Intelligent Discussion on Ferro

[barnakiel]

Originally Posted by goboatingnow

It's important to realise that proper fret cement is completely impervious to water, better then grp in fact ( which isn't impervious)

Dave

Cement more impervious than epoxy?

OK. Did not know this.

Seen a couple of marine constructions taken apart where cement was used to protect the metal grid. The metal was always corroded, so I thought cement lets some water thru.

b.

[BillAU]

Originally Posted by barnakiel

Yes, provided you do not own one.

Why are there no big craft build in ferro - tankers, tall ships, submarines? Why are there no mass production ferro-cement sailing boats?

My two cents. Good technology, except perhaps not for building sailing boats.

b.

G'day b,

During WW1 the Americans did build FC tankers.

Quote:
Back in the mid 1980?s I was camping on Monterey Bay at Seacliff State Beach and pier. Where I discovered that the pier was actually the concrete (ferro-cement) tanker the S.S. Palo Alto which had been built during World War I by the San Francisco Shipbuilding Company in Oakland, California and launched May 29, 1919.
With the war being over before her launch she was surplus at completion and was unused remaining docked in San Francisco Bay for over ten years until she was purchased by the Seacliff Amusement Company of Nevada and towed to Seacliff State Beach in Aptos, California. The ship was intentionally grounded in the bay in January 1930 and connected to the shore by a long pier. An arcade, dining room, dance hall and even a swimming pool were built on the ship.
Unfortunately, in the winter of 1931-32, with the stern grounded on the beach which is on a ledge of sand stone, and with the bow afloat in the water, a storm cracked the ship across her midsection. Then, as the depression worsened the Seacliff Amusement Company went out of business in 1932. The Palo Alto was stripped of all salvageable metal and fixtures and turned into a fishing pier. By 1948 the salt water had gotten to the steel in the cracked ngection and she was beginning to separate.
But, when I was looking at her after 60 years of total neglect the undamaged structure of the stern seemed to remain solid, and she just did not seem to be appreciably deteriorate except where cracks have allowed salt to get into the concrete. Today she is over 90 years old and has not received much maintenance since she was first launched.
End Quote:


The above quote was taken from http://www.captainhugenot.com The Captain is a marine surveyor and he provides good information on a number of boating subjects on his site so do check it out for yourself.

Why don't shipyards still build FC ships and tankers? Simple...They get steel ships out the door quicker and at less cost to the yard/company. I guess the same applies to Glass boats.

The Captain also states:
Quote:
INCOMPLETE KNOWLEDGE IS A TERRIBLE THING: This wrongful perception of ferro-cement as being an inferior material has been further exacerbated by the fact that most marine surveyors who learned their trade in the commercial yards and not as amateur back yard boat builders, are more familiar with wood, fiberglass, aluminum and steel construction, and simply have not been educated in the physics and chemistry of structural concrete. This lack of specific training necessary to acquire the ?insider? knowledge needed to properly understand, inspect and survey ferro-cement leaves the average marine surveyor with an information gap.

Often, a well meaning surveyor when asked to survey a ferro-cement boat may instead be forced to rely on the waterfront rumors and as a consequence will wrongly consider ferro-cement to be an inferior material, even though this is an entirely mistaken view.
End Quote.

As Dave, like Captain Alan Hugenot, points out.
Quote:
Ferrro-Cement IS IMPERVIOUS TO WATER PENETRATION: The great advantage to ferrro-cement is that it is completely impervious to water penetration. It simply does not get wet on the inside, Consequently, when the mortar covering any embedded metals is of sufficient thickness (over 9 mm or 3/8?), tests have shown that the embedded metal is fully protected from chemical attack by the impervious cement, even when full immersed in a corrosive such as salt water. In other words ferro-cement is better protection than many paints.

Unfortunately, this fact is counter intuitive to most people. Most folks are not schooled in the physics and chemistry of structural cement, so they nearly all believe that cement gets wet all the way through when it is immersed in water. They never realize that the wet look is only on the surface when the cement is properly formulated.

Actually, when ferro-cement is properly mixed and formed, it becomes an impervious monolith that water cannot penetrate. As Joe .P. Hartog, the professional Naval Architect who designed many ferro-cement vessels stated clearly in a technical paper on ferro-cement which he published in 1988:

?Because well-made ferrocement is impermeable (waterproof), there should be no need for painting?. Quoted from UNDERSTANDING FERROCEMENT CONSTRUCTION, (?1988, ISBN: 0-86619-284-0)
End Quote.

