Ferro Cement Hulls ?

[Talbot]

You have to wonder why some people like to repeat untruths about boats

The ferro story is one
catamarans capsizing is another

[Jeff H]

I just want to talk to one narrow point in the discussion above....You often see people say that "Ferrocement only gets stronger over time." That is a bit misleading. The portland cement used in ferrocement is a material that increases in compressive strength over time. Depending on the specific mixture, placement technique and curing method the cement typically reaches 75% to 85% of its ultimate compressive strength within a week and 90% to 99% of its ultimate compressive strength in 28 days. From there on out it will somewhat forever increase in compressive strength infinitely but at a very decreased rate of increase. That part is absolutely true......

What is misleading is to say that ferrocement continually gets stronger over time. Over time as portland cement increases in compressive strength it decreases in ductility. Impacts that might have achieved flexure without damage will over time cause failure. In engineering terms failure does mean catastrophic failure, but it does mean the formation of small fissures, sometimes microscopic and sometimes larger hairline cracking. On a macro level this cracking concentrates loads and cumulative allows greater flexure on a structure that is less able to withstand flexure over time due to lost ductility.

Similarly the steel reinforcing in the matrix also loses ductility over time as the numerous cycles of small amounts of flexure work hardens and fatigues the steel. The loss of ductility and tensile strength results in a material that is less resistant to impact and bending than it would have been when new. This long term weakening in one form or another is typical of almost all boat building materials (Fatigue resistance is often cited as one of the advantages of cold molded wooden construction.) and is certainly not unique to ferrocement and should not be viewed as a 'deal breaker' in and of itself.

The issue of hairline cracking is a tough one to really address. Depending on the building methods of the individual boat and the maintenance that has been performed, it can be either a negligable problem or it can mean widespread and seriously weakening corrosion of the steel and destruction of the bond between the portland cement and the steel. Depending on who you believe, while properly constructed ferrocement has very good resistance to the migration of water when new, the issue of macro cracking over time means that this impremiability is greatly reduced, which is why you sometimes see recommendations to barrier coat ferrocement in much the same way as you would a FRP hull.

Respectfully,
Jeff

[CSY Man]

They must have different FC hulls in New Zealand.

The boat across the canal from me is a Canadian built FC and it is weeping rust down the top sides.
The owner paints over the rust once a year, but it always comes back.

A real ugly eysore.

He is trying to sell the boat, a 60 foot pilot house ketch, hoping to get $25,000 for it, but no buyers so far.

A boat like that is what gives FC boats a bad name.

[Alan Wheeler]

I agree, it does give FC a bad name. But one important point of looking at FC needs to made here.

It is not the material the boat is constructed from's fault that FC has a bad reputation, it is the Dipsticks that have no clue how to build a boat that have given FC a bad reputation.

Sadly today, the opposite of that statement has been used to describe FC boats and thus ALL FC hulls get labled as inferior. It is simply NOT TRUE.
I suggest that if any of these backyarder boat builders could have gotten there hands on Steel and GRP, then we would have seen poor workmanship with those hulls as well. And the thing is, I HAVE seen poor workmanship with steel. But we never see the same comment made about steel hulls.

By the way CSY, just to explain this guy's rust problem, it's most likely it has been poorly plastered over the chicken mesh. Usuallythe mess has not been tied back to the armature properly. The mesh does little but to hold the cement palster to the armature and allow fairing etc. But if the mesh has not been tied back fair itself, small pieces of wire sit out at the surface of the plaster and then start to rust through. Most likely, the internals are actually good, but the outside is an eyesore. His best sceanrio is to sandblast the hull and applied a barrier coat of epoxy to the cement surface.

Here are two other very important points. When buying an FC hull, you can safeguard yourselves buy asking for one of two things. A Hull build certificate if it has been proffesionaly built or, if built by an amature, a certificate from the Ferrocmeent builders association. They overlook the construction and will offer a certificate if done correctly. Otherwise be careful. However, that is not to say you aren't looking at a good hull. As I said before, most problems no longer exist. They have either been destroyed by themselves or by the owner. Actually there is another point that has given FC a bad name. I know of a few FC hulls that were not constructed properly and had been taken out a sunk. THEN the owners claimed insurance. Total fraud.

[Alan Wheeler]

Actually I would like to go a step further. So how do you judge an FC hull if you look at one. Well mainly, there are a few points that are easily detectable.

How does the boat sit in the water? This is were the most common mistake was made. Over weight. The builder thought the strength was in the Cement. A properly built "to the design" hull is not that thick. And many builders over plastered adding no additional strength, just major excess weight. A properly built hull is lighter than the equivilent steel hull. Another mistake was to build all the topsides in cement as well. Now don't get this part wrong, some areas of deck will be FC, but none of the cabin work. This added a tremendouse excess in weight, especially high up and made the boat handle like a drunk elephant. It is easy to spot any of these mistakes. She won't sit at her designed waterline.

