predicted for applications like airframes because it’s been heavily studied, tested, and refined on that specific application for decades. But I’m not sure that rigor has been done in fiberglass boats? Maybe if it’s been done in racing, we could extrapolate to cruising boats for a slightly better answer than pure theory. But it also seems like it could easily be eclipsed by other variables, like seemingly minor design choices, the use case of a specific boat, minor material quality differences, and a dozen other things.

I’ve heard of plenty of hulls being damaged by finite events, like a hard grounding. But I’ve never heard of an actual failure from just fatigue. Again, maybe racing sees this, as they operate so much closer to the limits? (I don’t know, happy to learn if so). But for a recreational cruising boat?

It is an interesting point. I can see there are some boats that were cheaply built that just fall apart, I mean if you look at Uma from sailing Uma in the recent tear down videos, well she was not a well constructed boat, and they are having to do a massive refit just to make her whole again.


As far as structure failing, I can see where on boats with lots of core material, especially balsa or certain kinds of foam, as they start to rot, the delamination happens, and soon the boat is structurally compromised.

Hull to deck joints are also prone to failure, and many a factory built boat has a hull to deck that is bolted with the schmoo holding them together and keeping the water out having failed more than a decade ago.

On the flip side, there are some old boats that were built thick, sans core, that I suspect will still be sailing in 200 years assuming they are well maintained.



It really boils down to who built the boat in the first place, and who maintained it?