To wrap this post up, I recommend readers wanting to know more on FC boats, and boat safty subjects, should visit Captain Alan's site: Marine surveys, Captain Alan Hugenot San Francisco, CA Home

By the way, three of the four FC yachts in the pictures I published were built in professional FC boat building yards...2 in Canada, 1 in Holland. I'm not sure about the Hartley but as she has been owned by the same owner, full insured, for the past 14 years, I'm guessing the Hartley is also Pro built.

Cheers mates,

Bill
Australia

[barnakiel]

Originally Posted by BillAU

(...) Consequently, when the mortar covering any embedded metals is of sufficient thickness (over 9 mm or 3/8?), tests have shown that the embedded metal is fully protected (...)

Hi,

All the above very interesting. THX for sharing!

How heavy is a 20 mm thick piece of ferro-cement (e.g. per sq ft)?

How does it compare to same strength wood/metal/laminate?

b.

[James S]

I'm glad to see this thread revitalized...some interesting stuff.

[GordMay]

Originally Posted by BillAU

... By the way, three of the four FC yachts in the pictures I published were built in professional FC boat building yards ... 2 in Canada, 1 in Holland ...

Samson Marine Designs Enterprises?

Co-Author of
"A manual of ferro-cement boat building" (1969) by John Samson & Geoff Wellens

[clockwork orange]

BillAU, interesting stuff and while i agree that ferro is not an inferior material i have to disagree about the water penetration part,or rather, it is irelevant if a 9mm cover of cement over the armature is impervious because a well built ferro boat will simply not have anything like that much cover, more like 3mm or less if you have done a decent job of fairing the steelwork prior to plastering. Now i dont think the cement is going to be reliably impervious without a good epoxy barrier. As an example, when i built an RORC 39 the hull was 11/16" thick total with 5 gauge hard drawn wire stringers and 8 layers of 1/2" 22 gauge mesh. I actually think a layer of dynel in epoxy over a dry fero hull would be an excelent way of protecting it forever, just like sheathing a plywood or cold molded wood hull. A lot of the reputation of ferro boats being heavy comes from builders who do a crappy job of building a fair armature and then the plasterers try to fair it with cement, its really is a lot like GRP in that what you are after is a high steel to cement ratio ( glass to resin ratio) ,too much cement and you get a weaker, heavier hull, same with resin.
Steve.

[clockwork orange]

Barnakiel, GRP boats are almost all built with polyester resin, not epoxy, i doubt that a thin layer of cement is more impervious than epoxy, but maybe more so than polyester,i dont know.
Steve.

[clockwork orange]

I dont know the weight of a square ft of 20mm thickness ferro but you can calculate it, 20mm would suggest only longitudinals,no diagonals so lets say 5ga stringers on 50mm spacings so 7 lineal ft plus 8 square ft of 1/2" 22ga mesh, plus .62 cubic ft of cement. A google search should find the weights, i dont have time right now. On the boat i built that layup gave 11/16" of thickness so if you had diagonals the panel would be thicker than 20mm.
Steve.

[Dsanduril]

How heavy is a 20 mm thick piece of ferro-cement (e.g. per sq ft)?

The industry standard for steel-reinforced concrete is 150 lbs/cubic foot. Your 20mm skin would come in at about 10 lbs/square foot.

But that is highly dependent on two things; the amount of steel in your section (steel is significantly more dense than the cement portion), and what you use for aggregate. I used to do FC boats for competition, and we would use plastic aggregates and fiber reinforcing to get the density down below that of water (so, in other words, we could make a solid chunk of FC that would float). All without compromising the strength of the material (the concrete side it usually measured in compressive strength, with a typical value of 3000 psi, we could achieve 4-5000 psi at a density of 60 lbs/cubic foot). Costs were through the roof though, no way you could achieve the strengths we got on the open market for a fair price. Only reason we were doing is was because we were sponsored by the concrete industry to prove that it could be done.

From a boating perspective you need to know more than compressive strength, you'll need to know tensile and flexural values, and those depend on the section you build - how much steel, what kind, orientation, how much concrete/cement, what kind, what aggregate, etc.

[BillAU]

Originally Posted by GordMay

Samson Marine Designs Enterprises?

Co-Author of
"A manual of ferro-cement boat building" (1969) by John Samson & Geoff Wellens

G'day Gord,

I honestly don't know the answer That picture of the Sampson 46' is one of the FC yachts I'm looking at...From afar, I'm in Aus' and that FC yacht is in Central America but...When the time is right, I'll have a holiday and check-out the FC yachts that interest me...Hopefully they'll be in the same neighbourhood.

