Ferro Cement hulls

[Bergalia]

Originally Posted by lazeyjack

ah yes Koln Cathedral

Ah yes - the Dom. Staggered up those stairs one hot summer's day - behind a very fat, very sweaty lady. I remember the guide tellling is with immense pride that the only damage done during an RAF bombing raid was in cracking of a couple of roof tiles. "Gott es mitt uns..."
But a fabulous structure. Well worth going to see (and climb inside one of the spires)...But come on Lazey - this is well off the topic....

[darr]

A first hand testimony to the strength and durability of "ferro" construction can be found at http://1000daysatsea.blogspot.com/ Day 78.

In addition there are photos posted on smallyachts.com of our Fer-A-Lite hulled sailboat after hurricane Frances. I would note that the damage to the bow was a result of over 7 hours of battering on a concrete seawall. What is not shown is the large piece of seawall that was broken off as a result of the bow repeatedly pounding on it.

I question the repeated laments of fragility. Perhaps the portland cement versions have a tendency to radiate cracks, however Fer-A-Lite hulls appear to not suffer from that tendency.

[MikeJohns]

The impact strength of the thicker parts of the hull such as the stem, and keel LE are very great, what is not so strong is the shell between frames although Lloyds will give an Ice rating to correctly built ferro hulls.

They are usually stronger than prejudice dictates and I think they are similar in most respects to any other material that exhibits brittle failure.

The biggest problem with the material is the level of quality control and supervision needed in their construction to guarantee a trouble free hull. It is the only construction I am aware of that is almost completely impervious to long term neglect (Undamaged).

[darr]

I have more pictures that show that our hull also beat against the seawall on the starboard side for a couple of hours before her bow worked its way onto the seawall, and the lack of damage that was done (exception of scrapes and ripping off the rubrail).

Keeping in mind that in ferro-cement construction, the only purpose for the cement is to keep the water out. Fer-A-Lite on its own without the steel armature of the hull is incredibly strong, durable, abrasion resistant with a bending moment of aluminum plate. When you couple that with the steel hull armature you get an increased strength from the combination of the strength of the steel, plus the strength and flexibility of Fer-A-Lite.

We built a couple of test panels with 5 layers of mesh, 2 layers of 1/4" round stock and an overall thickness of 7/8". Beat on it with a sledge hammer, bounced off, shot it with a 45 cal, bounced off, attacked the untested panel with an air hammer, it took half an hour to get a 1 1/2" hole through the material.

We are currently beginning the application process to the Coast Guard for a determination, then we will be going to Lloyds.

In addition, Fer-A-Lite offers a 40% weight savings over the same volume of Portland.

It is slightly more expensive than Portland, but then piece of mind comes at a price.

Darr

[Andy]

Originally Posted by Raggi_Thor

I don't think ferrocement is as good as wood, grp or steel.

MikeJohns The impact strength of the thicker parts of the hull such as the stem, and keel LE are very great, what is not so strong is the shell between frames although Lloyds will give an Ice rating to correctly built ferro hulls.

They are usually stronger than prejudice dictates and I think they are similar in most respects to any other material that exhibits brittle failure.

The biggest problem with the material is the level of quality control and supervision needed in their construction to guarantee a trouble free hull. It is the only construction I am aware of that is almost completely impervious to long term neglect (Undamaged).

Bergalia Little to add to the above advice except question their 'fragility'. I spent a summer helping fit-out a couple of ferro-cement shells (cement mixed with chopped fibreglass over chicken mesh wire) built by an Inverness firm Concrete Afloat (since sunk).
The wire frames once erected were 'sheathed' by a couple of local plasterers and as they cured shaved into shape by a local stone mason...
Fitting out was done on pre-inserted wooden frames - 'nailed' and glued in place. However the finished articles did float - although I never heard of them going to 'sea' but used mainly for sailing in the Great Glen - Loch Ness and the Beauly Firth (sheltered). One did have a collision with the Navy pier at Cromarty, and demolished it - the pier that is - without apparent harm to the vessel. (The pier had been built by the Admiralty in the 1930's. It was elderly timber and it's only claim to modest fame was as a bit player in a mutiny by a handful of Naval Ratings).
They were cold vessels to work in, and according to their owners cold and wet in performance. But other than that....

People have built complete rubbish out of all boatbuilding mediums. Ferrocement suffered more due to the number of amateurs who gave it a shot but didnt know what they were doing. Anyone who has seen a new J122 delaminate around the keel whilst sailing can tell you that in any medium even the professionals can get it wrong. A lot of the amateur built ferro boats had poor impact resistance because a) they screwed up the mortar mix and b) they either designed the boat themselves or at least engineered them (using the term loosely) themselves. For a ferro boat to have good impact resistance, look for ones with integral floors and frames (which many amateur built ones dont) and look for signs of rusting on the surfaces. No rust means likely no air getting through the concrete and thus little chance of armature degradation through oxidisation. My own boat is proof of this (a few years ago a hole was chipped into the hull to examine the mesh, which was deemed by the surveyor to be in very good condition). I should also point out that I also have a cold-molded wooden Flying Dutchman and a clinker Yachting world Dayboat. If I were building a new boat I would go wood epoxy or steel, but a good ferro boat is as good as a good boat in any other material, as long as heavy displacement is ok. So if you want a great secondhand boat, look for a good ferro one if you are on anything of a budget (have to say everyone thinks mine is wood...)