A boat

[LittleSister]

I seem to recall that ferrocement mimics the distribution of weight found in big wooden boats

I hadn't heard that, but it would make sense.

I think it would have to be quite a big boat to mimic the amount, rather than just the distribution, of weight, because of the effective lower limit of thickness of a ferro hull.

At the Museum of the Broads, at Stalham, Norfolk, is a ferro-cement dinghy built years ago as a project by apprentices at Windboats. It looks a dinghy that would row well, and it would be robust, low maintenance and easy to repair. It does though take 6 (or was it 8?) people to lift it!

 

[veshengro]

LittleSister​

" The steel reinforcement in ferro-cement will eventually rust, and how quickly will depend on how well it is insulated from water (i.e., how well built it is). The big challenge with ferro-boats is knowing how well it was built, ....

That's an interesting point. When my steel Gaff Cutter hull was being built, I did much of the labour including ballasting the hollow keel. I painted the space with three coats of 2 pack epoxy and left it to thoroughly dry. My intention was to use iron sash window weights and a fine concrete mix as ballast. The thought of damp concrete and iron troubled me so much that I looked for professional advice. At Littlehampton in Sussex was a big Aggregates supply/Haulage company called Francis..Transport? Haulage? can't remember now, but I went to see them. I spoke to one of their technical people about sealing the window weights in concrete and the advice was that if I bedded the weights tightly in the mix and did not allow the weights to touch the sides of the keel even though epoxied, and excluded any voids around the weights, then the result would last for many decades.

Using the weights made quantity for required tonnage easy because they all had weight in LBS stamped on them and I knew how many bags 25 KGS of ready mix I was using. I laid the weights like Toad in the Hole, allow 48 hours for drying between each layer until the required weight was in the keel. After a couple of weeks ( The build was in a heated hanger) I sealed the concrete with a couple of thick coats of rubberised paint. I never had any problems with the result in the following 10 years.

 

[Wansworth]

On my steel boat I bought off Hillyards almost all their pigs of iron and weigh them .I st them in concrete in the hollow steel keel.In my ownership of fifteen years there was no problem ,she is still sailing somewhere in Galicia ….30 years later

 

[ducked]

Easier just to replace any failed balsa with plastic foam or GRP matrix (or even new balsa!). In principle it's an easy job, but if done internally it's horribly messy and access may be challenging.

Concrete would likely add a lot of weight, which would not be good at deck level. If not too concerned about weight, just simply add layers of GRP.

I'm thinking with lightweight aggregate and using the concrete as a matrix to hold lighter weight filler pieces, it shouldn't be too heavy, though maybe heavier than the original.

Not possible to layup GRP through holesaw-cut holes, which was how I envisaged doing it.

There might be an issue with the alkalinity of the cement attacking the glass reinforcement if the core got wet (not really reasonable to assume this wont happen on a boat since that's what I'm sneering at balsa core for) but the polyester should protect the glass to some extent, and there have been encapsulated concrete/reinforced concrete keels.

But its academic anyway, since I hopefully wont have to do it.

 

[Greenheart]

Just dawdling through Apollo Duck, I found this gorgeous schooner (I'm a complete sucker for gaff schooners)...

...she really looks as old and as wooden as can be, inside and out, but it seems she's late-80s built in ferrocement.

Only £79,000. There's a bit of me that could be persuaded...
.

 

[Wansworth]

Just dawdling through Apollo Duck, I found this gorgeous schooner (I'm a complete sucker for gaff schooners)...

...she really looks as old and as wooden as can be, inside and out, but it seems she's late-80s built in ferrocement.

Only £79,000. There's a bit of me that could be persuaded...
.

Ferrocement is ideally suited to this type of vessel for its shape and weight distribution