How are external fittings attached? Here again big mistakes were made. Bollards must be through bolted with plates on the underside and in some very well built boats, the actuall bolts are welded to the steel armature. Ofcourse, that part is hard to know, unless the owner can tell you that is how it was constructed. No Metal should ever be epoxied to the deck. The expansion rates are so greatly differing between the two materials, that the epoxy will share away fromt he cement surface. All fittings must be bolted right trough with an adhesive sealant doing the sealing.

Hull fairness Now this is not whether the hull is smooth enough for a reflection, you are looking for lines in the plaster. The plastering MUST have been done in one complete hit. You simply can't do it on your own, it takes a team of guys to start and finish in one day. If you don't, you can get a situation similar to painting and not maintaining a wet edge. So it will show as a ruff plastered line were the wet plaster has not "melded" into the dry plaster properly.

Is the boat true? Take some measurements from the centre line out to each side. Now don't panic if it is not identical to the fraction of an inch. But do if it is miles out. You don't want a lopsided boat.

Cracks! This is one of the most common causes of panic and misnomer. Have the boat hulled for inspection. Allow the hull to dry in the sun for awhile. Now you may find very fine hairline type looking cracks on the surface. Don't panic, these are mostly paint and extreme outer surface of the plaster cracks and can be normal and of no importance what so ever. What you are looking for is once the hull surface has dried out, look for cracks that have remained wet for sometime. This is a sure indication the a structural crack is evedent. Look for a sign of imnpact. It is possible that this is a damage area and repair is not hard to have carried out. But if you see several cracks around the hull that are damp, then be wery that the hull may have internal structural issues.

Rust! Another common cause of panic. Small spots of rust can be common. It is not a sign that water is entering the hull. Most of the time, rust will be seen on the deck and gunwales etc. This is because it is difficult to plaster these areas. Gravity makes it hard to get a coat on teh deck and the gunwales are fiddly. Sometimes the mesh underneath has a small "sprague" of wie sticking up close to the surface, and this little piece can cause rust. Don't panic, the Rust will not run down into the structure and destroy it. A rust problem that does need serouse concern is a large crack int eh hull that has rust weeping all the way down the crack. This is a structural issue and it means water is at the core. Does this mean the boat is a dud?!? no not at all. It is very rare that the rust will "wick" its way down the steel armature. I will come back to that in the next segment.

A rusty armature during construction!!! I have heard so many "chicken little" comments over the years about this. Here is the fact. It does not matter if rust is present on the armature during construction. Infact, it is now considered the best way of building. The cement acts on the rust and turns it into something else. Although I have been told what, I can't remember, but it is something to do with the strong alkaline nature of the cement. Now that some experiance has been gained with repairs to FC hulls, it has been seen that the pre-rusted armatures seem to have a better hold to the cement than was realised. So when the cement is broken away from the armature for repair years later, the armature has been found to be far from rusty.

Hull strength!!! Impact strength is very high. I am not going to try and argue that it is any higher than say steel or any other material, but I can argue one point. It is much harder to penatrate an FC hull than any other material. It may crack on impact, you may stove it in even, but the cement will remain intacked in even the most sever case of impact and even if it lets water weep in throught the impact zone, the hull will remain intacked and most likely get you home. Repair is simple, cheap and quick, with the result of being virtually impossible to see if you have it done right.

Thats all I can think of for now. If anyone has any other questions, please ask and I will try to answer if I can.

[jim lee]

You know, there must be some truth to the statment that the Down Under Ferro boats were built different than the ones up here in North America.

-All- of the Ferro boats I've seen up here have ranged from "Looks homebuilt, but -maybe- ok" to complete hulks. Most of these were complete hulks and none of them have I seen leave the dock more than once. Most never.

I remember the hippies building these things in the 70s. Big 'ol hulls lined up on the beach in Half Moon Bay with hippies n' thier kids living in them while they tried to finish them up.

It was the new generation, they were going to do great things and change the world. What happend? Why don't the kids now-a-days do anything at all? Maybe all the drugs wern't such a bad thing? Heck, I notice since everyone got fat, they now dance sitting down.

I think there's still one of those ferro hulls still sitting out there today, poor lonley old thing..

-jim lee

[CSY Man]

Heck, I notice since everyone got fat, they now dance sitting down.

He-he, I know the feeling.

No 'mo dancing for the CSY Man, been there done that when I had to, to pick up chicks and one "meets" them on the dance floor.
Whatever it takes to get "romantic" with strange girls.

As for ferro cement boats...:

Aye, Mr. Alan, you make it sound like FC boats are the best and cheapest to build and own, the easiest to repair and the strongest, etc, etc.

Yes, we can all build a case for what we got and what we belive in.
I am in the same boat for sure..

I owned and lived on a wooden boat in the tropics for 3 years.
Not a good idea in the long run, but it worked out because the boat was within my budget..($75,000 asking price, $30,000 selling price for a 44 foot Bermuda racer)

If the vessel had been fiberglass or high grade steel or alu, the price would have been about 10 times higher and way out of my range.

