We love Ferro cement but beware !

[PAR]

Terry, you're correct in principle that ferro is a building material and should be able capable of being shaped into a boat. The problem is three fold. The first is the armature is going to rust. Not maybe it will rust, but it will rust, this is a given. Someone with a trowel pushed some "mud" too hard and nicked the mesh's coating or other "problems". You know what happens next. The rust goes unseen until it's ruptured it's way through the area and stains appear. Secondly, the material isn't repairable easily, certainly not with more concrete. Lastly, the armature, which is the key to the build, can't be inspected after it's built. Well, okay it can, but you have to use an x-ray machine and most surveyors just don't carry these around in their back pocket.

[ancient kayaker]

All true Paul, but equally all apply to non-boat construction and the problems are routinely solved there. None of the materials I identified are immune to the problems you noted or their equivalents.

The difference is - compared to bridges and such - boats are generally privately owned and private citizens for the most part lack the deep pockets to maintain the oversight during construction and the maintenance following launch.

Concrete is cheap, widely available and easy to handle, as is rebar. They both demand skill to use properly, but skilled folks are available in some numbers from the construction industry and the output per labour-hour is high for a non-factory activity. I suspect if it were not for the fear factor there would be a lot more FC boats out there and they would be very cheap. The problems you identify don't show up until a few decades have passed in construction and by then a cheap boat has outlasted its attraction.

I don't think the problem is strength. A concrete boat with a steel heart has a steel heart, after all. Cracks in reinforced concrete structures do very little to weaken them, just creat a path for moisture, so rust is the problem, fear is the enemy and inspection is the cure.

I suspect the real snag is, the cost of the bare hull is not the only thing contributing to the cost of a boat. In the end, slashing the hull cost might knock off less than 10% of the boat's cost, but a concrete hull might knock off 50% of a boat's perceived value.

[gonzo]

Does anyone have experience with plastering a boat with the new type of cement with fibers in it?

[PAR]

Terry, you don't understand ferro cement structures well enough. They are thin, I mean really thin compared to land based structures. The armature is a much higher percentage of the finished product then it is in a bridge deck or building support column. Lets take a section of 1" thick ferro hull, 3/8" to 1/2" of it will be armature. Now imagine how much the steel can expand before this ruptures the shell. This is considerably different then a column that has 12" of concrete surrounding a couple pieces of heavy bar stock. The bar stock can move around a fair bit, locally crushing concrete along the bar, without transmitting these stresses to the surface.

[boat fan]

PAR is right about all of what he said.

I do think it`s a viable way to produce fixed pontoon based house boats , marina piers and gangways ,
or floating homes.
You could safely go a little thicker for those applications too.
Can be constructed with shotcrete in simple molds with galvanized steel re- enforcement - just unbolt and dismantle mold when cured.
Similar to building some swimming pools.Could last a long time .

[WestVanHan]

I've ocean kayaked around ten ships (on several occasions) that have been floating as a breakwater,with most of them being there since just after the war.

So 60 + years,with maintenance consisting of pumping out the rainwater on occasion.
One of them is pushing 90 years of age.

Done right,seems OK to me.

http://www.concreteships.org/ships/powellriver/

[Steve W]

