Is there a problem with concrete as ballast in steel sailboat?

Besides the lack of density.

 

No problem if done correctly. Usually better to add some punchings to up the density but not required if the volume/mass ratio is OK for the design. If the keel is stiff enough then the concrete will remain firmly adhered to the steel, however if the plating is likely to move relative to the ballast then you need to either cap it or use a good mastic paint to seal around the ballast top to stop moisture sitting in the interface.

Hope this helps

 

Thanks. Yes, there is steel punchings too.

 

what kind of concrete? im tempted to think of fiber filled hi psi w wire mesh reinforcement

 

I've found another great balast material by accident really !.
My dad had a stroke some years ago - 8 years, [ as it's relevant ] and I made him a counterballanced "elevator" as otherwise he was a virtual prisoner in their 2 story home .
I happened appon some drums of punchings, only these punchings were from thin galvanised sheet steel .
It was like heavy coarse sand. Heavy because it had large amounts of zink [ galvanising ] in it. more galvanising than steel I'd think.
it flowed & " packed " into the weight box [ for the lift counterweight] so easy.
This lift lived outside and worked fine for the 3 odd years he needed it. When I dismantled it, it occured to me to test the open toped steel weight box , or rather, the punchings in it, to a prolonged weather test .
I have left it out in the rain & being on the bank of a tidal river, one would have to say a somewhat marine environment,for around 5 years, to see if the steel box would :-
A; rust - thinking the galvanised punchings might give some sacraficial protection - &
B; "blow" the 3mm box.
The steel box, much to my amazement, has neither rusted, nor blown
[ pushed out of shape by the internal expantion/rusting of the punchings ]
The punchings got a rock hard crust of white oxide/rust and that's how it's stayed for all these years.
The punchings are way heavier than steel, or concrete for that matter.
I've shown the box to a freind who [ then ] was up to the balast stage for his 40' steel boat and he got a couple of 44gal drums of it for $200 per drum, poured it into his keel, plated it off and welded a BSP fitting into the top plate, then threw in 20 odd liters of water soluble oil to take care of any condensation problems.
The perferated sheet is used for decorative applications, usually outside [ hence the galvanising ] and I imagine someone in your neck of the woods must make same !?.
Pete.

 

I like zink plated sheet punchings too. usually we can get 1mm mild galvanised. The best are the circularhole punchings up to 10mm diameter. Triangular punchings are also common but are much harder to handle.

Yes the zinc gives both protection for the punching and for anything they are in contact with. The common approach is to simply fill the keel with the small galv punchings and cap the top with 4 to 6 inches of good waterproof plaster/concrete. You must factor inversed retention strength into the design\ but it works well enough. Some folks add water soluble oil topped up to the capping and this adds further weight. I have seen several vessels repaired with keels partially opened after 30 years and the inside was as new. I specify galv punchings for some applications.

 

Don't know, but the current infactuation is a boat with lead ballast, so my concrete question has become moot. Thanks.