Intelligent Discussion on Ferro

[barnakiel]

Originally Posted by NeptunesTrident

You must keep in mind that the weight of the material is directly proportional to the static strength ratio of material. So, with this in mind, a boat built of fiberglass may have a hull thickness of 3/4 to 1", where as in steel it may by only 3/16" thick. Strength to weight will still be roughly the same. So the 20 ton boat still weighs 20 tons.

Exactly - just look at my earlier posts and you will find that I alwayas said strength for strength!

Now the point is to establish what thickness of respective material represents equal physical properties (strength up front).

You gave an example of roughly 1 inch GRP for 3/16 of F-C. I guess you are wildly wrong here (my guess, not my knowledge). Please note that in the above postings someone clearly stated that the amount of cement to fully protect the steel is supposed to be about 9 mm (!!!), so, we are talking of roughly 18 mm F-C as a minimum. This would give us an equivalent in roughly 45 mm (!!!) of GRP.

The above paragraph aside (as I too can be very wrong in my assumptions!) WHAT WE NEED here is to find out how strength of GRP (say, or wood, or steel) corresponds to strength of F-C. Do you know of any place where we can find this? I think there are technical terms for this - but in any case we have to find pout the materials comressive, tensile and (bending?) strengths.

Right? Wrong?

As a final note, please observe that in 1 inch GRP glass will be distributed nearly everywhere and equally and the strands will run in all directions (unless we use special unidirectional glass. Now in a F-C the steel will be concentrated mostly inside (?) and will be mostly bi directional (or uni directional). This too may influence the properties.

b.

[barnakiel]

Originally Posted by NeptunesTrident

(...) So, with this in mind, a boat built of fiberglass may have a hull thickness of 3/4 to 1", where as in steel it may by only 3/16" thick.(...)

(Your quote only to show the idea that I am referring to, not to criticize anything)

OK. So I went out to do some reading and here is what I found:

Fiberglass strength:
compressive : 200 MPa, tensile : 450 MPa (averages, for 50/50 material)

Fiberglass - Wikipedia, the free encyclopedia

Ferrocement strength:
compressive : 45 MPa, tensile 270 MPa (tensile - not to be exeeded)

http://www.bpesol.com/bachphuong/med...ok/549r_97.pdf

Now, sure thing, I am not a boat designer, I may have gleaned the data wrongly.

Please note (e.g. via my yesterday's post) that both steel and concrete have higher specific gravity than resin and glass.

Now, from the data in my yesterday's mini-research and from the data above, it looks like the F-C boat has to be THICKER to match a GRP built. And since F-C is already HEAVIER (by say the factor of x3) then in result we will end up with a boat 9 times heavier, strength for strength.

Hahaha! ? ? ?

I think the only exception will be a heavily packed F-C panel where steel constitutes most of the material.

Such a boat is called a STEEL BOAT and we do not need concrete to build it. Right? Wrong?

b.

[boatman61]

This is to intelligent for me....

[sdowney717]

why not take a tight frame work of steel mesh and rebar and spray it with

[barnakiel]

hey - something happened to this thread - I cannot load it properly anymore - is it the videos perhaps?

admin?

THX,
b.

[clockwork orange]

Barnakiel, it is not neccessary to compare strengths of all the different materials,it simply does not mater if one is "stronger" than another,what materes is that the chosen material is "strong enough". Boats can be engineered to have adequate strength out of all manner of materials, each material has its own merits. If you plan on running your boat on the rocks on a regular basis your choice is simple, buy a metal boat, if you want a stiff,light, high performance boat you buy a cored composite or wood boat, for most other purposes a solid glass or ferro boat will both get the job done. What Bill said in his previous post is right on, if you find a nice example of a FC (or any) boat that is 40yrs old and has travelled far you dont need to concern yourself with whats inside the skin, do people get all bent out of shape about whats inside the skin of an old glass boat? no they dont and yet they dont know that any more than with fc,and no,your surveyor cant tell you that info either unless he has. Since you seem to have an interest in what is in there i can give you an example, a Hartley RORC39 has a backbone of 1" galvanised water pipe,trussed frames bent out of 5/16" mild steel rod with a molded depth of 3", longitudinal stringers of 5ga hard drawn wire, 2" OC wired to the framed with steel tie wire, there are 4 layers of 1/2"x22ga galv chicken mesh on each side of the stringers and frames wired to the stringers and as ive mentioned before, just a thin cover of mortar over the mesh, Hartley was a big proponent of the 2 shot plastering method where you plaster the outside first,water cure it for a couple of weeks, get inside and knock off the nubs that protrude past the stringers, then plaster the inside, the frames and underside of the deck and finally the top of the deck. BTW,when you try to calculate the weight of the panel you need to subtract the volume of the steel from the volume of the mortar which makes up your 3/4" thick panel, the steel takes up at least half if not more of the volume so you would be figuring on no more than 3/8" of mortar and i think that may be high. With his boats larger than 40ft he used diagonal wires 2" oc over the longitudinals so i think they would have a higher proportion of mortar to steel maybe. Anyway with this info you should be able to figure a pretty close weight psf. Please note, nobody in their right mind would use 9/16" of mortar over the steel, FC is like GRP, you want a high steel to mortar ratio.
Steve.