Just curious,do any of you guys have any actual experience building a ferro cement boat or are you just going by what you have read/seen/heard? I ask this because whenever i read one of these many ferro threads i find many people who have opinions based on nothing.I do have real experience with the method and although i havnt had anything to do with them for many years i am still quite fond of them.They actually have a lot going for them.
During my apprentice days in the early 70s while i was building custom cold molded wood and foam/glass boats as well as fitting out production glass boats at work i found time to build a modified Hartley RORC 39 for myself as well as act as a grunt on plastering day for a bunch of my friends who were also building ferro boats and i can tell you that there were many many boats built by both proffesional yards and amatures that were as fine as those in any other material.The hull of my 39ft boat was just 11/16"thick and inside that was 5 gauge hard drawn wire stringers on 2"centers fore and aft with 4 layers of 1/2"galv chicken mesh on each side of the stringers.The key is to spend a lot of time fairing the steel armature before plastering so the plasters are just skimming over the mesh maybe 1/16",thats all so there is very little unreinforced plaster,you absolutly do not want to be fairing with plaster.After the initial cure you run water over every square inch for a couple of weeks during which time you go over the entire hull with a carborundem stone which washes away all the loose sand etc,you become intimate with every inch of hull and know where every wire tie that is too close to the surface is as the start to rust.This is exactly what you want,if there were no rust spots you have applied too much plaster and produced a heavy hull.After you shut off the water and the hull dries out you chisel out the rust spots and leave the boat to thoroughly dry out while you move ahead with the fitout,you come back and fill the spots with epoxy filler months or years later when its good and dry before you paint the whole thing with epoxy.Water will no more get at the armature than at the core of a glass boat.Yes,if you bang something and damage the barrier coat you need to patch it promptly,just like you need to with a steel boat and especially a balsa core glass boat or a glassed wood boat,the consequences of not being dillegent are equally dire for all.A well built ferro boat is not any better or worse than any of the other methods for its intended purpose.We have a big steel Chris Craft Roamer in the shop that is getting the bottom replated because when we blasted the bottom we found it was so thin you could stab a screwdriver through it all over the place and this is a fresh water boat.I have recored more glass boats than i care to remember so i dont understand why so many people who should know better are so hung up on the same problem with ferro boats namely water penetration,its simply no worse a problem with ferro.The other big piece of nonsense is the statement the armchair experts so often sprout that you cant survey them because you dont know whats inside the skin, ive news for you,you have no idea whats inside the skin of a glass boat either unless you take core samples and i dont see surveyors doing that, i see many(most) glass boats that are horribly resin rich,over catylized,full of air bubbles,voids etc which transalates to weak and overweight,sound familiar,same issues as some ferro boats may have.My point is a well built ferro boat is as good as any other material for its purpose and a bad one is ,well,crap just like any other material.
Steve.

[boat fan]

i dont understand why so many people who should know better are so hung up on the same problem with ferro boats namely water penetration,its simply no worse a problem with ferro.

Not so I`m afraid....Once the chloride ( salt ) has entered the concrete / cement / crystal matrix it has access to the internal steel ,
(and I don`t care if you think you are god himself , or built a hundred ferro hulls ), you will NOT remove it , nor will you stop the corrosion.

Electrochemical corrosion of a metal is an involved process. The corrosion cell consists of an
anode, cathode, an ionic current path, and an electrical current path. A passivating or protective ferric
oxide film, formed on the reinforcement during the hydration process, usually protects reinforcing steel
in fresh concrete. The passivating film remains intact in the highly alkaline environment of the concrete
(pH approx. 13). If, however, chloride ions are introduced into the concrete, the passivating film on the
steel may break down and active corrosion may develop. Corrosion begins with the reduction of the
concrete pH that creates an environment conducive to the corrosion reaction. Depending on the exact
reactions involved, the products of the corrosion can take up a volume as much as six times that of the
original iron.You now have the ideal conditions for concrete to self destruct , from the inside out.Once
started , the process cannot be stopped.

The Navy in the US and authorities around the globe are battling to contain their older existing waterfront infrastructure :

QUOTE]
In coastal areas and in areas where de-icing salts are used, reinforcing and prestressing steel in
concrete members is vulnerable to corrosion. This problem is worse in members with a supply of both
oxygen and moisture, such as in the splash zone of bridge piers. Prevention of corrosion and related
damage is being addressed in new construction through the use of epoxy coated rebar, revised
construction procedures, and alternate rebar materials, including fiber-reinforced plastics. In retrofit
situations in the state of Florida, cathodic protection systems and pile jacketing, a repair technique in
which rigid FRP outer jackets or forms are placed around members and filled with either concrete or
mortar, are often employed (1). Although numerous methods exist and are presently used to protect the
reinforcement, none is without limitations.
This project investigated the use of carbon fiber reinforced polymer (CFRP) composite wraps.Wrapped, uncracked samples took four to five times
as long to reach a ninety percent probability of corrosion as unwrapped, uncracked samples[/quote]

There you have it in a nutshell......those carbon and frp wraps , jackets ,etc, etc , All are bandaid solutions!!!!
By their own admission : Extended service life is expected to be 20 years......

