Impact resistance of Ferro?

Hi,

I have been reading everywhere that ferro is strong, however I have also read in the same places that it does not have high impact resistance. Can someone explain this paradox to me please.

Thanks

Scylla :?:

 

Impact resistance of Ferro

Not really a paradox - more faulty logic. Ferro-cement is rigid. Hence if it meets an immovable object at high speed it will crack. Mind you steel will buckle, and GRP shatter. Timber has more elasticity and will bend to absorb the shock.
Ipso: If you sail ferro-cement - don't meet immovable objects at high speed.

 

All building materials have good points and bad.

About ferro most of the qualities can be traced back to it's internal wire structure. Concrete is actually pretty flexible stuff. I know this sounds hard to believe, but it is. Well built ferro hulls will have heavy gauge welded wire embedded in the structure. Poorly built ones will have used "chicken wire" or similar low quality and of not sufficient strength wire installed. It's very difficult to tell what the wire is without x-rays, damage or core samples which show the wire type used. Ferro has a bad reputation for cracking up like an egg shell, because of all the inferior wire used in it's construction. Well done ferro yachts are very strong, resists just about everything the marine environment can dish out and long lived.

The damage is different looking, but all materials have different types of damage. Steel dents and tears, Aluminum absorbs more energy then steel, but also dents and tears, 'glass fractures and tears, but looks quite different then metal tears, wooden structures, crush, pop or work loose fasteners and splinters, ferro cracks and fractures, but this looks different then 'glass fractures because of the load sharing and spreading the wire matrix provides.

Personally steel is at the bottom if the list in building materials I'd recommend, follow quickly by ferro. Aluminum for larger yachts and wooden for smaller are at the top of the list and 'glass is in the middle. They all have their issues, some have cost effective ways around them others less so. It's very difficult to beat the performance and price of a heavy duty 50' commercial fishing boat done in steel, in spite of the draw backs the material has. On the other hand it's difficult to compete with the performance of an aluminum mega yacht. You'll pay more for the material, but it will reward you with fuel and maintenance savings pretty quickly over steel.

They all have issues to address. If designed well, then the hull material of choice has limited bearing on the upkeep of the yacht anyway.

 

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 just posted on the other thread http://www.boatdesign.net/forums/showthread.php?t=16605&page=2