[clockwork orange]

You know ive been thinking about it and the biggest beef folks seem to have with Ferro is that they dont trust that all the steel is in there and they have no way of verifying it, well, most of us sail GRP boats and we also cant easily verify whats in the skin, i mean who of us knows how many layers of mat and roving is in our hull? what is the glass to resin ratio? is the laminate schedule what the designer specified or did the builder take cost cutting shortcuts? did you ask these questions of the surveyor you hired and did he provide you with answers? im thinking the answer is no to all of the above because i cant answer any of these questions about my own boats without doing destructive testing which im pretty sure a surveyor is not going to do so im just as much in the dark as if i were to buy a ferro boat. What i do know is that, having been a boatbuilder for 40yrs now and having worked in custom, production and repair that i would no more trust that my boat is not horribly resin rich or is built to spec than that a fc boat has the correct steel in there. During the years when i built my fc boat i visited a lot of boats in build and im pretty sure i never saw an armature without the correct steel, where the problems arose was when a builder did not understand the concept of fair and didnt put in the effort to get the armature perfect before plastering, then along comes the plastering crew who do their best to fair it with mortar which is a mistake as it leads to a heavy boat.
Steve.

[barnakiel]

Originally Posted by BillAU

G'day b,

I would only be interested in "How much steel do we need inside the ferro" if I were planning to build a FC boat (...)

G'day mate!

At least one source I went to claimed 'as much as feasible' - the more steel the better the result (sure - one needs cement too - to keep the steel together). Unlike glass matrix in GRP, steel matrix in F-C has plenty of intrinsic strength. (Hence my suggestion elsewhere to skip the C part and build a boat in F instead!) (;-)) The other thing is that a 'matrix dense' F-C will be a heavy boat (in any case it will be heavier than a 'cement dense' one.

Have a good look at the pdf source I quote. I liked browsing thru it and found it most informative (I am a F-C moron, but I like learning about boats).

I 100% agree that all hows should be given in boat plans that you acquire. After all a trained boat designer will know much more about F-C than we can gain from a handful of web sources.

Cheers,
barnakiel

[barnakiel]

Originally Posted by clockwork orange

(...) if you find a nice example of a FC (or any) boat that is 40yrs old and has travelled far you dont need to concern yourself with whats inside the skin (...)

Yes. This is what I call the classic way of building a boat. Please note, however that with this method boats changed little, sailed poorly, leaked badly and were generally overbuilt, underbuilt and anything in between.

But should we still build boats like this today when we have computers, accurate material data, aero tunnels and test basins???

Now please show me that 40 y.o. boat that has traveled far.

As I said elsewhere, I am in love with all boats and will be the last to claim that a boat cannot be well built in an X type of material. The point is I have never seen a fine F-C sailing boat this far. A SAILING boat.

b.

[BillAU]

Originally Posted by sdowney717

why not take a tight frame work of steel mesh and rebar and spray it with

[BillAU]

Originally Posted by barnakiel

Now please show me that 40 y.o. boat that has traveled far.

As I said elsewhere, I am in love with all boats and will be the last to claim that a boat cannot be well built in an X type of material. The point is I have never seen a fine F-C sailing boat this far. A SAILING boat.

b.