To be fair , these older examples of infrastructure date from ww2 or even older , so it`s a good service record.
The culprit is the Ferrous armature.It will spring the cement cover every time.

If anyone is considering cement boat construction, they would be well advised to look into the newer fiber armatures.
There are better ways to build a boat.

[MikeJohns]

I have surveyed everything from ferro-cement vessels to commercial concrete barges. Over the years I have seen a lot of problems not so much related to construction (they die early deaths) but from accidental damage. Surveys to determine layup can be done readily with x-ray equipment.

Most boat damage occurs not from the sea but from collisions, ferro-cement hulls lose local watertight integrity fairly easily and I like to see watertight bulkheads with this construction.

I have seen Swinging anchors that have gone through ferro-cement hulls. Any collision with rock reef or concrete dockside (if not taken directly on the stem or keel ) will usually sink the boat unless you can fother the hole, unfortunately this is usually impossible when the boat is grinding on the rock or reef.

Here are some insurance pics I have lots more and it's quite informative to look at the damage, it's usually very localized but often leads to the vessels loss similar to trad timber vessel planking damage.

[PAR]

I have also surveyed ferro built and also participated in a few builds back in the 70's, when I had long hair and the method was still fashionable.

It's one thing to design and build with it, having good intentions and all, but another to live with it in the realities of the marine environment.

[MikeJohns]

Originally Posted by PAR

I have also surveyed ferro built and also participated in a few builds back in the 70's, when I had long hair and the method was still fashionable.

Paul
Me too.
Iit was almost a movement and it was worth experiencing to fully appreciate where ferro yachts fit in the scheme of things.

The failure of the material is interesting, for example that skeg in the picture I posted took a heavy blowon the rudder from a rock on the side where the material is missing at the root, on the other side you can't see any damage at all and although structural integrity remains, the boat sank. What is surprising is how much plaster 'exploded' out of the gap, more like a ceramic failure.

One ferro advocate recommends lining the inside of the hull with several layers of GRP to overcome the results of such brittle failure after impacts and it does seem to work.

[PAR]

Yes, it was a "movement" and many children only a mother could love, rose from the depths of backyards around the country. On the other hand a few companies and designers were actually doing good work with the material, but they too got caught up in the "eventualities" of this material if used on small and mid size yachts.

With modern additives, fiber reinforcement, better mortar mixes and most importantly, thick enough hull shells, it's a good material. Those light ships and such of ferro cement that have survived 100 years of continuous use, should be looked at as examples of the method. Their hulls are massive, which is why they've survived. The first ferro builds took place in the early 1800's with many from the 1890's still around. One good look at how they were built shows why.

[boat fan]

Interesting Mike.

The thing with Ferro is , even if the boat does not sink after such localized damage , any fractures caused will allow the chlorides dissolved in sea water to wick into the cement matrix by capillary action.Even if you can repair the the damage around the area of impact and deformation , you essentially seal
in the chlorides.The longer the time of chloride exposure the worse the problem.

PAR put his finger on the root of the problem : thickness of armature cover is vital .Not all that useful for small craft.The good ones ( boats ) have low chloride
concentrations in the matrix.Not easy to determine.Some of the dodgy backyard builds had armatures that were not even galvanized .

This is interesting:http://www.google.com.au/url?sa=t&so...dZTie69wXKkGjA

[gonzo]

Don't forget that reinforced concrete was invented in France to build a boat.

Originally Posted by gonzo

Don't forget that reinforced concrete was invented in France to build a boat.

Was Kistinie, the Hybrid Corsair involved?