Same with a FC boat, you get a lot of boat for the money, and you may sail in safety and comfort, but financing and insurance may be hard to get and re-sale value may suffer..(Understatement)

If somebody wants to save money by building his own FC boat, he may also try to save money on gear and equipment.
The FC boat across the canal from me is a great example: The masts are wood and rotting away..Standing and running rigging has never been changed because nobody wants to put money into a boat that does not keep any kind of value.
Electronics, mechanical stuff and sails etc are pre-historic and of no value to anybody.
The massive brown rust weeping donw the top sides sort of completes the picture and for severeal hundred folks in the neigborhood, represents what FC boats are all about, in their minds anyway.

Never having owned or maintained a FC boat I can only speak from second-hand experience: Therefore, there may be some jewels out there, but I have not seen them..yet.

Nothing personal Mr Wheeler, but around here FC is the bottom of the bucket..

(Not being snobbish, my fiberglass boat have problems as well, and so did my wooden boat..Pick your devil, they all come home to roost)

[BC Mike]

If yuse all read The Nature of Boats by David Gerr, he will tell you that this is a discrepency in build quality in different locations. From memory he quotes NZ and France as the places where decent FC boats are built.
Michael

[Alan Wheeler]

Guy's, don't get me wrong. I am not saying FC is the be all and end all to boat building. I too have seen or heard of some real crap out there. I am just saying, don't judge all FC based on one poor example of a boat you may have in the neighbourhood.
As I said, most of the old crap has all but gone now. And I imagine that this thing you have across the canal is not used, nor has been for many years. Probably forgotten about? I would imagine if someone had any time for it, it probably would have been sunk many years ago as well.

Here's where I believe we FC owners are going to start having issues in the future. The old guy's with the experiance in FC building are getting few and far between now. There is just not enough knowledge out there anymore for surveys and advice on FC hulls. It's going to get harder and harder to get a hull inspected. One guy here that I have been learning a lot from, has long been retired. He doesn't want to be crawling around in bilges anymore and fair enough too. But the biggest problem he has is liability. So he has to have insurance and as he may only inspect 2-3 hulls a year here, the cost of holding insurance just can't be justified.

[BC Mike]

I always said they will pay me to teach inmates upholstery stuff when I am old, because all the tradesmen will be gone.
I made a dodger for a FC boat in Tauranga in 1969. I left it to the owner to fasten it to the hull 'cause I had nothing in my kit to use.
X upholsterer / canvas worker Michael.

[Alan Wheeler]

Funny you should say that Mike, Because NZ is presently experiancing a skilled labour shortage. All the skilled people have buggerd off to greener pastures. Mostly Australia, but rumour has it there maybe one or too in Canada
Anyways, skilled labour in this country at the mo, is as scarce as Hens teeth.

[CSY Man]

All the skilled people have buggerd off to greener pastures

Ft. Lauderdale is full of Kiwis working in the yacht business.
(And South Africans and a few token Aussies)

Not sure if it is greener pastures around here and with all the hurricanes we have had, I am sure some of the Kiwis will say to hell with this and go back home...

[Wynand]

Here is a useful link on ferrocement

http://www.boatdesign.net/forums/showthread.php?t=6683

Jim Lee, there are a number of good quality FC boats on the central coast. I owned one, refered to earlier in this thread, and almost purchased another. Both were built in the early 80's, and neither showed rust on the hull. The second one is still one of the nicest motor sailors I have ever seen. I was burned on the deal, as the seller took my offer, and told his friend to match it, and he could have the boat. But, sour grapes aside, if not for that, I would own a FC boat right now. As for the one I believe you are refering to, it is a very large FC boat that was run up on the beach at Capitola with the intention of turning it into a restaraunt. The restaraunt idea died, but the boat is still there. And probably will be for another hundred years.
As for the boats being built by hippies wanting to change the world, I disagree. Wrong timeline. Maybe hippies as a retirement plan to escape a society that they were unable to change. Regardless, most FC boats were not built by professional boat builders, and as talent is very selective, the percentage of good quality FC boats is relatively small, in contrast to the number that were built. But then, probably not as small if compared to the number actually launched and completed.

[Alan Wheeler]

I think it is fair to say, most ALL of those "problem" FC hulls no longer exist. It is tooo long ago and if they have survived from the 70's and 80's, then they are most likely a good hull. The few bad ones that are still afloat, look so bad you would never go near the thing, as CSY has noted. Or if they were heavey or sailed bad, then they were mostly sunk and had insurance claims against them, This is actually why it has been so hard to insure an FC boat. If you want to blame anything about the negativity towards FC, blame the Fraudsters that sunk their lumps of junk.

The three comments made by D'Artois in that link are once again, generalisations and not entirely true.
1: IF the hull has been built correctly, then the FC hull should be lighter to the equivilant in Steel.
2: The impact strength of FC is higher than GRP and Timber, with steel being the highest. As I have stated before, after 90 days of curing, the FC material has a tensile strength of 19,000PSI and a fully cured fully hardened hull will reach near 30,000PSI.
3:Repairing FC is the easiest of all materials and certainly the cheapest. When the repair is compleate, (if the job has been done well) it will be impossible to see the repair.

It is an interesting discusion on that link, but once again, many generalisations and comments made by ones that have only heard and not done.