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Old 09-08-2005, 16:58   #16
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Manfred Kanter is well-known for building premium Aluminum yachts, to Chuck Pain designs.. I didní know they built in steel.

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Old 09-08-2005, 19:47   #17
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Hi Jeff, I will come back to you about info on the "commercial" boat. Maybe what I have read has been "dressed up" a little.
Can you answer me this question, What exactly IS portland cement then. It is made here in NZ and I had always thought it as JUST a brand name. But is it a Type of cement different from another "type" of cement????

I don't want to beat a dead horse of dredge up an argument or what ever but going back over the old thread were discussions were brought up in regards to FC. I do have to say, some comments made by you *(don't take this the wrong way) I feel were not accurate. And that's not entirly your fault. It is the fact that there are two very different camps out there in the world in regards to FC. Now I know you backed up your arguments with some very good figures and I can not even dream to be able to do that on the side of a FC owner. I wish more detals were available. But I do have to say, you can't look at the strength of an FC hull from the aspect of the strength of just the individual materials. It would be like saying, Fibreglass on it's own is XX strong and resin on it's own is XX strong, thus the hull can ever only be XX strong. But we all know the combination of both in the perfect manner is XXXXXX (give or take an X;-) strong. The same can be said with FC. The combination of the two product results in unblievable strength. But sadly, it is only those of us that play with the stuff that can atest to that fact. Some many misnomers have been circulated over the years about FC. like rusty amatures, cracks allowing water in, blah blah blah. But it is understanding what is actually going on within that combination of materials that is seriuosly lacking in the camp of the down players of FC.
I didn't understand alot about FC untill I beocme a techincal Project manager/designer of electronic installations in some Stadiums in NZ. And I came to learn alot about concrete and steel and what goes on in the middle of it. Remember, Cement is NOT JUST concrete. It is a mess of chemicles that are alkilines are stuff that will work on and with Steel and specifficaly its oxide, rust. So rust is not an issue inside a SOUND steel armature. Rust on FC boats is usually only surface and not seriuose apart from cosmetics.
Oh look, I did get carried away, sorry I didn't mean to.


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Old 10-08-2005, 00:15   #18
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Do you like the boat....

I think that the real questions when buying a boat are :-
1. Do you like the boat?
2. Is the asking price fair given the condition?
3. Will the boat do what you want it to do?
4. Can you afford the risk of buying the boat?
The price of a boat has to reflect the cost of bringing it into servicable condition, so you must be able to properly check the hull and all major systems before making an offer.
The risk in buying the boat is that some of the price must be written off as soon as a contract is signed. This is the difference between the purchase price and what another buyer would pay for the boat plus brokers commission and interest lost, plus other purchase costs (surveyors etc), plus depreciation, plus the risk that the next buyer may be a good barginer.
So a $100,000 boat has a loss of $10,0000 (brokers commission) plus the cost of (say) a year on the market at 10% ($9,000 loss) plus other costs.
You can see why I find it hard to buy a boat.
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Old 10-08-2005, 00:57   #19
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From the Portland cement association, portland cement is a "hydraulic cement (cement that not only hardens by reacting with water but also forms a water-resistant product) produced by pulverizing clinkers consisting essentially of hydraulic calcium silicates, usually containing one or more of the forms of calcium sulfate as an inter ground addition." Got that.......

In other words, Portland cement is the 'glue' that holds concrete together. There are a variety of ways that portlland cement can be formulated and when used for ferrocement it is mixed as very thick formulation, high strength mixture. Ferrocement behaves just the same as any other form of reinforced concrete with the steel taking the tension and the portland cement taking the compression.

What makes ferrocement unusual relative to conventional reinforced concrete is the very high proportion of steel relative to cement which makes it stonger per square inch than normal concrete and weaker per square inch than steel.

The good news is that ferrocement is substanially lighter than steel and also, when properly applied, the portland cement creates a water proof membrane over the steel. There in lies the problem, as cement ages it gets continuously harder and stronger in compression but more brittle. Over time small hairline cracks from in the thin shell protecting the steel and those hairline cracks allow moisture and air to reach the steel reinforcing. Once that happens the rust spreads down the length of the steel and deteriorates the bond between the steel and the concrete and that pretty much ends the useful reliable lifespan of a ferro cement boat.

Of course the length of time required for that deterioration varies with the quality of the construction. On big boats (over 50 feet or so) the shell can be thick enough that it takes a very long time for moisture to reach the steel. But on small boats, in an effort to keep weight down, the thickness of the shell is often reduced to the point that the lifespan is quite short, OR the shell is made thicker to provide a longer lifespan at the price of ending up with an extremely heavy boat.

Which gets us back to the strength of Ferrocement relative to its weight. Ferrocement is one of the densest boat building materials that there is (just over twice the density of fiberglass) while offering roughly 5%-15% greater strength by cross sectional area. The numbers are easy to run, pound for pound, at least in the usual steel to cement ratios employed on smaller boats..... pound for pound ferro cement is the weakest of the boat building materials currently used in boat construction.

While no material is perfect, modern composites, when properly engineered, offer the most strength (including impact resistance) per pound of any of the other choices and when coupled with vinylester resin, the longest potential for a low maintenance lifespan.

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Old 10-08-2005, 07:35   #20
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Excellent post Jeff.

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Old 11-08-2005, 15:06   #21
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We love our steel boat. Any painting we do seems easier than the yearly, buffing, waxing etc we did on the fiberglass hull.
Our steel has been coated, so sandblasters beware or removing these special coatings.
Of course, flaking paints must be removed, bare steel MUST be dealt with immediately.
For dull paint and little scratches it is an easier job to sand a little and apply paint to the area. At least that is what we have found.
Our vessel was launched in 1982, she spent nine years in cold salt water, the rest of her life she has been in fresh water. There have been no rust issues to date.
Fair Winds

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paint, steel hull

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