The agent say on their sales page:
Samson 46' - Year 1976 - Sloop - Pilot house Ferro-cement
Build by professional yard in Holland on a Samson design

So I guess that yacht is not a true Samson.


I have worked many boats, steel, timber and my own little Careel 22' plastic boat but I know nothing about Ferro-cement boats, that's why I'm doing the research...To learn about them before jumping in and buying one.

[BillAU]

Almost forgot to ask this.
Anyone here know if a FC Hartley South Seas can sail well without the motor running, or do they need the motor running along with the sails, to make decent headway?

[BillAU]

Originally Posted by clockwork orange

BillAU, interesting stuff and while i agree that ferro is not an inferior material i have to disagree about the water penetration part,or rather, it is irelevant if a 9mm cover of cement over the armature is impervious because a well built ferro boat will simply not have anything like that much cover, more like 3mm or less if you have done a decent job of fairing the steelwork prior to plastering. Now i dont think the cement is going to be reliably impervious without a good epoxy barrier. As an example, when i built an RORC 39 the hull was 11/16" thick total with 5 gauge hard drawn wire stringers and 8 layers of 1/2" 22 gauge mesh. I actually think a layer of dynel in epoxy over a dry fero hull would be an excelent way of protecting it forever, just like sheathing a plywood or cold molded wood hull. A lot of the reputation of ferro boats being heavy comes from builders who do a crappy job of building a fair armature and then the plasterers try to fair it with cement, its really is a lot like GRP in that what you are after is a high steel to cement ratio ( glass to resin ratio) ,too much cement and you get a weaker, heavier hull, same with resin.
Steve.

G'day Steve,

I have never built a FC boat, nor do I have any plans to build one, so I bow to your knowledge as you have built a FC boat.
When I go viewing FC boats, I'll be sure to have a real close look in the bilge, to see if there's any sign of water/moisture. Last one I looked at, in Sydney, NSW, there was so much water in the bilge, you could have gone fishing inside the boat...She truely was a sad neglected mess. Even a blind man could have seen she was on her last legs, rust from all over her, plus she was "all" FC, hull, deck, coachouse, the lot! I doubt she could have been saved by anyone. The broker did his best to talk me into buying her, just to salvage the gear, which was only deck gear but I told him, if it's such a bargain, "you" should buy it...I don't have the time to strip her.
It's sad when any boat ends-up like that FC but I'm not a charity, I want a yacht I can live on and enjoy so I won't be rushed into buying anything.

Bill
Australia

[clockwork orange]

Bill, i believe the South Seas to be decent sailers,a lot of them have gone offshore.
Steve.

[BillAU]

Originally Posted by clockwork orange

Bill, i believe the South Seas to be decent sailers,a lot of them have gone offshore.
Steve.

G'day Steve,

Thanks for that information mate, I do like the FC 40' Hartley South Seas and...It's here in Australia but Hartley no-longer list their South Seas line, they do list a Hartley Tahitian line and a Hartley Fijian line, none of the yachts in either line are listed as 40'. All in the Fijian line are listed as "Ocean Sailors" and all yachts in the Tahitian line are listed as "Motor Sailers".

Stop the presses! After doing some more digging on Hartley South Seas, I found the following:
'Charmiela'. A 'Tahitian 37', (South Seas). She was line-winner by 2 days in the 'South Pacific Regatta', which is a 1,169 mile race for cruisers from Auckland to Fiji. F. & P. Beauchamp-Legg then took her on to Brisbane, Australia..

So I guess they don't need to run their motor when under sail in a race ...Unless racing yachts are permitted to run under sails and motor

Anyway Steve, I'll do my best to go see that Hartley South Seas ASAP

Cheers mate,

Bill

[barnakiel]

Originally Posted by clockwork orange

Barnakiel, GRP boats are almost all built with polyester resin, not epoxy, i doubt that a thin layer of cement is more impervious than epoxy, but maybe more so than polyester,i dont know.
Steve.

But glass does not corrode while metal does. Osmosis does not sink a boat and you see it coming long before it potentially could. What about the ferro corroding - do you see it coming or do you end up with rusto-cement boat one day?

I am not sure about polyester - I see more and more new boats built in / with other resins. Epoxy 'options' seem to be more common from many manufacturers too.

b.