Keels: Lead v Iron?

wklein said:
I was under the impression it was depleted uranium which if i can recall my school physics becomes lead when it has finished reacting. I would imagine it was just lead but more pure and dense. I would be interested in someone with a genuine understanding of the science's input.
Click to expand...

If you'd actually been paying attention you would also recall that U 238 ( the major, and non fissile, constituent of natural uranium ) has half life of 4.5 billion years so you are in for a long wait for your uranium keel to turn into lead.
 
Please lads..the keel was inert to all intents and purposes,Alain died at sea I seem too remember years later,(I know Tabarly fell overboard in the Irish Sea at night..and he was the advocate of NOT wearing a saftey harness).I also seem to recall the uranium was sold and maybe replaced with something else........What do I know I was only there far better to Wikopedia it ..Nite Nite
 
Back to the OP. Iron does rust and unfortunately expands with the rust products. So a GRP keel filled with Iron punchings or similar can rust and expand so splitting the GRP keel. A cast iron keel with paint treatment inevitably seems to rust. The rust products pop off the anti foul paint so giving premature fouling.
Lead while more expensive is more inert. Fine for inside GRP fin and Ok for exposed lead (with antimonyfor strength).
So if the OP is looking at a boat to buy. Cast iron keels are tough and the iron can be treated with epoxy to give reasonable protection between repaint but expect to retreat each winter. good luck olewill
 
Stork_III said:
Perhaps you should tell the Swedes then. Antimony is added to the lead to make it sufficiently stiff for the keel,with some residual softness, great for those Baltic rocks. Even Bavaria offer lead keels on some if not all models.
Click to expand...
The slight softness of lead also helps, as Stork says, if you hit a rock: it has considerable shock-absorbing properties and reduces the chance of hull damage at the aft end of the keel root - the usual consequence of hitting a rock at some speed with an iron keel.
 
Downside of DU, tungsten, gold etc (anybody else remember Desmond Bagley's book The Golden Keel?) or ununpentium - the new element that's just been announced, although having a keel that auto destructs is probably not a good idea - is that most rating rules ban it. E.g., IRC rule 19.4 In the construction of hull appendages, no material with specific gravity greater than 11.3 is permitted.

Means you can't go and race it. Might not matter to some, of course, but something tells me that the sorts of people willing to fork out for a DU keel are probably competitive, racing types.
 
Last edited:
maby said:
I was under the impression that most supposedly lead deep fin keels are actually iron keels with a hollow bulb that is filled with lead - it's more a performance thing than durability. Filling the bulb with lead allows you to get the balast weight lower and to reduce drag since a given weight occupies less volume.
Click to expand...

My Trintella 44 has a deep lead keel of some 6 ton. The yacht has 2.2m draught. boat is 33 years old and sails like a dream.

if you want less volume than lead than go for tungsten. Tungsten is 50% heavier than lead
 
VicS said:
If you'd actually been paying attention you would also recall that U 238 ( the major, and non fissile, constituent of natural uranium ) has half life of 4.5 billion years so you are in for a long wait for your uranium keel to turn into lead.
Click to expand...

:D
Clearly wklein's memory of school physics has a somewhat shorter half-life.

And to MadPad: Pen Duik's keel had a fairly short full-life, as you say: according to Wiki it was later replaced with lead.
 
macd said:
:D
Clearly wklein's memory of school physics has a somewhat shorter half-life.
Click to expand...

Actually even if you wait 4.5 billion years your Uranium keel wouldn't turn into lead.

On the subject of alchemy, how about a gold keel? Gold is even more dense than Uranium and is not radioactive. Also, it is so inert that marine growth does not stick - I spent a happy summer diving on the wreck of de Liefde in the Outskerries many years ago and the gold coins we found were like new. I am off to the patent office to patent my idea before all the AWB manufacturers steal my plan.
 
Why would marine growth not stick to gold? Surely the inertness is not relevant, just the ability to get a grip on the gold surface? Just curious.
 
Both isotopes that make up natural uranium U235 ( the fissile one) and U238 the main one at nearly 99.3% are only weakly radioactive by virtue of their very long half lives

Both decay by alpha particle emission.
Alpha emitters are easily shielded. A piece of paper will stop alpha particles, but they are potentially very damaging if ingested.

Yes I do know what a "half life" is.

If you want a really dense material for your keel perhaps you should consider osmium. At 22580 kg m-3 I dont think you'll beat it
 
VicS said:
Both isotopes that make up natural uranium U235 ( the fissile one) and U238 the main one at nearly 99.3% are only weakly radioactive by virtue of their very long half lives

Both decay by alpha particle emission.
Alpha emitters are easily shielded. A piece of paper will stop alpha particles, but they are potentially very damaging if ingested.

Yes I do know what a "half life" is.

If you want a really dense material for your keel perhaps you should consider osmium. At 22580 kg m-3 I dont think you'll beat it
Click to expand...

How about attaching a blackhole to the bottom of your boat? Or a piece of neutron star?
 
Joker said:
"how about a gold keel"

It was the basis for a thriller - how to smuggle gold undetected.
Click to expand...

And the twist at the end of the story (called "The Golden Keel" by Desmond Bagley) gave an excellent reason why keels should be made of the material specified by the designer!

Pretty much all of the debate here is moot - for reasons of engineering and weight distribution the correct material for ANY keel is the one that the designer specified. Anything else can put excessive loads on the structure, not be strong enough to bear hydrodynamic loads, make the vessel too stiff/crank or whatever.
 
You must log in or register to reply here.

Share this page

Top