There are plenty of nice looking, pro built and home built FC yachts around, you only need to look

How about a cutter rigged ketch with a clipper bow and sultry lines, just over 50' The Black Wind...I applied to buy The Black Wind but the owner, a Scotsman, withdrew her from sale, he dicided to keep her. The Black Wind is now in Mexico after sailing from the UK. To get from the UK to Mexico he must have covered a fair bit of water. you can read The Black Wind blog at the above link.
Or how about a Pro built, good looking, 1976, 46' Samson, built in Holland and now offered for sale in Guatemala. From Holland to Guatemala is also no short, day out on the bay trip.
Or there's a 1978, 40' Hartley South Seas here in Australia. This one has been with the same owner for the past 14 years and has been comprehensively insured for past 10 years. She has only done a few trips to Tasmania, (about 2,900KM if he sailed directly) he also sailed around Australia and did a few trips to Asia, anyway, I guess he proved he has a safe "Blue Water" FC boat

Personally I like the look of a Hartley or a Samson FC yacht, If you want to see some good, well built FC yachts, have a look at these Ferro Boats When you open the link, click on the "Samson Gallery" and when you finish there, have a look at the "Hartley Gallery", there you will see a number of well built FC yachts, true, some of them are at, only 20 + years old, babies but most of them have sailed the high seas, so do have a look-see

[BillAU]

Just thought you would all like to read this:

Ocean Racing Yacht of Ferrocement.

Britain's largest ferrocement yacht, the New Freedom, was a massive do-it-yourself exercise accomplished by Captain Tony Fincham and a team of 80 people, including 18 experienced plasterers and many volunteers. A highly sophisticated twin masted schooner 84 feet long overall, the boat is believed to be the largest ocean racing yacht built in Britain since World War II. The taller of her two aluminum masts rises 110 feet above the salt flats where she was built. The ferrocement finish of the yacht is smooth. The finished thickness of the hull is one and one-sixteenth of an inch, including reinforcement consisting of welded rods and six layers of tightly packed, galvanized welded wire mesh. The chief benefits of this type of ferrocement construction are strength, minimum maintenance and ease of repair.

From: Ocean Racing Yacht of Ferrocement - Concrete Construction - Concrete Construction

Now that's why I believe a well built FC yacht would be my kind of boat. i.e. strength, minimum maintenance and ease of repair.

[BillAU]

I believe I've narrowed my search down to a few pro built FC yachts here in Oz but with one of those yachts, I'm a little sus'. I'm wondering...Why would a FC sailing yacht, a Ketch, have 2,000LT fuel tanks
I would expect to find fuel tanks of this size on a motor yacht, not on a pro or properly built sail boat, built using whatever materials.
Any ideas why a FC sail Ketch would have such large fuel tanks

Bill
Australia

[barnakiel]

Originally Posted by BillAU

I believe I've narrowed my search down to a few pro built FC yachts here in Oz but with one of those yachts, I'm a little sus'. I'm wondering...Why would a FC sailing yacht, a Ketch, have 2,000LT fuel tanks
I would expect to find fuel tanks of this size on a motor yacht, not on a pro or properly built sail boat, built using whatever materials.
Any ideas why a FC sail Ketch would have such large fuel tanks

Bill
Australia

My guess is that that the design will sail very poorly hence the need for large fuel tanks (and a huge diesel).

Unless this is a huge ketch, then everything can be all right - big boat, big engines, big tanks.

What is the design. How much does she displace?

b.

[muskoka]

Originally Posted by clockwork orange

You know ive been thinking about it and the biggest beef folks seem to have with Ferro is that they dont trust that all the steel is in there and they have no way of verifying it, well, most of us sail GRP boats and we also cant easily verify whats in the skin, i mean who of us knows how many layers of mat and roving is in our hull? what is the glass to resin ratio? is the laminate schedule what the designer specified or did the builder take cost cutting shortcuts?
Steve.

I kind of get your point, but the basic difference is that glass is inert when immersed in seawater whilst steel is not. So, worries about the integrity of a steel armature require core samples to ease the mind. I've got a 7 year old boat and a 30 year old boat - both GRP. Grinding out an osmosis blister is easy and cheap. Messy, yes, but easy to self inspect and repair.

Your reference to the GRP structure is spot on when referring to self builds, but its really not that applicable to factory built vacuum bagged hulls. They are pretty simple.

I'm convinced that an FC hull can be built well, light and eggshell thin. But, I think that takes a professional builder. In which case the material costs become subordinate to the labour costs.....