View Full Version : Lead loading center board
10-05-2009, 04:42 AM
Continued from Casting Catboat rudder hardware:
What I had been thinking of is taking a sheet of ordinary mild steel, say 10mm thick and cut it roughly to the desired shape of the centerboard, drill holes for pivot pin, etc. Then cast lead around it until you achieve the desired thickness and weight. It won't rust, as all the steel is safely covered with lead and wont be as prone do deformation as ordinary lead, due to the steel backbone.
I think it's possible .You would need lots of holes through the steel to mechanically lock the lead to the inner board .Perhaps ever 3" at 1/2" diameter?
The main problem might be to preheat the steel to at least the melting point of the lead ,so as not to chill the lead as it flows into the mould .
An interesting idea and worthy of discussion .Perhaps a separate thread with a descriptive title ?
I got the idea after reading something similar to this article.
From what I understand it adheres to the steel without having to drill holes or anything fancy. I'd expect it would hold on the center board steel "back bone" too. No personal experience though, so I'll leave final judgement up to the more experienced.
10-05-2009, 05:43 AM
Howabout this: instead of a steel plate, why not use ribbed bars of steel like in concrete?
Not so much steel to be preheated, with 6 or even 4mm bars you might get away without any preheating. Grid of bars near both surfaces just like in reenforced concrete. The bars take the stretch and the lead takes the compression.
10-05-2009, 05:51 AM
So it is really a matter of whether to cast a coating an inch thick or to apply lead like a panel beater .It will depend on the thickness of the board you require .The panel beaters method sounds good , less setup ,reasonably easy and relatively safe .A home version of galvanising .If you mess up a section just melt it off with a torch and do it again .I like it !
10-05-2009, 06:34 AM
a sheet of ordinary mild steel, say 10mm thick and cut it roughly to the desired shape of the centerboard, drill holes for pivot pin, etc. Then cast lead around it until you achieve the desired thickness and weight. It won't rust, as all the steel is safely covered with lead and wont be as prone do deformation as ordinary lead, due to the steel backbone
The deformation comment is dodgy - all the "Backbone" is within 5mm of the neutral axis, so the steel offers very little in the way of stiffness to the overall structure.
If a 10mm (3/8 inch aprox) steel plate is strong enough then OK, but if not, then this is not a clever distribution of material.
I like Timo's suggestion.
10-05-2009, 09:07 AM
I was thinking of casting a 5mm+ layer of lead around a steel plate. But for now it is only thinking. When the jury comes with their opinion Iíll decide on how to do things further.
Timo, The bars idea is interesting too.
As for deformation, you can easily weld some reinforcement ribs on the steel on strategic places.
10-05-2009, 10:01 AM
Casting a thin skin around a steel plate is an entirely different proposition from wiping a thin layer onto sheet metal. If the plate isn't cleaned, fluxed and heated, I doubt the lead would stick. Then there's the problem of suspending the steel plate in the mold, precisely centered, while it's hot.
Although wiping lead works well for sheet metal, I think there'd be some difficulty getting a thick steel plate hot enough, with enough control, even in small areas, to use this method effectively. From the pipe sweating and gutter soldering I've done, it seems that the metal has to be hotter than the melting point of the lead alloy or nothing's going to stick to anything. But not too hot, if you see where this is going.
10-05-2009, 10:57 AM
Lead is SOFT. Centerboard slots are not. Hit something with a sideways impact and anything that is mostly lead will bend. Centerboard will then not retract. Bad juju.
So a steel plate with a lead coating will be fine, but a CB that is mostly lead would not be a good idea in my book.
Also I think that there have been some good discussions on the wisdom of trying to put a lot of ballast in a centerboard -- and the consensus from one or more NA's was that it wasn't. When down it puts *some* weight low where it belongs, but when up the weight is too high.
10-05-2009, 11:04 AM
How hard would the lead alloy have to be in comparison to pure lead (i.e. what addition of antimony, tin, etc.) so that it wouldn't eventually start sagging? Even if it does stick, would not a 5mm layer develop "runs" under its own weight, particularly with the bending loads that a C.B. undergoes?
Center boards are for directional stability. When you start adding weight to them for ultimate stability you also add the weight of the winch and wire to raise them. Keep the weight in the keel and only use enough weight in the cb to keep it down in my opinion.
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